Study of the industrial wastewater treatment process of Biyagama Export Processing Zone of Board of Investment of Sri Lanka

Abstract

The Biyagama Export Processing Zone (BEPZ) could be recognized as the Sri Lankas only Industrial Estate designed to accommodate high polluting type industries. Plans are underway to introduce few more industrial estates which could locate high polluting type industries and however it is unlikely that any such project would realize within the very near future. The common wastewater treatment plant (CWTP)of BEPZ has been constructed in 1988 and with the completion of 8 years of operation by 1996 it is high time that the treatment process and the circumstances are reviewed and evaluated in order to arrive at any conclusions and make recommendations based on the system performance. The BEPZ is located upstream of the raw water intake of the Greater Colombo Water Supply Scheme and therefore it is utmost important that the CWTP is operated strictly in compliance with the environmental norms as relevant. In this study, firstly, an attempt is made to ascertain the overall efficiency of the treatment process of the CWTP. In the next phase a detailed study is carried out to investigate the biological treatment process of the Aerated Lagoon No.1 with different operating sequences of aerators. The study concludes with an effort made to introduce improvements to the present treatment system with a view to enhance the efficiency of substrate removal. The biological treatment process in the aerated lagoon No.1 performs in compliance to "aerobic flow through" and consequently the substract removal efficiency exists within a limited range. Futher it has been revealed that the operation of two adjacent areators simulitaneously would yield best performance. Operation of all three areators simultanously did not produse satisfactory performance. It has been also identified that the substract removal efficiency could be enhanced by the conversion of the behavior in the areated lagoon to "facultivate" type. Based on the findings it is anticipated that by operating a single areator at a time on either edge of the lagoon would enhance the treatment efficiency because it is evident that a single aerator would be capable of produsing areobic conditions throughout the top layers of the water body while the deeper areas away from the aerator axis could have anaerobicity. In view of the high concentration of the suspended solids found in the treated effluent of the common wastewater treatment plant (due to the fact that the aerated lagoons operate to fully mixed situation) it has been recommended that primary settling be introduced.