Preparation and characterization of organic polymer modified composite polyaluminum chloride

Compared with traditional aluminum salts, polyaluminum chloride （PACI） has better coagulation-flocculation performance in turbidity removal. However, it is still inferior to organic polymers in terms of bridging function. In order to improve the aggregating property of PACl, different composite PACl flocculants were prepared with various organic polymers. The effect of organic polymer on the distribution or Al（Ⅲ） species in composite flocculants was studied using ^27TAl NMR and Al-ferron complexation methods. The charge neutralization and surface adsorption characteristics of composite flocculants were also investigated. Jar tests were conducted to evaluate the turbidity removal efficacy of organic polymer modified composite flocculants. The study shows that cationic polymer and anionic polymer have significant influences on the coagulation-flocculation behaviors of PACl. Both cationic and anionic polymers can improve the turbidity removal performancc of PACl but the mechanisms arc much different： cationic organic polymer mainly increases the charge neutralization ability, but anionic polymer mainly enhances the bridging function.     

Effect of algal flocculation on dissolved organic matters using cationic starch modified soils

Modified soils(MSs) are being increasingly used as geo-engineering materials for the sedimentation removal of cyanobacterial blooms. Cationic starch(CS) has been tested as an effective soil modifier, but little is known about its potential impacts on the treated water.This study investigated dissolved organic matters in the bloom water after algal removal using cationic starch modified soils(CS-MSs). Results showed that the dissolved organic carbon(DOC) could be decreased by CS-MS flocculation and the use of higher charge density CS yielded a greater DOC reduction. When CS with the charge density of 0.052, 0.102 and0.293 meq/g were used, DOC was decreased from 3.4 to 3.0, 2.3 and 1.7 mg/L, respectively.The excitation–emission matrix fluorescence spectroscopy and UV254 analysis indicated that CS-MS exhibits an ability to remove some soluble organics, which contributed to the DOC reduction. However, the use of low charge density CS posed a potential risk of DOC increase due to the high CS loading for effective algal removal. When CS with the charge density of 0.044 meq/g was used, DOC was increased from 3.4 to 3.9 mg/L. This study suggested, when CS-MS is used for cyanobacterial bloom removal, the content of dissolved organic matters in the treated water can be controlled by optimizing the charge density of CS. For the settled organic matters, other measures(e.g., capping treatments using oxygen loaded materials) should be jointly applied after algal flocculation.     

Demulsification performance and mechanism of oil droplets by electrocoagulation: Role of surfactant

Surfactants are widely used to improve the solubility of oil in water in petrochemical, making it more difficult to remove oil–water emulsions during the water treatment process. Electrocoagulation (EC) is an appropriate method for treating oily wastewater and destabilizing emulsions. However, the demulsification mechanism of oil–water droplets emulsified by surfactants with different charges have not been investigated systematically. The demulsification performance of electrocoagulation on emulsions wastewater containing cationic, non-ionic, and anionic surfactants was studied. The results showed that the removal rate of total organic carbon (TOC) in oily wastewater with anionic surfactant by EC reached 92.98% ± 0.40% at a current density of 1 mA/cm², while that of the non-ionic surfactant was 84.88% ± 0.63%. The characterization of flocs showed that EC has the highest coagulation and demulsification of oil droplets with a negative charge on the surface (−70.50 ± 10.25 mV), which indicated that the charge neutralization of oil droplets was beneficial for the destabilization of the formed oily flocs. However, when the zeta potential of the oil droplets reached 75.50 ± 1.25 mV, the TOC removal efficiency was only 11.80% ± 1.43%. The TOC removal could achieve 33.23% ± 3.21% when the current density improved from 1 mA/cm² to 10 mA/cm². The enhanced removal was due to the sweep coagulation rather than charge neutralization. This study provides a fundamental basis for the electrochemical treatment of oily wastewater.     

