Evaluation of Composted Sewage Sludge/Straw Mixture for Horticultural Utilization

Collaborative research between Southern Water and Wye College, University of London, has led to the development of a static aerated pile composting process for the treatment of dewatered activated sludge cake/straw mixtures. The process reduces bulk volume of the sludge producing an environmentally acceptable, stabilised, odour and pathogen-free product. Characteristics of the compost make it a suitable general purpose medium for container grown plants, providing the salt concentration is reduced by washing the compost prior to planting. Compared with peat the compost has a higher bulk density, a lower waterholding capacity, a lower cation exchange capacity, a high content of soluble salts, and a higher content of plant nutrients. A compost mixture was successfully developed in the growing trials containing equal quantities of compost, Sphagnum peat, and horticultural vermiculite. The compost has been used successfully to grow a wide range of plants. Plants grown in mixtures based on the compost were in general similar to those grown in peat-based growing media. The compost is a valuable soil conditioner and slow release fertilizer.