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.

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

*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.

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

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

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

Calculations from Metcalf and Eddy, Wastewater Engineering, 2003

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.

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.

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).

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).

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

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

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

Rough organic matter conversions based on the empiric factors from DuPont Water Resource Center for natural waters.

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

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.

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

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

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

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

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

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

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.

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

Equations from Benson and Krause,1980 and 1984.

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.

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.

*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.

*Bed volumes per hour.

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

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.

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.

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.

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.

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.

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

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

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.

Equilibrium constants at 25°, pK=9.24.

Equilibrium constants at 25°C, pK=9.24.

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.

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.

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.

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.

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

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

Equilibrium constants at 25°C, pK=3.15.

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.

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

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

Equilibrium constants at 25°C, pK=9.86.

Equilibrium constants at 25°C, pK=1.99.

Equilibrium constants at 25°C, pK=7.02.

¹ Usually the BOD₅, measured in the lab.

² 5 days if using the BOD₅.

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).

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.

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.

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.

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

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

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.

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

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