Abstract
Sequencing Batch Reactor (SBR) process has been evaluated as a cost-effective alternative treatment system for palm oil refinery effluent in Malaysia. This innovative process has successfully gone through laboratory and pilot scale studies. The technology has also successfully been transferred to full commercial scale application. The present study has demonstrated that SBR process is capable of producing highly purified final discharge with very low chemical oxygen demand (COD) (<100 mg/l) and suspended solids (SS) (<50 mg/1). The present study has also shown that the SBR process can be easily started if active sludge is available. The performance in terms of COD removal efficiency does not depend very much on the COD of the raw effluent. The quality of the final discharge can be controlled by delaying the discharge of the reactor content i.e. by prolonging the aeration period. Typically, when the COD of the raw effluent is less than 1,500 mg/1, a 12 hour cycle (fill: 4 hours; aeration: 8 hours; settling: 2 hour and idle: 2 hours.) is adequate to produce highly purified final discharge. It was found generally that simultaneous filling and aeration produced best results. Time of filling did not seem to influence the SBR performance in terms of COD removal. It did not affect the settle ability of the sludge. The optimum sludge level was found to be around 2500 mg/1. The dissolved oxygen (DO) level had to be maintained at above 2.5 mg/1 for effective treatment. The settle ability of the sludge was found to be very good. The SVI was always less than 60 ml/gm. The full scale commercial plant study has shown that very stable operation could be attained provided enough aeration time and DO (2.5 mg/1) are given. The SBR process can be fully automated and is virtually maintenance-free. Only a part-time operator is required to oversee the operation. For full scale plant operation, it is recommended to employ a 24-hour cycle operation, i.e. 4-hour FILL, 20-hour REACT, 2-hour SETTLE and 2-hour DECANT and IDLE. This operation strategy is able to sustain high fluctuations of COD of the refinery effluent, the low pH does not affect the performance of the process. The present study has shown that no pH adjustment was required. Only nitrogen has to be added to supplement the nutrient requirements when necessary. The presence of residual oil affects the SBR performance to a large extent. The oil was observed to form scum with the sludge and float on the surface of the reactor liquor. It has to be removed as soon as it is formed, otherwise the reactor will suffer substantial loss of sludge which will drastically affect the performance of the SBR.