Purpose and research contents of the thesis 1 Objectives of the thesis: - Analyzing the relationship between waste flows and energy flows in MSW management through the quantification o
Trang 1MINISTRY OF EDUCATION
AND TRAINING
VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
**********************
VU THI MINH THANH
STUDYING THE CORRELATION BETWEEN THE MATERIAL AND ENERGY FLOW IN URBAN WASTE MANAGEMENT, APPLYING TO AN INNER-CITY DISTRICT OF HANOI CITY
Major: Enviromental Engineering
Code: 9 52 03 20
SUMMARY OF DOCTORAL THESIS
IN ENVIRONMENTAL ENGINEERING
Hanoi - 2021
Trang 2The thesis was completed at: Graduate University of Science and Technology - Vietnam Academy of Science and Technology
Supervisor 1: Prof.Dr Tran Hieu Nhue
Supervisor 2: Prof.Dr Nguyen Thị Hue
The dissertation can be reached at:
- Library of the Graduate University of Science and Technology
- Vietnam National Library
Trang 3INTRODUCTION
1 The necessity of this topic
The fast urbanization speed in Vietnam has create a large volume of waste,
a majority of which is not treated The volume of generated municipal wastewater of cities in 2018 was approximately 7 million m3/day [1] (which has become over 10 million m3/day in 2020); household solid waste (HSW) volume is 61,600 tons/day, within which municipal solid waste (MSW) is around 37,200 tons/day [2] and increases 12% per year on average Only about 13% of municipal wastewater is treated at wastewater treatment plants (WWTP) [1], septic tank sludge are suctioned mostly by private companies and then discharged without treatment into the environment [3] Over 71% of municipal waste is buried [2] which creates overloading at landfills
The activities of WWTPs and solid waste (SW) cost a lot of energy If there is a waste management (WM) model that directs towards resource recovery and energy production, it can both solve environmental problems and bring about economic benefits In Vietnam, in the field of Urban and Environmental Infrastructure Engineering, there is not yet a model that fully considers the connection between material and energy streams in WM Wishing to provide more scientific basis for analyzing, evaluating, and planning, as well as providing reliable information to select the appropriate
waste treatment (WT) technology and WM model, the author implements the thesis: "Studying the correlation between the material and energy flow in
urban waste management, applying to an inner-city district of Hanoi city"
2 Purpose and research contents of the thesis
1) Objectives of the thesis:
- Analyzing the relationship between waste flows and energy flows in MSW management through the quantification of wastewater, septic tank sludge, sewage sludge from WWTP, and organic fraction (OF) of MSW flows
- Determining the relationships among above mentioned organic-rich waste lines through mass balance and energy balance quantification for a selected case study, from where a sustainable urban wastewater, sludge and SWM model is proposed
2) Research contents of the thesis:
(1)- Studying the relationship between waste and energy flows in MSW management systems in Vietnam and the world
(2) – Researching the mass, composition, and characteristics of the organic-rich MSW flows, as well as WT methods in the direction of resource recovery
Trang 4(3)- Experimental research on the composition and properties of WWTP sludge, septic tank sludge, and HSW, as well as the ability to recover energy from the anerobic decomposition process of HSW
(4)- Conducting specific case studies: development of waste management scenarios (wastewater, sewage sludge, septic tank sludge and MSW; quantify the above material flows, energy consumption and potential energy that can
be obtained from above WT processes; material flow analysis (MFA) and energy balance (EB) for each scenario
(5)- Assessing results, proposing methods of MSW management in the
direction of resource recovery, towards cyclic economy
3 Subjects and scope of research
- Subjects of research: organic-rich waste flows in urban waste
management: septic tank sludge, sewage sludge, OFMSW; relationships of these waste flows, through mass balance and energy balance calculations
- Scope of study: In area: Hanoi city, with case study in Long Bien
district; In time: from present to 2030, with vision to 2040
4 Research methods
The thesis has used the following research methods: Inheritance methods; Field survey methods; Experimental methods; Comparative method; Analytical methods; Simulation method; Expert methods
