Bio-reduction of nitrate from groundwater using a hydrogen-based membrane biofilm reactor

A hydrogen-based membrane biofilm reactor （MBfR） using H2 as electron donor was investigated to remove nitrate from groundwater. When nitrate was first introduced to the MBfR, denitrification took place on the shell side of the membranes immediately, and the effluent concentration of nitrate continuously decreased with 100% removal rate on day 45 under the influent nitrate concentration of 5 mg NO3^--N/L, which described the acclimating and enriching process of autohydrogenotrophic denitrification bacteria. A series of short-term experiments were applied to investigate the effects of hydrogen pressures and nitrate loadings on deniWification. The results showed that nitrate reduction rate improved as H2 pressure increasing, and over 97% of total nitrogen removal rate was achieved when the nitrate loading increased from 0.17 to 0.34 g NO3^--N/（m^2.day） without nitrite accumulation. The maximum deniwification rate was 384 g N/（m^3.day）. Partial sulfate reduction, which occurred in parallel to nitrate reduction, was inhibited by denitrififcation due to the competition for H2. This research showed that MBfR is effective for removing nitrate from the contaminated groundwater.

Cr(VI) removal from aqueous solution with bamboo charcoal chemically modified by iron and cobalt with the assistance of microwave

Bamboo charcoal （BC） was used as starting material to prepare Co-Fe binary oxideloaded adsorbent （Co-Fe-MBC） through its impregnation in Co（NO3）2 , FeCl3 and HNO3 solutions simultaneously, followed by microwave heating. The low-cost composite was characterized and used as an adsorbent for Cr（VI） removal from water. The results showed that a cobalt and iron binary oxide （CoFe2O4 ） was uniformly formed on the BC through redox reactions. The composite exhibited higher surface area （331 m2/g） than that of BC or BC loaded with Fe alone （Fe-MBC）. The adsorption of Cr（VI） strongly depended on solution pH, temperature and ionic strength. The adsorption isotherms followed the Langmuir isotherm model well, and the maximum adsorption capacities for Cr（VI） at 288 K and pH 5.0 were 35.7 and 51.7 mg/g for Fe-MBC and Co-Fe-MBC, respectively. The adsorption processes were well fitted by the pseudo second-order kinetic model. Thermodynamic parameters showed that the adsorption of Cr（VI） onto both adsorbents was feasible, spontaneous, and exothermic under the studied conditions. The spent Co-Fe-MBC could be readily regenerated for reuse.

Simultaneous removal of selected oxidized contaminants in groundwater using a continuously stirred hydrogen-based membrane biofilm reactor

A laboratory trial was conducted for evaluating the capability of a continuously stirred hydrogen-based membrane biofllm reactor to simultaneously reduce nitrate （NO3--N）, sulfate （SO42-）, bromate （BrO3-）, hexavalent chromium （Cr（VI）） and para- chloronitrobenzene （p-CNB）. The reactor contained two bundles of hollow fiber membranes functioning as an autotrophic biofiim carder and hydrogen pipe as well. On the condition that hydrogen was supplied as electron donor and diffused into water through membrane pores, autohydrogenotrophic bacteria were capable of reducing contaminants to forms with lower toxicity. Reduction occurred within 1 day and removal fluxes for NO3--N, SO42-, BrO3-, Cr（VI）, and p-CNB reached 0.641, 2.396, 0.008, 0.016 and 0.031 g/（day.m2）, respectively after 112 days of continuous operation. Except for the fact that sulfate was 37% removed under high surface loading, the other four contaminants were reduced by over 95 %. The removal flux comparison between phases varying in surface loading and 1-12 pressure showed that decreasing surface loading or increasing 1-12 pressure would promote removal flux. Competition for electrons occurred among the five contaminants. Electron-equivalent flux analysis showed that the amount of utilized hydrogen was mainly controlled by NO3--N and SO42- reduction, which accounted for over 99% of the electron flux altogether. It also indicated the electron acceptor order, showing that nitrate was the most prior electron acceptor while sulfate was the second of the five contaminants.

