Anatomy of chemically enhanced sewage settling by particle size distribution analysis

Abstract

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.

Impact of rainwater intrusion on wastewater characterization and performance of nutrient removal activated sludge process

“…Obviously, this also requires generation of experimental data related to biodegradation characteristics for each case. This approach involving the accord between experimental data and system modeling is well demonstrated in the literature 14‐17 …”

“…This approach involving the accord between experimental data and system modeling is well demonstrated in the literature. [14][15][16][17] Rainwater intrusion and mixing with sewage in the influent stream before treatment also should be recognized as an equally significant issue. Aside from the increase in the treated flow rate under wet weather conditions, runoff mixing modifies the magnitude of selected design parameters and the pollutant loads.…”

Retrofitting a poorly designed system into a full performing nitrogen‐removal activated sludge process—a scientific challenge

“…The implementation of the activated sludge process immediately after its invention required engineering common sense and ingenuity associated with successful applications; the accumulated experience gradually developed an empirical expertise, which proved to be satisfactory for organic carbon removing system configurations. [27][28][29] Although research efforts continually explored and uncovered the fundamental principles of nutrient removal, reported novel information was either diverted to formulate mathematical models establishing the basis for rational system design approach or, to formulate design prescriptions. The latter was evidently more attractive because it simplified related engineering work a great deal, to following the recipe without any fundamental background.…”