Assessment of toxicity of the untreated and Pleurotus ostreatus treated olive mill wastewater by using microbiotests

Abstract

Toxicity of raw and biotreated olive mill wastewater (OMW) was tested using three organisms, Daphnia pulex, Thamnocephalus platyurus and zebrafish (Danio rerio). Untreated samples demonstrated LC50 values of 1.27%, 0.96% and 0.48% v/v against the aforementioned organisms respectively. After treatment withthe white rot fungi Pleurotus ostreatus, 50% and 56% reduction in toxicity values were observed for Thamnocephalus platyurus and zebrafish respectively, but samples were categorised as ‘very toxic’. A significant reduction in phenols (53%), lignin (74%) and tannin (73%) as well as a differentiation in the impact of the physicochemical parameters on toxicity between the two groups of samples was detected. Toxicity values of untreated samples against the first two aforementioned tests were highly related to phenols and tannins, whereas of treated samples, only to ammonium and phenols. According to the present study, OMW treatment with Pleurotus ostreatus, despite the significant reduction in the toxic contents, does not produce effluents environmentally acceptable for safe disposal.