Degrees

°

minutes

seconds

Decimal degrees

°

Radians

rad

π.rad

Metric

m²

mm²

cm²

km²

ha

US

in²

ft²

mi²

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

Metric

µg/L

mg/L

g/cm³

g/L

kg/m³

mg/mL

US

lb/in³

lb/ft³

lb/gal

Metric

J

Wh

kWh

cal

kcal

N.m

kgf.m

US

BTU (iso)

hp.h

lbf.ft

lbf.in

Eq. ton of Coal

Eq. ton of Oil

Metric

kg/s

kg/min

kg/h

kg/day

g/min

US

lb/s

lb/min

lb/h

lb/day

Metric

m³/s

m³/min

m³/h

m³/day

L/s

L/min

L/h

L/day

ML/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)

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

Metric

N

kN

kgf

dyn

US

lbf

pdl

Hardness

mg/L CaCO3

meq/L

mmol/L

°dH

°e

°fH

gpg

Metric

m

cm

mm

µm

nm

km

US

in

mil

ft

yd

mi

Metric

kg

g

mg

µg

metric ton

US

lb

oz

ton

Metric

W (J/s)

kW

cal/s

kcal/h

kgf.m/s

hp(M) - Metric

US

hp (I) - Mechanic/Hydraulic

hp (S) - Boiler

hp (E) - Electric

BTU/s

Metric

bar

Pa

kPa

kg/cm² (kgf)

atm

mH2O

mmHg

US

psi

ftH2O

inH2O

inHg

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)

Metric

°C

Kelvin

US

°F

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.

Metric

m³

L

mL

µL

pL

US

gal (US)

gal (Imperial)

in³

ft³

fl oz

oil barrel

	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

	Diameter - D
	mm	in
	Height - H
	mm	in
	Volume - V
	L	ft³

	Diameter - D
	mm	in
	Height - H
	mm	in
	Volume - V
	L	ft³

	Sides length
	S1 mm	in
	S2 mm	in
	S3 mm	in
	Volume - V
	L	ft³

Diameter - D
mm	in
Radius - R
mm	in
Perimeter - P
mm	in
Area - A
mm²	in²
m²	ft²

	Diameter - D
	mm	in
	Water height - H
	mm	in
	Length - L
	mm	in
	Water volume - V
	L	ft³

	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 size / DN
Wall thickness designation
Equivalent thickness designations*
None

External diameter - OD
mm	in
Internal diameter - ID
mm	in
Internal area - A
mm²	in²
Wall thickness - WT
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.

	Catchment area - A
	m²	ft²
	km²	mi²
	Precipitation - P
	mm	in
	Volume - V
	m³	ft³

Standard US Number
Standard Tyler Mesh

Opening - W
mm	in

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

	Desired outputs
	A1, A2, A3
	S2, S3, A1
	S3, A1, A2
	Side dimensions
S1	mm	in
S2	mm	in
S3	mm	in
	Angles*
A1	°	rad
A2	°	rad
A3	°	rad
	Perimeter
	mm	in
	Area
	mm²	in²
	m²	ft²

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

	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

	Flow - Q
	m³/h	gpm
	Pipe roughness - R
	mm	in
	Kinematic viscosity
	cSt
	Length - L
	m	ft
	Internal diameter - D
	mm	in
	Head loss - H
	m	ft
	Velocity - V
	m/s	ft/s

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

	Reactor volume
	m³	ft³
	Dynamic viscosity (µ)
	Pa.s	cP
	Power
	kW	hp
	Velocity gradient
	s-1

Section geometry

Bottom width - B
mm	in
Side slope base width¹ - S
mm	in
Internal diameter - D
mm	in
Water depth - H
mm	in
Slope of the channel² - Z/L
m/m or in/in	%
Manning coefficient³
Kinematic viscosity
m²/s	cSt
Flow - Q
m³/h	gpm
Average velocity - V
m/s	ft/s
Reynolds
Froude
Kinetic energy
m	ft
Specific energy - E
m	ft
Hydraulic radius
mm	in
Wetted perimeter - P
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.

Pressure reading taps¹

Pipe internal diameter - D
mm	in
Orifice internal diameter - d
mm	in
Fluid density
kg/m³	lb/ft³
Dynamic viscosity (µ)
Pa.s	cP
Flow - Q
m³/h	gpm
Discharge coefficient
Pressure drop between taps - Δp
bar	psi
Overall headloss for the orifice plate - Δw
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.

Standard throat width¹ - B

Primary measurement head² - Ha
mm	in
Secondary measurement head³ - Hb
mm	in
Flow - Q
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).

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

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 - Q
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).

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

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

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^-.

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

	Feed concentration* - Xf
	mg/L	lb/gal
	Boiler concentration* - Xb
	mg/L	lb/gal
	Blowdown rate
	%
	Cycles
	Blowdown flow - Qb
	kg/h	lb/h
	Steam flow - Qs
	kg/h	lb/h

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

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 DuPont Water Resource Center for natural waters.

	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.

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

	Temperature
	°C	°F
	Pressure
	bar	psi
	Active membrane diameter¹
	mm	in
	Membrane area
	m²	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.

	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.

	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).

	Influent flow - Q
	m³/h	gpm
	Influent BOD concentration - B
	mg/L	lb/gal
	Mixed liquor suspended solids¹ - X
	mg/L	lb/gal
	Reactor volume - V
	m³	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).

	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.

	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 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.

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.

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.

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

Equations from Benson and Krause,1980 and 1984.

