混凝沉淀法处理含砷选矿废水

某钨矿含砷选矿废水砷含量高且砷以As(V)为主要存在形态,采用混凝沉淀法处理,详细考察了生石灰、硫酸亚铁和六水三氯化铁3种混凝剂对废水中砷的去除效果。实验结果表明,在PAM投加量40 mg/L,静沉时间60 min条件下,比较分析3种混凝剂对砷的去除效果,三氯化铁为最佳除砷混凝剂。三氯化铁最佳除砷工艺条件为:pH 7.5,三氯化铁投加量986.67 mg/L,混凝反应时间25 min,PAM投加量为40 mg/L,静沉60 min,含砷选矿废水经该工艺处理后,砷去除率可达99.14%,出水砷浓度降至0.361 mg/L,达到国家污水综合排放标准(GB8978-1996)。     

纳滤膜技术在地下水除砷应用中的研究进展

砷污染突发事件的频发严重威胁着地下水饮用水水源的水质安全，加之饮用水控制标准的提高，就对饮用水除砷技术提出了更高的要求，而纳滤(NF)膜分离技术为饮用水除砷提供了新的思路。首先概述了地下水中砷的存在形态、化学性质以及我国高砷地下水地区分布，然后分析了NF膜特点、除砷机理与性能，系统地阐述了各种因素包括膜操作因素（操作压力、膜回收率、膜排布方式等）和原水水质因素（pH、水温、共存离子、共存有机物及砷浓度与砷价态等），对NF膜除砷性能的影响。此外，对NF除砷的关键问题，如原水预处理、膜浓水处理、膜污染及其清洗等，也作了探讨。最后，总结了目前NF除砷应用中所面临的问题，探索性提出了NF膜技术在除砷应用中的研究方向。     

氢氧化镁混凝性能及絮体特性

以氢氧化镁作为混凝剂,不同浊度高岭土水样为研究对象,运用iPDA在线监测技术对混凝过程絮体形成进行监测,探求了操作条件对絮体特性和混凝过程的影响;同时讨论了FI值和浊度去除的关系。结果表明,当浊度分别为5、10和20 NTU时,最佳投加量分别为21.6、14.4和3.6 mg/L;随着pH的升高,FI指数增大,同时混凝剂的最佳投加量也逐步减小;随着慢速搅拌转速的增大,絮体破碎过程明显,FI指数降低;当转速为60 r/min时,浊度去除率最高。     

Removal of pesticides from surface waters by combined physicochemical processes. Part I: Dodine

The simultaneous action of powdered activated carbon and several coagulant agents on the removal of the fungicide dodine from spiked distilled water, was studied. As coagulants, ferric chloride (FeCl₃) and basic polyaluminium chlorosulfate ([Al(OH)_xCl_y(SO₄)_z]_n) were examined, using polyacrylamide, in certain cases, as coagulant aid (polyelectrolyte). The efficiency of dodine removal was investigated with respect to the added amount of powdered activated carbon (PAC), the pH value, as well as the type and dose of coagulant and polyelectrolyte. The experiments were performed applying the standard jar-test procedure. The initial concentration of dodine was 250 μg/L. At this concentration and pH range 5–8 it was found that a dose of 100 mg/L PAC was necessary to achieve more than 98% removal of dodine, whereas lower removal (91–93%) was obtained applying half the dose of PAC under the same conditions. However, when 10–100 mg/L FeCl₃ were simultaneously added with PAC, the removal efficiency increased to >98%, even with the half PAC dose.     

