Plutocalc Water and Wastewater

Plutocalc Water

Instant calculations for environmental professionals


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Unit conversions

Angle

Degrees
°
minutes
seconds
 
Decimal degrees
°
 
Radians
rad
π.rad

Area

Metric
mm²
cm²
km²
ha
 
US
in²
ft²
mi²

Conductivity and resistivity

Conductivity
µS/cm
mS/cm
S/cm
S/m (A/V/m)
µmho/cm
mmho/cm
mho/cm
mho/m
abmho/m
 
Resisitivity
MΩ.cm
Ω.m (V/A.m)
Ω.cm

Density and concentration

Metric
µg/L
mg/L
g/cm³
g/L
kg/m³
mg/mL
 
US
lb/in³
lb/ft³
lb/gal

Energy

Metric
J
Wh
kWh
cal
kcal
N.m
kgf.m
 
US
BTU (iso)
hp.h
lb/in
Eq. ton of Coal
Eq. ton of Oil

Flow - mass

Metric
kg/s
kg/min
kg/h
kg/day
g/min
 
US
lb/s
lb/min
lb/h
lb/day

Flow - volume

Metric
m³/s
m³/min
m³/h
m³/day
L/s
L/min
L/h
L/day
 
US
gal/s (gps)
gal/min (gpm)
gal/h (gph)
gal/day (gpd)
Mgal/day (mgd)
ft³/min (cfm)
ft³/s (cfs)
oil barrel/day (bpd)

Flux and rates

Metric
L/(m².h) LMH
m³/(m².day) m/day
m³/(m².h) m/h
m³/(m².min) m/min
m³/(m².s) m/s
   
US
gal/(ft².day) GFD
gal/(ft².h) GFH
gal/(ft².min) GFM
gal/(ft².s) GFS
ft³/(ft².day) ft/day
ft³/(ft².h) ft/h
ft³/(ft².min) ft/min
ft³/(ft².s) ft/s

Forces

Metric
N
kN
kgf
dyn
 
US
lbf
pdl

Hardness in water

Hardness
mg/L CaCO3
meq/L
mmol/L
°dH
°e
°fH
gpg

Length

Metric
m
cm
mm
µm
nm
km
 
US
in
mil
ft
yd
mi

Mass

Metric
kg
g
mg
µg
metric ton
 
US
lb
oz
ton

Power

Metric
W (J/s)
kW
cal/s
kcal/h
kgf.m/s
 
US
hp
bhp
BTU/s

Pressure

Metric
bar
Pa
kPa
kg/cm² (kgf)
atm
mH2O
mmHg
 
US
psi
ftH2O
inH2O
inHg

Speed

Metric
m/s
m/min
m/h
m/day
km/h
cm/h
cm/min
cm/s
 
US
in/h
in/min
in/s
ft/h
ft/min
ft/s
mi/h (mph)
mi/min (mpm)

Temperature

Metric
°C
Kelvin
US
°F

Time

Composite¹
days
hours
minutes
seconds
 
Decimal²
days
hours
minutes
seconds

1 Each input represents a component of the date/hour format: [dd][hh]:[mm]'[ss]''

2 Each input represents the sum of days, hours, minutes and seconds converted to the same base.




Volume

Metric
L
mL
µL
pL
 
US
gal (US)
gal (Imperial)
in³
ft³
fl oz
oil barrel

Geometry and capacities

Buffer tank capacity

Average flow
m³/h gpm
Maximum flow
m³/h gpm
Maximum flow duration
min h
Minimum flow
m³/h gpm
Minimum flow duration
min h
Buffer tank volume
L ft³

Cylinder volume

Diameter
mm in
Height
mm in
Volume
L ft³

Cone volume

Diameter
mm in
Height
mm in
Volume
L ft³

Cube volume

Sides length
mm in
mm in
mm in
Volume
L ft³

Circle properties

Diameter
mm in
Radius
mm in
Perimeter
mm in
Area
mm² in²
ft²

Horizontal cylindrical tank

Diameter
mm in
Water height
mm in
Length
mm in
Volume
L ft³

Municipal plant capacity

Production per capita*
L/day gal/day
Population
habitants
Plant flow
L/s mgd

*The World Health Organization (WHO) recommends between 100 and 300 L/day/hab for optimal drinking water service level.


