Nano silica removal from IC wastewater by pre-coagulation and microfiltration.

Microfiltration (MF) coupled with pretreatment by coagulation was adopted in the treatment of chemical mechanical polishing (CMP) wastewater from IC manufacturing plants, containing high concentrations of silica. Poly-aluminium chloride (PACl) was the coagulant, while the cationic polyacrylamide (PAA) was the flocculant aid. Preliminary tests were performed with the raw CMP wastewater in order to determine the optimal coagulation condition for subsequent microfiltration. Analysis of the particle size distribution shows that nearly all silica particles were enlarged from nano scale to at least 4 microm in diameter after the pre-treatment. The pre-treated wastewater was then filtered through a polytetrafluoroethylene (PTFE) membrane with a pore size 0.5 microm at a constant vacuum pressure. Trace amounts of PAA in addition to the PACl coagulation can effectively increases the permeate flux.     

Monitoring floc formation and breakage.

Monitoring of flocculation processes is of great practical importance and can give very useful information on the action of different coagulants under various conditions. It is shown that a continuous optical monitoring technique provides a convenient means of following the formation, break-up and regrowth of flocs under standard mixing and stirring conditions. Examples of results using this approach are given, with alum and PACl coagulants as well as a cationic polyelectrolyte. PACl products give larger flocs than with alum, but they show about the same relative degree of breakage when the shear rate is increased. With all of these coagulants, floc breakage is not fully reversible; i.e. flocs only re-grow to a limited extent when the shear rate is reduced. This is in marked contrast to the action of a cationic polyelectrolyte, where floc breakage is almost completely reversible. Some possible reasons for these observations are discussed, but, so far, there is no adequate model available.     

石英砂加载混凝工艺的DOM去除特征与混凝机理

为处理未纳入管网的市政污水,采用石英砂加载混凝工艺,考察石英砂的粒径及其投加量对处理效能的影响,分析了溶解性有机物(dissolved organic matters,DOM)的去除特征,并探讨了石英砂加载混凝机理。结果表明,与常规混凝相比,当石英砂的粒径和投加量分别为200目和 1.0 mg/L 时,石英砂加载混凝工艺对污水中浊度、COD的去除率分别为97.55%、59.2%,优于常规混凝;石英砂加载混凝工艺可明显去除芳香类、共轭双键、疏水性有机物,主要促进了腐殖质类物质的削减;石英砂通过架桥作用增加了絮体的密度,进而显著改善了絮体的沉降性能、强度;絮体的沉降性能、强度及再稳性能随着石英砂粒径的降低而升高。     

Phosphorus removal from synthetic and municipal wastewater using spent alum sludge.

In the present study, phosphorus removal was studied using as coagulant spent alum sludge from a water treatment plant of EYDAP (Athens Water Supply and Sewerage Company) and compared to alum (Al2(SO4)3.18H2O), iron chloride (FeCl3.7H2O), iron sulfate (Fe2(S04).10H2O) and calcium hydroxide (Ca(OH)2) at a constant pH (equal to 6).The comparison was based on their efficiency to remove phosphorus in synthetic wastewater consisting of 10 mg/L P as potassium dihydrogen phosphate and 50 mg/L N as ammonium chloride, The experiments were carried out using a jar-test apparatus and the measurements were performed according to the Standard Methods for the Examination of Water and Wastewater. Pure alum, iron chloride and iron sulfate were much more efficient in phosphorus removal than the spent alum sludge but in the case of calcium hydroxide, phosphorus removal was very low in pH = 6. Specifically, orthophosphate were totally removed by alum using 15 mg/L as Al, by alum sludge using 75 mg/L as Al and by FeCl3.7H2O or Fe2(SO4).10H2O using 30 mg/L of Fe while in the case of calcium hydroxide P removal was actually zero. pH measurements showed that the uptake of phosphates is associated to the release of OH ions in the solution and that the end of P uptake is accompanied by the stabilization of pH. Finally this spent alum sludge was tested on municipal wastewater and proved to be effective as apart from phosphorus it was shown to remove turbidity and COD.     

