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科学 技术学院毕业设计（论文）外 文 文 献 翻 译 学 科 部： 理工学科部 专 业： 给水排水工程 班 级： 101班 学 号： 姓 名： 指导教师： 王晓玭 日 期： 2013年12月30日 原文：from where?enhancement of the activated sludge process by activated carbon produced from surplus biological sludgemaria j. martin, adriana artola, ma dolors balaguer & miquel rigolalaboratori denginyeria qumica i ambiental, facultat de ciencies, universitat de girona, campus de montilivi, 17071 girona, spainauthor for correspondence (fax:+34972418150; e-mail: maria.martinlequia.udg.es)received 2 november 2001; revisions requested 8 november 2001; revisions received 21 november 2001; accepted 22 november 2001key words: activated sludge, adsorption capacity, phenol, porosity, powdered activated carbonabstractsurplus biological sludge from wastewater treatment operations was converted into activated carbon and then added to the aerated vessel of an activated sludge process treating phenol and glucose. the addition of activated carbon, either sludge-based or commercial, enhanced phenol removal from 58% to 98.7% and from 87 to 93% for cod with feed concentrations of 100 mg phenol l1 and 2500 mg cod l1. no differences were found between the activated sludge-activated carbon bench scale continuous reactors operating with either commercial or sludge-based activated carbon in spite of the higher adsorption capacity of the former.introductionmany industrial wastes may contain toxic organic materials that cannot be effectively treated by conventional biological systems. adsorption processes, in particular those using activated carbon, have been evaluated in different ways for removing these compounds from wastewater. one method of using activated carbon in wastewater treatment is the addition of powdered activated carbon to the aeration basin of an activated sludge system (as-pac), which integrates the effect of adsorption and biodegradation.activated carbon in an as-pac system provides an increased adsorption capacity for organic compounds and attachment sites for bacteria. the removal of toxic compounds by bacteria partially immobilized on activated carbon has been reported as a combination of physical adsorption and biological degradation (sublette et al. 1982). the adsorbed material desorbs, diffuses out of the carbon and is then metabolized. order of word of orate from activated carbon accompanied by biodegradation of the desorbed compound has been frequently referred to as bioregeneration (de jonge et al. 1996, ha et al. 2000). other materials such as non-activated carbon, plastic or sand have been used to improve the effectiveness of as treatment. different studies have reported the superior performance of activated carbon compared to those materials (apilanez et al. 1998, cohen 2001).the widespread use of activated carbon in wastewater treatment has promoted research in the manufacturing of activated carbon from alternative precursor materials, mainly carbonaceous wastes of agricultural origin (pollard et al. 1992, johns et al. 1998). previous investigations have demonstrated the feasibility of activated carbon production from surplus biological sewage sludge (martin et al. 1996).the aim of this paper is to evaluate the performance of the sludge-based activated carbon in a combined as-pac (activated sludge-powdered activated carbon) unit treating phenol. in the first stage, the porosity of sludge-based powdered activated carbon (pacsb) and its adsorption capacity for phenol were determined. in the second stage, pacsb was added to an activated sludge bench scale continuous reactor and the performance of the treatment under step increases in feed phenol concentration was evaluated.materials and methodsanalytical methodsphenol, chemical oxygen demand (cod), total and volatile solids (ts, vs) and total and volatile suspended solids (tss, vss) were determined according to standard procedures (apha-awwa-wpcf 1992). the distinction between tss due to activated carbon and tss due to biomass was made by acid digestion of the samples with conc. hno3/hcl (1:1 v/v).preparation of sludge-based activated carbonthe raw material used for activated carbon preparation was secondary sludge from an urban wastewater treatment plant dewatered by centrifugation, which contains 17.6 g ts/100 g sludge, with 77.5% of vs (w/w). for the manufacturing of the activated carbon, dewatered sludge was mixed with conc. h2so4 (17.5m) (1:2 v/w) and dried in air at 105 c. the dried material, about 300 g, was then put into a crucible, heated in a fixed bed furnace at a rate of 15 c min1 to 700 c in the presence of n2 and held for 30 min. the product was ground, washed with 2 m hcl and rinsed with distilled water until the ph of the rinse water was constant. the product was wet-screened through a 325-mesh sieve (particle size 45 m) and dried at 110 c overnight.commercial activated carbonthe commercial powdered activated carbon gw (chem. carbon) is manufactured by the gas activation of bituminous coal in a two-step carbonization and activation process.liquid phase adsorption isothermsadsorption isotherms of phenol on sludge-based activated carbon, commercial activated carbon and activated sludge flocs were studied in the presence of mineral nutrients and metabolic end products (mixed liquor). a stock phenol solution (200 mg phenol l1) was prepared in filtered (whitman gf/c) mixed liquor. for the determination of the adsorption capacity of powdered activated carbons, 100 ml phenol solution were added to different amounts of activated carbon and the resultant slurry agitated for 2 h at room temperature. the liquid fraction was then separated from the