Nominal pipe sizes

Nominal pipe size / DN
Wall thickness designation
Equivalent thickness designations*

None

External diameter
mm in
Internal diameter
mm in
Internal area
mm² in²
Wall thickness
mm in

*Other designations with the same diameters and wall thickness.

Nominal Pipe Size dimensions from the ASME Standards B36.10M, ASME B36.19M and ISO 6708. Valid for Stainless Steel, Ductile Iron, PVC and CPVC pipes.


Rainfall volume

Catchment area
ft²
km² mi²
Precipitation
mm in
Volume
ft³

Sieve sizes

Standard US Number
Standard Tyler Mesh
Opening
mm in

Designations and sizes according to the ASTM-E11 (2015).


Triangle properties

Desired outputs
Angle 1, Angle 2, Angle 3
Side 2, Side 3, Angle 1
Side 3, Angle 1, Angle 2
Side dimensions
Side 1 mm in
Side 2 mm in
Side 3 mm in
Angles*
Angle 1 ° rad
Angle 2 ° rad
Angle 3 ° rad
Perimeter
mm in
Area
mm² in²
ft²

*Angles are named according to the opposite side name (example: A1 refers to the side S1).


Energy and power

Blowers and compressors power

Flow
Nm³/h ft³/min
Air density at NTP
kg/m³ lb/ft³
Intake pressure*
bar psi
Output pressure*
bar psi
Temperature
°C °F
Mechanic eff.
%
Electric eff.
%
Power
kW hp


*Absolute pressures. Use the default value (1.013 bar) for intakes at the atmosphere pressure.

Calculations from Metcalf and Eddy, Wastewater Engineering, 2003


Head loss in pipes

Flow
m³/h gpm
Pipe roughness
mm in
Kinematic viscosity
cSt
Length
m ft
Internal diameter
mm in
Head loss
m ft
Speed
m/s ft/s


Metering pump stroke adjustment

Desired dosage flow
L/h gal/h
Maximum pump flow
L/h gal/h
Stroke
%

Mixing velocity gradient

Reactor volume
ft³
Dynamic viscosity (µ)
Pa.s cP
Power
kW hp
Velocity gradient
s-1


Open channels or partially filled pipes

Section geometry
Bottom width
mm in
Side slope base width¹
mm in
Internal diameter
mm in
Water depth
mm in
Slope of the channel²
m/m or in/in %
Manning coefficient³
Kinematic viscosity
m²/s cSt
Flow
m³/h gpm
Average velocity
m/s ft/s
Reynolds
Froude
Kinetic energy
m ft
Specific energy
m ft
Hydraulic radius
mm in
Wetted perimeter
mm in


¹ Base of the right-angle triangle with the water depth as height and the inclined side slope as hypotenuse. The solver considers both side slopes as identical.

² Inclination of the channel or the altitude loss per horizontal length.

³ Typical values from literature: 0.013 for concrete or cast iron, 0.03 for gravel and 0.01 for smooth plastic.

Orifice plates with incompressible fluids

Pressure reading taps¹
Pipe internal diameter
mm in
Orifice internal diameter
mm in
Fluid density
kg/m³ lb/ft³
Dynamic viscosity (µ)
Pa.s cP
Flow
m³/h gpm
Discharge coefficient
Pressure drop between taps
bar psi
Overall headloss for the orifice plate
m ft

Calculations from the ISO 5167 (2003) and from the ASME MFC-14M (2001) valid for incompressible fluids, sharp edged orifice plates; orifice diameter >=12.5mm, 1m >; pipe diameter > 25mm, 0.75 >; orifice diameter/pipe diameter > 0.1

¹ Tap type and distances from the orifice plate, upstream and downstream. D stands for the pipe internal diameter.


Parshall flumes flow measurement

Standard throat width¹
Primary measurement head² (Ha)
mm in
Secondary measurement head³ (Hb)
mm in
Flow
m³/h gpm
Submergence ratio

¹ Standard sizes and discharge coefficients according to the ASTM D1941 (2013).

² Head measurement in the convergence section.

³ Head measurement in the throat section. Used only for submerged flow measurements, leave blank for free flow.

Free flow calculations according to the ASTM D1941 (2003). Submerged flow calculations according to the ISO 9826 (1992).