Influence of type and dose of coagulants on effectiveness of PAH removal in coagulation water treatment

This study evaluated the influence of the type and dose of coagulants on the removal of 16 polycyclic aromatic hydrocarbons (PAHs) in the coagulation process. The effects of coagulant type and dose in reducing water turbidity, colour, and the total content of organic compounds were also assessed. The surface water samples had the turbidity of 9.3–11.2 NTU and colour of 25–35 mg/L. The content of organic compounds determined with total organic carbon (TOC) was 9.2–12.5 mg/L. For the coagulation process, pre-hydrolyzed polyaluminium chloride (PACl) coagulants with basicity values of 41%, 65%, and 85% were used. This shows that water purification performance increased as the basicity of the coagulant increased. When the coagulant with the highest basicity and a dose of 3 mg Al per litre was used, a removal efficiency of 83% in the concentration of benzo(a)pyrene was achieved, and efficiencies for the remaining 15 PAHs ranged from 80% to 91%. These values were 4%–9% higher than those achieved using other coagulants. The removal efficiencies of turbidity, colour, and TOC were 80%, 60%, and 35%, respectively. The water purification performance, including PAH removal, was improved with the increased coagulant dose. Increasing the coagulant dose had more pronounced effects on PAH removal than on the reduction of turbidity and TOC.     

Irreversible and reversible adhesion between virus particles and hydrolyzing-precipitating aluminium: a function of coagulation.

The infectivity of viruses (Qbeta, MS2, T4, and P1) after dosing virus-contaminated water with 4 types of aluminium coagulant was investigated. The concentrations of infectious viruses were determined after dissolving aluminium hydroxide flocs in alkaline solution. The concentration of infectious viruses did not recover to the initial value after a short floc-dissolution time (5 s). Although the infectious virus concentration increased as the floc-dissolution time was extended to 5 h, it did not recover fully. Irreversible adhesion between virus particles and aluminium coagulant is responsible for the insufficient recovery. We interpret this phenomenon as a virucidal activity of the aluminium coagulant. All tested aluminium coagulants (PACl, alum, and reagent grade aluminium chloride and aluminium sulfate) inactivated all types of viruses tested. PACl had the highest virucidal activity. The virucidal activity of aluminium coagulants was lower in river water, presumably owing to the presence of natural organic matter.     

Characterization of micro-flocs of NOM coagulated by PACl, alum and polysilicate-iron in terms of molecular weight and floc size.

Micro-flocs of NOM coagulated by polyaluminium chloride (PACl), alum and polysilicate-iron (PSI) were characterized by flocs size, HPSEC-based molecular weight and the captured content of coagulants-based aluminium and iron. Changes in floc composition with respect to the mass ratios of captured NOM to Al and Fe were examined. Lowering water pH to optimum levels was found to be capable of removing small NOM constituents that are generally difficult to be precipitated at neutral pH levels. For PACl and PSI, the distribution of micro flocs (0.1-5.0 microm) reached steady stage after rapid mixing for 30 seconds, with NOM being found existent within the non-coagulated fraction (d<0.1 microm) and the coagulated fraction with floc sizes above 5.0 microm (d >5.0 microm). For alum, however, the existence of NOM inside intermediate floc fractions of d = 0.1-1.0 microm, 1.0-3.0microm and 3.0-5.0 microm was confirmed.     

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.     

Temperature effects on flocculation, using different coagulants.

Temperature is known to affect flocculation and filter performance. Jar tests have been conducted in the laboratory, using a photometric dispersion analyser (PDA) to assess the effects of temperature on floc formation, breakage and reformation. Alum, ferric sulphate and three polyaluminium chloride (PACI) coagulants have been investigated for temperatures ranging between 6 and 29 degrees C for a suspension of kaolin clay in London tap water. Results confirm that floc formation is slower at lower temperatures for all coagulants. A commercial PACl product, PAX XL 19, produces the largest flocs for all temperatures; and alum the smallest. Increasing the shear rate results in floc breakage in all cases and the flocs never reform to their original size. This effect is most notable for temperatures around 15 degrees C. Breakage, in terms of floc size reduction, is greater for higher temperatures, suggesting a weaker floc. Recovery after increased shear is greater at lower temperatures implying that floc break-up is more reversible for lower temperatures.     

