Nghiên cứu đặc điểm lan truyền kim loại nặng từ bãi chôn lấp chất thải rắn hợp vệ sinh tại Kiêu Kỵ, Gia Lâm, Hà Nội ttta

Mục tiêu và đối tượng nghiên cứu của luận án - Mục tiêu nghiên cứu: Luận án nghiên cứu về đặc điểm ô nhiễm, nguồn ô nhiễm, xuất phát từ nước rỉ rác của bãi chôn lấp (BCL) chất thải rắn (CTR) hợp vệ sinh nhằm thấy rõ sự ảnh hưởng đến quá trình lan truyền chất ô nhiễm trong môi trường đất bãi chôn lấp. Đánh giá và dự báo được mức độ lan truyền ô nhiễm kim loại nặng (KLN) bằng phương pháp định lượng để xây dựng dữ liệu phục vụ công tác quản lý môi trường liên quan đến bãi chôn lấp. - Đối tượng nghiên cứu: Luận án tiến hành lựa chọn đối tượng nghiên cứu là ô nhiễm kim loại nặng trong môi trường đất bãi chôn lấp chất thải rắn hợp vệ sinh - ô chôn lấp đã đóng tại Kiêu Kỵ, huyện Gia lâm, Hà Nội. Nghiên cứu các yếu tố ảnh hưởng đến quá trình lan truyền chất ô nhiễm của bãi chôn lấp để đánh giá và dự báo mức độ ảnh hưởng ô nhiễm từ bãi chôn lấp đến môi trường đất xung quanh bãi chôn lấp theo không gian và thời gian. b) Các phương pháp nghiên cứu đã sử dụng Do tính chất của đối tượng nghiên cứu là ô nhiễm phát sinh từ nước rỉ rác tại BCL, luận án đã sử dụng các phương pháp nghiên cứu như nghiên cứu lý thuyết để tìm hiểu những dấu hiệu đặc thù, bản chất, cấu trúc của phương pháp số trong cách tính toán lan truyền ô nhiễm qua đó tiến hành phân tích nội suy khái niệm, xây dựng phương trình toán học mới xác định mức độ lan truyền ô nhiễm với điều kiện biên phức tạp; sử dụng phương pháp phần tử hữu hạn để tính toán lan truyền chất ô nhiễm. Nghiên cứu đã sử dụng phương pháp phần tử hữa hạn là phương pháp số gần đúng để giải các bài toán được mô tả bởi các phương trình vi phân đạo hàm riêng trên miền xác định có hình dạng và điều kiện biên bất kỳ mà nghiệm chính xác không thể tìm được bằng phương pháp giải tích, bằng phương pháp này có thể tính toán và mô phỏng sự thay đổi nồng độ của kim loại nặng theo thời gian trong không gian một cách định lượng và rõ ràng. c) Kết quả chính và kết luận - Kết quả chính: Luận án đã tổng hợp và đề xuất phương pháp tính toán nước rỉ rác phát sinh phù hợp điều kiện khí hậu khu vực và qui trình vận hành chôn lấp chất thải rắn hợp vệ sinh. Đánh giá và dự báo được mức độ ô nhiễm kim loại nặng trong môi trường đất từ khu vực ô chôn lấp đã đóng của bãi chôn lấp hợp vệ sinh với mô hình mô phỏng 3D. Bằng việc sử dụng các khái niệm về trường vectơ gradient ∇C (x, y, z, t), và các phép toán gradient có liên quan (∇⋅), ⊙, cơ chế khuếch tán - đối lưu của chất gây ô nhiễm trong nước rỉ rác được mô hình hóa một cách cụ thể và ngắn gọn, thấy được bản chất vật lý của quá trình lan truyền một cách trực quan hơn. Biến đổi phương trình lan truyền về dạng thức phương trình vi phân đạo hàm riêng, thuật toán PTHH đã được xây dựng để giải phương trình bằng phương pháp số một cách hiệu quả. Khai thác thuật toán và sử dụng phần mềm MATLAB để tính toán, dự báo được khả năng lan truyền nồng độ chất ô nhiễm theo thời gian và trong không gian lòng đất. - Kết luận: Từ các kết quả nghiên cứu lý thuyết và thực nghiệm luận án rút ra được các kết luận như sau: Các yếu tố ảnh hưởng đến quá trình lan truyền chất ô nhiễm trong môi trường bãi chôn lấp chất thải rắn tại Kiêu Kỵ Gia Lâm bao gồm: 1) nguồn gây ô nhiễm KLN từ nước rỉ rác, 2) nồng độ KLN As trong nước rỉ rác và hàm lượng KLN As trong đất bãi chôn lấp đều vượt quá qui định cho phép QCVN 40:2011/BTNMT và QCVN 03:2015/BTNMT, 3) thời gian tích lũy chất ô nhiễm KLN do bãi chôn lấp đã tồn tại hơn 10 năm. Các kim loại nặng khác được phát hiện trong nước rỉ rác là Cr, Pb, Hg, Cd…đều có hàm lượng cao hơn qui chuẩn cho phép do chất thải rắn được chôn lấp không phân loại tại nguồn. Nước rỉ rác là yếu tố gây ô nhiễm môi trường BCL rất nghiêm trọng. Nước rỉ rác được tính toán theo phương pháp đề xuất trong luận án bao gồm các yếu tố ảnh hưởng đến lượng phát sinh từ khi vận hành chôn lấp (lượng mưa, độ bốc hơi, độ ẩm của CTR, thiết bị đầm nén, qui trình vận hành…) đến khi đóng ô và thời gian sau đó (lớp che phủ không trồng cây, có trồng cây, lớp che phủ bị suy thoái…). Các yếu tố này là phù hợp với điều kiện thực tế để tính toán lượng nước rỉ rác khi vận hành BCL tại Việt Nam nói chung và tại BCL Kiêu Kỵ, Gia Lâm nói riêng. Vành đai an toàn đối với nguy cơ ô nhiễm KLN As đã được xác định dựa theo kết quả tính toán của mô hình 1D và 3D. Theo chiều sâu, kết quả mô hình 1D đã khẳng định cụ thể tại các vị trí dễ gây tổn thương tới tầng chứa nước là đáy ô chôn lấp (cách 1,5m đến tầng chứa nước), đáy hồ chứa nước rỉ rác (4,5m), thời gian lan truyền xảy ra rất nhanh nếu không tính đến khả năng hấp phụ đất đá thời gian tương ứng sẽ là 40 ngày và 105 ngày. Vành đai an toàn theo phương x và z tại bất kỳ vị trí nào xung quanh ô chôn lấp tính theo mô hình 3D là 3m và 3,5m sau 8 tháng nếu hàm lượng As ban đầu là không đổi, sau khoảng giá trị này, hàm lượng As tính toán được mới đạt được qui định cho phép của QCVN 03:2015/BTNMT. Kết quả trên 2 mô hình đều thấy kim loại nặng As có xu hướng di chuyển từ lớp đất trên xuống tầng chứa nước sâu hơn, tốc độ lan truyền theo phương z nhanh hơn phương x (mô hình 3D). Các kết quả nghiên cứu đạt được của luận án có thể được sử dụng như một bộ số liệu để làm cơ sở đánh giá và phát triển các giải pháp, chính sách hiệu quả trong việc phân loại, quản lý chất thải rắn nhằm giảm thiểu các tác động tiêu cực từ nguy cơ ô nhiễm kim loại nặng tới môi trường đất và ô nhiễm nước dưới đất tại các khu vực bãi chôn lấp CTR cũng như các trường hợp không kiểm soát chặt chẽ qui trình vận hành các bãi chôn lấp CTR.

