Wastewater Treatment Processes (Sep 27 th and 28 th, 2016) by Dr. Arun Kumar (arunku@civil.iitd.ac.in) Objective: To learn about processes used in tertiary treatment Courtesy: Dr. Irene Xagoraraki, MSU, USA September 29, 2016 Arun Kumar (arunku@civil.iitd.ac.in) 1
Sludge Disposal Method depends on RCRA regulations Q 0, C 0 Land Spreading lawns, gardens agricultural land forest land golf courses and other public recreational areas Q w, X w Q 0,= flow rate C 0,= initial concentration X=biomass concentration Q w =sludge withdrawal rate X w = biomass concentration in secondary settling tank Municipal Solid Waste Landfill Utilization in other materials (Q 0 -Qw); C eff
Biological Treatment Microorganism Gravity Soluble and colloidal organics + = For further treatment September 29, 2016 arunku@civil.iitd.ac.in Arun Kumar 3 (arunku@civil.iitd.ac.in)
Municipal Wastewater Treatment Systems Preliminary treatment (removes materials that can cause operational problems, equalization basins are optional) Primary treatment (remove ~60% of solids and ~35% of BOD) Secondary treatment (remove ~85% of BOD and solids) Advanced treatment (varies: 95+ % of BOD and solids, N, P) Final Treatment (disinfection) Solids Processing (sludge management)
Secondary Wastewater Treatment High treatment efficiency BOD to ~ 20-50 mg/l SS to ~ 20 mg/l Some pollutants are not removed by the conventional secondary wastewater treatment Low treatment efficiency Nitrogen Phosphorus Heavy Metals Poorly-biodegradable organic chemicals Small particles Resistant organisms
1. Particles Problem: Particles Presence of small particles that are too small to be removed by settling. Attached to these particles can be organic chemicals and metals. Particles may eventually settle in river or stream (longer detention time). Particles can also be bacteria, protozoans, etc.
Methods for removing particles Methods: (1)Sedimentation with and without addition of coagulants (example: secondary sedimentation tank (SST)with addition of ferric chloride or alum), (2)sand filtration after SST to remove remaining particles from supernatant Solids are called secondary solids Solids are settled at the bottom of tank and thickened. Mixed liquor suspended solids =10000mg/L Q w =solid wastage rate per day September 29, 2016 7
Problem: Trace Organics Organic compounds, pesticides, endocrine disruptors, homores, pharmaceuticals 2. Organics
Methods for removing organics Ozonation: organic compounds are oxidized Chlorination: organic compounds are oxidized Adsorption: organic compounds are adsorbed on materials (i.e., adsorbent surface) September 29, 2016 9
2. Organics Carbon Adsorption Carbon is heated to about 1500 o C to activate surfaces High surface area of particles with vast pore spaces Capable of absorbing high quantity of organics Surface area > 1,000 m 2 /g Wastewater effluent is passed through filter under pressure Carbon becomes exhausted replace carbon in system regenerate carbon (on-site or off-site)
Problem: Phosphorus 3. Phosphorus increase in nutrients and organic substances, sediments overstimulation in growth of algae and aquatic plants create conditions that interfere with recreational uses of lakes, and the health and diversity of indigenous life eutrophication
Phosphorus Removal 3. Phosphorus Most phosphate in the form of (HPO 4 2- ) Usually removal accomplished with chemical precipitation (salts) Ferric chloride: FeCl 3 Alum: Al 2 (SO 4 ) 3 14H 2 O Lime: CaO or Ca(OH) 2
Phosphorus Removal: Chemical method 3. Phosphorus FeCl 3 + HPO 4 2- = FePO 4 (s) + HCl Al 2 (SO 4 ) 3 14H 2 O + 2 HPO 4 2- = 2AlPO 4 (s) + 2H + + 3SO 4 2- Effective range for alum or ferric chloride is ph 5.5 to 7.0 If insufficient alkalinity - must add lime to neutralize H + There is another option: Biological Phosphorus Removal
4. Nitrogen Nitrogen Excess nutrients: nitrogeneous BOD exerts oxygen demand Anaerobic conditions in stream
4. Nitrogen Solution: Nitrogen Removal (chemical) Ammonia stripping Raise ph to convert ammonium ions to ammonia NH 4+ + OH - = NH 3 + H 2 O Ammonia purged from water in process similar to aeration Tray-type Air Stripper Packed Column Air Stripper (From: http://www.mittelhauser.com/airstrip.html) (From: http://www.carbonair.com/os.htm)
4. Nitrogen Solution: Nitrogen Removal (biological) Forms: NH 3, NH 4+, NO 2-, NO 3 - Nitrification/ De-nitrification Occurs in activated sludge process - by increasing the detention time in activated sludge basin in separate reactor Nitrification: NH 4+ + 2O 2 = NO 3 - + H 2 O + 2H + (2 steps) De-nitrification: 2NO 3- + organic matter = N 2 + CO 2 + H 2 O
Wastewater Treatment Preliminary Treatment (screening) Primary Treatment (primary settling) Secondary Treatment (e.g. activated sludge) Advanced Treatment (e.g. P removal) Final Treatment (disinfection) Solids Processing (sludge treatment)
Final Treatment (disinfecting) 1. Final treatment focuses on removal of diseasecausing organisms from wastewater. Treated wastewater can be disinfected by adding chlorine or by using ultraviolet light. 2. High levels of chlorine may be harmful to aquatic life in receiving streams. Treatment systems often add a chlorine-neutralizing chemical to the treated wastewater before stream discharge.