Optimization study of a hybrid alum coagulation-membrane filtration system for virus removal

Due to the intrinsically small sizes of enteric viruses (20-100 nm) and their relatively high resistance to most disinfectants, detection of viruses in treated drinking water is not a rare phenomenon. This study therefore evaluates various aspects involved in a hybrid alum coagulation-ultrafiltration (UF) system for virus removal. Coagulant doses (0, 1 and 10 mg Al(3+)/L) and pH conditions relevant to drinking water (pH 6-8) were investigated. With this hybrid system, removal was not attributable merely to MS2 adsorption to flocs and subsequent retention by UF membranes. MS2 removal comprises of inactivation by the effect of pH and coagulant and subsequently, rejection of virus-associated flocs by UF membrane. Coagulation with 1 mg Al(3+)/L at pH 6 and 7 resulted in an overall reduction brought about by an average of 0.62 log inactivation via the pH effect, 1.2 log inactivation by alum coagulant, and >5.4 log rejection by the 100 kDa polyethersulfone UF membrane. In contrast, negligible upstream inactivation was noted with a coagulant dose of 1 mg Al(3+)/L at pH 8, but 5.8 log rejection was attained with downstream UF filtration. By optimizing the conditions appropriate for upstream inactivation and subsequent membrane rejection, virus removal efficiencies can be enhanced.     

Enhancing flexible fiber filter (3FM) performance using in-line coagulation.

A new packing for deep bed filtration using Flexible Fibers has been proposed and developed on a very large scale for tertiary treatment of wastewater. The purpose of this study is to check the possibility of using this technology for the production of drinking water from surface water. In this study, the feasibility of the fiber filter application on water treatment was examined and the removal efficiency of fiber filter was improved using an in-line coagulant injection method. The experiments were carried out at pilot scale. The filter was packed with bundles of polyamide fibers with a bed porosity of 93%. Nak-dong River was used as the filter influent water and alum, PSOM, and PAC were used as the coagulants. The coagulants were injected by the in-line injection method. Small dosages (1-5 mg/L) of the polymeric coagulants (PSOM and PAC) showed an increase of removal efficiency compared to the operation without coagulants. Specifically, 1 mg/L of PAC showed the longest filtration time. Considering filtration time, filtrate quality, and filtered volume, the filtration velocity of 120 m/hr was chosen as an optimum value. For long-term operations, the effluent quality was 0.4 NTU and the removal efficiency was stable for the given optimum conditions.     

Impact of Microcystis aeruginosa on membrane fouling in a biologically treated effluent

Microcystis aeruginosa was cultured in biologically treated municipal effluent to simulate blue-green algal bloom conditions in a treatment lagoon. The effect of algae in the early, mid and late phases of growth on membrane fouling, chemical coagulation (alum or aluminium chlorohydrate (ACH)) and hydraulic cleaning on the microfiltration of this effluent was investigated. The effect of M. aeruginosa in the early phase was negligible and gave a similar flux profile and permeate volume to that of effluent alone. The increase in M. aeruginosa concentration for the mid and late phases caused a significant reduction in permeate volume compared with the early phase. Full flux recovery was achieved with an alum dose of 1 mg Al3+ L(-1) (early phase) and 10 mg Al3+ L(-1) (mid phase), demonstrating that membrane fouling was hydraulically reversible. For the late phase, the highest flux recovery was 89%, which was achieved with an alum dose of 5 mg Al3+ L(-1). Higher alum dosages resulted in a reduction in flux recovery. The use of 1.5 pm pre-filtration after alum treatment showed little improvement in water quality but led to a drastic reduction in flux recovery, which was attributed to diminishing the protective layer on the membrane surface, thus enabling internal fouling. The performance of ACH was comparable to alum at low dissolved organic carbon (DOC) and cell concentration, but was not as effective as alum at high DOC and cell concentration due to the formation of more compact ACH flocs, which resulted in a higher cake layer specific resistance, leading to the deterioration of performance.     

