Low-temperature inhibition of the activated sludge process by an industrial discharge containing the azo dye acid black 1.

A municipal wastewater treatment plant (WWTP) receiving industrial dyeing discharge containing acid black 1 (AB1) failed to meet NH(3) and BOD(5) discharge limits, especially for NH(3) during the winter. Dyeing discharge was combined with domestic sewage in volumetric ratios reflecting the range received by the WWTP and fed to sequencing batch reactors at 22 and 7 degrees C. Analysis of the various nitrogen species revealed complete nitrification failure at 7 degrees C with more rapid nitrification failure as the dye concentration increased. Slight nitrification inhibition occurred at 22 degrees C: NH(3) removal decreased from 99.9% for the control compared to only 97.0% removal with dye addition. Dye-bearing wastewater also reduced COD removal by half at 7 degrees C and by one-fifth at 22 degrees C, and increased effluent TSS nearly three-fold at 7 degrees C. Activated sludge quality at 7 degrees C deteriorated after exposure to AB1, as indicated by excessive foaming and the presence of filamentous bacteria and by a decrease in endogenous and exogenous oxygen uptake. Decreasing AB1 loading resulted in partial activated sludge recovery. Eliminating the dye-bearing discharge to the full-scale WWTP led to improved performance bringing the WWTP into compliance with discharge limits.

Design and performance characterization strategy using modeling for biofiltration control of odorous hydrogen sulfide.

Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S). Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures. Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration. Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time. However, a higher biofilter temperature results in lower effluent H2S concentrations. Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered. This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.

Optimization of biofiltration for odor control: model calibration, validation, and applications.

A dynamic model that describes the biofiltration process for hydrogen sulfide removal from wastewater treatment plant air emissions was calibrated and validated using pilot- and full-scale biofilter data obtained from the Cedar Rapids (Iowa) Water Pollution Control Facilities. After calibration, the model was found to predict the dynamic effluent concentrations of the pilot- and full-scale biofilters well, with the measured data falling within 58 to 80% of the model output values. In addition, the model predicted the trend of the field data, even under field conditions of changing input concentration and at effluent concentrations below 1 ppm by volume. The model demonstrated that increasing gas residence time and temperature and decreasing influent concentration decreases effluent concentration. In addition, model simulations showed that a longer residence time is required to treat dynamic loading increases, indicating that biofilter design should account for the maximum influent concentration. These results can be used to help design and operate biofilters for controlling odorous and hazardous air emissions.