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF CIVIL ENGINEERING

HOANG NGOC HA

STUDY ON THE SPREAD CHARACTERISTICS OF HEAVY METALS FROM SANITARY LANDFILL AT

KIEU KY, GIA LAM, HANOI

Specialization: Environmental Technology for Solid Wastes

Code: 9520320-1

SUMARY OF DISSERTATION

Ha Noi – 2022

The dissertation was completed at: Hanoi University of Civil

Engineering Scientific Advisor 1: Prof Nguyen Thi Kim Thai

Scientific Advisor 2: Assoc.Prof Nguyen Van Hoang

Reviewer 1 : Assoc.Prof Nghiem Van Khanh

Reviewer 2 : Assoc.Prof Nguyen Manh Khai

Reviewer 3 : Assoc.Prof Nguyen Thi Anh Tuyet

The dissertation will be defended before the University level

Committee

at Hanoi National University of Civil Engineering

At hour day month 2022

The dissertation can be found at the libraries:

- Hanoi National University of Civil Engineering

- The National Library

INTRODUCTION

I Research rationale

Research on the effects of leachate from landfills on the soil environment of the sanitary landfill area has received little attention and has almost not been carried out Therefore, within the research framework of the topic, the author mentions issues related to the spread of pollutants from sanitary landfill, factors affecting the spread

of pollutants that generated from landfill and using mathematical models to predict the spread of pollutants from landfills to the soil environment The topic selected to study the characteristics of heavy metal spread from the sanitary landfill at Kieu Ky, Gia Lam, Hanoi is necessary to study the factors affecting the pollutant transmission process By doing the research to assess and forecast the level of pollution impacts from the landfill as a basis for proposing solutions to overcome and prevent pollution, and form a database for the solid waste management in particular as well as environmental management in general

