Influence of temperature and oxidation-reduction potential on hydrolysis of swine manure wastewater

Abstract

Thermal and micro-aeration pretreatments were applied to swine wastewater in order to improve hydrolysis of the substrate for biogas production. The experiments were carried out in 5-L reactors using 1% total solids concentration swine manure wastewater. Thermal pretreatments were performed at temperature of 30 oC (room temperature), 45 oC and 55 oC, while the micro-aeration pretreatments were operated at controlled ORP of -300 and -420 mV. Results indicated that hydrolysis in terms of sCOD release was increased by 18.5% and 23.1% at 45 and 55 oC, respectively (compared to 30 oC). TVFA also increased as a result of heightened acidogenesis. Micro-aeration could improve hydrolysis by 10.1% and 21.3%, and TVFA by 7.23% and 12.87% (compared to non micro-aeration/uncontrolled ORP) at ORP -300 and -420 mV, respectively. Both pretreatment methods attained high hydrolysis efficiency within 24 hr. However, too long of micro-aeration could lead to a loss of organic carbon thru oxidation as evidenced by the disappearing organic acids in the test reactors. Both thermal and micro-aeration pretreatments are environmental friendly and could be a simple solution to increase efficiency of biogas production by means of pre-hydrolysis.