Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Khả năng hấp phụ dinh dưỡng và giảm phát thải khí nhà kính của than trấu và than lục bình.Bia tom tat luan an TS English 7 pdf MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY o0o SUMMARY OF PhD THESIS Specialization Land and Water Environment Code 62 44 03 03 NGUYEN ĐAT PHUONG ABILIT.
MINISTRY OF EDUCATION AND TRAINING CAN THO UNIVERSITY -o0o - SUMMARY OF PhD THESIS Specialization: Land and Water Environment Code: 62 44 03 03 NGUYEN ĐAT PHUONG ABILITY TO ADSORB NUTRIENTS AND REDUCE GREENHOUSE GAS EMISSIONS FROM RICE HUSK BIOCHAR AND WATER HYACINTH BIOCHAR Can Tho, year 2023 WORK COMPLETED AT SCHOOL CAN THO UNIVERSITY Scientific supervisor: Assoc Prof Dr Nguyen Xuan Loc Sub-instructor: Assoc Prof Dr Ngo Thuy Diem Trang The thesis is defended before the School-level PhD Thesis Evaluation Council Meeting at: Hall …………………….…, Can Tho University At …… hour …… …., 2023 Reviewer 1: Reviewer 2: Confirmation of review by the President of the Council Thesis can be found at the library: - Learning Resource Center, Can Tho University - Vietnam National Library LIST OF PUBLICATIONS International journal Loc X Nguyen, Phuong T M Do, Chiem H Nguyen, Ryota Kose, Takayuki Okayama, Thoa N Pham, Phuong D Nguyen, and Takayuki Miyanishi, 2018 Properties of Biochars Prepared from Local Biomass in the Mekong Delta, Vietnam Jounal of Bioresources, vol 13, pp 7325-7344, 2018 Domestic journal Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Huu Chiem, Pham Ngoc Thoa and Nguyen Xuan Loc, 2020 Adsorption study of nitrate from initial wastewater of biogas by Water Hyacinth (Eichhornia crassipes) biochars follow the Langmuir and Freundlich isotherms Jounal of Agriculture and Rural Development, vol 18(2), pp 90-96 Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Huu Chiem and Nguyen Xuan Loc (2020) The study of the NO3- adsorption of rice husk biochar (O Sativa L., OM 5451) according to kinetic and isothermal model Jounal of Agriculture and Rural Development, vol 20(2), pp 101-107 Nguyen Đat Phuong Nguyen Xuan Loc, 2020 Some influence factors for NH4+ adsorption on water hyacinth biochar (Eichhornia crassipes) TNU Journal of Science and Technology, vol 225(14), pp 113-119 Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Huu Chiem, Pham Ngoc Thoa and Nguyen Xuan Loc, 2021 Adsorption of nitrate by biochar prepared from rice husks (O sativa L., OM5451) Hue University Journal of Science: Natural Science, vol 130(1A), pp 31-39 Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Huu Chiem, Pham Ngoc Thoa, Lam Van Toan and Nguyen Xuan Loc, 2021 Study on adsorption of nitrate by water hyacinth (Eichhornia crassipes) biochar TNU Journal of Science and Technology, vol 226(02), pp 1724 i Nguyen Đat Phuong and Nguyen Xuan Loc, 2021 Study on the growth of water spinach when adding rice husk biochar was adsorbed ammonium TNU Journal of Science and Technology, vol 226(11), pp 371-379 Nguyen Đat Phuong Nguyen Xuan Loc, 2022 Effective of biochar prepared from rice husk to greenhouse gas emissions TNU Journal of Science and Technology, vol 227(07), pp 114-122 Đo Thi My Phuong, Phan Thi Thanh Tuyen, Nguyen Thi Thien Truc, Nguyen Đat Phuong, Pham Ngoc Thoa, Nguyen Huu Chiem and Nguyen Xuan Loc, 2020 Adsorption of Methyl Orange from aqueous solution using water hyacinth biochars (Eichhornia crassipes) Jounal of Agriculture and Rural Development, vol 18(2), pp 97-103 Pham Ngoc Thoa, Tang Le Hoai Ngan, Đang Thi Minh Thuy, Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Xuan Loc, Nguyen Huu Chiem 2021 Study on adsorption of ammonium ion from aqueous solution by melaleuca biochar Jounal of Agriculture and Rural Development, vol 17(1), pp 129-136 10 Pham Ngoc Thoa, Tang Le Hoai Ngan, Đang Thi Minh Thuy, Nguyen Đat Phuong, Đo Thi My Phuong, Nguyen Xuan Loc, Nguyen Huu Chiem 2021 Effects of pH, biochar dodage, retention time and nitrate concentration on nitrate adsorption of bamboo biochar in biogas effleent Can tho University, Journal of Science, Special issue Environment, vol 57 (Chuyên đề