A Comprehensive Review on Pretreatment Methods for Enhanced Biogas Production from Sewage Sludge

Abstract

The treatment of municipal wastewater is considered a cornerstone for the protection of public health and environment. However, a major issue derived from this process is the large quantities of produced sewage sludge. Although anaerobic digestion is a widely applied method in Wastewater Treatment Plants (WWTPs) aiming to stabilize the sludge and to recover energy in the form of methane, it is usually limited due to the reduced decomposition efficiency and slow biodegradation rate of this recalcitrant substrate. For this reason, various pretreatment methods have been proposed aiming to modify the sludge structure, solubilize the organic matter, and decrease the crystallinity of sludge so as to accelerate hydrolysis and consequently enhance methane production. The current research is a comprehensive collection of recent advances in pretreatment technologies that can be potentially applied in wastewater treatment facilities. The critical review analysis presented herein reveals the several advantages and drawbacks, as well as the technical opportunities of the pretreatment methods and provides an assessment of their feasibility/applicability from an energetic, environmental, and economic point of view.

Enhancing Biogas Production Amidst Microplastic Contamination in Wastewater Treatment Systems: A Strategic Review

“…Prior research has consistently investigated the impacts of MPs through direct introduction into AD systems, neglecting the customary pretreatment procedures that sludge typically undergoes before its introduction into AD systems [87]. Pretreatment methods, encompassing ultrasonication, high temperature, acid, thermo-chemical, low temperature, alkaline, ozonation, and thermo-mechanical techniques, are crucial in optimizing biogas production efficiency [88]. Table 1 presents a synthesis of studies incorporating various sludge pretreatment methods to assess their combined effect with MPs' presence on the efficiency of AD.…”

Recent Developments in the Application of Ultrasonication in Pre-Treatment of Municipal Sewage Sludge

“…Though, the main goal of all techniques is boosting methane productivity and reducing solid content. For example, the results of previous studies indicate that the increase in VS (volatile solids [g/L]) reduction for selected pretreatment technologies ranged from: 6-180% for US, 23-53.1% for microwaves, 7-138% for high-pressure homogenization, 10-45% for low temperature pretreatment, and 7-105% when using high temperature pretreatment (Neumann et al, 2016;Mitraka et al, 2022). This allows for reducing the digesters volume and hence decreasing investment and operational costs that finally might lead to improve the profitability of WWTPs (Kazimierowicz et al, 2022).…”

“…Another significant issue is the influence of pre-treatment methods on AD stability e.g. chemical methods might disturb the pH balance in digester (Mitraka et al, 2022). It is also important to evaluate that the chosen method does not generate toxic by-products which could adversely affect the AD process (Szaja et al, 2021).…”

“…Ultrasonication (US) is one of the most frequently applied methods of SS pre-treatment on a technical scale (Mitraka et al, 2022). It is recognised as most promising and highly effective method for SS disintegration (Pilli et al 2011;Zieliński et al, 2018).…”

“…These conditions promote subsequent actions e.g. impact of hydromechanical shear forces, radical formation, thermal decomposition as a result of temperature increment (Sharmila et al, 2022;Balasundaram et Mitraka et al, 2022). The application of US as a SS pre-treatment might lead to disruption of microorganism cells, dispergation of flocks, organic matter solubilization, enzyme release and biological activity enhancement (Neumann et al, 2016;Nguyen et al, 2021).…”