ABSTRACT
The article analyzes integrated ultrafiltration (UF) and nanofiltration (NF) processes for potato processing wastewater treatment for the purpose of which a laboratory filtration system for flat sheet membranes with the effective surface area of 1.4 × 10-2 m2 (UF: polysulfone, cut-off: 10,000 Da; NF: polypiperazine amide, cut-off: 150-300 Da) was used. As part of the study, the effect of the transmembrane pressure of UF (0.2 MPa and 0.4 MPa) and NF (1.0 MPa and 1.8 MPa) on the permeate flux and rejection coefficient was investigated and the impact of sewage preparation methods on the degree of pollution reduction was determined. Moreover, a method for a fouling layer removal from the UF membranes is also proposed. The results of the analyses conducted by the authors show that the pretreatment stage offers additional advantages to TSS and turbidity removal. In both cases (0.2 and 0.4 MPa), UF used after the pretreatment process resulted in a 97-99% reduction in these impurities. The analysis of the determined rejection coefficients shows that the use of NaOH and H2O2 for the regeneration of the UF membrane has a positive effect on filtration efficiency. Regarding NF, the rejection coefficients for most tested parameters were higher for the 1.8 MPa process compared to 1.0 MPa, and approximately 80% of water was recovered.
ABSTRACT
In this paper, the response surface methodology (RSM) was proposed for studying the synergistic extraction of chromium(III) ions by double-carrier supported liquid membrane (DCSLM) with organophosphorus carriers (D2EHPA/Cyanex272). At first, the optimization method of "one-factor-at-a-time" was adopted for determination of the best conditions for Cr(III) extraction by SLM with only one carrier (D2EHPA). The optimum/threshold D2EHPA concentration in the membrane phase increased linearly with initial concentration of Cr(III) ions in the feed phase. After the addition the second carrier (Cyanex272), the synergistic effect was observed. The largest percentage of extraction and the shorter time was obtained. The optimization of the synergistic extraction in DCSLM system by RSM using Box-Behnken design (BBD) for three variables (concentration and proportions of the carriers, initial concentration of Cr(III), and time of the process) was studied. The statistical model was verified with the analysis of variance (ANOVA) for the response surface quadratic model. The reduced quadratic model showed that the predicted values were in agreement with those obtained experimentally, as well as the fact that the concentrations and proportions of the carriers had a significant influence on the response. The developed model was considered to be verified and can be used to predict the optimal condition for the chromium ions extraction.
ABSTRACT
This paper describes the problem of recovery and reusing chromium from aqueous solutions. The authors studied a novel double-carrier supported liquid membrane system (DCSLM) with di(2-ethylhexyl) phosphoric acid (D2EHPA) and bis(2,4,4-trimethyl) phosphinic acid (Cyanex272) as a carrier of Cr(III) ions as a method to separate chromium (III) from acid solutions. As a result, they confirmed that the presence of two carriers in the DCSLM with the most effective carrier concentration ratios, leads to approximately three times shorter pertraction, compared to a process conducted with the D2EHPA only. It was found that synergistic effect is independent of the initial concentration of chromium in the feed solution. Higher initial concentrations of Cr(III) ≥ 0.01 mol dm-3 cause high 'exhaustion' of active carrier molecules at the interface. Moreover, the authors observed the increase in viscosity in the membrane phase and process inhibition. It was found that efficiency of separation of chromium ions from aqueous solutions using a liquid membrane depends on the transport rate for these ions in the membrane (ions pertraction). Therefore, it was concluded that the pertraction stage of the Cr(III) ions limits the efficiency of the whole separation process.