Influence of coagulation mechanisms and floc formation on filterability

Minimizing particles in water is a key goal for improving drinking water quality and safety.The media filtration process,as the last step of the solid–liquid separation process,is largely influenced by the characteristics of flocs,which are formed and controlled within the coagulation process.In a laboratory-based study,the impacts of the physical characteristics of flocs formed using aluminum sulfate on the filtration treatment of two comparative water samples were investigated using a photometric dispersion analyzer and a filterability apparatus.In general,the optimum dosage for maximizing filterability was higher than that for minimizing turbidity under neutral p H conditions.For a monomeric aluminum-based coagulant,the charge neutralization mechanism produced better floc characteristics,including floc growth speed and size,than the sweep flocculation mechanism.In addition,the charge neutralization mechanism showed better performance compared to sweep flocculation in terms of DOC removal and floc filterability improvement for both waters,and showed superiority in turbidity removal only when the raw water had high turbidity.For the different mechanisms,the ways that floc characteristics impacted on floc filterability also differed.The low variation in floc size distribution obtained under the charge neutralization mechanism resulted in the flocs being amenable to removal by filtration processes.For the sweep flocculation mechanism,increasing the floc size improved the settling ability of flocs,resulting in higher filter efficiency.     

Simultaneous nitrogen and phosphor removal in an aerobic submerged membrane bioreactor

Simultaneous nitrification and denitrification （SND） effect and phosphor removal were investigated in a one-staged aerobic submerged membrane bioreactor on pilot-scale with mixed liquor suspended solids （MLSS） 19--20 g/L. The effects of DO concentration, sludge floc size distribution on SND were studied. Test results suggested that SND was successfully performed in the membrane bioreactor （MBR） and about 70% total nitrogen removal efficiency was achieved when DO concentration was set to 0.2-- 0.3 mg/L. The main mechanisms governing SND were the suitable sludge floc size and the low DO concentration which was caused by low oxygen transfer rate with such a high MLSS concentration in the MBR. In the meantime, phosphor removal was also studied with polymer ferric sulfate （PFS） addition and 14 mg/L dosage of PFS was proper for the MBR to remove phosphor. PFS addition also benefited the MBR operation owing to its reduction of extracellular polymer substances （EPS） of mixed liquor.     

Effects of pre-ozonation on organic matter removal by coagulation with IPF-PACI

Ozone plays an important role as a disinfectant and oxidant in potable water treatment practice and is increasingly being used as a pre-oxidant before coagulation. The purpose of this study is to obtain insight into the mechanisms that are operative in pre-ozonized coagulation. Effects ofpre-ozonation on organic matter removal during coagulation with IPF-PAC1 were investigated by using PDA （photometric disperse analysis）, apparent molecular weight distribution and chemical fractionation. The dynamic formation of flocs during coagulation process was detected. Changes of aquatic organic matter （AOM） structure resulted from the influence of pre-ozonation were evaluated. Results show that dosage of O3 and characteristics of AOM are two of the major factors influencing the performance of O3 on coagulation. No significant coagulation-aid effect of O3 was observed for all experiments using either A1C13 or PAC1. On the contrary, with the application of pre-ozonation, the coagulation efficiency of A1C13 was significantly deteriorated, reflected by the retardation of floc formation, and the removal decreases of turbidity, DOC, and UV254. However, if PACl was used instead of AlCl3, the adverse effects of pre-ozonation were mitigated obviously, particularly when the O3 dosage was less than 0.69 （mg O3/mg TOC）. The difference between removals of UV254, and DOC indicated that pre-ozonation greatly changed the molecular structure of AOM, but its capability of mineralization was not remarkable. Only 5% or so DOC was removed by pre-ozonation at 0.6--0.8 mg/L alone. Fractionation results showed that the organic products of pre-ozonation exhibited lower molecular weight and more hydrophilicity, which impaired the removal of DOC in the following coagulation process.     

One-step synthesis of Cu(II) metal–organic gel as recyclable material for rapid, efficient and size selective cationic dyes adsorption

Efficient removal of non-biodegradable and hazardous dyes from wastewater remains a hot research topic. Herein, a rationally designed a Cu(Ⅱ)-based metal–organic gel(Cu-MOG) with a nanoporous 3 D network structure prepared via a simple one-step mixing method was successfully employed for the removal of cationic dyes. The Cu-MOG exhibited high efficiency, with an adsorption capacity of up to 650.32 mg/g, and rapid adsorption efficiency, with the ability to adsorb 80% of Neutral Red within 1 min. The high adsorption efficiency was attributed to its large specific surface area, which enabled it to massively bind cationic dyes through electrostatic interaction, and a nanoporous structure that promoted intra-pore diffusion. Remarkably, the Cu-MOG displayed size-selective adsorption, based on adsorption studies concerning dyes of different sizes as calculated by density functional theory. Additionally, the adsorption performance of the Cu-MOG still maintained removal efficiency of 100% after three regeneration cycles. These results suggested that the Cu-MOG could be expected to be a promising and competitive candidate to conveniently process wastewater.     

