VIET NAM NATIONAL UNIVERSITY HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY ---o0o--- LÊ GIANG TRÚC ANH EVALUATE THE IMPACT OF NITROGEN LOAD ON THE GREEN ROOF SYSTEM IN
INTRODUCTION
Significance of the research
Recent monitoring data indicates that weather patterns have become increasingly extreme, particularly in Ho Chi Minh City (HCMC), one of Vietnam's largest urban centers, where record temperatures have soared above 40˚C, approaching 50˚C The rise in air pollution from industrial parks and transportation contributes significantly to the greenhouse effect in these major cities Additionally, the diminishing area of green buildings, which are crucial for mitigating the greenhouse effect, raises concerns about their effectiveness in combating environmental challenges.
Constructed wetlands (CW) offer an eco-friendly and efficient solution for treating various types of wastewater, including domestic, industrial-agricultural, leachate, and aquaculture wastewater This technology is recognized for its high treatment efficiency, low operational costs, and stability (Parde et al., 2020), while also enhancing biological value The economic benefits derived from CW systems include plant biomass products, digested sludge, and treated wastewater However, one significant limitation of this technology is the substantial land area required for its implementation.
Green infrastructure represents a potential alternative solution to manage excess nitrogen at the local scale through wastewater recycling and treatment
Rooftops can account for up to 50% of impervious surfaces in urban areas, making Green Roof systems (GRs) a promising yet underutilized solution for addressing nitrogen pollution from domestic wastewater (Malaviya, 2021; Pradhan et al., 2019) These systems not only treat wastewater but also supply essential nutrients and organics to plants, offering multiple environmental benefits Despite their potential, the implementation of GRs for wastewater treatment remains limited in Vietnam However, globally, the integration of constructed wetlands (CW) with GRs is gaining traction, highlighting the need for further research on utilizing domestic wastewater to enhance the functionality of GRs.
Reseach objectives and Contents
The study aims to evaluate the pollutant removal efficiency of the GRs at different Nitrogen Loading Rate (NLR), through two main contents:
This study evaluates the pollutant removal efficiency of green roofs (GRs) by analyzing key parameters, including plant growth and water quality Two distinct plant species, Vernonia elliptica and Portulaca grandiflora, were selected to operate under varying nutrient loading rates (NLR).
- Evaluate the effectiveness of GRs in increasing urban green areas
Research scope
- Feed wastewater: Domestic wastewater from in Block B1 Ho Chi Minh City University of Technology (HCMUT)
- Plants using: Vernonia elliptica and Portulaca grandiflora
+ Located on top of Centre Asiatique de Recherche sur l’Eau (CARE) center
- Included 2 systems - GR_15 and GR_20 stand for Green roof system operated under NLR = 15 kg.N/ha/day and NLR = 20 kg.N/ha/day: 1 system included
2 batches stay on each side
- Place of parameters analysis: Key Laboratory of Advanced Waste Treatment Technology – Ho Chi Minh City University of Technology (HCMUT).
Method
- Research Vietnamese and foreign document and papers for effective design and operating parameters
- Conduct experiments on the model
- Analyze values, parameters and compare with column B QCVN 14:2008/BTNMT
- Analyze, comment and evaluate experimental results
- Data processing, writing report at the end of each week
- Thesis report claimed at the end of the project
LITERATURE REVIEW
Urban heat islands (UHI) in Ho Chi Minh City
Heat islands are urban areas that exhibit significantly elevated temperatures compared to surrounding regions due to the prevalence of heat-absorbing structures like buildings and roads, which re-emit solar heat more effectively than natural landscapes such as forests and water bodies This concentration of infrastructure and limited greenery leads to daytime temperatures that can be 1–7°F higher and nighttime temperatures that are typically 2-5°F higher in urban settings (Khaled et al, 2023).
Ho Chi Minh City (HCMC) is currently experiencing peak hot season temperatures, with air reaching 35-41˚C and surface heat soaring to 60-61˚C due to the urban heat island (UHI) phenomenon This issue is exacerbated by inadequate urban development policies that fail to accommodate population growth while leading to the destruction of green spaces The HCMC Institute for Development Studies emphasizes the importance of addressing UHI as the city prioritizes sustainable development through its Smart City project, which aims to tackle flooding, environmental pollution, and traffic congestion To mitigate surface heat, increasing urban green areas is essential, with plans to expand public green spaces to over 837 hectares Currently, HCMC's green space allocation is only 0.69 m² per person, far below the 2025 target of 7 m² per person, and significantly less than standards in cities like Singapore and Seoul The city's green coverage rate stands at 18%, highlighting the need for strategic planning to enhance this figure and combat the effects of rapid urbanization and UHI.
4 domestic wastewater to operate) brings many benefits to urban planning goals- efficient and sustainable city.
Domestic wastewater overview
Approximately 75% of domestic wastewater is produced by residential buildings, with the remainder coming from offices, commercial areas, and public facilities (Wirawan, 2020) While the activities generating wastewater in households and non-households are similar, the composition and quantity of domestic wastewater differ between these sources (Widyarani et al., 2022) In rapidly urbanizing cities like Ho Chi Minh City (HCMC), the challenge of managing wastewater is becoming increasingly urgent HCMC alone generates over 1.5 million cubic meters of wastewater daily, with an annual increase of about 6.7% in average wastewater volume from 2018 to 2021.
(Tran, 2024) Currently, HCMC has 3 wastewater treatment plants However, with more than 3 million cubic meters of urban domestic wastewater discharged every day, the amount collected and treated is only about 12.6%
Ho Chi Minh City (HCMC) is focused on enhancing its role as the socio-economic hub of southern Vietnam through the HCMC Wastewater and Drainage System Improvement Project This initiative aims to improve surface water quality and increase drainage capacity by expanding wastewater collection and treatment in key areas HCMC faces the dual challenge of managing its growing wastewater volume while implementing sustainable treatment solutions, which are essential for safeguarding the environment and public health.
Domestic wastewater is generated from everyday activities such as eating, bathing, and personal hygiene It is typically discharged into surface water bodies or coastal seawater designated for specific uses The composition of domestic wastewater fluctuates based on various factors, including time of day, season, and the household's dietary and lifestyle habits.
Domestic wastewater, a significant contributor to overall wastewater from human activities, contains pollutants that can adversely impact the environment and human health It is categorized into two types: black water and grey water Black water, originating from toilets, has high levels of organic matter, nitrogen, and phosphorus In contrast, grey water, which includes wastewater from sinks, showers, and laundry, is generated in volumes one to seven times greater than that of black water.
2019) and contains relatively low organic compounds, but some of them are considered persistent
The QCVN standard on wastewater outlines the permissible limits for pollutant parameters and concentrations based on water volume and flow It defines domestic wastewater as the waste solutions produced from human activities such as cooking, laundry, and bathing.
Inadequate treatment of domestic wastewater is a significant global health concern, as highlighted by Raheem (2018), leading to the spread of various illnesses Among the waste management methods, dewatering, composting, and incineration are identified as having the least negative impact on human health.
QCVN 14:2008/BTNMT is the National Technical Regulation on Domestic Wastewater in Vietnam The basic components in domestic wastewater are shown in
- This regulation specifies the maximum allowable values for pollution parameters in domestic wastewater before it is discharged into the environment
- It does not apply to domestic wastewater discharged into centralized wastewater treatment systems
- Applicable entities include public facilities, military bases, service establishments, residential areas, and enterprises that discharge domestic wastewater into the environment
- Domestic Wastewater: Wastewater resulting from human activities such as eating, bathing, and personal hygiene
- Receiving Water Source: The surface water or coastal area where domestic wastewater is discharged
Table 2.1 Maximum Allowable Values for Domestic Wastewater Parameters
The composition of domestic wastewater is mostly water, the rest is waste and biodegradable pollutants However, it contains many harmful substances such as:
- Biochemical Oxygen Demand (BOD) is discharged into ponds and lakes, it will reduce aquamarine biodiversity’s oxygen Therefore, before discharging wastewater, it is necessary to treat wastewater, reducing BOD
Total suspended solids (TSS) refer to the concentration of solid particles suspended in wastewater of a specific size When TSS is discharged directly into surface water, it can lead to environmental pollution, transport harmful pathogens, and obstruct the gills of fish, posing significant risks to aquatic life.
