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A microwave-enhanced advanced oxidation process to treat municipal wastewater sludge and as a pretreatment for anaerobic digestion

University of British Columbia

Sewage sludge is a by-product of wastewater treatment. It is considered a waste product and is generally disposed of in landfills; yet sludge is rich in nutrients like nitrogen and phosphorus – essential for plant life and valuable in agricultural fertilizers. However, getting these nutrients out of sludge is not always easy. The microwave-enhanced advanced oxidation process (MW-AOP) is a treatment method effective at releasing these nutrients from sewage sludge. The MW-AOP incorporates microwave irradiation with hydrogen peroxide, a combination that attacks the organic fraction of the sewage sludge and releases nutrients, proteins, and amino acids. MW-AOP-treated sludge also shows promise for anaerobic digestion, a process where organic matter is converted to methane. Previous studies in this research group used pilot-scale MW-AOP systems to treat sludge and other organic slurries. This current study focused on two aspects of MW-AOP: installing and operating a larger 25 kW MW-AOP system to treat municipal wastewater sludge; and studying the effects of MW-AOP-treated sludge used as a feed substrate for anaerobic digestion. The 25 kW MW-AOP system was consistent with expected results: volatile fatty acids (VFA) and solubilized chemical oxygen demand (COD) increased; total suspended solids (TSS) decreased; nitrogen and phosphorus were solubilized, as were calcium, magnesium, and potassium. The system was easily able to treat 100 litres of sludge, as opposed to 20 litres in past experiments using a 5 kW MW-AOP system. Based on the results of this study, the 25 kW MW-AOP system would be capable of treating larger quantities of sludge to desired standards. This study also showed that MW-AOP-treated sludge could be a good candidate for high-rate anaerobic digestion, especially in terms of sludge reduction. Using the MW-AOP-treated sludge as a feed substrate for anaerobic digestion showed that volatile solids (VS) and COD were greatly reduced when compared with raw sludge as a feed substrate, especially at very low hydraulic retention times (HRT). Additionally, using MW-AOP-treated sludge resulted in higher levels of alkalinity being produced, implying a strong buffer capacity able to withstand higher loading rates. This would make MW-AOP a suitable pre-treatment where maximizing sludge reduction is a priority.

Text

2019-04-10

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/69556

Civil Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/