Energy recovery potential from Altona treatment plant and meat industry wastes.

摘要

City West Water (CWW) operates the Altona Treatment Plant (ATP), which treats predominantly domestic sewage. Increasing energy prices have shifted how wastewater treatment plants and other sludge generating industries perceive sludge. The expected growth in population in the area, meaning more biosolids will be produced, and the cost associated with sludge treatment, handling and transportation have triggered the ATP to seek alternative sludge and biosolids management. Firstly, this study comprised a literature review of alternative technologies for energy recovery from WAS and biosolids. The study identified pyrolysis, gasification, incineration and anaerobic digestion (AD) as alternative energy recovery processes. These alternatives were assessed based on the selected criteria and AD was found to be the most feasible option. Secondly, the AD processes that were assessed as a part of this study comprised mesophilic AD (one phase) and temperature phased anaerobic digestion (TPAD). Considering that there are constraints for the installation of anaerobic digestion at the ATP site, this study also assessed the co-digestion of WAS and meat processing dissolved air flotation (DAF) sludge using mesophilic AD and TPAD with a view to transporting biosolids to an alternative site. Biochemical Methane Potential (BMP) laboratory batch tests were used to estimate the biogas yield from the different substrates of WAS, biosolids and biosolids and DAF sludge. Given the promising results obtained using batch BMP tests, the performance of the mesophilic AD (one phase) and TPAD processes were assessed under semi-continuous conditions and different operation conditions of HRT and OLRs. The biogas yields from the different substrates, using mesophilic AD, were 282, 188, 180 and 86 mL/gVS from DAF sludge, WAS, biosolids and WAS and DAF sludge, respectively. Using TPAD, the biogas yields from different substrates were 235, 206 and 84 mL/gVS of WAS, biosolids and WAS and DAF sludge, respectively. In terms of HRT, a typical relationship between the HRT and biogas yield was observed (e.g., biogas yield at a HRT of 23 days was higher than at a HRT of 14 days for all the substrates tested). Using TPAD improved biogas yield from WAS and DAF sludge but no significant effect was observed for the substrates biosolids and WAS and DAF sludge. Furthermore the results demonstrated that the type of waste was the factor that affected the AD performance the most. Overall, for the different substrates tested, biogas yield in descending order was as follows: WAS, biosolids, DAF sludge and WAS and DAF sludge. Lastly, the net energy recovery from the different substrates both mesophilic AD and TPAD was estimated. The results showed that replacing the current aerobic sludge treatment with anaerobic sludge digestion, there will be savings on the energy used for sludge aeration. In light of the potential energy recovery analysis, the highest energy recovery option is mesophilic AD of WAS, which can save 2,266 MWh/yr from replacing the current aerobic system and also generate 465 MWh/yr from WAS methane yield. Thus, based on results of the study, sludge from ATP can be a resource for energy recovery.