The transformation of aluminium species in the processes of coagulation, sedimentation and filtration.

The aluminium toxicity is closely related to aluminium species. In this work aluminium was fractionated into seven forms: Al(T), Al(Sus), Al(C + S), Al(S), Al(C), Al(O) and Al(I). Four Al-based coagulants and simulated raw water were used in the laboratory to investigate the aluminium transformation in coagulation, sedimentation and filtration processes. It is the use of Al-based coagulants that contributes more to the increase of the residual aluminium for the low-turbidity raw water, while the Al-based coagulants, especially the polymeric aluminium coagulants, work to remove the aluminium from the high-turbidity raw water. In the case of traditional coagulants, the increase of the turbidity or the dissolved organic carbon (DOC) concentration in the raw water results in a high concentration of Al(C + S). The removal rate of aluminium species in the filtration process is not only related to its size: RAl(Sus) > RAl(C+S), RAl(C) > RAl(S), but also to the physicochemical properties of aluminium species and filter. For the kaolin-polyaluminium chloride system, a lower removal rate of aluminium species results is due to the complexation of humic acid and aluminium species.     

Effect of enhanced coagulation by KMnO(4) on the fouling of ultrafiltration membranes

Pre-coagulation enhanced by KMnO(4) before ultrafiltration (KCUF) was compared with normal pre-coagulation by alum (CUF) in the ultrafiltration of water from the Songhua River, China. The trans-membrane pressure (TMP) with KCUF was much lower than that when alum alone was used. With KCUF a slower increment of TMP occurred, even under conditions of high river water turbidity. The results also showed that the removal of COD, UV(254) and TOC was appreciably higher after adding 0.5mg/L KMnO(4) compared with CUF. Although assimilable organic carbon (AOC) was increased by permanganate treatment, the AOC of the permeate from KCUF was nearly the same as that from CUF, showing that the cake layer on the surface of KCUF membrane could adsorb small molecules more effectively than that of CUF. This result was confirmed by the apparent molecular weight (MW) distribution measured by size exclusion chromatography (SEC). It was shown that flocs formed by KMnO(4) and alum were larger than those formed only by alum, causing higher removal of flocs and higher permeation flux. Lower NOM was found in the permeate from the KCUF systems because oxidation and adsorption of organic matter on the flocs occurred. The membrane was partly clogged by organic matter or other materials including some small flocs.     

Comparing the effluent organic matter removal of direct NF and powdered activated carbon/NF as high quality pretreatment options for artificial groundwater recharge.

Direct nanofiltration and nanofiltration combined with powdered activated carbon known as the PAC/NF process were tested regarding the removal of effluent organic matter for reclamation of tertiary effluent from a municipal wastewater treatment plant. They can be regarded as a promising treatment alternative for high quality water reuse applications, especially for direct injection. The total removal for DOC was above 90% with permeate concentrations below 0.5 mg/l. Size exclusion chromatography and fluorescence EEM proved to trace origin of the organic matter even in low concentration ranges. The type and dosage of adsorbent influences the process performance significantly and allows process optimization.     

九龙江流域水厂生产废水回用条件的初步研究

以九龙江原水为研究对象,从改善低浊水混凝条件优化净水工艺角度,对生产废水的回用条件和作用规律进行了研究。研究认为:回用具有适当含固率的生产废水可以改善水处理过程的混凝条件,节省投药量,节药率一般为10%～40%;存在改善混凝条件、节省投药量的最佳含固率和最佳混合水浊度范围,最佳含固率为0.1%～0.7%,最佳混合水浊度为60～400NTU;原水浊度是显著影响最佳含固率的因素。当原水浊度小于60NTU时,最佳含固率随原水浊度的升高而增加,当原水浊度大于60NTU时.最佳含固率随原水浊度的升高而降低,最佳混合水浊度表现出相同的规律;在生产过程中,建议以最佳混合水浊度控制生产废水的回用。     

Dissolved air flotation of polishing wastewater from semiconductor manufacturer.