Pb(Ⅱ) removal from water using Fe-coated bamboo charcoal with the assistance of microwaves

Bamboo charcoal（BC） was used as starting material to prepare iron-modified bamboo charcoal（Fe-MBC） by its impregnation in FeCl 3 and HNO 3 solutions simultaneously,followed by microwave heating.The material can be used as an adsorbent for Pb（Ⅱ） contaminants removal in water.The composites were prepared with Fe molar concentration of 0.5,1.0 and 2.0 mol/L and characterized by means of N 2 adsorption-desorption isotherms,X-ray diffraction spectroscopy（XRD）,scanning electron microscopy coupled with energy dispersive X-ray spectrometry（SEM-EDS）,Fourier transform infrared（FT-IR） and point of zero charge（pH pzc） measurements.Nitrogen adsorption analyses showed that the BET specific surface area and total pore volume increased with iron impregnation.The adsorbent with Fe molar concentration of 2 mol/L（2Fe-MBC） exhibited the highest surface area and produced the best pore structure.The Pb（Ⅱ） adsorption process of 2Fe-MBC and BC were evaluated in batch experiments and 2Fe-MBC showed an excellent adsorption capability for removal Pb（Ⅱ）.The adsorption of Pb（Ⅱ） strongly depended on solution pH,with maximum values at pH 5.0.The ionic strength had a significant effect on the adsorption at pH 〈 6.0.The adsorption isotherms followed the Langmuir isotherm model well,and the maximum adsorption capacity for Pb（Ⅱ） was 200.38 mg/g for 2Fe-MBC.The adsorption processes were well fitted by a pseudo second-order kinetic model.Thermodynamic parameters showed that the adsorption of Pb（Ⅱ） onto Fe-MBC was feasible,spontaneous,and exothermic under the studied conditions,and the ion exchange mechanism played an significant role.These results have important implications for the design of low-cost and effective adsorbents in the removal of Pb（Ⅱ） from wastewater.

Interactions between metal ions and the biopolymer in activated sludge： quantification and effects of system pH value

The quantification and effects of system pH value on the interactions between Pb（II） and the biopolymer in activated sludge were investigated. The biopolymer had two protein-like fluorescence peaks （Ex/Em = 280 nm1326-338 nm for peak A; Ex/Em = 220-230 nm/324-338 nm for peak B）. The fluorescence intensities of peak B were higher than those of peak A. The fluorophores of both peaks could be largely quenched by Pb（ll）, and the quencher dose for peak B was about half of that for peak A. The modified Stern-Volmer equation well depicted the fluorescence quenching titration. The quenching constant （Ka） values for both peaks decreased with rising system pH value, and then sharply decreased under alkaline conditions. It could be attributed to that the alkaline conditions caused the reduction of available Pb（II） due to the occurrence of Pb（OH）2 sediments. The Ka values of peak B were bigger than those for peak A at the same system pH values. Accordingly, the aromatic proteins （peak B） played a key role in the interactions between metal ions and the biopolymer.

Influence and mechanism of N-(3-oxooxtanoyl)-L-homoserine lactone(C_8-oxo-HSL) on biofilm behaviors at early stage

N-acyl-homoserines quenching, enzymatic quenching of bacterial quorum sensing, has recently applied to mitigate biofilm in membrane bioreactor. However, the effect of AHLs on the behavior of biofilm formation is still sparse. In this study, Pseudomonas aeruginosa biofilm was formed on ultra-filtration membrane under a series of N-（3-0xooxtanoyl）-L-homoserine lactone （C8-0xo-HSL） concentrations. Diffusing Cs-oxo-HSL increased the growth rate of cells on biofilm where the concentration of Cs-oxo-HSL was over 10-7 g/L. The C8-0xo-HSL gradient had no observable influence on cell density and extracellular polymeric substances of biofilm with over 10-7 g/L Cs-oxo-HSL. Surprisingly, 10-11-10-8 g/L of Cs-Oxo-HSL had no effect on cell growth in liquid culture. The cell analysis demonstrated that the quorum sensing system might enhance the growth of neighboring cells in contact with surfaces into biofilm and may influence the structure and organization of biofilm.

