Abstract
Abstract In current study, the effect of various organic substances as bulking agents (BAs) including wheat straw, pistachio hull wastes, and tree leaves at different levels (10, 25, 45% v/v) were investigated on total concentration and chemical forms of Cu, Pb, Cr, and As in sewage sludge (SS) compost prepared by windrow method. According to the results, the composting process (with/without BAs), due to losses of SS mass and volume, increased the total concentration of heavy metals (HMs) compared to the un-composted SS sample (RSS). Evaluation of HMs chemical forms in prepared compost sample without BAs application (CSS) showed that the composting process reduced the mobility factor of As (from 28% to 20%), Pb (from 11.6% to 9.3%), and Cr (from 14.5% to 9.2%) compared to the RSS. Application of three BAs considerably decreased the mobility factor of As (17.5-18.8%), Pb (4.8-7.9%), and Cr (1.4-6.8%) compared to CSS and RSS. Changes of Cu mobility in prepared compost samples showed an unclear trend, however in some treatments, due to transferred organic fraction into exchangeable and carbonate fractions, increasing of this factor was obvious. Generally, the composting appeared to reduce As, Pb, and Cr availability by stabilizing the three metals and making them more stable and less mobile. In addition, the BAs application effect on HMs behavior of SS compost samples were so different and no specific kind of BAs can be recommended as a superior BAs in SS composting process.
Highlights
In recent decades, the production of sewage sludge (SS) has increased with increasing the world’s population, which no specific consumption is defined for them in wastewater treatment plants
In current study, the effect of various organic substances as bulking agents (BAs) including wheat straw, pistachio hull wastes, and tree leaves at different levels (10, 25, 45% v/v) were investigated on total concentration and chemical forms of Cu, Pb, Cr, and As in sewage sludge (SS) compost prepared by windrow method
Jaafarzadeh Haghighifard et al (2015) showed that the increase pH of MSS compost was due to the ammonia and mineralization of organic nitrogen and the decrease pH was due to the nitrification and ammonium gas formation and release to the atmosphere and eventually release of H ions (Wong et al, 2001a)
Summary
The production of SS has increased with increasing the world’s population, which no specific consumption is defined for them in wastewater treatment plants. The composting process adds structuring materials, increasing the final volume and diluting heavy metals (Alvarenga et al, 2015) To solve this problem, addition of some amendments such as lime and fly ash (Samaras et al, 2008) to SS was suggested in composting process, which could decrease the availability of HMs. To solve this problem, addition of some amendments such as lime and fly ash (Samaras et al, 2008) to SS was suggested in composting process, which could decrease the availability of HMs The nature of these amendments is alkaline and their application may cause an increase in soil pH that limits its using in agricultural land, especially in alkaline calcareous soils of Iran. Few attempts have been done to assess the effects of organic BAs on HMs concentrations of SS compost and their chemical forms In current study, this hypothesis exists that the use of different organic BAs in composting process may reduce amount of HMs availability in SS compost. The present study tries to study the effect of mixture of SS and three BAs including tree leaves, wheat straw, and pistachio hull wastes in the composting process on total concentration and chemical forms of As, Cu, Pb, and Cr in produced compost from SS
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