The significant increase in the sewage sludge production in treatment plants makes anaerobic digestion more important as a stabilization process. However hydrolysis is the rate-limiting step of anaerobic digestion because of the semirigid structure of the microbial cells. Pretreatment of waste activated sludge
(WAS) leads to disruption of cell walls and release of extracellular and intracellular materials. Therefore biodegradability of sludge will be improved in terms of more biogas production and sludge minimization. Among the pretreatment methods, alkaline, thermal and thermochemical pretreatments are effectual ones. Considering the effect of thermal pretreatment, microwave technology in which the sample reaches to elevated temperatures very rapidly is a very new pretreatment method. However no previous research has been conducted to test the effectiveness of microwave (MW) irradiation combined with alkaline pretreatment. Since both of these techniques seem to be highly effective, their combination can act synergistically and even more efficient method can be obtained. Therefore the main objective of this study was to investigate the effect of combination of a chemical method (alkaline pretreatment) and a physical method (microwave irradiation) in improving anaerobic digestion of WAS.
In the first part of the study, alkaline and MW pretreatment methods were examined separately, then their combinations were investigated for the first time in the literature in terms of COD solubilization, turbidity and CST. Highest SCOD was achieved with the combined method of MW+pH-12. In the second part, based on the results obtained in the first part, alkaline pretreatments of pH-10 and pH-12 / MW pretreatment alone and combined pretreatments of MW+pH-10 and MW+pH-12 pretreated WAS samples were anaerobically digested in small scale batch anaerobic reactors. In correlation with the highest protein and carbohydrate releases with MW+pH-12, highest total gas and methane productions were achieved with MW+pH-12 pretreatment reactor with 16.3% and 18.9% improvements over control reactor, respectively. Finally the performance of MW+pH-12 pretreatment was examined with 2L anaerobic semi-continuous reactors. 43.5% and 53.2% improvements were obtained in daily total gas and methane productions. TS, VS and TCOD reductions were improved by 24.9%, 35.4% and 30.3%, respectively. Pretreated digested sludge had 22% improved dewaterability than non-pretreated digested sludge. Higher SCOD and NH3-N concentrations were measured in the effluent of pretreated digested sludge / however, PO4-P concentration did not vary so much. Heavy metal concentrations of all digested sludges met Soil Pollution Control Regulation Standards. Finally a simple cost calculation was done for a MW+pH-12 pretreatment of WAS for a fictitious WWTP. Results showed that, WWTP can move into profit in 5.5 years.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/3/12609685/index.pdf |
| Date | 01 July 2008 |
| Creators | Dogan, Ilgin |
| Contributors | Sanin, F. Dilek |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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