The feasibility of the dissolved air flotation (DAF) process in treating chemical mechanical polishing (CMP) wastewater was evaluated in this study. Wastewater from a local semiconductor manufacturer was sampled and characterised. Nano-sized silica (77.6 nm) with turbidity of 130 +/- 3 NTU was found in the slightly alkaline wastewater with traces of other pollutants. Experimental results indicated removal efficiency of particles, measured as suspended particle or turbidity, increased with increasing concentration of cationic collector cetyltrimethyl ammonium bromide (CTAB). When CTAB concentration was 30 mg/L, pH of 6.5 +/- 0.1 and recycle ratio of 30%, very effective removal of particles (> 98%) was observed in saturation pressure range of 4 to 6 kg/cm2, and the reaction proceeded faster under higher pressure. Similarly, the reaction was faster under the higher recycle ratio, while final removal efficiency improved slightly as the recycle ratio increased from 20 to 40%. An insignificant effect of pH on treatment efficiency was found as pH varied from 4.5 to 8.5. The presence of activator, Al3+ and Fe3+, enhanced the system performance. It is proposed that CTAB adsorbs on silica particles in polishing wastewater through electrostatic interaction and makes particles more hydrophobic. The increase in hydrophobicity results in more effective bubble-particle collisions. In addition, flocculation of silica particles through bridging effect of collector was found; it is believed that flocculation of particles also contributed to flotation. Better attachment between gas bubble and solid, higher buoyancy and higher air to solid ratio all lead to effective flotation.     

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.     

不同预处理方式与微滤联用处理城市污水对比实验研究

采用微滤法处理模拟二沉池出水,以期达到城市污水回用的目的.进水采用人工配水,主要考察微滤膜对模拟二沉池出水中CODMn,氨氮(NH3-N)及UV254的去除效果,以及预处理方式对微滤膜处理工艺的影响.实验主要采用了两种预处理方式,即颗粒活性炭(GAC)吸附及聚合氯化铝(PAC)混凝.实验结果表明,单独采用微滤膜效果不明显,高锰酸钾指数的去除率仅为32.5%,氨氯去除率约为5%,且膜污染严重,通量下降很快.活性炭-微滤组合工艺对污水的CODMn去除效果较好,去除率达到88%;而混凝-徽滤工艺对UV254的去除效果较好,去除率达到87%;混凝-微滤及活性炭-微滤工艺对氨氮的去除率均不高.组合工艺比起单独使用微滤膜流量下降缓慢,混凝-徽滤工艺在4.5h内,流量没有下降,污染情况明显改善.     

Wastewater reclamation systems in small communities.

The demands established in the rules and regulations by the administration in Catalonia seem to exclude small communities from wastewater reclamation and reuse, due to the comparatively high costs associated with the practice at small scale. In the framework of the DRAC project (Demonstration on Wastewater Reclamation and Reuse in Catalonia) two different pre-treatment systems, one extensive (infiltration-percolation) and another intensive (ring filter), each one followed by chlorine dioxide disinfection, were tested in order to be applied for small communities wastewater reclamation and reuse. The results of this study show that infiltration-percolation systems remove very efficiently physico-chemical contaminants and microorganisms. The ring filter system does not show a significant removal rate of contaminants, The use of infiltration-percolation as a pre-treatment for advanced chemical disinfection allows reducing the dose of disinfectant and the contact time needed to achieve a specific water quality, and diminishes disinfection byproducts (DBPs) generation. Therefore, this reclamation line is suitable for small communities due to its efficiency and low cost. However, further studies are needed in relation to the removal mechanisms of microorganisms, organic compounds in IP systems and the possible DBPs formation using chlorine dioxide.