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A series of poly-aluminum-chloride-sulfates (PACS), which have different OH/Al (gamma) and Al(3+)/SO4(2-) mole ratios, has been prepared using AlCl3 x 6H2O, A(SO4)3 x 18H2O and Na2CO3 as raw materials. The electrophoretic nature of PACS was investigated by electrophoresis. Laboratory experiments were undertaken to evaluate the PACS in comparison with polyaluminum chloride (PAC) for the coagulation of simulating water and actual wastewaters. The experimental results show that the gamma value and the Al(3+)/SO4(2-) mole ratio affect the electrophoretic nature of PACS. PACS has a maximum zeta potential at about a gamma value of 1.5 and Al(3+)/SO4(2-) mole ratio of 12-16. The zeta potential of PACS varies with pH. The performance of PACS as coagulant is affected by gamma value and Al(3+)/SO4(2-) mole ratio. PACS of gamma = 2.1 and Al(3+)/SO4(2-) = 15 gives best turbidity removal effectiveness. In comparison with PAC of gamma = 2.0, PACS of gamma = 2.0 and Al(3+)/SO4(2-) = 16 gives higher removal efficiency for turbidity and COD, and shows the following advantages in the clarification of waters and wastewaters: rapid aggregation velocity, larger and heavier flocs, and lower required dosage.
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PMID:Electrophoretic nature and evaluation of poly-aluminum-chloride-sulfate (PACS) as a coagulant for water and wastewater treatment. 1274 40

The biological kinetic processes for anaerobic digestion (AD) are integrated into a two phase subset of a three phase mixed weak acid/base chemistry kinetic model. The approach of characterising sewage sludge into carbohydrates, lipids and proteins, as is done in the International Water Association (IWA) AD model No 1 (ADM1), requires measurements that are not routinely available on sewage sludges. Instead, the sewage sludge is characterised with the COD, carbon, hydrogen, oxygen and nitrogen (CHON) composition and is formulated in mole units, based on conservation of C, N, O, H and COD. The model is calibrated and validated with data from laboratory mesophilic anaerobic digesters operating from 7 to 20 d sludge age and fed a sewage primary and humus sludge mixture. These digesters yielded COD mass balances between 107-109% and N mass balances between 91-99%, and hence the experimental data is accepted as reasonable. The sewage sludge COD is found to be 32-36% unbiodegradable (depending on the kinetic formulation selected for the hydrolysis process) and to have a C3.5H7O2N0.196 composition. For the selected hydrolysis kinetics of surface mediated reaction (Contois), with a single set of kinetic and stoichiometric constants, for all retention times good correlation is obtained between predicted and measured results for: (i) COD; (ii) free and saline ammonia (FSA); (iii) short chain fatty acids (SCFA); (iv) H2CO3 * alkalinity; (v) pH of the effluent stream; (vi) CO2; and (vii) CH4 gases in the gas stream. The measured composition of primary sludge from two local wastewater treatment plants ranged between C3.38H7O1.91 N0.21 and C3.91H7O2.04N0.16. The predicted composition based on mass balances is therefore within 5% of the average measured composition providing persuasive validation of the model.
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PMID:Integrated chemical, physical and biological processes modelling of anaerobic digestion of sewage sludge. 1708 76

Bacterial community structures in four sequencing anoxic/anaerobic-aerobic membrane bioreactors (SAMs) that were fed with synthetic medium composed of different organic compounds in substrate as carbon source; acetate-dominant (acetate/propionate = 4/1), propionate-dominant (acetate/propionate = 1/4), glucose-dominant (glucose/acetate = 4/1) and methanol-dominant (methanol/acetate/propionate = 6/3/1) were analyzed by respiratory quinone profile and fluorescent in situ hybridization (FISH) techniques. The SAMs were operated at controlled pH range 7-8.5 and at constant temperature 25 degrees C. Total nitrogen (TN), total phosphorus (TP) and COD removal performances were also evaluated and compared. In addition, trans-membrane pressure was monitored to observe the impact of substrate composition on membrane fouling. The dominance of the mole fraction of ubiquinone (UQ-8) in the SAMs indicated dominance of the beta-subclass of Proteobacteria; however, its population comparatively decreased when the substrate was glucose dominant or methanol dominant. A relatively higher and stable enhanced biological phosphorus removal performance was observed when methanol-dominant substrate was used concurrently with an increase in the gamma-subclass of Proteobacteria. The population of the alpha-subclass of Proteobacteria slightly increased along with a decrease in phosphate removal activity when the substrate was glucose-dominant. Results from FISH analysis also supported the findings of the quinone profile. The trans-membrane pressure variation in the SAMs indicated that fouling was relatively rapid when propionate-dominant or methanol-dominant substrate was used and most stable when glucose-dominant substrate was used. A combination of methanol and acetate would be a better choice as an external carbon source when nutrients removals, as well as fouling, are considered in the membrane bioreactor- (MBR-) coupled biological nutrients removing (BNR) process.
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PMID:Biological nitrogen and phosphorus removal and changes in microbial community structure in a membrane bioreactor: effect of different carbon sources. 1764 Jul 1