Nutrients such as phosphate, nitrate, and ammonia, often found in cooking waste, can lead to harmful consequences in aquatic environments While these substances provide essential nutrients, their excessive presence can promote the growth of toxic algae and result in fish mortality due to elevated nitrogen levels in the water.
Reusing wastewater can generate renewable energy by converting the energy stored in organic contaminants into usable energy carriers This process not only addresses the issue of wastewater treatment but also produces recyclable and reusable products Additionally, using domestic wastewater for irrigation in green spaces effectively tackles both irrigation needs and wastewater management.
Constructed Wetland (CWs)
Advancements in wastewater treatment technologies are primarily focused on three key areas Firstly, the modification of the activated sludge process, exemplified by aerobic granular sludge, has been extensively researched and successfully implemented in various wastewater treatment plants (WWTPs) across Europe and Africa, offering high effluent quality, energy savings, and a compact footprint Secondly, the Anammox process represents a significant innovation that bypasses traditional nitrification/denitrification, greatly reducing energy consumption and facilitating energy-producing carbon bioconversion processes like anaerobic membrane bioreactors Lastly, improvements in facility efficiency, materials, and process control techniques enhance the optimization of WWTP operations However, challenges such as unsuitable technologies, operational failures in larger plants, and high establishment costs have led to the direct discharge of untreated wastewater into rivers Constructed wetlands (CWs) have emerged as a promising solution for treating domestic wastewater, providing reliable efficiency, environmental benefits, ease of operation, and low maintenance costs.
CWs are engineered systems that have been designed and constructed to utilize the natural processes involving wetland vegetation, soils, and the associated
Constructed wetlands (CWs) utilize microbial assemblages to effectively treat wastewater, mimicking the natural processes found in wetlands within a controlled setting These systems can be categorized based on the dominant macrophyte life forms, including free-floating, floating-leaved, rooted emergent, and submerged macrophytes, as illustrated in Figure 2.1.
Artificial wetlands are primarily categorized into two types: free-water surface wetlands and subsurface flow wetlands, distinguished by the presence or absence of water on the surface Furthermore, hybrid constructed wetlands can be developed by integrating different types of these artificial systems Additionally, constructed wetlands are classified based on their flow direction, which includes vertically constructed wetlands and horizontally constructed wetlands.
Figure 2.1 Classification of CWs for wastewater treatment (Vymazal, 2007)
To protect natural wetlands and aquatic resources, constructed wetlands (CWs) are usually built on uplands, away from floodplains or floodways (Prathap et al., 2014) This source indicates that soluble reactive phosphorus (P) can be absorbed by plants or adsorbed onto wetland soils and sediments, highlighting the significance of P transformations in these ecosystems.
Wetlands play a crucial role in phosphorus (P) removal through various processes, including peat and soil accretion, adsorption and desorption, precipitation and dissolution, as well as plant and microbial uptake, fragmentation, leaching, mineralization, and burial While all these components contribute to the effectiveness of wetlands in P removal, it is important to note that soil accretion is a process exclusive to Free Water Surface (FWS) wetlands.
Flow systems reduce TP by 48.8%; Horizontal Subsurface Flow Wetlands (HSSF) reduce TP by 41.1%, and Vertical Subsurface Flow Wetlands (VSSF) reduce TP by
59.5% In conclusion, the source states that the removal of TP varied between 40 and
60% for all types of constructed wetlands “with removed load ranging between 45 and 75g Nm −2 yr −1 depending on CWs type and inflow loading.” (Vymazal, 2007)
2.3.2 Constructed Wetlands for Wastewater Treatment
Constructed wetlands (CWs) are adaptable systems employed for wastewater treatment, featuring diverse types that vary in their fundamental architectural components and the mechanisms utilized for pollutant removal, as illustrated in Table 2.2.
Table 2.2 Design, operation, and maintenance of CWs (Hassan et al., 2021)
Simple, requires a large land area, uses gravity flow
Low operation cost, simple operation procedure, high evapotranspiration, low temperature, affects the microbial activity
Greatly affected by temperature flocculation, odor and mosquito problems, low maintenance cost
Complex, needs less area than
FWS, needs sedimentation tank, needs pumping
Provides more sorption sites than FWS, relatively higher operation cost, flow should be uniform with low solid concentration, transpiration only
Greater cold tolerance, less odor and pests Clogging problems, higher maintenance cost
Complex, needs less area than HSSF, needs sedimentation pond, needs pumping
Provides more sorption sites than FWS, relatively higher operation cost, flow should be uniform with low solid concentration, transpiration only
Greater cold tolerance, less odor and pests Clogging problems, higher maintenance cost
In Figure 2.2.A wastewater flows through a shallow, planted basin or channel
Recent studies indicate that constructed wetlands (CWs) with exposed water surfaces and macrophytes can effectively mimic natural wetlands, leading to increased wildlife diversity, including insects, molluscs, birds, and mammals (Retta et al., 2023) However, the use of free water surface constructed wetlands (FWS CWs) is often limited due to heightened concerns regarding human exposure to pathogens.
Horizontal Subsurface-Flow Constructed Wetland (HSSF)
Wastewater flows slowly through a porous filter bed, reaching the effluent while interacting with various aerobic and anaerobic zones To prevent clogging, solids must be removed from the wastewater before it enters the channel Maintaining adequate oxygen levels in the Horizontal Subsurface Flow (HSSF) system is crucial for supporting the growth and metabolism of aerobic bacteria and plants.
Vertical Subsurface-Flow Constructed Wetlands (VSSF)
In Figure 2.2.C wastewater flows into the system through pipes on the surface
Water flows downward vertically, with a collection tube located near the bottom to extract the treated water In Vertical Subsurface Flow (VSSF) systems, the flow is facilitated either by gravity or pumps.
VSSF capital cost is less than the HSSF capital cost because the VSSF’s smaller size
It was also found that the VSSF is successful in removing the organic matter and suspended solids (Vymazal, 2011)
Figure 2.2 Schematic layout of (A) FWS CWs; (B) HSSF CWs; (C) VSSF CWs
Constructed wetlands (CWs) are designed to replicate natural wetlands, enhancing effluent quality through careful system management Researchers, engineers, and scientists, as noted by Brovelli et al (2018), emphasize the importance of straightforward design It is recommended to utilize indigenous and readily available materials, alongside environmentally friendly technologies Additionally, minimizing maintenance and pump usage is crucial, with media placement primarily at the bottom of the CWs.
When designing constructed wetlands (CWs), it is crucial to consider various factors, including the geometry of the CW, influent quality, media type, microorganisms, plant species, water depth, and hydraulic retention time The basin slope should ideally range from 3:1 to 5:1, and the hydraulic retention time must be maintained between 2 to 3 days The influent quality, particularly Biochemical Oxygen Demand (BOD) and Total Suspended Solids (TSS), should have loading rates of 20 to 30 mg/L or 45 to 50 kg/ha/day (Hassan et al., 2021) Additionally, previous research indicates that CWs should have a size of 1 m² for every 30 liters of influent, corresponding to a 5-day retention cycle (Nivala et al., 2013), with the length of the CW being twice its width.
After construction, the wetland should be tested for the water level The channeling and erosion, if any, should be fixed in the trial period (Haiming et al.,
To ensure effective wastewater treatment, it is recommended to allow a complete growing season before introducing the wastewater Maintaining the designed water level is crucial, as drying of the wetland can lead to the remobilization of contaminants.
Wetlands play a crucial role in enhancing water quality by utilizing plants as sorption sites for pollutants and facilitating microbial exchange These plants absorb nutrients, metals, and contaminants, while also providing organic carbon for microorganisms By slowing water flow, they promote sedimentation and pollutant settlement, contributing to the overall health of the ecosystem Common wetland plants, such as cattails (Typha latifolia) and reeds (Phragmites australis), not only support environmental functions but also add aesthetic value Research by Lavane et al (2021) highlights the effective growth and biomass of Napier grass (Pennisetum purpureum) in experimental systems, while Le et al (2017) demonstrated the use of Canna (Canna indica) and cattails (Typha angustifolia) in constructed wetlands for domestic wastewater treatment.
