Electrochemical reduction of Cr(VI) in the presence of sodium alginate and its application in water purification

Chromium (Cr) is used in many manufacturing processes, and its release into natural waters is a major environmental problem today. Low concentrations of Cr(VI) are toxic to human health and living organisms due to the carcinogenic and mutagenic nature of this mineral. This work examined the conversion of Cr(VI) to Cr(III) via electrochemical reduction using gold electrode in an acidic sodium alginate (SA) solution and subsequent removal of the produced Cr(III)-SA by the polymer-enhanced ultrafiltration (PEUF) technique. A solution of SA in nitric acid was used both as an electrolytic medium during the voltammetric measurements and bulk electrolysis and as an extracting agent during the PEUF technique. The electroanalysis of Cr(VI) was performed by linear sweep voltammetry in the presence of acidic SA solution to study its voltammetric behavior as a function of the Cr(VI) concentration, pH, presence of Cr(III), SA concentration and scan rate. In addition, the quantitative reduction of Cr(VI) to Cr(III) was studied through the bulk electrolysis technique.The results showed efficient reduction with well-defined peaks at approximately 0.3 V vs. Ag/AgCl, using a gold working electrode. As the pH increased, the reduction signal strongly decreased until its disappearance. The optimum SA concentration was 10 mmol/L, and it was observed that the presence of Cr(III) did not interfere in the Cr(VI) electroanalysis. Through the quantitative reduction by bulk electrolysis in the presence of acidic SA solution, it was possible to reduce all Cr(VI) to Cr(III) followed by its removal via PEUF.     

The effects of alginate microspheres on phytoremediation and growth of Lemna minor in the presence of Cd

Today, the removal of increased amount of contaminant concentrations in nature such as metals, nanoparticles, has become an essential issue to struggle with. In this paper, both the toxic effects of non-essential Cd on Lemna minor in presence of alginate microspheres and metal removal capacity of Cd-exposed L. minor and microspheres were investigated. Three test groups were constructed: group (L) containing Lemna, group (M) containing alginate microsphere and group (L?+?M) containing alginate microsphere and Lemna. Five different levels of Cd concentrations were added into these groups. Estimation models were constructed to estimate Cd removal capacities of L. minor and microspheres, and time-concentration-dependent growth (GRC) rates of both microsphere-containing and non-containing groups were modelled by regression analysis. It was seen that microspheres alone only had no positive or negative effects on Lemna growth. It was observed that, for all test groups the time-dependent growth rate has both increase–decrease trends in general. The toxicity effect of Cd on Lemna growth was reduced by adding microspheres into medium. Furthermore, the results stated that test groups containing only microspheres (M, 0–97.56%) and consortium groups (M?+?L, 0–98.26%) were slightly more successful in Cd removal process compared to Lemna (L) groups (L, 0–97.32%).     

Controlled release systems to prevent the agro-environmental pollution derived from pesticide use

Different controlled release formulations (CRFs) of isoproturon, imidacloprid and cyromazine have been studied to contribute to diminish, somehow, the problems related to the application of conventional formulations. The alginate-based CRFs were based on sodium alginate (1.90%), Technical grade (TG) isoproturon or imidacloprid (1.20%), natural bentonite (3.30%), and water (93.6%), and the lignin-based CRF was based on kraft lignin (50.0%) and TG cyromazine (50.0%). The mobility of non-formulated TG pesticides and CRFs were compared by using soil columns. The use of CRFs retard release and reduce the presence of pesticides in the leachate and, moreover, the pesticides stay in the soil longer. Sorption capacity of the soil for pesticides was measured using batch experiments. The results obtained (11.67 mg kg^{? 1} for isoproturon, 3.17 mg kg^{? 1} for imidacloprid and 0.63 mg kg^?1 for cyromazine) were in agreement with those obtained under dynamic conditions.     

配水管网中卤乙酸的研究

液氯消毒导致给水输配管网中产生消毒副产物对人体健康造成危害的问题引起了人们越来越多的关注。在对北方某城市配水管网水质大量调查的基础上,分析了卤乙酸与温度、余氯、氨氮、UV254等主要水质指标在配水管网中的变化规律。     

Maximum uptakes of cadmium on free and immobilised bacteria and actinomycetes cells

Studies of adsorption of cadmium by free bacterial and free actinomycete cells, alginate beads and immobilised bacterial or actinomycete cells in alginate beads were performed in ultrapure water. The immobilisation in alginate beads allows the survival of the microorganisms in non-ideal conditions. Here, we found the following affinity for the cadmium ion: R25 free cells<alginate beads<R25 immobilised cells<ZAN 044 immobilised cells<ZAN 044 free cells, obtained with the b Langmuir parameter. The maximum uptakes gave the series: ZAN 044 free cells<ZAN 044 immobilised cells<R25 free cells<alginate beads<R25 immobilised cells.     

