An enhanced coagulation using ferric chloride and poly-ferric chloride coagulant assisted by polyamidine:Performance and mechanisms

The deterioration of water caused by industrial production is a thorny problem.Solving the problem cogently through innovative coagulationstrategies has been recognized of important practical significance.In this work,a simple enhanced coagulation by using ferric chloride(FC)and poly-ferric chloride(PFC)coupled with polyamidine(PA)were tried to remove the toxic organics.The results shown that PA addition could obviously enhance coagulation performances of the iron-based coagulants.The synergic coagulation process and mechanism were studied and discussed in detail based on the coagulation behaviors,flocs properties,removal eficiency and zeta potentials.FC and PFC remove organics mainly through charge neutralization and adsorption-bridging,resulting in a good purification performance.While PA with a higher charge density showed better purification performance due to enhanced charge neutralization.It is worth mentioning that the addition of PA could make the coagulants adapt to a wider pH range,and remove the toxic organics more effectively.That is to say,the practical adaptability of the coagulant was enhanced.This work thus provides a simple strategy to effectively purify wastewater and further improve the water safety.

Performance of bimetallic nanoscale zero-valent iron particles for removal of oxytetracycline

In this study, bimetallic nanoscale zero-valent iron particles（nZVI）, including copper/nanoscale zero-valent iron particles（Cu/nZVI） and nickel/nanoscale zero-valent iron particles（Ni/nZVI）, were synthesized by one-step liquid-phase reduction and applied for oxytetracycline（OTC） removal. The effects of contact time and initial p H on the removal efficiency were studied. The as-prepared nanoscale particles were characterized by scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and X-ray diffraction（XRD）. Finally, the degradation mechanisms of OTC utilizing the as-prepared nanoparticles were investigated by using X-ray photoelectron spectroscopy（XPS） and mass spectrometry（MS）. Cu/n ZVI presented remarkable ability for OTC degradation and removed71.44% of OTC（100 mg/L） in 4 hr, while only 62.34% and 31.05% of OTC was degraded by Ni/nZVI and nZVI respectively. XPS and MS analysis suggested that OTC was broken down to form small molecules by ·OH radicals generated from the corrosion of Fe0. Cu/nZVI and Ni/n ZVI have been proved to have potential as materials for application in OTC removal because of their significant degradation ability toward OTC.

Fractionation of residual Al in natural water treatment from reservoir with poly-aluminum-silicate-chloride (PASiC): Effect of OH/Al, Si/Al molar ratios and initial pH

An aluminum fractionation study was conducted for a surface reservoir water treatment to understand the performance of poly- aluminum-silicate-chloride （PASiC） in terms of the residual A1 fractions as a function of initial pH. The coagulation performance expressed as turbidity and organic matter removal was established as supporting data. Some extra data were evaluated in terms of the residual A1 ratio of the composite PASiC coagulant. The main residual A1 sources were the A1 fractions derived from the use of PASiC. The turbidity and organic matter removal ability was optimal at initial pH 6.00-7.00, while the concentrations of various residual A1 species and the residual A1 ratio of PASiC were minimal at an initial pH range of 7.00-8.00. Under the conditions of OH/AI molar ratio = 2.00 and Si/A1 molar ratio = 0.05, PASiC had superior coagulation performance and comparatively low residual A1 concentrations. The A1 fraction in the composite PASiC coagulant seldom remained under such conditions. Experimental data also indicated that the suspended （filterable） AI fraction was the dominant species, and organic-bound or organo-A1 complex A1 was considered to be the major species of dissolved A1 in water treated by PASiC coagulation. Additionally, the dissolved inorganic monomeric A1 species dominated the dissolved monomeric A1 fraction.

