Spatial variations of aluminum species in drinking water supplies in Xi’an studied applying geographic information system

This article aimed to investigate the variation of aluminum species and the effects of coagulant type and water quality on aluminum speciation in drinking water.Statistical analysis showed that the concentration of total aluminum(AlT) of drinking water in Xi'an ranged from 0.051 to 0.417 mg/L and the concentration of AlT in about 24.7% studied samples was higher than the currently recommended value(0.2 mg/L).The areas fed by surface water plants had a larger portion(39.4%) of samples over the recommended value.In drinking water treated by alum coagulant,the average concentration of monomeric aluminum(Ala) was higher than that in water treated by poly aluminum chlorine(PACl) and poly aluminum ferric chloride(PAFC).The average concentrations of polynuclear aluminum(Alb) and colloidal/suspended aluminum(Alc) in the drinking water treated by alum were lower than those in water treated by PACl and PAFC.There was a notable decrease in AlT along with the delivery pipeline away from the plants,with an average decline of about 36 μg/(L·km).Besides coagulant type,water quality also could afflect aluminum speciation.In drinking water without orthophosphate,the concentrations of Ala and AlT were positively correlated with pH;while,in drinking water with orthophosphate,the concentrations of Ala and AlT were negatively correlated with pH.The addition of orthophosphate salts in the drinking water treatment process would be an effective method for aluminum control in pH range 6.5-8.2.     

Study on the effects of organic matter characteristics on the residual aluminum and flocs in coagulation processes

Characteristics of organic matter may affect the residual aluminum after the coagulation process. This study reported the results of a survey for one drinking water treatment plant and measured the concentration of residual aluminum species with different molecular weights.Survey results indicated that humic acid or organic matter whose molecular weight was smaller than 1500 Da had significant effects on residual aluminum. All the treatment processes were ineffective in removing dissolved organic matter whose molecular weight was smaller than1500 Da. These results also indicated that the addition of sand or polyacrylamide in the coagulation process could greatly decrease the concentration of humic acid, and the concentration of residual aluminum also decreased. These results revealed that for all water samples after filtration, the majority of total residual aluminum existed in the form of total dissolved aluminum, accounting for 70%–90%. The concentration of residual aluminum produced in bovine serum albumin solutions indicated that when the DOC was larger than4.0 mg/L, there were still significant differences when the solution p H value varied from 4.0 to 9.0.     

Biostability in distribution systems in one city in southern China：Characteristics, modeling and control strategy

This study investigated the bacterial regrowth in drinking water distribution systems receiving finished water from an advanced drinking water treatment plant in one city in southem China. Thirteen nodes in two water supply zones with different aged pipelines were selected to monitor water temperature, dissolved oxygen （DO）, chloramine residual, assimilable organic carbon （AOC）, and heterotrophic plate counts （HPC）. Regression and principal component analyses indicated that HPC had a strong correlation with chloramine residual. Based on Chick-Watson＇s Law and the Monod equation, biostability curves under different conditions were developed to achieve the goal of HPC 100 CFU/mL. The biostability curves could interpret the scenario under various AOC concentrations and predict the required chloramine residual concentration under the condition of high AOC level. The simulation was also carded out to predict the scenario with a stricter HPC goal （≤50 CFU/mL） and determine the required chloramine residual. The biological regrowth control strategy was assessed using biostability curve analysis. The results indicated that maintaining high chloramine residual concentration was the most practical way to achieve the goal of HPC ≤ 100 CFU/mL. Biostability curves could be a very useful tool for biostability control in distribution systems. This work could provide some new insights towards biostability control in real distribution systems.     

Factors effecting aluminum speciation in drinking water by laboratory research

Effects of aluminum on water distribution system and human health mainly attribute to its speciation in drinking water. Laboratory experiments were performed to investigate factors that may influence aluminum speciation in water supply system. The concentration of soluble aluminum and its transformation among other aluminum species were mainly controlled by kinetics processes of related reactions. Total aluminum concentration had a notable e ect on the concentrations of mononuclear and soluble aluminum in the first 4 day; then its e ect became weak. At pH above 7.50, both fluoride and orthophosphate had little e ect on aluminum speciation; while, when the solution pH was below 7.50, the concentrations of mononuclear and soluble aluminum were proportional to the concentration of fluoride and inversely proportional to the concentration of orthophosphate. Both mononuclear and polynuclear silicic acids could complex with mononuclear aluminum by forming soluble aluminosilicates. In addition, the adding sequence of orthophosphate and aluminum into drinking water would also a ect the distribution of aluminum species in the first 4 day. In order to minimize aluminum bioavailability in drinking water, it was suggested that orthophosphate should be added prior to coagulant process, and that the concentrations of fluoride and silicic acids should be controlled below 2.0 and 25 mg/L, respectively, prior to the treatment. The solution pH in coagulation and filtration processes should be controlled in the range of 6.50–7.50.     