Removal of F− and organic matter from coking wastewater by coupling dosing FeCl3 and AlCl3

Coagulation and precipitation is a widely applied method to remove F^? from wastewater. In this work, the effect of coagulation on the removal of F^? and organic matter from coking wastewater was studied using AlCl₃ and FeCl₃ as compound coagulants. The removal rates of F^? and organic matter under different coagulant doses and pH conditions were investigated. The results show that the highest removal rates of F^? by AlCl₃ and FeCl₃ are 94.4% and 25.4%, respectively; when the dosage is 10 mmol/L, the TOC removal rates of FeCl₃ and AlCl₃ reach 20.4% and 34.7%, respectively. Therefore, the removal rate of F^? by AlCl₃ is higher than that of FeCl₃, but the removal rate of organic matter by FeCl₃ is relatively higher. The addition of Ca²⁺ can promote the removal of F^?, but the removal rate of organic matter decreases. In addition, by investigating the effects of different pH and Fe–Al ratio on the removal rate, the removal effect of adding FeCl₃ and AlCl₃ at the same time was discussed. The results show that the most suitable working condition for the removal of organic matter and F^? is that the pH is 6.5 and the molar ratio of Al/Fe is 8:2. Overall, the removal mechanism of F^? and organic matter in coking wastewater by FeCl₃ and AlCl₃ was explored in this study. The experimental results can provide reference for the advanced treatment of coking wastewater.     

Study on the role of copper converter slag in simultaneously removing SO2 and NOx using KMnO4/copper converter slag slurry

To achieve “waste controlled by waste”, a novel wet process using KMnO4/copper converter slag slurry for simultaneously removing SO2 and NOx from acid-making tail gas was proposed. Through the solid-liquid separation for copper slag slurry, the liquid-phase part has a critical influence on removing NOx and SO2. Also, the leached metal ions played a crucial role in the absorption of SO2 and NOx. Subsequently, the effects of single/multi-metal ions on NOx removal was investigated. The results showed that the leached metal from copper converter slag (Al3+, Cu2+, and Mg2+) and KMnO4 had a synergistic effect on NOx removal, thereby improving the NOx removal efficiency. Whereas Fe2+ had an inhibitory effect on the NOx removal owing to the reaction between Fe2+ and KMnO4, thereby consuming the KMnO4. Besides, SO2 was converted to SO42? completely partly due to the liquid catalytic oxidation by metal ions. The XRD and XPS results indicated that the Fe (II) species (Fe2SiO4, Fe3O4) in copper slag can react with H+ ions with the generation of Fe2+, and further consumed the KMnO4, thereby resulting in a decrease in the NOx removal. The characterization of the slags and solutions before and after reaction led us to propose the possible mechanisms. The role of copper slag is as follows: (1) the alkaline substances in copper slag can absorb SO2 and NO2 by KMnO4 oxidation. (2) copper slag may function as a catalyst to accelerate SO2 conversion and improve NOx removal by synergistic effect between leached metal ions and KMnO4.     

Review of heterogeneous photochemical reactions of NOy on aerosol－A possible daytime source of nitrous acid (HONO) in the atmosphere

As an important precursor of hydroxyl radical, nitrous acid (HONO) plays a key role in the chemistry of the lower atmosphere. Recent atmospheric measurements and model calculations show strong enhancement for HONO formation during daytime, while they are inconsistent with the known sources in the atmosphere, suggesting that current models are lacking important sources for HONO. In this article, heterogeneous photochemical reactions of nitric acid/nitrate anion and nitrogen oxide on various aerosols were reviewed and their potential contribution to HONO formation was also discussed. It is demonstrated that HONO can be formed by photochemical reaction on surfaces with deposited HNO3 , by photocatalytic reaction of NO2 on TiO2 or TiO2 -containing materials, and by photochemical reaction of NO2 on soot, humic acids or other photosensitized organic surfaces. Although significant uncertainties still exist in the exact mechanisms and the yield of HONO, these additional sources might explain daytime observations in the atmosphere.     