Môi trường Biến đổi khí hậu), pp 14-23 ii Chapter INTRODUCE 1.1 Pose Biochar is a carbon-rich product obtained by pyrolysis of biomass such as wood, manure or leaves that are burned in the presence of little or no oxygen (Lehmann and Joseph, 2012) Raw materials are very diverse, where organic byproducts in agriculture are a common and inexpensive source In the environmental field, biochars have been applied to nutrient adsorption (Clough, et al., 2013; Mizuta, et al., 2004; Yao, et al., 2012) as a vector for soil improvement (Lehmann et al., 2011), carbon storage (Yoo, et al., 2015; Lin, et al., 2015; Chan, et al., 2008) and reduced greenhouse gas emissions (Mukherjee & Lal, 2013; Xie, et al., 2015) Wastewater from livestock production is a source of high nutrient content such as P-PO43− ranging from 37.2 to 51.1 mg L−1; N-NO3− from 0.30 to 1.14 mg L−1; N-NH4+ from 105.6 – 217.9 mg L−1 (Nu et al., 2015) If this concentration is not collected and treated, it will be a cause of surface water pollution Especially, if N-NH4+ content is high, it may cause harm to aquatic organisms and cause eutrophication in rivers and lakes In addition, nitrate concentrations in water may pose a threat to public health, such as cancer (Song, et al., 2015), nervous tissue and cognitive damage (Lefferts, et al., 2015) Nitrate has stable properties and high solubility in water Therefore, effective and economical removal of nitrate from water has become a problem In addition to the harmful effects of livestock activities, rice cultivation is also a source of greenhouse gas (GHG) emissions that increases the earth's temperature causing global warming For the production activities of the sector, the emissions from submerged rice farming amount to over 57% of the sector's GHG, mainly CH4 and N2O (Chan, et al., 2008a; Nguyen, et al., 2015); Trinh, et al., 2013) Rice husks and water hyacinth are two major sources of by-products in Vietnam According to calculations, the total amount of rice husks in the country is estimated at 6.54 million tons per year This amount of rice husk is mainly processed by heat-collecting method, thus causing large environmental pollution Besides, the rapid growth of water hyacinth (140 tons per year) (Gunnarsson and Petersen, 2007a) has become a problem in canals, ditches, and lakes in many parts of the world such as obstructing traffic on rivers and canals, especially when they die, they severely pollute the aquatic environment Currently, methods have been used to solve the above problems such as membrane filtration, advanced oxidation, photocatalytic decomposition, and adsorption methods Among them, adsorption is one of the simplest, most effective and suitable methods because the adsorbent material is made from cheap rice husk and water hyacinth available locally The material after adsorption is used as a carrier to supplement nutrients for plants, increase the ability to store carbon in the soil and reduce GHG emissions, limiting the impact of climate change Biochar can be produced from many sources, including organic agricultural by-products of rice shells and water hyacinth, which are common and inexpensive sources in the Mekong Delta, to achieve a dual purpose of economic and environmental performance Greenhouse gas emissions are an environmental concern and emissions must be restricted in line with Vietnam's international commitments The selection of locally available materials that absorb nutrients in water will help to reduce the cost of water pollution treatment In addition, soiladded materials must be tested to reduce total GHG emissions Stemming from the above reasons, the topic: "Ability to adsorb nutrients and reduce greenhouse gas emissions from rice husk biochar and water hyacinth biochar" was conducted 1.2 Research objectives 1.2.1 General objective Research on nutrient adsorption and reduction of greenhouse gas emissions by biochar produced from agricultural by-products, contributing to reducing environmental pollution and reducing GHG emissions from agricultural farming activities 1.2.2 Specific