Effect of pre-heating on microwave enhanced advanced oxidation process

Abstract

Aerobic sewage sludge and dairy manure were pre-treated by conventional heating (CH) (40, 50 and 60°C) followed by microwave enhanced advanced oxidation process (MW/H 2 O 2 -AOP) at 100 and 120°C for solids disintegration and nutrient release. Increasing CH and MW temperatures resulted in an increase in soluble chemical oxygen demand concentration and volatile fatty acids in the treated solution. The maximum ratio of soluble to total chemical oxygen demand obtained for sewage sludge and dairy manure was 60% and 22%, respectively. The synergistic effect of microwave irradiation and hydrogen peroxide (H 2 O 2 ) was more pronounced for sewage sludge at high CH and MW temperatures. Temperature and treatment time played a significant role in releasing orthophosphates. A maximum orthophosphate-to-total phosphate ratio of 55% and 85% was obtained for sewage sludge and dairy manure, respectively. A simple energy balance reveals that the CH step proves to be advantageous during continuous real-time operation of MW/H 2 O 2 -AOP technology.

Continuous‐flow microwave enhanced oxidation process for treating sewage sludge

“…[29] The MW/H 2 O 2 -AOP treatment of the sludge taken from the same MEBPR treatment system earlier (2 years ago) resulted in almost all of the soluble phosphorus being in the form of orthophosphate, and only a small fraction of polyphosphates being present in the microwave-treated solutions. [3,30] Based on our studies and others, it can be concluded that the release of phosphorus was dependent on its existent phosphorus forms in the sludge and EPS. In this study, polyphosphates might consist of elongated polyphosphate chemical bonds, which could not be easily hydrolyzed to form orthophosphate.…”

“…Similarly, preheating sludge at 40, 50, and 60 8C to deactivate catalase first, the highest SCOD was attained in the preheated solution of 60 8C after subsequent MW/H 2 O 2 -AOP treatment to 100 8C. [3] Catalase enzyme was completely deactivated at 60 8C, and more H 2 O 2 was therefore available for reacting with sludge particulates. [7,8] Set 3 was conducted with the same H 2 O 2 dosage and flow rate as Set 2; however, H 2 O 2 was introduced at 60 8C, instead of being added at the beginning of the experiment.…”

“…The results were similar to the thermal treatment conducted by other researchers. [3,[13][14] Under thermal treatment at temperatures below 100 8C, the solubilization process started only at temperatures > 50 8C, and had very low COD concentrations. The mechanisms involved include both decomposition of extracellular polymeric substances (EPS) and cell lysis during thermal treatment.…”

“…In addition, metals and inorganic materials are also released into the solution. [1][2][3] The resulting solution would produce a solution ideal for the subsequent struvite crystallization (magnesium ammonium phosphate) process for phosphorus recovery and/or anaerobic digestion to produce methane. It would also be used as a carbon source to facilitate biological phosphorus removal process in an activated sludge system.…”