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Sludge and manure treatment using the microwave enhanced advanced oxidation process Yu, Yang


Waste activated sludge (WAS) and dairy manure (DM) present serious environmental concerns since they contain high levels of nutrients, organic matter and pathogens contained. The microwave enhanced advanced oxidation process (MW/H₂O₂-AOP) was used to treat these waste materials for solids disintegration, nutrients solubilization and pathogen destruction. For pathogen reduction, fecal coliform concentrations were found below detection limits (1000 CFU/L) immediately after treatment when sludge was treated at 70ºC with more than 0.04% of H₂O₂. Significant regrowth of fecal coliforms was observed after the treated samples were stored at ambient temperature for 72 hours. However, no regrowth was observed for samples treated at 70ºC with 0.08% H₂O₂ or higher, suggesting a complete elimination of fecal coliforms. With extracted cells that are EPS-free, orthophosphate could be released at lower microwave temperatures and lower H₂O₂ dosages, compared to our previous studies. The amount of DNA in solution was a good indicator of the extent of cell damage; the high concentration of DNA released into solution after treatment indicated significant cell damage. The effects of pre-microwave heating, microwave irradiation and post-microwave setting on nutrients and organic matters solubilization in continuous MW/H₂O₂-AOP were studied. Pre-microwave heating did not improve the overall orthophosphate solubilization, but helped in organic matter solubilization. It was beneficial to operate a continuous mode of the MW/H₂O₂-AOP at a longer retention time for organic matter solubilization, and at a shorter retention time for orthophosphate solubilization. Sludge settleability was greatly improved with the microwave treatment, with or without the addition of H₂O₂. It was found that 69 to 92% of the TP and up to 90% of TCOD in DM were in the soluble form, after continuous MW/H₂O₂-AOP with an exit temperature of 90oC and acid dosage of 1.0% (vol/vol). Acid addition was important in phosphate solubilization but the dosage of acid affect the solubilization to a lesser extent. For organic matter solubilization, acid played an important role – SCOD release increased with the increase of acid dosage. Higher microwave exit temperature resulted in higher SCOD and ortho-P solubilization.

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