In Table 2.3 showed CWs play a vital role in sustainable water management, but careful planning and management essential to maximize their benefits while minimizing drawbacks
Table 2.3 Advantages and Disadvantages of CWs
- CWs utilize nature’s water purification methods
- They remove sediments, toxins, and pollutants from water
- Unlike natural wetlands, which benefit from environmental regulations, CWs are intentionally built for wastewater treatment
- Wetlands, especially swamps, can be breeding grounds for mosquitoes and other disease vectors Proper management is necessary to control mosquito populations
- CWs require significant land area Historically, natural wetlands were drained and filled
- They help further clean wastewater before it is returned to natural waterways
- Manual adjustments ensure proper functionality in treating wastewater
- By placing CWs near known sources of pollutants (such as farmlands with pesticide runoff), they prevent pollutants from spreading across ecosystems
- CWs provide habitat for a variety of plants and wildlife
- While not as high-quality as natural wetlands, they still benefit wildlife for urban development, but this practice has environmental consequences
- Wetlands naturally produce methane, a potent greenhouse gas About one-quarter of Earth’s atmospheric methane comes from wetlands
- CWs may not effectively treat highly toxic modern wastewater Pretreatment in specialized installations may be necessary, impacting visual beauty and wildlife
Constructed wetlands (CWs) have the drawback of requiring extensive land, making them unsuitable for urban environments with limited space To address this challenge, integrating wetlands with green areas in buildings is crucial for effective domestic wastewater treatment The Wetland Roof (WR) system emerges as an innovative solution that combines green roofs (GRs) and constructed wetlands A study conducted in Israel explored the use of greywater as a substrate for household-scale WR systems, highlighting their potential for sustainable urban water management.
WR to evaluate not only wastewater treatment efficiency, but also effect of energy saving during hot and humid climate (Cynthia,2016) In South Korea, there was a
CWs conducted on the roof of a six-story building in Seoul National University showed that the practical temperature of the roof was reduced and more stable
14 compared with conventional roofs due to macrophyte plant evaporation (Song et al.,
Green roof system
The history of green roofs (GRs), depicted in Figure 2.3, spans many years and cultures, and they are also known as eco-roofs, living roofs, or roof gardens These structures serve as an additional layer on rooftops and represent a significant advancement in building design across various countries, including Sweden, Finland, Iceland, Denmark, and Norway GRs are increasingly used to mitigate extreme climatic conditions, while also providing alternative spaces for planting vegetation (Rowe, 2011).
Urbanization is significantly driven by the migration of individuals from rural areas to urban centers, motivated by improved infrastructure, social and economic advancements, and lifestyle enhancements (Gong et al., 2022).
2012) According to the United Nations, two-thirds of the global population will reside in urban centers by 2050, while 86% of global population growth is expected
Green roofs (GRs) have gained popularity in urban areas over rural settings due to their sustainable practices In recent decades, they have emerged as an effective solution for domestic wastewater treatment and nitrogen removal, offering a unique opportunity to enhance hydrological management, energy efficiency, and water quality.
Green roofs (GRs) consist of several essential components, including a waterproof membrane, a root barrier membrane, a drainage layer, a filter membrane, a growing medium like soil, and vegetation Selecting each layer appropriately based on the specific location and climate is vital for ensuring long-term environmental benefits Careful consideration of each component is essential for achieving optimal performance in green roof systems.
Figure 2.4 Components of GRs (Shafique et al., 2018)
Green roofs (GRs) are engineered solutions specifically designed to address the challenges posed by urbanization, distinguishing them from traditional rooftop gardens These systems typically consist of multiple components tailored to the specific location and requirements, as illustrated in Figure 2.4 To ensure that GRs are environmentally friendly and fulfill long-term client expectations, the careful selection of efficient components is crucial.
Identifying the appropriate plants and vegetation layers is essential for effective system development, as it enhances the longevity of selected plants and reduces costs Key factors to consider when choosing plants include geographic location, rainfall intensity, humidity, wind exposure, and sunlight availability According to Shafique et al (2018), the best plants for large green roofs possess specific properties that support their growth and sustainability.
- Ability to withstand drought and extreme climate conditions;
- Local available and cost effective;
- Ability to survive under minimal nutrients conditions;
- Can reduce heat island phenomena;…
Green roofs (GRs) are categorized into three main designs: intensive, semi-intensive, and extensive, as detailed in Table 2.4 The primary distinction among these types lies in the design of the vegetation layer Each type of green roof features different modules, which vary in depth and composition, thereby differentiating intensive, semi-intensive, and extensive roofs.
Table 2.4 General features of GRs
Type Extensive Semi-intensive Intensive Use Ecological
Moss, Herbs, Grass Grass, Herbs, Shrubs Shrubs, Trees
Figure 2.5 Types of Green roof: (A) Extensive; (B) Semi-intensive and (C)
Semi-intensive and intensive green roofs utilize a diverse array of herbaceous plants, shrubs, and small trees, allowing them to retain more stormwater compared to extensive systems These roofing types, illustrated in Figure 2.5, are suitable for various applications, including residential buildings, sports grounds, patios, and terraces They are particularly popular in commercial and office centers, serving as recreational landscaping areas for building occupants on rooftops.
Extensive green roofs (GRs) are lightweight systems featuring small herbaceous plants and grasses, known for their low maintenance, nutrient, and irrigation needs This study was conducted in a small area with a limited budget, utilizing domestic wastewater for GR operation, which inevitably leads to nutrient deficiencies for the plants Thus, extensive GRs are the most suitable choice for this scenario.
GRs are being implemented in cities to improve the urban environment The benefits of GRs showed in Table 2.5 including three segments: environmental, social, and economic:
Environmental - Air Quality Improvement: GRs absorb pollutants and particulate matter, contributing to cleaner Photosynthesis in plants absorbs CO 2 emissions and releases oxygen,
18 resulting in cleaner air and lower emissions (Yahia et al.,
Vegetation and soil serve as effective sound insulation, significantly diminishing external noise In urban environments characterized by elevated noise levels, green roofs provide substantial benefits, potentially lowering noise levels by 8 to 10 decibels.
- Stormwater Management: They capture and slow down stormwater runoff, preventing flooding and improving water quality (Mulen et al., 2013)
- Biodiversity Enhancement: They provide habitat for insects, birds, and other wildlife
Energy efficiency is enhanced by green roofs (GRs), which provide an extra layer of insulation that lowers heating and cooling costs By effectively regulating indoor temperatures, GRs contribute to significant energy savings (Bianchini et al., 2012).
- GRs protect the underlying roof membrane from UV radiation, temperature fluctuations, and mechanical damage GRs protect building roofs from thermal, UV, and diurnal stresses, extending their lifespan
Plants play a crucial role in enhancing thermal comfort by mitigating the urban heat island effect, a significant issue in cities and urban areas Their ability to absorb shortwave radiation and cool the surrounding atmosphere contributes to lower temperatures and improved environmental conditions.
The natural landscapes of green roofs significantly enhance the visual appeal of buildings, creating inviting environments for both residents and visitors Rooftop gardens not only provide enjoyable spaces but also contribute to reducing stress and obesity by incorporating plants in close proximity to green areas.
In summary, constructed wetlands (GRs) provide numerous advantages, including environmental conservation and enhanced quality of life Horizontal subsurface flow constructed wetlands (HSSF CWs) effectively treat wastewater with low organic concentrations (BOD < 50-80 mg/l), which conventional systems like activated sludge cannot handle Due to their simplicity and cost-effectiveness, HSSF CWs are recommended for use in developing countries (Carballeira et al., 2017) Reports indicate that HSSF CWs achieve treatment efficiencies of 63-94% for COD and 39-70% for domestic wastewater.
Constructed wetlands (CWs) demonstrate effective nutrient removal, achieving 21-74% for NH4+-N and 41-96% for total phosphorus (TP) However, a significant drawback is their requirement for large land areas, making them less feasible in urban environments where land is limited To address this challenge, integrating wetlands with green areas in urban developments can provide both wastewater treatment and aesthetic benefits This innovative approach combines extensive green roofs (GRs) and CWs, offering a sustainable solution for urban wastewater management.
Research about CWs and GRs
CWs and GRs technologies are increasingly recognized for their effectiveness in reducing operating costs and resource consumption while enhancing the benefits of wastewater treatment.
Green Infrastructure enhances urban water management by effectively capturing rainwater and treating domestic wastewater for reuse in irrigation and non-potable applications According to Semeraro et al (2019) in their study on "Green Roof," these practices contribute significantly to sustainable urban development.
