Composting sewage sludge with green waste from tree pruning

Sarah Mello Leite Moretti,Edna Ivani Bertoncini,Cassio Hamilton Abreu-Junior

doi:10.1590/0103-9016-2014-0341

Abstract

Sewage sludge (SS) has been widely used as organic fertilizer. However, its continuous use can cause imbalances in soil fertility as well as soil-water-plant system contamination. The study aimed to evaluate possible improvements in the chemical and microbiological characteristics of domestic SS, with low heavy metal contents and pathogens, through the composting process. Two composting piles were set up, based on an initial C/N ratio of 30:1, with successive layers of tree pruning waste and SS. The aeration of piles was performed by mechanical turnover when the temperature rose above 65 ºC. The piles were irrigated when the water content was less than 50 %. Composting was conducted for 120 days. Temperature, moisture content, pH, electrical conductivity (EC), carbon and nitrogen contents, and fecal coliforms were monitored during the composting. A reduction of 58 % in the EC of the compost (SSC) compared with SS was observed and the pH reduced from 7.8 to 6.6. There was an increase in the value of cation exchange capacity/carbon content (CEC/C) and carbon content. Total nitrogen remained constant and N-NO3- + N-NH4+ were immobilised in organic forms. The C/N ratio decreased from 25:1 to 12:1. Temperatures above 55 ºC were observed for 20 days. After 60 days of composting, fecal coliforms were reduced from 107 Most Probable Number per gram of total solids (MPN g−1) to 104 MPN g−1. I one pile the 103 MPN g−1 reached after 90 days in one pile; in another, there was recontamination from 105 to 106 MPN g−1. In SSC, helminth eggs were eliminated, making application sustainable for agriculture purposes.

Highlights

Agriculture has become an alternative destination for the sizeable quantities of sewage sludge (SS) generated, due to the presence of plant nutrients in organic waste (Melo et al, 2007; Wang et al, 2008)
The water content in the compost produced was 58 %, compared with the water content of 70 % in sewage sludge. This reduction in water content facilitates the operation of compost application, since application of sewage sludge is hampered by its high water content
The cost of transporting compost becomes cheaper than sewage sludge transportation, and compost can be transported to areas more distant from its production centre

Summary

Introduction

Agriculture has become an alternative destination for the sizeable quantities of sewage sludge (SS) generated, due to the presence of plant nutrients in organic waste (Melo et al, 2007; Wang et al, 2008). SS can provide significant amounts of potentially toxic elements, such as heavy metals (Walter et al, 2006; Singh and Agrawal, 2008; Méndez et al, 2012), pharmaceuticals (Redshaw et al, 2008), hormones (Stumpe and Marschner, 2007), aromatic hydrocarbons (Cai et al, 2007), as well as pathogens such as helminth eggs, fecal coliforms, salmonella, protozoan cysts and viruses (Gaspard et al, 1997; Gerba and Smith, 2005) Such contaminants can be more available to plants and be accumulated in the soil. Tertiary treatment or post-treatment, to improve its chemical, physical, and microbiological properties is almost always required

Objectives

Methods

Results

Conclusion