Pump power

Flow
m³/h gpm
Fluid density
kg/m³ lb/ft³
Head
m ft
Mechanic eff.
%
Electric eff.
%
Power
kW hp


Rectangular flumes flow measurement

Measurement head¹ (h)
mm in
Approach channel width (B)
mm in
Throat width (b)
mm in
Throat length (L)
mm in
Bump height² (p)
mm in
Flow
m³/h gpm

Discharge coefficients and variable names according to the ISO 4359 (1983). Devices also known as Venturi flumes.

¹ According to the standard, the head is measured in the approach channel.

² Leave blank if the flume has a flat bottom (typical).


Reynolds number and speed

Hydraulic diameter
mm in
Flow
m³/h gpm
Average speed
m/s ft/s
Fluid density
kg/m³ lb/ft³
Dynamic viscosity (µ)
Pa.s cP
Reynolds


Contaminants

Periodic table of elements

Element
Atomic number
Atomic weight
Group
Electron configuration

None

Oxidation states

None

Melting point
°C °F
Boiling point
°C °F
Density
kg/m³ lb/ft³
Ionization energy
eV


Ionic balance and conductivity

Cations mg/L CaCO3 meq/L
Aluminum Al3+
Ammonium NH4+
Barium Ba2+
Calcium Ca2+
Copper Cu2+
Hydrogen H+
Ferrous ion Fe2+
Ferric ion Fe3+
Magnesium Mg2+
Manganese Mn2+
Potassium K+
Sodium Na+
Strontium Sr2+
Anions mg/L CaCO3 meq/L
Bicarbonate HCO3-
Carbonate CO32-
Chloride Cl-
Fluoride F-
Iodine I-
Hydroxide OH-
Nitrate NO3-
Phosphate (tribasic) PO43-
Phosphate (dibasic) HPO42-
Phosphate (mono) H2PO4-
Sulfate SO42-
Hydrogen Sulfate HSO4-
Sulfite SO32-
Sulfide S2-
Neutrals mg/L CaCO3 meq/L
Ammonia NH3
Silica* SiO2
Carbon dioxide CO2

Balance
Sum cations meq/L
Sum anions meq/L
Sum anions+silica+CO2 meq/L
Conductivity @ 25°C (if balanced) µS/cm
Total Dissolved Solids (TDS) mg/L

*For ion exchange purposes SiO2 is considered weakly ionized as H2SiO3(silicic acid). SiO2 has MW=60 and is removed as monovalent SiO2-.

CO2 conductivity and pH in pure water

Temperature
°C °F
Dissolved CO2
mg/L CO2 mg/L CaCO3
Conductivity and resistivity
µS/cm MΩ.cm
pH


Calculations from Truman S. Light, Elizabeth A. Kingman and Anthony C. Bevilacqua, Thornton Associates Inc, 1995, The Conductivity of low concentrations of CO2 dissolved in ultrapure water from 0-100°C


Boiler blowdown and concentration

Feed concentration*
mg/L lb/gal
Boiler concentration*
mg/L lb/gal
Blowdown rate
%
Cycles
Blowdown flow
kg/h lb/h
Steam flow
kg/h lb/h

*Concentrations measured at 25°C (77°F), not at the boiler temperature.


TOC, COD and KMnO4 relations

Chemical Oxygen Demand (COD)
mg/L O2
Organic Matter as Permanganate
mg/L KMnO4
Biological Oxygen Demand (BOD)
mg/L O2
Total Organic Carbon (TOC)
mg/L C

Rough organic matter conversions based on the empiric factors from DOW Water and Process Solutions Answer Center for natural waters.


Langlier Saturation Index - LSI

Temperature
°C °F
Calcium
mg/L CaCO3 mg/L Ca
Alkalinity
mg/L CaCO3 mg/L HCO3
Total Dissolved Solids
mg/L
pH
LSI

Calculations from Edstrom Industries, 1998, Scale Forming Tendency of Water MI-4170.


Modified Fouling Index - MFI

Temperature
°C °F
Pressure
bar psi
Active membrane diameter¹
mm in
Membrane area
ft²
Average flow during cake formation²
L/h gal/h
Inverse of the average flow during cake formation² (Δt/ΔV)
s/L s/gal
Filtrate volume during cake formation² (ΔV)
L gal
MFI
s/L²

Standard test conditions according to the ASTM D8002 (2015) for the MFI 0.45. The MFI will be normalized in case of different temperatures, areas or pressures from the standard test conditions.

