Effect of Pre-treatment using Ultrasound and Hydrogen Peroxide on Digestion of Waste Activated Sludge in an Anaerobic Membrane Bioreactor

Abstract

The rate of anaerobic digestion (AD) often depends on the rate-limiting hydrolysis step that makes organics available to microorganisms. To achieve efficient conversion of particulates to soluble materials and finally methane, the biomass in the digester must be provided with optimal operational conditions that will allow for biomass retention and substrate metabolism. Two approaches were employed in this study to improve the ultimate biodegradability of waste activated sludge (WAS) -Pre-treatment (PT) and operation using an Anaerobic Membrane Bioreactor (AnMBR).PT of WAS is one way of speeding up hydrolysis. It has been proposed that PT leads to the lysis of cells, which in turn causes the release and solubilisation, and thus availability of intracellular matter to microorganisms for microbial growth and metabolic activities. This study compared the effect of thermal, sonication, and sonication + hydrogen peroxide PT on chemical oxygen demand (COD) solubilisation of WAS. Based on the soluble COD (SCOD) release, it was concluded that combined chemi-sonic treatment resulted in better WAS degradation rather than individual ultrasonic pre-treatment and thermal PT. The highest solubilisation rate was observed at a chemi-sonic PT of 50gH 2 O 2 /kgTS and sonication duration of 60 minutes. At this PT, a COD solubilisation of 40% was observed which was significantly different than PT involving only sonication and no pre-treatment (0.88%) at 95% confidence. Therefore a peroxide-sonic PT was chosen to treat WAS in this study as it was expected to result in the greatest improvement in WAS biodegradability.In addition to PT, biodegradability of WAS can also be improved by coupling PT with an AnMBR. AnMBRs prevent biomass washout by decoupling the solids retention time (SRT) from the hydraulic retention time (HRT). Thus, a long SRT can be used to provide sufficient duration for biological activities without increasing the volume of the reactor. In this study, a 4.5L AnMBR with an HRT and SRT of 3 and 20 days, respectively was used to treat raw and PT WAS. In order to compare the biodegradability of PT and raw WAS, the AnMBR was operated in three phases. Phase 1 was operated with raw WAS, Phase 2 was operated with WAS pretreated with 50 gH 2 O 2 /kgTS and 20 minutes ultrasound (US), and Phase 3 was operated with WAS pre-treated with 50 gH 2 O 2 /kgTS and 60 minutes US. The anaerobic biodegradability of WAS following a combination of ultrasonic pre-treatment and H 2 O 2 addition was significantly improved, with Phase 3 resulting in the greatest improvement. The COD destruction for phases 1, 2, and 3 were 49%, 58%, and 63%, respectively whereas the volatile suspended solids (VSS) destruction for phases 1, 2, and 3 were 46%, 71%, and 77% respectively. Organic Nitrogen (Org-N) destruction increased from 44% to 52% for phases 1 and 2 respectively. A further increase of 18% in Org-N destruction was observed in phase 3. This improvement in biodegradability of WAS was attributed to the high solubilisations of COD, VSS, and ON...

Codigestion of high pressure thermal hydrolysis‐treated thickened waste activated sludge with primary sludge in two‐stage anaerobic digestion

“…The values of COD solubilisation were estimated to range from 24 to 33% through pretreatment. The literature has reported values of 28 to 45% solubilisation through HPTH [6,[27][28][29]. Hence the results obtained in this study were comparable to previous findings.…”

Effect of thermal pretreatment on digestability of thickened waste activated sludge and primary sludge in two-stage anaerobic digestion

“…PCODi was the initial particulate COD. Burger and Parker (2013) showed 41% COD solubilisation was achieved for a synthetic WAS at 150 0 C. Joshi (2014) reported 35% and 27% COD solubilisation of WAS collected from the Waterloo WWTP as a result of thermal pretreatment at 170 0 C and 150 0 C respectively. Xue et al (2015) found COD solubilisation varied from 4.5-53.4% for a temperature range of 120 0 C to 180 0 C. Donoso-Bravo et al…”