Objectives Produce rice husk biochar and water hyacinth biochar Determination of nutrient adsorption capacity in biogas wastewater by rice husk biochar (RHB) and water hyacinth biochar (WHB) for reducing soil and water pollution Determine the ability to reduce GHG emissions when adding RHB and WHB for reduces air pollution 1.3 Research content - Content 1: Research on the physical and chemical composition of RHB and WHB - Content 2: Research on nutrient adsorption capacity in biogas wastewater by RHB and WHB - Content 3: Determine the ability to reduce CH4 and N2O emissions of RHB and WHB 1.4 Research limitation Study on the NH4+ and NO3− adsorption capacity of biogas wastewater and the possibility of reducing CH4 and N2O emissions by RHB and WHB produced at 700oC under the conditions of the net house 1.5 Meaning of the thesis 1.5.1 Science The results of the thesis show that two types of biochar produced from local biomass sources are rice husk and water hyacinth made in laboratory conditions with controlled temperature, N2 gas environment The physical and chemical properties of the two biochars were determined using modern, scientific analytical methods Adsorption capacity of NH4+ and NO3− in the biogas wastewater; ability to reduce CH4 and N2O emissions from rice cultivation land of two types of biochar has been evaluated through results published in journals with domestic and international indexes such as: Journal of Agriculture & Rural Development (ISSN 1859-4581), TNU Journal of Science and Technology (ISSN 1859-2171; 2734-9098) and Journal of Bioresources (UGC-CARE Quality Journal, ISSN 2394-4315 – E-ISSN 2582-2276) 1.5.2 Practice Biochar is produced from low-cost local agricultural by-products (rice husk and water hyacinth) to adsorb nutrients (NH4+ and NO3−) into livestock wastewater, reducing environmental pollution Biochar after adding to the soil has the ability to reduce greenhouse gas emissions (CH4 and N2O) in agricultural production in the Mekong Delta These results of the research can be used as documents for teaching and research at institutes and universities 1.6 New point of the thesis Rice husk biochar and water hyacinth biochar produced at 700oC are both capable of adsorption of NH4+ and NO3− in biogas wastewater The highest adsorption capacity of NH4+ and NO3− of RHB and WHB was 5.51 mg/g and 4.31 mg/g, respectively; 9.87 mg/g and 9.59 mg/g, respectively (efficiency 24.71% and 26.71%; 69.70% and 64.14%) Adding 20 tons/ha of RHB or WHB to agricultural land was most effective in reducing CH4 and N2O emissions such as 15.99%, 48.47% of RHB and 20,14%, 51,90% for WHB, respectively Biochar is produced from cheap local materials such as rice husk, a by-product of rice production, and water hyacinth, a plant that can be found in many parts of Vietnam as a nutrient absorbent Reduces environmental pollution and reduces greenhouse gas emissions from crop farming, which enhances economic and environmental benefits for people in the region and contributes to limiting the impact of global climate change Chapter SUBJECTS AND METHODOLOGY 2.1 Research subjects Rice husk biochar and water hyacinth biochar at 500°C, 700°C and 900°C; adsorption capacity of NH4+ and NO3− in biogas wastewater; and ability to reduce CH4 and N2O emissions from rice cultivation land 2.2 Research Methodology 2.2.1 Content 1: Research on the physical and chemical composition of rice husk biochar and water hyacinth biochar Research materials - Materials: Rice husk biochar and water hyacinth biochar at 500oC, 700oC and 900oC; BaCl2, MgSO4, EDTA, NaOH and HCl - Equipment: pH meter, EC, centrifuge, sample shaker, analytical balance, electric furnace, carbon, hydrogen and nitrogen analyzer, electron microscope S-4800 and surface area meter Treatments design The experiment was performed with replicates for each treatment Analytical method Chỉ tiêu pH, EC Moisture Volatile matter CEC Morphology and structure Surface area pHpzc Phương pháp Direct measurement with pH, EC meter (METER HM-31P) Drying method according to TCVN 1867:2001 Heated