Parametric studies during the removal of ammonia by membrane contactor with various stripping solutions.

Although membrane contactors (MCs) have been recognized to be an efficient approach for the removal of ammonia from water streams, factors affecting the MCs performance were not clearly investigated. In this study, the effects of stripping solution chemistry (acid types and concentration), feed solution chemistry (pH, temperature, and ammonia concentration), and stages of MCs system have been comprehensively evaluated. Interestingly, the type of stripping solutions significantly affected the removal of ammonia, and the comparative effectiveness were in the order of H3PO4 > H2SO4 > HCOOH. However, the concentration of stripping solutions and ammonia in the feed has little impact to the performance of MCs. Among the feed solution chemistry, pH and temperature were the most crucial factors for ammonia removal in MCs, because the increase of pH and temperature enhanced the free ammonia fraction in the solution and facilitated the mass transfer through pores. At the absorbent concentration of 0.5 M H3PO4, pH of 10, and temperature of 40 °C, single-stage MCs could achieve 51% of ammonia removal within 40 s, and the ammonia removal rate in two-stage MCs reached 90% at the 1.5 min of hydraulic retention time (HRT). The results suggested the superior feasibility of multi-stage MCs system compare to the conventional stripping processes for the removal of ammonia in various waste or wastewater.

Novel method for the facile control of molecular weight cut-off (MWCO) of ceramic membranes.

This study demonstrates a simple and novel preparation method to prepare ceramic nanofiltration membranes with a precise and tunable molecular weight cut-off (MWCO) by packing variously sized nanoparticles into existing membrane pores. As a result, ceramic membranes with a MWCO from 1000 Da to 10,000 Da were successfully prepared with the narrow distribution of the pore size after the filtration-coating process. In addition, the effective porosity of the ceramic membranes was calculated from the results of the membrane properties by the Hagen-Poiseuille equation which fit within the range of the sphere packing theory from 17.3% to 41.8%. Furthermore, the results of nonlinear curve fitting between the MWCO and the nanoparticle size show a high accuracy, which implies that the MWCO of the ceramic membranes can be predicted using the curve fitting model with variously sized nanoparticles in the filtration-coating process. In conclusion, the novel filtration-coating method enables precise pore control and provides a tunable MWCO to ceramic membranes by preparing various sizes of nanoparticles.

The impact of gamma-irradiation from radioactive liquid wastewater on polymeric structures of nanofiltration (NF) membranes.

In this study, the impacts of gamma-irradiation from the low- and intermediate-level liquid radioactive wastewaters (LILW) to polyamide (PA) structures of nanofiltration (NF) membranes were investigated. As the gamma-irradiation increased to 300 kGy in the aqueous solution at 5 bar, both the salt rejection and the water permeability of NF membranes were decreased from 95.6 ±â€¯0.1%-74.6 ±â€¯0.5%, and from 33.7 ±â€¯0.3 LMH to 21.4 ±â€¯0.5 LMH, respectively. The surface free energy and Young's modulus of the membrane indicated the decrease in hydrophilicity and the increase in fragility of PA structure after gamma-irradiation. X-ray photoelectron spectroscopy and the streaming potential analysis exhibited that the gamma-irradiation resulted the increase in the cross-linked portion of the amide bonding from 28% to 45% due to the gamma-induced new bonding between unbound carboxylic groups and amine groups. Nuclear magnetic resonance analysis confirmed that the poly(p-phenylene) in polyamide structure were changed to poly(cyclohexane) and poly(cyclohexene) by hydrogen radical disproportionation generated from the gamma-irradiated water, and it is responsible to the increase of the cross-linked PA structures. The decrease in salt rejection and water permeability is attributed to the aging of PA structures by gamma-irradiation, thus, should be carefully monitored during the treatment of LILW using NF membrane processes.

Comprehensive reuse of drinking water treatment residuals in coagulation and adsorption processes.

While drinking water treatment residuals (DWTRs) inevitably lead to serious problems due to their huge amount of generation and limitation of landfill sites, their unique properties of containing Al or Fe contents make it possible to reuse them as a beneficial material for coagulant recovery and adsorbent. Hence, in the present study, to comprehensively handle and recycle DWTRs, coagulant recovery from DWTRs and reuse of coagulant recovered residuals (CRs) were investigated. In the first step, coagulant recovery from DWTRs was conducted using response surface methodology (RSM) for statistical optimization of independent variables (pH, solid content, and reaction time) on response variable (Al recovery). As a result, a highly acceptable Al recovery of 97.5 ± 0.4% was recorded, which corresponds to 99.5% of the predicted Al recovery. Comparison study of recovered and commercial coagulant from textile wastewater treatment indicated that recovered coagulant has reasonable potential for use in wastewater treatment, in which the performance efficiencies were 68.5 ± 2.1% COD, 97.2 ± 1.9% turbidity, and 64.3 ± 1.0% color removals at 50 mg Al/L. Subsequently, in a similar manner, RSM was also applied to optimize coagulation conditions (Al dosage, initial pH, and reaction time) for the maximization of real cotton textile wastewater treatment in terms of COD, turbidity, and color removal. Overall performance revealed that the initial pH had a remarkable effect on the removal performance compared to the effects of other independent variables. This is mainly due to the transformation of metal species form with increasing or decreasing pH conditions. Finally, a feasibility test of CRs as adsorbent for phosphate adsorption from aqueous solution was conducted. Adsorption equilibrium of phosphate at different temperatures (10-30 °C) and initial levels of pH (3-11) indicated that the main mechanisms of phosphate adsorption onto CRs are endothermic and chemical precipitation; the surfaces are energetically heterogeneous for adsorbing phosphate.

Decolorization of Acid Orange 7 by an electric field-assisted modified orifice plate hydrodynamic cavitation system: Optimization of operational parameters.

In this study, the decolorization of Acid Orange 7 (AO-7) with intensified performance was obtained using hydrodynamic cavitation (HC) combined with an electric field (graphite electrodes). As a preliminary step, various HC systems were compared in terms of decolorization, and, among them, the electric field-assisted modified orifice plate HC (EFM-HC) system exhibited perfect decolorization performance within 40 min of reaction time. Interestingly, when H2O2 was injected into the EFM-HC system as an additional oxidant, the reactor performance gradually decreased as the dosing ratio increased; thus, the remaining experiments were performed without H2O2. Subsequently, an optimization process was conducted using response surface methodology with a Box-Behnken design. The inlet pressure, initial pH, applied voltage, and reaction time were chosen as operational key factors, while decolorization was selected as the response variable. The overall performance revealed that the selected parameters were either slightly interdependent, or had significant interactive effects on the decolorization. In the verification test, complete decolorization was observed under statistically optimized conditions. This study suggests that EFM-HC is a useful method for pretreatment of dye wastewater with positive economic and commercial benefits.