Case study of the implementation of a membrane bioreactor (MBR) package wastewater plant for treatment of domestic effluent in a remote location

Master Thesis


Permanent link to this Item
Journal Title
Link to Journal
Journal ISSN
Volume Title
The global population is more than it has ever been before; as it continues to grow, pressure on water resources increases due to the demand for the inalienable human right of access to basic services. Additionally, the detrimental impact of human activity on the environment has been realized and active measures to mitigate the threats posed by pollution (amongst other forms of environmental impact) are receiving high priority by numerous stakeholders and throughout the various parts of industry. These challenges all come into play in a unique manner when focusing on sanitation provision and wastewater treatment in rural areas. Rural communities are often disenfranchised by the lack of opportunities and services available to them and this is certainly compounded by the unique and challenging conditions for service provision and infrastructure implementation and management in these areas. Decentralized wastewater treatment is an emerging approach that is well suited to meeting the needs of people in rural areas and as a result has attracted the interest of researchers and started to gain traction in industry. Principles of conventional technologies such as the Activated Sludge (AS) system are incorporated with newer technologies such as the membrane bioreactor (MBR) to come up with innovative solutions that have promising potential but must be designed and implemented to be fit for purpose. The stringent emission control that is now common in many countries and being applied in South Africa under the National Water Act (NWA) means that sewage and effluent need to be handled according to the highest quality requirements which will not be met in areas with insufficient infrastructure (such as many rural areas). As with all things, the cost of implementing and maintaining a solution could determine the feasibility thereof and thus understanding through quantifying and optimizing the cost would be prudent. Some researchers have found that MBR plants tend to cost more than conventional treatment systems, but that they do carry their own strategic advantages of which not least is the high-quality effluent that it produces. This study provides a case study of a design and implementation of an MBR wastewater treatment plant (WWTP) on an agricultural farm in a rural area in the Western Cape of South Africa. The objectives were to (a) design the plant fit for purpose, using a scientifically accepted wastewater treatment process model, (b) evaluate the plant's performance in terms of effluent/emissions produced and (c) perform the operation cost evaluation of the designed WWTP. The AS model with biological nutrient removal (BNR) was developed in a Modified-Ludzack Ettinger (MLE) system adapted for MBR while using experimental raw water data as input. The outputs acquired from the model were used to size and design the practical implementation of the WWTP. The raw and treated effluent water and sludge quality data was obtained by experimental samples taken on site at the operational WWTP and tested by an analytical laboratory. The data was evaluated based on its trends, using statistical methods, using the effluent quality index for pollution and emissions, and using mass balances for verification. The operational costing was performed and evaluated according to the operational cost index. The wastewater treatment plant was designed for 49.2 kl/day of wastewater in a bioreactor with MLSS of 12 000 mg/l and a sludge age of 25 days which yielded a reactor volume of 22 kilolitres. The minimum anoxic mass fraction was determined as 0.14 and then chosen as 0.24, but since it is an MBR plant the volume fraction of the anoxic was 0.27. The optimal a-recycle was determined as 3.5 and then chosen at 5. The total oxygen demand was found to be 28.6 kgO/day of which the membrane air scouring blower supplied 4.7 kgO/day and reduced the air supply required from the aeration blower to 23.8 kgO/day. To be conservative, two hundred membrane sheets were used which would operate at a flux of 15.4 LMH. The reactor volume was also enlarged by a safety factor of 25% to 28 kilolitres. The small footprint of the WWTP comes at the cost of high energy usage. The model compared fairly well with the implemented WWTP particularly in terms of effluent ammonia and nitrate concentration. The effluent water quality was good with all measured parameters on average being compliant with general limits for wastewater discharge. Particularly the removal of TSS (99%) and of COD (93.5%) was highly effective and there were less than 5 outlierresults in total, which were for ammonia and nitrate. Out of the total number of parameters tested across all samples, 93% were compliant. The EQI for water was calculated as 12.1 with all contributions being positive while the EQI for sludge was 431.8 with one negative contribution from faecal coliforms amongst only positive contributions from the other parameters. The operational cost was determined as R123 316 ex VAT per year of which more than 80% is attributed to energy usage. The aeration energy alone is 58% of the operational cost. The cost per kilolitre of treated effluent is R6.73 ex VAT, which for comparison is less nearly half the cost of what the local municipal rates for sanitation would be for the application and it is also less than the cost of irrigation water from the municipality which makes it an attractive prospect for reuse. The conclusion from the study is that the WWTP design and implementation was accomplished by its cogent performance and reasonable operational cost. The objectives were achieved so that the design was developed and implemented with success, the effluent water quality was compliant, and the operational cost was understood and found to be feasible. The implications of the study are that decentralized sanitation service is being provided to a community that did not previously have access to this and that the wastewater produced by this community is now being adequately treated according to regulations, which ensures protection of the environment and advances public health.