Coagulant recovery from water treatment plant sludge and reuse in post-treatment of UASB reactor effluent treating municipal wastewater

In the present study, feasibility of recovering the coagulant from water treatment plant sludge with sulphuric acid and reusing it in post-treatment of upflow anaerobic sludge blanket (UASB) reactor effluent treating municipal wastewater were studied. The optimum conditions for coagulant recovery from water treatment plant sludge were investigated using response surface methodology (RSM). Sludge obtained from plants that use polyaluminium chloride (PACl) and alum coagulant was utilised for the study. Effect of three variables, pH, solid content and mixing time was studied using a Box–Behnken statistical experimental design. RSM model was developed based on the experimental aluminium recovery, and the response plots were developed. Results of the study showed significant effects of all the three variables and their interactions in the recovery process. The optimum aluminium recovery of 73.26 and 62.73 % from PACl sludge and alum sludge, respectively, was obtained at pH of 2.0, solid content of 0.5 % and mixing time of 30 min. The recovered coagulant solution had elevated concentrations of certain metals and chemical oxygen demand (COD) which raised concern about its reuse potential in water treatment. Hence, the coagulant recovered from PACl sludge was reused as coagulant for post-treatment of UASB reactor effluent treating municipal wastewater. The recovered coagulant gave 71 % COD, 80 % turbidity, 89 % phosphate, 77 % suspended solids and 99.5 % total coliform removal at 25 mg Al/L. Fresh PACl also gave similar performance but at higher dose of 40 mg Al/L. The results suggest that coagulant can be recovered from water treatment plant sludge and can be used to treat UASB reactor effluent treating municipal wastewater which can reduce the consumption of fresh coagulant in wastewater treatment.     

Evaluating of arsenic(V) removal from water by weak-base anion exchange adsorbents

Arsenic contamination of groundwater has been called the largest mass poisoning calamity in human history and creates severe health problems. The effective adsorbents are imperative in response to the widespread removal of toxic arsenic exposure through drinking water. Evaluation of arsenic(V) removal from water by weak-base anion exchange adsorbents was studied in this paper, aiming at the determination of the effects of pH, competing anions, and feed flow rates to improvement on remediation. Two types of weak-base adsorbents were used to evaluate arsenic(V) removal efficiency both in batch and column approaches. Anion selectivity was determined by both adsorbents in batch method as equilibrium As(V) adsorption capacities. Column studies were performed in fixed-bed experiments using both adsorbent packed columns, and kinetic performance was dependent on the feed flow rate and competing anions. The weak-base adsorbents clarified that these are selective to arsenic(V) over competition of chloride, nitrate, and sulfate anions. The solution pH played an important role in arsenic(V) removal, and a higher pH can cause lower adsorption capacities. A low concentration level of arsenic(V) was also removed by these adsorbents even at a high flow rate of 250–350 h^?1. Adsorbed arsenic(V) was quantitatively eluted with 1 M HCl acid and regenerated into hydrochloride form simultaneously for the next adsorption operation after rinsing with water. The weak-base anion exchange adsorbents are to be an effective means to remove arsenic(V) from drinking water. The fast adsorption rate and the excellent adsorption capacity in the neutral pH range will render this removal technique attractive in practical use in chemical industry.     

皮革废水混凝处理实验研究

采用混凝剂对皮革废水进行混凝处理。对3种无机混凝剂和一种有机混凝剂进行了筛选,研究了pH值和投药量对废水中SS、COD、铬和色度等污染物去除效果的影响。结果表明,当pH值在酸性和中性时,效果不明显;当pH值为碱性时,效果显著。硫酸亚铁、硫酸亚铁+PAM和聚合氯化铝(PAC)+PAM 3种混凝剂组合具有良好的混凝效果,在合适的pH值和投药量下,SS和COD的去除率分别达到80%和30%以上,铬和色度的去除率分别达到95%和50%以上。且硫酸亚铁混凝效果好,成本低,适合小型皮革企业需求。     

饮用水除砷技术研究进展

饮用水中的砷对人体健康危害很大。介绍了从饮用水中去除砷的各种方法，总结了目前除砷技术存在的不足，指出混凝微滤工艺具有除砷效率高、能耗低、操作简单等优点，应成为今后饮用水除砷技术的发展方向。     

Water reclamation during drinking water treatments using polyamide nanofiltration membranes on a pilot scale

