Abstract
Vermicomposting is at suitable methods for stabilization and converting of sewage sludge into useful products. To investigate the effects of bulking material on vermicompost quality, an experiment was conducted in a factorial design with three replications. In this experiment, the final dried sludge in lagoons was mixed with bulking materials (woodchips, three leaves, and wheat straw) in four mixing proportion with swage sludge (0, 15, 30 and 45%, V/V). Chemical properties of bulking materials, sewage sludge, and produced vermicomposts were determined. Vermicomposts had relatively low pH and electrical conductivity (EC). The nutrients content of vermicompost, especially N, P, Fe, and Zn, were high. These properties showed its suitable quality for use in agriculture. Heavy metals concentrations of vermicomposts, except Zn, were lower than recommended values by EPA. Mixing of Bulking materials with sewage sludge decreased pH, N, Pb, Co, and Cd, but increased Ca, Mg, Fe, Cu, Mn, Zn, and Ni content of produced vermicomposts. In most cases, the concentrations of nutrients were higher in 30% mixing proportion. Therefore, 30% (v/v) mixing of bulking material with sewage sludge is recommended for vermicompost production.
Highlights
There are a large amount of sewage sludge produced in wastewater treatment plants that caused potential risks for human health and environmental problems (BAZRAFSHAN et al, 2005)
Sewage sludge can use as organic fertilizer and soil amendment, but its odors, heavy metal content, toxic organic compounds, and pathogens show the necessity of treatment and stabilization before application to farm lands (TIQUIA et al, 2002)
After 5 months of incubation of pots, the colour of materials turned to dark brown black and the activity of worms declined that these conditions indicated the maturity of vermicomposts
Summary
There are a large amount of sewage sludge produced in wastewater treatment plants that caused potential risks for human health and environmental problems (BAZRAFSHAN et al, 2005). Sewage sludge can use as organic fertilizer and soil amendment, but its odors, heavy metal content, toxic organic compounds, and pathogens show the necessity of treatment and stabilization before application to farm lands (TIQUIA et al, 2002). Some of beneficial effects of land application of sewage sludge are supplying nutrients (N, P, secondary nutrients, and micronutrients), improving of soil physical conditions, and elevating of soil organic matter level. Heavy metals and organic pollutants concentration limits the use of sewage sludge as organic fertilizer (QUATMANE et al, 2000). Biological composting of sewage sludge stabilizes its organic content and decreases the pathogens population (BURGE; ENKIRI, 1978). Total concentration of heavy metals increase during composting, the available forms of them decline in this process; probably due to production of insoluble complexes with humic substances (PARÉ et al, 1999)
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