Physicochemical analysis, toxicity assessment and nutrition source potential of sugarcane distillery spent wash

Abstract

Sugarcane molasses-based ethanol industries in Sri Lanka generate large volumes of high strength spent wash, causing severe environmental issues. The potential toxicity of spent wash on biological systems and the possibility of using it as a nutrition source in agriculture has been given less attention in Sri Lanka. The present study was conducted to assess the physicochemical characteristics of the raw spent wash and possible cytogenotoxic effects of diluted spent wash using a plant-based bioassay with Allium cepa (common onion). Further, to evaluate the potential of raw spent wash as a liquid nutrition source to improve the growth of commonly grown vegetable variety, tomato (Solanum Lycopersicum). Selected physicochemical parameters of raw spent wash collected from the distillery industry of Lanka Sugar Company (Pvt) Ltd, Pelwatta, were evaluated using APHA (2017) standard procedures. Toxicity assessment was carried out after exposure of Allium cepa bulbs to diluted spent wash (1:8) along with aged tap water (negative control) following standard protocols. The tomato crop experiment was conducted as an open field experiment using agricultural guidelines provided by the Department of Agriculture with certified organic fertilizer as positive control and tap water as a negative control. Growth morphometric attributes of the plants and fruits were monitored for 60 days. The data were statistically analyzed using univariate statistical methods. The physicochemical analysis revealed that the spent wash is highly acidic with high EC (21.93 ± 0.09 mS/cm), COD (92,101 ± 0.33 mg/L), BOD (26,116 ± 2.33 mg/L)TSS (4,076 ± 0.55 mg/L), TDS (68,656 ± 0.13 mg/L), Nitrate (255 ± 0.04 mg/L) and phosphate (38 ± 0.07 mg/L), and contained heavy metals viz. Cd, Cu, Ni, Zn, As and Mn and K in trace amounts. Significantly decreased root growth was found in Allium roots exposed to diluted raw spent wash with the highest root growth delay (92%) after two days of exposure compared to the negative control (p < 0.05). The mitotic index did not show any difference in all exposure conditions. Significantly increased nuclear abnormalities, including micronuclei, nuclear buds, binuclei and condensed nuclei, were observed in root tip meristematic cells of diluted spent wash compared to the negative control (p < 0.05). Among growth-related morphometric attributes of tomato plants treated with different spent wash doses (0.5, 1.5, 2.5, 5.0, 7.5 and 10 mL), shoot lengths, the number of leaves and number of buds and flowers were found to have less significant variations. In contrast, other treatment categories recorded significantly reduced fresh fruit weight compared with the positive control (p < 0.05). Measured fresh fruit weight was more favourable toward high-end doses. However, this should be confirmed by repeated scientific studies. Results of the experiments reflect that the raw spent wash may have a cytogenotoxic effect, and the spent wash may use as a nutrition supplement by mixing with other organic ingredients. Further experiments for different crops, soil testing, and frequent biological effects monitoring are recommended to verify the spent wash's nutritional use and toxic effects