5 Scientific and practical significance of the thesis
- The thesis has identified some important parameters of the composition and properties of organic waste lines such as sludge from WWTP, septic tank sludge, organic HSW, as well as identifying the potential of methane generation from the anaerobic decomposition of urban organic SW
- The thesis defines the energy demand and potential energy recovery per waste unit, and the potentially recovery of embodied energy per capita, as a basis for other studies
Practical significance
- The management model combining organic waste at the urban waste
Trang 5treatment center (WTC) on a district scale towards resource recovery from anaerobic digestion and other related processes is very potential, bringing multiple benefits This meets the practical needs of Vietnam where so far there
is no appropriate, effective and sustainable urban waste management model (both for SW, septic tank sludge, wastewater, and sewage sludge)
- This result can be considered for application when formulating or adjusting wastewater and SW management planning in urban areas
- Long Bien District wastewater and SW management plans have not yet been implemented The thesis’ results can be considered as a scientifically based proposal for authorities and interested investors
- Simulation tools for material flows (STAN) and energy balance (SANKEY) can help leaders to have a visual view, easy to detect problems,
to make the right and appropriate decisions
6 The novelty of the thesis
(1) - The theory has proposed the model of general management with resource
recovery, towards the realization of cyclic economy By combining material
balance and energy balance calculations, using the MFA and EB tools to quantify the material flows at general sludge of WWTP, septic tank sludge, urban HSW), the research has shown that combining anaerobic decomposition treatment for energy generation and resource recovery from organic-rich CT
lines is very feasible
(2) - The thesis has calculated specifically the energy demand and the potential for energy recovery (electricity and heat) from organic waste disposal of an urban area On the condition of Long Bien district, Hanoi city in 2030, the
energy to handle wastewater needs 0.61kWh/𝑚", to treat of organic HSW combined with septic tank sludge, and to process compost is 35.83kWh/ton Combined bio-anaerobic decomposition treatment of MSW not only meets 100% of the energy needs of the WT center, but also produces energy in total exceeding 222.66% of demand and can provide out 78,865.75 kWh/day of residual electricity and 197,689.24 kWh/day of residual heat Pre-treatment of materials before anaerobic decomposition is with hydrolysis heat, producing energy totaling up to 265.16% of the needs of the WT plant Recovered energy
is calculated for 1 person in 1 year according to concrete calculated treatment options
(3)- For the first time, the research has determined potential energy recovery from embodied chemical energy in municipal waste flows in Vietnamese conditions Excluding thermal energy and losses, potential electricity recovery from wastewater treatment is 13.75 kWh/cap/year; from septic tank sludge is 1.33 kWh/cap/year; from OFMSW is 144.93 kWh/cap/year
Trang 67 Composition of the thesis
- Opening
- Chapter 1: Overview of studies on the correlation between urban waste and
energy streams towards sustainable management of wastewater and SW
- Chapter 2: Scientific basis and methods of wastewater treatment and urban
SW; potential for recovery of energy
- Chapter 3: Results of research and discussion
- Conclusion, Proposal
CHAPTER 1 OVERVIEW OF RESEARCH ON CORRELATION
BETWEEN URBAN WASTE AND ENERGY STREAMS TOWARDS SUSTAINABLE MANAGEMENT OF WASTEWATER
AND SOLID WASTE 1.1 Water-energy correlation in technical infrastructure and waste management
Humans need water and energy for their essential needs All technological systems for energy transformation need water Mining, treatment, storage, distribution of water supply, collection, treatment of wastewater and sludge residue all need energy Water, wastewater, sludge, SW containing latent energy can create electricity and thermal energy
1.2 Water-energy relationship in waste management in some countries around the world
1.2.1 Solutions to use energy efficiently and produce energy from WT
Energy saving and manufacturing solutions in water supply and production, SW and wastewater collection/treatment are mainly: [10] [11]
