板间距对电絮凝处理微污染水的影响

电絮凝作为一种具有广泛应用前景的低廉高效污水处理技术,已经被证明在工业废水、生活污水等污染严重的水体处理上具有显著效果,但是目前对于电絮凝净化微污染水的相关研究较少。通过对电絮凝分批处理河水的实验研究,分析电絮凝方法处理微污染水的可行性,讨论极板间距的改变对电絮凝处理效果的影响。结果表明,电絮凝处理技术可以用于微污染水净化中,在电流密度为17.75 A/m2、极板间距为1.5 cm的条件下,反应30 min时,色度去除率为73.76%,浊度去除率为76.00%,悬浮固体去除率为85.71%,化学需氧量去除率为42.86%,总磷去除率为61.36%。在电絮凝反应中,极板间距对于微污染水的色度、浊度、悬浮固体和总磷去除效果具有明显的影响。     

Removal of boron (B) from waste liquors.

This paper explores the use of electrocoagulation to remove boron from waste effluent in comparison with alum coagulation. In treating model test wastes, greater boron removals were achieved with electrocoagulation at low doses than conventional alum coagulation when reaction was undertaken for the same conditions (pH 8.5, and initial boron concentration was 500 mg/L). Al electrocoagulation can achieve good boron removal performance (68.3%) at a dose of 2.1 (as molar ratio of Al:B, and for current density of 62.1 A/m2), while alum coagulation can only achieve the maximum boron removal of 56% at a dose of 2.4. Also, Al electrocoagulation can remove 15-20% more boron than alum coagulation for the same dose compared in the treatment of both model test wastes and industry effluent. The estimation of running costs shows that to achieve 75% boron removal from industry waste effluent, i.e. removing 150 g of boron from 1 m3 of effluent, electrocoagulation was 6.2 times cheaper than alum coagulation. The economic advantage of electrocoagulation in the treatment of boron-containing waste effluent is thus significant.     

Comparison of electrocoagulation, coagulation and the fenton process for the treatment of reactive dyebath effluent.

In this paper, experimental studies were performed on a simulated reactive dyebath effluent to compare coagulation-flocculation and Fenton's oxidation with electrocoagulation using stainless steel (SS 304) and aluminium electrodes in terms of colour and COD removals as well as AOX formation potential and improvement of biological treatability. Results have indicated that FeCl3 and alum coagulation had little effect on colour removal whereas comparable colour removal efficiencies with those of electrocoagulation with steel electrodes and Fenton's oxidation were attained by FeSO4 coagulation. Almost complete colour removals accompanied with 77% COD abatement were obtained by both electrocoagulation with steel electrodes and Fenton's oxidation under optimised reaction conditions. Although electrocoagulation with aluminium electrodes yielded very limited colour removal and produced a high amount of sludge upon extended reaction time, this application brought about a marked improvement in biodegradability.     

Electrocoagulation technique in enhancing COD and suspended solids removal to improve wastewater quality.

This paper presents a preliminary study for the removal of COD and suspended solids in wastewater treatment by combining magnetic field and electrocoagulation (EC) technology. The experiments were carried out using batch apparatus and setup in the static method. Batch experiments with two monopolar iron (Fe) plate anodes and cathodes were employed as electrodes. Wastewater samples were prepared from milk powder with an initial COD of 1,140 mgL(-1) and suspended solids of 1,400 mgL(-1) and acidic conditions were employed (pH approximately 3). DC current was varied from 0.5-0.8 A and operating times were between 30 and 50 min. The results show that the effluent wastewater was very clear (turbidity approximately 9 NTU) and its quality exceeded the direct discharge standard. The suspended solids and COD removal efficiencies were as high as 30.6 and 75.5%, respectively. In addition, the experimental results also show that the electrocoagulation could neutralise the pH of wastewater.     

