Abstract
This work deals with the effect of combined microwave-ultrasonic pretreatment on the anaerobic biodegradability of primary, excess activated and mixed sludge. The characteristics, biodegradability and anaerobic digester performance for untreated primary, excess activated and mixed sludge were compared to combined microwave-ultrasonic pretreated primary, excess activated and mixed sludge. All sludge samples were subjected to Microwave treatment at 2450 MHz, 800 W and 3 min followed by ultrasonic treatment at a density of 0.4 W/mL, amplitude of 90%, Intensity of 150 W, pulse of 55/5 for 6min. Methane production in pretreated primary sludge was significantly greater (11.9 ml/g TCOD) than the methane yield of the untreated primary sludge (7.9 ml/g TCOD). Cumulative methane production of pretreated Excess Activated Sludge (EAS) was higher (66.5 ml/g TCOD) than the methane yield from pretreated mixed sludge (44.1 ml/g TCOD). Furthermore, digested EAS showed significantly higher dewaterability (201 s) than digested primary sludge (305 s) or mixed sludge (522 s). The average Methane: Carbondioxide ratio from EAS (1.85) was higher than that for mixed untreated sludge (1.24). VS reduction was also higher for EAS than the other two sludge types. However, pretreatment of EAS resulted in significant reduction in dewaterability due to higher percentage of fine floc particles in the pretreated EAS.
Highlights
Anaerobic digestion is a very effective sludge treatment technology applied in municipal and industrial wastewater treatment plants to stabilize organic matter [1]
This work deals with the effect of combined microwave-ultrasonic pretreatment on the anaerobic biodegradability of primary, excess activated and mixed sludge
It was reported that ultrasonic pretreatment results in disruption of cells and large sized macromolecules by the hydro-mechanical shear forces produced by ultrasonic cavitation [8]
Summary
Anaerobic digestion is a very effective sludge treatment technology applied in municipal and industrial wastewater treatment plants to stabilize organic matter [1]. The microorganisms in the excess sludge contain Extracellular Polymeric Substances (EPS) that are resistant to biodegradation which in turn limits the rate of the whole anaerobic digestion process [2,3]. Different pretreatment technologies were found to enhance sludge hydrolysis and anaerobic digestion performance [4]. Pretreatment of sludge through ultrasonic, mechanical, chemical or thermal techniques result in bacterial cell wall disruption, disintegration of EPS and release of enzymes enhance the rate of hydrolysis and biodegradation [5,6]. Ultrasonic, micro- wave, oxidative, and thermal pretreatment techniques are well documented in literature as viable methods to enhance biodegradability, hydrolysis rate and digester peformance [7]. Microwave pretreatment increased SCOD up to 4 fold, soluble protein concentration up to 1.8 fold and soluble carbohydrate concentration up CWEEE
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