Decomposition of organic wastes added to colliery spoils - their nitrogen, phosphorus and heavy metal transformation

Laboratory incubation studies (6 weeks at 26°C) were conducted to analyze the changes of chemical properties in three kinds of colliery spoils after addition of two sewage sludges (Dewmus and Yorkshire Bounty) and two animal manures (Chiguano and Poultry Manure). In the acidic Whitwood spoils, the nitrification was inhibited and NH₄⁺N became the dominant form of nitrogen. The neutral Thorne spoil had the quickest nitrification followed by Ashington. Addition of organic wastes significantly improved the nitrogen status of all spoils and the rate of nitrification was in the order of Poultry Manure > Chiguano > Dewmus > Yorkshire Bounty. Inorganic nitrogen fertilizer, ammonium sulphate, although supplying the highest amount of NH₄⁺N to spoils, increased nitrate nitrogen less than some of the organic wastes. The organic waste additions caused an immediate and significant increase in P content. Although the waste effect decreased as incubation proceeded, higher P content was found in spoil with waste amendments than in the control throughout incubation. Total nitrogen and phosphorus mineralization was relatively low in all treatments. This showed that microbial immobilization might be important. Addition of animal manures significantly raised the pH of the two acidic spoils. Similar to the changes of P content, pH also followed a slight and gradual decline during incubation. Results further indicated that waste addition did not raise the spoil heavy-metal contents; it might even reduce the heavy-metal toxicities of spoil samples. This study shows that organic wastes are slow-releasing and complete fertilizers but that the degree of mineralization depends on the chemical nature of organic fraction of individual waste.