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1、An Introduction to Urban Water and Wastewater Treatment Technologies 1 1 Contents 1. Contaminants in Water 2. Contaminant Sources and Treatability 3. Best Available Technologies 4. Trend of Development 2 2 1. Contaminants in Water 1.1 Target of Water Quality Control Wastewater Discharge Regulation K
2、ey point: Protection of human health 3 3 1.2 Capacity of Water Environment A simple calculation Ci : Concentration of contaminant i Mi : Mass of contaminant i in water V : Water volume Mi0 : Mass of contaminant i received Mir : Mass of contaminant i assimilated (removed) by the water body itself (se
3、lf purification) 4 4 1.2 Capacity of Water Environment Water quality criteria This is equivalent to Mir is a measure of the environmental capacity Cis : Standard for contaminant i Mis : Maximum permissible mass of contaminant i in water 5 5 1.3 Water Environmental Standard American standard: Clean W
4、ater Act (CWA) uAmbient Water Quality Criteria for the Protection of Human Health uAquatic Life Criteria uNutrient Criteria 6 6 1.3 Water Environmental Standard American standard: Clean Water Act (CWA) The NRWQC 2002 includes uCriteria for priority toxic pollutants: 120 items (15 for inorganic, 105
5、for organic pollutants) uCriteria for non priority pollutants: 45 items uCriteria for organoleptic (taste and odor) effects: 23 items Downloadable at http:/www.epa.gov/waterscience/criteria/ wqcriteria.html 7 7 1.3 Water Environmental Standard Chinese standard: Environmental Quality Standards for Su
6、rface Water (GB 3838-2002) uFundamental parameters (地表水环境质量标 准基本项目标准限值): 24 items uSupplemental parameters for source water for community water supply (集中式生活饮用 水地表水源地补充项目标准限值): 5 items uSpecific parameters for source water for community water supply (集中式生活饮用水地 表水源地特定项目标准限值): 80 items 8 8 表1 地表水环境质量标
7、准基本项目标准限值 (单位: mg/L) 9 9 表1 地表水环境质量标准基本项目标准限值 (单位: mg/L) 1010 表1 地表水环境质量标准基本项目标准限值 (单位: mg/L) 1111 表2 集中式生活饮用水地表水源地补充项目标准限值 (单位：mg/L) 1212 表3 集中式生活饮用水地表水源地特定项目标准限值 (单位：mg/L) 1313 表3 集中式生活饮用水地表水源地特定项目标准限值 (单位：mg/L) 1414 表3 集中式生活饮用水地表水源地特定项目标准限值 (单位：mg/L) 1515 1.4 Pollutants of Public Concern Indicati
8、ve parameters uSuspended solids: SS uDissolved solids: TDS (salinity) uOrganic substances: COD, BOD, TOC, UV uDissolved oxygen: DO uAcidity: pH Nutrients uNitrogen: TN, NH3-N, NO3-N, NO2-N uPhosphorous: TP, Portho, Ppoly, Poranic 1616 1.4 Pollutants of Public Concern Synthetic organic chemicals (SOC
9、s) uIndustrial products such as PCBs (Polychlorinated biphenyls) uIndustrial byproducts such as Dioxin uPesticides and herbicides DBP precursors uNatural organic matter (NOM) such as humic acids etc. Persistent organic pollutants (POPs) uDDT, PCBs, PAHs, Hexachlorobenzene, Dioxins, Furans 1717 1.4 P
10、ollutants of Public Concern Endocrine disruptive chemicals (EDCs) uHeavy metals such as Cr, Pb etc. uPCBs, hormones, dioxins uOrgano-chlorinated pesticides Microorganisms uGiardia uCryptosporidium uViruses and bacteria 1818 2. Contaminant Sources and Treatability 2.1 Contaminant Sources Point source
11、s: Sources of pollutants from a discrete location such as a pipe, tank, pit, or ditch. Non-point sources: Source of pollutants from a number of points that are spread out and difficult to identify and control. Non-point sources attribute a great deal to water pollution: lNutrients, pesticides, NOM l
12、Certain POPs and EDCs 1919 2.2 Treatability of Pollutants The treatability of pollutants depends on their Size lSuspended lColloidal lSoluble Chemical properties lOrganic lInorganic Biodegradability lBiodegradable lBio-non-degradable 2020 Water quality and treatability matrix 2121 Domestic wastewate
13、r as an example Methods of pollutants classification uSuspended and soluble: using a 0.45 mm filter uSettleable and non-settleable: plain settling for 2 hours uCoagulable and non-coagulable: coagulation and settling uSecondary treatment: activated sludge process (oxidation ditch) 2222 2323 2.3 Limit
14、ation of Conventional Treatment Conventional treatment uTypical process for water treatment: Coagulation sedimentation filtration chlorination uTypical process for wastewater treatment (activated sludge process): Screening primary settling biological unit secondary settling chlorination 2424 2.3 Lim