at 900°C±20°C for minutes in an airless condition Determined by extraction with BaCl2 0.1 M solution three times to exchange exchangeable cations with Ba2+ Then, add standard 0.02 M MgSO4 solution to replace Ba2+ and BaSO4 precipitate occurs Determined by electron microscope S-4800 Measure by Quantachrome Instruments version 11.0 Method of Balistrieri and Murray (1981) 2.2.2 Content 2: Research on nutrient adsorption capacity in biogas wastewater by rice husk biochar and water hyacinth biochar Research materials - Rice husk biochar and water hyacinth biochar at 700°C - Chemical: NaOH, HCl NH4+, NO3− solutions were obtained from biogas wastewater from pig farmers in Binh Thuy district, Can Tho city - Tools and equipment: Air blower, pH meter, DO meter, EC meter, NH4+ and NO3− meter Treatments design to determine the effect of pH The experiment was performed with treatments (ammonium), 10 treatments (nitrate) and repeated times Prepare a solution of ammonium with concentration 80 mg/L, nitrate with concentration 50 mg NO3− L−1, use 0.1M NaOH, 0.1M HCl to change pH from to 11 (pH = 2, 4, 6, 7, 8, 9, 10, 11) for ammonium; (pH = 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) for nitrate Weigh 0.5 g of RHB/WHB into a centrifuge tube Next, add 50 mL of pH adjusted solution (NH4+/NO3−) Then shake for 120 minutes at a speed of 190 rpm, finally filter through Whatman 0.45 µm filter paper, analyze NH4+ and NO3− content Treatments design to determine the effect of adsorbent dosage The experiment was performed with treatments and repeated times Prepare a solution of ammonium with concentration 80 mg/L, nitrate with concentration 50 mg NO3− L−1, use 0.1M NaOH, 0.1M HCl to change pH (pH = for RHB; pH = for WHB) for ammonium; pH = for nitrate Weigh: 0.25, 0.5, 1, 1.5, g of RHB/WHB for ammonium; 0.05, 0.5, 1, 1.5, g of RHB/WHB put nitrate into a centrifuge tube Next, measure 50 mL of pH adjusted solution (NH4+/NO3−) Then shake it for 120 minutes with shaking speed of 190 rpm, finally filter through Whatman 0.45 µm filter paper, analyze NH4+ and NO3− content Treatments design to determine the effect of contact time The experiment was performed with 11 treatments and repeated times Prepare a solution of ammonium with concentration 80 mg/L, nitrate with concentration 50 mg NO3− L−1, use 0.1M NaOH, 0.1M HCl to change pH (pH = for RHB; pH = for WHB) for ammonium; pH = for nitrate Weigh: g of RHB/WHB for ammonium; 0.5 g of RHB/WHB put nitrate into a centrifuge tube Next, measure 50 mL of pH adjusted solution (NH4+/NO3−) Then shake with shaking speed 190 rpm with time of 1, 2, 5, 10, 15, 30, 60, 90, 120, 240 and 360 minutes, respectively Finally filter through Whatman 0.45 µm filter paper, analyze NH4+ and NO3− content Two kinetic models have been used such as apparent kinetics of order and order Treatments design to determine the effect of the initial concentration The experiment was performed with treatments and repeated times Prepare a solution of ammonium and nitrate with concentrations RHB ∆pH = pHi - pHf ∆pH = pHi - pHf -2 101112 -4 -6 pHi WHB -2 101112 -4 -6 pHi 10 H qe 0,8 0,6 0,4 0,2 20 H (%) RHB 15 qe (mg g-1) H (%) 20 WHB 15 10 H qe 0,8 0,6 0,4 0,2 qe (mg g-1) Fig 3.3 pHpzc of RHB and WHB From the above results, it is shown that biochar at 700oC can give better adsorption results at 500oC and 900oC Therefore, we chose RHB and WHB at 700oC to conduct the next experiments 3.2 Research on ammonium adsorption capacity in biogas wastewater using rice husk biochar and water hyacinth biochar 3.2.1 Effect of pH on adsorption capacity The results of the analysis are presented in Fig 3.4 101112 pH 101112 pH Fig 3.4 Effect of pH on NH4+ adsorption (Biochar dosage 0.5 g, time 120 minutes, initial concentration of NH4+ 80 mg/L, pH = – 11) The NH4+ adsorption of RHB and WHB at pH = - does not increase; pH = - increases strongly and reachs the maximum at pH = (RHB) and pH = (WHB) This can be explained because the pH of the solution is lower than the pHpzc of RHB (pHpzc = 9.51) and WHB (pHpzc = 10.1), so the surface of the biochar