II Purpose and content of research

Research and evaluate the characteristics of pollution - the source of pollution comes from leachate of the sanitary landfill in order to clearly see the influence on the pollutant spread process in the landfill soil environment

Assess and forecast the spread of heavy metal pollution by quantitative methods to build data for environmental management related to landfills

To achieve the above objectives, the thesis conducts research on the following contents:

1) Studying the factors affecting the formation of leachate quantity and properties, investigating the change of pollutant concentration in leachate and the factors affecting this process;

2) Building a model to calculate leachate suitable to the study object and conditions; 3) Research on the theory of pollutant spread by mathematical model Apply numerical methods to solve established equations to predict heavy metal concentrations in leachate spreading in landfill soil;

4) Studying the risks of soil environmental pollution arising from sanitary solid waste landfills and assessing the level of heavy metal pollution in the landfill soil environment

III Object and scope of the study

Research object: Heavy metal pollution in the soil environment of the sanitary solid waste landfill - the closured cell is located in Kieu Ky landfill, Gia Lam District, Hanoi

Research scope: Sanitary solid waste landfill

IV Scientific basis

The field survey and assessment of Kieu Ky landfill in Gia Lam district, Hanoi city have been researched Studying the effects arising from landfills on the soil environment specifically, including quantifying the processes involved, the formation of pollutants in leachate over time under the influence of environmental landfill factors On the basis of mathematics, by means of finite element method, the subject builds simulation models and quantifies the spread components in the transmission mechanism for the risk of soil pollution following space and time of the study area

V Methodology

- Methods of synthesis, inheritance and theoretical research

- Experimental research methods

- Modeling and simulation methods, using finite element method to calculate pollutant spread

VI New contributions of dissertation

- The thesis has synthesized and proposed a method to calculate the generated leachate suitable to the regional climatic conditions and sanitary landfill operation process

- Assess and forecast the level of heavy metal pollution in the soil environment from the closed landfill cell area of the sanitary landfill with 3D simulation model By using the concepts of the gradient vector field ∇C (x, y, z, t), and related gradient operations (∇⋅), and algorithm exploitation, using MATLAB software to calculate,

predict the ability to spread pollutant concentrations over time and in underground space

VII Scientific and practical significance of the dissertation

Scientific significance:

The dissertation has proposed a method to calculate leachate generated in accordance with the conditions of Vietnam, detailed calculation of leachate generated during operation and after closing the landfill

The dissertation has calculated the risk of As pollution spread by 1D and 3D mathematical simulation models Simulation of the spread of heavy metals from solid waste landfills in the soil environment in 3D space

Practical significance:

The research results of the thesis are a reference source to help researchers and managers have orientations and solutions in the management of closed landfills as well as contribute in proposing design and build options of landfills suitable to the conditions of Vietnam

Defining the safety belt of landfills over time, providing the information needed

to reduce the spread of pollution arising from landfill as well as to improve and rehabilitate solid waste landfills in Vietnam

1.1 Related Concepts

- The concept of solid waste

According to Decree 38/2015/ND-CP dated April 24, 2015 of the Government on waste and scrap management (Article 3), the terms are construed as follows: Solid waste is waste in solid or viscous form (also known as sludge) is discharged from production, business, service, daily life or other activities

- The concept of landfill

According to the provisions of TCVN 6696 - 2009, a sanitary solid waste landfill (hereinafter referred to as a landfill) is: A landfill that is planned in terms of location, structure and construction in accordance with regulations and the function for burial includes cells to bury normally solid waste generated from residential areas and industrial zones

- The concept of leachate from landfill

According to the provisions of TCVN 6696-2009, leachate from a landfill is defined as follows: All liquids, including components suspended in that liquid, that infiltrate through or flow out from the waste that buried in a landfill cell of a solid waste landfill

1.2 Sources of heavy metals in landfills

The source of heavy metals in landfills is mainly due to simultaneous burying of industrial wastes, incinerator ash, mining waste and household waste containing hazardous ingredients such as batteries, paints, dyes, printing ink, …[58] Heavy metals can exist in solid waste at all stages of the product life cycle, a diagram showing the source of heavy metals in solid waste as illustrated in Figure 1

