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Anaerobic sequencing batch reactors (ASBR) are preferred for treating dilute wastewaters but the retention of adequate active biomass, in successive-cycles, is always a challenge. This research investigated the efficacy of using a cationic polyacrylamide (PAM) flocculant for enhanced sludge retention in an ASBR treating flushed dairy manure, operated under psychrophilic conditions. Three PAM doses (10, 25, and 50 mg [PAM] l−1) were tested in duplicate reactors. At 6 d hydraulic retention time (HRT) and dosing of the feed-manure, steady state specific biogas yield for the 50 mg [PAM] l−1 treatment was 491 ± 7 ml g−1 [TCOD] (56% greater than control). At 4 d HRT the 50 mg [PAM] l−1 dose resulted in 465 ± 8 ml g−1 [TCOD] (20% higher than the control) at steady state conditions. The ratio of total volatile fatty acid to alkalinity was 0.29 ± 0.08 during the 6 d HRT and 0.14 ± 0.02 during the 4 d HRT, which were both below the trigger point for digester souring. This study shows that the use of PAM for high sludge retention in ASBR is a viable approach for, not only enhancing biogas yield, but also for improved and high-rate treatment of flushed dairy manure under psychrophilic conditions. |
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