has a positive charge, therefore, the lower solution pH is the less positive ion adsorption capacity This result is consistent with the study of Tuyet et al.,, (2018), Mai & Tuyen (2016), and Fidel, et al., (2018a) When the pH continued to increase to 11 is the adsorption capacity decreased sharply This can explain when the pH increases, NH4+ will be converted into NH3 so reducing the adsorption capacity Therefore, the pH = (RHB) and pH = (WHB) were selected to perform the next adsorption experiments 10 3.2.2 Effect of biochar dosage on adsorption capacity Figure 3.5 shows the adsorption efficiency at different biochar dosage with 5% significant difference, except for biochar dosages of 1, 1.5 and 2g are no 5% significant difference This proves that at the biochar dosage of 1g, the adsorption performance is the best 10 H qe 1,6 1,2 20 0,8 10 0 0,5 1,5 2,5 0,4 H qe 0,5 RHB dosage (g) 1,5 qe (mg g-1) 20 30 H (%) 1,6 1,2 0,8 0,4 qe (mg g-1) H (%) 30 2,5 WHB dosage (g) Fig 3.5 Effect of biochar dosage on NH4+ adsorption (pH = (RHB), pH = (WHB), time 120 minutes, initial concentration of NH4+ 80 mg/L and biochar dosage 0.25 – g) H qe 1,2 0,8 0,6 0,4 0,2 WHB 14 12 10 H qe 1,2 0,8 0,6 0,4 0,2 qe (mg g-1) RHB H (%) 14 12 10 qe (mg g-1) H (%) The NH4+ adsorption efficiency of both coals increased sharply at biochar dosage from 0.25 to 1g, however, the adsorption efficiency increased very low and did not increase at biochar dosage from to 2g This can be explained because increasing the biochar dosage will increase the competition for NH4+ adsorption on the coal surface In the treatment of 1g, the highest adsorption amount of RHB and WHB were 0.930 mg/g and 0.904 mg/g, respectively This result is completely consistent with the research results of Fidel, et al., (2018a), Mai & Tuyen (2016) This is the condition for performing the next experiment 3.2.3 Effect of contact time on adsorption capacity The results of the analysis are presented in Fig 3.6 60 120180240300360 60 120 180 240 300 360 Time (minutes) Time (minutes) + Fig 3.6 Effect of time on NH4 adsorption (pH = (RHB), pH = (WHB), biochar dosage g, initial concentration of NH4+ 80 mg L−1 and time – 360 minutes) Figure 3.6 shows that between the time groups (1 - 120 minutes) and (120 - 360 minutes), there is a significant difference of 5%, the 11 1,2 0,8 0,6 0,4 0,2 RHB qt (mg g-1) qt (mg g-1) adsorption amount from 120 to 360 minutes is no statistical difference (p> 0.05) This can be explained before 120 minutes, the penetration of adsorbent into biochar has not reached equilibrium because the capillary size in biochar is empty, so the adsorption capacity increases strongly After 120 minutes, the capillary size of biochar was filled, so the adsorption capacity and efficiency increased slightly This is the time chosen for the next experiment Compared to the study of Tuyet et al., (2018), the study of treating ammonium in water by biochar produced from corncob with modified by HNO3 with adsorption time of 150 minutes, the absorption capacity reached 18.75 mg/g According of Mai & Tuyen (2016), N-NH4+ was quickly eliminated in the first 30 minutes and reached balance at 60 minutes Results of NH4+ adsorption of RHB and WHB according to two kinetic models of order and level are described in Fig 3.7 Experimental data Pseudo-first-order Pseudo-second-order 60 120 180 240 300 360 Time (minutes) 1,2 0,8 0,6 0,4 0,2 WHB Experimental data Pseudo-first-order Pseudo-second-order 60 120 180 240 300 360 Time (minutes) Fig 3.7 Ammonium adsorption kinetics (pH = (RHB), pH = (WHB), biochar dosage g, initial concentration of NH4+ 80 mg/L and time – 360 minutes) Table 3.2 Adsorption kinetic parameters of NH4+ Adsorbents RHB WHB Pseudo-first-order equation qe, exp qe, cal k1 R2 (1/minute) (mg/g) (mg/g) 0.94 0.94 0.035 0.97 0.91 0.91 0.036 0.97 Pseudo-second-order equation qe, exp qe, cal k2 R2 (mg/g) (mg/g) (g/mg/minute) 0.99 1.03 0.03 0.97 0.96 1.01 0.03 0.96 Table 3.2 shows that the NH4+ adsorption by the kinetic model of order and has correlation coefficient (R2 > 0.95), this proves that