Biomethane production improvement by hydrothermal pretreatment of thickened waste activated sludge.

This study evaluated the impact of hydrothermal pretreatment on thickened waste activated sludge (TWAS) for solubilization enhancement and biomethane production improvement through the mesophilic anaerobic digestion process. In order to assess the effect of temperature, retention time and severity index (SI) of the hydrothermal pretreatment, TWAS was exposed to fifteen different pretreatment conditions within a combination of 10 different pretreatment temperature range (150-240 °C), five different retention times (5-30 min) and five different severity indexes (SI = 3, 3.5, 4, 4.5 and 5). The solubilization enhancement was observed in all hydrothermally pretreated samples with the highest solubilization efficiency of 49% in pretreatment conditions of 200 °C and 10 min retention time within the corresponding SI = 4. Biomethane production was not improved in all fifteen pretreatment conditions, pretreatment with SI beyond 4 decreased the biodegradability of TWAS. The highest biomethane production was observed in the pretreatment condition of 170 °C and 10 min with a 40% increase compared to non-pretreated TWAS.

Methods of pretreatment and their impacts on anaerobic codigestion of multifeedstocks: A review.

Anaerobic codigestion (AnCoD) has attracted attention owing to its advantages over conventional anaerobic digestion, and attempts are still going on to develop methods for improving the efficiency of this technology. Mostly, addition of cosubstrates without applying a proper pretreatment cannot adequately enhance the performance of the digestion. However, there is a lack of a comprehensive study on different pretreatment methods specific to the wide range of cosubstrates. This review aimed to (i) categorize pretreatment techniques that have been developed for improving AnCoD, (ii) present the results of the studies on the effect of pretreatment on improving AnCoD, and (iii) provide a comparison between pretreatment methods and their application for different types of cosubstrates. The findings primarily validated the influence of pretreatment to enhance the process by increasing biodegradability, improved hydrolysis, reduced hydraulic retention time (HRT), and improved methane production. The five main categories of pretreatment employed in codigestion included the following: mechanical, thermal, chemical, biological, and hybrid pretreatment. Among them, mechanical and biological pretreatment have the most and least application in codigestion, respectively. Greater efforts are required on the application of biological pretreatment and cost-benefit analysis of different pretreatment options on the variety of the cosubstrates. PRACTITIONER POINTS: Pretreatment can significantly enhance biomethane production in anaerobic digestion Anaerobic codigestion along with pretreatment can further enhance the conventional anaerobic digestion of single feedstock Mechanical and biological methods have been the most and least practiced pretreatment options Selection of applicable pretreatment option to enhance methane production is subject to the type of cosubstrates in the system There is a research gap in evaluating the application of biological pretreatment for various types of cosubstrates.