- Water saving and wastewater reuse; reduce, recycle, reuse SW and sludge
- Saving energy consumption in water supply and drainage, SW management
- Bio-anaerobic decomposition and bio-gas recovery to produce energy
- Burning sludge, SW for heat, etc
1.2.2 Saving energy consumption in WWTP
Energy consumption accounts for 25-40% of the operating costs of large WWTP [12] Using bio-anaerobic technology to treat sludge, with combined heat-power system (CHP) can save an average of 42% of energy consumed
in WWTP [22] And the potential to save 20–50% of energy in WWTP with
Trang 7a capacity of 1,500-45,000 m"/day in Europe [8]
1.2.3 Water reuse saves energy
Water reuse lowers by more than 5.5 times of energy compared to saltwater dewatering (costing 2.5-2.8 kWh/m3) [23] Rainwater collection and supply only costs 0.3-1.2 kWh/m3 [25]
1.2.4 Production of renewable energy from MSW
Compost from organic HSW, anaerobic biodegradation of sludge to recover methane, or SW combustion to recover heat and produce electricity and heat have been widely applied in countries around the world
1.3 Overview of the volume, composition, characteristics and current status of urban wastewater and SW management in Vietnam
1.3.1 Current management of wastewater and sludge in some major urban areas of Vietnam; Volume, composition, properties of sludge
- Hanoi: Total volume of household wastewater is 750,000 m"/day; industrial/service wastewater ~270,000/m"day [32], with 6 concentrated WWTP, capacity ~170,000 m"/day [31], has treated ~22% of industrial/service wastewater
- Ho Chi Minh City: inner-city household wastewater ~1,750,000 𝑚"/day, [36] industrial and service wastewater ~200,000 m"/day [37], with 3 concentrated WWTP operating, actual capacity of 185,000 m3/day, which
treats ~ 10% of service HSW
- WWTP sludge contains many organic matter and nutrients and can be used
as fertilizer The analysis results show that the sludge has a high organic ratio (VS/TS ~ 60-70%), the C:N:P ratio is suitable for anaerobic stabilization, and the N:P nutrient composition: K ~ 2.5:1.6:0.4 Currently, WWTP sludge is mainly dewatered and then buried, only WWTP Yen So, Hanoi has an anaerobic sludge digestion tank and collects biogas, but because the amount of sludge generated is very small, the tank is not active, and generated biogas is also only designed to be burned wastefully
- Septic tank sludge: has a high humidity of 97-99% [48], so it is difficult
to collect and transport The sludge has a high content of organic matter and nutrients and is capable of being decomposed by biological methods; contains many helminth eggs and pathogenic microorganisms; has high COD, ranging from 15,600-79,500 mgO2/l; High TN, large fluctuation, 80-1689 mg/l; TP 82-
678 mg/l; VS/TS ~ 68%-83%; [51] The amount of sludge generated in big cities is ~50,000-218,490 m3/year; collection rate reached 32%, with 4% being disposed of and landfilled in a sanitary manner [52] URENCO Hanoi collects
Trang 8~10% of the generated sludge (~50 tons/day) [53] [54], the remaining 90% comes from the private sector Hai Phong city collects about 33,000-35,000 tons/year [55] Ho Chi Minh City collects about 300-350 m3/day, out of a total
of 2,450 m3 of sludge generated [47]
1.3.2 Current status and planning of solid waste management in major cities of Vietnam; Mass, composition, properties of urban organic solid waste-
- In Hanoi: The rate of solid waste collection in the inner city is about 95%, the suburban rate is 60% [56]; SW volume increases by 15%/year on average Currently, the city has 4 landfills and 3 waste disposal plants The total volume
of MSW generated in 2017 was 7,500 tons/day, accounting for 68.7% of the city's total solid waste [56] Inner-city MSW is collected and brought to Nam Son Wastewater Treatment Complex with an area of 83.5 ha and up to 95% is buried; The complex is currently overloaded The organic composition of MSW reaches ~60% [2]
- Ho Chi Minh City: the amount of MSW generated in 2018 was 7,800 tons/day [38] [2] and was treated in two main solid waste treatment complexes, which are the Northwest Waste Treatment Complex (Cu Chi) and Da Phuoc (Binh Chanh) The organic composition of MSW reached 57-77.1%
In 2018, the total amount of MSW collected nationwide was 22.5 million tons, with 71% being buried, 16% composted; 13% incinerated [2] The country has
381 incinerators, 37 composting facilities, 80% of the 904 BCLs are unhygienic [2], with a tendency to shift from landfill to incineration [2] [50] [64] [60]