Electrochemical treatment of Baker's yeast wastewater containing melanoidin: optimization through response surface methodology

Effluents from Baker's yeast production plant contain a high percentage of color and a large amount of organic load. In the present study, Baker's yeast wastewater (BYW) is treated with the electrocoagulation (EC) process using Al electrodes. Operating parameters (pH, current density, color intensity and operating time) are optimized by response surface methodology (RSM). Quadratic models are developed for the responses which are removal efficiencies of color, chemical oxygen demand (COD) and total organic carbon (TOC) and operating cost (OC). Optimum operating parameters and responses are determined as initial pH 5.2, current density of 61.3 A/m(2) and operation time of 33 min, and 71% of color, 24% of COD, 24% of TOC removal efficiencies and OC of 0.869 €/m(3), respectively. The quadratic model fits for all responses very well with R(2) (>0.95). This paper clearly shows that RSM is able to optimize the operating parameters to maximize the color, COD and TOC removal efficiencies and minimize the OC.     

Kinetic study of slaughterhouse wastewater treatment by electrocoagulation using Fe electrodes

In this study, treatment of slaughterhouse wastewater by electrocoagulation was investigated in batch system using Fe electrodes. The effect of various variables such as electrode number, current density and operating time was tested. Pollutant removal efficiency increased with increasing electrode number and operating time. The biochemical oxygen demand (BOD(5))(,) chemical oxygen demand (COD), total suspended solid (TSS), and total nitrogen (TN) removal efficiencies using eight electrodes at a contact time of 50 min and a current density of 10 A/m(2) were 66, 62, 60, and 56%, respectively. Higher electrode numbers will allow shorter operating times to achieve certain removal efficiencies. Also, removal efficiencies increased by increasing the current density; the highest removal efficiencies of BOD(5,) COD, TSS, and TN at a contact time of 50 min and a current density of 25 A/m(2) were 97, 93, 81, and 84%, respectively. The results also show that the reactor pH varies directly with the current density; at 25 A/m(2), the reactor pH increased from an initial value of 7.1 to 7.7 after 50 min. The experimental results showed that the kinetics of BOD(5), COD, TSS and TN removal could be fitted adequately using a first order kinetic model (higher R(2)).     

Evaluation of bipolar electrocoagulation applied to biofiltration for phosphorus removal.

To reduce the residual organic matter and phosphorus contained in secondary effluent, a biofiltration system combined with electrocoagulation using bipolar iron electrodes was evaluated as a supplementary treatment to existing small-community sewage treatment. Based on the results of batch tests, bipolar electrocoagulation (BEC) was found to be more effective on phosphorus removal than monopolar electrocoagulation (MEC) but energy consumption was less in monopolar electrocoagulation. Optimum conditions of BEC to treat the secondary effluent were current density 15 A/m2, electrode spacing 1 cm and pH < 8. The removals of COD(Cr) and phosphorus by biofiltration system without BEC were 69.1% and 9.6%, respectively. However, biofiltration system combined with BEC showed 76.6-83.7% and 70.7-93.0% removal for COD(Cr) and phosphorus respectively. Extraordinary increase in phosphorus could be achieved by introducing electrocoagulation to biofiltration, and BEC/biofiltration system was evaluated to be applicable to existing small-community sewage treatment plants as a supplementary process.     

Application of chemical precipitation for piggery wastewater treatment.

Several series of experiments were conducted to investigate the treatment of piggery wastewater using chemical precipitation (CP) where various types of coagulants such as aluminium sulfate (Al2(SO4)3), poly aluminium chloride (PAC), ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), ferrous sulfate (FeSO4) and ferrous chloride (FeCl2) were used. Throughout the experiments, CP was found to achieve high removal efficiencies for organic compounds and nutrients (nitrogen and phosphorus) from the piggery wastewater. Experimental results showed the optimal doses of FeCl3, Fe2(SO4)3, FeCl2 and FeSO4 was 2.0 g/L, while 0.31 g/L and 2.5 g/L were the optimum dose for PAC and Al2(SO4)3, respectively. The pH range 4-5 resulted in the best performance to all coagulants except FeCl2 and FeSO4, whose optimum pH were more than 6. Percentage removal efficiencies for COD were in the ranges of 70-80%, 90-95% for SS, 80-90% for organic-N and TP. Those removal efficiencies were achieved within 5 min of operation. Three times of repetition in CP resulted in higher removal efficiencies for COD, SS and colour up to 74%, 99% and 94% respectively, in which Al2(SO4)3 was used as the coagulant. Removal efficiencies of various water quality parameters in a continuously operated reactor were similar to those of the batch experiments. Biodegradable ratios (BOD5/COD) increased up to 65% after the application of CP.     

