Treatment of Cane Sugar Mill Wastewater in Upflow Anaerobic Sludge Blanket (UASB) Reactors
High BOD wastewaters from cane sugar mills are among the major polluters of water bodies in India. Seasonal nature of the industry is not conducive to treatment by conventional biological processes. Sanitary disposal of sugar mill wastes in India has thus proved to be a difficult problem for want of a suitable treatment method. The present work pertains to the treatment of sugar industry wastes in UASB reactors. This process works at low hydraulic retention times (HRT, 3-6 h) and long solids retention time (SRT, 200-300 d), and produces methane as a byproduct. Long SRTs are achieved by immobilization of bacteria as sludge granules which are retained in the reactor by providing a gas solids separator. After a few weeks of start-up of the reactor, the seed sludge becomes granular. Granulation facilitates large hydraulic and organic loading potential of the UASB concept, particularly for treating liquid wastes with predominantly soluble organics, such as those from sugar mills. Organic and hydraulic loadings are interrelated factors through strength of the waste to be treated. Sludge loading capacity depends on the quality of the sludge developed. The laboratory work described here was undertaken to determine: l) the loadings that could be applied satisfactorily; 2) the performance of the reactors under various combinations of loadings; and 3) the effect of loading on quality of sludge.