Enhancement of Methanogenic Activity in Volumetrically Undersized Reactor by Mesophilic Co-Digestion of Sewage Sludge and Aqueous Residue

Abstract

To date, energy recovery from biological sewage sludge (BSS) by anaerobic digestion has been very popular. However, it can often happen that anaerobic reactors are volumetrically undersized, thus reducing performance in terms of biogas production. A continuous-flow pilot-scale plant was used to investigate, for the first time, the effects of mesophilic anaerobic co-digestion (MACoD) of sewage sludge and aqueous residue (AR) from a biosolids treatment plant (BTP) on methanogenic activity under low hydraulic retention time (HRT) conditions (to simulate the undersizing of the reactor). The results showed that the digestate is always more rapidly biodegradable than the matrices fed, while particulate COD hydrolyzed (12 ± 1.3%) is independent of the quantity of AR dosed. Feeding over 35% of soluble OLR, the total VFAs in the system strongly decreased, despite the low HRT. In correspondence with higher dosages of AR, the percentage of CH4 increased up to 77–78% and the CO2 CH4−1 ratio decreased to 0.25 ± 0.2. Specific methane production increased from 0.09 ± 0.01 m3CH4 kgCODremoved−1 with BSS alone to 0.28 ± 0.01 m3CH4CH4 kgCODremoved−1 in the case of BSS co-digested with AR. Moreover, co-digestion with AR from a BTP allowed continuous specific methanogenic activity to be enhanced from 1.76 ± 0.02 m3CH4 tVSS−1 d−1 to 6.48 ± 0.88 m3CH4 tVSS−1 d−1. Therefore, the MACoD of BSS and AR from a BTP could be a good solution to enhance methanogenic activity in a volumetrically undersized anaerobic digester with reduced HRT.

Comparison of Mixed and Door-to-Door Systems for Urban Waste Collection in Terms of Effectiveness and Greenhouse Gas Emissions: A Case Study from Two Mountainous Italian Valleys

“…In order to reach the goals imposed by these directives (EC, SDGs and Fit for 55), the separate collection (SC) of USW is necessary before the potential recovery of matter [12][13][14] and energy [15][16][17][18]. In recent years, many cities have transitioned from traditional curbside systems to door-to-door systems to increase the effectiveness of separate waste collection and enhance the quality of collected materials [19][20][21][22].…”

Review of rheological behaviour of sewage sludge and its importance in the management of wastewater treatment plants

“…In fact, despite the management of SeS involves high costs (Zhang et al 2017), they represent an interesting resource due to the high energetic value (Oladejo et al 2019;Das et al 2020) and high content of nutrients (Kirchmann et al 2017;Das et al 2020). Before, any possible reuse options, thickening and dewatering processes decrease the volume of the SeS, whereas aerobic or anaerobic digestion reduce the microbial contamination, and the residual organic substances stabilizing the SeS (Guo et al 2013;Bertanza et al 2014;Ukwatta et al 2015;Torretta et al 2021).…”