Effects of fulvic acid and humic acid on aluminum speciation in drinking water

This article focused on the influences of fulvic acid and humic acid on aluminum speciation in drinking water. Factors including the concentration of residual chlorine and pH value had been concerned. Aluminum species investigated in the experiments included inorganic mononuclear, organic mononuclear, mononuclear, polymer, soluble, and suspended forms. It was found that the e ects of fulvic acid and humic acid on aluminum speciation depended mainly on their molecular weight. Fulvic acid with molecular weight less than 5000 Dalton had little influence on aluminum speciation; while fulvic acid with molecular weight larger than 5000 Dalton and humic acid would increase the concentration of soluble aluminum significantly even at concentration below 0.5 mg/L (calculated as TOC). Aluminum species, in the present of fulvic acid with molecular weight larger than 5000 Dalton and humic acid, were more stable than that in the present of fluvic acid with molecular mass less than 5000 Dalton, and varied little with reaction time. Within pH range 6.5–7.5, soluble aluminum increased notably in water with organic matter. As the concentration of residual chlorine increased, the e ects of fulvic acid and humic acid became weak. The reactions between humic acid, fulvic acid with large molecular weight, and aluminum were considered to be a multi-dentate coordination process. With the consideration of aluminum bioavailability, reducing the concentration of fulvic acid and humic acid and keeping the pH value among 6.5–7.5 were recommended during drinking water treatment.     

Modeling of residual chlorine in water distribution system

Water quality within water distribution system may vary with both location and time.Water quality models are used to predict the spatial and temporal variation of water quality throughout water system.A model of residual chlorine decay in water pipe has been developed, given the consumption of chlorine in reactions with chemicals in bulk water,bio-films on pipe wall, in corrosion process, and the mass transport of chlorine from bulk water to pipe wall.Analytical methods of the flow path from water sources to the observed point and the water age of every observed node were proposed .Model is used to predict the decay of residual chlorine in an actual distribution system.Good agreement between calculated and measured values was obtained.     

Drinking water treatment using a submerged internal-circulation membrane coagulation reactor coupled with permanganate oxidation

A submerged internal circulating membrane coagulation reactor(MCR) was used to treat surface water to produce drinking water. Polyaluminum chloride(PACl) was used as coagulant,and a hydrophilic polyvinylidene fluoride(PVDF) submerged hollow fiber microfiltration membrane was employed. The influences of trans-membrane pressure(TMP), zeta potential(ZP) of the suspended particles in raw water, and KMnO_4 dosing on water flux and the removal of turbidity and organic matter were systematically investigated. Continuous bench-scale experiments showed that the permeate quality of the MCR satisfied the requirement for a centralized water supply, according to the Standards for Drinking Water Quality of China(GB 5749-2006), as evaluated by turbidity(1 NTU) and total organic carbon(TOC)(5 mg/L)measurements. Besides water flux, the removal of turbidity, TOC and dissolved organic carbon(DOC) in the raw water also increased with increasing TMP in the range of 0.01–0.05 MPa. High ZP induced by PACl, such as 5–9 mV, led to an increase in the number of fine and total particles in the MCR, and consequently caused serious membrane fouling and high permeate turbidity.However, the removal of TOC and DOC increased with increasing ZP. A slightly positive ZP, such as 1–2 mV, corresponding to charge neutralization coagulation, was favorable for membrane fouling control. Moreover, dosing with KMnO_4 could further improve the removal of turbidity and DOC, thereby mitigating membrane fouling. The results are helpful for the application of the MCR in producing drinking water and also beneficial to the research and application of other coagulation and membrane separation hybrid processes.     

