Operation of an anaerobic filter and an EGSB reactor for the treatment of an oleic acid-based effluent: influence of inoculum quality

An expanded granular sludge bed (EGSB) reactor and an anaerobic filter (AF), inoculated with granular and suspended sludge, respectively, were operated with an oleic acid-based synthetic effluent. The granular inoculum exhibited a specific methanogenic activity with acetate, ethanol and H2/CO2 as substrates, in average 2–7 times higher than the suspended biomass. Resistance to oleic acid toxicity was ten-fold higher in the granular than in the suspended sludge. Due to the better characteristics of the granular inoculum a faster start-up strategy was adopted in the EGSB than in the AF, being oleic acid fed since the beginning and the co-substrate eliminated on Day 70. In the AF, a co-substrate was fed until Day 150 and oleic acid was introduced only on Day 94. Organic loading rates of 8 and 12 g COD/l d of oleate as the sole carbon source were achieved in the EGSB and AF, with removal efficiencies of 70 and 80%, respectively. At these maximal loads, the average effluent volatile suspended solids were 2.7 and 5.6 g/l in the EGSB and AF, respectively. The methane yield decreased from 280 to 27 l CH4/kg COD-removed in the EGSB and from 362 to 91 l CH4/kg COD-removed in the AF. The possibility of using a faster start-up procedure using a better inoculum was investigated and results suggest that inoculum quality was not, in this case, a dominant factor for the operation of reactors with high LCFA content.