Figure 1 Source of heavy metal formation in solid waste

Source: Vitalii Ishchenko, (2019) [111]

Soil contamination by heavy metals source from waste landfills is a serious problem associated with urban and industrial development Soil layers are considered

as the final storage place for heavy metals released into the environment and also for heavy metals existing in the soil Therefore, when considering the pollutants in the soil and leachate at the contaminated sites, the pollutant content needs to be measured directly and specifically, because determining the properties of the soil is necessary before recommending technical remediation solutions

1.3 Calculate the amount of leachate generation

Calculation of leachate is important for landfill operation management There are many calculation methods, however, depending on the actual conditions of each locality, the appropriate method can be selected

The fact that the layers in the landfill are not constructed at the same time and in the same season of the year, in addition to take advantage of the available sites for landfilling at the same area, and are often removed daily cover that do not conform

to the operational design requirements

Table 1.Comparative summary of leachate calculation methods

Method Paramater

Water Balance Method -

WBM

Hydrological Evaluation Landfill Leachate - HELP

Serial Water Balance - SWB

Calculation

Method

Water Balance Equation

Software base on Water Balance Equation

Water Balance Equation

Input

requirements

Hydrogeological data (soil,

weather and climate)

- Hydrogeological data

- Design data of landfill

Physical properties of solid waste

Input

requirements

related computer equipment

stages

Operation landfill

to the current landfill operation and operation in Vietnam

1.4 The influence of leachate on the soil and underground water environment When studying the accumulation of heavy metals in soil, only considering the total content, it is not possible to properly assess their toxicity to plants as well as their tendency to change in the soil They can exist in many different forms, but mainly in the following forms: mobile, organic, carbonate, iron oxide, and manganese oxides [64]

Heavy metals spread by routes such as inhalation, ingestion, skin contact and surface absorption through fish gills, microbial membranes, and roots and leaves The toxicity potential of heavy metals depends on many different factors such as: concentration, routes of entry, form of existence and duration of exposure In the environment it is necessary to determine the degree of harm to individuals or species,

or to ecosystems

1.5 Literature review of heavy metal spread from landfills

1.5.1 Studies on the spread of heavy metals from landfills to the soil

environment

Sharma and Lewis [94] studied a mathematical model of leachate propagation that included the evaporation and dispersion of a contaminant Varank et al [109] investigated the migration of contaminants in landfill leachate through alternative composite liners Issues related to landfill hydraulic conductivity of different types

of contaminating clay liners, when studying leachate migration from a landfill, dehumidification of synthetic geology clay liners was also evaluated by Hoor and Kerry Rowe [59]

Some studies have focused on building leachate migration models and using digital to simulate the transport of pollutants from leachate into soil layers such as Abriola 1987 [ 17], Al-Niami ANS and Rushton KR (1997) [24], Bear J (1975) [29], Gao G, et al (2013) [55] , Mirbagheri S A (2009) [75], Reddy K, et al (2015) [84] Recently, several numerical methods have been developed to solve equations and simulate the transport of pollutants in space; and other specific mathematical approaches are also used such as Lai SH (1971) [71]; Moldrup P (1996) [77] Ataie-Ashtiani B (1996) [25] and Mirbagheri F (2013) [76] used finite difference (FD) and finite volume (FV) methods to calculate spread

Many studies in the world have long built a mathematical model to predict the spread of pollutants in the wastewater such as Ogata (1970) [79]; Ataie-Ashtiani B (1996) [25]; Thongmoon M (2006) [102]; Mirbagheri SA (2009) [75]; Patil S (2014) [81] researched and built a mathematical model to calculate the contaminant spread

of leachate in the soil, but only in 1 or 2 dimensional models

In a number of published studies, the general equation has been simplified by removing convection terms or using linear techniques to obtain analytical solutions under ideal conditions and the partial derivative equation have only been transformed and represented in one or two dimensions recently, such as Beidokhti MZ et al (2019) [30], Buaisha M et al (2020) [33]

Thus, from the study of literature review from abroad, it is shown that building a mathematical model to predict the spread of heavy metals in leachate in 3D space is necessary and meaningful when evaluating solid waste landfill pollution

1.5.2 Literature review in Vietnam

There are few domestic studies on heavy metal component in leachate and soil and groundwater contamination by heavy metals from leachate in Vietnam Most of the research on leachate focuses on organic compounds, nitrogen compounds, phosphorus and leachate treatment methods on these criteria

