1 pollutants in wastewater microorganisms (pathogens) nutrients metals other inorganic substances...
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POLLUTANTS IN WASTEWATERPOLLUTANTS IN WASTEWATER
•Microorganisms (pathogens)•Nutrients •Metals •Other inorganic substances•Radioactive substances•Biologically degradable organic substances•Other organic substances•Odor and taste matters•Heat
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• Chemical characterisation
Individual components:
Sewage – impossible
Industrial wastewaters – sometimes there is a possibility
Municipal wastewater - impossible
CHARACTERISATION OF POLLUTANTSCHARACTERISATION OF POLLUTANTS
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• 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
CHARACTERISATION OF POLLUTANTSCHARACTERISATION OF POLLUTANTS
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MEASURE OF ORGANIC SUBSTANCESMEASURE 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
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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
MEASURE OF ORGANIC SUBSTANCESMEASURE OF ORGANIC SUBSTANCES
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time
BO
D [
mg/
l]
BIOCHEMICAL OXYGEN DEMANDBIOCHEMICAL OXYGEN DEMAND
CBOD = BOD5, BOD7
NBOD = BOD20
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MEASURE OF ORGANIC SUBSTANCESMEASURE 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
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MEASURE OF ORGANIC SUBSTANCESMEASURE 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%
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ORGANIC POLLUTANTS
SUBSTANCE PROPORTION OF ORGANIC CARBON [%]
Carbohydrates 11 - 18
Proteins 8 - 10
Free amino acids 0.5 - 1.5
Higher fatty acids 23 - 25
Dissolved organic acids 7 - 9
Esteres fatty acids (fat) 9 - 12
Tensides 4 - 6
Other 25 -28
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INORGANIC SUBSTANCESINORGANIC SUBSTANCES
DISSOLVED SALTS MAINLY
DETERMINED BY THE IONIC COMPOSITION AND SALT CONCENTRATION OF WATER
NORMALLY UNIMPORTANT
WHAT IS IMPORTANT? NITROGEN
PHOSPHORUS
HEAVY METALS
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NITROGENNITROGEN
ORGANICALLY BOUND
INORGANICAMMONIUM (NH4-N)
NITRATE (NO3-N)
NITRITE (NO2-N)
TOTAL KJELDAHL NITROGEN (TKN)
NON-OXIDISED FORMS (NH4-N + orgN)
TOTAL NITROGEN (TN)
30 mg/l
50 mg/l
0.1 mg/l
0.5 mg/l
80 mg/l
20-700 mg/l
No exact values!!!
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NITROGENNITROGEN
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
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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
NITROGENNITROGEN
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PHOSPHORUSPHOSPHORUS
MAIN SOURCEDETERGENTS (50%)
HUMAN EXCRETA (50%)
ORGANICALLY BOUNDSOLID
INORGANICPOLYPHOSPHATES
ORTHOPHOSPHATES (PO43-)
DISSOLVED
TP
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PHOSPHORUSPHOSPHORUS
• ORGANICALLY BOUND0 - 4 mg/L
• POLYPHOSPHATES0 - 5 mg/L
• ORTHOPHOSPHATES (PO43-)
4 - 14 mg/L
• TOTAL PHOSPHORUS
8 - 14 mg/L
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OTHER POLLUTION PARAMETERSOTHER 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)
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OTHER POLLUTION PARAMETERSOTHER 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 SOLIDSsuspended 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
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OTHER POLLUTION PARAMETERSOTHER 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
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pH OF WATERpH OF WATER
Dissociation of water = self ionisation2H2O = H3O+ + OH-
[H3O +][OH-] = Kw = 10-14 (constant at constant temperature)
pH = parameter describing acidity or basicity pH = - log [H+]range: 0 - 14natural waters: pH = 6.5-9importance: natural processes take place in a certain interval of pH
how can we influence pHaddition of acid/baseaddition of salts
NH4+ + H2O = NH3 + H3O+
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OTHER PARAMETERSOTHER PARAMETERS MEASURED MEASURED AT A WWTPAT 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
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OTHER PARAMETERSOTHER PARAMETERS MEASURED AT WWTP 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.
