Sorption and Biodegradability of Sludge Bacterial Extracellular Polymers in Soil and Their Influence on Soil Copper Behavior

Abstract

Bacterial extracellular polymers (BEP) affect the translocation and fate of organic and inorganic pollutants in terrestrial and aquatic ecosystems. In this study, BEP from activated sludge was compared with sludge dissolved organic matter (DOM) in terms of behavior and effects on the mobilization and bioavailability of Cu in a well-aged Cu-contaminated orchard sandy loam. Addition of sludge BEP (10-200 mg dissolved organic carbon [DOC] L(-1)) to the soil resulted in 1.6- to 12.8-fold-higher soil soluble Cu concentration over the control and 1.3- to 2.2-fold over sludge DOM of the same concentration. Consequently, the Cu uptake by the ryegrass (Lolium perenne L., cv. Target) grown in the soil was increased by 31% due to interval watering of 100 mg DOC L(-1) of sludge BEP solution in a 35-d period. The influence of sludge BEP on mobilizing soil Cu could be maintained as long as 60 d or more, depending on BEP biodegradation status. The findings that sludge BEP promoted Cu mobilization and bioavailability could be attributed to less adsorption of BEP by soil, slow degradation, and higher affinity with Cu. For example, after 3 wk of aerobic incubation, the soluble Cu present in the sludge DOM-treated soil was reduced to about the level of the control, while the concentration of soluble Cu in BEP-treated soil was 6.2 times higher than that in the control. Therefore, sludge BEP could act as a facilitated-transport carrier of Cu. The environmental risk of Cu should receive much attention if BEP is incorporated into soils.

Biosolids and Sludge Management

“…Broos and others (2004) soil resulted in several-fold higher soluble Cu concentration, and also increased Cu uptake by ryegrass grown in the soil. They suggested that these may be attributed to less sorption of BEP by soil, slow degradation, and higher affinity with Cu, and advised that the environmental risk of Cu should receive more attention if BEP is added to soils (Zhou et al, 2004b). Weggler and others (2004) report that increasing chloride (Cl) concentration in soil solution has been shown to increase Cd concentration in soil solution and Cd uptake by plants, when grown in phosphate fertilizer-or biosolid-amended soils.…”

Sorption and Leaching of Metals in the Soil Due to Application of Dissolved Organic Matter

“…Investigations have revealed that the presence of DOM in soil can facilitate mobility and transport of heavy metals, acting as "transporter" through the formation of soluble metal-organic complexes (Temminghoff et al 1997, Zhou et al 2004, Li and Zhou 2010. Thus, the application of organic materials such as manures, compost, and sewage sludge improves the physicochemical and biological conditions of the soil; however, DOM present in these wastes can affect speciation, transformation and the behavior of heavy metals in the environment (Benedetti et al 1996).…”