Effect of Fe（Ⅲ） on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment. In this study, experiments were conducted to determine the reduction capacity of humic acid in the man-ix of bromate and Fe（Ⅲ） solutions and the role of Fe（Ⅲ） in this redox process. The results showed that the humic acid regenerated Fe（Ⅱ） and reduced bromate abiotically. The addition of Fe（Ⅲ） could accelerate the bromate reduction rate by forming humic acid-Fe（Ⅲ） complexes. Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid, in which humic acid transfers electrons to the complexed Fe（Ⅲ） to form Fe（Ⅱ）, and the regenerated Fe（Ⅱ） donate the electrons to bromate. The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe（Ⅲ） complexes is pH dependent. The rate decreased by 2-fold with the increase in solution pH by one unit. The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River, indicating that such redox process is expected to occur in the environment.     

Effect of ozone on the performance of a hybrid ceramic membrane-biological activated carbon process

Two hybrid processes including ozonation-ceramic membrane-biological activated carbon （BAC） （Process A） and ceramic membrane-BAC （Process B） were compared to treat polluted raw water. The performance of hybrid processes was evaluated with the removal efficiencies of turbidity, ammonia and organic matter. The results indicated that more than 99% of particle count was removed by both hybrid processes and ozonation had no significant effect on its removal. BAC filtration greatly improved the removal of ammonia. Increasing the dissolved oxygen to 30.0 mg/L could lead to a removal of ammonia with concentrations as high as 7.80 mg/L and 8.69 mg/L for Processes A and B, respectively. The average removal efficiencies of total organic carbon and ultraviolet absorbance at 254 nm （UV254, a parameter indicating organic matter with aromatic structure） were 49% and 52% for Process A, 51% and 48% for Process B, respectively. Some organic matter was oxidized by ozone and this resulted in reduced membrane fouling and increased membrane flux by 25%-30%. However, pre-ozonation altered the components of the raw water and affected the microorganisms in the BAC, which may impact the removals of organic matter and nitrite negatively.     

Effect of viscosity, basicity and organic content of composite flocculant on the decolorization performance and mechanism for reactive dyeing wastewater

A coagulation/flocculation process using the composite flocculant polyaluminum chloride-epichlorohydrin dimethylamine (PAC-EPI-DMA) was employed for the treatment of an anionic azo dye (Reactive Brilliant Red K-2BP dye). The effect of viscosity (ηup), basicity (B = [OH]/[Al]) and organic content (W_P) on the flocculation performance as well as the mechanism of PAC-EPI-DMA flocculant were investigated. The ηup was the key factor affecting the dye removal efficiency of PAC-EPI-DMA. PAC-EPI-DMA with an intermediate ηup (2400 mPa.sec) gave higher decolorization efficiency by adsorption bridging and charge neutralization due to the co-effect of PAC and EPI-DMA polymers. The W_P of the composite flocculant was a minor important factor for the flocculation. The adsorption bridging of PAC-EPI-DMA with ηup of 300 or 4300 mPa.sec played an important role with the increase of W_P, whereas the charge neutralization of them was weaker with the increase of W_P. There was interaction between W_P and B on the removal of reactive dye. The composite flocculant with intermediate viscosity and organic content was effective for the treatment of reactive dyeing wastewater, which could achieve high reactive dye removal efficiency with low organic dosage.     

