Bioavailability and fractionation of Cd and Zn in contaminated soils amended by filter cake, vinasse and boiler ash from ethanol production plant

Abstract

Boiler ash (BA), filter cake (FC), and vinasse (VN) are three major wastes produced from ethanol production processes. Waste utilization from ethanol production as soil amendments and metal immobilizing agents is one of a promising and sustainable options to help utilize materials effectively, reduce waste disposal, and adds values to these waste-products. As a consequence, this research was carried out by adding BA, FC, and VN at different ratio (3% w/w) in two different Cd and Zn concentration levels of low Cd (LCdS) and high Cd (HCdS) contaminated soils, respectively for 3 months. The results showed that the addition of single BA and FC (3% w/w), and a combination of 1.5% BA and 1.5% VN (w/w) caused the significant reduction in the bioavaialble Cd concentration (BCR1+2) during the first few week of the soil pot experiment. Based on this, a four-month pot experiment of sugarcane (Saccharum officinarum L.) cultivation was further conducted to determine the effect of these waste-products on sugarcane growth, metal accumulation in sugarcane, and fractionation of Cd and Zn in soils by the BCR sequential extraction. Two studied soils (LCdS and HCdS) showed different results. LCdS showed the improved sugarcane biomass production; 6 and 3-fold higher for the aboveground parts (from 8.46 to 57.6 g plant-1) and root (from 2.10 to 6.59 g plant-1), respectively as compared to non-amended soil, while no positive effect was observed in HCdS. There was no significant difference in metal uptake by sugarcane among different treatments in LCdS (0.44 to 0.52 mg Cd kg-1 and 39.9 to 48.1 mg Zn kg-1), however, the reduction of the most bioavailable Cd concentration (BCR1+2) in the treated soils (from 35.4% to 54.5%) and the transformation of Cd into organic-matter bound fraction (BCR3) at the end of the pot experiment highlighted the beneficial effects of these waste-products in promoting the sugarcane growth and Cd stabilization in LCdS. Alternatively, the addition of single BA and FC (3% w/w) to HCdS contributed to the reduction of Cd uptake in aboveground part of sugarcane (61.9% and 48.9%, respectively) and bioavailability of Cd (BCR1+2) in the treated soils, but not significantly at *p<0.05 (6.8% and 4.0%, respectively). No metal toxicity visually seen in both studied soils and low metal translocation to sugarcanes was observed as indicated by low translocation index (TF<1). The results from this study could provide useful information for the recycling sugarcane waste-products generated from ethanol production plant on agricultural lands for improving sugarcane productivity and predicting metal mobility in the future use.