15、itation of Conventional Treatment Pollutants that can be removed uSuspended solids uColloidal matter uBiodegradable organic matter uBacteria and viruses Pollutants that cannot be removed uMost of the dissolved solids uBio-non-degradable organic matter uChlorine persistent microorganisms (e. g. Crypt
16、osporidium) 2525 3. Best Available Technologies 3.1 Strategic Considerations on the Selection of Available Technologies uConventional technologies are fundamental technologies and their enhancement should be the first choice uConversion of the property of pollutants is sometimes more important than
17、a complete removal of the pollutants uCombination of different technologies is the key for effective removal of pollutants 2626 3.2 Enhancement of Conventional Technologies Enhanced coagulation uFor the removal of NOM in drinking water treatment uFor the enhancement of primary treatment in wastewate
18、r treatment Taking NOM removal as an example USEPA Enhanced Coagulation Rule 2727 3.2 Enhancement of Conventional Technologies Enhanced coagulation uRequirements for enhanced coagulation: Enhanced coagulation required as TOC 2 mg/L uStep 1: percent removal requirements 2828 uStep 2: 0.3/10 slope 292
19、9 upH adjustment is the key point 3030 3.2 Enhancement of Conventional Technologies Enhanced filtration uFor the safeguard of drinking water quality especially the control of Giardia and Cryptosporidium lGiardia lamblia: cyst size 8-12mm x 7-10mm lCryptosporidium parvum: oosyst size 4.5-5 mm uFor te
20、rtiary wastewater treatment to acquire high quality effluent 3131 3.2 Enhancement of Conventional Technologies Enhanced filtration uRelationship between turbidity and particle size 3232 Example of turbidity and Cryptosporidium oocyst data 3333 3.2 Enhancement of Conventional Technologies Enhanced fi
21、ltration uIron oxide-coated media for NOM sorption and particulate filtration uIron and aluminum hydroxide-coated media for the removal of Cryptosporidium 3434 Breakthrough curves for NOM sorption onto coated sand 3535 Zeta potential of uncoated sand and sand coated with iron and aluminum hydroxide
22、3636 Improvement of the removal of Cryptosporidium oocysts in sand filters 3737 3.2 Enhancement of Conventional Technologies Enhancement of biological process uFluidized pellet bed (FPB) bioreactor as an example through a combination of physicochemical process and biological process lHRT reduced to
23、less than 1 hour lPrimary settling and secondary settling omitted lOrganic removal equivalent to activated sludge process lHigh TP removal achieved 3838 Flow diagram of the FPB bioreactor 3939 Pellets (granule sludge) formed in the bioreactor SEM image of microbes on the surface of the pellets 4040
24、Distribution of aerobic and anaerobic bacteria 4141 Removal of SS, COD, TP and TN by the bioreactor 4242 3.3 Ozone and Advanced Oxidation Processes Reactivity of ozone in aqueous solution In an aqueous solution, ozone may act on various compounds by lDirect reaction with the molecular ozone lIndirec
25、t reaction with the radical species that are formed when ozone decomposes in water Advanced oxidation Oxidation by free radical reaction 4343 Pathways of ozonation Pseudo first-order kinetic equation of ozone decomposition 4444 Ozone decomposition process 4545 Initiators, promotors, and inhibitors o
26、f free-radical reactions uInitiators: the compounds capable of inducing the formation of a superoxide ion O2- from an ozone molecule uPromotors: all organic and inorganic molecules capable of regenerating the O2- superoxide anion from the hydroxyl radical uInhibitors: compounds capable of consuming
27、OH radicals without regenerating the superoxide anion O2- 4646 Mechanism of ozone decomposition 4747 Ozone decomposition process by hydroperoxide ions 4848 Ozone decomposition process by UV radiation 4949 3.3 Ozone and Advanced Oxidation Processes Ozonation of synthetic organic chemicals Two ozonoly
28、sis pathways of ozonation: uDirect attack by electrophilic or dipolar cyclo addition uIndirect attack by free radicals produced by reaction with water and water constituents 5050 Kinetics of ozonation of dissolved organic micropollutants uOzonation pathways uLet 5151 uThe OH radicals are generated b
29、y ozone attack on organic and inorganic initiators, and there exists a relation as uThe total oxidation rate of the particular substrate i can be written as 5252 Characteristics of ozonation of organic compounds uDecrease of aromaticity uUnsaturated structure to saturated structure uGeneration of in
