A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1992

Pilot scale experiments to study the various anaerobic reactor configurations for the treatment of synthetic fibre production wastewater were conducted on site. Two Fixed Bed, one UASB and one RAUS were used in this study. All reactors were seeded with same sludge from an anaerobic pond of a starch factory and started up with wastewater diluted with pond water and the dilution ratio was 3 kept at 1:1. The COD-loading during start was fixed at 0.5 kg/(m .d). The anaerob] c reactors were able to take a maximum COD loading of 2 kg/(m3.d), however, beyond this loading, due to quick acidification, volatile fatty acids ( VFA) increased within the r e actors which resulted in pH drop and COD increase in the effluent of all the reactors. This was in contrast to the ongoing pilot scal e experim,nts in AIT laboratory, where a maximum COD loading of 4 kg/(m .d) was achieved with the same wastewater without pH drop. The reason could be the differences in the inoculum sludge, or due to the fluctuations in wastewater characteristics. It shows that we still do not have the tools for quick identification of the causes of the differences between the actual practice and the work done in the laboratory. The cause could also be the laboratory units itself. It was speculated that the temperature was the limiting factor, therefore, F.B.1, UASB and RAUS(R/S) were heated up to 30 - 35°C. Within two we~ks it was possible to increase the COD-loading from 0.5 to 2 kg/(m .d)r The Fixed Bed and UASB achieved a maximum COD-load of 3 kg/(m .d), however, beyond this loading VFA accumulation and pH drop again prevailed. However, anaerobic treatment of synth eti c fibre production wastewater is technically feasible in relation to energy conservation and econo~ical in c hemical consumption as compared to aerobic treatment. 8 m /day of methane gas will be produced from one cubic meter of wastewater when the COD is reduced from 20 g/l to 1 5 g/l and 1 kg of Sodium hydroxide per cubic meter of wastewater will be saved by anaerobic treatment. Further investigation is still being carried out in order to find out the limiting factor in the anaerobic treatment of synthetic fibre production wastewater.