The effect of aging on element plant availability and bacterial counts of mixtures of wood ash and sewage sludge

Yudani Pousada-Ferradás,Socorro Seoane-Labandeira,Avelino Núñez-Delgado,Miguel Blanco

doi:10.4067/s0718-221x2011000300006

Yudani Pousada-Ferradás, Socorro Seoane-Labandeira + Show 2 more

Open Access

https://doi.org/10.4067/s0718-221x2011000300006

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Abstract

This study investigated the chemical composition of a mixture of 70% wood ashes (a by-product of timber-industry) and 30% sewage sludge (% dry weight), immediately after preparation and after storage (42 days). The mixture had higher Mehlich 3 extractable Ca, Mg and K concentrations than either component alone, and low plant-available heavy metal concentrations, both immediately after mixing and after storage for up to 6 weeks. The results support the view that mixtures of this type may be useful for liming and fertilizing, given their neutralizing capacity and phyto nutrient concentrations. Furthermore, we compared the survival of Escherichia coli in a wood ash and sewage sludge mixture with their survival in mixtures of sewage sludge and two levels of quicklime. The time needed to eliminate most bacteria was 29 days in the ash-sludge combination, while nine days were required for one of the quicklime-sludge mixtures, and counts were minimal for the quicklime-sludge mixture with a pH>12.

Highlights

Wood ash is produced in large quantities by timber-industry factories which burn waste biomass as fuel for energy production
Timber-industry wood ash is stored on land allocated for this use, or is dumped on general waste tips; a small proportion is used as a construction material, or for agricultural liming and fertilization
In preliminary studies we found that mixtures with 70% ash and 30% sludge were optimal in terms of ease of handling and application

Summary

Introduction

Wood ash is produced in large quantities by timber-industry factories which burn waste biomass as fuel for energy production. Timber-industry wood ash is stored on land allocated for this use, or is dumped on general waste tips; a small proportion is used as a construction material, or for agricultural liming and fertilization. The main components of wood ash are generally calcium, potassium and magnesium (Demeyer et al 2001, Vance 1996). Combustion is often incomplete, so that carbon concentration is usually high. The addition of wood ash to acid soils generally has positive effects, since it increases pH, reduces exchangeable Al, increases exchangeable Ca and Mg, and increases cation exchange capacity (Van Hees et al 2003). The use of wood ash for soil amendment over long periods may lead to excessive build-up of sulphates, nitrates or soluble organic carbon (Lundström et al 2003), or of low-molecular-weight organic compounds (Holmström et al 2003). Wood ashes can contain high heavy metal concentrations, and organic pollutants, and spreading wood ashes in a forest would be a major anthropogenic interference with the natural biogeochemical

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