Transcript water
Sustainable Development in China Water resources in China WANG Hongtao, Ph.D., Associate Professor College of Environmental Science and Engineering, Tongji University [email protected] Outline Drinking water treatment Conventional treatment process Advanced treatment process Wastewater treatment Wastewater situation in China Wastewater treatment process Case Study of wastewater treatment plant Algae separation Reuse of wastewater Question: Which technology is “sustainable?” Why? Drinking water treatment Conventional scheme of water cycle Production of drinking water To protect the quality of the environment reject Assume a safe water Effluents WW treatment plant Adequate sanitation Sludges Open system-closed system Conventional treatment process of drinking water Coagulant Cl2 Disinfection Source Water Coagulation Sedimentation Filtration Clean water Distribution Customer Pump 5 Source: US EPA Coagulation Physical-chemical process involved in Coagulation-Flocculation Coagulation-flocculation: The use of chemical reagents to destabilise and increase the size of the particles; mixing; increasing of flocs size. Source: SNF FLOERGER (2003) Coagulation destabilises the particles’ charges. Coagulants with charges opposite to those of the suspended solids are added to the water to neutralise the negative charges on dispersed non-settable solids such as clay and organic substances. Once the charge is neutralised, the small-suspended particles are capable of sticking together. flocculation Following coagulation, flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles. Coagulation Coagulation agitator Jar tester, Nairobi, 1938 Coagulation Poly Aluminum Chloride for Drinking Water Liquid Index Solid Al2O3 Content %≥ High-class product 10.0 First-class product 10.0 Basicity % 40-85 Density (20%)/(g/cm3) ≥ High-class product First-class product 30.0 28.0 40-80 40-90 40-90 1.15 1.15 - - Non-dissolved Substances /%≤ 0.1 0.3 0.3 1.0 pH(1% aqueous suspension) 3.5-5.0 3.5-5.0 3.5-5.0 3.5-5.0 0.0001 0.0002 Pb /%≤ 0.0005 0.001 Cd /%≤ 0.0001 0.0002 Hg /%≤ 0.00001 0.00001 Cr6+ /%≤ 0.0005 0.0005 As /%≤ Ore: calcium aluminate Drinking water treatment in Ethiopia • Jar test • Raw water turbidity: >500 NTU • Treated water turbidity:1-2 NTU Drinking water treatment in Kenya WTP NG’ETHU SASUMUA KABETE PAC-SDD 97.7% 81.9% 91.8% PAC-CFII 98% 84% 92% ALUM 89.8% 75% 89% Questions: Do you think COAGULATION is a “sustainable?” technology? What do you think of the advantages and disadvantages of COAGULATION? Chemical consumption: coagulant Energy consumption: agitator Residual coagulant dissolved in water: Al Safety issue: heavy metals Sedimentation/Settling Sludge What is the problem of sedimentation/settling? Pollutants separated from water to sludge(not degraded); Sludge is a problem. Residual coagulant in sludge (Al, Fe, PAM); Filtration Rapid Sand Filter (Conventional US Treatment) Size (mm) Anthracite Influent Sand Gravel Drain Effluent Specific Depth Gravity (cm) 0.70 1.6 30 0.45 - 0.55 2.65 45 5 - 60 2.65 45 Wash water Filtration Backwash • Wash water is treated water! Anthracite Influent Pollution? Sand Gravel Drain Effluent Wash water Disinfection Chlorine Disinfection (Cl2): one of the most commonly used disinfectants for water disinfection. can be applied for the deactivation of most microorganisms and it is relatively cheap. Advantages: efficient oxidant and disinfectant effectively eliminates unpleasant taste and odors featured with aftereffect (Free chlorine residual of 0.2-0.5 mg/L) prevents and controls growth of algae, biological slimes and microbes decomposes organic contaminants (phenols, etc.) oxidizes iron and magnesium decomposes hydrogen sulfide, cyanides, ammonium and other nitrogen compounds. Disadvantages: strict requirements for transportation and storage ; potential risk to health in case of leakage; formation of disinfection by-products, such as