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(M/EH106) Degradation of organic priority pollutants in sewage sludge applied to agricultural soil. Hesselsoe, Martin1, Skals, Kim1, Jensen, Dennis1, Roslev, Peter1, Moldrup, Per1, Olesen, Torben1, Mortensen, Gerda2, Henriksen, Kaj1, 1 2 ABSTRACT- Stabilized sewage sludge applied as organic fertilizers to agricultural land is incorporated into the top soil layer in clumps of varying size which may stay partly anaerobic for unknown periods of time. Two types of laboratory experiments were carried out to investigate the effect of reduced oxygen availability on mineralization rates of 14C labeled 4-nonylphenol (NP) and di-(2-ethylhexyl)phtalate (DEHP). i) Sludge was mixed homogeneously with soil (fully aerobic conditions) and ii) sludge aggregates of different size and shape was imbedded in soil. Half life in homogeneous mixtures of the investigated compounds were 3 days (NP) and 14 days (DEHP). Equal rates of mineralization were obtained in parallel mixtures of sludge and sterilized sand, indicating that the actively degrading microbial population mainly was present in the sludge. Mineralization of DEHP was retarded by a factor 4 (half life of 60 days) in 1.4 cm sludge aggregates compared to homogenized soil-sludge mixtures. Mineralization of NP was retarded by factor 8-12 in 2 cm sludge aggregates of planar and spherical shape (half life of 25-35 days) and was even more retarded in the 4cm aggregates. Oxygen penetration into the sludge aggregates was monitored with microelectrodes. Initial oxygen penetration was 0.6 mm and increased to 1.7 mm within 50 days. Oxygen penetration was not enhanced by dry soil conditions. Residual concentrations of NP measured after 120 days was 1-7% of the initial concentration in 2cm aggregates and 35% of initial concentration in 4 cm aggregates.The results indicate that sludge aggregates may stay partly anaerobic for prolonged periods of time after incorporation into soil. This limited oxygen availability may delay degradation of organic pollutants in sludge from time spans of weeks to month or even years, depending on size of sludge aggregates in the soil. Key words: degradation of nonylphenol, degradation of dehp, oxygen availability, sewage sludge |