30、termediate products uTotal degradation often needs very high ozone dose and takes longer time 5353 Example: Ozonation of aromatic compounds 5454 3.3 Ozone and Advanced Oxidation Processes Ozonation of natural organic matter (NOM) Aquatic humic substances (AHS): uIsolation method: microfiltration of
31、the water and adsorption of organics on XAD-8 resin at pH=2, followed by NaOH elution and separation by precipitation at pH=1. uTwo main groups: Humic acid precipitated fraction Fulvic acid remaining part in the solution 5555 Possible reaction of zone consumption in a natural aquatic environment d i
32、nhibitorsi initiatorsp promotorss - scavengers 5656 Ozone action on AHS 5757 The effects of ozonation on AHS uFormation of hydroxyl, carbonyl and carboxyl groups; uIncrease of polarity and hydrophilicity; uLoss of double bonds and aromaticity; uShift in the molecular weight distribution toward lower
33、-molecular-weight compounds. 5858 Py-GC-MS analysis results 5959 THMs and HPLC analysis results 6060 Specific UV adsorption (SUVA) as a parameter showing the biodegradability of AHS uTOC or DOC: total amount of organic carbon uUV254: concentration of organics with unsaturated structure uSUVA: UV-to-
34、TOC ratio which represents the fraction of unsaturated functional groups in unit concentration of organic matter uHigh SUVA value: less biodegradable uLow SUVA value: more biodegradable 6161 3.4 Membrane Technologies Spectrum of impurities in water and applicable filtration processes 6262 3.4 Membra
35、ne Technologies Membrane operation 6363 3.4 Membrane Technologies Pressure-driven membrane operation uRO: at least twice the osmotic pressure must be exerted 5 to 8 MPa for seawater uNF: osmotic backpressure much lower than RO typically 0.5 to 1.5 MPa uUF: operating pressure 50 to 500 kPa uMF: opera
36、ting pressure similar to UF 6464 3.4 Membrane Technologies Permeation behavior uDarcys law uTo account for the effects of osmotic pressure 6565 3.4 Membrane Technologies Reduction in Permeate Flux Rc: resistance of concentration boundary layer Rcp: resistance of concentration-polarization layer D: d
37、iffusivity 6666 3.4 Membrane Technologies Reduction in Permeate Flux The accumulation of materials on, in, and near a membrane in the presence of a cross flow Reductions in permeate flux over time 6767 3.4 Membrane Technologies Mechanism of membrane fouling uCake formation uPore blockage uAdsorptive
38、 fouling uBiofouling SEM image of a biofilm formed on a membrane 6868 Conventional UF or MF process 6969 Conventional NF or RO process 7070 3.4 Membrane Technologies Membrane bioreactor (MBR) uPrinciple of MBR (a) MBR (b) Membrane for tertiary treatment 7171 3.4 Membrane Technologies Membrane biorea
39、ctor (MBR) uMBR configuration (a) Recirculated MBR(b) Integrated MBR 7272 3.4 Membrane Technologies Membrane bioreactor (MBR) uAdvantages of MBR lGreater biomass concentration and greater loads lHigh removal efficiency lLess sludge production lGreater reliability and flexibility of application lAbil
40、ity to absorb variations and fluctuations in the applied hydraulic and organic load lComplete control of the sludge age to allow the development of slow-growing microorganisms (such as nitrifying bacteria) 7373 4. Trend of Development 4.1 Integration of Water and Wastewater System Fundamental consid
41、erations uWater supply and wastewater systems are subsystems in the series of urban metabolic system of water uWater supply according to the purposes of use regarding both quantity and quality uDesign of water and wastewater systems as one comprehensive water system 7474 Future urban water system wi
42、th application of membrane technology 7575 4.2 Decentralized Systems for Wastewater Treatment and Reuse Philosophy of decentralization uNon-mixing lGrey water: Large volumes, COD diluted, little nutrients, pathogens, no pharmaceuticals, personal care products lBlack water: Little volumes, possibilit
43、ies to minimise them even further, high COD and nutrients, pathogens, pharmaceuticals and hormones uSeparate treatment lTreatment depends on the objective uRecovery of useful resources lWater, energy, fertilizer 7676 4.3 Control of Micropollutants in Water and Wastewater Treatment uControl of pollutant source uUtilization of hybrid process lAdvanced oxidation and carbon adsorption uUtilization of hybrid membrane process lMembrane-powdered activated carbon reactor lIon exchange membrane reactor 7777