Recycling of sewage sludge and household compost to arable land: fate and effects of organic contaminants, and impact on soil fertility

Effective use of organic wastes for agricultural production requires that risks and benefits be documented. Two types of sewage sludge, household compost and solid pig manure were studied under field and greenhouse conditions to describe their fertilizer value and effects on soil properties and soil biota, the fate of selected organic contaminants, and their potential for plant uptake. A 3-year field trial on two soil types showed no adverse effects of waste amendment on crop growth, and a significant fertilizer value of one sludge type. Accumulation of N and P-i was indicated, as well as some stimulation of biological activity and micro-arthropod populations, but these effects differed between soil types. There was no detectable accumulation of polycyclic aromatic hydrocarbons (PAH), di(2-ethy Ihexyl)phthal ate (DEHP), nonylphenol and ethoxylates (NP + NPE) or linear alkylbenzene sulfonates (LAS) after three repeated waste applications, and no plant uptake was suggested by analysis of the third crop. A plot experiment with banded sludge was conducted to examine sludge turnover and toxicity in detail. Less than 5% of NP or LAS applied in organic wastes was recovered after 6 months, and less than 6% of DEHP applied was recovered after 12 months. Potential ammonium oxidation (PAO) at 0-1 cm distance from the banded sludge was stimulated despite toxic concentrations in the sludge, which suggested that contaminants were degraded inside sludge particles. Phospholipid fatty acid (PLFA) profiles suggested a gradual shift in the composition of the microbial community within sludge, partly due to a depletion of degradable substrates. A pot experiment with sludge-amended soil and soil spiked with contaminants showed no plant uptake of NP, DEHP or LAS. Degradation of LAS and NP added in sludge was delayed and the degradation of DEHP was faster than when the contaminants were added directly to the soil. In conclusion, adverse effects of organic waste application on soil or crop were not found in this study, and for some waste products positive effects were observed. (C) 2003 Elsevier Science B.V. All rights reserved.