A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering of the Asian Institute of Technology, Bangkok, Thailand.

Thesis (M.Eng.) - Asian Institute of Technology, 1971

Biological disc filter units, comprising an upper aerobic contact chamber with a series of rotating discs and a lower anaerobic digestion chamber, were used for the treatment of a high COD nitrogen deficient waste and a low COD waste under tropical conditions. The experimental process unit had a cross 'section similar to that of an Imhoff tank with the modification that the sedimentation portion incorporated the series of rotating discs. Factors affecting the performance of the system such as detention time, volumetric COD loading, disc areal COD loading, disc rotational speed, and influent nitrogen level were studied in the outdoor environment using four laboratory-scale units fed with Pepsi Cola bottle washing waste with COD ranging from 1,000-1,200 mg/1. The most effective detention time and COD loading for treating a low COD waste, sewage were also evaluated at a disc rotational speed of 10 rpm. The results indicated that for treating Pepsi Cola waste a detention period of 6 hours, with COD loading 4000 kg/1000 m³ day and disc areal COD loading of 20 kg/1000 M² day at a disc rotational speed of 10 rpm gave a COD removal of 95% under tropical conditions. Disc rpm and detention period in the unit were found to hove an important bearing on the dissolved oxygen concentration of the effluent. Disc rotational speeds above 5 rpm or detention periods above 6 hours did not improve COD removal. The nitrogen removal efficiency of the system was found to increase with increasing detention period and disc rotational speed. There were indications of lower COD removal efficiencies if nutrient supplementation of a nutrient deficient waste was .not practiced, however, it may be possible in practice to reduce the level of nutrient supplementation due to nutrient recycle from the anaerobic digestion compartment. In the ranges of detention period of 2-12 hours and disc rotational speed of 1-10 rpm studied, the effect of detention time was most significant in suspended solids removal efficiency for Pepsi Cola waste. For: a low COD domestic waste a detention period of 2 hours, volumetric COD loading of 4800 kg/1000 m3 day and disc areal COD loading of 24 kg/1000 m2 day were found to be optimum at a disc rotational speed of 10 rpm. With sewage, detention period was found to have an important effect on the NH3-N removal efficiency. The ecological flexibility indicated by the changing growth characteristics of the bacterial slime on the disc at different feed conditions suggests that the system would tolerate shock loadings or variable loadings without difficulty or loss of COD removal efficiency. An analysis of the volatile solids in the mixed liquor and digested sludge from the anaerobic compartment showed a volatile solids removal of 75-80% in the anaerobic digestion process which indicated very efficient digestion after 30 days of operation.