Arsenic removal from groundwater by acclimated sludge under autohydrogenotrophic conditions

Arsenic in the environment is attracting increasing attention due to its chronic health effects. Although arsenite （As（III）） is generally more mobile and more toxic than arsenate （As（V））, reducing As（V） to As（III） may still be a means for decontamination, because As（III） can be removed from solution by precipitation with sulfide or by adsorption or complexation with other metal sulfides. The performance of As（V） bio-reduction under autohydrogenotrophic conditions was investigated with batch experiments. The results showed that As（V） reduction was a biochemical process while both acclimated sludge and hydrogen were essential. Most of the reduced arsenic remained in a soluble form, although 20% was removed with no addition of sulfate, while 82% was removed when sulfate was reduced to sulfide. The results demonstrated that the reduced arsenic was re-sequestered in the precipitates, probably as arsenic sulfides. Kinetic analysis showed that pseudo first-order kinetics described the bio-reduction process better than pseudo second-order. In particular, the influences of pH and temperature on As（V） reduction by acclimated sludge under autohydrogenotrophic conditions and total soluble As removal were examined. The reduction process was highly sensitive to both pH and temperature, with the optimum ranges of pH 6.5-7.0 and 30-40℃ respectively. Furthermore, Arrhenius modeling results for the temperature effect indicated that the As（V） reduction trend was systematic. Total soluble As removal was consistent with the trend of As（V） reduction.

Novel perspective for urban water resource management: 5R generation

Demand for water is expanding with increases in population,particularly in urban areas in developing countries.Additionally,urban water system needs a novel perspective for upgradation with urbanization.This perspective presents a novel 5R approach for managing urban water resources:Recover(storm water),Reduce(toilet flushing water),Recycle(gray water),Resource(black water),and Reuse(advanced-treated wastewater).The 5R generation incorporates the latest ideas for harvesting storm water,gray water,and black water in its several forms.This paper has briefly demonstrated each R of 5R generation for water treatment and reuse.China has the chance to upgrade its urban water systems according to 5R principles.Already,a demonstration project of 5R generation has been installed in Qingdao International Horticultural Exposition,and Dalian International Convention Center(China)has applied 5R,achieving over 70%water saving.The 5R offers promise for moving solutions for urban water scarcity from“hoped for in the future”to“realistic today”.

New insight into adsorption characteristics and mechanisms of the biosorbent from waste activated sludge for heavy metals

The adsorption characteristics and mechanisms of the biosorbent from waste activated sludge were investigated by adsorbing Pb2＋and Zn2＋in aqueous single-metal solutions. A p H value of the metal solutions at 6.0 was beneficial to the high adsorption quantity of the biosorbent. The optimal mass ratio of the biosorbent to metal ions was found to be 2. A higher adsorption quantity of the biosorbent was achieved by keeping the reaction temperature below 55°C. Response surface methodology was applied to optimize the biosorption processes, and the developed mathematical equations showed high determination coefficients（above 0.99 for both metal ions） and insignificant lack of fit（p = 0.0838 and 0.0782 for Pb2＋and Zn2＋, respectively）. Atomic force microscopy analyses suggested that the metal elements were adsorbed onto the biosorbent surface via electrostatic interaction. X-ray photoelectron spectroscopy analyses indicated the presence of complexation（between –NH2,-CN and metal ions） and ion-exchange（between –COOH and metal ions）. The adsorption mechanisms could be the combined action of electrostatic interaction, complexation and ion-exchange between functional groups and metal ions.

Enhanced struvite recovery from wastewater using a novel cone-inserted fluidized bed reactor

The feasibility of struvite recovery at low （12.5 mg/L） and high （120 mg[L） phosphorus concentrations was studied by constructing a novel fluidized bed reactor with cones （FBRwc） and without cones （FBRwoc）. The crystallization process was continuously operated for 133 days under different hydraulic retention times （HRT = 1-10 hr）, pH （7.5-10）, and molar ratios of Mg/P （0.75-1.75）, N/P （1-10） and Ca/Mg （0-2）. The optimum operating conditions of HRT, pH, Mg/P and N/P molar ratios were found to be 2 hr, 9, 1.25, and 7.5, respectively. Under these optimum conditions, the phosphorus precipitation efficiencies of FBRwc were 93% for low and 98% for high phosphorus influent; however, the efficiencies were 78% and 81% for FBRwoc, respectively. Due to crystal losses at each junction （17%-31%）, the crystal recovery efficiency of FBRwoc was relatively low （47%-65%） for both influent concentrations. However, the losses were minimal in FBRwc, which showed 75% and 92% crystal recovery for low and high phosphorus concentrations, respectively. At low calcium concentration, crystal chemical analysis showed the product to be pure struvite （〉 99%）. The scanning electron microscope and X-ray diffraction results further confirmed that the crystal recovered from FBRwc contained pure struvite, which could be considered a high quality fertilizer. Except HRT, all parameters （pH, Mg/P, N/P and Ca/Mg） were found to be influencing factors for FBRwc performance. Overall, inserting cones in each part of the reactor played a significant role in enhancing struvite recovery from a wide range of phosphorus-containing wastewater.

