Biosolids partnership explores benefits of sewage sludge
As sustainability pressures increase and awareness of resource recovery opportunities grows in communities, the wastewater sector is researching and trialling innovative new approaches to biosolid management and reuse options.
Members of the Australian and New Zealand Biosolids Partnership (ANZBP), which was created to promote the sustainable management of biosolids, have been working on a range of different applications of wastewater by-products for land use and energy production.
ANZBP Chair and Process Engineer Kelly Hopewell said sustainability is a big part of the drive towards more innovative biosolids management.
“When people think of sewage sludge, they think of it as a waste that needs to be gotten rid of. But there are so many benefits to be had from reusing the nutrients present within biosolids,” she said.
“There’s demand for these nutrients from the agricultural sector, farmers are asking for these types of fertilisers more and more.
“Sustainability is also about managing the risks. That’s where the research is really important, particularly in terms of microplastics and emerging contaminants. But there are benefits that come with the risks.”
Hopewell said some of the benefits include biosolids replacing chemical fertilisers, which require a lot of energy to produce. Further, reusing biosolids reduces reliance on landfill or burning.
“Gasification pilots have been conducted, but we are still waiting to see how this avenue works on a large scale, which is why the Logan City Council’s gasification works are so exciting,” she said.
“We live in a throwaway society, and we need to do a lot better. Waste is society's problem, as a whole, but the wastewater and waste industry gets left with a problem. We have to find ways to reuse a lot more of what we’ve got.”
“There is a big push for research at the moment, backed by Federal Government funding, Hopewell said, and the ANZBP members are all proactively considering the risks and benefits of their respective biosolids management programs.
Hopewell said that it was great to see Australia leading the way for sustainable biosolids management.
"We have joined forces with New Zealand, too, because we are all in the same boat," she said.
"We all have the means to produce a product that could be beneficially used, so long as we manage the risks."
Nutrient nursery trials
One innovative approach to trialling biosolids reuse is being conducted by New Zealand’s Watercare. The water authority has been getting its hands dirty testing the efficacy of different biosolid and struvite mixes on seedlings at its very own nursery.
Watercare Resource Recovery Manager Rob Tinholt said the fourth seedling trial is set to begin this summer, following the successful use of pasteurised biosolids mixed with bark to grow healthy native plant species.
“The trials started during a lockdown in September last year. When we heard there was going to be another lockdown, I visited the treatment plant and got some biosolids and bark and the 300 seedlings we had already ordered. Over two months, they grew really, really well,” he said.
“We asked a professional nursery to do 3000 seedlings, trialling the comparative growth between their own potting mix, and also a mix of half struvite and bark. At the same time, I did a few thousand plants, testing ratios of biosolids to bark, and also struvite and bark.”
By March 2021, Tinholt had enough confidence in the trials to upscale again, with the onsite nursery set up at the Auckland wastewater treatment plant growing to about 10,000 plants, with many then donated to local schools and community groups.
“We have learned a lot about mixing and will start the fourth trial over summer with about 4000 plants. We will be picking the species more specifically around planting programs, but also to play around more with how our mixes work on different varieties,” he said.
“The onsite nursery is currently about the size of a badminton court. But we are hoping to get permission to build a 100,000 tree nursery. At that point, the project will be getting pretty serious.”
Creating positive stories
While the Watercare nursery trials are an exciting new way of developing and piloting different biosolid mixes for growing plants, Tinholt said one of the biggest drivers behind the project is to generate positive stories about how useful biosolid reuse can be.
“This whole project is about creating stories. There is the revenue aspect, but we are really starting with the stories behind this kind of resource recovery. We want to show that our biosolids can be turned into a really high-quality, premium end product,” he said.
“Biosolids aren't considered to be the most pleasant materials, but they have all those inherent qualities that premium, commercial-grade potting mix and fertiliser products have. We are showcasing to the community how biosolids can become a premium product.
“When you start having conversations with community groups, people focus a lot on risk. People have concerns about contamination. But when you show healthy plants that are very clearly thriving, people start asking why we have only just started doing this now.
“We’ve noticed a shift in attitudes towards biosolid reuse. People are becoming more invested in resource recovery and are now becoming a lot more open to what can be achieved.”
Moving outside the box
Tinholt said the trials are also about ensuring Watercare knows its fertiliser and soil products well, with plans to upscale the biosolid and struvite blends for commercial use.
“We want to develop these products, primarily to create stories, but also for us to know our products so that, when it comes to marketing upscale, we already know what our products can do,” he said.
“We have independent turf trials happening with our struvite Emerge product, testing for grass and pasture growth. When we expand the nursery, we will be exploring non-native species as well, including decorative plants and fruit trees.
“We are also looking at tying in effluent reuse for our irrigation water at the expanded nursery. What we will have moving forward is a facility the community can visit and see the results of the reuse of our nutrients, but also the water cycle story, too.”
Tinholt said that, compared to Australia, New Zealand doesn’t reuse a lot of biosolids or water, but that the growing awareness of sustainability considerations is pushing the wastewater sector to think outside the box.
“Traditionally, we haven’t explored the externalities. We are really good at planning, designing and incorporating engineered infrastructure, but we haven’t been very good at managing what happens to materials after they have worked their way through our networks,” he said.
“For new, sustainable and innovative operations management, we need to start thinking about what’s next and how to engage with communities and commercial components effectively.”
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