Wastewater treatment objecives Removal of suspended and floatable materials Degradation of biodegradable organics Removal of nutrients Elimination of priority pollutants Elimination of pathogenic organisms Untreated wastewater Contaminants Units Concentration Solids, total mg L -1 350-1200 BOD 5 mg L -1 110-400 COD mg L -1 250-1000 Nitrogen mg L -1 20-85 Phosphorous mg L -1 4-15 Total coliforms N o L -1 10 7-10 10 Treated wastewater Contaminants Units Concentration Solids, total mg L -1 30 BOD 5 mg L -1 30 COD mg L -1 60 Nitrogen mg L -1 5 Phosphorous mg L -1 2 Total coliforms N o L -1 10 3 1
Unit operations and processes for ww treatment Suspended solids Screening Sedimentation Filtration Flotation Coagulation Biodegradable organics Activated sludge Trickling filters Nitrogen Biological nitrogen removal Ammonia stripping Phosporous Chemical precipitation Lime coagulation Biological phosphorous removal Volatile organic compounds Air stripping Carbon adsorption Refractory organics Carbon adsorption Advanced oxidation Heavy metals Chemical precipitation Ion exchange Dissolved inorganic compounds Ion exchange Reverse osmosis Pathogens Chlorination Ozonation UV radiation 2
Methods of wastewater treatment - 1 Preliminary wastewater treatment: removal of those constituents that may cause maintenance or operational problems with the treatment operations, processes and ancillary systems. Screening and comminution for the removal of debris Grit removal for the elimination of coarse suspended solids Floatation for the removal of oil and grease Primary wastewater treatment: removal of a portion of the suspended solids and organic matter. Primary sedimentation Secondary wastewater treatment: removal of biodegradable organics and suspended solids. Activated sludge Trickling filters Lagoons 3
Methods of wastewater treatment - 2 Nutrient removal: Removal of nitrogen and posphorous, required for i) discharge to confined bodies where cultural eutrophication may occur; ii)discharge to flowing streams where nitrification can tax oxygen resources. Biological processes (coupled with secondary treatment) Chemical processes Combination of biological and chemical processes. Advanced wastewater treatment: the level of treatment required beyond conventional secondary treatment and nutrient removal to remove: i) increased amounts of organic material, suspended solids and nutrients (for water reuse) ii)constituents of concern, including toxic compounds Chemical coagulation, flocculation and sedimentation Filtration Activated carbon Ion exchange Reverse osmosis 4
Methods of wastewater treatment - 3 Sludge processing: unit operations and processes or systems used to process the sludge removed from the liquid portion of the wastewater (partcularly in primary and secondary treatment). Thickening (concentration): a procedure used to increase the solids content of sludge by removing a portion of liquid. Gravity thickening Floatation thickening Centrifugation thickening Stabilisation: sludges are stabilised to: i) reduce pathogens; ii) eliminate offensive odors; iii) Reduce or eliminate potentials for putrefaction. Biological reduction of the volatile matter Chemical oxidation of the volatile matter Chemical inhibition of microbial growth Thermal disisnfection Conditioning: to increase the sludge dewatering characteristics. Chemical Thermal Dewatering: mechanical unit operation used to reduce the moisture content of sludge. Press filtration centrifugation 5
Process flow diagram influent bar screen grit chamber primary clarifier aeration tank secondary clarifier contact tank effluent chlorine debris grit O 2 return sludge supernatant return dewatered sludge digested sludge belt press anaerobic digester gravity thickener 6
Wastewater treatment plant Università di Pisa 7
Screens 8
Grit chambers 9
Dissolved air floatation system 10
Primary clarifiers - 1 11
Primary clarifiers - 2 Università di Pisa 12
Primary clarifier with flocculator 13
Aeration tanks 14
Air diffusers Fine bubble diffuser Jet aerator Surface turbine aerator 15
Secondary clarifiers 16
Chlorine contact tanks 17
Sludge thickener -1 Gravity sludge thickener 18
Sludge thickener - 2 Centrifugal sludge thickener 19
Sludge digestor - 1 Microbiological pathways of anaerobic digestion 20
Sludge digestor - 2 Low-rate anaerobic disgestor 21
Sludge digestor - 3 Low-rate anaerobic disgestor 22
Belt filter 23
Adsorption on activated carbon 24
Trickling filters 25
Membrane bioreactors 26
Particulate biofilm reactors 27