Removal natural organic matter in typical south-China source water during enhanced coagulation of a with IPF-PACl

Systematic investigation on enhancing removal of natural organic matter （NOM） using inorganic polymer flocculant （IPF）, polyaluminum chloride（PACI） and polyacrylamide（PAM） was performed in a typical south-China source water. Enhanced coagulation and applying polymer flocculant-aid were compared through jar tests and pilot tests. Raw water and settled water were characterized and fractionated by resin adsorption. The results show that DOC composes major part of TOC. The DOC distribution keeps relatively stable all around the year with typical high amounts of the hydrophilic matter around 50%. The distribution between HoB, HoA and HoN varies and undergoes fluctuation with the year round. During the summer season, the HoN becomes gradually the major part in hydrophobic parts. PACI with the species being tailor-made shows little pH effect during coagulation. The enhanced coagulation dosage for PACI could be 4.5 mg/L for the typical source water. The highest TOC removal achieved 31%. To be economically, 3 mg/L dose is the optimum dosage. Although hydrophilic fractions of NOM of both treatment strategies are removed about 30%, NOM causing UV254 absorbance were well removed（about 90%）. Hydrophobic bases and acids fractions are much more removed under enhanced conditions. The hydrophilic fraction could be better removed using PAM, the polymer coagulant aid.     

Application of ferrate（VI） in the treatment of industrial wastes containing metal-complexed cyanides ： A green treatment

Ferrate(VI) was employed for the oxidation of cyanide (CN) and simultaneous removal of copper or nickel in the mixed/complexed systems of CN-Cu, CN-Ni, or CN-Cu-Ni. The degradation of CN (1.00 mmol/L) and removal of Cu (0.095 mmol/L) were investigated as a function of Fe(VI) doses from 0.3–2.00 mmol/L at pH 10.0. It was found that Fe(VI) could readily oxidize CN and the reduction of Fe(VI) into Fe(III) might serve e ciently for the removal of free copper ions. The increase in Fe(VI) dose apparently favoured the CN oxidation as well as Cu removal. Moreover, the pH dependence study (pH 10.0–13.0) revealed that the oxidation of CN was almost una ected in the studied pH range (10.0–13.0), however, the maximum removal e ciency of Cu was obtained at pH 13.0. Similarly, treatment was carried out for CN-Ni system having the initial Ni concentration of 0.170 mmol/L and CN concentration of 1.00 mmol with Fe(VI) dose 2.00 mmol at various pH values (10.0–12.0). Results showed a partial oxidation of CN and partial removal of Ni. It can be observed that Fe(VI) can partially degrade the CN-Ni complex in this pH range. Further, Fe(VI) was applied for the treatment of simulated industrial waste/e uent waters treatment containing CN, Cu, and Ni.     

Performance of dithiocarbamate-type flocculant in treating simulated polymer flooding produced water

Produced water from polymer flooding is di cult to treat due to its high polymer concentration, high viscosity, and emulsified characteristics. The dithiocarbamate flocculant, DTC (T403), was prepared by the amine-terminated polyoxypropane-ether compound known as Je amine-T403. The product was characterized by IR spectra and elemental analysis. The DTC agent chelating with Fe2+ produced a network polymer matrix, which captured and removed oil droplets e ciently. Oil removal by the flocculent on simulated produced water with 0, 200, 500, 900 mg/L of partially hydrolyzed polyacrylamide (HPAM) was investigated for aspects of e ectiveness of DTC (T403) dosage and concentrations of HPAM and Fe2+ ions in the wastewater. Results showed that HPAM had a negative influence on oil removal e ciency when DTC (T403) dosage was lower than 20 mg/L. However, residual oil concentrations in tested samples with di erent concentrations of HPAM all decreased below 10 mg/L when DTC (T403) dosage reached 30 mg/L. The concentration of Fe2+ in the initial wastewater had a slight e ect on oil removal at the range of 2–12 mg/L. Results showed that Fe3+ could not be used in place of Fe2+ as Fe3+ could not react with DTC under flocculated conditions. The e ects of mineral salts ions were also investigated.     

Flocculation performance of a novel synthesized flocculant with low ecological risk

Combined flocculants with low ecological risk are urgently required in water supply and wastewater treatment in China. A novel flocculant was thus developed under the condition of low ecological risk( noted as CAS).The experiments to examine wastewater treatment performance of the new product showed that there was favourable performance in the flocculation process in contrast to commercial flocculants in treating kaolin suspensions, municipal effluent and domestic wastewater. Flocculation performance included the turbidity removal rate, sediment character and a decrease in COD(chemical oxygen demand). The sediment time of flocculation is short and the removal rate of turbidity treated by CAS is high compared with PAC(polyaluminum-chloride), PAM (polyacrylamide) and the combined addition of PAC and PAM. The optimal concentration required to affect flocculation processes is dependent on kaolin concentration and the character of the wastewater within the range examined. It also showed that CAS is effective to treat wastewater with high turbidity.     