¹ 47mm diameter membrane with 0.45µm mean pore size operating at 200±2KPa (2±0.02 bar). Active membrane diameter depends on the filter holder used.

² The cake formation is the linear segment of the (t/V) vs (V) graphic where t is the time in seconds and V is the filtrate volume in liters.




Silt Density Index - SDI

Time for the first 500mL
s min
Total elapsed time (T)*
s min
Time for the last 500mL
s min
SDIT
Maximum SDI for T

*Total time of 15 minutes is the default for RO/NF membranes warranty terms.




Sludge Volume Index - SVI

Settled volume in 30min
mL/L
Total suspended solids
mg/L lb/gal
Sludge volume index (SVI)
mL/g

¹ This is also referred as the MLSS (mixed liquor suspended solids).




Food-to-microorganisms ratio - F/M

Influent flow
m³/h gpm
Influent BOD concentration
mg/L lb/gal
Mixed liquor suspended solids¹
mg/L lb/gal
Reactor volume
ft³
Food-to-microorganisms ratio (F/M)

¹ This can be either the MLVSS (mixed liquor volatile suspended solids) or the MLSS (mixed liquor suspended solids).




Solutions

Chemical dosing

Water flow
m³/h gpm
Chemical dosage*
mg/L (ppm) lb/ft³
Stock concentration
%w/w mg/L (ppm)
Stock density
kg/m³ (g/L) lb/ft³
Chemical flow - mass
kg/h lb/h
kg/day lb/day
Chemical flow - volume
L/h gph
L/day gpd

*Chemical dosage as if the product is at 100% concentration.


Dry chemical dosing

Water flow
m³/h gpm
Chemical dosage*
mg/L (ppm) lb/ft³
Chemical flow
g/min lb/min
kg/h lb/h
kg/day lb/day

*Chemical dosage as if the product is dry at 100% concentration.


Chemical solutions density

Chemical solution

Temperature
°C °F
Concentration
%w/w mg/L (ppm)
Density
kg/m³ (g/L) lb/ft³
Specific gravity
Baumé density
°B


Properties interpolated from the tables provided by the chemical suppliers and from the Perry's Chemical Engineers Handbook.


Water properties

Temperature
°C °F
Density
kg/m³ lb/ft³
Dynamic Viscosity (µ)
Pa.s cP
Kinematic Viscosity (v)
m²/s cSt
pH
Conductivity and resistivity
µS/cm MΩ.cm

Properties at the atmospheric pressure (100 KPa) in the liquid form. Equations from R.C. Weast, 1983, CRC Handbook of Chemistry and Physics, 64th edition; from the David R. Maidment, 2003 Handbook of Hydrology, McGraw-Hill; from Truman S. Light, Elizabeth A. Kingman and Anthony C. Bevilacqua, Thornton Associates Inc, 1995, The Conductivity of low concentrations of CO2 dissolved in ultrapure water from 0-100°C; and from IAEA: Environmental Isotopes in the hydrological cycle: Principles and Applications Vol 1.


Gases properties

Gas
Temperature
°C °F
Density
kg/m³ lb/ft³
Molecular weight

Properties at the atmospheric pressure (100 KPa). Equations from MWH, 2005, Water Treatment Principles and Design 2nd edition.


Oxygen solubility in water

Temperature
°C °F
Barometric pressure
atm mmHg
Salinity
%w/w mg/L (ppm)
Solubility
mg/L

Equations from Benson and Krause,1980 and 1984.


Blending

Stream 1
Flow1
%
Concentration2
 
Stream 2
Flow1
%
Concentration2
 
Stream 3
Flow1
%
Concentration2
 
Result mixture
Total flow
Concentration

1 Allows any unit of flow or volume (L/h, m³/h, gpm, m³, L, gal, etc...).

2 Allows any unit of concentration (mg/L, ppm, ppb, %, etc...) or temperatures.




Specific gravity, Baumé, Brix and API relations

Temperature
°C °F
Density
kg/m³ lb/ft³
Specific gravity at 60°F (15.6°C)
Baumé for liquids heavier than water
°B
Baumé for liquids lighter than water
°B
API gravity
°API
Brix¹
°Bx

Equations from Perry's Chemical Engineers Handbook (8th Edition), 2008, McGraw-Hill and from the API Manual of Petroleum Measurement Standards Chapter 11, 2004.

