The Challenge
Using dried and treated wastewater ‘sludge’ as a soil improver to grow crops or produce biodiesel may not sound appetising – unless you’re a wastewater treatment plant seeking to sustainably diversify your income base.
Western Water operates a Recycled Water Plant also known as ‘Surbiton Park wastewater treatment plant’ in Melton. The plant is currently spreading its treated, but not de-watered, sludge on the ground. However, a de-watering plant is now under construction to remove water from the sludge.
The process of de-watering the sludge will enable the plant to recover more water from it, and will also result in a product called biosolid. The treated biosolid product might then put to good use as a fertiliser and soil ameliorant/improver.
In conjunction with Western Water, RMIT University is conducting experiments at Surbiton Park to encourage the use of biosolids in Victoria and develop sustainable biosolids management programs.
The Smart Water Fund awarded RMIT a grant of $130,000 over three years for this project, which includes three rounds of field harvest trials.
Crops such as oats and canola, fertilised with biosolids, can be fed to animals or used to produce biodiesel. Crop and biodiesel production would benefit Water Authorities by enabling them to find a diversified market for the biosolids, and potentially generate additional income. Biosolids can be sold as fertiliser or used onsite to produce crops for stock-feed or biodiesel production, which may also be sold or utilised for meeting onsite energy needs.
The Project
The project aims to determine the best application rate for biosolids, balancing maximum crop growth with negligible leaching of nutrients into surrounding groundwater.
The trials are taking place onsite at Surbiton Park, on a plot of land measuring 40 metres by 30 metres. Planted with canola and oats, the plots are divided into three sections: the control plot is conventionally fertilised; the second is fertilised with a commercial product (a composted mixture of green waste and biosolids produced by PineGro); while a third is fertilised with de-watered biosolids directly from Surbiton Park.
Both canola and oats are planted side by side because crop rotation is beneficial for long-term soil sustainability. Oats can potentially be used to produce ethanol, or as cattle feed.
The Outcome
Lessons Learnt
The first trial has been harvested, and the second canola and oat crops have been planted and are growing. RMIT’s Dr Nichola Porter explained that the project team initially utilised a greenhouse for the first trial (in addition to the open field), but the environment proved too artificial.
“We’re pleased to see that the plants in plot three, grown using biosolids alone, are growing taller and more rapidly than the other crops. The more you increase biosolids application, the taller the plants grow!” Dr Porter said.
While inorganic fertiliser only ‘feeds the crops’, biosolids has long-term advantages as a soil ameliorant/improver because it adds organic matter to the soil and actually changes soil structure.
Utilising biosolids to grow crops also reduces the potential for nitrogen and other nutrients leaching into the surrounding environment.
The Benefits
- The project is demonstrating that using biosolids to grow crops onsite is of greater benefit to wastewater treatment plant operators than simply spreading biosolids on the ground.
- The project trials have found that the nutrient value of biosolids could be utilised more efficiently by applying fresh biosolids rather than composted biosolids.
- The project demonstrates the potential to recover energy from biosolids by growing energy crops for subsequent production of biodiesel (as opposed to direct burning of biosolids).