"Technology as a Sustainable Strategy to Improve Urban Water Availability" highlights the integration of water conservation, economic growth, and public health Living walls and green roofs provide benefits like cooling, air filtration, and enhanced aesthetics in urban settings However, their high water consumption makes them less suitable for arid environments that require passive cooling and urban greening solutions Additionally, the article discusses the importance of grey water recycling in buildings as a viable strategy for enhancing water sustainability in urban areas.
The article "Using Living Walls and Green Roofs: A Review of the Applicability and Challenges" by Snigdhendubala Pradhan et al (2019) highlights the potential of integrated greywater treatment through green building vegetated structures as an effective solution for dual-purpose water recycling and urban cooling The authors emphasize the necessity for further research to fully implement these innovative practices.
CWs are recognized as a reliable wastewater treatment technology and they represent a suitable solution for the treatment of many types of wastewater In
“Constructed Wetlands for Wastewater Treatment: Five Decades of Experience” by
(Vymazal, 2011) has describe the development of CWs technology from 1950s to
In the 2000s, constructed wetlands (CWs) gained significant recognition for their effectiveness in treating various types of wastewater A decade later, Song et al (2020) advanced this research by focusing on full-scale CWs and conducting long-term studies to enhance CW technology while addressing existing challenges and opportunities Recently, the potential of CWs has been increasingly acknowledged, highlighting their importance in wastewater treatment solutions.
The article "Wastewater Treatment Using Constructed Wetland: Current Trends and Future Potential" by Hassan (2021) assesses the present status of constructed wetlands (CWs) technology, offering clear definitions and performance metrics to align the rapidly expanding CWs community It highlights emerging trends in CWs and suggests future avenues for research and development in this field.
Green roofs (GRs) support fewer species compared to ground-level ecosystems and should not be seen as substitutes; however, enhancing the structural variety of green roofs can lead to increased species richness and abundance While limited research has focused on the functional diversity of green roofs, existing studies have identified general characteristics of the species involved According to Knapp et al (2019) in their work “Biodiversity Impact of Green Roofs and Constructed Wetlands as Progressive Eco-Technologies in Urban Areas,” integrating green roofs with constructed wetlands can significantly benefit urban biodiversity.
(2020) with “Recent research challenges in constructed wetlands for wastewater
Recent advancements in constructed wetlands (CWs) research emphasize the need for full-scale implementations and long-term studies to enhance CW technology while addressing associated challenges and opportunities The growing recognition of CWs in wastewater treatment is highlighted in the article “Wastewater Treatment Using Constructed Wetlands: Current Trends and Future Potential” by Hassan, showcasing their expanding potential in sustainable environmental solutions.
The study evaluates the current state of constructed wetlands (CWs) technology, offering definitions and performance metrics to unify the rapidly growing CWs community It also highlights emerging trends in CWs and suggests future research and development directions.
Green roofs (GRs) are gaining global popularity due to their numerous social, environmental, and economic benefits, making them an increasingly accepted solution in the construction industry for environmentally friendly buildings Despite this, the adoption of GR technologies remains limited, primarily due to challenges faced by contractors in executing green roof projects Research indicates that optimizing carbon uptake in green roofs requires maintaining substrate moisture above 0.05 m³/m³, as highlighted in studies by Heusinger and Weber (2017) and Shafique (2018), which also address the research gaps and challenges in enhancing green roof performance Additionally, policy barriers hinder the implementation of GRs, as explored in Zhang's (2021) study, which encourages further exploration of the interrelationships among various factors to aid decision-makers in developing effective policies for green roof adoption.
In Vietnam, the method of treating wastewater by CWs or GRs is still quite new, initially only being tested by some environmental technology centers and universities
A study by Le et al (2017) demonstrated the effective operation of a constructed wetland system utilizing Canna Indica and Typha angustifolia, achieving a retention time of five days This system managed a water load of 437.5 m³/ha.day and facilitated the transduction of organic matter at a rate of 30.33 kg/ha.day, successfully treating domestic wastewater with high pollution concentrations.
Pham (2018) demonstrated that Portulaca grandiflora, a plant used in green remediation (GR), can effectively treat wastewater with a capacity of 300 kg COD/ha.day The treatment efficiencies achieved were impressive, with chemical oxygen demand (COD) reduction at 85.6% (20.0 ± 5.0 mg/L), total nitrogen (TN) reduction at 66.9% (12.0 ± 1.0 mg/L), total phosphorus (TP) reduction at 61% (2.5 ± 0.5 mg/L), and coliform bacteria reduction at 98.2% (180 CFU/100mL).
Recent studies in Vietnam, including "Treatment of Domestic Wastewater by Underground Filter Beds Planted with Vertical Flow Plants" by the Center for Urban and Industrial Environmental Engineering and "Building an Artificial Wetland System to Treat Domestic Wastewater in Minh Nong, Ben Got, Viet Tri" by Hanoi National University, demonstrate the feasibility of this wastewater treatment method in the country's context Prof Nguyen Nghia Thin from the University of Natural Sciences at Hanoi National University highlights that Vietnam boasts 34 types of plants suitable for water purification, which are readily available in nature and possess strong vitality.
“Application of Wetland Roof system for domestic wastewater treatment” by
Dr Vo Thi Dieu Hien from Ho Chi Minh City University of Technology conducted research on a horizontal underground flow flat roof wastewater treatment system utilizing Melampodium paludosum This system effectively treats domestic wastewater at a hydraulic loading rate (HLR) of 338 ± 9 m³/ha.day and a hydraulic retention time of 18 ± 1 hours The treatment efficiency for chemical oxygen demand (COD) reaches 77 ± 9%, equivalent to 20 ± 2 kg/ha.day under sunny conditions, with an overall efficiency of 78%.
23 ± 4% or 28 ± 11 kg/ha.day (rainy); TN is 88 ± 6% or 17 ± 6 kg/ha.day (sunny) and
The study found that during rainy conditions, the treatment efficiency was 91 ± 5% or 20 ± 5 kg/ha.day, while during sunny conditions, total phosphorus (TP) removal was 78 ± 13% or 1.6 ± 0.2 kg/ha.day, and during rainy conditions, TP removal was 72 ± 12% or 1.6 ± 0.2 kg/ha.day Importantly, the quality of the treated water meets Vietnam's discharge criteria for surface water sources and aligns with water reuse standards in several other countries.
“Application of artificial wetland system planted Vetiveria Zizanioides L and
METHODOLOGY
Research contents
Figure 3.1 illustrates the research findings on green roof systems operating under various nutrient loading rates (NLR) The study aimed to assess two primary objectives: first, to evaluate the pollutant removal efficiency of green roofs (GRs), and second, to determine their effectiveness in enhancing urban green spaces.
Figure 3.1 Contents of the research
Green roof system(plants used: Vernonia elliptica and
Portulaca grandiflora) operated under diferent NLR
Evaluate the pollutant removal efficiency (TSS, COD, amoni, nitrat, nitrit, TP) of the GRs under different NLR Adaptability of plants in wastewater
Evaluate the effectiveness in increasing urban green areas:
− Cost-effective when increasing urban green areas by Green roof system
NLR = 20 kg.N/ha/day (GR_20)
Content 1: Evaluate pollutant removal efficiency at different nitrogen loads
- Evaluate the survival and adaptation ability of plants (Vernonia elliptica and
Portulaca grandiflora) in the GRs at different Nitrogen loads (NLR = 15 ± 2 and 20 ± 2 kgN/ha/day) through:
• Analysis wastewater parameters at the influent and effluent of the GRs
(pH, TSS, NO 2 − − N, NO 3 − − N, NH 4 + − N, TKN, TP, sCOD)
• Measure the length of the plants at each stage (beginning- end) of the process
Contents 2: Evaluate the effectiveness of GRs in increasing urban green areas
To evaluate the cooling efficiency of green roofs (GRs), a temperature survey should be conducted in three key locations: the roof without GRs, the roof with GRs, and an area without GRs Once the plants have adapted and established stable growth, the collected temperature data will be processed and statistically analyzed to compare the cooling effects of the GRs.
This case study utilizes the cost-benefit analysis method to evaluate the advantages gained from implementing green roofs (GRs) in Ho Chi Minh City (HCMC) By assessing the costs and benefits associated with GRs, the study highlights their potential to enhance urban sustainability, improve air quality, and provide economic savings The findings emphasize the importance of integrating green infrastructure in urban planning for HCMC, showcasing the significant long-term benefits that can be achieved through strategic investment in green roofs.
