Abstract
Wastewater from confined animal feeding operations (CAFOs) can interfere significantly with the natural nitrogen and phosphorus balance in the environment if not treated adequately prior to disposal. In this work, a modified Lutzak-Ettinger (MLE) consisting of sequential pre-denitrification/ nitrification was used to determine the effects of nutrient loading rates and hydraulic retention times (HRT) on total nitrogen (TN) and organic carbon (TOC) removal from swine wastewater. MLE reactor was continuously fed swine wastewater for over 205 days using different recycle ratios (Rr) and HRT. Higher TN and TOC removal efficiencies (90.7% and 96.1%, respectively) were obtained when recycling effluent from the nitrification tank (4.5:1) combined with effluent from the final clarifier (1:1). Removal efficiencies of 96% for TOC and 90% for TN were obtained for the maximum loading rates of 0.56 gTN L-1 d-1 and 2.15 g TOC L-1 d-1, respectively. TN and TOC removal rates were achieved with HRT in as little as 3.5 days. Overall, MLE was a robust bioprocess withstanding variations in wastewater physical-chemical composition and/or changes in operational conditions without significant impairment of N and TOC removal efficiencies.
Highlights
Concentrated animal feeding operations (CAFOs) are increasingly being used for the enhancement of swine production
modified Ludzack-Ettinger (MLE) reactors start up NH3-N concentrations in the batches were continuously monitored over time to account for significant losses
Measured NH3-N concentrations at the MLE effluent were higher at the beginning of the experiments, probably due to the lack of significant nitrifying-specific biomass (Figure 2)
Summary
Concentrated animal feeding operations (CAFOs) are increasingly being used for the enhancement of swine production. Different system configurations are considered including intermittent aeration, the use of selective membranes, sequencing batch reactors (Lee and Han, 2012), and/or the modified Ludzack-Ettinger (MLE). The MLE, known as anoxic pre-denitrification process (Rajagopal et al, 2011; Hafez et al, 2010), was initially proposed by Ludzack and Ettinger for treatment of municipal sewage (Ludzack and Ettinger, 1962). In the MLE, the oxidized nitrogen species (NOx = NO2- + NO3-) are recycled into an anoxic reactor to serve as electron acceptors for heterotrophic denitrification. MLE has been used to remove TOC and nitrogen from a wide variety of effluents, including landfill leachate (Hafez et al, 2010) and wastewaters from animal farming (Castrillón et al, 2009; Vanotti et al, 2009)
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