the NH4+ adsorption of both types of biochars are suitable for both kinetic models of order and 3.2.4 Effect of the initial concentration on adsorption capacity The results of the analysis are presented in Fig 3.8 12 10 H qe WHB 20 10 H qe qe (mg g-1) H (%) 20 30 H (%) qe (mg g-1) RHB 30 50 100 150 200 250 300 Ce (mg L-1) 50 100 150 200 250 300 Ce (mg L-1) Fig 3.8 Effect of concentration on NH4+ adsorption (pH = (RHB), pH = (WHB), biochar dosage g, time 120 minutes, initial concentration of NH4+ 10 – 300 mg/L) RHB Experimental data Langmuir Freundlich 0 qe (mg g-1) qe (mg g-1) Figure 3.8 shows that when the initial concentration increases from 10 – 300 mg/L, the NH4+ adsorption increases However, when the concentration increased from 80 to 300 mg/g, the adsorption efficiency decreased At the concentration of 80 mg/g, the adsorption efficiency was highest This can be explained when the concentration of increasing NH4+ is the level and contact between biochar and NH4+ increases, thus promoting the penetration of NH4+ into biochar In other words, the adsorbent is in a saturated state and cannot be absorbed anymore On the other hand, too high concentration of NH4+ will cause competition between ions of NH4+ to be adsorbed onto the surface, so the adsorption efficiency will decrease, if the concentration of NH4+ is too high This result is consistent with the study of Tuyet et al.,, (2018) and Dung (2016) NH4+ adsorption of RHB and WHB were 2.54 mg/g, 2.33 mg/g, achieving efficiency of 25.24% and 27.51%, respectively Figure 3.9 shows the adsorption of NH4+ according to the Langmuir and Freundlich adsorption isotherms of RHB and WHB WHB Experimental data Langmuir Freundlich 0 50 100 150 200 250 300 Ce (mg L-1) 50 100 150 200 250 300 Ce (mg L-1) Fig 3.9 Langmuir and Freundlich isotherms (pH = (RHB), pH = (WHB), biochar dosage g, time 120 minutes, initial concentration of NH4+ 10 – 300 mg/L) Table 3.3 The model parameters of isothermal adsorption NH4+ Biochar types Langmuir KL (L/mg) 0.004 Rice husk qmax (mg/g) 5.51 R 0.98 13 Water hyacinth KL qmax (L/mg) (mg/g) 0.004 4.48 R2 0.98 Biochar types KF 0.047 Freundlich Rice husk n 1.375 R2 0.97 Water hyacinth KF n 0.053 1.458 R2 0.97 60 40 20 H qe H (%) RHB qe (mg g-1) H (%) 80 80 60 40 20 WHB H qe qe (mg g-1) Table 3.3 shows that the adsorption of NH4+ according to Langmuir and Freundlich has R2 > 0.95, and the Langmuir correlation coefficient is greater than Freundlich This proves that the NH4+ ion adsorption of these two biochars described according to Langmuir shows a better fit than Freundlich, or in other words, the NH4+ adsorption process of these two biochars are monolayer adsorption and adsorption in the dominant heterogeneous material surface conditions The largest adsorption capacity according to Langmuir model of RHB and WHB are 5.51 mg/g and 4.48 mg/g, respectively 3.3 The ability to adsorb nitrate in biogas wastewater by rice husk biochar and water hyacinth biochar 3.3.1 Effect of pH on adsorption capacity The results of the analysis are presented in Fig 3.10 1011 pH 1011 pH Fig 3.10 The effect of pH on the adsorption of NO3− (Biochar dosage 0.5 g, time 120 minutes, initial concentration of NO3− 50 mg/L and pH = – 11) Figure 3.10 shows that when pH increases from – 4, the NO3− adsorption capacity and efficiency increases slightly but there is no significant difference of 5%; At pH = 4, the NO3− adsorption capacity was the highest for both RHB and WHB This result is consistent with the study of Fidel, et al., (2018b) This can be explained because pHpzc of RHB (9.51) and WHB (10.1) are greater than pH of the adsorbed solution, so the surface charge of biochar is positively charged Therefore, when the pH lows, the adsorption capacity of biochar is greater because the adsorbent is negatively charged (NO3−) According to Tan, et al., (2015), if the pH of the adsorbed solution is less than the pHpzc of the adsorbent, the surface charge of the adsorbent is positive and vice versa At pH = 11, the nitrate adsorption capacity of RHB and WHB is the lowest This can be explained