Experimental set-up
The schematic layout of the lab-scale green roofs (GRs) is illustrated in Figure 3.2 This study features two GR systems installed on the terrace of the Care Center at HCMC University of Technology, with the roof dimensions detailed in Appendix 1.
Figure 3.2 Schematic layout of lab-scale GRs
The domestic wastewater tank will pump water into the system at flow rates corresponding to Nitrogen Loading Rates (NLR) of 15 and 20 kg/ha/day The system features an influent water distribution pipe at the beginning and an effluent water collection pipe, both with drilled holes of 21 mm in diameter for sampling and analysis Detailed dimensions of the system, measuring 3600 mm in length, 300 mm in width, and 170 mm in height, are provided in Table 3.1.
The 27 model consists of two consecutive working compartments, each featuring a bottom layer arrangement that includes an 80 mm charcoal layer, a 40 mm oyster shell layer, and a 120 mm thick rock layer at both ends The design maintains a water level height of 140 mm and incorporates a 1% slope from input to output to facilitate free flow throughout the tank Wastewater inflow is regulated by a valve, while the charcoal and barnacle layers serve as attachment points for plants, effectively adsorbing organic substances and nutrients from the wastewater to support plant growth.
Table 3.1 Design parameters of GRs
Parameters Symbol Unit Design parameters
After collection, wastewater is stored in a tank, from which it is pumped and distributed into two compartments equipped with adjustable valves The operational parameters are detailed in Table 3.2 The wastewater then flows along the surface of the model before exiting through the outlet water collection pipe.
Determine Organic Loading rate (OLR), Nitrogen Loading Rate (NLR) of Green roof system
Materials
Materials play a crucial role in helping roots establish, attach, and grow effectively As detailed in Table 3.3, these materials include charcoal and oyster shells, which serve as a supportive cushion, allowing tree roots to firmly adhere to the substrate.
Table 3.3 Weight of material layers in experimental module per one component of the GRs
In addition, there are 1x2 stones at the beginning and end of the model to prevent clogging of the output because there are many suspended sediments in the wastewater.
Domestic wastewater
Domestic wastewater was collected from the septic tank of Block B1 at HCMC University of Technology (HCMUT) Initially sourced directly from the septic tank, the wastewater was stored in a 30L container and subsequently diluted three times, resulting in an NH4+-N concentration of 70 ± 10 mg/L, as detailed in Table 3.4 This dilution was implemented to mitigate the impact of nitrogen concentration fluctuations in real wastewater, facilitating plant adaptation to the anticipated living conditions associated with wastewater.
Table 3.4 Characteristics of domestic wastewater
Raw Diluted 3 times pH - 8.6 ± 0.2 8.3 ± 0.2 5 - 9 sCOD mg/L 100 ± 10 20 ± 10 -
Column B outlines the concentration values of pollution parameters used to determine the maximum allowable limits for domestic wastewater discharged into water sources not intended for domestic water supply These values correspond to the water quality standards specified in columns B1 and B2 of the National Technical Regulations on surface water and coastal sea water quality.
Plants
The selected plants for the study, as outlined in Table 3.5, possess several key characteristics: they are easy to grow, climbers that thrive in harsh conditions such as heavy rainfall and high light intensity; capable of treating wastewater; exhibit well-developed roots with strong adhesion, ensuring longevity and effective ground coverage; ideally locally sourced, aesthetically pleasing, and cost-effective; and notably, there is a lack of extensive research on these plants globally.
Table 3.5 Selected plant’s actual parameters
Plants Scientific Name Vernonia elliptica Portulaca grandiflora
Common Name Curtain creeper, Vernonia creeper Japanese Rose, Moss Rose
Mature size length range from 60 – 120 cm Maximum Height: 25-27 cm
Characteristic Vernonia elliptica is a slender- bodied creeper with strong vigor, fast growth and few pests and diseases
The curtain creeper can be propagated through seeds or stem cuttings In either case, the growing procedure is simple and effortless
This low-growing annual plant is favored for its ornamental groundcover qualities It propagates quickly from seeds, which germinate in under five days, ideally in a light, well-drained seedling mix or directly in the garden With rapid growth, this plant can begin flowering in less than eight weeks.
Figure 3.3 Plants used: (A) Vernonia elliptica; (B) Portulaca grandiflora
This study evaluated the adaptability and treatment efficiency of two plant species for domestic wastewater The characteristics of the plants, including their height and freshness, are detailed in Table 3.6.
32 weight, Dry weight, density to evaluate the growth of plants at the end of the experiment
Table 3.6 Plants characteristics Plant Vernonia elliptica Portulaca grandiflora
Experimental plants were measured for length at the beginning and end of each growth stage under varying loads The growth rate is calculated as the fraction of the increase in the plant's length over the experimental period.
During each phase of the experiment, the number of plants, plant length, and
N and P content in the plants were observed
- Measurement location: randomly take 3 plants/compartment (beginning, middle, and end of the compartment)
- That frequency: first day and end day of each period
- The growth rate of plants is calculated according to the following formula: Growth rate (cm/day ) = L (last day) − L (first day)
Method of sample digestion (10TCN 450:2001)
This standard specifies methods for digestion of dried plant samples prepared to determine the content of elements P, K, Ca, Mg, S, Fe ( except N)
- Using H 2 SO 4 and H 2 O 2 decompose a sample and determine Phosphorus
Step 1: Accurately weigh 0.25g of sample into the Erlenmeyer flask
Step 2: Add 5ml of pure concentrated sulfuric acid (H2SO4) (d= 1.84)
Step 3: Add 1ml hydrogen peroxide (H2O2) 30%
Step 4: Leave the sample overnight, then decompose at 225 o C until the remaining acid is only about 2ml
Step 5: Take out the flask to cool, then add 1 drops of 30% H2O2, shake gently and continue to cook on the stove for about 10-30 seconds
Step 6: Cool the sample and transfer to a 25 ml volumetric flask, add dilute water to the mark
Method of determination total phosphorus in plant (10TCN 453:2001)
To analyze the phosphorus content in a plant sample, all phosphorus compounds must be converted to orthophosphate The phosphorus concentration is then determined using the hotometric method, where a yellow complex is formed between orthophosphate and vanadomolybdate.
Use 25ml volumetric flask following 25ppm P standard, The details were shown in Table 3.7:
Table 3.7 Calibration curve set up
No of ml standard 25ppm P uses for
- Step 1: Add 5.0 ml of Nitric Acid (HNO3) 2N solution to each flask, and fill up to 20ml of distilled water
- Step 2: Add 2.5 ml of vanadomolybdate solution and make up to the 25 ml mark with distilled water and mix well
- Step 3: Leave it cool for 20 minutes then measured on a spectrophotometer at 420 nm
- Step 1: Pipette 2.5 ml of phosphorus determination solution into a 25 ml volumetric flask
- Step 2: Add 5.0 ml of Nitric Acid (HNO3) 2N solution and make up to 20ml of distilled water
- Step 3: Add 2.5 ml of Vanadomolybdate solution and fill up to the 25 ml mark with distilled water and mix well
- Step 4: Leave it cool for 20 minutes then measured on a spectrophotometer at 420 nm
- Step 5: Calculate %P of chosen plant using the following formula:
With m: Mass of digested sample (g)
V: Volume of sample solution (ml) v: Volume of extract solution (ml) a: The mass of P found in the volume of extraction solution (mg) k: Drying-out coefficient
3.4.2.2 Nitrogen (%N) analytical in plants (Bradstreet et al, 1954)
The inorganicization of a sample involves the use of hydrochloric acid (HCl) and a catalyst, followed by the addition of a strong alkali like sodium hydroxide (NaOH) or potassium hydroxide (KOH) to release ammonia (NH3) from ammonium sulfate ((NH4)2SO4) The NH3 content is then determined using 0.25N HCl.
