A thesis submitted to the Department of Civil Engineering at the Khulna University of Engineering & Technology (KUET), Khulna, Bangladesh in partial fulfillment of the requirements for the degree of. This confirms that the thesis submitted by Shurna Rani Saha entitled "Investigation on the Decentralized Sewage Treatment Plants in Khulna" has been approved by the Board of Examiners in partial fulfillment of the requirements for the Master's degree in the Department. of Civil Engineering, Khulna University of Engineering & Technology, Khulna, Bangladesh in July 2014.
LIST OF TABLES
INTRODUCTION
- Background
- Statement of the Problem
- Scope of this Study
- Thesis Outline
The first is to evaluate the performance of the two DEWAT plants based on field and laboratory investigations. The first part is Analysis of wastewater data from two existing DEWAT plants at Panchtola Colony in Khalishpur, Khulna.
LITERATURE REVIEW
General
- Characteristics of wastewater
- Why should Sewage/Wastewater be treated before disposal?
Sanitation and waste water, classification of waste water, characteristics of waste water, the necessity of waste water treatment and the benefit of recycling waste water are focused. Sewage is a subset of wastewater that is contaminated with feces or urine, although many people use the term sewage to refer to sewage.
Wastewater Treatment Systems
Centralized Wastewater Treatment System
- Classification of Conventional Wastewater Treatment
Tunisia's main cities and secondary cities are served by sewage collection systems and central sewage treatment plants; in Jordan, 65% of the population is connected to collection systems, and the largest cities are served by central sewage treatment plants, etc. In the United States, about 60 million people use some form of on-site wastewater treatment systems, of which about 20 million use the conventional septic tank system [28].
Centralized VS. Decentralized system
Example not much flexibility, in the city of Jericho in the USA, 95% of the delivery and disposal options. unit decreases as the number of units increases economies of scale. the unit would be scaled up if long distance pumping deep sewage were needed. homeowners rely on individual on-site wastewater systems to help protect groundwater and surface water quality. In the past, decentralized policies and regulations have meant individual septic systems responsible for their tanks with local government responsible for management.
Anaerobic Process
Aerobic Process
In general, aerobic systems are suitable for treating low-strength wastewater (biodegradable COD concentrations less than 1000 mg/L) while anaerobic systems are suitable for treating high-strength wastewater (concentrations of of biodegradable COD above 4000 mgfL) [57]. Principle of the process • Microbial reactions take place • Microbial reactions take place in the presence of the molecule/ site in the absence of.
Anaerobic - Aerobic Treatment System
High overall treatment efficiency: Aerobic post-treatment polishes the anaerobic effluent and results in very high overall treatment efficiency. When volatile organics are present in the wastewater, the volatile compound is broken down in the anaerobic treatment, eliminating the possibility of volatilization in the aerobic treatment.
Mechanism of DEWAT System
- Septic Tank/Settler
- Anaerobic Baffled Reactor
- Anaerobic Filters
- Polishing Pond
- Biogas composition
- What can 1 m3 biogas do? [721
The tanks in the series are said to aid in the digestion of hard-to-degrade substances, especially towards the end of the process. It works through the combined effects of the filter material, the plants and their roots growing in the filter medium.
Biogas Sanitation Systems
Regarding the removal of organic matter and nutrients, biogas remediation is mainly a primary or secondary treatment step, which may require post-treatment depending on the disposal or reuse strategy. Therefore, buffer tanks or biogas clarifiers must be built as pre-treatment units for smoothing the wastewater flow. A biogas purification system is technically more complicated because it includes more components than just a (urine diversion) toilet.
The biogas tank (with or without baffle plate(s), depending on the additional treatment step selected) or the biogas septic tank (always with integrated baffle plates) is mainly used as a household-based on-site system with secondary treatment of waste water in compost (solids) and drainage/subsoil irrigation (liquid ) [73]. The biogas separator is used as a pretreatment step in combined anaerobic/aerobic multistage systems or as pretreatment in combination with. The accumulated settled sludge must be periodically removed from the bottom of the biogas separator, based on experience this will be necessary every 5-7 year [73].
