A Biosolids Composting Challenge: Meeting Demand for a Peat-Free Horticultural-Grade Product

In 1996, Thames Water launched a range of peat-free compost products based on biosolids. In order to keep up with demand and to maintain the high standards of product quality, the company has investigated higher-rate composting processes and optimisation of the maturation stage. Agitated-bay composting systems are the preferred in-vessel technology for large sludge treatment centres using woodchip as a bulking agent. These automated systems (i) accelerate the composting process, (ii) maximise throughput on a smaller footprint, and (iii) achieve better control of odour emissions.
A maturation trial with composted material from the US Filter agitated-bay system confirmed that a horticultural-grade product could be attained. Small-scale maturation trials showed that seeding with mature green waste compost can accelerate nitrification to such a rate that near zero levels of ammonia can be achieved after one month of maturation.