The chemical species distribution and transformation of polyaluminum silicate chloride coagulant

The chemical species distributions of polyaluminum silicate chloride (PASC) and polyaluminum chloride (PACl) determined by Al-Ferron complexation timed spectrophotometric and 27Al-NMR methods, respectively, have been compared and analyzed. The experimental results show that the species distribution and transformation of PASC are different from those of PACl, due to the interaction of polysilicic acid and hydrolyzed aluminum species. At the same basicity (B), the contents of, Al(b), Al13 and the monomer species Almono (also determined by 27Al-NMR) in PASC are lower than those in PACl, while the contents of Al(c) and the Alother determined by 27Al-NMR in PASC are higher than those in PACl. The differences between PASC and PACl with respect to these species enlarge as the molar ratio of Al/Si in PASC decreases. Further, in PACl the ratio of Al13 to Al(b) closes to 1.0, indicating that the amount of the two fractions are similar. In PASC, however, such an agreement does not exist at the lower B values and Al/Si molar ratios. When the B value and Al/Si molar ratios increase, however, the amount of Al13 and Al(b) species tends to close. The study findings indicate that polysilicic acid can react with hydrolyzed aluminum species to form an aluminum silicate polymer composite and result in the change in species distribution of PASC.     

聚合氯化铝混凝强化新生态铁锰复合氧化物吸附去除水中的磷

采用氧化-共沉淀法制备出新生态铁锰复合氧化物(FMBO),研究了单独投加FMBO和聚合氯化铝(PACl)强化FMBO吸附除磷效能及吸附磷后的颗粒物特性。结果表明,单独投加FMBO后形成的颗粒物表面带负电荷,颗粒物聚集和沉淀性能较差。PACl的投加降低了颗粒物的表面电荷,促进了颗粒物的聚集,平均粒径明显增加,改善了颗粒物的沉淀性能;通过SEM-EDAX发现,投加PACl形成的复合颗粒物表面更为粗糙,Al元素在复合颗粒物表面相对富集。PACl的投加强化了FMBO的吸附除磷效果,在实验原水条件下FMBO和PACl最佳投量分别为12和30 mg/L,此时TDP去除率高达95.6%。并且出水中Fe、Mn、Al浓度均远低于《地表水环境质量标准》中规定的限值。PACl强化新生态FMBO易于实现原位投加,在水体和水处理除磷工艺中具有较好的应用潜力。     

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.     

Effect of SO4 2-/Al3+ ratio and OH-/Al3+ value on the characterization of coagulant poly-aluminum-chloride-sulfate (PACS) and its coagulation performance in water treatment

A poly-aluminum-chloride-sulfate (PACS) was prepared at various experimental conditions. It was found that the coagulation performance of PACS in water treatment was affected by the PACS particle size distribution and zeta potential value. The experimental results indicated that the PACS particle size distribution and zeta potential value were highly influenced by SO(4)(2-)/Al(3+) molar ratio and bacicities (gamma,gamma=[OH]/[Al]) value. At a fixed gamma value of 2.0, the average PACS particle size increased from 25 to 80nm with the increase of SO(4)(2-)/Al(3+) ratio from 0 to 0.1. Further increase of the SO(4)(2-)/Al(3+) ratio resulted in acute increment particle size of PACS extremely, which can be attributed to its aggregation. At a fixed SO(4)(2-)/Al(3+) ratio of 0.0664, the largest average size of PACS occurred at gamma=2.0. It was also found that the zeta potential value of PACS was strongly influenced by the SO(4)(2-)/Al(3+) ratio, gamma value and pH of the aquatic solution. The zeta potential value of PACS increased with increasing of SO(4)(2-)/Al(3+) ratio. At a fixed SO(4)(2-)/Al(3+) ratio of 0.0664, PACS achieved greatest zeta potential value at gamma value of around 2.0. The maximum positive zeta potential value of PACS was found at pH5.3. At a fixed gamma value of 2.0 and SO(4)(2-)/Al(3+) ratio of 0.0664, the PACS achieved an optimum natural organic matter and turbidity removal efficiency.     

