Use of Biosludge from Wastewater Treatment Plant as Soil Conditioner

Summary

Woodman Point is Water Corporation largest wastewater treatment plant. 99.97% of the wastewater arriving at Woodman Point is just wastewater, from household kitchens, bathrooms and laundries, as well as toilets. First the wastewater is screened to remove any large objects (paper, rags etc) before passing through settling tanks to remove grit (sand etc). Next, the wastewater spends several hours in large sedimentation tanks to remove settleable solids. Sludge from these tanks receives further treatment.

Sludge is stabilised using Woodman Point’s two 38-metre high anaerobic sludge digesters. Egg-shaped for efficiency, they are the biggest of their type in the southern hemisphere. Bacterial action at 35 degrees Celsius in the digesters converts sludge into a residue that is an excellent soil conditioner for landscaping or agricultural use. The stabilised sludge – known as biosolids – is trucked off-site daily to enrich market gardens and farms around Western Australia. Another by-product of this digestion process is biogas that is used to power the plant’s on-site generators.

Industry

Industry Sector	Specific Industry
water utility sector	water supply and treatment company
agricultural sector	feedcrop farmers

Region

Kwinana Industrial Area, Kwinana, Western Australia

Applied Technologies

Anaerobic digestion is the decomposition of organic matter under anaerobic conditions. This process occurs naturally in anaerobic environments (i.e. in the absence of oxygen) such as in sediments, soils, landfills, and in the gut of animals. In an anaerobic system, a mixture of different species of anaerobic micro-organisms degrade organic matter in a sealed-off tank (the digester) into a biogas and nutrient rich biosludge. The biogas can be used for electricity generation on-site or can be sold as a supplementary fuel, the biosludge can be sold as a high quality fertiliser. There are numerous types of digestion systems available, all designed to suit the characteristics of the waste, space availability, technical expertise, and the economic objectives of the organisation.

Triple Bottom Line Aspects (direct at operational level)

Economic	capital and operational costs of anaerobic digestion system
Environmental	biosludge is reused, rather than going to landfill
Social	increased employee satisfaction due to improved environmental performance of the wastewater treatment plant

Additional Comments

None.

References

• van Beers, D, Bossilkov, A and van Berkel, R (2005) “Capturing Regional Synergies in the Kwinana Industrial Area – 2005 Status Report”, CSRP Report (for Project 3B1), August 2005
• Water Corporation (2005) "Woodman Point Wastewater Treatment Plant", Retrieved from: http://www.watercorporation.com.au/W/wwtp_woodmanpoint.cfm
• Yuncken, A L, and Offszanka J (1999) "Energy Recovery from Digester Gas – The Woodman Point Experience", Environment Industry Development Network – Sludge Management for the 21st Century, Fremantle, Australia, 8th-10th April 1999

Last Update

20 July 2010