常规混凝沉淀工艺对阴离子表面活性剂的去除研究

随着阴离子表面活性剂(LAS)在民用和工业上的广泛应用,由此带来的水污染问题也日益加剧,对供水安全造成了很大威胁。针对目前大部分水厂仍采用混凝沉淀常规水处理工艺,考察了常规混凝沉淀工艺对LAS的去除效果。以Al2(SO4)3,PAC,FeCl3,PFS为混凝剂,非离子PAM为助凝剂进行了试验,结果表明混凝沉淀对LAS有一定的去除效果,而且有机物和LAS的去除有一定相关关系。但浊度与LAS的去除相关性较差。试验条件下对于LAS去除最佳混凝方案是投加量为40 mg/L的FeCl3。相同水质条件下铁盐混凝剂在除浊、除有机物和除LAS方面优于铝盐混凝剂。pH和水温对LAS的去除有一定影响,较低的pH和较高的水温均有利于LAS的去除。     

Column studies to determine mercury settling in road runoff

A study was performed using a settling column to remove mercury (Hg) from road runoff. The emphasis was placed on the relationship between Hg removal and critical settling velocities, as well as the distribution of total suspended solids (TSS). The impact of rainfall characteristics and temperature on Hg removal was also discussed. Results indicated that Hg removal was significant within the initial 30 min of the settling process. The Hg removal rate increased with the decrease of critical settling velocity, and this trend became gradually significant, which could be used as an important reference for the optimization of sedimentation basin design. Hg removal at different settling times was significantly related to initial distribution of TSS. The impact of rainfall intensity on Hg removal was greater than other parameters of precipitation features, followed by rainfall. In addition, Hg removal was moderately related to temperature. The effect of antecedent dry periods on Hg removal was restricted by rainfall and rainfall intensity.     

Removal of Cu(II) ions from aqueous solutions using N-carboxymethyl chitosan

N-carboxymethyl chitosan (NCMC) was synthesized by reacting chitosan with chloroacetic acid in water under triethylamine (Et(3)N) as catalyst. The chemical structures of NCMC were characterized by Fourier transform infrared (FT-IR) and hydrogen-1 nuclear magnetic resonance ((1)H-NMR) spectroscopy and confirmed that carboxymethylation occurred on the amino groups. Samples of NCMC were used for removal of Cu(II) from aqueous solution. The effects of degree of substitution of NCMC, initial pH value and adsorption kinetics on the adsorption were studied. Adsorption experiments showed that NCMC has a high adsorption speed and high adsorption capacity for remove Cu(II) from aqueous solution. The adsorption kinetics data were best fitted with the pseudo-second-order model. The experimental equilibrium data of Cu(II) on the NCMC were both fitted to the Langmuir model and Freundlich model, which revealed that the maximum capacity for monolayer saturation was 147.93 mg/g.     

Removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone

In this study, the removal of copper(II) and cadmium(II) ions from aqueous solutions by biosorption onto pine cone was studied. Variables that affect the biosorption process such as pH, biosorbent dosage, initial metal ion concentration, contact time and temperature of solution were optimized. Experimental data were fitted to Langmuir, Freundlich, Dubinin Radushkevich and Temkin isotherm models to investigate the equilibrium isotherms. Pseudo-first-order, pseudo-second-order and intraparticle diffusion kinetic models were used to determine the biosorption mechanism. The thermodynamics of biosorption were studied for predicting the nature of biosorption. Experimental results showed that pine cone could be evaluated as an alternative precursor for removal of heavy metal ions from aqueous solutions, due to its high biosorption capacity, availability, and low cost.     

