Cement Energy and Environment

·- ' hydrogen sulphide, etc. Biogas can be used for thermal applications, such as water heating, drying, boiler fuel , etc., or for electricity generation. The digested material available after the anaerobic treatment may be used as a soil conditioner after composting/ vermicomposting. Dual benefits reaped using anaerobic digestion processes for organic solid waste are simultaneous removal of organic pollutants and waste stabilization as well as production of renewable energy in the form of biogas . Studies carried out at the Sardar Patel Renewable Energy Research Institute (SPRERI) have shown that biomethanation of the dairy effluent scum is an attractive alternative method for the milk processing industries in terms of energy generation for captive use, besides, significant reduction of the organic pollutant load. Source of Dairy Effluent Scum In dairy effluent treatment plants, effluents generated from various sections of the production facilities are first received in a collection tank. Before mixing in an equalization tank, the effluents are passed through a fat trap unit. The low density semi-solids, which float in the tank and contain fats, proteins, packing materials, etc., are known as 'dairy effluent scum' and are removed manually. After removing the dairy effluent scum (top layer), the effluents are further treated in aerobic or anaerobic conditions. The characteristics of dairy effluent scum vary with the products being produced in the plant and their relative proportion and the methods of the operation used. The schematic diagram of the source of dairy effluent scum generation in a dairy effluent treatment system has been shown in Figure 1. Composition of Dairy Effluent Scum Dairy effluent scum was collected from a dairy industry at Anand (Gujarat) processing liquid milk, ice– cream, ghee, and cheese. The physico-chemical characteristics of fresh dairy effluent scum have been given in Table 1. All the parameters were estimated according to the procedures recommended in the standard methods for examination of water and waste water. Rich organic content of the scum indicates its suitability as a feedstock for biomethanation. Biomethanation of Dairy Effluent Scum The laboratory scale followed by pilot scale studies for biomethanation have been carried out at SPRERI using the dairy effluent scum as the substratein daily fed reactors for 10 per cent total solids concentration and 40 days hydraulic retention time . The pictorial view of a 900 L capacity biogas plant used for biomethanation studies of the dairy effluent scum is shown in Picture 1. Performance of the plant has been given in Table 2. Table 2: P4H-f'orrnanc:.e of' the blorne-=~na'tion plant: P.ar ·amet:cr V.""i:lues IHFH t~t) A,t) ~-ff~~\JVQ "IWWffi~ 4>f f;)t)t) .. , ., r,;;a~t~f 0-.l J)alfY ilc:t.. .Ofl't f~~~ "' W~H t-t1ils!ic (kQ}c:i) ;;..:;. _ ~ ... iif)l( t"ti<lf<f< (kQ/~f) ::t. ~~ T~ f~J (X)· ~t) T:i f.e!ft1a."~ l ."} t).~ C!!fftC.:I~fHl)l (~) AV~ - t;)la.r:~Ji :it).'} () PfQ&J"-• f.lt on C.l-.1~) ~'W""' :,rl<'llu:J <.1-.lkQ -'ltW ·~ 'f~f) M~thlilfl ~ (X) ,~ C!#lltbt:)f'\ ~lt3itlf-i~ (") ~ft . ;) Hy~,f!QQ~n a t...dpi'IIC.ico .$0 tppm> 55