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BIOLOGICAL PARAMETERSBIOLOGICAL PARAMETERS
• viruses• bacteria (Total Coliform, Faecal Coliform,
Streptococcus, Salmonella)• Most often indicator parameters
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ESTIMATING POLLUTANT LOAD AND ESTIMATING POLLUTANT LOAD AND CONCENTRATIONCONCENTRATION
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
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ESTIMATING POLLUTANT CONCENTRATIONESTIMATING 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
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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
POPULATION EQUIVALENTPOPULATION EQUIVALENT
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REGIONAL STANDARDS
COUNTRY STANDARDS
MAXIMUM ADMISSIBLE MAXIMUM ADMISSIBLE CONCENTRATIONS (MAC)CONCENTRATIONS (MAC)
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COUNCIL DIRECTIVECOUNCIL DIRECTIVEof 21 May 1991of 21 May 1991
concerning urban waste water treatment concerning urban waste water treatment (91/271/EEC)(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
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Parameters ConcentrationMinimum
percentage of reduction
Reference method of measurement
Biochemical oxygen demand (BOD5 at 20
°C) without nitrification
25 mg/L O2 70-90 40 underArticle 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 underArticle 4 >10 000 pe)
60 underArticle 4 (2 000-10 000 pe)
90* 90 underArticle 4 (> 10 000 pe) 70 underArticle 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
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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
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.
* 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.
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CONVENTIONAL TREATMENT OF SEWAGECONVENTIONAL TREATMENT OF SEWAGE
• PHYSICAL (MECHANICAL)SEPARATION OF SETTLEABLE and FLOATING SOLIDS
• BIOLOGICALSEPARATION OF SUSPENDED OR DISSOLVED SOLIDS WITH THE USE OF MICROORGANISMS
• CHEMICALPRECIPITATION, COAGULATION, FLOCCULATION
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MECHANICAL TREATMENTMECHANICAL TREATMENT
1. SEPARATION OF COARSE MATERIALS
SCREENING - floating debrish, leaves, nylon sacks, etc.
GRIT (SAND) TRAP - sand (inorganic, inert substances)
2. SETTLING OF OTHER SUBSTANCES
SEDIMENTATION TANK - organics (COD, BOD, TP, TN)
(OR FLOTATION)
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SCREENINGSCREENING
BAR SCREENS
aim: defending the subsequent instruments
retain floating debrish (wood, rags, etc.)
long, narrow metal bars 25 mm (1 in.) apart
in a frame
vertical or tilted
cleaned automatically (75-80°)
or by hands (60°, 1-2 times a day with rake)
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BAR SCREENSBAR 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
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BAR SCREENSBAR 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%
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DESIGN OF SCREENSDESIGN OF SCREENS
HYDRAULIC HEAD LOSS (damming)
depends on :
size of free gap
velocity
slope of screen
shape of screen
ALLOWED MAXIMUM DAMMING
hmax = 5 – 15 cm
h = vf2 / 2g
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COMMUNITORCOMMUNITOR
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
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SEDIMENTATIONSEDIMENTATION
DISCRETE PARTICLES (do not tend to flocculate)
HEAVIER PARTICLES FALL TO THE BOTTOM
v < vcr SETTLING
CRITICAL VELOCITY – KEEPS THE PARTICLE SUSPENDED
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SEDIMENTATIONSEDIMENTATION
G
F
S = f ()
Stokes’ law
ρ)(ρ18μ
gdω s
2
- settling velocity
- absolute viscosity of the fluid
- mass density of fluid
s - mass density of particle
g - gravitational constant
d – diameter of the particle
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GRIT TRAP / SAND TRAPGRIT 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
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SAND TRAPSAND TRAP
VERTICAL FLOW
AERATED
HORIZONTAL FLOW
TANGENTIAL
good efficiency difficult to place
high flow, uneven load DO oil skimming
like horizontal flow, but inflow from the side
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SAND TRAPSAND 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
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SEDIMENTATION BASINSEDIMENTATION 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
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SEDIMENTATION BASINSEDIMENTATION BASIN
Q = 150 – 2000 m3/d h/l = 1/15 – 1/20
h = 1.5 – 3.0 m w= 4 – 8 m
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SECONDARY (BIOLOGICAL)SECONDARY (BIOLOGICAL) TREATMENT TREATMENT
WITH THE USE OF MICROORGANISMS
ORGANIC MATTERmicroorganisms oxidise the organic matter while producing new cell material, CO2 and H2O
NITROGENammonification, nitrification, denitrification
PHPSPHORUSBiological P-removal
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CONVERSIONS IN BIOLOGICAL CONVERSIONS IN BIOLOGICAL WWWWTREATMENTTREATMENT
biological growth
hydrolysis
decay
Slowly degradable material
Easily degradable material
Biomass
Inert material
hydrolysis
biological growth
decay
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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
TYPE OF TYPE OF REACTORSREACTORS
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BIOLOGICAL PARAMETERSBIOLOGICAL PARAMETERS
• Activated sludge processes– Aeration basin systems
– Oxidation ditch
– Aerated sewage lagoons
• Biofilm processes– Trickling filters
– Rotating biological contactors (biological rotors)
– Thin biofilm systems