城市污水处理技术（英文课件）.ppt

An Introduction to Urban Water and Wastewater Treatment Technologies,2,Contents,1. Contaminants in Water 2. Contaminant Sources and Treatability 3. Best Available Technologies 4. Trend of Development,3,1. Contaminants in Water,1.1 Target of Water Quality Control,Wastewater Discharge Regulation,Key point: Protection of human health,4,1.2 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 (self purification),5,1.2 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,6,1.3 Water Environmental Standard American standard: Clean Water Act (CWA) Ambient Water Quality Criteria for the Protection of Human Health Aquatic Life Criteria Nutrient Criteria,7,1.3 Water Environmental Standard American standard: Clean Water Act (CWA) The NRWQC 2002 includes Criteria for priority toxic pollutants: 120 items (15 for inorganic, 105 for organic pollutants) Criteria for non priority pollutants: 45 items Criteria for organoleptic (taste and odor) effects: 23 items Downloadable at /waterscience/criteria/ wqcriteria.html,8,1.3 Water Environmental Standard Chinese standard: Environmental Quality Standards for Surface Water (GB 3838-2002) Fundamental parameters (地表水环境质量标准基本项目标准限值): 24 items Supplemental 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 Specific 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,9,表1 地表水环境质量标准基本项目标准限值 (单位: mg/L),10,表1 地表水环境质量标准基本项目标准限值 (单位: mg/L),11,表1 地表水环境质量标准基本项目标准限值 (单位: mg/L),12,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),13,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),14,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),15,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),16,1.4 Pollutants of Public Concern Indicative parameters Suspended solids: SS Dissolved solids: TDS (salinity) Organic substances: COD, BOD, TOC, UV Dissolved oxygen: DO Acidity: pH Nutrients Nitrogen: TN, NH3-N, NO3-N, NO2-N Phosphorous: TP, Portho, Ppoly, Poranic ,17,1.4 Pollutants of Public Concern Synthetic organic chemicals (SOCs) Industrial products such as PCBs (Polychlorinated biphenyls) Industrial byproducts such as Dioxin Pesticides and herbicides DBP precursors Natural organic matter (NOM) such as humic acids etc. Persistent organic pollutants (POPs) DDT, PCBs, PAHs, Hexachlorobenzene, Dioxins, Furans ,18,1.4 Pollutants of Public Concern Endocrine disruptive chemicals (EDCs) Heavy metals such as Cr, Pb etc. PCBs, hormones, dioxins Organo-chlorinated pesticides Microorganisms Giardia Cryptosporidium Viruses and bacteria,19,2. Contaminant Sources and Treatability,2.1 Contaminant Sources Point sources: 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: Nutrients, pesticides, NOM Certain POPs and EDCs,20,2.2 Treatability of Pollutants The treatability of pollutants depends on their Size Suspended Colloidal Soluble Chemical properties Organic Inorganic Biodegradability Biodegradable Bio-non-degradable,21,Water quality and treatability matrix,22,Domestic wastewater as an example Methods of pollutants classification Suspended and soluble: using a 0.45 mm filter Settleable and non-settleable: plain settling for 2 hours Coagulable and non-coagulable: coagulation and settling Secondary treatment: activated sludge process (oxidation ditch),23,24,2.3 Limitation of Conventional Treatment Conventional treatment Typical process for water treatment: Coagulation sedimentation filtration chlorination Typical process for wastewater treatment (activated sludge process): Screening primary settling biological unit secondary settling chlorination,25,2.3 Limitation of Conventional Treatment Pollutants that can be removed Suspended solids Colloidal matter Biodegradable organic matter Bacteria and viruses Pollutants that cannot be removed Most of the dissolved solids Bio-non-degradable organic matter Chlorine persistent microorganisms (e. g. Cryptosporidium),26,3. Best Available Technologies,3.1 Strategic Considerations on the Selection of Available Technologies Conventional technologies are fundamental technologies and their enhancement should be the first choice Conversion of the property of pollutants is sometimes more important than a complete removal of the pollutants Combination of different technologies is the key for effective removal of pollutants,27,3.2 Enhancement of Conventional Technologies Enhanced coagulation For the removal of NOM in drinking water treatment For the enhancement of primary treatment in wastewater treatment Taking NOM removal as an example USEPA Enhanced Coagulation Rule,28,3.2 Enhancement of Conventional Technologies Enhanced coagulation Requirements for enhanced coagulation: Enhanced coagulation required as TOC 2 mg/L Step 1: percent removal requirements,29,Step 2: 0.3/10 slope,30,pH adjustment is the key point,31,3.2 Enhancement of Conventional Technologies Enhanced filtration For the safeguard of drinking water quality especially the control of Giardia and Cryptosporidium Giardia lamblia: cyst size 8-12mm x 7-10mm Cryptosporidium parvum: oosyst size 4.5-5 mm For tertiary wastewater treatment to acquire high quality effluent,32,3.2 Enhancement of Conventional Technologies Enhanced filtration Relationship between turbidity and particle size,33,Example of turbidity and Cryptosporidium oocyst data,34,3.2 Enhancement of Conventional Technologies Enhanced filtration Iron oxide-coated media for NOM sorption and particulate filtration Iron and aluminum hydroxide-coated