Combined effects of adsorption and photocatalysis by hybrid TiO2/ZnO-calcium alginate beads for the removal of copper

The use of nanosized titanium dioxide(TiO_2) and zinc oxide(ZnO) in the suspension form during treatment makes the recovering and recycling of photocatalysts difficult.Hence,supported photocatalysts are preferred for practical water treatment applications.This study was conducted to investigate the efficiency of calcium alginate(CaAlg) beads that were immobilized with hybrid photocatalysts,TiO_2/ZnO to form TiO_2/ZnO-CaAlg.These immobilized beads,with three different mass ratios of TiO_2:ZnO(1:1,1:2,and 2:1) were used to remove Cu(Ⅱ) in aqueous solutions in the presence of ultraviolet light.These beads were subjected to three cycles of photocatalytic treatment with different initial Cu(Ⅱ) concentrations(10-80 ppm).EDX spectra have confirmed the inclusion of Ti and Zn on the surface of the CaAlg beads.Meanwhile,the surface morphology of the beads as determined using SEM,has indicated differences of before and after the photocatalytic treatment of Cu(Ⅱ).Among all three,the equivalent mass ratio TiO_2/ZnO-CaAlg beads have shown the best performance in removing Cu(Ⅱ) during all three recycling experiments.Those TiO_2/ZnO-CaAlg beads have also shown consistent removal of Cu,ranging from 7.14-52.0 ppm(first cycle) for initial concentrations of10-80 ppm.In comparison,bare CaAlg was only able to remove 6.9-48 ppm of similar initial Cu concentrations.Thus,the potential use of TiO_2/ZnO-CaAlg beads as environmentally friendly composite material can be further extended for heavy metal removal from contaminated water.     

Dye removal by eco-friendly physically cross-linked double network polymer hydrogel beads and their functionalized composites

Hydrogels have attracted large attention in wastewater treatment fields due to their low-cost and good interaction with pollutants, among which novel double network hydrogel is an outstanding class. To expand the application of double network hydrogel in water treatment, in this study, eco-friendly physically cross-linked double network polymer hydrogel beads (DAP) are prepared and studied in depth on the mechanism of Methylene Blue (MB) adsorption; and then the polymer hydrogels are further functionalized by inorganic materials. MB adsorption on DAP favors alkaline condition which is due to the increase of electrostatic attraction and adsorption site, and it reaches equilibrium within 10?hr, which is faster than that of the single network hydrogel beads (SAP). Through thermodynamics study, the process shows to be an exothermic and spontaneous process. The adsorption isotherms are well fitted by Langmuir model, with a maximum monolayer adsorption capacity of 1437.48?mg/g, which is larger than SAP (1255.75?mg/g). After being functionalized with common inorganic materials including activated carbon, Fe₃O₄ and graphene oxide (GO), the composites show to have larger pore sizes and have obvious increases in adsorption capacity especially the one contains GO. Then the composites contains Fe₃O₄ are used as heterogeneous Fenton catalyst which shows to have excellent performance in MB degradation. The results indicate the potential of polymer double network to be functionalized in environmental areas.     

高分子凝胶球去除废水中重金属离子的研究

用海藻酸钠（SA）、海藻酸钠-聚乙烯醇（SA—PVA）、海藻酸钠-聚氧化乙烯（SA—PEO）凝胶球作为吸附剂吸附溶液中的Pb^2＋。探讨了凝胶球固定化时间、吸附时间、溶液pH值、溶液初始浓度对Pb^2＋去除率的影响,并对吸附动力学方程进行了分析。结果表明：固定化时间对去除率的影响较小;反应速率较快,吸附时间在10min时,三种凝胶球对Pb^2＋的去除率就分剐达到了80％、82％和88％,吸附时间在2h后基本达到吸附平衡,三种凝胶球对Pb^2＋的吸附能力为：SA—PGE〉SA—PVA〉SA;三种凝胶球吸附铅离子的行为均符合一级反应动力学方程;溶液的pH在4～6时有较高的去除率;三种凝胶球对不同金属的吸附能力为Pb^2＋〉Cu^2＋〉Cd^2＋;饱和吸附后的三种凝胶球均可以再生利用。     

高分子凝胶球用于城市污水深度处理的研究

制备海藻酸钠-钙(SA-Ca)、海藻酸钠-铁(SA-Fe)、包埋活性炭海藻酸钠-铁(SA-Fe-AC)凝胶球,对城市污水处理厂二级出水的COD和无机磷进行深度处理。结果表明:SA-Ca凝胶球对COD的去除率为10%,SA-Fe凝胶球对COD及无机磷的去除率分别为42%和93%。SA-Fe-AC凝胶球对COD及无机磷的去除率分别为75%和87%。SA-Fe及SA-Fe-AC对COD的吸附符合Langmuir型,均属于单分子层吸附,其饱和吸附量分别为416.7mg/g、909mg/g。     

Alginate immobilized enrichment culture for atrazine degradation in soil and water system

An atrazine degrading enrichment culture, a consortium of bacteria of genus Bacillus along with Pseudomonas and Burkholderia, was immobilized in sodium alginate and was used to study atrazine degradation in mineral salts medium (MSM), soil and wastewater effluent. Sodium alginate immobilized consortium, when stored at room temperature (24 ± 5°C), was effective in degrading atrazine in MSM up to 90 days of storage. The survival of bacteria in alginate beads, based on colony formation unit (CFU) counts, suggested survival up to 90 days and population counts decreased to 1/5^th on 120 days. Comparison of atrazine degrading ability of the freely suspended enrichment culture and immobilized culture suggested that the immobilized culture took longer time for complete degradation of atrazine as a lag phase of 2 days was observed in the MSM inoculated with alginate immobilized culture. The free cells resulted in complete degradation of atrazine within 6 days, while immobilized cells took 10 days for 100% atrazine degradation. Further, immobilized cultures were able to degrade atrazine in soil and wastewater effluent. Alginate beads were stable and effective in degrading atrazine till 3rd transfer and disintegrated thereafter. The study suggested that immobilized enrichment culture, due to its better storage and application, can be used to degrade atrazine in soil water system.