Sewage to fertilise EU farmlands?
Municipal sewage sludge may actually be safe to use and beneficial for agriculture if hazardous pollutants such as pesticides, lead, pathogens and pharmaceuticals can be removed from it. The sludge contains large amounts of much-needed phosphorus, which can be very beneficial to fertilisation of farmland. The EU project 'Sustainable and safe re-use of municipal sewage sludge for nutrient recovery' (SUSAN) studied processes that can transform the sludge into a safe fertiliser. It concluded that a process called mono-incineration can be used to destroy all pathogens and organic pollutants before recovery of phosphorus begins. It also noted, however, that the incineration process must be done in a facility where only sewage is treated and not other kinds of waste. This is important for avoiding dilution of valuable substances such as phosphorus. Another step is also required to diminish heavy metals in sludge and to improve the bioavailability of the phosphorus. The project worked on developing eco-friendly technology to treat sludge in a way that would encourage nutrient recovery. The two-step thermal treatment managed to destroy organic pollutants through mono-incineration before removing metals through thermochemical processes. The resulting ashes contain approximately 20 % bio-available phosphorus, as well as calcium, potassium and magnesium, ideal properties for manufacturing fertilisers. As phosphorus is a non-renewable resource that may become scarce, particularly in Europe, this technology can allow the EU to produce its own source rather than import it from abroad. New large facilities for treating sewage sludge ashes will soon be established in Europe, and a related pilot study is already underway. At the end of the day these innovations will support agriculture and provide a cost efficient, environmentally friendly way to produce fertiliser for the EU.
