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: This study investigated the anatomy of organic carbon (as chemical oxygen demand, COD) removal from sewage through chemically assisted settling, by means of particle size distribution (PSD) analysis: it showed which size fractions were affected, aside from the particulate COD. The experiments were conducted on the effluent of the existing preliminary treatment plant before deep-sea discharge into the Bosphorus. FeCl 3 , alum and polyaluminum chloride (PAC) were used as coagulants at different doses. The performance of the coagulants on the effluent COD was interpreted with PSD.RESULTS: PAC at 25 mg L −1 , selected as the optimum coagulant, reduced COD below soluble COD level, to around 145 mg L −1 , with an overall efficiency of more than 70%. Although chemical settling was most effective on particulate COD at >450 nm, it also provided a COD removal of 28% in 220-450 nm of the colloidal range and 40% in 13-220 nm of the range, representing soluble hydrolysable COD. The lowest removal rate was observed in the soluble range, consisting of readily biodegradable (only 5%) and a part of the inert COD (<2 nm) identified as 12%twice as high as ordinary domestic wastewaters, with only 1%.CONCLUSION: PSD and COD fractionation analyses were instrumental in depicting the potential of chemically enhanced settling to reduce COD in the soluble range, identifying the distribution of remaining COD fractions in different size intervals. The results also suggested a novel treatment process with additional membrane filtration, namely membrane chemical reactor, (MCR), reflecting a potential for replacing the conventional activated sludge process.
BACKGROUND:The study defined a sustainable management scheme to eliminate the toxic impact of extreme salinity on the ecology and performance of an activated sludge process. The scheme was implemented on a plant treating pickle plant effluents involving significant flow and salinity transients. It was conducted in two phases. Firstly, the plant was operated without attenuating extreme salinity transients, enabling observation of all adverse impacts on the microbial ecology. The second phase was implemented with a new management scheme tempering all salinity gradients revealing the recovery of the microbial ecology into a stable and sustainable state. RESULTS: Initially, the microbial community could not cope with rapid salinity increase and exhibited significant changes resulting in the predominance of filamentous microorganisms, disruption of the floc structure and almost total loss of eukaryotic microorganisms. Settling problems and deterioration of effluent quality were observed, followed by plasmolysis and repeated total loss of the biomass. The new waste management strategy allowed only transients limited to ±500 ∼S cm −1 in the influent; in this way, the microbial ecology steadily improved. The effluent chemical oxygen demand could be maintained below 80-90 mg L −1 with no appreciable particulate matter escape. CONCLUSIONS: Results identified sharp salinity transients as the key factor triggering total destruction of activated sludge. The novel scheme provided conclusive evidence that a stable microbial community could be maintained even when continuously exposed to a salinity level of around 10 000 ∼S cm −1 in the reactor, provided that variations remained limited to ±500 ∼S cm −1 , ensuring satisfactory effluent quality.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.