Cement, Energy and Environment

Abstract An evalua on and comparison of different scenarios for the management of CETP sludge at Vapi has been performed using Life Cycle Analysis. The outcome of this study indicates that landfilling, as prac ced in Vapi, has the highest impact to the environment for all impact categories and therefore should be avoided for the CETP sludge management. Although the long transport distance to the cement plant, the most environmentally friendly scenarios are those where the CETP sludge is co- processed in cement kilns due to the replacement of fossil fuel and no residual waste. Nevertheless, it is recommended to implement drying of the sludge at the CETP plant to reduce the impacts associated with the transport. Among the available op ons for drying, based on this environmental study, solar drying should be preferred, however one should also evaluate the techno- commercial feasibility. The obtained results are site specific and depend strongly on the characteris cs of the sludge, the type of drying and the required transport. Therefore, the findings for this study cannot be used for the selec on of a sludge management scenario for another site. Introduc on Common Effluent Treatment Plant (CETP) in Vapi was built 20 years ago with design capacity of 55 mld (million litres per day) or 3 55 000 m per day. The sludge handling at the CETP involves sludge thickening and sludge decan ng. The smaller part gets dewatered with three filter presses which have a higher efficiency than decanters but limited capacity. The sludge from the decanters are packed in PP bags and stored in interim storage sites (concrete vats). The sludge quality and quan ty depend strongly on the treatment steps of the CETP and the wastewater quality. The moisture content of the sludge is reduced to 60% in the following processes: · 5-6 % a er sludge thickeners (sludge has 5% solid content or 95% moisture); there are two sludge thickeners. · 15-20% a er mechanical de- watering by decanters and filter press (sludge on average has 20-25% solid content or 75-80% moisture); there are six decanters. · Approximately 20% a er temporary storage (in PP/cement bags in concrete vats) for 30-40 days inside CETP. The water (moisture) oozes out because of stacking of bags on top of one another (sludge on average has 40% solid content or 60% moisture). · The leachate from the decanters, drying beds and the thickener overflow are collected and pumped to the upflow anaerobic sludge blanket (UASB) (as per the recent modifica ons) The CETP currently generates 110 tpd (tonnes per day) of CETP sludge at 40% solid which are currently landfilled at the TSDF facility. However, in future, when the CETP is upgraded for trea ng 3 100 mld or 100 000 m per day of industrial wastewater, the quan ty of sludge generated will increase to approximately 200 tpd (at 40% solid content); an increase by more than 80% from EVALUATION AND COMPARISON OF MANAGEMENT ALTERNATIVES FOR COMMON EFFLUENT TREATMENT PLANT (CETP) SLUDGE IN VAPI, INDIA 1 1 2 Dr. Kamal Azrague , Palash Kumar Saha and Dr. Kåre Helge Karstensen 1 2 SINTEF, Norway; SINTEF, Norway andAsian Institute of Technology, Thailand, 54