Treatment of agro-industrial effluents with silver nanoparticles to reduce chemical oxygen demand and microorganisms

Sugarcane vinasse is a highly polluting by-product generated in sugarcane mills during the distillation process to produce ethanol. The vinasse is mainly composed of water with acidic pH and micronutrients for plants. Chemical oxygen demand (COD) is a parameter associated to the polluting load of liquid waste. This work investigated the treatment of sugarcane vinasse with silver nanoparticles (AgNPs) to reduce COD and amounts of colony forming units (CFU) in vinasse. AgNPs were synthesized from the chemical reduction of silver nitrate (AgNO3) using sodium borohydride (NaBH4), later confirmed by yellowish staining and UV-Vis spectrophotometry with detection of the plasmonic peak at 400 nm. The vinasse in natura showed a COD of 32,975 mg O2/L and the addition of 21.6 mu g.mL-1 of Ag reduced CFU by 66.70% after 5 days. AgNPs also inhibited the proliferation of microorganisms and thus presented as an alternative for wastewater treatment of the sugarcane mills.