Transfer and transport of aluminum in filtration unit

Aluminum salt coagulants were used prevalently in various water works.In this article,the effects of filtration on residual aluminum concentration and species distribution were researched by determining the concentration of diiferent aluminum species before and after single layer filter,double layer filter,and membrane filtration units.In the research,size exclusion chromatography(SEC)was used to separate colloidal and soluble aluminum,ion exchange chromatography(IEC)was used to separate organic and inorganic aluminum, and inductivity coupled plasma-atomic emission spectrometry(ICP-AES)was used to determine the aluminum concentration.The results showed that the rapid filtration process had the ability of removing residual aluminum from coagulant effluent water,and that double layer filtration was more effective in residual aluminum removal than single layer filtration,while nano filtration was more effective than micro filtration.It was found that when the residual aluminum concentration was below 1mg/L in sediment effluent,the residual aluminum concentration in treated water was above 0.2 mg/L.The direct rapid filtration process mainly removed the suspended aluminum.The removal of soluble and colloidal aluminum was always less than 10% and the natural small particles that adsorbed the amount of soluble or small particles aluminum on their surface were difficult to be removed in this process.Micro filtration and nano filtration were good technologies for removing aluminum;the residual aluminum concentration in the effluent was less than 0.05 mg/L.     

Preferential binding between intracellular organic matters and Al13 polymer to enhance coagulation performance

Coagulation is the best available method for removing intracellular organic matter (IOM), which is released from algae cells and is an important precursor to disinfection by-products in drinking water treatment. To gain insight into the best strategy to optimize IOM removal, the coagulation performance of two Al salts, i.e., aluminum chloride (AlCl₃) and polyaluminum chloride (PACl, containing 81.2% Al₁₃), was investigated to illuminate the effect of Al species distribution on IOM removal. PACl showed better removal efficiency than AlCl₃ with regard to the removal of turbidity and dissolved organic carbon (DOC), owing to the higher charge neutralization effect and greater stability of pre-formed Al₁₃ species. High pressure size exclusion chromatography analysis indicated that the superiority of PACl in DOC removal could be ascribed to the higher binding affinity between Al₁₃ polymer and the low and medium molecular weight (MW) fractions of IOM. The results of differential log-transformed absorbance at 254 and 350?nm indicated more significant formation of complexes between AlCl₃ and IOM, which benefits the removal of tryptophan-like proteins thereafter. Additionally, PACl showed more significant superiority compared to AlCl₃ in the removal of < 5?kDa and hydrophilic fractions, which are widely viewed as the most difficult to remove by coagulation. This study provides insight into the interactions between Al species and IOM, and advances the optimization of coagulation for the removal of IOM in eutrophic water.     

Evaluation of drinking water treatment combined filter backwash water recycling technology based on comet and micronucleus assay

Based on the fact that recycling of combined filter backwash water（CFBW）directly to drinking water treatment plants（WTP）is considered to be a feasible method to enhance pollutant removal efficiency,we were motivated to evaluate the genotoxicity of water samples from two pilot-scale drinking water treatment systems,one with recycling of combined backwash water,the other one with a conventional process.An integrated approach of the comet and micronucleus（MN）assays was used with zebrafish（Danio rerio）to investigate the water genotoxicity in this study.The total organic carbon（TOC）,dissolved organic carbon（DOC）,and trihalomethane formation potential（THMFP）,of the recycling process were lower than that of the conventional process.All the results showed that there was no statistically significant difference（P>0.05）between the conventional and recycling processes,and indicated that the genotoxicity of water samples from the recycling process did not accumulate in 15 day continuous recycling trial.It was worth noting that there was correlation between the concentrations of TOC,DOC,UV₂₅₄,and THMFPs in water and the DNA damage score,with corresponding R² values of 0.68,0.63,0.28,and 0.64.Nevertheless,both DNA strand breaks and MN frequency of all water samples after disinfection were higher than that of water samples from the two treatment units,which meant that the disinfection by-products（DBPs）formed by disinfection could increase the DNA damage.Both the comet and MN tests suggest that the recycling process did not increase the genotoxicity risk,compared to the traditional process.     