Adsorptive removal of phosphate by the bimetallic hydroxide nanocomposites embedded in pomegranate peel

This study aimed to fabricate new and effective material for the efficiency of phosphate adsorption.Two types of adsorbent materials,the zirconium hydroxides embedded in pomegranate peel(Zr/Peel)and zirconium-lanthanum hydroxides embedded in pomegranate peel(Zr-La/Peel)were developed.Scanning electronic microscopy(SEM),x-ray photoelectron spectroscopy(XPS)and x-ray diffraction(XRD)were evaluated to give insight into the physicochemical properties of these adsorbents.Zr-La/Peel exceeded the adsorption efficiency of Zr/Peel adsorbents in batch adsorption experiments at the same pH level.The peel as a host can strive to have a strong"shielding effect"to increase the steadiness of the entrenched Zr and La elements.La and Zr are hydroxide metals that emit many hydrogen ions during the hydrolysis reaction,which contribute to protonation and electrostatic attraction.The highest adsorption capacity of La-Zr/Peel for phosphate was calculated to be40.21 mg/g,and pseudo second-order equation is very well fitted for kinetic adsorption.Phosphate adsorption efficiency was reduced by an increase of pH.With the background of coexisting Cl-,little effect on adsorption efficiency was observed,while adsorption capacities were reduced by almost 20-30%with the coexistence of SO42-,NO3-and humic acid(HA).

Synchronous removal of CuO nanoparticles and Cu2+ by polyaluminum chloride-Enteromorpha polysaccharides: Effect of Al species and pH

Copper oxide nanomaterials have been extensively applied and can have serious impacts when discharged into the aquatic environment, especially when complexed with humic acid(HA) to form composite contaminants.As an innovative recycled coagulant aid,Enteromorpha polysaccharides(Ep) were associated with polyaluminum chloride(PACl)(denoted as PACl-Ep) to simultaneously remove CuO nanoparticles, Cu2+and HA in this study.The influence of different Al species coagulants(AlCl3, PAClb and PAClc) and water pH on coagulation performance, floc properties and reaction mechanisms was investigated in detail.Results showed that in the three PACl-Ep systems, PAClb-Ep gave the highest removal efficiencies for turbidity and Cu2+, and the best UV254 removal effect was reached by using PAClc-Ep.Higher contents of Alb and Alc contributed to great coagulation performance because of their stronger bridging and sweeping effects.For all the Al species coagulants, alkalescent conditions were more conducive to removing Cu and HA compared to acidic conditions.Additionally, smaller and more agminated flocs with great recovery ability were formed by PAClb-Ep and PAClc-Ep systems(bridging and enmeshment effects cooperated with the chelated reticular structure formed by the Ep and Al species).Similarly,due to the increased hydrolysis and hydroxide precipitates, flocs formed under the condition of alkalescence were smaller, denser and stronger compared with weakly acidic conditions.

Characterization of dissolved organic matter and membrane fouling in coagulation-ultrafiltration process treating micro-polluted surface water

Coagulation–ultrafiltration(C–UF) is widely used for surface water treatment. With the removal of pollutants, the characteristics of organic matter change and affect the final treatment efficiency and the development of membrane fouling. In this study, we built a dynamic C–UF set-up to carry out the treatment of micro-polluted surface water, to investigate the characteristics of dissolved organic matter from different units. The influences of poly aluminum chloride and poly dimethyldiallylammonium chloride(PDMDAAC) on removal efficiency and membrane fouling were also investigated. Results showed that the dosage of PDMDAAC evidently increased the UV254 and dissolved organic carbon removal efficiencies,and thereby alleviated membrane fouling in the C–UF process. Most hydrophobic bases(HoB)and hydrophobic neutral fractions could be removed by coagulation. Similarly, UF was good at removing HoB compared to hydrophilic substances(HiS) and hydrophobic acid(HoA)fractions. HiS and HoA fractions with low molecule weight accumulated on the surface of the membrane, causing the increase of transmembrane pressure(TMP). Membrane fouling was mainly caused by a removable cake layer, and mechanical cleaning was an efficient way to decrease the TMP.

