Use of agro industry treatment plant sludge for agrcultural purposes

Land application of sewage sludge is performed in an environmentally safe and cost-effective manner in many communities. Although land application of sewage sludge has become a common practice over the past several decades, the application of sludge generated by industrial plants is limited due to fears of the accumulation of toxic matter in soils and plants. However, the accumulation of heavy metals and their availability to plants depend strongly on the composition of the sludge, the application rate, soil properties, and the crop species. Therefore, agro-industries have considerable potential due to the low heavy metal content and high organic matter content of their sludges. The main objective of this study was to investigate the land use potential of the agro-industry sludges. In this framework, physico-chemical and biological properties of sludges were investigated. Characterization study stated that sludge generated from agro-industries was deficient in terms of nutrients, but rich in organic matter. In general, heavy metal concentrations detected in the sludge samples were lower than the tolerance limits. However, coliform densities were higher thus improvement of the sludge characteristics in terms of coliform was required. Therefore, in order to improve the microbiologic quality chemical stabilization, thermal stabilization and combination of these methods were performed. The results were shown that 3% lime dosage was sufficient to keep pH over 12 during 24 hours. Pathogen reduction was affected from the increasing temperatures. Lower temperatures, i.e. 50 and 70 oC were not enough to reduce the pathogen levels below 1000 MPN/g DS. However, the high temperature thermal stabilization (180 oC) can fulfill the USEPA Class A Pathogen requirements. Besides, results obtained from high pH-high temperature process indicated that the high pH (> 12) can considerably reduce the heating time required for an effective pathogen reduction. v When the chemically stabilized sludge was heated to a temperature of 70°C, 30 minutes heating time was necessary to fulfill Class A biosolid requirements. For the 180°C (heating temperature), 10 minutes heating time was sufficient to fulfill Class A biosolid requirements. Key Words: Sewage sludge, biosolids, agricultural use, plant nutrients, soil properties, stabilization