In anaerobic filters, as with the aerobic filters, there is a microbial film growing on an inert support (Chian and DeWalle, 1977). Anaerobic filters may be operated in an upflow or downflow mode, and a wide variety of packings are used; both natural and synthetic (Young, 1983). The first full-scale anaerobic filters were constructed in the 1970s and in 1982 the Bacardi Corporation brought into operation a 100,000-m3 plant to treat distillery effluents (Szendrey, 1983). Many other effluents are found to be amenable to treatment using anaerobic filter systems; antibiotic fermentation wastes, citric acid fermentation wastes, yeast production wastewater and brewery and winery wastewaters (Szendrey, 1983), molasses distillery slops (Silvero et al., 1986) and fermentation and pharmaceutical wastes (Bonastre and Paris, 1989).
UP-FLOW ANAEROBIC SLUDGE BLANKETS (UASB)
In this system (originally developed in the Netherlands) high levels of active biomass are retained in the reactor by flocculation (Lettinga et al, 1980, 1983). No support media is added to the reactor, instead the flocculated sludge develops in the reactor and acts as a fluidized bed. Feed is pumped through the bed (the sludge blanket), above which fine particles flocculate and settle back to the blanket as sludge, thus preventing washout of organisms. Anaerobic sludge blankets have been found to be effective in the treatment of many wastewaters, including sugar-beet wastes, domestic sewage, slaughterhouse wastes, agricultural wastes (Lettinga et al, 1983), brewery wastes (Fang et al., 1989, 1990), winery wastes (Cheng et al., 1990) and distillery wastes (Burgess and Morris, 1984; Ghosh et al., 1985).
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