The aim of this study was to investigate the performances of polyamide nanofiltration membranes during water reclamation. The study was conducted using nanofiltration concentrates obtained from two different nanofiltration drinking water treatment plants placed in the northern part of Serbia (Kikinda and Zrenjanin). Used nanofiltration concentrates contained high concentrations of arsenic (45 and 451 μg/L) and natural organic matter (43.1 and 224.40 mgKMnO₄/L). Performances of polyamide nanofiltration membranes during water reclamation were investigated under various fluxes and transmembrane pressures in order to obtain drinking water from nanofiltration concentrates and, therefore, reduce the amount of produced concentrates and minimize the waste that has to be discharged in the environment. Applied polyamide nanofiltration membranes showed better removal efficiency during water reclamation when the concentrate with higher content of arsenic and natural organic matter was used while the obtained permeates were in accordance with European regulations. This study showed that total concentrate yield can be reduced to ~5 % of the optimum flux value, in both experiments. The obtained result for concentrate yield under the optimum flux presents considerable amount of reclaimed drinking water and valuable reduced quantity of produced wastewater.     

Synthesized magnetic nanoparticles coated zeolite for the adsorption of pharmaceutical compounds from aqueous solution using batch and column studies

The contamination of fresh water with pharmaceutical and personal care products (PPCPs) has risen during the last few years. The adsorption of some PPCPs namely, Diclofenac-Na, Naproxen, Gemfibrozil and Ibuprofen from aqueous solution has been studied, magnetic nanoparticles coated zeolite (MNCZ) has been used as the adsorbent. Batch adsorption experiment was conducted to study the influences of different adsorption parameters such as contact time, solution pH and PPCPs concentrations in order to optimize the reaction conditions. The removal was favored at low pH values. Thus, as pH turns from acidic to basic conditions these compounds were less efficiently removed. The initial concentration does not appear to exert a noticeable effect on the removal efficiency of the studied PPCPs at low concentrations, but it showed less removal efficiency during high concentration of PPCPs especially for Ibuprofen. The removal of Diclofenac-Na was independent on time, while the contact time was of significant effect on the adsorption of Naproxen, Gemfibrozil and Ibuprofen even though these compounds were removed up to 95% during 10 min using MNCZ. From the isotherm adsorption study, the adsorption of PPCPs studied on MNCZ was best fitted with Freundlich isotherm equation. Pseudo-second order model providing the best fit model with the experimental data. Column adsorption study was conducted to compare the removal efficiency of MNCZ with other processes used at drinking water treatment plants (DWTPs), MNCZ showed high removal efficiency (>99%) than other used processes at DWTPs.     

Evaluation of Al30 polynuclear species in polyaluminum solutions as coagulant for water treatment

Polyaluminum coagulant with a content of 76.8% of Al30 (PACAl30) was prepared. Its coagulation behaviors were compared with high Al13 content polyaluminum coagulant (PACAl13) and AlCl3. The species stability was studied using Al-Ferron method and 27Al NMR. The coagulation performances were investigated by studying the rate of flocs development, the turbidity removal efficiency and charge neutralization capacity under fixed pH conditions and uncontrolled pH conditions. The effect of pH on coagulation was also studied. The results show that PACAl30 are stable for using as coagulant. PACAl30 causes less pH depression than PACAl13. The charge neutralization capacity of PACAl30 is slightly lower than that of PACAl13 at pH6.8 and higher at pH 6.5. PACAl30 achieves the most effective turbidity removal in these three coagulants. And it acts effectively within a much broader dosage range and a wider pH range when compared with PACAl13. PACAl30 achieves the highest turbidity removal due to its strong flocs formation capacity. The results verify that Al30 is another highly active coagulation/flocculation species for turbidity removal.     

The application of novel coagulant reagent (polyaluminium silicate chloride) for the post-treatment of landfill leachates