¹ Brix will be calculated by the simplified formula. Specific gravity used on this solver was set to 15°C so it might be slighlty different from the standard at 20°C used in common Brix calculations.


Adsorption and Ion Exchange

Sorption/Exchange capacity

Flow
m³/h gpm
Inlet solids
mg/L
Outlet solids
mg/L
Media capacity*
mg/L
Media volume
L ft³
Run length
h days
Run volume
gal
Contact time
BV/h min

*The media capacity is expressed as mg of solute per Liter of filter media. For ion exchange, the mg/L concentrations can be replaced by meq/L values.




Empty Bed Contact Time and BV/h

Flow
m³/h gpm
Media volume
L ft³
Contact time
BV/h* min

*Bed volumes per hour.




Ion Exchange regeneration

Media volume
L ft³
Water density
kg/m³ lb/ft³
Stock concentration
%w/w mg/L (ppm)
Stock density
kg/m³ (g/L) lb/ft³
Regenerant dosage*
g/Lresin lb/ft³resin
Diluted concentration
%w/w mg/L (ppm)
Contact time
min BV/h
Stock regenerant
L gal
kg lb
L/h gal/h
Diluted regenerant
L gal
kg lb
L/h gal/h
Dilution water
L gal
L/h gal/h

*Chemical dosage per liter of resin at 100% concentration.


Ion Exchange Softener design

Gross flow
m³/h gpm
Run length
h days
Run volume
gal
Feed water Hardness
mg/L CaCO3 meq/L
Feed water Sodium concentration
mg/L meq/L
Design temperature
°C °F
Desired safety factor¹
Regeneration level
g/Lresin
NaCl injection concentration
%
 
Resin type²

Not defined

 
Resin volume
L ft³
Column internal diameter
mm in
Column cylindrical height
mm in
Resin height
mm in
 
Pressure drop at design temperature
bar psi
Final safety factor from column design¹
Contact time
min BV/h
Hardness leakage
mg/L CaCO3 meq/L
NaCl @ 100% for regeneration
kg lb
Diluted NaCl volume for regeneration
L gal
Water consumption for regeneration
gal
Overall regeneration duration
min h
 
Regeneration step 1 - backwash³
m³/h gpm
min h
Regeneration step 2 - NaCl injection³
m³/h gpm
min h
Regeneration step 3 - displacement³
m³/h gpm
min h
Regeneration step 4 - fast rinse³
m³/h gpm
min h

Design based in the Ion Exchange resins engineering manuals.

¹ Safety factor over the calculated resin volume. The final safety factor might be higher because the solver rounds up the resin volume. Typical: 1.05 to 1.15.

² Suggested resins: Amberlite™ IR120, Amberjet™ 1200, DOWEX™ Marathon™ C or DOWEX™ HCR-S.

³ Backwash in upflow direction. Operation, injection, displacement and rinse in downflow direction.


Filters and membranes

Cylindrical filter rate and speed

Flow
m³/h gpm
Diameter
mm in
Rate
m/h ft/h

Membranes flux

Gross permeate flow
m³/h gpm
Element area
ft²
Element quantity
elements
Total area
ft²
Flux
LMH GFD

Recovery

Feed flow
m³/h gpm
Net product flow
m³/h gpm
Concentrate flow
m³/h gpm
Recovery
%
Concentration factor

Recovery for membranes in series

Average individual element recovery
%
Elements in series
Total system recovery
%

MF/UF comparison and normalization

Flux
LMH GFD
Net driving pressure
bar psi
Current temperature
°C °F
Reference temperature
°C °F
Water permeability¹
LMH/bar GFD/psi

Valid for Microfiltration, Ultrafiltration and other porous membranes. Permeability is used for datasheet comparisons and real plant performance evaluation. Fouling decreases the permeability.

¹ If the "current temperature" is different than the "reference temperature", calculates the normalized permeability.




RO membranes comparison

Test solution
Solution concentration
mg/L (ppm) %w/w
Temperature
°C °F
Feed pressure
bar psi
Recovery
%
Element area
ft²
Product flow
m³/day gpd
Salt rejection
%
Water transport coefficient¹ at 25°C
LMH/bar GFD/psi
Salt transport coefficient² at 25°C
LMH GFD


The mass transport coefficients allow the datasheet comparison between Reverse Osmosis and some Nanofiltration membranes that were tested under different conditions or between new and used elements. This solver was calibrated for single element tests only. More information about the equations can be found here.