trihalomethanes. Disinfection Sodium hypochlorite (NaClO): Advantages: effective against most of pathogenic microorganisms relatively safe during storage and use when produced on site does not require transportation and storage of hazardous chemicals Disadvantages: looses its activity during long-term storage ineffective against cysts (Giardia, Cryptosporidium) produces disinfection by-products, such as trihalomethanes generated on-site requires immediate use Other disinfectants: Chlorine dioxide; Chloramine; Ozone; Ultraviolet Solar Disinfection(SODIS) Heating water to 65°C (149°F) in a solar cooker will pasteurize the water and kill disease causing microbes. What is the problem of disinfection? Disinfection Byproducts(DBPs) Cl2+natural organic matter——trihalomethanes（THMs, carcinogenic） Advanced treatment process of drinking water Coagulant O3 Source Water Coagulation Sedimentation Oxidation Filtration Chlorine Activated carbon Clean water Pump Customer Ozone biological activated carbon technology 24 Oxidation Oxidation and Reduction • Oxidation- complete or partial loss of electrons or the gain of oxygen. • Reduction- complete or partial gain of electrons or loss of oxygen 25 Oxidation Oxidizing Strength of ·OH Oxidizing agent Half reactions Standard-State Potentials, Eo MnO2 MnO2(s)+4H++2e- =Mn2++2H2O2 1.23 Cl2 Cl(g)+2e-=2Cl- 1.36 ClO2 ClO2+2e-= Cl-+ O2 1.50 H2O2 H2O2+ 2H++2e-=2 H2O 1.77 O3 O3+2H++2e-= H2O+ O2 2.07 ·OH ·OH+ H++2 e-= H2O 2.80 F2 F2(g)+ 2H++2e-=2HF 3.06 ·OH oxidizing properties are comparable to Fluorine (F2) the most electronegative element in the periodic table Reduction hydroxyl radical 26 Oxidation • Taihu Lake algae crisis(2007): Oxidant: potassium permanganate (KMnO4) What is the problem of KMnO4 addition? Erosion to the pipelines (Fe) Hazardous to human health Adsorption Adsorption Increasing magnification Adsorbent: activated carbon Applications in water treatment usually involve adding AC as a media to the filtration unit. In some cases a contactor is added just before the final chlorination step. Breakthrough of Adsorbent Effluent Concentration Adsorption (Fixed Bed Absorber). C CoE Breakthrough Curve Exhaustion point Breakpoint CB Volume of Effluent VB VE What is the problem of Adsorption? expensive regeneration Pollutants transferred, not degraded Wastewater treatment wastewater treatment in Shanghai Wastewater treatment ratio in Shanghai Wastewater treatment plants in Shanghai How to Choose the Process Wastewater treatment process in China 一级处理 Primary treatment Bar Screen 二级处理 三级处理 Secondary treatment Tertiary treatment Conventional activated sludge Grit chamber Disinfection Coagulation BNR Primary sedimentation Enhanced primary sedimentation Biological phosphorus removal Biological nitrogen &phosphorus removal Biofilm BNR: Biological Nutrient Removal MBR: Membrane Bioreactor RO: Reverse Osmosis Filtration MBR RO Ecological treatment Discharge or Reuse How to Choose the Process General concept and process of wastewater treatment plant Exhaust Smell treatment Wastewater Bar screen Primary treatment Secondary treatment Disposal Sludge treatment Advanced treatment Drainage/ reuse Case study: Shidongkou WWTP,Shanghai,China COD BOD5 SS NH3-N TP Influent (mg/L) 400 200 250 30 4.5 Effluent (mg/L) 60 20 20 8(15) 1.5 项 目 Treatment technologies of Shidongkou WWTP,Shanghai 鼓风机房 Coarse Lift Fine Screen Pump Screen 粗 格 栅 进 水 泵 房 细 格 栅 进水 Influent Grit Flow Chamber meter 沉 砂 池 计 量 槽 Aeration station Chlorination Disinfection Unitank 一反 体应 化池 加 氯 消 毒 出 水 泵 房 排放 Effluent 主体工艺 Grid Residue 栅渣压干机 Presser 栅渣外运 Landfill 栅渣 栅渣 栅渣压干机 Presser 砂 Sand 砂水分离器 Separator 剩余污泥 Surplus sludge 剩余污泥泵 Sludge Pump 至剩余污泥处理段 To Sludge treatment Case study: Shidongkou WWTP,Shanghai,China Reclaimed water Effluent discharge Effluent: Discharged to Yangtze River; Reclaimed and reused for road flushing, firefighting, irrigation Sludge treatment Sludge dewatering Incineration