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POLLUTANTS IN WASTEWATER

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POLLUTANTS IN WASTEWATER

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  1. POLLUTANTS IN WASTEWATER Microorganisms (pathogens) Nutrients Metals Other inorganic substances Radioactive substances Biologically degradable organic substances Other organic substances Odor and taste matters Heat

  2. CHARACTERISATION OF POLLUTANTS • Chemical characterisation • Individual components: • Sewage – impossible • Industrial wastewaters – sometimes there is a possibility • Municipal wastewater - impossible

  3. CHARACTERISATION OF POLLUTANTS • Group characterisation • Carbon • Chemical Oxygen Demand (CODMn, CODCr) • Biochemical Oxygen Demand (BOD5, BOD7, BOD20) • Total Organic Carbon (TOC) • Dissolved Organic Carbon (DOC) • Volatile Organic Carbon (VOC) • Nitrogen • Phosphorus • Suspended solids • Extractable matters • Detergents

  4. MEASURE OF ORGANIC SUBSTANCES CHEMICAL OXYGEN DEMAND Quantity of the pollutants in water that can be oxidised by a chemical oxidant Consumption of oxidant (potassium dichromate - CODCr or potassium permanganate - CODMn) gives the content of organic substances CODCr = 250 – 900 mg O2/l in raw wastewater

  5. MEASURE OF ORGANIC SUBSTANCES BIOCHEMICAL OXYGEN DEMAND Measure of the content of biologically degradable substances Quantity of oxygen consumed by microorganisms over a period of 5 days (BOD5) or 7 days (BOD7) in decomposing the organic pollutants (carbon) BOD5 = 120 – 400 mg/l in raw wastewater BOD7 = 1.15  BOD5 BOD20: including decomposition of organic nitrogen as well

  6. BIOCHEMICAL OXYGEN DEMAND NBOD = BOD20 BOD [mg/l] CBOD = BOD5, BOD7 time

  7. MEASURE OF ORGANIC SUBSTANCES TOTAL ORGANIC CARBON (TOC) Quantity of carbon dioxide produced from oxidation (combustion, ultra violet radiation, chemical oxidants) of a sample CO2 is measured by infrared analyser for example DISSOLVED ORGANIC CARBON (DOC) Sample filtered through 0.45 m pore size membrane filter (colloidal matter is included as well) VOLATILE ORGANIC CARBON (VOC) Organic compounds with boiling point  100 °C

  8. MEASURE OF ORGANIC SUBSTANCES THEORETICAL ORGANIC CARBON : ThOC = 100% can be calculated if we now the chemical formula of the organic matter TOC - 95% DOC - 70% CODCr - 80% CODMn - 45% BOD7 - 60% BOD5 - 50%

  9. ORGANIC POLLUTANTS

  10. INORGANIC SUBSTANCES DISSOLVED SALTS MAINLY DETERMINED BY THE IONIC COMPOSITION AND SALT CONCENTRATION OF WATER NORMALLY UNIMPORTANT WHAT IS IMPORTANT? • NITROGEN • PHOSPHORUS • HEAVY METALS

  11. 30 mg/l • 50 mg/l • 0.1 mg/l • 0.5 mg/l • mg/l • 20-700 mg/l NITROGEN ORGANICALLY BOUND INORGANIC AMMONIUM (NH4-N) NITRATE (NO3-N) NITRITE (NO2-N) TOTAL KJELDAHL NITROGEN (TKN) NON-OXIDISED FORMS (NH4-N + orgN) TOTAL NITROGEN (TN) No exact values!!!