Bioelectrochemical acidolysis of magnesia to induce struvite crystallization for recovering phosphorus from aqueous solution

A novel struvite crystallization method induced by bioelectrochemical acidolysis of magnesia (MgO) was investigated to recover phosphorus (P) from aqueous solution using a dual-chamber microbial electrolysis cell (DMEC).Magnesium ion (Mg2+) in the anolyte was firstly confirmed to automatically migrate from the anode chamber to the cathode chamber,and then react with ammonium (NH4+) and phosphate (PO34-) in the catholyte to form struvite.Recovery efficiency of 17.8%-60.2% was obtained with the various N/P ratios in the catholyte.When MgO (low solubility under alkali conditions) was added into the anolyte,the bioelectrochemical acidolysis of MgO naturally took place and the released Mg2+ induced struvite crystallization in the cathode chamber for P recovery likewise.Besides,there was a strong linear positive correlation between the recovery efficiency and the MgO dosage (R2 =0.935),applied voltage (R2 =0.969) and N/P ratio (R2 =0.905).Increasing the applied voltage was found to enhance the P recovery via promoting the MgO acidolysis and the released Mg2+ migration,while increasing the N/P ratio in the catholyte enhanced the P recovery via promoting the struvite crystallization.Moreover,the electrochemical performance of the system was promoted due to more stable anolyte pH and lower pH gradient between the two chambers.Current density was promoted by 10%,while the COD removal efficiency was improved from 78.2% to 91.8% in the anode chamber.

Bioreduction of vanadium(V) in groundwater by autohydrogentrophic bacteria:Mechanisms and microorganisms

As one of the transition metals, vanadium（V）（V（V）） in trace amounts represents an essential element for normal cell growth, but becomes toxic when its concentration is above 1 mg/L. V（V） can alter cellular differentiation, gene expression, and other biochemical and metabolic phenomena. A feasible method to detoxify V（V） is to reduce it to V（IV）, which precipitates and can be readily removed from the water. The bioreduction of V（V） in a contaminated groundwater was investigated using autohydrogentrophic bacteria and hydrogen gas as the electron donor. Compared with the previous organic donors,H2 shows the advantages as an ideal electron donor, including nontoxicity and less production of excess biomass. V（V） was 95.5% removed by biochemical reduction when autohydrogentrophic bacteria and hydrogen were both present, and the reduced V（IV）precipitated, leading to total-V removal. Reduction kinetics could be described by a first-order model and were sensitive to p H and temperature, with the optimum ranges of p H 7.5–8.0 and 35–40°C, respectively. Phylogenetic analysis by clone library showed that the dominant species in the experiments with V（V） bioreduction belonged to theβ-Proteobacteria. Previously known V（V）-reducing species were absent, suggesting that V（V）reduction was carried out by novel species. Their selective enrichment during V（V）bioreduction suggests that Rhodocyclus, a denitrifying bacterium, and Clostridium, a fermenter known to carry out metal reduction, were responsible for V（V） bioreduction.

Biogenic palladium prepared by activated sludge microbes for the hexavalent chromium catalytic reduction: Impact of relative biomass

Palladium,a kind of platinum group metal,owns catalytic capacity for a variety of hydrogenations.In this study,Pd nanoparticles(PdNPs)were generated through enzymatic recovery by microbes of activated sludge at various biomass/Pd,and further used for the Cr(VI)reduction.The results show that biomass had a strong adsorption capacity for Pd(II),which was 17.25 mg Pd/g sludge.The XRD and TEM-EDX results confirmed the existence of PdNPs associated with microbes(bio-Pd).The increase of biomass had little effect on the reduction rate of Pd(II),but it could cause decreasing particle size and shifting location of Pd(0)with the better dispersion degree on the cell surface.In the Cr(VI)reduction experiments,Cr(VI)was first adsorbed on bio-Pd with hydrogen and then reduced using active hydrogen as electron donor.Biomass improved the catalytic activity of PdNPs.When the biomass/Pd(w/w)ratio increased to six or higher,Cr(VI)reduction achieved maximum rate that 50 mg/L of Cr(VI)could be rapidly reduced in one minute.