Stream 1
Flow1 - Q1	flow unit
	%
Amount2 - X1	units
Stream 2
Flow1 - Q2	flow unit
	%
Amount2 - X2	units
Stream 3
Flow1 - Q3	flow unit
	%
Amount2 - X3	units
Result mixture
Total flow - Qf	flow unit
Amount - Xf	units

¹ Allows any unit of massic flow, volumetric flow or volume (kg/h, lb/min, L/h, m³/h, gpm, m³, L, gal, etc...). Use the same unit for all streams.

² Allows any unit of quantity (mg/L, ppm, ppb, etc...) or temperatures. Use the same unit for all streams.

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.

	Flow - Q
	m³/h	gpm
	Inlet solids - Ci
	mg/L
	Outlet solids - Co
	mg/L
	Media capacity*
	mg/L
	Media volume - V
	L	ft³
	Run length
	h	days
	Run volume
	m³	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.

	Flow - Q
	m³/h	gpm
	Media volume - V
	L	ft³
	Contact time - t
	BV/h*	min

*Bed volumes per hour.

	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.

Gross flow - Q
m³/h	gpm
Run length
h	days
Run volume
m³	gal
Feed water Hardness - Ci
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 - Cr
%
Resin type²
Not defined
Resin volume - Vr
L	ft³
Column internal diameter - D
mm	in
Column cylindrical height - H
mm	in
Resin height - Hr
mm	in
Pressure drop at design temperature
bar	psi
Final safety factor from column design¹
Contact time
min	BV/h
Hardness leakage - Co
mg/L CaCO3	meq/L
NaCl @ 100% for regeneration
kg	lb
Diluted NaCl volume for regeneration
L	gal
Water consumption for regeneration
m³	gal
Overall regeneration duration
min	h
Regeneration step 1 - backwash³ - Qb
m³/h	gpm
min	h
Regeneration step 2 - NaCl injection³ - Qr
m³/h	gpm
min	h
Regeneration step 3 - displacement³ - Qd
m³/h	gpm
min	h
Regeneration step 4 - fast rinse³ - Qf
m³/h	gpm
min	h

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™ IRC120, Amberlite™ HPR1300, Amberlite™ HPR1200 or TapTec™ HCR-S.

³ Backwash in upflow direction. Operation, injection, displacement and rinse in downflow direction. Displacement is done only with water, no NaCl.

	Flow - Q
	m³/h	gpm
	Diameter - D
	mm	in
	Rate - q
	m/h	ft/h

	Gross permeate flow - Q
	m³/h	gpm
	Element area - A
	m²	ft²
	Element quantity - N
	elements
	Total area
	m²	ft²
	Flux
	LMH	GFD

	Feed flow - F
	m³/h	gpm
	Net product flow - P
	m³/h	gpm
	Concentrate flow - C
	m³/h	gpm
	Recovery
	%
	Concentration factor

	Average individual element recovery - r
	%
	Elements in series - N
	Total system recovery
	%

	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.

Test solution

Solution concentration
mg/L (ppm)	%w/w
Temperature
°C	°F
Feed pressure
bar	psi
Recovery
%
Element area
m²	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.

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
m²	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.

Product flow
m³/h	gpm
Recovery
%
Element area
m²	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.

Media type¹

Filtration rate/velocity - q
m/h	ft/h
Media height - H
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.

Media type¹

Media height - H1
mm	in
Desired expansion
%
Final height - H2
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 - q
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.

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.

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.

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 4.3).

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.

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.

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.

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.

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.

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.

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.

pH correction chemical

Temperature
°C	°F
Alkalinity¹
mg/L CaCO3	meq/L
Solution initial pH²
Solution final pH
Chemical dosage³
mg/L (ppm)	%w/w

Calculations based on Acids and Bases dissociation equilibrium. pK_a and pK_b constants from CRC Handbook of Chemistry and Physics, 84^th Edition (2004).

¹ Carbonates equilibrium for closed system - no CO₂ exchange with the atmosphere.

² Set to 7 to find the pH of acid or base solutions in pure water.

³ Real dosage may be higher due chemical consumption by other contaminants. Negative values if the chemical needs to be neutralized to reach the pH.

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.

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.

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.

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.

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.

	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.

	Flow - Q
	m³/h	gpm
	Diameter - D
	m	ft
	Rate - q
	m³/m².h	ft³/ft².h

	Flow - Q
	m³/h	gpm
	Sides length
	S1 m	ft
	S2 m	ft
	Rate - q
	m³/m².h	ft³/ft².h

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

	Plant flow - Q
	m³/h	gpm
	Waste sludge flow - Qw
	m³/h	gpm
	Solids concentration in the reactor¹ - X
	mg/L	lb/gal
	Solids returning from the clarifier² - Xr
	mg/L	lb/gal
	Solids in the clarified/product water - Xp
	mg/L	lb/gal
	Reactor volume - V
	m³	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).

	Clarifier influent flow - Q
	m³/h	gpm
	Solids influent concentration¹ - Xi
	mg/L	lb/gal
	Clarifier cross-sectional area - A
	m²	ft²
	Solids loading rate - s
	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.

	Influent flow - Q
	m³/h	gpm
	Solids influent concentration¹ - Xi
	mg/L	lb/gal
	Clarifier/reactor volume - V
	m³	ft³
	Volumetric solids loading rate - s
	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.

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

	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).

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

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

	Influent flow - Q
	m³/h	gpm
	Influent suspended solids¹ - Xf
	mg/L	lb/gal
	Suspended solids in the reactor² - X
	mg/L	lb/gal
	Reactor volume³ - V
	m³	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.

	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.

	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.

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

Interest rate

% year

% month

% day