Waste activated sludge (WAS) from the bioreactors is drawn from the returned activated sludge (RAS) underflow from the clarifiers and treated by aerobic digestion for approximately 10 days.
Wastewater treatment is by a twin stream activated sludge process. The annual median inflow of domestic wastewater to the plant is 10 ML day −1 however, there is significant seasonal variation due to the holiday homes in the area. The plant accepts domestic wastewater and tankered waste, including leachate, from the local area, and serves a population equivalent to approximately 47,800 persons.
The Boneo WwTP is located 83 km south-east of Melbourne, in the south-eastern corner of the Mornington Peninsula, Victoria.
#Victoria 2 stockpile not being used for units verification#
One year stockpiling is not a prescribed treatment process to produce T1 biosolids, therefore verification of this alternative procedure is necessary ( EPA Victoria 2004). Hence, SEW has sought to adopt a shorter storage period of one year as an alternative treatment process to produce biosolids compliant with the T1 grade. However, constructing new stockpile areas to accommodate at least three years' storage and drying treatment required by the EPA guideline would be difficult at most WwTPs. Achieving the T1 treatment grade is necessary to market the biosolids as the outlets for lower grade products are very limited in Victoria. Accommodating the extra sludge requires considerable capital investment to provide additional facilities and land suitable for processing, handling and storage. However, sludge production is increasing due to population growth across the operational area of SEW.
The prescribed treatment process adopted to produce T1 grade biosolids at SEW WwTPs, as well as at other treatment plants in Victoria, includes drying followed by three years of storage of sludge ( EPA Victoria 2004). Thus, biosolids may be treated to eliminate or reduce the pathogen content to background residual values and, under these circumstances, where a single barrier to pathogen transmission is provided, the biosolids may be utilised without restriction ( US EPA 2003). Cropping and harvest restrictions are implemented to provide further barriers to pathogen transmission from the soil to food when biosolids (treated sewage sludge) are land applied, depending on the degree of treatment and pathogen reduction achieved ( Karkashan et al. Before sewage sludge can be recycled for beneficial purposes, for example, as an agricultural soil improver and fertiliser, it must be stabilised to reduce odour and pathogens so that it presents minimal nuisance and risk to public health. Sewage sludge, the organic residue from wastewater treatment, may contain a range of pathogenic microorganisms, including bacteria, viruses, protozoa and parasites, depending on the pathogenic load of the resident population in the catchment area ( Grant et al. No Ascaris eggs were detected in the influent to the WwTPs, confirming previous studies that the presence of helminth infections in Victoria is extremely low and that Ascaris is not applicable as a control criterion for the microbiological quality of biosolids in the region. The sludge treatment processes at both WwTPs achieved T1 grade biosolids with respect to prescribed pathogenic bacterial numbers (3 log 10 enteric virus reduction after a storage period of one year. A verification programme of sampling and analysis for enteric pathogens was conducted at two WwTPs where sludge is treated by aerobic and anaerobic digestion, air drying (in drying pans or solar drying sheds) and stockpiling, to enumerate and, if present, monitor the decay of a range of enteric pathogens and parasites. However, extended stockpiling is costly, may increase odour nuisance and greenhouse gas emissions, and reduces the fertiliser value of the biosolids. At South East Water wastewater treatment plants (WwTPs) in Victoria, Australia, biosolids are stockpiled for three years in compliance with the State guidelines to achieve the highest pathogen reduction grade (T1), suitable for unrestricted use in agriculture and landscaping.
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