Facile one-step synthesis of functionalized biochar from sustainable prolifera-green-tide source for enhanced adsorption of copper ions

The use of biochars formed by hydrothermal carbonization for the treatment of contaminated water has been greatly limited, due to their poorly developed porosity and low content of surface functional groups. Also, the most common modification routes inevitably require post-treatment processes, which are time-consuming and energy-wasting. Hence, the objective of this research was to produce a cost-effective biochar with improved performance for the treatment of heavy metal pollution through a facile one-step hydrothermal carbonization process coupled with ammonium phosphate, thiocarbamide, ammonium chloride or urea, without any posttreatment. The effects of various operational parameters, including type of modification reagent, time and temperature of hydrothermal treatment, and ratio of modification reagent to precursor during impregnation, on the copper ion adsorption were examined. The adsorption data fit the Langmuir adsorption isotherm model quite well. The maximum adsorption capacities （mg/g） of the biochars towards copper ions followed the order of 40-8h-1.0-APBC （95.24） 〉 140-Sh-O-BC （12.52） 〉 140-8h-1.0-TUBC （12.08） 〉 140-Sh-1.0-ACBC （7.440） 〉 140-Sh-1.0-URBC （5.277）. The results indicated that biochars modified with ammonium phosphate displayed excellent adsorption performance toward copper ions, which was 7.6-fold higher than that of the pristine biochar. EDX and FT-IR analyses before and after adsorption demonstrated that the main removal mechanism involved complexation between the phosphate groups on the surface of the modified biochars and copper ions.

Flocculation behaviors of a novel papermaking sludge-based flocculant in practical printing and dyeing wastewater treatment

In our previous studies,several papermaking sludge-based flocculants(PSBFs)were synthesized from wood pulp papermaking sludge.The structure-activity relationships of the PSBFs have been investigated in simulated dye wastewater treatment,but their efficiencies in practical printing and dyeing wastewater(PPDW)treatment are unknown.Herein,an PSBF was prepared,and its performance is discussed in comparison to polyaluminium chloride(PAC)and polyacrylamide(PAM)in PPDW treatment.The PSBF was used in three ways:as an independent flocculant,as a PAC aid,or used to treat the effluent of the PAC system.The results indicated that adding PSBF alone produced similar color and chemical oxygen demand(COD_(Cr))removals as the PAC system alone,but PSBF performed better than PAC when the pH of PPDW was higher than 7.0.Adding PSBF as a PAC aid improved the color,COD_(Cr)and turbidity removals,but the elimination efficiencies were slightly lower than those of the PAC+PAM system.However,when PSBF was used as a flocculant to treat the effluent of the PAC system(PAC→PSBF),the effluent qualities were enhanced.Compared with the PAC system,the color and COD_(Cr)removals of PAC→PSBF system increased by 16.21%and 13.26%,respectively.The excitation and emission matrix fluorescence results indicated that PSBF removed tryptophan-like pollutants more efficiently than PAC.Considering the pH requirements of the subsequent bioreactor treatment in practice,the PAC→PSBF system were also investigated at the PPDW pH level of 7.0.Its maximum removal efficiencies of color,COD_(Cr)and turbidity were 90.17%,32.60%and 82.50%,respectively.

Effect of six kinds of scale inhibitors on calcium carbonate precipitation in high salinity wastewater at high temperatures

Precipitation of calcium carbonate （CaCOs） scale on heat transfer surfaces is a serious and expensive problem widely occurring in numerous industrial processes. In this study, we compared the scale inhibition effect of six kinds of commercial scale inhibitors and screened out the best one （scale inhibitor SQ-1211） to investigate its scale inhibition performance in highly saline conditions at high temperature through static scale inhibition tests. The influences of scale inhibitor dosage, temperature, heating time and pH on the inhibition efficiency of the optimal scale inhibitor were investigated. The morphologies and crystal structures of the precipitates were characterized by Scanning Electron Microscopy and X-ray Diffraction analysis. Results showed that the scale inhibition efficiency of the optimal scale inhibitor decreased with the increase of the reaction temperature. When the concentration of Ca^2＋ was 1600 mg/L, the scale inhibition rate could reach 90.7% at 80℃ at pH 8. The optimal scale inhibitor could effectively retard scaling at high temperature. In the presence of the optimal scale inhibitor, the main crystal structure of CaCOs changed from calcite to aragonite.