Evaluation of an electrolysis apparatus for inactivating antineoplastics in clinical wastewater

We recently reported a system for inactivating antineoplastics in which sodium hypochlorite is supplied by the electrolysis of sodium chloride solution. In this study, we designed an electrolysis apparatus for inactivating the cytotoxicity of antineoplastics in clinical wastewater using the system. The apparatus consists of an electrolysis cell with platinum-iridium electrodes, a pool tank, a circulating system for wastewater, a safety system for explosive gas and overflow, and an exhaust duct. The free chlorine concentration increased linearly up to 6500 mg l(-1), and pH also increased to 9.0-10.0 within 2h, when 0.9% sodium chloride solution was electrolyzed. We examined its efficacy with model and clinical wastewaters. The reciprocal of dilution factor for disappearance of cytotoxicity using Molt-4 cells was compared before and after electrolysis. In the model wastewater, that was 9.10 x 10(4) before electrolysis, and 3.56 x 10(2) after 2h of electrolysis. In the clinical wastewater (n=26), that was 6.90 x 10(3)-1.02 x 10(6) before electrolysis, and 1.08 x 10(2)-1.45 x 10(4) after 2h of electrolysis. Poisonous and explosive gases released by the electrolysis were measured; however, they were found to be negligible in terms of safety. The environmental load was evaluated by carbon dioxide generation as an index and it was found that the carbon dioxide generated by the electrolysis method was 1/70 lower than that by the dilution method with tap water. Moreover, the cost of the electrolysis method was 1/170 lower than that of the dilution method. This method was found to be both effective and economically valuable.     

Electrochemical oxidation of benzene on boron-doped diamond electrodes

This work presents an electrochemical investigation of the benzene oxidation process in aqueous solution on boron-doped diamond (BDD) electrodes. Additionally, in order to determine the main products generated during the oxidation process, electrolysis and high performance liquid chromatography experiments were carried out. The complete degradation of this compound was performed aiming to a further application in waste water treatment. The cyclic voltammetry studies indicate that benzene is irreversibly oxidized in acid medium (H₂SO₄ 0.5 M) on the BDD electrode surface at 2.0 V versus Ag/AgCl in a diffusion controlled process. During the cycling, other products are generated, and a pair of peaks was observed that can be associated with the oxi-reduction of anyone of the following species: hydroquinone, benzoquinone, resorcinol or catechol. The electrolysis experiments were carried out at 2.4 and 2.5 V on the BDD electrode surface in a solution containing 1 × 10⁻² M of benzene (below the saturation concentration in aqueous solution), for 3 and 5 h, respectively. The main products measured were: hydroquinone, resorcinol, p-benzoquinone, catechol and phenol. The complete electrochemical benzene degradation was performed in the electrolysis experiments using a rotating BDD disc electrode (2.5 V for 5 h) and the main products detected were all measured at concentrations lower than 10⁻⁵ M in this condition. The boron-doped diamond electrode had proved to be a valuable tool for the electrochemical degradation of the benzene, a very stable chemical compound.     

Effect of Al(III) speciation on coagulation of highly turbid water

In Taiwan, the turbidity of raw water for fresh water treatments can sometimes reach as high as 40 000 NTU due to intensive rainfall, especially in typhoon seasons. In response, water works often apply large quantities of coagulants such as polyaluminium chloride (PACl). In this study, simulated and natural highly turbid water was coagulated with two PACls, a commercial product (PACl-1) and a laboratory product (PACl-E). The Al species distributions of PACl-1 and PACl-E under various pH conditions were determined, and the corresponding coagulation efficiency was evaluated. The PACl-E has a wider range of operational pH, while the efficiency of PACl-1 peaks at around neutral pH. For simulated water up to 5000 NTU, the PACl-E was superior to PACl-1 at low dosage and in the pH range studied. Similar results were discovered with natural water, except that when the turbidity was extremely high, the coagulation efficiency of PACl-E decreased significantly due to the presence of large amounts of organic matter. The coagulation of PACl-E was closely related to the content of polycationic aluminium (Al₁₃) while that of PACl-1 was dictated by the amount of Al_c. The sludge from PACl-E coagulation had better dewaterability when the optimum dosage was applied. The experimental results suggest that for natural water up to 5000 NTU, PACl containing high Al₁₃ species is recommended for coagulation. In cases when the water contains high organic matter, efficient coagulation depends upon enmeshment by amorphous aluminium hydroxide.     

