Anaerobic Pretreatment of Agro Chemical Wastewater

An Agro Chemical Firm in the Midwest manufactures a number of products, including a naturally occurring insect control agent produced via fermentation. Expansion of the production capacity at the facility necessitated installation of a pretreatment system to ensure as to not overload the local POTW. Although most of the compounds present in the condensate are readily treated anaerobically, the fate and effect of the solvent and residual insect control agent were not well understood. Described in this paper are the sequence of steps taken to determine treatability, develop design criteria via pilot testing and initial performance of the full-scale high rate anaerobic pretreatment system installed after successful pilot testing. Driving forces behind the desire to use high rate anaerobic treatment included the potential to operate the evaporator to take more mass overhead reducing the mass of still bottoms requiring disposal, a small footprint (space is a premium at the site), low residuals (excess sludge) production by the treatment process and a small offset in fuel requirements for an air thermal treatment system in place at the site due to the biogas produced.As mentioned, the wastewater contained residual concentrations of a naturally occurring insect control agent produced via fermentation. Little was known about the effect this compound would have on anaerobic treatment. Accordingly, an anaerobic toxicity assay was conducted to assess potential inhibitory effects over a broad range of potential concentrations. No significant inhibition was observed at concentrations well above the highest concentrations historically observed in the wastewater and anticipated for the future.