- Step 1: Take 1g of test sample, 5g of Potassium sulfate (K2SO4) and copper sulfate (CuSO4) catalysts and 10ml of concentrated H2SO4 into a Kjeldahl flask
- Step 2: Carry out slow heating until a clear, colorless or pale blue solution of CuSO4 is obtained when cooled
Note: The process of inorganicization of the test sample in the Kjeldahl flask
36 will release SO2 gas, so it must be carried out in the suction cup and during the combustion process should be placed slightly tilted
- Step 1: After complete inactivation of the test sample, add some distilled water to the Kjeldahl flask for rinsing and then into a 500ml volumetric flask
- Step 2: Rinse the Kjeldahl flask and funnel several times and then add it directly to the volumetric flask
- Step 3: Put about 10-15ml of 40% NaOH and a few drops of phenolphthalein in the volumetric flask
- Step 4: Then add distilled water just enough 300ml into the bottle
- Step 1: Take the collection vessel and titrate it with 0.25N HClsolution
- Step 2: Calculate %N in following formula:
+ 0.0035: Nitrogen (g) equivalent to 1ml HCl 0.25N
+ V: HCl solution for blank sample (ml)
+ V': HCl solution used for the test sample (ml)
Water quality analysis methods adhere to the Water Standard Methods outlined in Table 3.8 The parameters evaluated were conducted at the VNU-HCM Key Laboratory of Advanced Waste Treatment Technology.
Table 3.8 Methods for analyzing water quality
Standard Deviation (SD) pH - SMEWW4500- H+B HANA pH 21 ± 0.01
COD mg/L SMEWW5220 D 150 0 C Heater ± 0.01 mg/L
TSS mg/L SMEWW2540 D 105 0 C Heater ± 0.01 mg/L
When the model begins to work and the plants begin to adapt and grow Conduct temperature survey measurements at three locations:
- The roof does not have GR; (roof without GR)
- The roof has GR (Roof with GR)
- There is no roof (Without roof – temperature outside)
The cooling effect is evaluated based on the temperature difference between the above 3 locations
Roof without GRs Roof with GRs
Measure the temperature inferior surface of the GRs
Measure the temperature inferior surface of the concrete roof
RESULTS AND DISCUSSIONS
Evaluate the pollutant removal efficiency of the GRs under different NLR 39 1 The growth of Vernonia elliptica and Portulaca grandiflora over time 39 2 The treatment efficiency of nutrients and organic matter of GRs
Figure 4.1 (A) The survival rate of Vernonia elliptica and Potulaca grandiflora of
GR_15 and (B) The survival rate of Vernonia elliptica and Potulaca grandiflora of
The survival rates of Vernonia elliptica and Portulaca grandiflora exceeded 90% in both the GR_15 and GR_20 systems Initially, the plant densities were 130 and 175 plants/m², respectively During the first 20 days in the GR_15 system, both species struggled to adapt to the diluted wastewater, resulting in survival rates of 91% for Vernonia elliptica (119 plants) and 95% for Portulaca grandiflora (166 plants) By day 30, following the introduction of additional plants, both species showed significant adaptation, with real biomass increasing throughout the experiment Subsequently, their survival rates stabilized at approximately 98-99%, reaching nearly 99% by the end of the operational phase Similarly, in the GR_20 system, the survival rate at day 20 also reflected these positive trends.
Portulaca grandiflora were 92% (120 plants) and 97% (169 plants), respectively
In contrast to the GR_15 system, after supplementing plants to match the initial density on day 30, both Vernonia elliptica and Portulaca grandiflora demonstrated good adaptation; however, Vernonia elliptica exhibited a lower survival rate compared to Portulaca grandiflora Over the subsequent days, both species maintained a survival rate of approximately 97-99% By the end of the operational stage, the survival rate for both plants reached around 99%.
Vegetation performance is significantly shaped by environmental conditions and resource availability, making the identification of suitable plants essential for system development This approach not only maximizes the lifespan of selected plants but also reduces costs Key factors to consider when selecting plants include geographical location, rainfall intensity, humidity, wind, and sunlight For large green roofs, optimal vegetation should exhibit characteristics such as drought resistance, local availability, cost-effectiveness, minimal irrigation needs, short and soft root systems, adaptability to low-nutritional environments, and low maintenance requirements.
More transpiration; Can reduce heat island phenomenon, Vernonia elliptica and
Portulaca grandiflora exhibits several beneficial properties, but it can experience mortality during certain stages due to environmental changes, such as transitioning from land to water, extreme weather conditions, and an inability to adapt to variations in nutrient levels.
During the operational periods of GR_15 and GR_20, the growth in length of Vernonia elliptica and Portulaca grandiflora was observed, highlighting the differences in their growth patterns Figure 4.2 illustrates the comparative growth metrics for both plant species, showcasing their development over time in response to varying operational conditions.
In the early adaptation phase with a nutrient loading rate (NLR) of 8 ± 2 kg N/ha/day, plant growth was initially slow due to their adjustment to utilizing nutrients from domestic wastewater and the limited nutrient availability However, as the operation progressed and the plants became accustomed to receiving water and nutrients from domestic wastewater, they exhibited significant growth and vitality by the end of the NLR period.
During the initial 30 days of adaptation to nitrogen loading rates (NLR) of 15 and 20 kg.N/ha/day, plant growth is minimal as they acclimate to their new environment By day 30, plants have fully adapted to wastewater, resulting in a significant increase in growth rate from day 30 to day 95 In the operational phase from day 95 to day 125, Vernonia elliptica exhibits a growth rate of 0.558 cm/day, surpassing Portulaca grandiflora's rate of 0.06 cm/day Additionally, during this period, the growth rates of both species change, with an observed increase to 0.61 cm/day as nitrogen loading is elevated.
Vernonia elliptica consistently exhibits a higher growth rate than Portulaca grandiflora, surpassing 0.07 cm per day Throughout the study period, both plants demonstrated improved growth at a nitrogen loading rate (NLR) of 20 kg N/ha/day compared to lower rates In conclusion, the optimal growth for both species occurs at an NLR of 20 kg N/ha/day, indicating favorable conditions for their development.
4.1.2 The treatment efficiency of nutrients and organic matter of GRs
The efficiency of nitrogen treatment in green roofs (GRs) relies on key mechanisms such as ammonia evaporation, nitrification, and denitrification Additionally, nitrogen is absorbed by plants and symbiotic bacteria present in the roots, further enhancing the overall treatment process.
Figure 4.3 pH value at different NLR
The pH levels in the wastewater treatment process were unstable, primarily due to the mixing of wastewater with clean water During treatment, the pH values at the tank's effluent measured 7.5 ± 0.2 and 7.5 ± 0.3, indicating a decrease influenced by the plants and materials used Despite this reduction, the pH remained within the acceptable range for plant growth Notably, during the operational period, the pH experienced a significant drop compared to the influent levels, attributed to more frequent wastewater collection and decreased sunlight penetration into the tank, which inhibited algae growth.
The influent and effluent values comply with the permissible limits set by QCVN 14:2008/BTNMT During the chemical nitrification process, the pH value decreases, indicating a reduction in water alkalinity (NH4+/NH3), as shown by a higher nitrate output than input The pH levels recorded are 7.5 ± 0.3 for GR_15 and 7.4 ± 0.3 for GR_20, which fall within the acceptable range established by Galve et al (2021) for vertical subsurface flow constructed wetlands in the Philippines, which is between 6.5 and 8.0.
44 higher than Ilyas et al (2020) vertical subsurface flow constructed wetland in
Figure 4.4 Variation of TSS value in GR_15 and GR_20
Suspended solids in constructed wetlands (CW) are effectively removed from wastewater through physical processes like filtration and sedimentation, as demonstrated in this study where total suspended solids (TSS) removal was significantly achieved The enhanced removal efficiency can be attributed to the horizontal surface flow configuration of the gravel beds, which extends the water path and improves filtration Additionally, the influent wastewater, sourced from the surface of the septic tank's sedimentation compartment and diluted three times, contained minimal suspended solids The physicochemical mechanisms, including sedimentation and adsorption, facilitate the retention of larger solid residues within the system's material layers, such as coal, oyster shell, and rock, leading to a substantial decrease in TSS concentration during the operational period.
The study found that Total Suspended Solids (TSS) concentrations for two nitrogen load rates, 15 kgN/ha/day and 20 kgN/ha/day, were measured at 22 ± 6 mg/L, 10 ± 2 mg/L, and 10 ± 3 mg/L, respectively Importantly, these effluent values remain within the permissible limits set by QCVN 14:2008/BTNMT, which stipulates a maximum TSS concentration of 100 mg/L.
During operational stage, the TSS’s removal rate of the GR_20 (1.57 ± 1.08 kgTSS/ha/day) is higher than the TSS’s removal rate of the GR_15 (1.24 ± 0.68 kgTSS/ha/day)
Figure 4.5 COD concentrations at different NLR
The concentration of Chemical Oxygen Demand (COD) in wastewater is partially reduced by granular reactors (GRs) through the decomposition and absorption of organic matter This process is facilitated by bacteria that parasitically inhabit the material layer and plant roots, effectively aiding in wastewater treatment.
