There is world-wide interest in disposal technologies suitable for handling farm wastes. The Northern Ireland mushroom industry generates 200,000 tonnes/year of “spent” mushroom compost waste containing excess salts (P, K, Ca) and heavy metals. Its disposal by landspreading is restricted by EU, U.K. legislation. Farmers in Europe and the United States use this waste as a soil nutrient improver, but such operations are deleterious to the environment owing to microbial loading of soil and the release of human and animal pathogens. An ideal option is to reduce salt levels and pathogen content before granulating the waste into fertilizers. Electroremediation is a novel, in situ environmental technology which utilises low voltage electrical fields to remove salts or metals in contaminated soil sites. We developed electroremediation methods for the removal of excessive salts from `spent' mushroom compost or from soils contaminated with this waste. Electroremediation of excess salts / heavy metals from the horticultural waste was carried out in an anti-corrosive electrolysis tank with a built-in central holding bay for the waste material. A thin layer of charged fluid (rain water, pH 5.5; adjusted with 0.005 n HCl) maintained over the mushroom compost waste achieved the removal of salts when electrical fields ranged from 20 to 200 V were applied across electrodes (spacing 1.5 m apart) in our investigations. Electrode saturation by H+ or OH- and thermal/alkaline front build up were minimised by flushing with cooled (15 °C) fresh rainwater circulated via peristaltic pumps. The above prototype is useful for nutrient tailoring of spent compost waste in bagged compost prior to producing commercially viable granulated fertilizers from wastes.
Juluri Rao*, John Moore, and Andrew Stewart
The EU Regional Draft Waste Management Plan (1999-2004) identified pig slurry (501,590 tonnes), poultry manure (217,110 tonnes) and spent mushroom compost (221,665 tonnes) as the main contributors to the 3.5 million tonnes of waste generated annually in Ireland. Current legislative restrictions prevent pig wastes from intensive pig units and horticultural wastes mainly spent compost produced in mushroom farms being disposed via landspreading due to pollution threat from nutrient run-off and the health hazards due to animal and human risk pathogen contents in wastes. Composting is a world-wide popular option for environmentally sustainable means of recycling farm wastes. In Ireland, profitable conversion of farm wastes such as pig slurry solids and spent mushroom compost has not yet been fully explored for their economic viability as `green' fertilizers. In this study, we produced pelleted formulations of the composted pig waste solids, (20%) blended with spent mushroom compost (26%), turkey litter (26%) cocoa husks (18%) and shredded paper (10%) to an environmentally safe, organic-based fertiliser resulting in N:P:K = 3:5:10, ideally suitable for use on amenity grassland such as golf course fairways and greens in Ireland, wherein spring and summer fertilizers with slow release of nutrients would aid an even growth of grass. We describe the composting methods used, processing technology developed and additional amendments such as dried blood or feather meal that were used during the pelletisation operation yielding specific N:P:K target ratios from the pig manure and spent compost wastes. We also report on the rigorous microbiological tests carried out throughout the composting phase and ascertained the pathogen-free status of the final pelletised fertilser products.