carbon by vacuum filtration through whitman 2v filter paper, and the concentration of phenol remaining in solution measured.to determine the adsorption capacity of biomass for phenol, sludge samples were withdrawn from a conventional activated sludge pilot plant. the same procedure described above for the adsorption on powdered activated carbon was followed. the low contact time provided (2 h) in the adsorption tests ensures that no biodegradation of phenol occurred simultaneously to adsorption.operation of activated sludge-powdered activated carbon bench scale continuous reactors.experiments were carried out in three activated sludge laboratory scale plants. each unit consisted of an aerated tank (3.5 l) and a clarifier (3.5 l). one unit was operated as a conventional activated sludge (as) without activated carbon addition. the other two were operated as as-pac units with the addition of sludge-based activated carbon (as-pacsb) or commercial activated carbon (as-paccom).the three reactors were inoculated with aerobic sludge (tss = 4050 mg l1, vss = 2750 mg l1, codsol = 54mg l1). synthetic wastewater containing glucose (glucose = 500 mg l1, cod = 550 mg l1) and the necessary nutrients was introduced at a flow rate of 0.2 l h1, which lead to a hydraulic residence time of 15h. once a steady state was achieved as measured by cod and vss concentration in the mixed liquor(mlvss), the powdered activated carbon addition was started at the two as-pac units.for the start-up of the as-pac units, powdered activated carbon was added as aqueous slurry (400 mg pac l1) until the concentration of activated carbon in the aeration tank of each as-pac unit built up to 1000 mg pac l1. to maintain this concentration during the whole operation period, powdered activated carbon was added to compensate for pac withdrawal with sludge wastage.the three units were subjected to step disturbances of phenol and glucose and operated at mlvss concentration of around 2000 mg l1 and variable sludge residence time, which was between 1020 days. pac make-up rates were accordingly between 200400 mg day1.table 1. specific surface area and porosity determined by nitrogen gas adsorption at 196 c.activated carbon typesludge-basedcommercialsurface area (m2 g1)2531026microporea area90630average pore diameter (nm)2.31.8pore volumeb (cm3 g1)0.20.49microporea volume0.080.39microporea volume0.120.1a）pores are classified by average diameter (d) as micro pores (d 2 nm), mesopore (2 d 50 nm).b）n2 gas adsorption allows the determination of pore volume due to micro pores and mesopores.results and discussioncharacteristics of sludge-based and commercial activated carbonthe sludge-based activated carbon (pacsb) was characterized by nitrogen adsorption to determine the porous structure. results are shown in table 1,where the porosity of the commercial activated carbon(paccom) is also shown for comparison. pacsb has a considerably lower specific surface area than paccom as measured by n2 adsorption and calculated by the bet method (jankowska et al. 1991). the low surface area is related to the little micro porosity developed in comparison with the commercial product. pacsb is mainly mesoporous in nature, with an average pore diameter of 2.27 nm (table 1). scanning electron micrographs showed a higher presence of macropore in pacsb than in paccom.the adsorption capacity of sludge-based activated carbon for phenol was compared with the commercial activated carbon and the experimental results modeled by the langmuir equation (table 2). the superiority of the commercial activated carbon over sludge-based activated carbon is clear if the maximum adsorption capacity values, xm (mg phenol g1 activated carbon), in table 2 are compared. since phenol is mainly adsorbed in pores with a diameter under 0.7 nm (jankowska et al. 1991), the differences in the adsorption capacity of both activated carbons are in agreement with the pore size distribution and surface area determined by nitrogen adsorption (table 1).desorption experiments demonstrated that phenol was reversibly held by both carbons, allowing a fulltable 2. langmuir parameters for the adsorption of phenol on powdered activated carbon (pac).activatedcarbon typex = xmb phenoleq1+b phenoleqsludge-basedxm b r2(mg phenol g1 pac) (l mg1)26.7 0.164 0.975commercial125.6 0.309 0.988recovery of previously adsorbed phenol when brought in contact with phenol-free water.adsorption of phenol on biological sludge flocs was found almost negligible even at high phenol initial concentrations.performance of an activated sludge reactor operating with sludge-based activated carbonto evaluate the performance of pacsb as a support material in biological treatment, three bench scale continuous reactors were run in parallel. one unit was operated as a conventional activated sludge (as) unit. the other two were operated as as-pac units by the addition of commercial (as-paccom) or sludge based activated carbon (as-pacsb). the three units were subjected to step increases in phenol and glucose feed concentrations and the performance of the treatment was evaluated by effluent phenol and cod concentration during transient and steady state conditions. results are shown in figure 1, expressed as the increase in cod and phenol percent removal of the as-pac units with respect to that achieved in the conventional as unit (_cod% and _phenol%, respectively). the incremental percent removals were calculated as follows:effluent cod and phenol concentrations at a steady state for the different feed concentrations tested are summarized in table 3.at first, the three reactors were run at low initial phenol concentration (10 mg l1) and initial cod of 575 mg l1, which corresponds to the period from 021days in figure 1. no differences were found between the reactors operating as a conventional asfig 1. incremental () percent removal of (a) cod and (b) phenol of activated sludge units operating with sludge-based powdered activated carbon ()or commercial powdered activated carbon () over the activated sludge reactor.table3. steady state performance of the activated sludge (as) and the activated sludge units operating with sludge-based activated carbon (as-pacsb) or commercial activated carbon(as-paccom).unit configurationinlet concentration (mg l1)outlet concentration (mg l1)codaphenolcodaphenol 24 0.2 575 10 22 0.2 21 0.2 74 18 840 50 44 1 43 1 322 42 2500 100 180 1.3 183 1.8a) cod: chemical oxygen demand.b) mixed liquor volatile suspended solids 2050 mg l1.c) operating with 1000 mg l1 powdered activated carbon.the as and the two as-pac units were then subjected to a step increase in glucose and phenol feed concentration. inlet cod was 840 mg l1 and phenol concentration was set at 50 mg l1 during the period 2163 days shown in figure 1. the initial effects of the step increase in glucose and phenol concentration were more important in the activated sludge unit than in the two units operating with pac, as reflected by the higher values of incremental percent removal for cod and phenol during the transient period. after about 3 days of operation under these feed conditions, the phenol removal of the activated sludge reactor had recovered from the effects of the shock load and the performance of the three units was almost equivalent. however, the presence of pac, either sludge-based or commercial activated carbon, enhanced cod removal by about 3.5% of the level without carbon. this enhancement may be attributed to the flocculating effect of pac (meidl 1997).after the second step in feed concentration, this set cod at 2500 mg l1 and phenol around 100mg l1, the three units were operated during the period 63100 days (figure 1). an increase inthe efficiency of as-pac units over the as unit was again observed during the transient period. under these feed conditions, differences in steady-state performance capabilities between the as and as-pac reactors were also manifested. effluent cod concentration with only biological degradation taking place was 322.5 mg l1, while in the presence of activated carbon it was reduced to about 180 mg l1. in addition, phenol in the as-pac effluent units was around 1.5mg l1 compared to the 42 mg l1 found in the as unit effluent (table 3).no significant differences were found during the whole operational period between the two as-pac units running with pacsb or paccom in spite of the differences in adsorption capacity shown by both activated carbons for phenol (table 2). investigations on the combined adsorption-biodegradation treatment in batch cultures pointed to the irreversibility of adsorption to explain the better performance of activated carbon with the lowest adsorption capacity (de jonge et al. 1996). since phenol was reversibly adsorbed on both pacsb and paccom, the results obtainedcannot be explained by desirability limitations. it is suggested that phenol removal by adsorption onpaccom in the combined as-pac system may be impaired by the obstruction of pores due to bacterial growth.conclusionsin this process, waste biological sludge is converted to activated carbon by chemical activation with sulphuric acid. the adsorbent obtained is then applied to the aerated vessel of an activated sludge process treating glucose and phenol to improve the quality of the treated effluent.the addition of activated carbon to the aerated vessel of an activated sludge process increases stability and enhances the performance over a conventional activated sludge process. no differences were found between bench scale continuous reactors operating with sludge-based or commercial activated carbon in spite of the higher adsorption capacity of the commercial product for phenol as determined in a batch test.adsorption capacity determined in a batch test is not a critical aspect for the selection of an activated carbon to be applied to an activated sludge-powdered activated carbon combined process since the performance is conditioned by internal surface access ibility and not by total surface area.acknowledgementsthe authors would like to gratefully acknowledge the funding of the ministry of the environment (generalitat de catalunya) and the spanish ministry of science and technology (ref. dpi2000-1586).references1.american public health association, american water works association, water pollution control federation (1992) standard methods for the examination of water and wastewater, 18th end.washington.2.apilnez i, gutirrez a, diaz m (1998) effect of surface materials on initial biofilm development.bioresour. technol. 66: 225230.3.cohen y (2001) biofiltration-the treatment of fluids by microorganisms immobilized into the filter bedding material: a review. bioresour. technol. 77: 257274.4.de jonge rj, breuer am, andel jg (1996) bioregeneration of powdered activated carbon (pac) loaded with aromatic compounds. water res. 30: 875882.5.ha s, vinitnantharat s, ozaki h (2000) bioregeneration by mixed microorganisms of granular activated carbon loaded with a mixture of phenols. biotechnol. lett. 22: 10931096.6.jankowska h, swiatkowski a, choma j (1991) active carbon. newyork: ellis horwood.7.johns mm, marshall we, toles ca (1998) agricultural byproducts as granular activated carbons for adsorbing dissolved metals and organics. j. chem. technol. biotechnol. 71: 131140.8.mar