Fenton process has been widely used to treat landfill leachate. The "design of experiments" methodology was used to study the main variables affecting the Fenton process as well as their most relevant interactions. Results of two-level-factorial-design indicated that pH, COD, and the interaction of pH and COD gave negative effects, but Fe(II) dosage and H(2)O(2)/Fe(II) mole ratio showed positive effect, respectively. The quadratic model was derived based on the results of both two-level-factorial-design experiment and further runs of star points and center points. The response surface plots of quadratic model were obtained accordingly and the optimal conditions were derived from the quadratic model.
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PMID:Multivariate approach to the Fenton process for the treatment of landfill leachate. 1855 85

The development of granular sludge in thermophilic (55 degrees C) upflow anaerobic sludge blanket reactors was investigated. Acetate and a mixture of acetate and butyrate were used as substrates, serving as models for acidified waste-waters. Granular sludge with either Methanothrix or Methanosarcina as the predominant acetate utilizing methanogen was cultivated by allowing the loading rate to increase whenever the acetate concentration in the effluent dropped below 200 and 700 mg COD/L, respectively. The highest methane generation rates, up to 162 kg CH(4)-COD/m(3) day, or 2.53 mole CH(4)/L day, were achieved at hydraulic retention times down to 21 min, with granules consisting of Methanothrix. The formation of Methanothrix granules did not depend on the type of seed material, nor on the addition of inert support particles. The growth of granules proceeded rapidly with adapted seed material, even when the reactors were inoculated with low concentrations. With mesophilic seed materials growth of granules took much longer. Thermophilic Methanothrix granules strongly resemble mesophilic granules of the "filamentous" type. Some factors governing the thermophilic granulation process are discussed.
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PMID:Granulation of biomass in thermophilic upflow anaerobic sludge blanket reactors treating acidified wastewaters. 1855 83

The control of membrane fouling is an essential issue in membrane bioreactor (MBR) process. It has been recognized that the most important factors that affect membrane fouling are presence of soluble microbial products (SMP) and extracellular polymeric substances (EPS) in a reactor. The objective of this study was to examine the effect of the coagulant addition on the membrane fouling in the MBR process. Accordingly, laboratory scale batch experiments and MBR experiments were conducted using coagulant. In batch experiments, effective SMP removal and control of EPS release were observed by coagulant addition. Fe coagulant was slightly more effective than Al coagulant in the addition of same mole amount. Therefore, Fe was used as coagulant in MBR experiments. In MBR experiments, Fe solutions of 0 mg/L, 2,260 mg/L and 4,520 mg/L were added into the tanks (Run1, Run2 and Run3, respectively) with the flow rate of 200 mL/d. COD removal efficiencies of 97% and phosphorus removal efficiencies of 92% were observed by Fe addition in the MBR experiment. Membrane fouling occurred more often in Run1 than in the other two Runs. Membrane was cleaned 18, 9 and 5 times in Run1, Run2 and Run3, respectively during 40 days runs. This suggested that the membrane fouling was reduced by the coagulant addition. The protein and carbohydrate concentrations of the SMP in the fraction of 1 microm-0.4 microm in Run2 and Run3 were significantly lower than that in Run1 and the particle size of the activated sludge was obviously increased in Run2 and Run3. These results suggested that the coagulant addition is effective to control the membrane fouling.
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PMID:Control of membrane fouling in membrane bioreactor process by coagulant addition. 1938 Sep 89

The properties of novel nanosized iron sulphide produced by sulfate reducing bacteria (SRB) and its application to the removal of Cr (VI) from wastewater were studied. The structural properties were examined by transmission electron microscope (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The influences of pH, temperature and dosage on removal of Cr (VI) from wastewater by nanosized iron sulphide were investigated, and the effect comparison of nanosized iron sulphide and other traditional wastewater treatment was also evaluated. TEM result shows that the length of the nanosized iron sulphide is approximately 45-80 nm, and the ratio of length to width is 10-15. XPS and XRD results indicate that the Fe/S is 1.07-1.11, and the main composition of nanosized iron sulphide is amorphous FeS and mackinawite. While in treating wastewater containing Cr (V), pH, temperature and dosage of nanosized iron sulphide are the main factors to control the reaction. The Cr (VI) reduction rate increases with decrease of pH and increase of dosage and temperature. Among these factors, pH is the most significant influence factor. At 25 degrees C, pH 3, when the mole ratio of nanosized iron sulphide to chromium (VI) reaches 1.17/1, wastewater containing Cr (VI) 0.03 mol/L can be treated to meet the discharge standard within 10 min. Moreover, in treating wastewater containing Cr (VI), compared with commercial iron sulfide (AR.), nanosized iron sulphide has advantages of low dosage and short treatment time, and compared to conventional biological treatment by SRB, nanosized iron sulphide has advantages of low effluent COD and small amount of sludge.
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PMID:[Property analysis of nanosized iron sulfide produced by sulfate reducing bacteria and its application in the treatment of wastewater containing high concentration of Cr (VI)]. 1954 6

