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Abstract:Differing from municipal wastewater, rural wastewater in salinization areas is characterized with arbitrary discharge and high concentration of salt, COD, nitrogen and phosphorus, which would cause severe deterioration of rivers and lakes. To overcome the limits of traditional biological processes, a spiral fiber based salinity-persistent Sequencing Biofilm Batch Reactor (SBBR) was developed and investigated with synthetic rural wastewater (COD = 500 mg/L, NH stable efficiency reaching 92%, 82% and 80%, respectively. Although TP could be removed at high efficiency of 90% in low salinity conditions (from 0.0 to 5.0 g/L of NaCl), it was seriously inhibited due to nitrite accumulation and reduction of Phosphorus Accumulating Organisms (PAOs) after addition of 10.0 g/L of salt. The behavior proposed in this study will provide theoretical foundation and guidance for application of SBBR in saline rural wastewater treatment.

BACKGROUND: While various granular adsorbents have been studied for fluoride removal from water, this study focuses on the optimization of mixture proportions of volcanic rock, bentonite, corn starch and aluminum sulfate using a four-component simplex-centroid mixture design (SCMD) method to achieve preferable fluoride removal ratio and ceramsite mechanical strength. To illustrate the adsorption mechanism, a series of experiments, including adsorption isotherms, adsorption kinetics and effects of pH value and co-existing anions, was carried out. RESULTS: The synthesized adsorbent was mesoporous with 77.82% pore size distribution in the range 1.70-38.80 nm by detailed physicochemical characterization. A stable fluoride removal ratio (87.5%) was obtained in the wide pH range of 4.0-11.0, and the adsorption capacity was 10.17 mg g −1 at 298 K. The adsorbent remained high selectivity for F − in the presence of sulfate (SO 4 2− ), chloride (Cl − ) and nitrate (NO 3 − ), while carbonate (HCO 3 − ) posed a slight adverse effect on F − adsorption due to ion competition. This adsorption process was well fitted with the pseudo-second-order kinetic model and the Freundlich isotherm model. Electrostatic attraction and M + -H 2 O and M + -F ligand exchange were dominant in the adsorption mechanisms. CONCLUSION: The synthesized ceramsite adsorbent will be competitive in the application for F − removal from aquatic environments.

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