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During an iron-electrocoagulation (Fe-EC) process, floc formation is essential for achieving high contaminants removal. Thus, the complete oxidation of the Fe2+ dosed as coagulant is a critical step for ferric oxides flocs formation. Since the fluctuation in the quality of the influent wastewater affects the kinetics of Fe2+ oxidation, the estimation of optimal operating conditions (i.e. the retention time, dissolved oxygen (DO) concentration, etc.) for high Fe2+ oxidation is required. In this study, the kinetics of Fe2+ oxidation was simulated using PHREEQC software by theoretically optimizing, validating and improving the previously published kinetic models. During model simulation, the process parameters were varied from low to high ranges: Fe2+ dosage (10–100 mg/L) and retention times under the influence of changing pH (7.5–8.2), temperature (12–22 °C), alkalinity (5–10 mEq/L) and initial DO (8.6–10.5 mg/L). Fe2+ oxidation rate was more affected by pH variations in the influent than by temperature variations. A pH increase (+0.4 to +1.7 pH units) was observed due to the low wastewater alkalinity, promoting high Fe2+ oxidation rates. To ensure optimum Fe2+ oxidation levels (≥98%), a minimum retention time of 20 minutes was estimated. Finally, the residual DO concentration should be >3.5 mg/L to avoid a decrease in the oxidation rate. This study contributes to the ongoing research in the field of physico-chemical wastewater treatment with EC by establishing the optimal process parameters required for system optimization and process scalability.

Membrane bioreactor (MBR) systems need to be controlled in order to extend the period of effective performance. The local critical flux (LCF) concept is a good starting point for a modelbased control strategy. Use of a novel linearly reparametrized recursive parameter estimation technique illustrated that, instead of a constant, the transmembrane pressure parameter is timevarying and obeying a hyperbolic relationship with respect to time. The hyperbolic relationship, which allows a physical interpretation, was substituted in the original LCF model. The modified LCF model was subsequently used in a linearly reparametrized recursive state estimator for the estimation of mass of deposited solutes and the number of open pores. Copyright © 2015 IFAC

The potential of a membrane bioreactor (MBR) system to treat Fischer-Tropsch (FT) reaction water from gas-to-liquids (GTL) industries was investigated and compared with the current treatment system: a conventional activated sludge system followed by an ultrafiltration (CAS-UF) unit. The MBR and the CAS-UF systems were inoculated with municipal activated sludge and operated in parallel for 645 days with four interruptions using synthetic FT reaction water. Both treatment systems achieved a removal efficiency of 98 ± 0.1% within 60 days after inoculation, the COD influent concentration was 1014 ± 15 mg L−1. This suggests that MBRs form a suitable alternative to CAS-UF systems for the treatment of FT reaction water from the GTL industries. Moreover, the total fouling rates (Ft) of the membranes used from day 349 till the end were assessed. The average Ft was 7.3 ± 1.0 1010 m−1 day−1 for CAS-UF membranes and 2.8 ± 00.7 1010 m−1 day−1 for MBR-MT membranes. This indicates that MBR systems for the treatment of FT reaction water from the gas-to-liquids industries are less prone to fouling than CAS-UF systems.

Temperature is known to influence the biological performance of conventional activated sludge systems. In membrane bioreactors (MBRs), temperature not only affects the bioconversion process but is also shown to have an effect on the membrane performance. Four phenomena are generally reported to explain the higher resistance for membrane filtration found at lower temperatures: (1) increased mixed liquor viscosity, reducing the shear stress generated by coarse bubbles, (2) intensified deflocculation, reducing biomass floc size and releasing EPS into the mixed liquor, (3) lower backtransport velocity and (4) reduced biodegradation of COD. Although the higher resistance at low temperatures has been reported in several papers, the relation with supernatant composition has not been investigated before. In this paper, the composition of the soluble fraction of the mixed liquor is related to membrane performance after exposing the sludge to temperature shocks. Flux step experiments were performed in an experimental system at 7, 15, and 25° Celsius with sludge that was continuously recirculated from a pilot-scale MBR. After correcting the permeate viscosity for temperature, higher membrane fouling rates were obtained for the lower temperature in combination with low fouling reversibility. The soluble fraction of the MBR mixed liquor was analysed for polysaccharides, proteins and submicron particle size distribution. At low temperature, a high polysaccharide concentration was found in the experimental system as compared to the MBR pilot. Upon decreasing the temperature of the mixed liquor, a shift was found in particle size towards smaller particles. These results show that the release of polysaccharides and/or submicron particles from sludge flocs could explain the increased membrane fouling at low temperatures.

Extracellular polymeric substances (EPS) are generally negatively charged polymers. Membrane fouling in membrane bioreactors (MBRs) by EPS is therefore influenced by the water chemistry of the mixed liquor (calcium concentration, foulant concentration and ionic strength). We used alginate as a model compound to study this fouling in detail. Flux-step experiments were performed with a flat sheet test cell, varying the free calcium concentration, total ionic strength and alginate concentration. There was a strong relation between calcium concentration and fouling rate. An increased ionic strength had no impact on fouling rate in low fouling experiments, but decreased fouling with 66–72% at high fouling conditions. Reversibility of the fouling decreased with increasing calcium concentrations to values as low as 3%. Several fouling mechanisms were identified and the reducing effect of increased ionic strength on alginate fouling was explained by competition for carboxyl groups on the alginate polymer. Further research will focus on the interaction of polysaccharides with other compounds typically present in the MBR supernatant (e.g. proteins, humic acids and sludge particles) and a more detailed analysis of the fouling layer.

BioDeNO(x), a novel technique to remove NOx from industrial flue gases, is based on absorption of gaseous nitric oxide into an aqueous Fe(II)EDTA(2-) solution, followed by the biological reduction of Fe(II)EDTA(2-) complexed NO to N-2. Besides NO reduction, high rate biological Fe(III)EDTA(-) reduction is a crucial factor for a succesful application of the BioDeNO(x) technology, as it determines the Fe(II)EDTA(2-) concentration in the scrubber liquor and thus the efficiency of NO removal from the gas phase. This paper investigates the mechanism and kinetics of biological Fe(III)EDTA(-) reduction by unadapted anaerobic methanogenic sludge and BioDeNO(x) reactor mixed liquor. The influence of different electron donors, electron mediating compounds and CaSO3 on the Fe(III)EDTA(-) reduction rate was determined in batch experiments (21 mM Fe(III)EDTA(-), 55 degrees C, pH 7.2 +/- 0.2). The Fe(III)EDTA(-) reduction rate depended on the type of electron donor, the highest rate (13.9 mM h(-1)) was observed with glucose, followed by ethanol, acetate and hydrogen. Fe(III)EDTA(-) reduction occurred at a relatively slow (4.1 mM h(-1)) rate with methanol as the electron donor. Small amounts (0.5 mM) of sulfide, cysteine or elemental sulfur accelerated the Fe(III)EDTA(-) reduction. The amount of iron reduced significantly exceeded the amount that can be formed by the chemical reaction of sulfide with Fe(III)EDTA(-), suggesting that the Fe(III)EDTA(-) reduction was accelerated via an auto-catalytic process with an unidentified electron mediating compound, presumably polysulfides. formed out of the sulfur additives, Using ethanol as electron donor, the specific Fe(III)EDTA(-) reduction rate was linearly related to the amount of sulfide supplied. CaSO3 (0.5-100 mM) inhibited Fe(III)EDTA(-) reduction, probably because SO32- scavenged the electron mediating compound. 3