1.4 Energy demand and potential for energy recovery from wastewater treatment, sludge and solid waste
1.4.1 Demand for energy in water treatment
Average energy for water supply treatment and wastewater is ~ 0.2- 1.5 kWh/m3
1.4.2 Demand for energy in solid waste management
In addition to the energy needed for solid waste collection and transportation, composting technology consumes energy for solid waste classification, aeration, mixing, sieving, and bagging Combustion consumes the most energy, but recovered heat can be utilized
1.4.3 Potential for energy recovery from MSW lines
Trang 9Energy can be produced from biogas recovered from landfills; from the process
of burning solid waste to generating electricity; from the anaerobic digestion
of organic-rich MSW flows In addition to the energy produced from the combined heat-power (CHP) system, the energy can be recovered in the form
of pellets, generated from solid waste or sludge treatment Combined treatment
of organic-rich MSW lines by anaerobic digestion to recover energy is a potential direction at present
CONCLUSION OF CHAPTER 1 AND RESEARCH ISSUES
All processes of water supply, drainage, wastewater treatment, collection and treatment of solid waste consume energy In order to save, recover or produce energy in urban waste management, it is necessary to apply solutions to use energy efficiently, reuse wastewater, recover energy from processes of treating wastewater, sludge, and solid waste
Urban wastes such as wastewater, WWTP sludge, septic tank sludge, urban solid waste in big cities in Vietnam are rich in organic matter and have great potential for energy recovery In which, anaerobic treatment combined with organic-rich waste flows is a potential solution The thesis sets out to build a scientific basis and conduct quantification of material flows (water, WWTP sludge, septic tank sludge, solid waste, products of wastewater processes), quantification of energy consumed or generated in the treatment process, using the MFA and EB simulation tools Specific calculation for a district in the inner city of Hanoi will illustrate the theoretical bases that the thesis researches, thereby proposing a sustainable urban program management model
CHAPTER 2 SCIENTIFIC BASIS, METHODOLOGY ON WASTEWATER TREATMENT, URBAN SOLID WASTE AND
ENERGY RECOVERING POTENTIAL
2.1 Scientific basis in the study of water-energy correlation
2.1.1 MFA (Material Flow Analysis) Research Methodology
MFA is an effective tool with potential to be applied in strategic management, allowing quantification of material flows [79][80] in a system, at different scales; allows for early problem detection; can be used to forecast and evaluate new approaches and methods [81]
2.1.2 Material flow analysis with STAN software
STAN software (subSTance flow ANalysis) solves the problems in the process
Trang 10of using MFA [5], making MFA easy to use, highly reliable, because STAN automatically calculates errors, verifies unknown data Calculation results are
displayed in the form of SANKEY diagrams
2.1.3 Research methodology on energy balance in the system of
competitive management
The principle of the energy balance problem (EB) is:
Input energy = Output energy + Accumulation
The thesis uses EB to calculate the waste treatment center, recover resources, and use the SANKEY tool to display and analyze the results
2.1.4 Method of determining energy consumption of equipment in wastewater treatment facilities
Determine the power consumption capacity, the number of operating hours of the equipment based on the technology calculations The total power consumption of the system is equal to the total power consumption of each device, per unit time Calculation results are verified with data determined by referencing literature and taking energy consumption of similar processes/equipment
2.2 Technological solutions for solid waste, wastewater, and sludge recovery
2.2.1 Biogas recovery from landfills
After closing the landfills, the anaerobic decomposition of organic compounds will produce a significant amount of methane-rich biogas
2.2.2 Anaerobic digestion to recover energy
There are many factors affecting the anaerobic digestion that determine the substrate metabolism in the reaction It is possible to combine multiple organic-rich waste streams together during decomposition
2.2.4 Pretreatment before anaerobic digestion
