Influence of cationic polyacrilamide flocculant on high-solids’ anaerobic digestion of sewage sludge under thermophilic conditions

Abstract

Treatment of sewage sludge (SS) by biodegradable polyacrylamide-based flocculants (PAM) is considered to be an effective way to increase total solids' (TS) content prior to anaerobic digestion (AD). However, data on how PAM addition influences the efficiency of AD process are quite contradictory; moreover, no data are available for thermophilic AD (TAD). This study showed that at an optimal inoculum-to-substrate ratio (ISR, 55/45), PAM addition resulted in some decrease in initial methane production during the TAD of SS due to the formation of large flocs (up to 2-3 mm in diameter), which deteriorated the mass transfer. However, at non-optimal ISR (40/60), which led to the destabilization of TAD, PAM addition (40 mg/g TS) could restore the methanogenesis despite the inhibiting accumulation of volatile fatty acids (14-15 g/l) and pH drop (5.5). The observed positive effect of PAM-forced flocculation proposes a new interesting alternative for recovery of 'soured' reactors.

High-solid anaerobic digestion of sewage sludge: achievements and perspectives

“…They also revealed that PAM can be hydrolysed at different position of its carbon-chain backbone, and that the hydrolysed PAM fragments combined with tyrosine-rich proteins to form colloid complexes during the HS-AD of SS. These findings were further confirmed by Litti et al (2019), who reported that the addition of PAM led to decreased methane production in the HS-AD of SS. The researchers attributed this to the formation of large flocs and the consequent suppression of mass transfer.…”

“…Methanogenic activity decreases at a pH < 6.3 or>7.8 -Lay et al, 1997;Bitton, 2002;Gerardi, 2003;Xu et al, 2020a Ammonia -Boráň et al, 2010;Luo et al, 2011;Qi et al, 2011;Dai et al, 2014b;Dai et al, 2015;Litti et al, 2019;Zhi and Zhang, 2019 Rheological properties The stability decreases with an increase in the viscosity or an decrease in the diffusion coefficient -Decrease with high viscosity or low diffusion coefficient - Kirby, 1988;Slatter, 1997;Cheng and Li, 2015;Sajjadi et al, 2016;Zhang et al, 2016;Hu et al, 2018 Notes: HS-AD: high solid-anaerobic digestion; SS: sewage sludge; VS: volatile solid; TS: total solid; SRT: solid retention time; FAN: free ammonia-nitrogen; TAN: total ammonia-nitrogen; VFAs: volatile fatty acids; PAM: polyacrylamide. Nges and Liu (2010) shortened the SRT from 35 days to 12 days in the HS-AD of SS under both thermophilic and mesophilic conditions, and found that this increased the biogas-production rate and volumetric methane productivity, and decreased the VS-reduction efficiency.…”

“…They also revealed that these antibiotics affected the archaeal community, but did not significantly affect the bacterial community. In related research, polyacrilamide (PAM), a refractory and common flocculant used in SS dewatering, has been found to be ubiquitous in HS sludge (Boráň et al, 2010;Qi et al, 2011;Dai et al, 2015;Litti et al, 2019). Dai et al (2014b) determined that the biodegradation of PAM in SS processed via HS-AD was usually accompanied by the accumulation of high concentrations of toxic acrylamide monomers (AMs), which inhibited microbial activity (Luo et al, 2011).…”

Feasibility Study of Anaerobic Codigestion of Municipal Organic Waste in Moderately Pressurized Digesters: A Case for the Russian Federation

“…The temperatures of the injector, oven and thermal conductivity detector were set to 45 • C, 60 • C and 200 • C, respectively. The gases were calibrated using an external standard method based on a standard curve of detector response to known gas concentrations [41].…”

Residuals, sludge, and biosolids: Advancements in the field

“…The addition of polyacrylamide‐based flocculants (40 mg/g total solids) was shown to be effective in restoring methanogenesis in thermophilic anaerobic digestion even with the inhibition of accumulation of volatile fatty acids and pH decrease (Litti et al, 2019). The addition of zerovalent iron nanoparticles to anaerobic digesters resulted in an increase biogas yield 132 (control) to 310 ml/gVS with an increase in the percentage of methane from 63.2% (control) to 77.6%, which corresponded to a maximum yield of 238 mLCH 4 /gVS (Lizama, Figueiras, Pedreguera, Figueiras, Pedreguera, & Ruiz Espinoza, 2019).…”