Advanced lignin-acrylamide water treatment agent by pulp and paper industrial sludge: Synthesis, properties and application

A novel flocculant LA （lignin-acrylamide polymer）, which was used as aid for aluminum sulfate and polyaluminum chloride in this study, was prepared by grafting acrylamide onto lignin that deriving from pulp and papermaking sludge. Physicochemical properties of LA were measured by X-ray photoelectron spectroscopy and scanning electron microscopy. The experimental outcome indicated acrylamide was grafted onto the lignin backbone successfully. The effects of LA addition were evaluated on coagulation performance and floc characteristics as a function of aluminum （Al） dosage, such as floc size, growth rate, strength and recoverability. Effects of different dosing sequences, Al dosed first and LA dosed first, were also investigated. LA used as coagulant aid markedly enhanced the removal efficiency of turbidity and dissolved organic carbon, especially at low Al dosages. The dissolved organic carbon removal efficiencies of aluminum sulfate and polyaluminum chloride at the Al dosage range selected in this study were improved more than 30% and 5% by LA, respectively. LA dramatically enlarged floc size and it was in the order： Al dosed first 〉 LA dosed first 〉 Al. Floc strength and recoverability were also improved by LA. LA played a significant role in charge neutralization, adsorption and bridging in floc formation.

Carbon-based single atom catalyst: Synthesis, characterization, DFT calculations

Carbon-based single-atom catalysts(SACs) with atomic sizes of active sites have become the promising candidates for a variety of catalytic systems because of their high atom utilization, and unique electronic structures. Different types of single-atom sites can be fabricated via multiple preparation strategies, which would demonstrate distinct different coordination configurations and electronic features, and ultimately affected the structure-catalysis relationship of SACs in targeted reactions. As a result, it is necessary to identify the active sites of SACs and understand the structure-catalysis relationship of SACs at the atomic scale. In this review, a variety of preparation strategies of carbon-based SACs were documented. Then, the recent development on versatile characterization techniques and computational achievements were summarized regarding in understanding the electronic and geometric characteristics of carbon-based SACs.Finally, major challenges and development directions concerning single-atom sites identification and advanced tools development are discussed to shed light on future research of carbon-based SACs.

Coagulation behavior and floc properties of compound bioflocculant–polyaluminum chloride dual-coagulants and polymeric aluminum in low temperature surface water treatment

This study was intended to compare coagulation behavior and floc properties of two dualcoagulants polyaluminum chloride–compound bioflocculant（PAC–CBF）（PAC dose first） and compound bioflocculant–polyaluminum chloride（CBF–PAC）（CBF dose first） with those of PAC alone in low temperature drinking water treatment. Results showed that dualcoagulants could improve DOC removal efficiency from 30% up to 34%. Moreover, CBF contributed to the increase of floc size and growth rate, especially those of PAC–CBF were almost twice bigger than those of PAC. However, dual-coagulants formed looser and weaker flocs with lower breakage factors in which fractal dimension of PAC–CBF flocs was low which indicates a looser floc structure. The floc recovery ability was in the following order：PAC–CBF 〉 PAC alone 〉 CBF–PAC. The flocculation mechanism of PAC was charge neutralization and enmeshment, meanwhile the negatively charged CBF added absorption and bridging effect.

