Assessing the impact of hydraulic conditions and absence of pretreatment on the treatability of pesticide formulation plant wastewater in a moving bed biofilm reactor

Abstract

This study examined the treatability of a wastewater composed by industrial pesticide formulation and sanitary wastewaters using a bench scale moving bed biofilm reactor (MBBR). Throughout 742 days and 7 operational phases, tests were performed for several experimental conditions, including: 3 and 6 h hydraulic retention time (HRT); variation of the industrial effluent proportion from 2 to 8% v/v; utilization of various lots of the pretreated pesticide effluent or its raw form. Distinct responses were obtained regarding removal of chemical oxygen demand (COD) (varying from 48 to 84 %) and ammoniacal nitrogen (varying from 36 to 95 %), whereas sludge production remained always low (average 0.18 kg/(m3.d)). Maximum specific removal rates obtained in batch trials showed that the pretreatment of the pesticide wastewater is truly beneficial for keeping higher biofilm activities and preventing nitrification inhibition. Nevertheless, even in the absence of pretreatment, the pesticide wastewater showed high biodegradability, corresponding to 65 % of soluble COD for the operational conditions. Overall, it was shown that the MBBR, at HRT of 6 h and media filling ratio of 50 %, is a viable alternative for the secondary treatment of highly polluted pesticide wastewater even in the absence of pretreatment while preserving a biofilm with good depuration capacity, diverse microfauna and volatile fraction consistently over 85 %.