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© 2019 Anaerobic co-digestion of sewage sludge with four beverage wastes (namely beer, soft drink, fruit juice, and wine)was evaluated using a dedicated pilot research plant. Temporal variation in the sludge's organic content highlighted the importance of using a mono-digestion control reactor for a systematic comparison with co-digestion. Results indicate that chemical oxygen demand (COD)is a better parameter compared to volatile solids (VS)for determining the organic loading rate during co-digestion with beverage waste that contain solubilised organic carbon. In this study, all beverage wastes investigated here (with the exception of wine)were suitable for co-digestion. H2S content in biogas decreased during co-digestion, possibly due to the dilution effect by the additional biogas generated from sulphur-lean organic rich waste. Results from this study show that the organic content in most beverage waste can be readily and completely converted to biogas. At 10% substrate addition (v/v)beer, soft drink and juice addition did not observably affect total COD and VS in the digestate, whilst increasing biomethane production relative to the control by 39, 41 and 64% respectively. Furthermore, the interchanging of co-substrates did not result in any observable impact on digestion performance. Further investigation is recommended to ascertain the low performance of wine waste co-digestion with sewage sludge.

© 2018 Soft drink beverage waste (BW) was evaluated as a potential substrate for anaerobic co-digestion with sewage sludge to increase biogas production. Results from this study show that the increase in biogas production is proportional to the increase in organic loading rate (OLR) rate due to BW addition. The OLR increase of 86 and 171% corresponding to 10 and 20% BW by volume in the feed resulted in 89 and 191% increase in biogas production, respectively. Under a stable condition, anaerobic co-digestion with BW did not lead to any significant impact on digestate quality (in terms of COD removal and biosolids odour) and biogas composition. The results suggest that existing nutrients in sewage sludge can support an increase in OLR by about 2 kg COD/m3/d from a carbon rich substrate such as soft drink BW without inhibition or excessive impact on subsequent handling of the digestate.

© 2018 A pilot-scale study was conducted to investigate the fate of trace organic contaminants (TrOCs) during anaerobic digestion of primary sludge. Of the 44 TrOCs monitored, 24 were detected in all primary sludge samples. Phase distribution of TrOCs was correlated well with their hydrophobicity (>67% mass in the solid phase when LogD > 1.5). The pilot-scale anaerobic digester achieved a steady performance with a specific methane yield of 0.39–0.92 L/gVSremoved and methane composition of 63–65% despite considerable variation in the primary sludge. The fate of TrOCs in the aqueous and solid phases was governed by their physicochemical properties. Biotransformation was significant (>83%) for five TrOCs with logD < 1.5 and electron donating functional groups in molecular structure. The remaining TrOCs with logD < 1.5 were persistent and thus accumulated in the aqueous phase. Most TrOCs with logD > 1.5 were poorly removed under anaerobic conditions. Sorption onto the solid phase appears to impede the biodegradation of these TrOCs.

© 2017 Acid phase digestion pretreatment resulted in an increase in biogas production and volatile solids (VS) removal at the West Camden plant which was fed with only waste activated sludge. Without the acid phase digesters, the specific methane yield of waste activated sludge (WAS) was 190 L/kgVSadded, whereas a specific methane yield of WAS of 231 L/kg VSadded was observed from sludge sampled from the acid phase digester. The specific methane yield obtained from BioWin® simulation was 331 L/kgVSadded and was slightly higher than that from BMP assessment (231 L/kgVSadded). In addition, the overall VS removal values obtained from BioWin® simulation (44%) and biomethane potential (BMP) evaluation (49%) were close to the actual VS removal value (45%) achieved by the plant. The consistency between full scale evaluation data, BioWin® simulation, and BMP assessment suggests that BioWin® simulation and BMP study can be used to guide future design and optimisation of acid phase digestion pretreatment to intensify anaerobic digestion of sewage sludge.

© 2016 Anaerobic mono-digestion and co-digestion of primary sludge and two organic wastes (namely food waste or paper pulp reject) were evaluated by biomethane potential assessment and kinetics modelling to elucidate the synergistic effect. The specific methane yields were 159, 652 and 157 mL/g VS added during mono-digestion of primary sludge, food waste and paper pulp reject, respectively. Co-digestion of primary sludge with either food waste or paper pulp reject resulted in much higher specific methane yields of 799 and 368 mL/g VS, respectively. pH and intermediate inhibitions (e.g. volatile fatty acids and ammonium-N) were not observed. The synergistic effect was also confirmed by examining the VS and COD removals. COD balance also identified and validated the enhanced specific methane yields from both primary sludge and organic waste (i.e. additional 32 and 19% of COD was converted to biogas during co-digestion of primary sludge with food waste or paper pulp reject, respectively). The apparent first order rate constant derived from kinetics modelling increased from 0.18 to 0.63 d−1 during mono-digestion of paper pulp reject and co-digestion of primary sludge with paper pulp reject, which can be attributed to the initial high soluble biodegradable fraction in primary sludge.

Co-digestion of organic rich wastes and wastewater sludge to enhance biogas production has become an attractive economic possibility for water utilities. The suitability of the organic rich waste depends on its ability to produce biogas as well as its influence on the overall anaerobic digestion process. Biomethane potential evaluation was conducted to screen seven organic wastes and dehydrated algae. All co-substrates increased the bio-methane yield by three to six times compared with conventional anaerobic digestion of sewage sludge. Maximum co-digestion ratios were identifiable for most solid co-substrates including algae (6% wt/wt), undiluted food waste (5% wt/wt), bakery waste (5% wt/wt), and diluted commercial food waste (10% wt/wt). On the other hand, the maximum co-digestions ratio of beverage reject and sewage sludge was 10% (wt/wt). With the exception of fat-oil-grease, all solids free liquid co-substrates evaluated in this study showed a notable synergistic effect, to enhanced removals of total solids, volatile solids (VS) and chemical oxygen demand (COD) during anaerobic digestion. The increase in COD removal when co-digesting wastewater sludge and liquid waste was from 2 to 41%. Conversely, the co-digestion of most solid co-substrates resulted in additional VS and COD residuals in the final biosolids. Elevated concentrations of sulphur and phosphorous in all food waste co-substrates suggest that control measures to address H2S in biogas and the accumulation of phosphorus in sludge centrate may be necessary during full scale operation. Data presented here provide the basis for subsequent pilot scale evaluation of anaerobic digestion of these organic rich wastes and wastewater sludge.