EFFECTS OF SUPPORT MATERIAL ON THE PATTERN OF VOLATILE FATTY-ACID ACCUMULATION AT OVERLOAD IN ANAEROBIC-DIGESTION OF SEMISOLID WASTE

Anaerobic degradation of a semi-solid waste with a total solids conten t of 4% particulate matter, much of it insoluble, was investigated in four laboratory-scale reactors. Two of the reactors were equipped with different textile materials for immobilisation of microorganisms, whi le the other two were used as continuously-stirred-tank reactor refere nces, A constant organic loading rate and hydraulic retention time wer e used in the start-up period; the hydraulic retention time was then d ecreased and the effects of this change were monitored. Volatile fatty acid (VFA) concentration and pH were chosen as indicators of the micr obial status in the reactors. The reactors with support material showe d a greater resistance to overload than did the continuously-stirred-t ank reactors. This is in agreement with many studies undertaken on the anaerobic treatment of wastewater. However, no problems with clogging occurred, showing that a support material is also applicable in syste ms treating waste containing large amounts of insoluble, particulate m atter. The pH was comparable to VFA for indicating an approaching proc ess failure. However, the pattern of VFA accumulation was qualitativel y different between the reactors with and without support material, Ob viously the metabolic pattern of mixed cultures changes when the micro organisms are immobilised.