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。     

电沉积处理电解锌漂洗废水的实验研究

采用电沉积技术对电解锌漂洗废水进行初步处理,以求达到废水回用和重金属锌的回收。研究了电沉积法处理含锌废水过程中各个影响因素对电沉积效果的影响,并且设计了正交实验。结果表明,极板间距、槽电压、进水pH、极板材料等对二维电沉积处理模拟废水具有显著影响。适宜的电沉积条件是：极板间距20 mm、槽电压5～6 V、阴极板材料为铝板、电沉积时间为30～45 min。     

活性炭三维电极法处理超高盐榨菜腌制废水

将粒状活性炭作为三维电极的粒子电极处理超高盐榨菜腌制废水。采用静态实验,对比了二维电极与三维电极对该废水COD和磷酸盐的去除效果,考察了三维电极条件下极板间距、活性炭填充量、电解时间、电解电流及初始pH等对该废水COD和磷酸盐去除率的影响。结果表明：三维电极对超高盐榨菜腌制废水COD和磷酸盐的去除率明显高于二维电极;在原水pH（4．3—5．0）,废水体积600mL,电流8A,活性炭填充量250g,极板间距6．5cm,电解时间150min时,处理效果良好,COD和磷酸盐去除率分别为76．47％和97．81％。由波长扫描图可初步认为部分有机物直接被氧化为二氧化碳。     

Electrocatalytic reduction of nitrate in water with a palladium-modified copper electrode.

A highly active electrocatalytic electrode for nitrate reduction was prepared by the electro-deposition of palladium onto a copper electrode. The capacity of nitrate reduction by a palladium-modified copper electrode has been studied using cyclic voltammetry (CV). The existence of a reduction peak at -0.605 V versus saturated calomel electrode in 0.1-M sodium nitrate + 0.1-M perchloric acid solution (pH = 0.86) can be found in the CV measurement. The influence of solution properties, such as pH, nitrate concentration, and other anions in solution, on nitrate reduction was determined in detail. Results showed that nitrate reduction was suppressed in alkaline solution, while it was beneficial to nitrate reduction in acid or neutral solution. At low nitrate concentrations (0.01 to 0.5 M), nitrate reduction current increased with increasing nitrate concentration, but was hindered by sulfate. At high nitrate concentrations (1 to 5 M), no significant difference on nitrate reduction was observed. Compared with other different electrodes prepared in our work (copper, titanium, and palladium-modified titanium electrodes), the palladium-modified copper electrode showed the highest electrocatalytic capacity and stability in the nitrate-reduction process.     

Phenol electrooxidation on Fe-Co3O4 thin film electrodes in alkaline medium

Fe-Co₃O₄ thin film with different amounts of Fe have been used for the electro-oxidation of phenol in alkaline medium at room temperature. The electrodes were prepared by coating stainless steel supports with successive layers of the oxides, obtained by thermal decomposition at 673 K. The electrolysis was carried out at constant potential and the phenol disappearance, during the electrolysis, was monitored by UV-Vis absorbance measurements between 250 and 500 nm. After 3 h of electrolysis, the intermediates were identified by comparing the HPLC data and UV-Vis spectra to those from pure standards. The results indicate that the same oxidation products are formed on the different prepared electrodes, namely the decomposition products of phenol such as benzoquinone, hydroquinone and cathecol in basic medium. Simulated results show clearly the decrease of the amount of phenolic species with the electrolysis time. An enhancement of the phenol removal is observed with the presence of iron in the oxide. Under the operating conditions, around 30% of the initial phenol has been removed at ca. 3 h and the complete degradation is obtained after 54 h of electrolysis, when Fe-Co₃O₄ thin film with 10% of Fe is used as anode.     

