BIOSORPTION OF LONG-CHAIN FATTY-ACIDS IN UASB TREATMENT PROCESS

Biosorption of long-chain fatty acids (LCFA) in the upflow anaerobic s ludge blanket (UASB) treatment process was investigated using batch te sts and continuous reactor runs. Batch experiments were conducted, for characterization of the biosorption, with two active and one inactiva ted (autoclaved) sludge granules as sorbents and with a single (oleic acid) or a mixture of LCFA (LCFA(m); 50% oleic, 35% palmitic and 15% s tearic acid) as sorbates. The LCFA(m) showed a faster adsorption onto the granules than oleic acid. With the active sludge granules, adsorpt ion was followed by desorption. Methane production increased significa ntly, either simultaneously (at lower LCFA concentrations) or succeedi ngly (at higher concentrations) with desorption. The desorption was me diated by biological activity, since it did not prevail with inactivat ed granules or with active granules inhibited at higher LCFA(m) concen trations. The inactivated granules had a slightly higher initial bioso rption capacity. Increased LCFA concentrations resulted in more LCFA a dsorbed and greater inhibition of their biodegradation. A hypothesis i s proposed to explicate the relationship between biosorption, desorpti on and biodegradation of LCFA by sludge granules: adsorption is a prer equisite for biodegradation while desorption is a consequence of biode gradation. Isothermal studies with oleate showed that the apparent bio sorption could be described by the physical multilayer adsorption theo ry and the sorption isotherm derived was consistent with the Freundlic h model. The quantitative relation between LCFA biosorption and granul ar sludge flotation was investigated in a UASB reactor fed with LCFA(m ). Sludge flotation depended on the LCFA(m) loading rate rather than o n their concentration. The higher the loading implemented, the more fl otation occurred and the shorter rime required for complete flotation of the sludge bed. Flotation started when the LCFA(m) loading rate exc eeded 0.09 g COD/g VSS-d, while complete flotation occurred at the loa ding rates exceeding 0.2 g: COD/g VSS-d. These results suggest that sl udge bed wash-out is likely to be encountered before inhibition of met hanogenesis during the treatment of LCFA-containing wastewaters by the UASB process. (C) 1998 Elsevier Science Ltd. All rights reserved.