Thickening; Dewatering; incineration; Landfill What is your opinion on the technologies adopted in Shidongkou Wastewater Treatment Plant? Efficient to remove pollutants from water Energy consumption Air pollution (incineration) Landfill leachate pollution Wetland wastewater treatment system in Nanhui District, Shanghai Benefits of Treatment Wetlands Constructed and natural treatment wetlands provide several major benefits compared to more conventional treatment alternatives: • less expensive to construct than traditional secondary and tertiary wastewater treatment systems. • less maintenance and are less expensive to operate than traditional treatment systems. • may provide important wetland wildlife habitat, as well as human recreational opportunities such as birdwatching, hiking, and picnicking. • Treatment wetlands are viewed as an asset by regulatory agencies in many regions and as a potentially effective method for replacing natural wetlands lost through agricultural practices, industrial and municipal development, and groundwater withdrawal. Case study: Separation of Algae from Tai Lake Tai Lake Shanghai Tai Lake to Shanghai: 130 km Shanghai is located in the downstream of Yangtze River Huangpu River and entrance of Yangtze River provide raw water for Shanghai. Tai Lake is in the upstream of Huangpu River Introduction of Tai Lake China's famous scenic spot Algae bloom in Tai Lake Blue-green algae is seen on the surface of Tai Lake Blooming algae fills large areas of the Tai Lake Tai Lake turns green after an algae bloom Ducks swim in the algae-rich Tai Lake Algae Separation from Tai Lake • Algae collection • Algae separation Algae Separation from Tai Lake 2,000 m3/d Designed by Tongji University Solid content: 0.5-1% Algae Separation from Tai Lake Coagulant:150 ppm A:algae slurry B:+absorbent modified with chitosan C:+poly aluminum chloride (PACl) D:+poly ferric sulfate E: +alum A B C D E A1:algae slurry B1:+absorbent modified with chitosan C1: +poly aluminum chloride (PACl) D1: +alum A1 B1 C1 D1 Algae Separation from Tai Lake (a)SEM of modified fly ash coagulant(10 um) (b)SEM of modified fly ash coagulant(2 um) (c) SEM of the algae cell after treatment(5 um) (d) SEM of the algae cell after treatment(2 um) Energy producing and carbon sequestration Energy producing and carbon sequestration Table 1. Elementary analysis table of algae sludge element C content（%） 37.63 H N S P 3.453 3.050 0.94 0.57 1ton algae(dry)=600 m3 methane +100 kg N +10 kg P Carbon sequestration=0.85~3.39 ton carbon/d Energy producing and carbon sequestration Algae Separation from Tai Lake Algae bloom is a serious problem in Tai Lake Algae can be separated from water by coagulation/adsorption and dewatering Algae can produce energy and fertilizer Significant for carbon sequestration Reuse of Wastewater: Desalination Example: wastewater reuse in Tongji University Source: Prof. XIA Siqing Wastewater reuse-Desalination in Libya Wastewater reuse-Desalination in Libya Sirte City Project profile Tertiary treatment Grit and insoluble material removal Biological treatment Sedimentation tank Chemical treatment filtration ((activated sludge)) Sample 2 Sand filter Sample 1 Return sludge To sea Sample 3 Sludge to dryers Chlorine injection Sludge digestion Wastewater reuse-Desalination in Libya Sirte Wastewater Treatment Pant: •Constructed in 2001 •Capacity: 30000m3/d •Treatment Process: activated sludge Existing Problem: TDS (Total Dissolved Solid) is too high! Acceptable TDS for irrigation: 600~1000 mg/L Current TDS in S WWTP: 2500 mg/L Desalination is needed! Reuse of Waste Water for Forest Plantation Irrigation project in Libya Sampling in Sirte City, Libya Preliminary scheme of tertiary treatment and reuse of wastewater in Sirte City, Libya Libya-Desalination What is your opinion on the wastewater reuse? Save water Cost-effective? Too expensive! Reliability (power system; infrastructure; solar power?) thanks for your attention