Worms turn most sludges into soil
A new environmental research centre at the University of Hull in England was launched by the UK Secretary of State for Trade and Industry, Alan Johnson, on 16 September. Natasha Wiseman took the opportunity to find out more about a pilot project investigating into the use of worms for sludge sewage treatment.
The wormery relies on the unique digestive processes of a common ragworm, known as Nereis diversicolor. Dr Jörg Hardege spotted the potential of these "health police of the estuaries" when studying their natural presence at sewage outfalls, where he discovered they significantly reduced the quantities of organic material and at the same time reduced toxicity.
The next stage was to produce a bioreactor to optimise this capacity to treat sewage and liquid wastes. A pilot wormery has already shown astonishing results, with solid waste volumes being reduced by 50-60%. A further bonus is that the system actually generates, as a by-product, water that can be reused.
Hardege explains, "The process is inexpensive and sustainable - it requires little energy, unlike conventional systems, and also offers companies a solution to landfill, with waste being made less toxic and the waste volume dramatically reduced. The system can be used at a local community level as well as having application in large centralised, processing facilities, making it attractive for small treatment works or enterprises."
The pilot scheme was originally set up over ten years ago in Aldenburg in Germany and then restarted in the UK recently. It consists of small, portable tanks of 2-3m3, some filled with sediment and worms and others filled with sediment, worms and phragmites reeds. Current research is to find out which works best. The system is self-sustaining, being visited every two weeks, and the water levels and animal health are monitored by webcam by a wastewater expert in Cologne, Germany.
"We take what you get in nature and put it in a tank and optimise it," sums up Hardege.
The worms consume the sludge and transform it into fecal material, which creates much better sediment than sludge. The worms may eat it again and again and transform it into soil. Every couple of years, the sediment is removed and further processing can be done by topsoil worms.
"They eat everything and everything eats them," explained Hardege. "They have mechanisms to survive in very difficult conditions, they have mechanisms to live in heavy metal polluted areas, some they break down with others, they form organic complexes with, others they excrete actively."
Following the success of the pilot scheme, ETCIC is keen to demonstrate the potential of the approach in full-scale applications for treatment of sewage and animal wastes of high liquid state. Already working with Emden University in Germany, the centre seeks to develop working relationships with other organisations and is seeking funding for an EU Life demonstration project. Dr Hardege envisions demonstration tanks of 200-500m3.
Changes in EU rules will soon make sludge disposal very expensive, Dr Hardege explained, sludge can no longer be spread directly onto fields due to biological risks. Drying and incineration are costly in terms of energy consumption and environmental impact, and they still produce waste.
Given that sludge disposal costs are forecast to rise, Hardege believes the capital expenses for companies to establish the wormery are conservative compared to a conventional plant. The wormery involves the costs of setting it up, and relatively high land use, but running costs are low.
Dr Hardege sees global potential for the commercial application of worm-treated sludge in small-scale plants in coastal areas. An experimental station on the Algarve in Portugal is demonstrating that worms make an ideal sludge treatment for aquaculture, not least because the worms are an excellent fish food.
Further research will determine the levels of residues of heavy metals left in the soil after treatment. However, at this stage, Hardege's team is excited that a reduction in the volume of sludge by two-thirds and a 90% reduction in toxicity can be achieved with the worms. Optimisation of the system through the development of bioreactors is also a future goal, as is a full environmental impact study and cost-benefit analysis.