¹ Membrane flux per effective driven pressure (permeability) or A-value. Membranes with lower A coefficients will operate at higher pressures for the same permeate flow.

² Diffusion rate of the salt through the membrane or B-value. Elements with lower B coefficients have higher salt rejections. Note that each ionic compound has it's own B coefficient so you can't compare a membrane tested using NaCl with another using CaCl2.


RO plant normalization and comparison

Permeate flow
m³/h gpm
Concentrate flow
m³/h gpm
Recovery
%
Feed pressure
bar psi
Concentrate pressure
bar psi
Pressure drop¹
bar psi
Permeate pressure
bar psi
Temperature
°C °F
Total membrane area
ft²
Feed dissolved solids
µS/cm mg/L
Permeate dissolved solids
µS/cm mg/L
Salt rejection
%
Water transport coefficient² at 25°C
LMH/bar GFD/psi
Salt transport coefficient³ at 25°C
LMH GFD


This solver was based in the ASTM D4516 (2010) but the normalized permeate flow is expressed as permeability and the normalized salt passage as a transport rate. This format allows the direct comparison between data from different plants. More information about the equations can be found here.

¹ Manufacturers recommend cleaning membranes after an increase of 10% of this value compared with the startup.

² Permeability or A-value. Proportional to the normalized permeate flow. RO manufacturers recommend cleaning membranes after decrease of 10% of this value compared with the startup.

³ Salt passage rate or B-value. Proportional to the normalized salt passage. Manufacturers recommend cleaning membranes after an increase of 10% of this value compared with the startup.


RO/NF skid design

Product flow
m³/h gpm
Recovery
%
Element area
ft²
Target flux
LMH GFD
Elements per vessel
elements
Pressure vessels per stage

None

Flux from design
LMH GFD


The result design may require adjustments in case of high temperatures, high recoveries or use of very low pressure membranes. Always validate the design using the membrane manufacturer projection software.


Granular media head loss

Media type¹
Filtration rate/velocity
m/h ft/h
Media height
mm in
Dynamic viscosity (µ)
Pa.s cP
Fluid density
kg/m³ lb/ft³
Mean particle effective size
mm in
Porosity
%
Ergun coefficients
Kv Ki
Head loss
m in

¹ Input values for particle sizes, porosity and Ergun coefficients.

Equations from MWH, 2005, Water Treatment Principles and Design 2nd edition.




Granular media backwash expansion

Media type¹
Media height
mm in
Desired expansion
%
Final height
mm in
Dynamic viscosity (µ)
Pa.s cP
Fluid density
kg/m³ lb/ft³
Particle density
kg/m³ lb/ft³
Mean particle effective size
mm in
Settled bed porosity
%
Ergun coefficients
Kv Ki
Backwash rate/velocity
m/h ft/h

¹ Input values for particle sizes, porosity and Ergun coefficients.

Equations from MWH, 2005, Water Treatment Principles and Design 2nd edition based in the Akgiray and Saatçi, 2001 models.




Reactions

Ammonia equilibrium

pH
Total Ammonia Nitrogen
mg/L N µmol/L
Ammonium ion NH4+
mg/L µmol/L
Ammonia NH3 (gas)
mg/L µmol/L

Equilibrium constants at 25°, pK=9.24.


Boric Acid equilibrium

pH
Total dissolved Boron
mg/L B µmol/L
Boric Acid H3BO3
mg/L µmol/L
Borate ion B(OH)4-
mg/L µmol/L

Equilibrium constants at 25°C, pK=9.24.


Carbonates equilibrium

Temperature
°C °F
pH
Total dissolved inorganic Carbon
mg/L CaCO3
M-Alkalinity or Total ¹
mg/L CaCO3
P-Alkalinity ²
mg/L CaCO3
Carbon Dioxide CO2 (gas)
mg/L mg/L CaCO3
Bicarbonate HCO3-
mg/L mg/L CaCO3
Carbonate CO32-
mg/L mg/L CaCO3

¹ Total or M-Alkalinity refers to the Methyl-Orange indicator endpoint (pH 4.6).

² P-Alkalinity or Carbonate Alkalinity refers to the Phenolphthalein indicator endpoint (pH 8.3).

Calculations for pK1 from Harned and Davis, 1943 and for pK2 from Harned and Scholes, 1941.