  12. NITROGEN NITRIFICATION NH4+ + 1,5 O2 NO2- + H2O + 2H+ + energy Nitrosomonas NO2-+ 0,5 O2 NO3- + energy Nitrobacter necessary: ammonium-N aerobic condition (DO) bacteria – pH, T, toxic matters, operation

  13. NITROGEN DENITRIFICATION 2 NO3-+ org C + 2H+  CO2 + H2O + N2+ energy NO3-  NO2-  NO  N2O  N2 necessary: organic carbon (easily degradable) anoxic condition (DO=0, NO3-, NO2-) bacteria – pH, T, toxic matters, operation

  14. PHOSPHORUS MAIN SOURCE DETERGENTS (50%) HUMAN EXCRETA (50%) ORGANICALLY BOUND SOLID INORGANIC POLYPHOSPHATES ORTHOPHOSPHATES (PO43-) DISSOLVED TP

  15. PHOSPHORUS ORGANICALLY BOUND 0 - 4 mg/L POLYPHOSPHATES 0 - 5 mg/L ORTHOPHOSPHATES (PO43-) 4 - 14 mg/L TOTAL PHOSPHORUS 8 - 14 mg/L

  16. OTHER POLLUTION PARAMETERS TOTAL SOLIDS (TS) SUM OF PARTICULAR AND DISSOLVED MATTERS (residue remaining after a wastewater sample has been evaporated and dried at 105 ºC) TOTAL VOLATILE SOLIDS (TVS) Solids that can be volatilised and burned off when TS are ignited (550 ºC)

  17. OTHER POLLUTION PARAMETERS TOTAL SUSPENDED SOLIDS (TSS) Portion of the TS reatined on a filter (0.45 ; 1.58 m), measured after drying at 105 ºC) SETTLEABLE SOLIDS suspended solids, expressed in mL/L, that will settle out of suspension within 30 min (1 h) Imhoff cone (1 L) 60% of TSS is settleable

  18. OTHER POLLUTION PARAMETERS EXTRACTABLE MATTERS (fats and oils) DETERGENTS (surface active matters) METALS (dissolved or particulate, heavy metals) Fe, Hg, Ni, Cd, Zn, Cu, Cr, Pb, Mn, As pH

  19. pH OF WATER Dissociation of water = self ionisation 2H2O = H3O+ + OH- [H3O +][OH-] = Kw = 10-14 (constant at constant temperature) pH = parameter describing acidity or basicity pH = - log [H+] range: 0 - 14 natural waters: pH = 6.5-9 importance: natural processes take place in a certain interval of pH how can we influence pH addition of acid/base addition of salts NH4+ + H2O = NH3 + H3O+

  20. OTHER PARAMETERS MEASURED AT A WWTP anions: Cl-, SO3-, HCO3-, CO32-, F- cations: K+, Na+, Ca2+, Mg2+, Fe2+, Fe3+, Mn2+ organic micropollutants phenols (C6H5OH) chlorinated hydrocarbons detergents pesticides, herbicides, fungicides, etc

  21. OTHER PARAMETERS MEASURED AT WWTP ALKALINITY (amount of hydrocarbons) amount of matters in water that can be titrated with acids caused by hydro-carbons (mainly Ca- and Mg-hydro-carbons) analysis with titration SALT CONTENT (electric conductivity) DRY MATTER CONTENT (dried at 105 ºC) TEMPERATURE WASTEWATER VOLUME INGINITION LOSS (TVS) TECHNOLOGICAL PARAMETERS Recirculation rate, sludge concentration, sludge age, etc.

  22. BIOLOGICAL PARAMETERS viruses bacteria (Total Coliform, Faecal Coliform, Streptococcus, Salmonella) Most often indicator parameters

  23. ESTIMATING POLLUTANT LOAD AND CONCENTRATION BOD5: 60 g/d/person COD: 120 g/d/person TSS: 70 g/d/person TN: 11 g/d/person TP: 2.5 g/d/person drinking water consumption: qd = 60-200 l/d/person 

  24. ESTIMATING POLLUTANT CONCENTRATION BOD5: 60 g/d/person TN: 11 g/d/person TP: 2.5 g/d/person calculating with 200 l/d/person: BOD5 concentration: 60/200 = 0.03 g/L = 300 mg/L TN concentration: 11/200 = 0.055 g/L = 55 mg/L TP concentration: 2.5/200 = 0.0125 g/L = 12.5 mg/L