From the literature review results in the world and in Vietnam, it can be seen that untreated leachate containing many heavy metals with high concentration is the most obvious direct source of surface water pollution Most of the studies have shown that the soil and groundwater at the solid waste landfill area and its vicinity have not been contaminated with heavy metals at a level greater than the allowable standard for agricultural land However, all studies show that solid waste and leachate play a pollutant role in increasing the concentration of heavy metals in soil and groundwater based on the analysis of spatial assessment and the heavy metal concentration in buffer capacity environment

1.6 Selected research direction

The previous studies carried out to develop forecasting and calculation methods

to determine heavy metal pollution but are not general and quite cumbersome, many studies only stop at 1D and 2D models The method of predicting the spread often

uses available models for calculation, is costly and not suitable for the conditions of Vietnam

Therefore, it is very necessary to conduct research on the risk of heavy metal pollution in the sanitary landfill, build a general mathematical model, apply and exploit it on modern tools to calculate and predict pollution in 3D is necessary and has practical significance in the solid waste management in Vietnam

2 Chapter 2 THEORY OF POLLUTION TRANSMISSION AND

METHODOLOGY OF RESEARCH 2.1 Pollutants spread in the soil

Pollutants in soil exist in many different forms (or phases) depending on the physical and chemical nature of the pollutant Pollutants can dissolve into groundwater and move through the pores of the soil On a large scale, this process can

be modeled according to the flow and direction of groundwater, but on a narrow scale, this process is directly related to the particle size and porosity of the soil When moving in the soil, the pollutant (or in other words, the stream containing the pollutant) does not pass through the soil particles but through the voids in the soil 2.2 Mechanism of pollutant transmission in soil

2.2.1 Permeable flow rate

Flow rate of groundwater in the soil can be estimated using the formula of Darcy law Q=k i.A (2-1)

Q: flow (cm3/s); k: permeability coefficient (cm/s); i: hydraulic gradient; A: sectional area (cm2)

cross-2.2.2 Diffusion coefficient of the pollutant

When modeling the contaminant spread along the infiltration stream in the soil, it

is necessary to determine an important parameter, which is the diffusion coefficient

of the pollutant in the soil In fact, this diffusion coefficient depends on the pollutant and soil type, so it is necessary to conduct experiments to find the most accurate diffusion coefficient

According to the study of Çamur et al [35], Rowe et al [89], Yang [116] the diffusion coefficient found by the authors can be used as a reference in calculating the dispersion of pollutants and heavy metals in the soil

2.3 Research methods to determine the spread of pollution

2.3.1 Method to determine the composition and charateristics of leachate

Leachate is sampled and analyzed to determine the content of pollutants and heavy metals for the calculation and prediction of the spread of heavy metals in the landfill

The leachate sample was taken at the leachate collection pit from the landfill cells before being pumped into the wastewater receiving lake Sampling location is shown

in figure 2.3

Figure 2.3 Soil and leachate sampling locations 2.3.2 Methods to determine the composition and characteristics of the soil

To determine the spread of pollutants, in the field, drilling methods are often used

to take soil samples The holes are drilled in depth from 0.3m, 0.6m, 0.9m,… 6m Sampling location in Figure 2.3, soil samples were taken and analyzed to determine the concentration of heavy metals in the soil

2.3.3 Analytical solution – differential equations for contamination spread The spread equation of the pollutant in the soil can be solved through analytical solutions or by numerical methods (finite difference or finite element) Analytical methods usually only solve problems with simple boundary and initial conditions and the ground is considered homogeneous and isotropic To be able to give a unique solution to a differential equation, the initial and boundary conditions need to be clearly specified The first condition describes the starting values of some variables

in the problem, in this case the pollutant concentration Boundary conditions describe the relationship or interaction between the studied area and the outer areas

2.3.4 Finite element method

The finite element method is an approximate numerical method for solving problems in engineering and mathematical physics

The finite element method is a very general and effective method for numerical solutions of many different classes of engineering problems

A system of linear equations is created from elemental equations by converting the coordinates from the local nodes of the subdomains to the global nodes of the domain This spatial transformation includes the appropriate orientation adjustments

as applied relative to the coordinate reference system This process is usually performed by finite element method software using coordinate data generated from subdomains

2.3.5 Formulate the model of the contaminant transport in 3D

To formulate equation, we consider a model of a landfill cell, in which, the source

of leachate is on the horizontal surface The leachate stream containing heavy metal pollutants spreads vertically and horizontally to the surrounding environment During this process, pollutant concentrations change in all directions and over time

Figure 2.4 The gradient field of the concentration function C (x, y, z, t) in the

coordinate system Oxyz