Investigating the coagulation of non-proteinaceous algal organic matter: Optimizing coagulation performance and identification of removal mechanisms

The removal of algal organic matter(AOM) is a growing concern for the water treatment industry worldwide. The current study investigates coagulation of non-proteinaceous AOM(AOM after protein separation), which has been minimally explored compared with proteinaceous fractions. Jar tests with either aluminum sulphate(alum) or polyaluminium chloride(PACl) were performed at doses of 0.2–3.0 mg Al per 1 mg of dissolved organic carbon in the p H range 3.0–10.5. Additionally, non-proteinaceous matter was characterized in terms of charge, molecular weight and carbohydrate content to assess the treatability of its different fractions. Results showed that only up to 25% of non-proteinaceous AOM can be removed by coagulation under optimized conditions. The optimal coagulation p H(6.6–8.0 for alum and 7.5–9.0 for PACl) and low surface charge of the removed fraction indicated that the prevailing coagulation mechanism was adsorption of non-proteinaceous matter onto aluminum hydroxide precipitates. The lowest residual Al concentrations were achieved in very narrow p H ranges, especially in the case of PACl. High-molecular weight saccharidelike organics were amenable to coagulation compared to low-molecular weight( 3 k Da)substances. Their high content in non-proteinaceous matter(about 67%) was the reason for its low removal. Comparison with our previous studies implies that proteinaceous and nonproteinaceous matter is coagulated under different conditions due to the employment of diverse coagulation mechanisms. The study suggests that further research should focus on the removal of low-molecular weight AOM, reluctant to coagulate, with other treatment processes to minimize its detrimental effect on water safety.     

Reaction mode between Si and Fe and evaluation of optimal species in poly-silicic-ferric coagulant

A kind of Fe-polysilicate polymer, poly-silicic-ferric （PSF） coagulant was prepared by co-polymerization （hydroxylation of mixture of Fe^3＋ and fresh polysilicic acid （PS））, in which PSF0.5, PSF1 or PSF3 denotes Si/Fe molar ratio of 0.5, 1 or 3, respectively. The effects of Si/Fe ratio and reaction time （co-polymerization time or aging time） on the reaction mode between Si and Fe were studies, and the optimal species of PSF was evaluated by pH change during the preparation of PSF and coagulation tests. The results showed that the characteristics of PSF are largely affected by both reaction time and Si/Fe ratio. PSF is found to be a essential complex of Si, Fe, and many other ions. The reaction mode between Si and Fe differs with various Si/Fe ratios. The pH of PSF0.5, PSF1 or PSF3 tended to be stable when reaction time is 10, 25 or 55 rain, respectively, which is almost consistent with the time reaching the relative stable morphology that is just the optimal species of higher coagulation efficiency. The optimal reaction time reaching optimal species can be evaluated by measuring the pH change during the polymerization process.     

Coagulation of micro-polluted Pearl River water with IPF-PACIs

Water samples collected from early March 2001 to the end of April 2002 at the branch of Pearl River around the Guangzhou City were analyzed for its micro-polluted characteristics. The coagulation behavior of polyaluminum chlorides(PACIs) was then examined focusing on the effect of primary water quality and speciation distribution. The results showed that PACIs exhibit better coagulation efficiency than alum in accordance with the different speciation.The turbidity removal property of PACIs is evidently better than alum at low dosage. While in neutral zone(about 6.5--7.5), the turbidity removal of PACIs decreases owing to the restabilization of particles at higher dosage. The organic matters in raw water exhibit marked influence on coagulation. In acidic zone, organic matters complex with polymer species and promote the formation of flocs. With an increase in pH, the complexation of organics with polymer species gradually decreases, and the removal of organics mainly depends on adsorption. The effect is evidently improved with the raise of B value.