Abstract
Abstract Anaerobic digestion (AD) is a proven technology for energy production from the stabilization and reduction of sewage waste. The AD and impact of ultrasonic pretreatment of four waste activated sludges (WASs) from conventional and three non-conventional municipal wastewater treatment plants were investigated. WAS from a conventional activated sludge (CAS) system, a rotating biological contactor (RBC), a lagoon, and a nitrifying moving-bed biofilm reactor (MBBR) were pretreated with ultrasonic energies of 800–6,550 kJ/kg total solids to illustrate the impact of sludge type and ultrasonic pretreatment on biogas production (BGP), solubilization, and digestion kinetics. The greatest increase in BGP over the control of pretreated sludge did not coincide consistently with greater sonication energy but occurred within a solubilization range of 2.9–7.4% degree of disintegration and are as follows: 5% ± 3 biogas increase for CAS, 12% ± 9 for lagoon, 15% ± 2 for nitrifying MBBR, and 20% ± 2 for RBC. The effect of sonication on digestion kinetics was inconclusive with the application of modified Gompertz, reaction curve, and first-order models to biogas production. These results illustrate the unique response of differing sludges to the same levels of sonication energies. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).
Highlights
Biological treatment is the conventional means of treating municipal wastewaters
The investigation of ultrasonic pretreatment on sludges collected from different municipal wastewater treatment plants (WWTPs) has resulted in a wide range of reported performance parameters such as optimal energies, solubilizations, and biogas increases (BGI) (Appels et al b; Cano et al )
Sonication pretreatment was proved to significantly increase total chemical oxygen demand (tCOD) biogas yield in mesophilic batch assays of the four sludge types tested. It had a greater impact on increasing biogas production (BGP) from biofilm type sludge (15–20% for moving-bed biofilm reactor (MBBR) and rotating biological contactor (RBC)) as compared to conventional, suspended growth technologies (5–12% for conventional activated sludge (CAS) and Lagoon)
Summary
Biological treatment is the conventional means of treating municipal wastewaters. the conversion of soluble substrates into biomass results in a stream of waste activated sludge (WAS) that requires further management. Digestion can be enhanced through the application of various pretreatment strategies designed to disintegrate the recalcitrant cell material of WAS resulting in a shorter hydrolysis phase and a smaller fraction of undigested material in the effluent (Bougrier et al ; Carrère et al ; Alqaralleh et al ; Cano et al ) This reduces the HRT requirements and increases biogas production (BGP). The investigation of ultrasonic pretreatment on sludges collected from different municipal wastewater treatment plants (WWTPs) has resulted in a wide range of reported performance parameters such as optimal energies, solubilizations, and biogas increases (BGI) (Appels et al b; Cano et al ). Linear and non-linear regression models based on cumulative BGP were applied to compare and interpret digestion results These investigations provide necessary information for the application of ultrasonic pretreatment to alternative sludges to determine potential viability and BG response of the AD of varying sludges
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