Reducing ammonia losses by adding FeCl3 during composting of sewage sludge

The release of ammonia nitrogen during composting of sewage sludge mixed wi th a lignocellulosic bulking agent leads to a reduction in the agronomic va lue of the final compost and to harmful effects on the environment. We prop ose adding a cheap salt FeCl3 which can be used without special precaution to reduce ammonia losses by decreasing pH conditions. An in-vessel co-compo sting experiment was conducted in a large reactor (100 L) in which FeCl3 wa s added to sludge mixed with a bulking agent (pine shavings and sawdust) an d compared with a control mixture without FeCl3. Temperature, oxygen consum ption and pH were monitored throughout the composting of both mixtures. The final balance of organic matter, organic and inorganic nitrogen permitted to conclude that the addition of FeCl3 reduced nitrogen loss (by a factor o f 2.4 in relation to the control) and increased mineralisation of the organ ic nitrogen by 1.6.