Disinfection

Disinfectant

Temperature
°C °F
Log removal
log %
CT
min.mg/L
Dosage*
mg/L (ppm) %w/w
Contact time*
min h


CT stands for Concentration vs Time and is defined by the EPA Interim Enhanced Surface Water Treatment Rule (IESWTR). CT Values interpolated from the EPA Disinfection Profiling and Benchmarking Guidance Manual Appendix C, 1999. *Not required for the CT calculation.


Disinfection with Chlorine for Giardia Cysts

pH
Free Chlorine
mg/L (ppm) %w/w
Temperature
°C °F
Log removal
log %
CT
min.mg/L
Contact time
min h


CT stands for Concentration vs Time and is defined by the EPA Interim Enhanced Surface Water Treatment Rule (IESWTR). CT Values calculated using the regression method according to the EPA Profiling and Benchmarking Guidance Manual Appendix E, 1999.


Disinfection with UV

Target pathogens
Log removal
log %
UV Dose
µW.s/cm² mJ/cm²
Intensity*
µW/cm²
Contact time*
s min


Dosage values interpolated from the EPA Ultraviolet Disinfection Guidance Manual for the LT2ESWTR, 2006. *The contact time and the intensity are not required for the calculation of the required dose.


Iron oxidation and precipitation

Oxidant
Process flow
m³/h gpm
Fe2+ concentration
mg/L
Oxidant dosage (as 100%)*
mg/L
kg/h lb/h
kg/day lb/day
Alkalinity consumed
mg/L
kg/h lb/h
kg/day lb/day
Dry sludge production
kg/h lb/h
kg/day lb/day

*Stoichiometric values, no safety factors. Equations from ASCE/AWWA Water Treatment Plant Design, 3rd edition, 2003.


Manganese oxidation and precipitation

Oxidant
Process flow
m³/h gpm
Mn2+ concentration
mg/L
Oxidant dosage (as 100%)*
mg/L
kg/h lb/h
kg/day lb/day
Alkalinity consumed
mg/L
kg/h lb/h
kg/day lb/day
Dry sludge production
kg/h lb/h
kg/day lb/day

*Stoichiometric values, no safety factors. Equations from ASCE/AWWA Water Treatment Plant Design, 3rd edition, 2003.


Nitrous Acid equilibrium

pH
Total Nitrites
mg/L NO2 µmol/L
Nitrous Acid HNO2
mg/L µmol/L
Nitrite ion NO2-
mg/L µmol/L

Equilibrium constants at 25°C, pK=3.15.


Phosphate equilibrium

pH
Total Phosphorous
mg/L P µmol/L
Phosphoric Acid H3PO4
mg/L µmol/L
Dihydrogen Phosphate H2PO4-
mg/L µmol/L
Hydrogen Phosphate HPO42-
mg/L µmol/L
Phosphate ion PO43-
mg/L µmol/L

Equilibrium constants at 25°C. pK1=2.12, pK2=7.21, pK3=12.33.


Sludge from chemicals

Process flow
m³/h gpm
Chemical dosage
Aluminium Sulfate mg/L
Ferric Sulfate mg/L
Ferric Chloride mg/L
PAC mg/L %Al
Polymer mg/L
Turbidity removed
NTU
Dry sludge production*
kg/h lb/h
kg/day lb/day

*Average values from real plant data. Equations from MWH, 2005, Water Treatment Principles and Design 2nd edition.


Silicic Acid equilibrium

pH
Total dissolved Silica
mg/L SiO2 µmol/L
Ortho Silicic Acid Si(OH)4
mg/L µmol/L
Silicate ion Si(OH)3-
mg/L µmol/L

Equilibrium constants at 25°C, pK=9.86.


Sulfate equilibrium

pH
Total Sulfates
mg/L SO4 µmol/L
Hydrogen Sulfate HSO4-
mg/L µmol/L
Sulfate SO4-2
mg/L µmol/L

Equilibrium constants at 25°C, pK=1.99.


Sulfide equilibrium

pH
Total Sulfides
mg/L H2S µmol/L
Hydrogen Sulfide H2S
mg/L µmol/L
Bisulphide ion HS-
mg/L µmol/L

Equilibrium constants at 25°C, pK=7.02.


Ultimate BOD

BOD at the time t¹
mg/L
Ultimate BOD
mg/L
Time²
days
Deoxygenation rate constant
1/day

¹ Usually the BOD5, measured in the lab.