Relatively "old" (stabilized) landfill leachates are a special category of wastewaters, which are difficult to treat further, mainly due to their bio-refractory organic content (humic substances). In this study, coagulation-flocculation was examined as post-treatment method for the biologically pre-treated stabilized leachates. The purpose was to examine the coagulation performance of alternative coagulant agents, i.e. the composite coagulant polyaluminium silicate chloride. Composite coagulants with different Al to Si molar ratio and different preparation methods were tested. Their efficiency was evaluated by monitoring from turbidity and phosphate content, other parameters strongly correlated with the presence of organic matter, such as UV absorbance at 254nm, COD and colour. The results suggest that the silica-based coagulants exhibit better coagulation performance, than the relevant conventional coagulant (alum) or simple pre-polymerized coagulants (PACl). Polyaluminium silicate chloride has greater tolerance against pH variation than alum or PACl, whereas this novel coagulant works better at pH values between 7 and 9. Coagulation-flocculation has proved to be an efficient post-treatment method for the biologically pre-treated leachates, promoting the removal of the refractory humic substances, while the treatment efficiency of coagulation can be improved by the application of the new coagulant agent.     

Significance of design and operational variables in chemical phosphorus removal

Batch and continuous experiments using model and real wastewaters were conducted to investigate the effect of metal salt (ferric and alum) addition in wastewater treatment and the corresponding phosphate removal from a design and operational perspective. Key factors expected to influence the phosphorus removal efficiency, such as pH, alkalinity, metal dose, metal type, initial and residual phosphate concentration, mixing, reaction time, age of flocs, and organic content of wastewater, were investigated. The lowest achievable concentration of orthophosphate under optimal conditions (0.01 to 0.05 mg/L) was similar for both aluminum and iron salts, with a broad optimum pH range of 5.0 to 7.0. Thus, in the typical operating range of wastewater treatment plants, pH is not a sensitive indicator of phosphorus removal efficiency. The most significant effect for engineering practice, apart from the metal dose, is that of mixing intensity and slow kinetic removal of phosphorus in contact with the chemical sludge formed. Experiments show that significant savings in chemical cost could be achieved by vigorously mixing the added chemical at the point of dosage and, if conditions allow, providing a longer contact time between the metal hydroxide flocs and the phosphate content of the wastewater. These conditions promoted the achievement of less than 0.1 mg/L residual orthophosphate content, even at lower metal-to-phosphorus molar ratios. These observations are consistent with the surface complexation model presented in a companion paper (Smith et al., 2008).     

Fenton-混凝法处理焦化废水的试验研究

对Fenton预氧化-混凝法联用技术处理焦化废水进行了研究，探讨了Fenton氧化阶段H2O2投加量、混凝阶段pH值以及混凝剂投加量等因素对焦化废水COD去除率的影响，确定了最佳处理条件。结果表明，Fenton预氧化一混凝法处理焦化废水取得了良好效果，COD去除率达97．5％，为该工艺实际处理焦化废水提供了实验依据。     

Fenton-混凝法处理焦化废水的试验研究

对Fenton预氧化-混凝法联用技术处理焦化废水进行了研究,探讨了Fenton氧化阶段H2O2投加量、混凝阶段pH值以及混凝剂投加量等因素对焦化废水COD去除率的影响,确定了最佳处理条件.结果表明,Fenton预氧化-混凝法处理焦化废水取得了良好效果,COD去除率达97.5%,为该工艺实际处理焦化废水提供了实验依据.     

优化混凝处理低温低浊黄河水及对余铝的控制

考察了4种混凝剂，高效聚合氯化铝（HPAC），聚合氯化铝（PACl），硫酸铝（Al2（SO4）3），混合PACl和氯化铁（FeCl3），对低温低浊黄河原水的混凝效果与沉后水残留铝含量的关系。结果表明，当采用Al2（SO4）3或PACl做混凝剂时，在取得较好浊度去除的投药量下，水中余铝浓度会超过国家标准（0．2131g／L）。而采用HPAC或FeCl3和PACl复配药剂，在取得与Al2（SO4）3或PACl类似的浊度去除效果的同时，也能较好地控制水中的余铝含量。当HPAC投加量为21mg／L时，沉后水浊度降至1．3NTU，残留铝含量为0．147mg／L。复配投加PACl 15mg／L和FeCl3 12mg／L后，沉后水浊度为1．18NTU，残留铝含量为0．074mg／L。PACl和氯化铁的复配比例需要精确的调控，否则容易导致出水余铁余铝含量增加。而HPAC投加量小于21mtg／L时出水余铝浓度均低于国家标准。因此，在这4种混凝剂中，就混凝效果及余铝控制而言，HPAC更适合充当低温低浊水源水的混凝处理药剂。     

