Sewage sludge treatment by a continuous microwave enhanced advanced oxidation processA paper submitted to the Journal of Environmental Engineering and Science.

Abstract

A continuous flow mode of the microwave enhanced advanced oxidation process (MW/H2O2-AOP) was used for sludge treatment as opposed to a batch operation mode from past studies. The effects of pre-microwave heating, microwave irradiation and post-microwave holding on organic matter solubilization were studied. Pre-microwave heating did not improve the overall orthophosphate solubilization, but helped in organic matter solubilization. Nutrients and organic matter were found to have increased during the post-microwave holding period, indicating overall sludge solubilization can be more effective when maintained at a high temperature after treatment with the MW/H2O2-AOP. 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. The pre-heating of sludge before treatment with the microwave process by the means of heat exchange can be beneficial for the overall organic matter solubilization in the MW/H2O2-AOP.Résumé : Un mode en écoulement continu du procédé d'oxydation avancée améliorée par micro-ondes (MW/H2O2-AOP) a été utilisé pour traiter des boues par rapport à un mode de fonctionnement par lot dans des études antérieures. Les effets du chauffage avant les micro-ondes, l'irradiation par micro-ondes et le maintien de la solubilization des matières organiques après les micro-ondes ont été étudiés. Le chauffage avant les micro-ondes n'a pas amélioré la solubilization globale des orthophosphates, mais a aidé à la solubilization des matières organiques. Les nutriments et les matières organiques ont augmenté durant la période de maintien après les micro-ondes, indiquant qu'une solubilization globale des boues peut être plus efficace lorsqu'elles sont maintenues à une température élevée après le traitement par le MW/H 2 O 2 -AOP. Il a été profitable de faire fonctionner le MW/H 2 O 2 -AOP en mode continu pour un temps de rétention plus élevé pour la solubilization des matières organiques, et à un temps de rétention plus court pour la solubilization des orthophosphates. La décantabilité des boues s'est grandement améliorée à la suite du traitement par micro-ondes, avec ou sans ajout de H 2 O 2 . Le préchauffage des boues par échange de chaleur avant le traitement par micro-ondes peut être avantageux pour la solubilization globale des matières organiques dans le MW/H 2 O 2 -AOP.

Continuous‐flow microwave enhanced oxidation process for treating sewage sludge

“…SCOD concentrations increased with an additional heating time of 5 min for most sets (Tables –3). The heating period is also a factor affecting SCOD release, although it is not as significant as temperature and H 2 O 2 dosage …”

“…The process is capable of destroying microbial cells in sewage sludge, as well as oxidative cleavage of many organic compounds, resulting in an increase of soluble substrates. In addition, metals and inorganic materials are also released into the solution . 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.…”

“…In a continuous‐flow process, the heating rate of the substrate is controlled by its flow rate through the microwave applicator; a higher flow rate results in a lower heating rate of the substrate, and a shorter process retention time. A higher flow rate also reduces the amount of microwave radiation transmitted to the substrate . H 2 O 2 can be broken down by catalase, into water and molecular oxygen, before it can react with sludge particulates.…”

Investigation on Characteristics of Microwave Treatment of Organic Matter in Municipal Dewatered Sludge

“…In the change process, a lot of heat is produced due to friction among the molecules, resulting in the temperature increase of the municipal dewatered sludge. Thus, the thermal effect of microwave treatment can promote the degradation of the organic matters [10][11][12].…”