media for the removal of Cryptosporidium,35,Breakthrough curves for NOM sorption onto coated sand,36,Zeta potential of uncoated sand and sand coated with iron and aluminum hydroxide,37,Improvement of the removal of Cryptosporidium oocysts in sand filters,38,3.2 Enhancement of Conventional Technologies Enhancement of biological process Fluidized pellet bed (FPB) bioreactor as an example through a combination of physicochemical process and biological process HRT reduced to less than 1 hour Primary settling and secondary settling omitted Organic removal equivalent to activated sludge process High TP removal achieved,39,Flow diagram of the FPB bioreactor,40,Pellets (granule sludge) formed in the bioreactor SEM image of microbes on the surface of the pellets,41,Distribution of aerobic and anaerobic bacteria,42,Removal of SS, COD, TP and TN by the bioreactor,43,3.3 Ozone and Advanced Oxidation Processes Reactivity of ozone in aqueous solution In an aqueous solution, ozone may act on various compounds by Direct reaction with the molecular ozone Indirect reaction with the radical species that are formed when ozone decomposes in water Advanced oxidation Oxidation by free radical reaction,44,Pathways of ozonation Pseudo first-order kinetic equation of ozone decomposition,45,Ozone decomposition process,46,Initiators, promotors, and inhibitors of free-radical reactions Initiators: the compounds capable of inducing the formation of a superoxide ion O2- from an ozone molecule Promotors: all organic and inorganic molecules capable of regenerating the O2- superoxide anion from the hydroxyl radical Inhibitors: compounds capable of consuming OH radicals without regenerating the superoxide anion O2-,47,Mechanism of ozone decomposition,48,Ozone decomposition process by hydroperoxide ions,49,Ozone decomposition process by UV radiation,50,3.3 Ozone and Advanced Oxidation Processes Ozonation of synthetic organic chemicals Two ozonolysis pathways of ozonation: Direct attack by electrophilic or dipolar cyclo addition Indirect attack by free radicals produced by reaction with water and water constituents,51,Kinetics of ozonation of dissolved organic micropollutants Ozonation pathways Let,52,The OH radicals are generated by ozone attack on organic and inorganic initiators, and there exists a relation as The total oxidation rate of the particular substrate i can be written as,53,Characteristics of ozonation of organic compounds Decrease of aromaticity Unsaturated structure to saturated structure Generation of intermediate products Total degradation often needs very high ozone dose and takes longer time,54,Example: Ozonation of aromatic compounds,55,3.3 Ozone and Advanced Oxidation Processes Ozonation of natural organic matter (NOM) Aquatic humic substances (AHS): Isolation method: microfiltration of the water and adsorption of organics on XAD-8 resin at pH=2, followed by NaOH elution and separation by precipitation at pH=1. Two main groups: Humic acid precipitated fraction Fulvic acid remaining part in the solution,56,Possible reaction of zone consumption in a natural aquatic environment,d inhibitors i initiators p promotors s - scavengers,57,Ozone action on AHS,58,The effects of ozonation on AHS Formation of hydroxyl, carbonyl and carboxyl groups; Increase of polarity and hydrophilicity; Loss of double bonds and aromaticity; Shift in the molecular weight distribution toward lower-molecular-weight compounds.,59,Py-GC-MS analysis results,60,THMs and HPLC analysis results,61,Specific UV adsorption (SUVA) as a parameter showing the biodegradability of AHS TOC or DOC: total amount of organic carbon UV254: concentration of organics with unsaturated structure SUVA: UV-to-TOC ratio which represents the fraction of unsaturated functional groups in unit concentration of organic matter High SUVA value: less biodegradable Low SUVA value: more biodegradable,62,3.4 Membrane Technologies Spectrum of impurities in water and applicable filtration processes,63,3.4 Membrane Technologies Membrane operation,64,3.4 Membrane Technologies Pressure-driven membrane operation RO: at least twice the osmotic pressure must be exerted 5 to 8 MPa for seawater NF: osmotic backpressure much lower than RO typically 0.5 to 1.5 MPa UF: operating pressure 50 to 500 kPa MF: operating pressure similar to UF,65,3.4 Membrane Technologies Permeation behavior Darcys law To account for the effects of osmotic pressure,66,3.4 Membrane Technologies Reduction in Permeate Flux Rc: resistance of concentration boundary layer Rcp: resistance of concentration-polarization layer D: diffusivity,67,3.4 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,68,3.4 Membrane Technologies Mechanism of membrane fouling Cake formation Pore blockage Adsorptive fouling Biofouling,SEM image of a biofilm formed on a membrane,69,Conventional UF or MF process,70,Conventional NF or RO process,71,3.4 Membrane Technologies Membrane bioreactor (MBR) Principle of MBR,(a) MBR,(b) Membrane for tertiary treatment,72,3.4 Membrane Technologies Membrane bioreactor (MBR) MBR configuration,(a) Recirculated MBR,(b) Integrated MBR,73,3.4 Membrane Technologies Membrane bioreactor (MBR) Advantages of MBR Greater biomass concentration and greater loads High removal efficiency Less sludge production Greater reliability and flexibility of application Ability to absorb variations and fluctuations in the applied hydraulic and organic load Complete