An incubation study to assess the effect of waste sludge additions on some chemical characteristics of mine spoils : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticulture in Soil Science at Massey University

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Massey University
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In 1985 a study undertaken by the New Zealand Soil Bureau identified a major shortfall in topsoils for mining rehabilitation works and the use of surrogate materials to overcome this shortfall was postulated (Wills, 1992). The Resource Management Act 1991 places constraints on the disposal of wastes and may act as a catalyst for research into the beneficial utilisation of once waste products for land rehabilitation. The most common problem reclaiming of derelict and degraded land is a shortage of organic matter (Pulford, 1991) in the growing medium. The overall objective of the research reported in this study was to investigate chemical interactions between various mine spoils and sludge materials as organic amendments and to determine the level of sludge application (based on organic matter content) that maximised the chemical benefit to the mine spoils. A controlled incubation study was used to achieve the objectives of the study. Six mine spoils from two sources (a gold mine and a coal mine) and three sludge amendments from two sources (municipal sewage sludge and paper sludge) were used. The sludge amendments were applied to the mine spoils to supply three different rates of organic matter (2, 5 and 10% in the amended spoils) and incubated for 38 weeks. The incubations were sampled every four weeks until week 20 and finally at week 38 for chemical analysis. Results of the study revealed that organic matter, total and mineral N, total and Olsen P levels of the amended spoils could be predicted directly from the characteristics of the sludge and spoil constituents but pH, EC, CEC could not. The benefit of sludge addition on many of the chemical characteristics of the mined spoil increased with increasing level of sludge addition. Manukau sewage sludge was the most beneficial sludge to apply with respect to P fertilisation. North Shore sewage sludge presented the greatest benefit for mine spoil rehabilitation with respect to N and it provided less risk of heavy metal contamination than Manukau sewage sludge. Paper sludge presented the most benefit with respect to pH and organic matter and the least risk of heavy metal contamination; however, nutritionally it was inferior to the sewage sludges.
Sewage sludge as fertilizer, New Zealand