Water-dispersible clay in soils treated with sewage sludge

João Tavares Filho,Graziela Moraes De Césare Barbosa,Adriana Aparecida Ribon

doi:10.1590/s0100-06832010000500005

João Tavares Filho, Graziela Moraes De Césare Barbosa + Show 1 more

Open Access

https://doi.org/10.1590/s0100-06832010000500005

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Abstract

A by-product of Wastewater Treatment Stations is sewage sludge. By treatment and processing, the sludge is made suitable for rational and environmentally safe use in agriculture. The aim of this study was to assess the influence of different doses of limed sewage sludge (50 %) on clay dispersion in soil samples with different textures (clayey and medium). The study was conducted with soil samples collected from native forest, on a Red Latosol (Brazilian classification: Latossolo Vermelho distroférrico) loamy soil in Londrina (PR) and a Red-Yellow Latosol (BC: Latossolo Vermelho-Amarelo distrófico) medium texture soil in Jaguapitã (PR). Pots were filled with 3 kg of air-dried fine earth and kept in greenhouse. The experiment was arranged in a randomized block design with six treatments: T1 control, and treatments with limed sewage sludge (50 %) as follows: T2 (3 t ha-1), T3 (6 t ha-1), T4 (12 t ha-1), T5 (24 t ha-1) and T6 (48 t ha-1) and five replications. The incubation time was 180 days. At the end of this period, the pots were opened and two sub-samples per treatment collected to determine pH-H2O, pH KCl (1 mol L-1), organic matter content, water-dispersible clay, ΔpH (pH KCl - pH-H2O) and estimated PZC (point of zero charge): PZC = 2 pH KCl - pH-H2O, as well as the mineralogy of the clay fraction, determined by X ray diffraction. The results showed no significant difference in the average values for water-dispersible clay between the control and the other treatments for the two soil samples studied and ΔpH was the variable that correlated best with water-dispersible clay in both soils.

Highlights

Wastewater Treatment Stations produce sewage sludge with an average composition of 99.9 % water and 0.1 % solids
Bearing in mind that wastewater treatment units have been providing rural producers with large quantities of sewage sludge at zero cost, and that the organic matter and calcium added by biosolids improves soil aggregation, the aim of this study was to assess the influence of different doses of limed sludge (50 %) on clay dispersion in soil samples with different textures
At the end of this period, the pots were opened and two sub-samples per treatment (A1 and A2) and sample collected to determine: pH-H2O, pH-KCl (1 mol L-1) (according to Embrapa (1997)), organic matter content according to the Anne method, waterdispersible clay using the pipette method of samples stirred with an orbital agitator at 30 rpm for 3 h, as well as ΔpH (pH-KCl – pH-H2O, according to Mekaru & Uehara (1972)) and point of zero charge (PZC), estimated by the following formula: PZC = 2 pH-KCl (1 mol L-1) – pH-H2O (according to Keng, apud Uehara (1979))

Summary

Introduction

Wastewater Treatment Stations produce sewage sludge with an average composition of 99.9 % water and 0.1 % solids. 70 % are organic (proteins, carbohydrates, lipids, etc.) and 30 % inorganic (sand, salts, metals, etc.) Their disposal is one of the greatest operational problems of wastewater treatment stations (Barbosa & Tavares Filho, 2006). Agricultural recycling is a more appropriate way of disposing of sewage sludge (biosolids) in technical, economic and environmental terms, given an appropriate application (Tsutiya, 1999). It is the cheapest method of recycling organic matter and nutrients (Matthews, 1998), and conditions and fertilizes the soil. In the United States, for instance, sludge has been used as fertilizer since 1927 (Neiva, 1999) and around 25 % of all biosolids produced (13,106 Mg year-1) is used in agriculture (Tsutiya, 1999) and 41 % in forest soils (USEPA, 1993)

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