AEROBIC OXIDATION OF COMMON EFFLUENT TREATMENT PLANT WASTEWATERS AND SLUDGE CHARACTERIZATION STUDIES

Abstract

With the fact that sustainable industrial growth in small‐scale sector is essential for socio‐economic development, a new concept of collective responsibility in the form of common effluent treatment plants (CETP) is emerging as an techno‐economic solution for waste treatment. High initial and operational costs besides limited space availability and technical know‐how in industries prompted for the installation of CETP in many cities. Many industries are clustered together in various industrial estates and thus pool their resources and establish ETP as an industry in itself to collect and treat their wastes at a common facility. Thus CETP's have their basic objective to provide facility to treat their effluents effectively at one place. However major difficulty faced by a CETP is to assess the extent of pollution from each industry and provide suitable treatment. In the present study an attempt was made to evaluate the treatability of CETP wastewater using lab‐scale activated sludge process. Wastewater required to carry out the study was collected from the equalization tank of a CETP. The wastewater was mainly contributed by pharmaceutical origin besides textile, dairy, etc. These wastes were characterized to be containing high COD and a high COD: BOD ratio and require effective aerobic biological treatment systems to ensure safe disposal. Since aerobic microorganisms grow faster than the anaerobic microorganisms besides faster respiration rate and short acclimatization time, the present study is carried out using extended aeration lab‐scale activated sludge process to evaluate the treatability efficiency by varying F/M ratio. For each F/M ratio considered the performance is evaluated at three MLSS concentrations of 2000 mg/L, 3000 mg/L and 4000 mg/L. The studies are carried out at two different HRT's. The efficiency of the treatment is determined in terms of % COD, BOD reduction and SVI values. The studies revealed that COD reduction at a HRT of 5.0 days ranged between 63%–78% while SVI values ranged between 43–62 for all the F/M ratios studied. A maximum of 78% COD reduction was observed at 0.10 F/M ratio (4000 mg/L MLSS concentration) and the corresponding SVI value of 60 was observed at the same. Further at an HRT of 3.5days COD reduction ranged between 60%–75% while the SVI values ranged between 47–60. A maximum COD reduction of 75% was observed at 0.10 F/M ratio (3000 mg/L MLSS concentration) and the corresponding SVI value of 55 was observed at the same. The reduction in BOD values for both the HRT's studied were in good validation with the COD values and a BOD reduction of over 85% was observed for almost all the concentrations studied. Further, the activated sludge from the aeration tank was subjected to microbiological analysis to determine the probable organisms involved in waste stabilization. Characterization of the dried sludge was carried out to assess the suitability and applicability of the sludge as manure.