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The aim of this study is to assess the effects of fulvic acid and iron oxide on the Fe2+ and Mn2+ removal by an aerated-submerged membrane system. To construct empirical models for the relationship, polynomial regression method is applied. Ultrafiltration hollow fiber membrane module is submerged into aeration tank. The pressure changes in the membrane system are continuously monitored by means of pressure gauge. Dissolved organic carbon, UV254, iron and manganese concentrations are measured in the raw, unfiltered and filtered waters. While iron oxide's presence increases the removal efficiency of Fe2+ and Mn2+, high concentration of fulvic acid affects adversely. The relationship between these contaminants and membrane fouling is investigated. Also, in order to model the relationship, regression analysis using least squares (LS) approximation method is performed. This method is based on a polynomial of degree n to compute the best approximation to data. Mathematical models are evaluated and compared to identify an adequate model to represent the flux data collected with different ingredients. The results obtained by LS show that the method is feasible. [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate oxidative precipitation of As(III) with ozone and sodium hypochlorite in Fe(II) containing water. As guideline value was achieved with both ozone and hypochlorite for 100 μg/l of initial As(III) concentration. High As removal efficiencies were achieved by dosing 2.5 and 5 times the stoichiometric amounts of hypochlorite in the presence of 10 mg/l of initial Fe(II). When the dose of hypochlorite was increased to 10 and 50 times the stoichiometric amount, similar removal efficiencies were achieved with 2.5 and 5 mg/l of initial Fe(II) concentrations. When ozone was dosed at 10 times the stoichiometric amount, 2.5 mg/l of initial Fe(II) presence was sufficient to meet As standard. Simultaneous oxidation and co-precipitation results gave an almost perfect fit to Langmuir isotherm for ozone (r² ≈ 0.99). The value of r2 was found as 0.87 for hypochlorite. It was concluded that simultaneous oxidation of As(III) and Fe(II) by ozone and hypochlorite was an effective option to remove low level As(III) from water. As guideline value was not achieved either by ozone or by hypochlorite for high As(III) concentration, even with 10 mg/l of initial Fe(II) existence. Supplemental Fe(II) addition can be taken into consideration to overcome this limitation. [ABSTRACT FROM AUTHOR]

The removal of arsenic was investigated by four types of thin-film polyamide nanofiltration (NF) (NF270, NF90) and reverse osmosis (RO) (XLE, BW30) membranes in a flat-sheet module. The influence of membrane types, pressure, pH, and pre-oxidation step on the removal of arsenic (As(III)) was investigated. Initial As(III) concentration was 100 μg/l for all of the experiments. Flux was determined over a pressure range of 3.5–10 bar for both NF and RO membranes. Experiments were conducted at pH 3.5, 5, 7.5, and 10 to evaluate the effect of pH on As(III) removal. The impact of pre-oxidation and oxidant concentrations on As(III) removal were also evaluated. It was found that the percentage of As(III) removal of RO membranes were in the range of 97–99 for all transmembrane pressure applied. In the range of operating conditions, As(III) and As(V) rejection were found almost equally good by RO membranes. RO permeate met the WHO and Turkish standard for arsenic. Pre-oxidation step improved the rejection performance of NF. Nevertheless, NF permeate did not meet the standards in the range of operating conditions. [ABSTRACT FROM PUBLISHER]