Water Journal : Water Journal November 2016
www.awa.asn.au 38 Biosolids In more recent years, adding commercial waste to anaerobic digesters has been shown to boost energy production and attract a gate fee, without significantly adding to the amount of biosolids to be disposed of, Woods said. "All of that [residual from anaerobic digestion] goes for re-use in agriculture as a fertiliser either directly or via composting," he said. NEW THINKING Barwon Water, meanwhile, built Australia's first thermal drying plant to produce biosolids pellets after running out of on-site storage space. "Benefits are the small footprint required ... it's fully-enclosed so we can control things like noise, odour and dust," said Infrastructure Services General Manager Paul Northey. "Biosolids in the form of pellets are more easily re-used. Because we've got a high-quality product, we don't have the same restrictions that more traditional treatment methods have. Then there are environmental benefits, including a 40% reduction in greenhouse gas emissions compared to long-term storage and air-drying [Barwon Water's previous management approach]." The plant began operating in 2013 and was delivered through a public-private partnership aimed at selling a product, rather than treating biosolids in the most convenient way for the utility. "We got in partners who had the experience and capabilities to not only deliver a biosolids treatment facility, but also develop the market," Northey said. The product is now sold to farmers across Victoria, New South Wales and South Australia, but the venture is yet to turn a profit. "Revenue is certainly not outstripping our expenses at this stage; however, it is going some way to offsetting the cost," he said. South East Water (SEW) was also facing storage restrictions when it gained Environment Protection Authority approval in December 2015 to slash the minimum three-year drying and storage period to just one year at two of its treatment plants. The utility had been processing its sewage sludge in an aerobic NEW ZEALAND REVAMPS ITS APPROACH Whether it be human, bovine, poultry or piggery waste, New Zealand's new management guidelines propose to acknowledge both their common benefits and common contaminant content. "If you consider the things in biosolids that interest people from a pathogen and health- check point of view -- E Coli, salmonella, campylobacter -- the same things are in cow manures, pig manures and poultry manures," Water New Zealand Technical Manager Nick Walmsley said. "So rather than having separate guidelines for human waste, we propose they'll all be dealt with in a common manner. What we're trying to do is get a level playing field -- biosolids isn't a total ogre and everything else is wonderful." Water NZ has been working with the Waste Management Institute New Zealand Inc, the Institute of Environmental Science and Research, the Land Treatment Collective as well as central government ministries to come up with a document to replace the 2003 NZ Biosolids Guidelines. The new regime will be more aligned with existing manure management guidance in the farming sectors. "What we had before was an assumed soil quality and a mass-balance approach," Walmsley said. "Further research shows that really as long as you limit applications based on the nitrogen-loading, it is very hard to over-dose any of the contaminants, and hence degrade the soil. "So as long as the product has the prescribed minimum quality, by matching the nitrogen dose to what's being grown in the soils, we don't need to have a lot of other fancy formulae."
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