Bench-Scale Evaluation of Activated Carbon Treatment for the Reduction of Acute Ceriodaphnia Dubia Toxicity of Diazinon
Creators: name: D'Amato, Victor A.
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 1994

description: The focus of this work was on the direct laboratory evaluation of activated carbon treatment processes for their efficacy in reducing the acute toxicity of diazinon, a common organophosphorus pesticide to Ceriodaphnia dubia, a common toxicity test organism. Powdered Activated Carbon (PAC) and Granular Activated Carbon (GAC) processes were evaluated for their toxicity reduction potential using direct measurements of residual toxicity and effluent toxicity for batch equilibrium and Rapid-Small-Scale Column Tests (RSSCT), respectively. The results of these bench-scale process screening experiments utilized in this project may be used during the initial stages of a Toxicity Reduction Evaluation (TRE), as set forth by the US Environmental Protection Agency (EPA), perhaps as a supplement or replacement for the traditional Toxicity Identification Evaluation (TIE) protocol. Direct process screening may be more feasible and economical for some municipal wastewater treatment plants (WWTPs), particularly those with a complex influent. PAC batch equilibrium experiments were conducted and adsorption isotherm relationships developed using residual concentration (for samples in the mg/L range), and residual acute toxicity (for samples in the μ/L range) to measure treatment effectiveness. During PAC experiments, it was discovered that the activated carbon itself contributed to sample toxicity at PAC dosages of 20mg/L and greater. An acid-wash procedure was therefore developed for the removal of this artifactual toxicity. RSSCTs were designed based, in part, on isotherm results and conducted in order to evaluate the dynamic breakthrough characteristics of diazinon adsorption onto GAC at high and low ranges of feed concentration using effluent concentration and acute toxicity, respectively, as measures of treatment effectiveness. The RSSCTs were successful at containing diazinon breakthrough at both concentration ranges using practical design and operating conditions for the small-scale columns, based on previously-developed scaling equations. Experimentally-obtained breakthrough curves were fit with those obtained using the homogenous surface diffusion model (HSDM). The quantitative results of the bench-scale experiments were further examined for their implication for the selection of practical alternatives for full-scale municipal wastewater treatment. The effect of competitive adsorption of natural organic matter (NOM), present to a large degree in secondary treated and clarified effluent, was estimated for its effect on the experimental results obtained using organic-free reagent water. An example showing the design considerations for a full-scale GAC column adsorber for the removal of diazinon toxicity is presented, and a simple model was developed for the evaluation of the powdered activated carbon treatment (PACT) process. This model was used to evaluate the relative contributions of PAC adsorption and activated sludge biomass sorption for diazinon removal during municipal wastewater treatment.