  25. POPULATION EQUIVALENT converting industrial pollutant load - expressing it as a municipal load The population equivalent is a unit of measurement of organic biodegradable pollution representing the average load of that pollution produced by one person in one day; in the EU Directive it is fixed at 60 grams of B0D5 per day. e.g. industry producing ww of 1000 pe means 60000 g/d BOD5 load

  26. MAXIMUM ADMISSIBLE CONCENTRATIONS (MAC) REGIONAL STANDARDS COUNTRY STANDARDS

  27. COUNCIL DIRECTIVEof 21 May 1991concerning urban waste water treatment (91/271/EEC) This Directive concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors. Member States shall ensure that urban waste water entering collecting systems shall before discharge be subject to secondary treatment or an equivalent treatment

  28. Parameters Concentration Minimum percentage of reduction Reference method of measurement Biochemical oxygen demand (BOD5 at 20 °C) without nitrification 25 mg/L O2 70-90 40 under Article 4 Homogenized, unfiltered, undecanted sample. Determination of dissolved oxygen before and after five-day incubation at 20 °C ± 1 °C, in complete darkness. Addition of a nitrification inhibitor Chemical oxygen demand (COD) 125 mg/L O2 75 Homogenized, unfiltered, undecanted sample Potassium dichromate Total suspended solids • 35 mg/L • 35 under • Article 4 >10 000 pe) • 60 under • Article 4 • (2 000-10 000 pe) 90* 90 under Article 4 (> 10 000 pe) 70 under Article 4 (2 000-10 000 pe) ·Filtering of a representative sample through a 0,45 m filter membrane. Drying at 105 °C and weighing ·Centrifuging of a representative sample (for at least five min with mean acceleration of 2 800 to 3 200 g), drying at 105 °C and weighing

  29. Requirements for discharges from urban waste water treatment plants to sensitive areas which are subject to eutrophication. One or both parameters may be applied depending on the local situation. The values for concentration or for the percentage of reduction shall apply. Parameters Concentration Minimum percentage of reduction Reference method of measurement Total phos-phorus 2 mg/L P (10 000 - 100 000 pe) 1 mg/LP (> 100 000 p e) 80 Molecular absorption spectrophotometry Total nitrogen 15 mg/L N (10 000 - 100 000 pe) 10 mg/L N (> 100 000 p e)* 70-80 Molecular absorption spectrophotometry * Alternatively, the daily average must not exceed 20 mg/l N. This requirement refers to a water temperature of 12° C or more during the operation of the biological reactor of the waste water treatment plant. As a substitute for the condition concerning the temperature, it is possible to apply a limited time of operation, which takes into account the regional climatic conditions.

  30. CONVENTIONAL TREATMENT OF SEWAGE PHYSICAL (MECHANICAL) SEPARATION OF SETTLEABLE and FLOATING SOLIDS BIOLOGICAL SEPARATION OF SUSPENDED OR DISSOLVED SOLIDS WITH THE USE OF MICROORGANISMS CHEMICAL PRECIPITATION, COAGULATION, FLOCCULATION

  31. MECHANICAL TREATMENT SEPARATION OF COARSE MATERIALS SCREENING - floating debrish, leaves, nylon sacks, etc. GRIT (SAND) TRAP - sand (inorganic, inert substances) SETTLING OF OTHER SUBSTANCES SEDIMENTATION TANK - organics (COD, BOD, TP, TN) (OR FLOTATION)

  32. in a frame SCREENING BAR SCREENS aim: defending the subsequent instruments retain floating debrish (wood, rags, etc.) long, narrow metal bars 25 mm (1 in.) apart vertical or tilted cleaned automatically (75-80°) or by hands (60°, 1-2 times a day with rake)

