Composting and evaluation of racetrack manure, grass clippings and sewage sludge

Two experimental/demonstration composting operations were operated in 1993 and 1994. At one site, racetrack manure was composted by itself. At another site, composts were produced from mixtures of racetrack manure, grass clippings and sewage sludge on four specially constructed pads. These pads were lined with plastic to facilitate leachate collection in adjoining containment ditches. Different ratios of two types of sewage sludge or sludge and grass clippings were mixed with the racetrack manure and composted in temperature-monitored, passively aerated static piles; both types of sludge were composted with and without aeration pipes. Temperature profiles were developed and illustrated. All the mature composts and the leachates from the first composting cycle were evaluated for various chemical and biological properties. The quality of the composts was assessed as soil amendments and fertilizers in several replicated plant growth experiments. The chemical analysis of the composts was very much related to the source of the feedstocks. The use of aeration pipes had little effect upon the temperature profiles or compost analysis. Leachate analysis proved that macro- and micronutrients were not lost in large quantities during the composting operation, although some concern must be addressed to nitrate leaching. Plant-growth experiments in the greenhouse showed that a combination of sewage sludge compost and peat outperformed 100% compost or the commercial potting mix. No major phytotoxic effects, however, were observed from the use of sewage sludge compost in germination and seedling growth trials.