超声强化混凝去除蓝藻实验研究

研究了超声波对藻类的混凝去除强化,证明超声波可以快速、高效地提高藻类混凝去除效率,减少混凝剂用量.在混凝剂投加量为0.8 mg/L时,5 s超声处理,藻类去除效果比对照样好30%.同样,藻类去除率都为92%时,5 s超声预处理可以将混凝剂投加量降低至1/3.超声预处理时间对强化混凝效果有很大的影响,在实验条件下,1～5 s的超声处理均可产生满意的结果,1 s为最优、最经济时间,而预处理超过30 s反而降低混凝效果.低频下不同处理频率对超声强化混凝效果影响不大,在80 kHz的频率下,最佳功率为50 W.最佳pH值在8～9范围内.     

Removal processes for arsenic in constructed wetlands

Arsenic pollution in aquatic environments is a worldwide concern due to its toxicity and chronic effects on human health. This concern has generated increasing interest in the use of different treatment technologies to remove arsenic from contaminated water. Constructed wetlands are a cost-effective natural system successfully used for removing various pollutants, and they have shown capability for removing arsenic. This paper reviews current understanding of the removal processes for arsenic, discusses implications for treatment wetlands, and identifies critical knowledge gaps and areas worthy of future research. The reactivity of arsenic means that different arsenic species may be found in wetlands, influenced by vegetation, supporting medium and microorganisms. Despite the fact that sorption, precipitation and coprecipitation are the principal processes responsible for the removal of arsenic, bacteria can mediate these processes and can play a significant role under favourable environmental conditions. The most important factors affecting the speciation of arsenic are pH, alkalinity, temperature, dissolved oxygen, the presence of other chemical species - iron, sulphur, phosphate -, a source of carbon, and the wetland substrate. Studies of the microbial communities and the speciation of arsenic in the solid phase using advanced techniques could provide further insights on the removal of arsenic. Limited data and understanding of the interaction of the different processes involved in the removal of arsenic explain the rudimentary guidelines available for the design of wetlands systems.     

Removal of arsenic from water by electrocoagulation

In the present study electrocoagulation (EC) has been evaluated as a treatment technology for arsenite [As(III)] and arsenate [As(V)] removal from water. Laboratory scale experiments were conducted with three electrode materials namely, iron, aluminum and titanium to assess their efficiency. Arsenic removal obtained was highest with iron electrodes. EC was able to bring down aqueous phase arsenic concentration to less than 10 microgl(-1) with iron electrodes. Current density was varied from 0.65 to 1.53 mAcm(-2) and it was observed that higher current density achieved rapid arsenic removal. Experimental results at different current densities indicated that arsenic removal was normalized with respect to total charge passed and therefore charge density has been used to compare the results. Effect of pH on arsenic removal was not significant in the pH range 6-8. Comparative evaluation of As(III) and As(V) removal by chemical coagulation (with ferric chloride) and electrocoagulation has been done. The comparison revealed that EC has better removal efficiency for As(III), whereas As(V) removal by both processes was nearly same. The removal mechanism of As(III) by EC seems to be oxidation of As(III) to As(V) and subsequent removal by adsorption/complexation with metal hydroxides generated in the process.     

冬季不同生境下菹草的水质净化效果研究

在室外通过人工构建静态模拟生态系统,研究冬季不同底质、水深、水质条件下,菹草对水体营养盐的吸收净化效果。结果表明,在不同水深或水质污染程度的相应组实验中,添加土壤改良剂的各组实验的TN、TP、NO3--N、高锰酸盐指数去除率均高于相应的未添加组,而NH4+-N去除情况相反;添加土壤改良剂有助于菹草对水体营养盐的综合去除,菹草在水深较深且营养盐负荷较高的水体中对营养盐的去除效果更好;水深35cm比水深25cm更适宜菹草的生长;菹草在实验设计的水质条件下能正常生长和对水质进行高效净化,适合在冬季运用于一般河道的水体修复。