UASB TREATMENT OF WASTE-WATER WITH CONCENTRATED MIXED VFA

The upflow anaerobic-sludge blanket (UASB) process consistently remove d 97-99% of chemical oxygen demand (COD) from wastewater containing co ncentrated mixed volatile fatty acids (VFA) at 37-degrees-C at loading rates of up to 24 g-COD/(L.d), corresponding to a food/microorganism ratio of 0.78 g-COD/[g-volatile suspended solids (VSS).d]. It suggeste d that, with preacidification, the UASB process can be effective for a wide variety of wastewaters. The COD removal efficiency deteriorated at higher loading rates; there was no butyrate in the effluent, sugges ting that butyrate degradation was not a rate-limiting step. Of the CO D removed, 92.6% was converted to methane; the rest was converted to g ranular biomass with an average yield of 0.054 g-VSS/g-COD. The granul es had a size of 1-2 mm and settled satisfactorily. Each gram of granu le in the reactor was capable of converting a daily maximum of 0.86 g of COD into methane. The granules had a fluffy surface mostly composed of interwound filamentous Methanothrix-like bacteria. Syntrophic asso ciations between Methanothrix-, Methanospirillum hungatei-, and Syntro phobacter-like bacteria were prevalent in the granule interior. The sy ntrophic relation between these species was elucidated by thermodynami cs.