CO-COMPOSTING OF SEWAGE-SLUDGE AND COAL FLY-ASH - NUTRIENT TRANSFORMATIONS

Co-composting of sewage sludge with coal fly ash was carried out for e valuating the effect of coal fly ash on nutrient transformations durin g sludge composting. Dewatered anaerobically-digested sewage sludge wa s mixed with sawdust used as a bulking agent at 2:1 (w/w), and the mix tures were amended with coal fly ash at 0, 10, 25 and 35% (why) and co mposted for 100 days. Addition of coal fly ash raised the pH of the sl udge compost throughout the composting period: but significant inhibit ion of decomposition activity occurred only at 35% ash amendment level . Soluble organic carbon and total C decreased according to composting time, whereas total N showed an opposite trend for all treatments. Ad dition of coal fly ash did not affect the carbon cycle significantly e xcept at an ash amendment level of 35%. Coal fly ash amendment caused a significant loss of NH4-N only during the thermophilic phase. Additi on of coal fly ash also inhibited the nitrification process and phosph orus transformation as indicated by the lower soluble NO3-N and PO4-P contents in ash-amended sludge composts. The C/N ratios in solid and a queous phases decreased with composting time but did not show any sign ificant difference after 63 days of composting for all treatments indi cating that ash amendment did not affect compost maturity. (C) 1998 El sevier Science Ltd. All rights reserved.