Pretreatment breaks down the structure of non-biodegradable components, reduces the size of solid impurities in the sludge, improves the efficiency of
the decomposition process and produces methane
2.2.5 Sludge burning to recover heat
The moisture content of the WWTP sludge from the SBR tank is 99% [17], the septic tank sludge is 97.05% [95] so it must be thickened, dehydrated, and dried before burning
Trang 112.2.6 Solid waste incarceration
Incineration reduces the volume of solid waste and recovers heat, but it is
10-15 times more expensive than sanitary landfilling and 8-10 times more expensive than composting [97]
2.3 Experimental study to determine the anaerobic decomposition of research wastes
2.3.1 Experiment purpose:
- Analysis of the composition and properties of organic-rich urban waste that can be anaerobically digested and recovered: WWTP and septic tank sludge, urban solid waste
- BMP test to evaluate the methane generation ability of organic CTR by anaerobic digestion in warm fermentation mode (370C), determining the specific parameters for the decomposition process, focusing on: CH4 gas yield produced NmL CH4/gVS substrate
2.3.2 Sampling, analyzing solid waste components:
According to TCVN 9461:2012 (ASTM D5231-92)
2.3.3 Sampling and analyzing the composition of septic tank sludge
In 2016-2017, 59 septic tanks of households in Hanoi city were sampled Samples were taken during sludge aspiration (private suction truck) Each household has 3-6 people, using a septic tank for 5-20 years, with tank volume 1.2-4.0 m3, sucking up all the sludge 10 samples/1 duplicate sample were taken; 8 samples/1 duplicate with cross-check were analyzed, using standard methods and HACH-Lange kit for COD, NH4 and PO4
2.3.4 Sampling, analyzing sludge composition of WWTP
- 2016- 2017: Sampling sludge in sludge compaction tank after primary settling tank (PS), secondary settling tank (WAS) 2 WWTP Kim Lien and Truc Bach; Analysis in the laboratory (5 batches)
2.3.5 Experiment to determine the potential for methane generation BMP
Seeding sludge: 40L anaerobic sludge tank, operating continuously at a temperature of 350C±0.50C; The feed material is artificial wastewater, with COD = 500-1,000 mg/l, C:N:P = 100:5:1; Loaded 1 time/day, load 0.5-1kg COD/m3/day
2.3.6 Experimental model:
Trang 12a) b)
Figure 2.2.1 Experimental model of BMP-methane production potential:
a) Reactors; b) Seeding sludge growing chamber;
c) Setting-up diagram; d) Reactor details
The experiment was carried out from October-December 2019, with an anaerobic reaction system in 2 batches: 3 replicate samples + 1 blank sample each Ratio of sludge and substrate is F/M = 0.5gVS/gVS; Sludge + Substrate + Nutrients = 300mL/jar Operating temperature 350C±0.50C Biogas is led through 3M NaOH solution to absorb CO2 The volume of CH4 produced daily was measured by the liquid displacement method The experiment was
stopped after 26 days when no gas production was found
2.4 Research on the waste management model for Long Bien district,
Hanoi city
2.4.1 Choosing a research site
Long Bien District meets all the criteria for selection:
- Having a complete database on land use planning and technical
infrastructure
- In Hanoi, it is convenient for survey and additional data collection
- The study area is relatively isolated, with little interference with other areas (to ensure accurate calculation of waste flows)
- Medium and large scale WWTP capacity, so that anaerobic sludge digestion can be applied [122] The amount of solid waste generated is large (several
Trang 13hundred tons/day), in order to apply appropriate treatment and recycling technology solutions on an industrial scale [88]
- The study area includes both old and new urban areas, which can represent many urban areas in Vietnam
- The area has few interspersed industrial and agricultural zones
2.4.2 Current status of water drainage, wastewater treatment and environmental sanitation
- The drainage system is not synchronized, currently overloaded
- Solid waste is collected at 33 collection points and brought to Nam Son WWTP
- Collected septic tank sludge, sludge from WWTP of industrial zones and sludge from sewers are transported to Nam Son landfill
2.4.3 Input data for calculation
The data from the Long Bien District Development Plan to 2030, with a vision to 2050 [125] [127] [128] were used Some key parameters: Population size in 2020: 352,000 people; 2030: 428,860 people; Land area: 6038.24ha; Standard of water use for daily life: 160l/person/day; The rate of wastewater collection is 90%; Unit solid waste emission: 1.3kg/person/day