In Figure 4.5, the input and output COD concentrations at different nitrogen loads: the input, output of COD concentrations at 2 loads NLR = 15 and 20
46 kgN/ha/day are 26 ± 8; 19 ± 6 and 18.6 ±6, respectively In general, the COD concentration in both loads is below the allowable standard according to QCVN
Figure 4.6 COD’s removal rate of GRs Note:
RR-15: Removal rate of GR_15 system
RR-20: Removal rate of GR_20 system
GRs’ COD removal mechanism is based on biodegradation and filtration through the material layer Aerobic, anaerobic and anaerobic processes exist in the
The root systems of plants play a crucial role in reducing carbon content in groundwater resources (GRs) by fostering an optimal environment for microbial growth This process of biodegradation takes place when dissolved organic matter permeates the microbial layer that adheres to submerged plant stems, root systems, and filter media.
The effectiveness in increasing urban green areas
Urban green spaces serve as vital habitats and resources for wildlife in cities Commonly found in suburban areas, these green spaces include parks and roadside vegetation However, as urban populations continue to rise and available space diminishes, the importance of preserving and expanding these areas becomes crucial for supporting urban biodiversity.
54 limited, space-efficient green solutions like green roofs and walls in metropolitan areas are becoming increasingly common
Urban Heat Island (UHI) effects can lead to various health issues, including transient thermal fatigue, heat rash, fainting, and respiratory problems, primarily due to significant water loss through perspiration and potential salt depletion In urban areas, elevated temperatures increase the demand for air conditioning systems by nearly threefold, while their efficiency declines by approximately 25% (Santamouris et al., 2014) Utilizing plants on green roofs (GRs) can help mitigate the absorption of solar radiation and reduce the heating of traditional roof surfaces (Mirnezhad et al.).
Table 4.1 showed temperature at three places during three specific time during
NLR operation days The results were recorded from 01/04 -> 30/04/2024
Table 4.1 Temperature variation during NLR (Unit: o C)
Afternoon (4pm) Without roof (Air temperature) 36.2 ± 0.4 38.4 ± 0.7 37.5 ± 0.5
Figure 4.12 Temperature variation during NLR
The Figure 4.12 shows that highest temperature is around noon (12 PM) around 38˚C without roof and lowest in the morning around 35.8˚C on roof with GRs
Research indicates that green roofs (GRs) can slightly reduce rooftop temperatures by approximately 0.1˚C during the morning and afternoon, with no significant difference at noon A study conducted at a large wetland facility in the Middle East found that constructed wetlands (CWs) lowered temperatures by 10°C over a one-kilometer distance (Stefannakis, 2019) Additionally, GRs enhance the thermal insulation of buildings, leading to a reduction in cooling energy demand by 10% to 40% in top-floor apartments, depending on climatic conditions and building structure (Scharf et al., 2019) In buildings lacking air conditioning, temperatures on the top floors can be about 2°C cooler than those with traditional roofs (Santamouris et al., 2014) However, the cooling effects of GRs are more pronounced at a lab scale with smaller areas.
Morning (8am) Noon (12pm) Afternoon (4pm)
Set - up timeWithout roof Roof with GR Without GR
Green roofs (GRs) are acknowledged for their sustainability and ability to enhance building envelope performance Research by Rosasco et al (2019) indicates that when evaluating the entire lifespan of a roof, extensive green roofs offer lower costs compared to conventional flat roofing solutions.
Bianchini and Hewage (2012) highlighted that green roofs offer sustainable long-term solutions for urban environments These eco-friendly installations significantly reduce sound exposure both near and within buildings (Renterghem et al., 2018) Additionally, green roofs are acknowledged as effective water-sensitive urban design systems, enhancing the quality of urban water runoff.
The adoption of Green Roofs (GRs) is limited by various challenges, including a lack of technical knowledge among designers, increased structural load on buildings, roof shape and slope considerations, and property rights issues Additionally, economic factors such as the initial investment and ongoing maintenance costs further complicate the implementation of this sustainable solution.
In today's context, selecting a greening system requires careful consideration of various environmental, social, and economic factors A SWOT analysis, as illustrated in Table 4.2, can effectively evaluate the elements that promote or obstruct the adoption of green roofs.
A SWOT analysis is a strategic planning tool designed to identify the Strengths, Weaknesses, Opportunities, and Threats related to a project or organization This framework helps align an organization’s objectives and capabilities with its operational environment This factsheet explores the four key elements of SWOT, offers guidance on conducting the analysis, and includes a practical SWOT analysis template It also discusses the ideal scenarios for utilizing a SWOT analysis, along with its benefits and drawbacks.
Table 4.2 SWOT analysis for expanding GRs
- Using domestic wastewater from the existing system, plants absorb domestic wastewater as a source of nutrients
- Reduce pressure on the general wastewater treatment system
Utilizing domestic wastewater for irrigation and as a nutrient solution for plants can significantly lower operating and treatment costs while providing essential minerals beneficial for plant growth This practice not only enhances water efficiency but also minimizes environmental losses.
- + The amount of wastewater used to operate the system, as well as the treatment costs corresponding to that amount of wastewater
- + System operating costs (human and material resources, )
Treatment benefit = Cost of conventional wastewater treatment – Cost of operating a green roof system
- Energy saving: Reduce electricity costs by helping to balance environmental temperature: in the temperature
- Water requirement: depending on the characteristic and amount of domestic wastewater, it can cause a lack of nutrients for plants
- Seasonal limitations: depends on weather factors because it is an open system
- Complex Installation: Costly and complicated:
+ The system is placed high up so there are problems with transportation and the pressure of the system's weight on the roof
Many businesses in Vietnam have yet to implement green roof systems in their factories As a result, those interested in adopting this sustainable solution face significant expenses related to feasibility assessments, renovations, and design modifications.
- Human requirement: This is a system with an unstable
58 measurement results in places with and without green roof systems, we have evidence of indirectly contributing to reducing electricity costs (Boafo et al.,,
- Meeting demand for green solutions: solution to help increase green areas in the trend of increasingly shrinking green areas in HCMC
- Storm-water management: for cities that frequently face flooding after heavy rains, green roofs can be an interesting solution
Vegetation, if arranged scientifically, can retain rainwater falling on the roof, then gradually return it to the atmosphere through the natural process of condensation and evaporation (Palla et al., 2010)
- Using common materials: Plants are easy to adapt and take care; Raw materials are easy to find and cheap (seashells, charcoal, )
- Simple operating model operating flow (because the input water is not stable), so it requires a technical operator
- Climate change: global warming, requiring measures to respond
- Government initiatives and incentives: encouraging the adoption of eco-friendly practices by providing incentives and
- Environmental impact: watering and suitability for the climate need evaluations
59 subsidies for homeoners who invest in sustainable measures
- Diversification of building market: a new facade solution that can be novelty
- Rising awareness of health benefits:
Green roof not only provide environmental benefits but also contribute to improved air quality and overall well-being
- Weight of materials: verification of the back wall and the anhor systems
The TOWS matrix was shown in Table 4.3 is expressed through 4 strategies
The SO, ST, WO, and WT strategies are derived from the analysis of the four key elements of the SWOT matrix: Strengths, Weaknesses, Opportunities, and Threats Conducting a SWOT analysis is essential as it serves as the foundational step before progressing to the TOWS matrix, where strategic planning takes shape.
‒ SO: using strengths to take advantages of opportunities
‒ ST: Using strengths to avoid threats
‒ WO: Overcome weakness to take advantage of opportunities
‒ WT: Minimize weaknesses and avoid threats
- Using domestic wastewater from available systems, respond government requirements to support environmentally friendly and sustainable initiatives
- Simple operating model to minimize the impact of lack of technical tools
- Using common materials are easy to grow and easy to
- Storm-water management for cities that frequently face flooding after heavy rains, especially with the increasingly complicated climate change situation, green roofs can be an interesting solution
- Using common materials create conditions for diversification of building market
- Simple operating model increases community access and contributes to improvement awareness take care, minimizing the effects of lack of knowledge
, easier to access and promote
- Using water from the available wastewater system reduces pressure on the amount of water needed for irrigation -> saving money
- Depends on weather factors because it is an open system, but it is also an inevitable trend of climate change (forcing early adaptation)
Choosing suitable (eco-friendly) materials will contribute to regulating extreme weather
- Although it depends on domestic wastewater (nutrient deficiency may occur), it meets the government's requirements to encourage projects that improve the environment
- Requires human resources with operational techniques that can rise awareness of learning about and accessing the system in particular as well as the benefits of projects
To effectively design and install a green roof system from the outset, it is essential to calculate the building's structure and assess the weight pressure of the green roof This proactive approach minimizes knowledge gaps in installation and renovation, thereby preventing structural changes, technological issues, and unexpected cost escalations.