Preparation and characterization of β-FeOOH-coated sand and its adsorption of Cr（VI） from aqueous solutions

Batch adsorption experiments were conducted to explore the adsorption of Cr（VI） in aqueous solutions by fl-FeOOH-coated sand. We investigated the key factors which affected the adsorption process such as adsorbent dosage, initial pH, initial Cr（VI） ion concentration, contact time and temperature. The uptake of Cr（VI） was very rapid and 44.3%, 51.6%, 58.9% of the adsorption happened during the first 180minutes at 293K, 303K and 313K, respectively. The pseudo-second-order rate equation successfully described the adsorption kinetics. To study the adsorption isotherm, two equilibrium models, the Langmuir and Freundlich isotherms, were adopted. At 293K, 303K and 313K, the adsorption capacities obtained from the Langmuir isotherm were 0.060, 0.070 and 0.076 mg Cr（VI） per gram of the adsorbent, respectively. Thermodynamic parameters such as the change of energy, enthalpy and entropy were calculated using the equilibrium constants. The negative value of AGO and the positive value of △H^0 showed that the adsorption of Cr（VI） in aqueous solutions by β-FeOOH-coated sand was spontaneous, endothermic and occurred by physisorption.

Properties and effect of forming sewage sludge into lightweight ceramics

In this work we investigated the chemical, thermal and toxic properties of dried sewage sludge （DSS）, the preparation and properties of lightweight sludge ceramic （LSC） and the mechanisms of action of the organic and inorganic foaming agents （OFAs and IFAs）. The chemical components and thermal properties of the raw materials were studied by Energy Dispersive X-ray Detection （EDX） and Thermogravimetric Analysis and Differential Scanning Calorimetry （DSC/TGA）. The mineral phases of the raw materials and the formed ceramics were determined by X-ray Diffraction （XRD）. The leaching characteristics of heavy metals were investigated with inductively Coupled Plasma Atomic Emission Spectrometry （ICP-AES）. Different ratios of DSS and clay were mixed and pressed into raw pellets. After drying and preheating treatment, the raw pellets were sintered at 1150℃ for 10 rain. The physical properties of LSC （50 wt% DSS added） were tested. The results showed that when the addition of DSS was above 50 wt%, LSC began to shrink, and a maximum density occurred. The environmental safety of LSC was satisfactory. XRD showed that some new mineral phases formed in the LSC. Observation of the microstructure by Scanning Electron Microscope （SEM） indicated that the body of LSC was porous.

Novel cationic polyamidine:Synthesis,characterization,and sludge dewatering performance

In this study,a new and facile route was employed for synthesis of polyamidine with abundant cations and attractive five-membered ringlike structural unit.N-vinylformamide and acrylonitrile copolymerized firstly to form intermediates,and the intermediates were processed with hydrochloric acid to produce polyamidine.A series of polymerization conditions（e.g.polymerization time,temperature and dosage of initiator） were optimized through productivity,viscosity and cationic degree as evaluation.SEM analysis illustrated that the amidinization process could reduce the size of spaces between molecular and created compact structure,which would contribute to good flocculation performance and high viscosity.FT-IR,XPS and NMR spectra presented a rather clear structure of polyamidine.34.3%of sludge was sedimentated through the flocculation of polyamidine in the early stages.In contrast,only 6.8%of sludge was sedimentated by polyacrylamide.The moisture content in dehydrated floc could be reduced to 77.7%when 60 mg/L polyamidine was added.These results demonstrated that the polyamidine showed a great potential in the practical application of sludge dewatering.

Pre-treatment of pyridine wastewater by new cathodic–anodic-electrolysis packing

A novel cathodic–anodic-electrolysis packing（CAEP） used in the treatment of pyridine wastewater was researched, which mainly consisted of 4,4′-diamino-2,2′-disulfonic acid（DSD acid） industrial iron sludge. The physical properties and morphology of the packing were studied. The CAEP was used in a column reactor during the pretreatment of pyridine wastewater. The influence of p H, hydraulic retention time（HRT）, the air–liquid ratio（A/L）and the initial concentration of pyridine were investigated by measuring the removal of total organic carbon（TOC） and pyridine. The characterization results showed that the bulk density, grain density, water absorption percentage and specific surface area were 921 kg/m3,1086 kg/m3, 25% and 29.89 m^2/g, respectively; the removal of TOC and pyridine could reach50% and 58% at the optimal experimental conditions（p H = 3, HRT = 8 hr, A/L = 2）. Notably,the surface of the packing was renewed constantly during the running of the filter, and the handling capacity was stable after running for three months.