There are different forms of biogas settlers such as fixed dome plant, bag digester, fiberglass (halt) bowl plant, water submerged floating drum, PE or PVC pre-designed tanks, covered anaerobic lagoons.
MATERIALS AND METHODS
- General
- Study Area
- Survey before implementation of DEWAT plant
- Survey after implementation of DEWAT plant
- Necessary Information of the DEWAT System
- Detail Design of DEWAT Plants
- Laboratory Experiments
Recently, two DEWAT plants were constructed at Panchtola Peoples Colony in Khalishpur in Khulna City Corportaion (KCC) area. Two DEWAT plants have already been built in Panchtola Colony in Khalishpur in Khulna by a local NGO called Nabolok. This was done with the help of a staff of Nabolok A questionnaire was prepared for users of DEWAT plants taking into account many information such as general, socio-economic, environmental condition, hygiene practices, benefits of DEWAT plant, maintenance of DEWAT plants and aesthetic appearance of the DEWAT Plant, and recommendation for existing DEWAT plants.
Comparison of the performance of existing two DEWAT installations is the second objective of this study. Various data were analyzed and the performance of the existing two DEWAT installations was compared with the recommended values (Table 3.2). Identification of technical problems in existing DEWAT plants is the third objective of this study.
Through the questionnaire survey and data analysis, technical problems in the operation and maintenance of DEWAT plants were identified.
CHAPTER 1V
RESULTS AND DISCUSSION
General
The third part is Identification of Technical Problems in existing DEWAT plants based on experimental results. To get a broad view of community acceptance and management of the system, key stakeholders were interviewed. All interviewees are satisfied for DEWAT system and aware of alarming situation created before implementation of DEWAT system.
However, the interviews of the president of the social service development committee (Munshi Abdul wyadud), the secretary of the social service development committee (Abdul Razzak . - Khan), the joint secretary of the social service development committee (Sarder Ali Ahmed), to. In this study, six sampling points of two DEWAT plants and eleven experimental parameters were selected as stated by Nabolok with the help of Water Aid Bangladesh. These points are the inlet and outlet of the column tank, between the choked anaerobic filter bed reactor, the choked anaerobic reactor outlet, the seeded gravel filter, and the polishing pond, shown in Figure 3.6.
Data Analysis
Performance of the 1st DEWAT plant
- Variation of pH in 1 d
- Variation of Temperature in l DEWAT plant
- Variation of TDS of 1 DEWAT plant
- Variation of FC of 1' DEWAT plant
- Variation of Nitrate of l DEWAT plant
The laboratory test results of the temperature of the collected wastewater samples from the DEWAT plant are shown in Figures 4.2. As the wastewater percolated through the DEWAT plant, there was a significant reduction in COD concentration. As the wastewater flows through the DEWAT plant, there was a significant decrease (greater than 95% removal) of suspended solids.
The laboratory test results of TDS of the collected wastewater samples from the first DEWAT plant are shown in Figures 4.6. It can therefore be concluded that the I't DEWAT installation is a promising solution for the treatment of bacteria. Thus, it can be concluded that the DEWAT plant is a promising solution for the treatment of bacteria.
The laboratory test results of nitrate from the collected wastewater samples from the DEWAT plant are presented in Figure 4.10.
Performance of the 2m1 DEWAT plant
- Variation of pH in 2' DEWAT plants
- Variation of Temperature in 2" DEWAT plants
- Variation of BOD5 of 2 d DEWAT plant
- Variation of COD of 2 DEWAT plant
- Variation of TDS of 2 d
- Variation of FC of 2' DEWAT plant
- Variation of DO of 2nd DEWAT plant
- Variation of Phosphate of 2nd DEWAT plant
- Variation of Nitrate of 2 d DEWAT plant
- Removal efficiency of the 1 and 2nd DEWAT plant
As the wastewater flows through the DEWAT plants there was a significant reduction (greater than 95% removal) of suspended solids in the 2nd DEWAT plants. Fluctuation in influent TDS concentration may be related to changes in wastewater characteristics due to different water use pattern. Therefore, the FC values increased than the raw wastewater in the submerged anaerobic reactor.