² 5 days if using the BOD5.




Clarifiers

Surface loading rate - circular

Flow
m³/h gpm
Diameter
m ft
Rate
m³/m².h ft³/ft².h

Surface loading rate - rectangular

Flow
m³/h gpm
Sides length
m ft
m ft
Rate
m³/m².h ft³/ft².h

Hydraulic retention time - HRT

Flow
m³/h gpm
Reactor or clarifier volume
ft³
Hydraulic retention time - HRT
min h

Solids retention time - SRT

Plant flow
m³/h gpm
Waste sludge flow
m³/h gpm
Solids concentration in the reactor¹
mg/L lb/gal
Solids returning from the clarifier²
mg/L lb/gal
Solids in the clarified/product water
mg/L lb/gal
Reactor volume
ft³
Solids retention time³ (SRT)
h days

¹ For activated sludges this can be the MLVSS (Mixed liquor volatile suspended solids) concentration in the aeration tank.

² Solids in the recirculation return to the reactor. For activated sludges this is the concentration in the return activated sludge (RAS) or the concentration in the waste sludge.

³ Also known as Mean Cell Residence Time (MCRT).




Solids loading rate

Clarifier influent flow
m³/h gpm
Solids influent concentration¹
mg/L lb/gal
Clarifier cross-sectional area
ft²
Solids loading rate
kg/(m².h) lb/(ft².h)

¹ For activated sludges this can be the MLVSS (Mixed liquor volatile suspended solids) concentration from the aeration tank. For water treatment clarifiers this is usually the TSS.




Volumetric solids loading rate

Influent flow
m³/h gpm
Solids influent concentration¹
mg/L lb/gal
Clarifier/reactor volume
ft³
Volumetric solids loading rate
kg/(m³.day) lb/(ft³.day)

¹ For activated sludges this can be the MLVSS (Mixed liquor volatile suspended solids) load in the clarifier or the BOD load in the aeration tank. For anaerobic reactors this is usually the COD load.




Return activated sludge recycle - RAS

Plant flow
m³/h gpm
Recirculation sludge flow
m³/h gpm
Return activated sludge recycle ratio¹
%
Solids concentration in the reactor²
mg/L lb/gal
Solids returning from the clarifier³
mg/L lb/gal

¹ This ratio can be calculated either from the flows or from the solid concentrations.

² For activated sludges this can be the MLVSS (Mixed liquor volatile suspended solids) concentration in the aeration tank.

³ Solids in the recycle activated sludge (RAS) stream.




Discrete sedimentation

Particle diameter
mm in
Particle density
kg/m³ lb/ft³
Fluid density
kg/m³ lb/ft³
Kinematic viscosity
m²/s cSt
Sedimentation rate*
m/h ft/h
Reynolds

*Equation from Stokes law valid for round particles and laminar movement (Re lower than 1).




Sludge concentration and mass

Solids mass
kg lb
Solids density*
kg/m³ lb/ft³
Solids percentage
%w/w mg/L (ppm)
Sludge volume
gal

*Typical biological sludge has a solids density of 1550kg/m³, mineral sludge has a density of approx. 2600kg/m³.




Sludge age

Influent flow
m³/h gpm
Influent suspended solids¹
mg/L lb/gal
Suspended solids in the reactor²
mg/L lb/gal
Reactor volume³
ft³
Sludge age
h days

¹ This can be either the VSS (volatile suspended solids) or the TSS (total suspended solids).

² This can be either the MLVSS (mixed liquor volatile suspended solids) or the MLSS (mixed liquor suspended solids). If using MLVSS, the inlet concentration must be VSS.

³ For activated sludges, the reactor is the aeration tank.




Finance

Ordinary annuity

Present value
Future value
Interest rate
% per period
Number of payments
Payment value

Ordinary annuity: Payments are required at the end of each period, compound interests.



Annuity due

Present value
Future value
Interest rate
% per period
Number of payments
Payment value

Annuity due: Payments are required at the beginning of each period, compound interests.



Compound annual growth rate - CAGR

Beginning value
End value
Number of periods
Compound annual growth
% per year


Interest rate conversions

Interest rate
% year
% month
% day


Simple interest

Principal
Interest rate
% per period
Number of periods
Simple interest
Total value


Help and product information

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