ABSTRACT
Thickened waste activated sludge (TWAS) was pretreated with microwave irradiation to temperatures higher than the boiling point (between 110 and 175 degrees C) using different microwave intensities. Biochemical methane potential (BMP) assays demonstrated that, although mesophilic anaerobic digestion (MAD) inoculum used was acclimated for 4 months with microwave pretreated TWAS (to 175 degrees C), acute methanogenic inhibition was observed. Additionally, the microwave conditions applied increased the soluble chemical oxygen demand (sCOD)-to-total COD (tCOD) ratio; however, no significant enhancement in the rate or extent of TWAS stabilization was observed for the microwave-pretreated samples. Microwave pretreatment to between 110 and 175 degrees C at lower microwave intensity with a better acclimated MAD inoculum (acclimatized for an additional 3 months) resulted in minimal methanogenic inhibition (improved acclimation) and improved the rate and extent of TWAS biodegradation, as determined by volatile solids removal and biogas production (microwave applied at lower microwave intensity). The TWAS pretreated to 175 degrees C produced 31 +/- 6% more biogas than the control (raw TWAS) by the 18th day of the BMP test, whereas the highest improvement observed from the first set of BMP experiments was 13 +/- 1%.
Subject(s)
Hot Temperature , Microwaves , Waste Disposal, Fluid/methods , Water Purification/methods , Anaerobiosis , Animals , Biodegradation, Environmental , Bioreactors , Methane/chemistry , Methane/metabolismABSTRACT
Effect of microwave pretreatment (MW) high temperature (175 degrees C) and MW intensity to waste activated sludge digested with acclimatized inoculum in single- and dual-stage semi-continuous mesophilic anaerobic digesters at different sludge retention times (SRTs) (20, 10 and 5 days) were investigated. MW pretreatment led to similar sludge stabilization at low SRTs (5 and 10 days). Although lowering MW intensity slightly improved sludge solubilization, it had a negative effect on digestion at low SRTs. Single-stage digesters with MW pretreatment surpass dual-stage digesters performances.