Purification,characterization and application of dual coagulants containing chitosan and different Al species in coagulation and ultrafiltration process

The objective of this study was to investigate the effect of different Al species and chitosan（CS） dosages on coagulation performance,floc characteristics（floc sizes,strength and regrowth ability and fractal dimension） and membrane resistance in a coagulation-ultrafiltration hybrid process.Results showed that different Al species combined with humic acid in diverse ways.A1_a had better removal efficiency,as determined by UV_（254） and dissolved organic carbon,which could be further improved by the addition of CS.In addition,the optimal dosage of different Al species was determined to be 4.0 mg/L with the CS concentration of 1.0 mg/L,by orthogonal coagulation experiments.Combining Al_a/A1_b/A1_c,with CS resulted in larger flocs,higher recovery,and higher fractal dimension values corresponding to denser flocs;in particular,the floc size at the steady state stage was four times larger than that obtained with Al species coagulants alone.The results of ultrafiltration experiments indicated that the external fouling percentage was significantly higher than that of internal fouling,at around 85%and 15%,respectively.In addition,the total membrane resistance was significantly decreased due to CS addition.

Fertilizer drawn forward osmosis as an alternative to 2nd pass seawater reverse osmosis: Estimation of boron removal and energy consumption

Agriculture is the largest consumer of freshwater.Desalinated seawater is an important alternative water source for sustainable irrigation.However,some issues of the current desalination technology hinder its use for agriculture irrigation,including low boron removal and high energy consumption.This study systematically explored the feasibility of employing fertilizer drawn forward osmosis(FDFO)as an alternative to 2nd pass reverse osmosis(RO)by considering the boron removal performance and specific energy consumption(SEC).Different operating conditions were investigated,such as the boron and NaCl concentrations in feed solution(FS),draw solution(DS)concentration,pH,the volume ratio of FS to DS,membrane orientation,flow rate,and operating temperature.The results indicated that a low boron concentration in FS and high DS pH(pH=11.0)decreased the boron solute flux,and led to low final boron concentration in the DS.The other operating conditions had negligible influence on the final DS boron concentration.Also,a lower flow rate and higher specific water flux with certain permeate water volumes were conducive to reducing the SEC of the FDFO process.Overall,our study paves a new way of using FDFO in irrigation,which avoids the phytotoxicity and human health risk of boron.The results show the potential of FDFO as an alternative to 2nd pass RO for irrigation water production.

Fatty acid fouling of forward osmosis membrane:Effects of pH,calcium,membrane orientation,initial permeate flux and foulant composition

Octanoic acid（OA） was selected to represent fatty acids in effluent organic matter（EOM）. The effects of feed solution（FS） properties, membrane orientation and initial permeate flux on OA fouling in forward osmosis（FO） were investigated. The undissociated OA formed a cake layer quickly and caused the water flux to decline significantly in the initial 0.5 hr at unadjusted p H 3.56; while the fully dissociated OA behaved as an anionic surfactant and promoted the water permeation at an elevated p H of 9.00. Moreover, except at the initial stage, the sudden decline of water flux（meaning the occurrence of severe membrane fouling） occurred in two conditions： 1.0.5 mmol/L Ca2＋, active layer facing draw solution（AL-DS） and 1.5 mol/L Na Cl（DS）; 2. No Ca2＋,active layer-facing FS（AL-FS） and 4 mol/L Na Cl（DS）. This demonstrated that cake layer compaction or pore blocking occurred only when enough foulants were absorbed into the membrane surface, and the water permeation was high enough to compact the deposit inside the porous substrate. Furthermore, bovine serum albumin（BSA） was selected as a co-foulant.The water flux of both co-foulants was between the fluxes obtained separately for the two foulants at p H 3.56, and larger than the two values at p H 9.00. This manifested that, at p H 3.56,BSA alleviated the effect of the cake layer caused by OA, and OA enhanced BSA fouling simultaneously; while at p H 9.00, the mutual effects of OA and BSA eased the membrane fouling.