聚硅酸对不同形态铝沉积行为的影响

针对给水管网中残余铝沉积和再溶解现象可能引起的水质问题,研究了聚硅酸对不同水解聚合形态铝沉积、再溶解的影响,并以石英微晶天平为表征手段,初步探讨了聚硅酸对不同形态铝沉积、再溶解过程影响的机理.结果表明,聚硅酸能显著改变不同水解聚合形态铝的沉积、再溶解行为.聚硅酸可与3种水解聚合形态的铝迅速结合而生成可沉积产物,但产物性质不同.以单体形态为主的Al_0与聚硅酸的反应产物性质较稳定,部分以溶解态存在,部分以非溶解态(可沉积态)存在;尽管铝的两种聚合形态Al_(13)和Al_(30)与聚硅酸反应也生成了部分可沉积产物,但随着时间的推移,这些产物又逐渐向溶解态转化.铝硅比对Al_0体系中铝的沉积溶解行为影响较小,而对Al_(13)和Al_(30)影响较大,且在0.2∶20(以Al和SiO_2计的质量比)时,沉积态铝的溶解速率最快.     

不同铝聚合形态对聚合铝混凝效果的影响

通过氯化铝(铝单体或初聚物形态Ala)、高Alb含量聚合铝(中等聚合形态Alb)、高Alc含量聚合铝(铝溶胶等高聚合形态Alc)和工业PACl(不同聚合度铝的混合形态Alabc)对某水厂沉后水实际水样进行烧杯混凝实验,依据絮体生长状况、浊度、UV254、颗粒数和过滤指数等参数综合评价不同铝形态的混凝作用效果,从而得出铝的最佳混凝形态.结果表明,高Alb含量聚合铝对浊度去除较好;而高Alc含量聚合铝对于颗粒物和UV254的去除效果较佳.     

铝系混凝剂优势形态分析及其混凝特性

聚合氯化铝（PACl）是常用的水处理混凝剂,在应用过程中通常表现出比传统铝盐更为优异的效果.研究表明,这种优异性能主要得益于其特殊的组成,特别是高分子聚合物Al₁₃和Al₃₀独特的物化特性.Al₁₃和Al₃₀是铝离子水解过程中的中间产物,在地球科学和环境化学等领域有着重要的研究价值.于水处理而言,二者的结构和分子特性是研究者关注的重点,大量研究基于此展开,很多重要的发现为实际应用奠定了基础.基于对PACl及其组成性质的研究,本文对PACl的混凝特性及其优势形态分子的分析进行了综合阐述.     

铝盐混凝剂的混凝效果与残留铝含量和组分之间的关系研究

研究了氯化铝、硫酸铝、聚合氯化铝(poly-aluminum chloride, PAC)3种铝盐混凝剂在腐殖酸-高岭土模拟水样中的应用,以比较3种混凝剂在该水样中的混凝效果与残留铝含量和组分之间的关系.结果表明, 3种铝盐混凝剂在试验选取的投加量下对浊度和UV254的去除率最高可达90%左右,PAC能在较高的投加量下达到较好的混凝效果;较高投加量下PAC混凝沉淀出水中残留总铝含量为0.9 mg/L左右,余铝率为-3.0%左右,均明显低于传统的铝盐混凝剂;3种混凝剂混凝处理腐殖酸-高岭土模拟水样时,残留铝均大部分以溶解性总铝的形式存在,且溶解性有机铝在总溶解性铝中所占比例较大;PAC在腐殖酸-高岭土混凝沉淀出水中残留总铝的含量下降最快,且能够有效降低出水中毒性较大的溶解性铝的含量,其混凝沉淀出水中残留总溶解性铝含量为0.6 mg/L左右.     

Al13形态在混凝中的作用机制

从铝的水解形态转化角度考察了铝盐在高碱度和高有机物浓度水体中的混凝行为.结果表明,铝盐的混凝效能是与混凝过程中的Al₁₃含量成正比.高投药量时氯化铝(AlCl₃)既可以有效调节水体pH值又能在混凝过程中原位水解产生较多的Al₁₃形态,因而混凝效能要高于聚合氯化铝(PACl).在铝盐混凝中,调节pH值到6～7之间可以控制铝形态分布从而达到提高混凝效能和减少残留铝的目的.在调节pH值强化混凝的方法中使用传统铝盐的效果要好于无机高分子絮凝剂.     