The catalytic advanced oxidation process (CAOP) of O(3)/MgO/H(2)O(2) was integrated with a sequencing batch reactor (SBR) system to completely treat concentrated formaldehyde wastewater, demonstrating that this combination is an effective method for treating such wastewaters. The influence of several operational variables--including pH, MgO powder dosage, and the concentrations of H(2)O(2) and O(3)--was investigated for the O(3)/MgO/H(2)O(2) degradation of a 7000 mg/L formaldehyde wastewater. The optimum conditions were found to be a pH of 8, 5 g/L dose of MgO powder, 0.09 mole/L concentration of H(2)O(2), and 0.153 g/L min dose of O(3). The formaldehyde and COD concentrations were reduced 79% and 65.6%, respectively, in the CAOP for 120 min of reaction time under the optimum condition stated above. The remaining concentrations of formaldehyde and COD were 1500 mg/L and 3200 mg/L, respectively, in the effluent. The degradation of formaldehyde in CAOP was determined to be a first-order reaction with a constant of 0.015/min, and radical oxidation was the predominant degradation mechanism. This effluent was post-treated in SBR system for a total cycle time of 24h. The SBR completely removed the formaldehyde and removed 98% of the COD, reducing the COD concentration to lower than 60 mg/L. Therefore, the integrated O(3)/MgO/H(2)O(2) and SBR process is demonstrated as a promising technology for the complete treatment of wastewater with high concentrations of toxic and inhibitory compounds such as formaldehyde.
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PMID:The removal of formaldehyde from concentrated synthetic wastewater using O3/MgO/H2O2 process integrated with the biological treatment. 1961 92

La-Ce codoping nano-TiO2 catalyst was prepared by microwave-assisted sol process with TBT and distilled water as forerunner body, ethanol as solvent and glacial acetic acid as inhibitor. The prepared samples were characterized by using XRD, XPS and UV-Vis techniques. Results of structural characterization indicated that the prepared samples were all pure anatase phase nano-TiO2 and their diffraction peak broadened obviously after La and Ce doping. Results of XPS analysis revealed that La-O bond existed in the samples and many oxygen vacancies were produced on the surface of TiO2 nanoparticles after La and Ce codoping. UV-Vis absorption spectra demonstrated that the prepared samples had strong and wide absorption band between 200 and 400 nm and the absorption intensity increased after La and Ce doping because of La(III)-O charge-transfer transition, Ce (IV) f --> d transition and Ce (IV)-O charge-transfer transition. Photocatalytic experiment results showed that the titanium dioxide's photocatalytic activity increased obviously after La and Ce codoping. The optimal parameters for the preparation were obtained by adjusting the mole ratio of La and Ce in photocatalysts. When the doping amount of La and Ce was 2% and 0.04% respectively, the prepared sample exhibited high photocatalytic activity, the decoloration ratio of methyl orange solution was above 90%, and COD removal of cigarette factory wastewater was 86.11%.
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PMID:[La-Ce-Codoping nano-titania photocatalyst: preparation via microwave-assisted sol process, spectroscopy characterization and photocatalytic activity]. 1983 35

The partial oxidation (POX) characteristics of municipal sludge in supercritical water (SCW) were investigated by using batch reactor. Effects of reaction parameters such as oxidant equivalent ratio (OER), reaction time and temperature were investigated. Activated carbon (AC) could effectively improve the mole fraction of H(2) in gas product at low OER. However, high OER (greater than 0.3) not only led to the combustion reaction of CO and H(2), but also caused corrosion of reactor inner wall. Hydrogenation and polymerization of the intermediate products are possible reasons for the relative low COD removal rate in our tests. Metal oxide leached from the reactor inner wall and the main components of the granular sludge were deposited in the AC catalyst. Reaction time had more significant effect on BET surface area of AC than OER had. Long reaction time led to the methanation reaction following hydrolysis and oxidation reaction of AC in SCW in the presence of oxygen. Correspondingly, the possible reaction mechanisms were proposed.
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PMID:Partial oxidation of municipal sludge with activited carbon catalyst in supercritical water. 2043 15


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