Evaluation of an Extended Aeration System for Nutrient Removal, A Case Study of a Wastewater Treatment Plant in Kulai, Johor Baharu, Malaysia

Sammanfattning: Malaysia is one of the most developed countries in Southeast Asia, and strives to be acknowledged as a high income country by the year of 2020. According to Malaysian Environmental Quality (Sewage) Regulations from 2009 there are effluent limitations regarding nutrient emission from wastewater treatment plants. The company responsible for the municipal wastewater treatment, Indah Water Konsortium, have found that the performances of nutrient removal at their wastewater treatment plants are varying and the company is interested in examining the reason for the difference. This study has investigated nutrient removal at one of Indah Water Konsortium’s wastewater treatment plants in order to evaluate how well it is working and what could be done in order to improve the nutrient reduction. The investigated wastewater treatment plant is an activated sludge plant with extended aeration and a primary treatment consisting of grit and grease removal. The characteristics of the influent wastewater are purely domestic. The plant is designed for 1216 population equivalents and at present 1160 population equivalents are connected. The aims were to evaluate the nutrient reduction, analyse whether biological phosphorus removal called Bio-P could be possible and to give suggestions for possible upgrades and improvements of the plant. It was done by constructing a nitrogen and phosphorus mass balance. Also, analyses were performed to assess the nitrification rate, measure the amount of volatile fatty acids in the influent and basic parameters such as dissolved oxygen, pH, mixed liquor suspended solids and aerobic sludge age. Samples were taken three times a week during a five-week period starting from the 21st of March 2016. The analyses showed that organic matter, measured as BOD and COD, were satisfactorily reduced. The nitrogen mass balances showed that nitrification and denitrification occurred, however the processes were uneven and not reliable. The results also showed that both the measured maximum and full-scale nitrification rate were very low which probably was due to low oxygen concentration and pH-levels in the aerobic tank. The mixed liquor suspended solids concentration and the aerobic sludge age was found to be enough for the bacteria to carry out the nitrification process, assimilate nutrients and for BOD-reduction. The phosphorus mass balances showed that more phosphorus than expected was removed from the wastewater treatment plant; there was high phosphorus content in the sludge. The high removal may be due to Bio-P. Furthermore, investigations showed that there were enough volatile fatty acids in the wastewater to obtain Bio-P. If the characteristics of the wastewater are similar at other places, Bio-P could be an option for the future at wastewater treatment plants in Malaysia. In order to upgrade the plant, calculations were made to evaluate if the size of the tank used for biological treatment is sufficient for nitrification and if there is space to incorporate an anoxic tank in order to get a predenitrification treatment. The results showed that with an expected nitrification and denitrification rate at the wastewater treatment plant the present volume is large enough for a pre-denitrification process. One of the main improvements that could be made at the wastewater treatment plant is to increase the nitrification rate by improving the aeration.