纳米聚硅酸铝锌絮凝剂的制备及表征简

在SiO₂含量为3%,pH为3,活化时间为85 min,（Al+Zn ）/Si摩尔比为1.5,Al/Zn摩尔比为2,表面活性剂硬脂酸钠加入量为0.1%,超声频率为40 Hz,超声时间为60 min的最佳制备条件下制备出液体PSAZS絮凝剂,用超声法制成纳米级Nano-PSAZS,用环境扫描电子显微镜（ESEM）和智能型傅里叶变换红外光谱（FT-IR）等仪器进行分析。结果表明,硅有助于絮凝剂分子链的延伸,有助于生成更大分子的聚合物;铝盐和锌盐的加入到聚硅酸中,并不是简单的混合,而是发生了缩聚和配位反应,有助于生成链网状结构,能更好地发挥吸附架桥和网捕卷扫作用。同时Nano-PSAZS陈化时间为24 h时的结构有利于絮凝效果的发挥。     

Influence of some additives to aluminium species distribution in aluminium coagulants

Aluminium ions hydrolyse and polymerise into different species in water. Main aluminium species in aluminium coagulant solutions are monomeric Al species (Al1) and polymeric Al species Al13O4(OH)24(7+) (Al13). The aluminium species distribution in coagulant solutions can be influenced by many parameters. This paper studies influences of concentrations of total aluminium species (Al(t)) and other species--OH-, polysilicic acid and ferric species, which were added in aluminium coagulant solutions, on the aluminium species distribution through 27Al nuclear magnetic resonance (NMR) analysis. Results show that only Al1 and no Al13 exist in coagulant solutions at higher Al(t) concentrations (over 1 mol l(-1)), while both species exist at lower Al(t) concentrations (0.1 mol l(-1)). The increase of OH/Al value (molar ratio) increases the concentration of Al13 in coagulant solutions, while the addition of polysilicic acid and ferric species decreases the concentration of Al13.     

超声强化电絮凝处理洗车废水的试验研究

针对洗车行业对水资源的浪费及污染现状,采用超声强化电絮凝处理洗车废水.考察了电流密度、初始pH、极板间距、处理时间等因素对洗车废水处理效果的影响,并讨论了超声强化电絮凝机制.结果表明,超声强化电絮凝处理洗车废水的最佳条件是电流密度1,500 mA/cm2、初始pH无需调节、极板间距为1.5cm、处理20 min,COD与浊度去除率分别为68.77％、96.89％,出水达到《城市污水再生利用城市杂用水水质》(GB/T 18920-2002)要求.可见,超声能改变电絮凝反应动力学过程,强化电絮凝去除污染物效果.     

Electrochemical destruction of p-chlorophenol and p-nitrophenol -- Influence of surfactants and anode materials

The electrochemical oxidative removal of p-chlorophenol and p-nitrophenol was studied by cyclic voltammetry (CV) and constant current electrolysis on commercially available graphite and titanium substrate insoluble anodes (TSIA). The effect of cationic cetyl trimethylammonium bromide (CTAB), anionic sodium dodecyl sulphate (SDS) and non-ionic polyoxyethylene(23)lauryl ether (Brij-35) surfactants, which prevent adherent film formation on the electrode surface were also studied. CV experiments indicate that p-chlorophenol exhibits a relatively higher tendency for film formation on graphite and that sodium chloride is a better medium for the destruction of phenols. The electrochemical oxidation of phenols under galvanostatic conditions in chloride medium with CTAB enhanced the detoxification process with significantly lower fouling effects on TSIA. The surfactants, however, did not improve phenol removal on graphite under identical experimental conditions. A charge of 2.5F per mol was found to be sufficient to achieve 44-48% removal of phenol on both the electrodes in the absence of the surfactants. A 55-65% removal was achieved in the presence of the cationic surfactant on the TSIA electrode. Phenol was removed as a low molecular weight polymer (MW approximately 4450).     