Use of sesame stalk biomass for the removal of Ni(II) and Zn(II) from aqueous solutions

In this study an agricultural residue, sesame stalk, was evaluated for the removal of Ni(II) and Zn(II) metal ions from aqueous solutions. Biosorption studies were carried out at different pH, biosorbent dosage, initial metal ion concentrations, contact time, and solution temperature to determine the optimum conditions. The experimental data were modeled by Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models. Langmuir model resulted in the best fit of the biosorption data. The pseudo-first-order and pseudo-second-order kinetic models were used to describe the kinetic data and to evaluate rate constants. The best correlation was provided by the second-order kinetic model. The thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated for predicting the nature of adsorption. The experimental results showed that sesame stalk can be used as an effective and low-cost biosorbent precursor for the removal of heavy metal ions from aqueous solutions.     

Biosorption of chromium(VI), nickel(II) and Remazol blue by Rhodotorula muciloginosa biomass

The passive removal of commonly used reactive dye and two heavy metals, from aqueous solutions by inexpensive biomaterial, yeast Rhodotorula muciloginosa biomass, termed biosorption, was studied with respect to pH, initial dye concentration and initial metal ion concentration. The biomass exhibited maximum dye and chromium(VI) uptake at pH 5 and pH 6 for nickel(II) in media containing 50 mg/L heavy metal and 50 mg/L remazol blue. It was found that the highest chromium(VI) removal yields measured were 31.3% for 49.0 mg/l initial chromium(VI) concentrations. The nickel(II) removal yield was 32.5% for 22.3 mg/L. Higher R. Blue removal yields were obtained, such as 77.1% for 117.5 mg/L. The maximum dye biosorption yield was investigated in medium with a constant dye (approximately 50 mg/L) and increasing heavy metal concentration. In the medium with 48.8, 103.8 and 151.8 mg/L chromium(VI) and constant dye concentration, the maximum chromium(VI) biosorption was 7.4, 9.3 and 17.1%, whereas the maximum dye biosorption was 61.6, 56.6 and 55.9%. The maximum nickel(II) biosorptions in the medium with dye were 38.1, 22.1 and 8.8% at 23.7, 37.7 and 60.1 mg/L nickel(II) concentrations. In these media, dye biosorptions were 93.9, 86.4 and 93.3%, respectively.     

Equilibrium, kinetic and thermodynamic studies of mercury adsorption on almond shell

The application of almond shell as a low cost natural adsorbent to remove Hg(2+) from aqueous solution was investigated. Batch experiments were carried out to evaluate the adsorption capacity of the material. The chemical and physical parameters such as pH, sorbent amount, initial ion concentration, and contact time were optimized for the maximum uptake of mercury onto the solid surface. Adsorption isotherms were expressed by Langmuir and Freundlich adsorption models, and the experimental data were found to fit the Langmuir model rather than the Freundlich. The maximum adsorption capacity obtained from the Langmuir isotherm was 135.13 mg/g. A kinetic study was carried out with pseudo-first-order and pseudo-second-order reaction equations and it was found that the Hg(2+) uptake process followed the pseudo-second-order rate expression. The thermodynamic values, ΔG(0), ΔH(0) and ΔS(0), indicated that adsorption was an endothermic and spontaneous process. The potential of this material for mercury elimination was demonstrated by efficient Hg(2+) removal from a synthetic effluent.     

利用电凝聚-气浮法研究印染废水的脱色性能

自制电解装置,以铁板作为阳极,以NaCl作为电解液,采用电凝聚-气浮法对模拟印染废水偶氮染料活性绿RG19和活性蓝RBu171进行脱色研究,探索废水的pH值、浓度、电凝聚时间、电解质浓度等因素对废水的色度去除率的影响.实验结果显示:染料废水浓度低于300 ppm,电解质NaCl浓度为2g/L,溶液的pH初始值小于7,两种染料RG19和RB171在120 min内,脱色效率均可达到90％.     

