Thermal hydrolysis of solid fraction reduces waste disposal and provides a substrate for anaerobic photobiological treatment of refinery wastewater

Abstract

Oil refineries generate vast amounts of refinery wastewater (RWW) and oily sludge (OS). Conventional treatments typically manage these effluents separately, and resource recovery potential is not considered. The thermal hydrolysis (TH) of oily sludge at different temperatures from 175 to 200 °C and several hydrolysis times from 30 to 90 minutes has been assessed. The TH reduced the solid fraction of the oily sludge by up to 50% and released substrates in the liquid stream with up to 14 g L⁻¹ of soluble chemical oxygen demand (SCOD) and 592 mg L⁻¹ of NH₄⁺-N. Additionally, the hydrolyzed fraction was assessed as a substrate for the biological treatment of the refinery wastewater. An anaerobic photobiological system based on purple phototrophic bacteria (PPB) was considered to evaluate the co-treatment of both effluents. Batch experiments showed a 10- to 30-fold enhancement of the biomass yield, using both the RWW and the hydrolyzed fraction of the oily sludge. The less energetic TH conditions in terms of temperature and operation time produced the most biodegradable hydrolyzed stream with biomass yields close to those obtained for the control under optimal growth conditions. These results demonstrate the feasibility of the proposed integrated strategy to reduce the solid fraction of the oily sludge by the TH process and to release soluble substrates for a novel anaerobic photobiological treatment along with the RWW.