61 that help improve environmental issues in general
- Complex installation but can create a new construction market (businesses can exploit the potential for energy saving, aesthetics, etc.)
Concluded, expanding the GRs with available domestic wastewater sources, common materials, simple models, and appropriate roof systems -> is the optimal solution to increasing urban green areas
Cost-benefit analysis is a systematic approach used to evaluate the financial advantages of a decision by subtracting the associated costs from the anticipated benefits This analysis focuses on quantifiable financial metrics, such as revenue generated or expenses reduced, that arise from the decision to undertake a specific project.
Calculated based on the system's parameters: the total green area is 1.08 m 2
In Ho Chi Minh City, the current domestic water pricing is governed by Decision 25/2019/QD-UBND, with the lowest rate set at 6,700 VND/m³ for households consuming up to 4 m³ per person per month For usage between 4-6 m³, the price is 12,900 VND/m³, while consumption exceeding 6 m³ is charged at 14,900 VND/m³ Administrative agencies pay a rate of 13,000 VND/m³, and production units are charged 12,100 VND/m³, whereas businesses and services face a higher rate of 21,300 VND/m³ Additionally, the cost for drainage and wastewater treatment services is outlined in Decision 17/2021/QD-UBND, with a projected price of approximately 3,250 VND/m³ in 2024, which will be 25% of the clean water selling price excluding VAT Given that GRs generates about 15 liters of wastewater daily, the annual treatment cost for GRs in 2024 is estimated to be around 18,000,000 VND.
Life Cycle Assessments (LCA) provide a comprehensive analysis of the environmental, social, economic, and technical aspects of green roofs (GRs) Coban et al conducted a comparison between traditional gravel ballasted roofs and green roofs, highlighting the advantages of adopting green roofing solutions.
CONCLUSION AND RECOMMENDATION
Conclusions
This study demonstrates that the use of Vernonia elliptica and Portulaca grandiflora in constructed wetlands effectively treats domestic wastewater, meeting the National Technical Regulation for Domestic Wastewater QCVN14:2008/BTNMT column B standards Vernonia elliptica shows superior adaptability, with higher survival rates and biomass growth, alongside enhanced wastewater treatment capabilities Notably, the Chemical Oxygen Demand (COD) removal rate is greater at a Nitrogen Loading Rate (NLR) of 20 kgN/ha/day (0.92 ± 0.70 kg.COD/ha/day) compared to 15 kgN/ha/day (0.74 ± 0.42 kg.COD/ha/day) Additionally, the total nitrogen (TN) removal efficiency of the full-process model is exceptionally high, achieving 96-97%, with a TN removal rate of 12.5 ± 6.3 kgN/ha.day at 20 kgN/ha/day, surpassing the 10 ± 4 kgN/ha.day at 15 kgN/ha/day The total phosphorus (TP) removal rate at 15 kgN/ha/day is recorded at 0.07 ± 0.03 kgP/ha.day.
The removal rate of total phosphorus (TP) at a nitrogen loading rate (NLR) of 20 kg N/ha/day is significantly higher, measuring 0.08 ± 0.07 kg P/ha/day This indicates that an increase in NLR enhances both treatment efficiency and the removal rate of growth responses (GRs) The findings demonstrate that plants are capable of effectively removing organic matter from water.
The system showcases effective cooling performance even under fluctuating temperatures of ± 0.1˚C Expanding green roofs (GRs) using accessible domestic wastewater sources, readily available materials, straightforward designs, and suitable roofing systems is the best approach to enhance urban green spaces.
Recommecdations
To accurately assess treatment efficiency and make comparisons, the system should be operated under various nitrogen loads Simultaneous monitoring of plant development cycles in greenhouse conditions is essential Further research on plant varieties can enhance environmental and ecological efficiency while increasing commercial value Additionally, exploring new materials that are lighter, more cost-effective, and available in different thicknesses can help reduce stress on roofs in practical applications.
For an accurate evaluation of installation, operation, and maintenance costs in small-scale deployments, it is essential to conduct a thorough assessment The development and performance analysis of the system suggest increasing the nitrogen load to better understand the green roof system's load-bearing capacity, which will aid in further research and topic development.
Agarry, S E., Oghenejoboh, K M., Latinwo, G K., & Owabor, C N (2020) Biotreatment of petroleum refinery wastewater in vertical surface-flow constructed wetland vegetated with Eichhornia crassipes: lab-scale experimental and kinetic modelling
Environmental technology, 41(14), 1793–1813 https://doi.org/10.1080/09593330.2018.1549106
Ahasan, T., Ahmed, S.F., Rasul, M.G., Khan, M.M.K & Azad, A.K (2014) Performance
Evaluation of Hybrid Green Roof System in a Subtropical Climate Using Fluent
Journal of Power and Energy Engineering, 2, 113-119 http://dx.doi.org/10.4236/jpee.2014.24017
Alves Sanchez, A., Carolina Ferreira, A., Martins Stopa, J., Cardoso Bellato, F., Araújo de
The study by Jesus et al (2018) investigates the effectiveness of planted (Typha sp and Eleocharis sp.) and unplanted constructed wetlands in removing organic matter, turbidity, and apparent color from wastewater The research, published in the Journal of Environmental Engineering, highlights the significant role that vegetation plays in enhancing the treatment efficiency of constructed wetlands The findings suggest that integrating specific plant species can improve water quality outcomes, making these systems a viable option for sustainable wastewater management For further details, refer to the publication at https://doi.org/10.1061/(ASCE)EE.1943-7870.0001443.
Bianchini, F., & Hewage, K (2012) Probabilistic social cost-benefit analysis for green roofs: A lifecycle approach Building and environment, 58, 152-162 https://doi.org/10.1016/j.buildenv.2012.07.005
Brovelli, A., Carranza-Diaz, O., Rossi, L., & Barry, D (2011) Design methodology accounting for the effects of porous medium heterogeneity on hydraulic residence time and biodegradation in horizontal subsurface flow constructed wetlands
Ecological Engineering, 37(5), 758–770 https://doi.org/10.1016/j.ecoleng.2010.04.031
Choi, J Y., Maniquiz-Redillas, M C., Hong, J S., Lee, S Y., & Kim, L H (2015)
Comparison of the treatment performance of hybrid constructed wetlands treating stormwater runoff Water Science and Technology, 72(12), 2243-2250 https://doi.org/10.1038/s41586-019-1001-1
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APPENDICES Appendice 1 GR-lab scale system with Vernonia elliptica and Potulaca grandiflora
The dimensions of Roof (length x width) are 4m x 2m
Appendice 2 Biomass increased throughout the experiment (01/12/2023- 30/05/2024)
COD results achieved at NLR = 15 and 20 kgN/ha.day by Vernonia elliptica and Potulaca grandiflora
COD concentration (mg/L) NLR = 15 kgN/ha.day
COD concentration (mg/L) NLR = 20 kgN/ha.day
COD removal rate (kgCOD/ha day) NLR = 15 kgN/ha.day
COD removal rate (kgCOD/ha day) NLR = 20 kgN/ha.day
TN results achieved at NLR = 15 and 20 kgN/ha.day by Vernonia elliptica and
TN concentr ation (mg/L) NLR = 15 kgN/ha.d ay
TN concentr ation (mg/L) NLR = 20 kgN/ha.d ay
TN removal rate (kgN/ha day) NLR =
TN removal rate (kgN/ha day) NLR =
TN removal efficien cies (%) NLR =
TN removal efficien cies (%) NLR =
TP results achieved at NLR = 15 and 20 kgN/ha.day by Vernonia elliptica and
TP concentr ation (mg/L) NLR = 15 kgN/ha.d ay
TP concentr ation (mg/L) NLR = 20 kgN/ha.d ay
TP removal rate (kgP/ha day) NLR =
TP removal rate (kgP/ha day) NLR =
TP removal efficien cies (%) NLR =
TP removal efficien cies (%) NLR =