The structure of existing activated models is inherently deficient in reflecting the major role of the membrane filtration. The study developed a novel model, MASM, for the membrane activated process. The effective filtration size imposed by the membrane module, entrapping larger particles, was adopted as the basis of the proposed model. The model defines a modified form of COD fractionation that accounts for the captured COD fractions as additional model components and utilizes related mass-balance relationships. It was implemented to test the fate of soluble hydrolyzable COD and the system performance of super-fast membrane activated sludge based on real data for the characterization and process kinetics of domestic sewage and denim processing effluents. Model evaluation was carried out for parallel systems with gravity settling and membrane filtration operated at a sludge age range of 0.5–2.0 d. Results reflected significantly better performance by the super-fast membrane activated sludge system for both wastewaters, underlining that it was crucially important to account for the captured COD fractions to provide an accurate evaluation of system behavior and effluent quality. This should also be identified as the major shortcoming of the ASM models for evaluating and predicting the system performance of activated sludge configurations with membrane separation.
A new model for the activated sludge process with membrane separation is presented, based on the effective filtration size. A new size threshold is imposed by the membrane module. The model structure requires a modified fractionation of the chemical oxygen demand and includes chemical oxygen demand fractions entrapped in the reactor or in the flocs as model components. This way, it offers an accurate mechanistic interpretation of microbial mechanisms taking place in membrane activated sludge systems. Denim processing wastewater was selected for model implementation, which emphasized the significance of entrapped fractions of soluble hydrolysable and soluble inert chemical oxygen demand responsible for better effluent quality, while underlining the shortcomings of existing activated sludge models prescribed for systems with conventional gravity settling. The model also introduced particle size distribution analysis as a new experimental instrument complementing respirometric assessments, for an accurate description of chemical oxygen demand fractions with different biodegradation characteristics in related model evaluations.
BACKGROUND The study aimed to set forth a model simulation approach for an accurate calculation of denitrification potential (NDP) and selection of appropriate anoxic volume (VD) in biological nitrogen removal. Simulations utilized the characteristics of a typical sewage and the model coefficients associated with a model structure that included all relevant microbial processes. They were carried out first for a fully anoxic reactor sustained with excess nitrogen and then for a pre‐denitrification system operated with different anoxic volume ratios (VD/VT) of 0.1–0.4 when the influent nitrogen (TKN) level was set as 57 and 85 mg N L−1. RESULTS Without nitrate limitation, generated NDP could reach 37 mg N L−1 for VD/VT = 0.1 and gradually escalated to 56, 75 and 86 mg N L−1 when VD/VT was raised to 0.4. Results for the pre‐denitrification system showed the effect of nitrate limitation on both substrate removal and NDP levels: At VD/VT = 0.4, NDP associated with TKN = 85 mg N L−1 was approximately 60 mg N L−1, while it remained basically around 40 mg N L−1 with TKN = 57 mg N L−1. Simulation also indicated that the hydrolysis kinetics significantly affected NDP generation. CONCLUSION Simulation results revealed that stoichiometric estimations always underestimated NDP, recommending unnecessarily high anoxic volumes, where the oxidized nitrogen was consumed within the 20–25% portion of the provided volume. The remaining volume fraction was then totally wasted since it was forced to operate under anaerobic conditions, with practically no useful microbial activity and negligible substrate utilization. © 2019 Society of Chemical Industry
BACKGROUND This study investigated the water and pollution footprints of a dye house, which processed cotton knits, polyester (PES) knits and PES‐viscose woven fabrics. Experimental evaluation was carried out for each processing sequence. Variations in wastewater flow and quality were established as a function of the production program in the plant. A model evaluation of wastewater dynamics was performed and defined specifications of an appropriate treatment scheme. RESULTS The plant was operated with a capacity of 4300 t year−1 of fabric, which generated a wastewater flow of 403 500 m3 year−1 and a COD load of 675 t year−1. The overall wastewater footprint of the plant was computed as 91 m3 t−1 and the COD footprint as 160 kg t−1 of fabric. Depending on the fabric type, results indicated expected changes in wastewater flow between 600 and 1750 m3 day−1; in COD load between 1470 and 2260 kg day−1 and in COD concentration between 1290 and 3400 mg L−1. CONCLUSION A model simulation structured upon COD fractionation and related process kinetics revealed partial removal of slowly biodegradable COD, coupled with high residual COD, which would by‐pass treatment. Resulting biodegradation characteristics necessitated an extended aeration system, which could also enable partial breakdown of residual COD. Effluent COD could be reduced to 220–320 mg L−1 with this wastewater management strategy. © 2018 Society of Chemical Industry
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