that when the pH is greater 14 H qe 0,5 1,5 100 80 60 40 20 H qe RHB dosage (g) 25 20 15 10 0,5 1,5 qe (mg g-1) 25 20 15 10 H (%) 100 80 60 40 20 qe (mg g-1) H (%) than 7, there is a competition between OH− and NO3−, leading to a decrease in NO3− adsorption capacity This result is consistent with the study of Tan, et al., (2015), Chintala, et al., (2013), Zhao, et al., (2017) and Yang, et al., (2017a) Therefore, pH = was selected to perform the next experiments 3.3.2 Effect of biochar dosage on adsorption capacity The results of the analysis are presented in Fig 3.11 WHB dosage (g) Fig 3.11 The effect of biochar dosage on NO3− adsorption (pH = 4, time 120 minutes, initial concentration of NO3− 50 mg/L and biochar dosage 0.05 – g) Figure 3.11 shows that when increasing biochar dosage of RHB and WHB are the nitrate adsorption efficiency increased by 47.19 - 77.59% and 42.41 - 72.12% respectively In contrast, the adsorption capacity of RHB and WHB decreased by 22.9 - 0.94 mg/g and 20.58 - 0.87 mg/g, respectively This result is consistent with research by Hu, et al., (2018) This can be explained, when increasing biochar dosage is the number of adsorbent centers increases, but when biochar dosage increases to a certain threshold, biochar dosage of adsorbent centers calculated on the volume of the adsorbent decreases According to Deveci and Kar (2013) due to competition between ions for binding with the available adsorbent centers of the adsorbent This result is similar to that of Divband Hafshejani, et al., (2016) To determine the best adsorption mass, use statistics with the Tukey test at 5%; The results showed that, at the weight of 0.5, 1, 1.5 and 2g, the NO3− adsorption efficiency of RHB and WHB were 74.2, 71.4, 74.2, 77.6%; and 67, 66, 68.9, 72.1%, respectively which were not statistically different (p > 0.05); The results are consistent with the study of Yang, et al., (2017b) Therefore, a mass of 0.5 g is chosen for the next experiment arrangement 3.3.3 Effect of contact time on adsorption capacity The results of the analysis are presented in Fig 3.12 15 H qe 80 60 40 20 WHB H Qe 0 60 120 180 240 300 360 Time (minutes) qe (mg g-1) H (%) qe (mg g-1) H (%) RHB 80 60 40 20 0 60 120 180 240 300 360 Time (minutes) Fig 3.12 The effect of time on the adsorption of NO3− (pH = 4, biochar dosage 0.5 g, initial concentration of NO3− 50 mg/L and time - 360 minutes) RHB Experimental data Pseudo-first-order Pseudo-second-order qt (mg g-1) qt (mg g-1) Figure 3.12 shows that the adsorption process occurs in two phases: the first phase, the fast adsorption rate (1-120 minutes) and the slower the next stage (120 - 360 minutes) This increase in concentration leads to an increase in adsorption capacity in the early stage When the concentration decreases, the adsorption capacity decreases (Uddin, et al., 2008) This result is similar to that of Divband Hafshejani, et al., (2016) and Hu, et al., (2018), nitrate adsorption also has two phases: fast adsorption rate in the first stage, then slowly and reach equilibrium However in the study of Divband Hafshejani, et al., (2016) equilibrium occurs more rapidly at the 60th minute The difference in the adsorption rate can be attributed to the study of Divband Hafshejani, et al., (2016) only used 0.1 g of TSH denatured bagasse, leading to a small number of adsorption centers, so the adsorption equilibrium process took place quickly According to the results of statistical analysis with the Tukey test at 5%, the nitrate adsorption efficiency of RHB and WHB at the times of 120, 240 and 360 minutes were not statistically different Thus, time of 120 minutes was chosen to proceed for the next experiments The results of NO3− adsorption of RHB and WHB according to two kinetic models of order and level are presented in Fig 3.13 WHB Experimental data Pseudo-first-order Pseudo-second-order 60 120 180 240 300 360 Time (minutes) 60 120 180 240 300 360 Time (minutes) Fig 3.13 Adsorption kinetics of nitrate (pH = 4, biochar dosage 0.5 g, initial concentration of NO3− 50 mg/L and time - 360 minutes) 16