无定形氢氧化铝吸附剂的制备及其除氟性能研究

降氟措施对高氟地下水地区居民饮用水安全具有重要意义。吸附法除氟技术被广泛应用,但仍存在适宜于偏酸性环境等难点。以提高适应高氟地下水pH值的能力为目标,通过控制反应过程中pH值制备无定形氢氧化铝吸附材料,开展吸附等温线试验、吸附动力学试验、pH值适应性试验、竞争离子试验、可重复利用性能试验和吸附机理试验。试验结果表明无定形氢氧化铝对氟离子的吸附属于优惠型吸附,Langmuir最大吸附容量为166.67 mg/g。与传统Al_2O_3吸附材料相比,在pH值为7.0~9.0时,无定形氢氧化铝吸附材料可减缓除氟效果下降速率,提高了适应地下水pH值的能力。氟去除率随着溶液中HCO_3~-、CO_2-3、PO_4~(3-)等离子浓度升高而降低。在初始氟浓度为5.00 mg/L时,可重复利用5个周期。因此,改进铝型吸附材料制备过程可显著提高吸附性能和适应高氟地下水的能力,是今后研制和改进吸附材料的重要方向。     

Lab scale study on electrocoagulation defluoridation process optimization along with aluminium leaching in the process and comparison with full scale plant operation

An excess or lack of fluoride in drinking water is harmful to human health. Desirable and permissible standards of fluoride in drinking water are 1.0 and 1.5 mg/L, respectively, as per Indian drinking water quality standards i.e., BIS 10500, 1991. In this paper, the performance of an electro-coagulation defluoridation batch process with aluminium electrodes was investigated. Different operational conditions such as fluoride concentration in water, pH and current density were varied and performance of the process was examined. Influence of operational conditions on (i) electrode polarization phenomena, (ii) pH evolution during electrolysis and (iii) the amount of aluminium released (coagulant) was investigated. Removal by electrodes is primarily responsible for the high defluoridation efficiency and the adsorption by hydroxide aluminium floc provides secondary effect. Experimental data obtained at optimum conditions that favored simultaneous mixing and flotation confirmed that concentrations lower than 1 mg/L could be achieved when initial concentrations were between 2 and 20 mg/L. pH value was found to be an important parameter that affected fluoride removal significantly. The optimal initial pH range is between 6 and 7 at which effective defluoridation and removal efficiencies over 98% were achieved. Furthermore, experimental results prominently displayed that an increase in current density substantially reduces the treatment duration, but with increased residual aluminium level. The paper focuses on pilot scale defluoridation process optimization along with aluminium leaching and experimental results were compared with a full-scale plant having capacity of 600 liter per batch.     

Application of mulch for treating metals in urban runoff: batch and column test.

Among the many methods available for the removal of heavy metals in urban nonpoint source pollution (NSP), adsorption has been shown to be an economically feasible alternative. To adsorb the amount of heavy metals in runoff, filtration of runoff through a specially constructed filter system is one possible treatment method. The mulch layer in a specially constructed filter system functions through adsorptive-filtration, where some pollutants are immobilised through sorption and some pollutants associated with suspended solids are immobilised through filtration. Therefore, the major interest of this study was to investigate the possibility of utilising mulch for the adsorption of heavy metals such as cadmium, copper, lead and zinc for a solution typical of those found in urban runoff using the flask-type adsorption batch tests and laboratory column tests. From the equilibrium sorption batch tests, it was observed that the adsorption of heavy metals on mulch with the same initial concentrations of metals in the solution decreased in the order Pb(II) > Cu(II) > Zn(II) > Cd(II) regardless of changes in pH. In column tests, the breakthrough curves for various heavy metals' adsorption by mulch showed that the binding strength of the following metal ions onto mulch was as follows: Pb(II) > Cu(II) > Zn(II) > Cd(II).     

Combining photo-Fenton process with biological sequencing batch reactor for 2,4-dichlorophenol degradation.

The effect of the photo-Fenton process on biodegradability enhancement of 100 mg x L(-1) aqueous 2,4-dichlorophenol (2,4-DCP) solution has been investigated. An initial concentration of 65 mg x L(-1) H2O2 and 10 mg x L(-1) Fe (II) during 35 minutes of irradiation time was sufficient for total 2,4-DCP removal. At these working conditions, biodegradability, measured as BODS/COD ratio, was increased from 0 for the original solution up to 0.15. Biological oxidation of photo-Fenton pre-treated solutions was performed in a sequencing batch reactor (SBR). After 32 days of start-up, the reactor was fed with different pre-treated solutions and cycle duration was reduced progressively. TOC removal efficiencies in the SBR went from 30 up to 70%.