토질개선제로서 하수슬러지와 석탄재 혼합물의 적용가능성

The Utility of Mixture of Sewage Sludge and Coal Fly Ash as a Soil Conditioner

This study was performed to investigate the possibility of using coal fly ash as a stabilizing agent for anaerobically digested sewage sludge, and the utility of this mixture as a soil conditioner. Sludge and ash were combined with the mixing ratios of 1:0, 1:0.2, 1:0.4, 1:0.6, 1:0.8, 1:1, 0:1 (sludge:ash, dry weight basis). Each mixture was composited with a portion of soil to make a ratio of 1:3 (mixture:soil, dry weight basis), then stabilized for 21 days under laboratory conditions. The results were as follows. 1. Mixtures of sewage sludge and coal fly ash improved the fertility of soil. 2. In leachate from each treatment, heavy metal concentrations were below the regulatory standard through the stabilization period. Nitrate concentrations were decreased during the process of stabilization and were lower than the regulatory limit in groundwater after 14 days. 3. The pH of soil increased after being applied with sludge-ash mixture, then decreased through stabilization process. In soils with smaller portions of coal fly ash (treatment 1 to 3), pH which increased initially, was not maintained as decomposition of sludge led to soil acidification. 4. Available K in soil decreased by reducing the amount of sludge amendment, however concentrations of Mg and Ca were increased as the amount of ash in mixture increased. Available B concentrations were in safe range for plants. Concentration of available elements increased after the stabilization process in most treatments, since decomposition of sludge decreased pH. 5. Cation exchange capacity (CEC) and heavy metal adsorption capacity of soil were enhanced with application of sludge-ash mixture. Distribution coefficient KF was well correlated with CEC and pH (p<0.05). 6. Optimal mixing ratio of sludge and coal fly ash which could protect soil from heavy metal toxicity and acidification was 1:0.8 on the basis of dry weight.