Biological treatment of oil field wastewater in a sequencing batch reactor

This work reports the results of experiments carried out in a sequencing ba tch reactor (SBR) operated under 24 hour cycles, treating an effluent conta ining a mixture of oil field wastewater and sewage, in different percentage s. The removal of phenols, ammonium. and COD was monitored in several exper imental runs, varying the dilution degree of the oilfield wastewater (10 to 45% v/v). The volatile suspended solids (VSS) content in the reactor was a lso monitored and the protein (PTN) and polysaccharide (PS) contents of the suspended biomass were determined. The removal of ammonium and phenols did not vary significantly in the experimental runs, attaining average values of 93% and 65%, respectively. COD removal efficiencies in the range of 30 t o 50% were attained in the experiments carried out with dilution percentage s of 45 and 35% (v/v) respectively. An experiment carried out with a lower proportion of produced water (15% v/v), keeping the salinity level correspo nding to a higher proportion of industrial effluent (45% v/v), led to an im provement in the COD removal, indicating that the recalcitrance of the orga nic compounds found in the effluent is the main cause of the moderate COD r emoval efficiencies attained in the SBR system. With regard to the composit ion of the microbial flocs, no significant variation was observed in the PS /PTN, PS/VSS and PTN/VSS ratios when the effluent composition changed (incr eased salinity and levels of organic material).