2.4.4 Calculation options
Long Bien district, Hanoi city was selected as a case study on the integrated waste management model, with 3 options for urban waste management:
- Option 1: The traditional waste management model is currently being widely
applied in Vietnam's urban areas
- Option 2: Integrated waste management model, with a waste treatment center
Sources of rich organic waste (organic solid waste and septic tank sludge) are brought to the Center and treated together with WWTP sludge with anaerobic copper digestion and energy recovery
- Option 2a: Integrated waste management model similar to option 2, but with
an additional step of pre-treatment by pyrolysis of the waste mixture before being put into anaerobic co-digestion tank to improve the recovery efficiency MFA with STAN application, and EB with SANKEY application, were selected as calculation tools in the thesis
The detailed technological calculation of treatment works, material flow analysis and energy balance of the 3 options are presented in Chapter 3
Trang 14CHAPTER 3 EXPERIMENTAL RESULTS AND DISCUSSION 3.1 Laboratory experimental results
3.1.1 Components and characteristics of organic solid waste, septic tank sludge, and WWTP sludge
a) Results of analysis of composition and properties of urban organic solid waste
- Urban organic solid waste has an average VS/TS ratio = 89%
- High VS, COD values, with great gas generation potential
- COD: N: P = 229: 3.2: 1, suitable for anaerobic methane decomposition,
and tends to have excess C or lack of N, P
Table 3.1 Analysis results of urban organic solid waste samples
Variables pH TS (g/l) VS (g/l) COD (g/l) TN (g/l) TP (g/l)
Sample 1 6.32 154.36 141.04 237.7 3.45 1.07 Sample 2 6.28 152.46 137.58 213.5 3.19 1.02 Sample 3 6.29 158.82 138.65 243.8 3.09 0.94
Average 6.30 155.21 139.08 231.67 3.24 1.01 Standard deviation 0.021 2.67 1.77 16.03 0.19 0.07
b) Analysis results of septic tank sludge
The postgraduate has analyzed the composition and properties of septic tank sludge in Hanoi (International cooperation project on septic tank management) The results show that COD values = 2.83 - 83.0g/L; VS = 1.7 - 45.4g/L; VS/TS = 47.5 - 87.7 (average 72%); TN = 1.179mg/L; TP = 287mg/L COD/VS ratio = 1,946 gO2/gVS From the analysis results, the chemical formula of the septic tank sludge was determined to be ~ C18H39O8N, the ratio C:O:H:N = 54.4%:32.2%: 9.8%:3.5 %
The septic tank sludge has the ability to decompose by biological methods, the sludge after decomposition has high nutritional value About 50%
of the organic matter is hydrocarbons, proteins, fats, the rest is fibers (about 10g/L~ 40% TS), VFA, alcohols, amino acids, etc VFA is quite low, average 0.12g/L
Impurities that can inhibit and slow down anaerobic digestion are present
in the septic tank sludge: 𝑁𝐻&', 𝑆𝑂&*+, fibrous
Trang 15Solutions for high efficiency and stable anaerobic digestion:
- Pretreatment before anaerobic stabilization
- Mix septic tank sludge with C-rich substances, creating a suitable environment for decomposition
c) WWTP sludge analysis results
Similar to the above, the primary sludge (PS) has a moisture content of 91 - 99.7%; Secondary sludge (WAS) has a moisture content of 98.8 - 99.6%; Sludge mixture: VS/TS = 53.5 – 69.5% (lower than other countries, due to the characteristics of wastewater collection network); high VS, COD; high composition of hydrocarbons, proteins, fats, and gas generation potential; COD:N:P ratio ~ 92:4,8:1, suitable for anaerobic reaction (lack of organic C); WAS contains higher N, P and nitrogen than PS, but lower hydrocarbon and fat content than primary sludge With a common drainage system, the C:N:P ratio is even lower; The mud contains many nutritional elements such as N, K,
S, Fe ; The product after stabilization can be used as fertilizer; The content of heavy metals Cd, Pb, Cu, Zn is within the allowable threshold
3.1.2 Determination of methane generation ability of organic solid waste
in laboratory
Table 3.2 Input material parameters of BMP experiment – batch I, II
Input material
Input material volume (mL)
pH (g/L) TS (g/L) VS COD (g/L) (g/L) TN (g/L) TP
- Experiment
batch I:
Seeding sludge 275,68 7,74 19,0 8,21 13,52 0,23 0,06 Masticated organic
solid waste 8,0 6,3 158,08 141,46 237,64 2,03 0,56 Nutrient,
solid waste 8,0 6,28 153,54 136,7 225,68 1,75 0,48 Nutrient,
micronutrients
solution