Phosphate rises slightly in the anaerobic blinded reactor and falls in the planted gravel filter according to Figure 4.19. The DEWAT plant was in the range of 4 mg/L to 36 mg/L, but the value of nitrate at the polishing pond effluent was in the range of 0 mg/L to 16 mg/L. The results in Table 4.3 and Table 4.4 show the overall removal efficiency for the 2nd DEWAT plant, respectively.
The lower DO may be due to the use of anaerobic reactor in the DEWAT plants and contained more organic matter in raw wastewater.
- Operation and Maintenance
- Agricultural use
- Toilet flushing
- Disposal in natural water bodies
- Identification Technical Problems
- Clogging of filter media
- Proposed Design of the Modified DEWAT Systems
- Alternative first option
- Akernative second option
- Replication
Longer sludge removal intervals will thicken the sludge accumulated at the bottom and result in low efficiency of the DEWAT. He understands that daily cleaning and monitoring is necessary for the proper operation of the DEWAT device. The gravel filter is the aerobic unit of the DEWAT plant, which requires a large amount of space above ground.
Additionally, the total construction cost of the DEWAT plant was 900000 BDT, while the construction cost of the gravel seeded filter was 343112 BDT (Table 4.9). Additionally, the total construction cost of the 2 DEWAT plants was BDT 1,500,000, while the cost of constructing the gravel seeded filter was BDT 834,762 (Table 4.9). From the analysis of the experimental result, it is understood that most of the problems related to the selection of suitable filter materials, clogging, space, maintenance and overall cost of the DEWAT plant are related to the gravel seeded filter bed.
Modified version of DEWAT plant consists of four components as (i) Sedimentation tank with biogas collector, (ii) Six-compartment Anaerobic Baffled Reactor, (iii) Four-compartment Anaerobic Filter Bed Baffled Reactor and (iv) Polishing Pond (Figure 4.22) .
CONCLUSIONS AND RECOMMENDATIONS
Background
Although the performance of the DEWAT plants was found to be good, the DEWAT plant had some problems. 34;A Study of Performance of Wastewater Treatment Systems for Small Sites." World Academy of Science, Engineering and Technology. A., (2009), Decentralized Approaches to Wastewater Treatment and Management: Applicability in Developing Countries, Journal of Environmental Management 90 PP .
Schölzel and Bower, (1999), Small Wastewater Treatment Plants, Phase 1, Report on Project Criteria, Guidelines and Technologies. Emerging technology in urban areas of developing countries for sustainable wastewater treatment and reuse, Global Journal of Environmental Research 6(3): PP.91-99. Desigu Handbook for Wastewater Treatment and On-Site Disposal Systems, United States Environmental Protection Agency, Washington DC, USA.
Deutsche Gesellschaft für Internationale Zusammenarbeit GmbH (GIZ). 2005) Bewertung der Leistung anaerob-aerober Kläranlagen.
L Description Quantity Unit Price Amount in Taka
L Description Quantity
Annual housing expense (holding tax): BDT 193 Monthly expense due to waste disposal: BDT 40 Expense due to construction expense: BDT 3500 Participation in management of DEWAT system: Participate honestly Satisfaction level using DEWAT facility: Fully satisfied. Loss of income due to illness: Before implementation of DEWAT facility Medical expenses: Decreased after implementation of DEWAT facility.
Annual housing expenses (holding tax): BDT 193 Monthly expenses due to waste disposal: BDT 40 Expenses due to construction cost: BDT 3500. Loss of income due to illness: Before implementation of DEWAT plant Medical expenses: Decreases after implementation of DEWAT plants Participation of DEWAT system management: Participation sincerely Level of satisfaction using DEWAT plant: Fully satisfied.
