Enhanced Lipid Degredation in Upflow Aanerobic Sludge Blanket Reactor by Inetergration with Acidogenic Reactor

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Courtesy of Water Environment Federation (WEF)

INTRODUCTION
Lipids are the major organic component in wastewaters from many industries including dairy product, edible oil refinery, slaughterhouse and wool scouring (Pereira et al., 2001). By anaerobic bacteria, lipids can be degraded via hydrolysis and β-oxidation to acetate and hydrogen, which in turn are converted to methane. A large amount of CH4 can be produced from lipids because they are highly reduced organics. Theoretically 1 g of glycerol trioleate (C57H104O6), a common lipid in nature, is equivalent to 1.08 L of methane at standard temperature and pressure (STP), while 1 g of glucose (C6H12O6) is equivalent to only 0.37 L. However, accumulated lipids in attached-growth anaerobic processes would cause the operational problems such as clogging, scum formation and wash out of active biomass due to their low solubility and adsorption onto the surface of sludge or media (Kim et al., 2004a). Moreover, long-chain fatty acids (LCFAs), the hydrolysates of neutral fat, are inhibitory to many kinds of anaerobic bacteria including methanogens (Kim et al., 2004b). It was reported that more double-bonded and longer LCFA was more toxic (Alosta et al., 2004). Some researchers found saturation of double-bonds in acidogenesis, and then suggested the phase separation as an alternative for the treatment of lipids-containing wastewaters (Komatsu et al., 1991). Kim et al. (2004a) operated a two-phase system composed of a continuously stirred tank reactor (CSTR) and an upflow anaerobic sludge blanket (UASB) reactor as well as a single phase system of a UASB reactor, which were fed with a synthetic wastewater containing major LCFAs and glucose. An enhanced treatment performance of the two-phase system and degradation (19-30%) and saturation (10-12%) of LCFAs in acidogenesis was found. The enhancement of lipids degradation and performance by phase separation in the treatment of real lipids-containing wastewaters, however, has not been proved yet. The dairy industry generates strong wastewaters containing high organic content. Since the reagent costs are high and the soluble organics removal is poor in physico-chemical treatment processes, biological processes are preferred (Ince, 1998). Aerobic treatments are commonly employed so far; however, high sludge production and energy requirement for aeration is a significant drawback. Dairy wastewaters are warm and strong, enabling them suitable for anaerobic treatments, which do not need aeration or produce excess sludge. Effective treatment results of dairy wastewater using attached-growth anaerobic processes such as blanket (UASB) reactor have been reported in the literature (Demirel et al., 2005). However, several operational problems such as sludge flotation and activity decrease were sometimes found (Vidal et al., 2000). The main organics in dairy wastewaters are lactose, casein andlipids. Many researches presumed that lipids are the most problematic component in the treatment of dairy wastewater. However, data concerning lipids in the treatment of dairy wastewater are scarce (Demirel et al., 2005). This work, therefore, was focused on the lipids inhibition and their degradation in dairy wastewater treatment. A UASB reactor integrated with an acidogenic reactor was operated and compared with a conventional UASB reactor. Serum bottle tests were also performed to examine effects of lipids on on dairy wastewater treatment.

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