Review of water pollution control in China

Water resource shortage and pollution has seriously threatened the survival and development of developing countries.Because of China’s specific economical and social circumstances,complete adoption of developed countries’experience is unrealistic.At present,China needs to develop strategies and technologies in source water pollution control and municipal environmental remediation that embrace the country’s specific need to battle the water resource problem.Among them,efficient source water pretreatment is a critical step to ensure a safe municipal water supply.Unlike developed countries,it is not yet feasible in China to treat water supplied to the household and have it meet the standard of direct drinking;therefore,it is more appropriate to refer to it as service water.As a beneficial supplement,an additional community drinking water network and household drinking water apparatus can be considered.

Biosorption of Direct Black 38 by dried anaerobic granular sludge

The biosorption of Direct Black 38 by dried anaerobic granular sludge in a batch system under specific temperatures and initial pH was investigated.The adsorption reaction is pH dependent with higher removal at low pH.The adsorption equilibrium data fit very well with both Langmuir and Freundlich models in the concentration range of Direct Black 38 at all chosen temperatures.The adsorption parameters show that the adsorption of Direct Black 38 is an endothermic and more effective process at high temperatures.The kinetics of adsorption was found to be second order and adsorption rate constants increased with increasing temperature.Activation energy was determined as 26.8 kJ/mol for the process.This suggests that the adsorption of Direct Black 38 by dried anaerobic granular sludge is chemically controlled.

Reduction of hexavalent chromium with scrap iron in a fixed bed reactor

The reduction of hexavalent chromium by scrap iron was investigated in continuous long-term fixed bed system. The effects of pH, empty bed contact time （EBCT）, and initial Cr（VI） concentration on Cr（VI） reduction were studied. The results showed that the pH, EBCT, and initial Cr（VI） concentration significantly affected the reduction capacity of scrap iron. The reduction capacity of scrap iron were 4.56, 1.51, and 0.57mg Cr（VI）-g1 Fe0 at pH 3, 5, and 7 （initial Cr（VI） concentration 4 mg.L 1, EBCT 2 min, and temperature 25℃）, 0.51, 1.51, and 2.85 mg Cr（VI）.g-I Fe0 at EBCTs of 0.5, 2.0, and 6.0rain （initial Cr（VI） concentration 4mg.L-1, pH 5, and temperature 25℃）, and 2.99, 1.51, and 1.01 mg Cr（VI）. gl Fe0 at influent concentrations of 1, 4, and 8 mg.L ^-1（EBCT 2 min, pH 5, and temperature 25℃）, respectively. Fe（total） concentration in the column effluent continuously decreased in time, due to a decrease in time of the iron corrosion rate. The fixed bed reactor can be readily used for the treatment of drinking water containing low amounts of Cr（VI） ions, although the hardness and humic acid in water may shorten the lifetime of the reactor, the reduction capacity of scrap iron still achieved 1.98 mg Cr6 ＋- g-~ Fe. Scanning electron micro- scope equipped with energy dispersion spectrometer and X-ray diffraction were conducted to examine the surface species of the scrap iron before and after its use. In addition to iron oxides and hydroxide species, iron-chromium complex was also observed on the reacted scrap iron.

Potential acute effects of suspended aluminum nitride (AlN) nanoparticles on soluble microbial products (SMP) of activated sludge

The study aims to identify the potential acute effects of suspended aluminum nitride（Al N）nanoparticles（NPs） on soluble microbial products（SMP） of activated sludge.Cultured activated sludge loaded with 1,10,50,100,150 and 200 mg/L of Al N NPs were carried out in this study.As results showed,Al N NPs had a highly inverse proportionality to bacterial dehydrogenase and OUR,indicating its direct toxicity to the activated sludge viability.The toxicity of Al N NPs was mainly due to the nano-scale of Al N NPs.In SMP,Al N NPs led to the decrease of polysaccharide and humic compounds,but had slight effects on protein.The decrease of tryptophan-like substances in SMP indicated the inhibition of Al N NPs on the bacterial metabolism.Additionally,Al N NPs reduced obviously the molecular weight of SMP,which might be due to the nano-scale of Al N.