Comparison of the effects of aluminum and iron(III) salts on ultrafiltration membrane biofouling in drinking water treatment

Coagulation plays an important role in alleviating membrane fouling, and a noticeable problem is the development of microorganisms after long-time operation, which gradually secrete extracellular polymeric substances (EPS). To date, few studies have paid attention to the behavior of microorganisms in drinking water treatment with ultrafiltration (UF) membranes. Herein, the membrane biofouling was investigated with different aluminum and iron salts. We found that Al₂(SO₄)₃·18H₂O performed better in reducing membrane fouling due to the slower growth rate of microorganisms. In comparison to Al₂(SO₄)₃·18H₂O, more EPS were induced with Fe₂(SO₄)₃·xH₂O, both in the membrane tank and the sludge on the cake layer. We also found that bacteria were the major microorganisms, of which the concentration was much higher than those of fungi and archaea. Further analyses showed that Proteobacteria was dominant in bacterial communities, which caused severe membrane fouling by forming a biofilm, especially for Fe₂(SO₄)₃·xH₂O. Additionally, the abundances of Bacteroidetes and Verrucomicrobia were relatively higher in the presence of Al₂(SO₄)₃·18H₂O, resulting in less severe biofouling by effectively degrading the protein and polysaccharide in EPS. As a result, in terms of microorganism behaviors, Al-based salts should be given preference as coagulants during actual operations.     

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride(FeCl3), aluminum sulfate(Al2(SO4)3),polyaluminum chloride(PACl) and composite polyaluminum(HPAC), in order to remove dissolved organic matter(DOM). Considering the disinfection byproduct(DBP) precursor treatability, DOM was divided into five chemical fractions based on resin adsorption.Trihalomethane formation potential(THMFP) and haloacetic acid formation potential(HAAFP) were measured for each fraction. The results showed that hydrophobic acids(HoA), hydrophilic matter(HiM) and hydrophobic neutral(HoN) were the dominant fractions.Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally,HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation.HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions.DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PACl. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PACl under enhanced coagulation could reach51% and 59% respectively.     

Preparation of high concentration polyaluminum chloride by chemical synthesis-membrane distillation method with self-made hollow fiber membrane

A method of direct contact membrane distillation (DCMD) with a self-made hollow polyvinylidene fluoride membrane was applied to prepare high concentration polyaluminum chloride (PACl) with high Al_b content based on chemical synthesis. The permeate flux and Al species distribution were investigated. The experimental results showed that the permeate flux decreased from 14 to 6 kg/(m²·hr) at the end of the DCMD process, which can be mainly attributed to the formation of NaCl deposits on the membrane surface. The Al_b content decreased slightly, only from 86.3% to 84.4%, when the DCMD experiment finished, correspondingly the Al_c content increased slightly from 7.2% to 8.5%, and the Al_a content remained at 7% during the whole DCMD process. A PACl with Al_b content of 84% at total aluminum concentration 2.2 mol/L was successfully prepared by the chemical synthesis-DCMD method.     

藻形态及混凝剂组成对混凝-超滤过程的影响

为了保证藻类暴发阶段优质的饮用水供应,提高藻类的去除率,缓解藻类对水处理过程的影响,本研究以铜绿微囊藻(蓝藻)、小球藻(绿藻)和小环藻(硅藻)这3种不同形态藻细胞为研究对象,使用了3种具有不同铝形态分布的混凝剂[Al_2(SO_4)_3(AS)、Al_(13)、Al_(30)]进行混凝-超滤实验.在分离胞外有机物(EOM)的情况下,考察混凝过程中絮体的特性(粒径,强度因子,恢复因子)以及不同条件下形成的絮体对膜通量的影响.结果表明Al_(13)与Al_(30)的混凝作用以静电簇作用为主导,AS主要是以电中和作用为主导.对于铜绿微囊藻与小球藻体系,由于藻颗粒表面存在一定的凹陷,当Al_(13)与Al_(30)做混凝剂时,在投加量较低的情况下,吸附在颗粒表面凹陷处的混凝剂“失活”,其他部位由于仍带有一定的负电荷而造成絮体形成不明显,而AS做混凝剂时,混凝机制主要是电中和作用,可以明显降低颗粒之间的排斥力,在较低投加量下即可形成絮体.对于小环藻体系,由于其藻细胞呈现光滑的表面,Al_(13)与Al_(30)可有效发挥其静电簇作用机制,絮体在较低投加量下即可有效形成.膜通量与絮体粒径有明显的相关性,絮体粒径越大,超滤过程中形成的沉积层越疏松,膜比通量越大.