  33. BAR SCREENS increased clogging during winter time (ice) debrish has to be collected massive, oversized structures if mechanical unitsdefense against overload shearing element greater treatment plant  at least 2 parallel screens

  34. BAR SCREENS COARSE SCREENS 50-100 mm free gap  20-30 mm FINE SCREENS 10-50 mm free gap  1.5-15 mm BOD removal  5%

  35. DESIGN OF SCREENS h=   vf2 / 2g HYDRAULIC HEAD LOSS (damming) depends on : size of free gap velocity slope of screen shape of screen • ALLOWED MAXIMUM DAMMING • hmax = 5 – 15 cm

  36. COMMUNITOR MECHANICAL CUTTING DEVICE SLOTTED CYLINDRICAL SCREEN WITH MOVING CUTTER BLADE CHOPS SOLIDS THAT PASSED THROUGH THE BAR SCREEN SHREDDED MATERIAL IS REMOVED BY SEDIMENTATION OR FLOATING

  37. SEDIMENTATION DISCRETE PARTICLES (do not tend to flocculate) HEAVIER PARTICLES FALL TO THE BOTTOM v < vcr  SETTLING CRITICAL VELOCITY – KEEPS THE PARTICLE SUSPENDED

  38. F S = f () G SEDIMENTATION Stokes’ law  - settling velocity  - absolute viscosity of the fluid  - mass density of fluid s - mass density of particle g - gravitational constant d – diameter of the particle

  39. SEDIMENTATION v1 > vs particles retain in a ratio of v1/vs v1 < vs particles settle

  40. GRIT TRAP / SAND TRAP SAND CAUSES WEAR-AND-TEAR ON PUMPS  HAVE TO BE REMOVED HEAVIER PARTICLES FALL TO THE BOTTOM v < 0.3 m/s (1 ft/s)  SETTLING OFTEN COMBINED WITH SOME FORM OF AERATION TO MAINTAIN DO + SEPARATION OF GREASE

  41. SAND TRAP HORIZONTAL FLOW good efficiency difficult to place VERTICAL FLOW AERATED TANGENTIAL high flow, uneven load DO oil skimming like horizontal flow, but inflow from the side

  42. SAND TRAP DESIGNING MIN 2 BASINS PARALLEL (dry flow and higher flow) PEAK FLOW RESIDENCE TIME (10 min) HYDRAULIC SPECIFIC LOAD (30 m3/h/m2) SLUDGE RAMOVAL: MECHANICAL GRAVITATIONAL

  43. SEDIMENTATION BASIN PRETREATMENT (no dissolved substances removed) AIM: removal of suspended solids smaller than sand REMOVES 25-35% OF THE ORGANIC MATTER SPECIFIC LOADING : 1-3 m3/h/m2

  44. SEDIMENTATION BASIN

  45. SEDIMENTATION BASIN Q = 150 – 2000 m3/d h/l = 1/15 – 1/20 h = 1.5 – 3.0 m w= 4 – 8 m

  46. D = 30 –40 m h = 2-4 m SEDIMENTATION BASIN

  47. SECONDARY (BIOLOGICAL) TREATMENT WITH THE USE OF MICROORGANISMS ORGANIC MATTER microorganisms oxidise the organic matter while producing new cell material, CO2 and H2O NITROGEN ammonification, nitrification, denitrification PHPSPHORUS Biological P-removal

  48. CONVERSIONS IN BIOLOGICAL WWTREATMENT biological growth hydrolysis decay Slowly degradable material hydrolysis Easily degradable material biological growth Biomass decay Inert material 

  49. TYPE OF REACTORS • activated sludge reactors • microorganisms are suspended in water (mobilised) • different conditions at different places • biofilm reactors • microorganisms are hold on a fixed surface • different conditions are at the same place but at other time

  50. BIOLOGICAL PARAMETERS Activated sludge processes Aeration basin systems Oxidation ditch Aerated sewage lagoons Biofilm processes Trickling filters Rotating biological contactors (biological rotors) Thin biofilm systems 