Anaerobic digestion of wastewater screenings for resource recovery and waste reduction

Estimation of Energy Recovery Potential from Primary Residues of Four Municipal Wastewater Treatment Plants

“…Nevertheless, the fat content in the samples presented values reaching up to 30% of the total dry content, with great variation between the samples collected even from the same treatment plant. Similar values of volatile solids content have been reported in the literature ranging from 77 up to 95% of dry solids, depending on the screen size and the wastewater origin, with raw samples exhibiting considerably great variations in the moisture and the total solids content [11,17].…”

“…Additional effects on digestate quality should be encountered, as soon as the feasibility of the process will be justified through the estimation of BMP potential. Nevertheless, a study has been reported on the quality of digestate from anaerobically treated screenings which was similar to the corresponding one from sewage sludge, towards its valorization through phosphorous recovery [17]. The overall estimation of potential economic and energy revenues due to the introduction of these side streams in existing treatment plants requires an integrated assessment of all potential benefits expected, including energy earnings from their utilization, reduction of landfilling costs, environmental costs revenues associated with fewer total GHG emissions, etc.…”

“…However, very few studies have been reported in the literature dealing with the examination of biogas production potential of screenings and FOGs, mainly due to the non-homogeneous character of these wastes and the utilization of FOGs for biodiesel production [11,16]. The concentration of volatiles solids in screenings may exceed 90% of total solids [13,17], resulting in biogas production as high as 0.62 L/kg vs. [18]. The application of fine screenings in a municipal wastewater treatment plant and the following anaerobic digestion demonstrated a 40% reduction of energy demand in the Netherlands [19].…”

Energy Valorization of Fine Screenings from a Municipal Wastewater Treatment Plant

“…Anaerobic biodegradability tests were performed in the fine solids obtained from a 6 mm fine screen, revealing a two-stage hydrolysis process attributed to the complex nature of the screenings, and resulting in about 550 mL/g VS of methane release, corresponding to 52% of the average anaerobic degradability of the samples [8]. The methane yield of the screenings from an urban wastewater treatment plant were measured in another study, and reached 355 mL/g VS [14], while the biogas production from screening degradation in a pilot-scale study exceeded 600 mL/g VS, supporting the feasibility of co-digestion as an alternative treatment method for the valorization of screenings [28]. It should be acknowledged that the methane production measured by this work, as well as that reported by studies in the literature, revealed values well above the potential of other substrates of industrial or agricultural origin that could be used in sewage sludge co-digestion, with the maximum methane not exceeding 200 mL/g VS [24].…”

“…However, few studies have been reported on the energy valorization of fine screenings, and they have mainly focused on the examination of the anaerobic digestion potential of solids from 6 mm screens or FOG [7], while studies investigating the combination of solid fractions with biodegradation are even more limited [13,14], without particular efforts towards identifying the relationship between the particle size fraction and the energy content [15]. The determination of the solid fraction with the maximum biogas production potential would enhance the decision towards the selection and installation of fine mesh screens with an optimal mesh size.…”