Clay charge reversal effects on aqueous polymer sorption on lateritic soils

The effects of charge reversal about the measured point of zero charge (pH(0) approximately 5.2) of untreated and treated Sete Lagoas lateritic soil of Brazil on aqueous polymer sorption was investigated. The polymers are anionic sodium carboxymethyl cellulose (CMCA), nonionic polyethylene oxide (PEO), and cationic polyacrylamide (PAM). They were prepared at aqueous concentrations and pH ranges of 0.1-2.0 g l(-1) and 2-9, respectively. Soil treatment involved the removal of iron oxides by treatment with dithionate-bicarbonate-citrate. Batch sorption test results show that the presence of iron oxides in lateritic soil tends to suppress sorption of CMCA (especially at pH=pH(0)) and PEO (for the whole pH range) but has uncertain effects on cationic PAM sorption. CMCA sorption on the untreated soil improves on either side of pH(0), in direct proportionality to solution concentration, except at pH<4.0, where disassociation of the polymer molecules may decrease sorption energy. Increase in the sorption of non-cationic polymers (CMCA and PEO) at pH>pH(0) is attributable to dispersion of clay, cation bridging and polymer molecular reconfiguration. For cationic PAM, electrostatic bonding to negatively charged soil particle surfaces accounts for the sorption increase. For treated soil samples, polymer sorption pattern is similar to those expected for the montmorillonitic clayey soils of temperate zones. These results indicate that the pH(0) of lateritic soils, within the regime that exists in the field, should be considered in assessing the potential effectiveness of polymer dust suppressants for tropical lateritic soils.     

Aniline degradation by Electro-Fenton and peroxi-coagulation processes using a flow reactor for wastewater treatment

The degradation of 10-30 l of a 1000 ppm aniline solution in 0.050 M Na2SO4 + H2SO4 at pH 3.0 and 40 degrees C by Electro-Fenton and peroxi-coagulation processes at constant current until 20 A has been studied using a pilot flow reactor in recirculation mode with a filter-press cell containing an anode and an oxygen diffusion cathode, both of 100 cm2 area. H2O2 is produced by the two-electron reduction of O2 at the cathode, being accumulated with a current efficiency between 60% and 80% at the first stages of electrolyses performed with a Ti/Pt anode. In the presence of 1 mM Fe2+, less H2O2 is accumulated, but it is not detected using an Fe anode. The Electro-Fenton process with 1 mM Fe2+ and a Ti/Pt or DSA anode yields an insoluble violet polymer, while the soluble total organic carbon (TOC) is gradually removed, reaching 61% degradation after 2 h at 20 A. In this treatment, pollutants are preferentially oxidized by hydroxyl radicals formed in solution from reaction of Fe2+ with H2O2. The peroxi-coagulation process with an Fe anode has higher degradation power, allowing to remove more than 95% of pollutants at 20 A, since some intermediates coagulate with the Fe(OH)3 precipitate formed. Both advanced electrochemical oxidation processes (AEOPs) show moderate energy costs, which increase with increasing electrolysis time and applied current.     

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.     

Evaluation of different electrochemical methods on the oxidation and degradation of Reactive Blue 4 in aqueous solution

The oxidation of a reactive dye, Reactive Blue 4, RB4, (C.I. 61205), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode and reticulated vitreous carbon electrode occurs in only one step at 2.0 < pH < 12 involving a two-electron transfer to the amine group leading to the imide derivative. Dye solution was not decolorized effectively in this electrolysis process. Nevertheless, the oxidation of this dye on Ti/SnO2/SbO(x) (3% mol)/RuO2 (1% mol) electrode showed 100% of decolorization and 60% of total organic carbon removal in Na2SO4 0.2 M at pH 2.2 and potential of +2.4V. Experiments on degradation photoelectrocatalytic were also carried out for RB4 degradation in Na2SO4 0.1 M, pH 12, using a Ti/TiO2 photoanode biased at +1.0 V and UV light. After 1h of electrolysis the results indicated total color removal and 37% of mineralization.