Abstract
This study aims to investigate the relationship between key physicochemical parameters related to composting process and bioavailability of Cd, As and Cr during swine manure composting through regulating different initial carbon to nitrogen (C/N) ratios (15:1, 20:1, 25:1) and bulking agent types (straw, green waste). Results showed that higher initial C/N ratio of 20:1 or 25:1 and straw as bulking agent were optimal to reduce the bioavailability of Cd, As and Cr (62.4%, 20.6% and 32.2% reduction, respectively). Redundancy analysis implied that the bioavailability of Cd was significantly associated with total phosphorus and total nitrogen, deducing the formation of phosphate precipitation and biosorption might participated in the reaction process, while that of As and Cr were mainly influenced by organic matter (OM), cation exchange capacity (CEC) and OM, CEC, electric conductivity, respectively. A total of 48.5%, 64.6% and 62.2% of Cd, As and Cr redistribution information could be explained by the above parameters. Further correlation analysis revealed that bioavailable As and Cr were negatively correlated with humic acid to fulvic acid ratio. In summary, this study confirms that the mechanisms of phosphate precipitation, biosorption and humification played critical role in reducing Cd, As and Cr bioavailability during swine manure composting.
Highlights
This study aims to investigate the relationship between key physicochemical parameters related to composting process and bioavailability of Cd, As and Cr during swine manure composting through regulating different initial carbon to nitrogen (C/N) ratios (15:1, 20:1, 25:1) and bulking agent types
Results showed that compared with green waste, straw could better promote the increase of pH value
Compared with low initial C/N ratio (15:1) and green waste as bulking agent, higher initial C/N ratio (20:1 and 25:1) and straw were more conductive to decreasing bioavailability of Cd, As and Cr during swine manure composting
Summary
This study aims to investigate the relationship between key physicochemical parameters related to composting process and bioavailability of Cd, As and Cr during swine manure composting through regulating different initial carbon to nitrogen (C/N) ratios (15:1, 20:1, 25:1) and bulking agent types (straw, green waste). The effects of parameters that can directly regulate the composting process and compost quality on the changes of heavy metal speciation during composting have been widely investigated, such as aeration rate, moisture content, C/N ratio, and bulking agent t ype[5,6]. With the help of mathematical analysis methods, present work aims to explore the key influencing factors on heavy metals bioavailability during the basic process of composting by regulating the initial C/N ratio and selecting bulking agent type. Capacity, so as to regulate the nitrogen loss, organic matter degradation and stabilization during c omposting[10,11] Both initial C/N ratio and bulking agent can significantly influence the composting process, and more importantly, they are easy to be adjusted and changed. As a multivariate analysis method, RDA is more widely used to relate microbial community changes with environmental c hanges[12], but it has great application potential in analyzing the correlation between heavy metal speciation and composting related physicochemical parameters
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