Disinfectants: NaOCl Ca(OCl) 2 Cl 2 gas Chloramines Ozone UV irradiation Disinfection
Disinfection Water is often disinfected before it enters the distribution system to ensure that potentially dangerous microbes are killed. Chlorine, chloramines, or chlorine dioxide are most often used because they are very effective disinfectants, not only at the treatment plant but also in the pipes that distribute water to our homes and businesses. Ozone and ultraviolet radiation are effective disinfectants for relatively clean source waters, but neither of these are effective in controlling biological contaminants in the distribution pipes.
Courtesy: Dr. Irene Xagoraraki (MSU, USA) Disinfection (chlorination) Full-scale Bench-scale September 29, 2016 (C) Arun Kumar, IIT Delhi 21
UV Disinfection
Wastewater Treatment Preliminary Treatment (screening) Primary Treatment (primary settling) Secondary Treatment (e.g. activated sludge) Advanced Treatment (e.g. P removal) Final Treatment (disinfection) Solids Processing (sludge treatment)
Sludge Types Primary sludge 3 to 8% solids About 70% organic material Secondary sludge Consists of wasted microorganisms and inert materials About 90% organic material WAS: 0.5 to 2% solids Trickling filter sludge: 2-5% solids Tertiary sludge If secondary clarifier is used to remove phosphate, this sludge will also contain chemical precipitates (more difficult to treat) Denitrification sludges - similar to WAS sludge
Treatment processes include: Sludge Treatment Thickening separates water from solids by gravity or flotation Stabilization converts organic solids to more refractory forms through digestion Conditioning treats sludge with chemicals or heat so that the water can be readily separated Dewatering separates water by vacuum, pressure or drying Reduction decreases the volume of sludge by incineration
Big Picture September 29, 2016 26
BP_Ex 1_Exposures of nanoparticles from contaminated edible Plants C 0 Singh and Kumar (2013) BCF=bioconcentration Factor C soil = concentration in soil C human
See how contaminants from different products finally end up in compartments where human exposure is possible. See how much material is lost in different compartments and how much is transferred to next compartment For every compartment, write down names of parameters required for calculating fate of contaminants Determine relationship between C 0 ; C water; C soil ; C plant ; C human September 29, 2016 28
BP_Ex2_Fate of Nanoparticles in Environment Raw Animal Solid C Biosolids 0 Wastewater Manure Waste C 1 Wastewater Treatment Land Application Landfills Raw Drinking Water Removal and/or transformation Runoff, Infiltration, Sorption, Microbial activity, other transformations Runoff, Infiltration, Sorption, Microbial activity, other transformations Drinking Water Treatment Removal and/or transformation C 2 Natural waters ECs present in human urine and feces C 4 C 3 Potential human exposure via drinking water September 29, 2016 arunku@civil.iitd.ac.in 29
See how contaminants from different products finally end up in compartments where human exposure is possible. See how much material is lost in different compartments and how much is transferred to next compartment For every compartment, write down names of parameters required for calculating fate of contaminants Determine relationship between C 0 and C 4 September 29, 2016 30
BP_Ex4_Environmental Fate Water solubility 32-40 mg/l Weakly volatile Low sorption to soil INCINERATION DUST Physical Properties & Environmental Fate Occurrence & Exposure Assessment LOW WATER SOLUBILITY MOVES SLOWLY IN WATER September 29, 2016 LOW ADSORPTION HENCE MOVES FROM SOIL TO WATER Arun Kumar (arunku@civil.iitd.ac.in) Detection Methods Risk Assessment Regulation 31 Source: Layton D. et al., 1987 Treatment Methods
Write down different processes shown in this figure Describe fate of organic compounds in soil, plant, air and water Which processes are involved in soil; in water; in air What is the role of Sun in these processes September 29, 2016 32
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