Total combined flow
– m³/h
Total chemical added
– L/h
Resulting alkalinity
– mg/L
Total chemical cost
£– /day
Plan view — injection, mixing & blended stream (flow left → right)
Steady-state mass balance into the combined stream. Pipe colour downstream indicates the blended chemical(s); a static mixer ensures full mixing for the stated concentrations.
Per-line dosing, residual, CT, alkalinity & cost
Dose (mg/L = ppm) = active mass ÷ total flow. Residual = dose − demand (oxidants). CT = residual × contact time (= contact volume ÷ flow). Alkalinity change is a strong-acid/base meq balance as CaCO₃ (indicative; full pH needs the carbonate buffer). Reaction kinetics, decay & temperature not modelled.
Blended water composition — live analysis of the mixed stream
Treated-water chemistry after all active dosing lines blend into the main flow. Stability indices: LSI (Langelier 1936), RSI (Ryznar 1944), AI (aggressiveness, BS EN 12502). Free CO₂ from the carbonate equilibrium (pK₁ 6.35); conductivity ≈ TDS ÷ 0.64; ionic strength ≈ 2.5×10⁻⁵·TDS (Langelier–Russell). Indicative screening — confirm with a full ionic balance & lab analysis for design.
Clarifier / DAF dosing — scenario library (adjustable)
Pick a worked scenario and load it with one click — it sets the flow, influent water and three dosing lines. Then adjust anything in the Inputs panel and every tab updates live.
Municipal Surface-Water Clarification
Alum coagulation, polymer flocculation and chlorination for a drinking-water works.
Food & Beverage DAF Pre-Treatment
pH correction, ferric coagulation and polymer to float FOG & protein.
Heavy-Metals Precipitation
Lime pH-raise, ferric co-precipitant and polymer to clarify metal hydroxides.
Cooling-Water Side-Stream Softening
Lime–soda softening and polymer to control scale and cut blowdown.
Loaded scenario — Municipal Surface-Water Clarification
Live dosing setup & chemistry check
Worked screening scenarios — confirm all doses, pH targets and clarifier overflow rates with jar tests, a full ionic balance and the relevant design standards.
Methods & references — science & math used at each step
Every calculation in this tool, the equation as implemented, and its scientific basis. Sources are APHA Standard Methods, USEPA guidance, the standard water-treatment texts, and the primary journal papers for each index.
1 · Dosing & mass balance
| Step / quantity | Equation as implemented | Scientific basis / reference |
|---|---|---|
| Dose (mg/L = ppm) | dose = (q·c) / Q_tot — steady-state mass conservation (q = pump flow, c = active conc.) | Crittenden et al., MWH's Water Treatment: Principles & Design, 3rd ed., Wiley 2012, Ch. 6 |
| Active strength | c (g/L) = %w/w × 10 × SG | Perry's Chemical Engineers' Handbook, 8th ed. (solution concentration) |
| Total combined flow | Q_tot = Q_main + Σ q_i (continuity) | Mass/volume conservation |
| Dilution ratio | 1 : Q_tot / q | Mass balance |
2 · Disinfection (oxidants)
| Residual | residual = dose − demand (breakpoint) | White's Handbook of Chlorination & Alternative Disinfectants, 5th ed., 2010 |
| Contact time | t = V_contact / Q_tot (plug-flow basis) | USEPA SWTR Guidance Manual, EPA 815-R-99-014 |
| Disinfection CT | CT = residual × t | USEPA Surface Water Treatment Rule; DWI guidance (UK) |
3 · Acid–base & alkalinity (as CaCO₃)
| Alkalinity balance | Alk_f = Alk₀ + Σ(dose_i × f_i); meq/L × 50 = mg/L CaCO₃ | APHA Standard Methods 2320; Snoeyink & Jenkins, Water Chemistry, Wiley 1980 |
| H₂SO₄ factor | −1.02 mg CaCO₃ / mg = 2 eq·mol⁻¹ × 50 / 98 (diprotic) | Stumm & Morgan, Aquatic Chemistry, 3rd ed., 1996 |
| NaOH factor | +1.25 mg CaCO₃ / mg = 50 / 40 | Acid–base stoichiometry |
| pH ↔ hydroxide | [OH⁻] = 10^(pH − 14) (K_w = 10⁻¹⁴, 25 °C) | Water self-ionisation; Stumm & Morgan |
4 · Coagulation / flocculation
| FeCl₃ alkalinity demand | FeCl₃ + 3H₂O → Fe(OH)₃ + 3HCl → 0.92 mg CaCO₃/mg (3×50/162.2) | Twort's Water Supply, 7th ed. (Ratnayaka et al.), 2017; Amirtharajah & Mills, 1982 |
| Coagulant ratio | mg Fe per g TSS = dose·(55.85/162.2)/TSS (jar-test calibrated) | BS EN ISO 5667 (sampling) & jar test; Twort's Water Supply |
| Rapid-mix intensity | G = √(P/μV); design 300–400 s⁻¹ | Camp & Stein, J. Boston Soc. Civ. Eng. 30:219, 1943 |
5 · Water-stability indices (treated stream)
| Saturation pH | pHs = (9.3+A+B) − (C+D) — A,B,C,D from TDS, T, Ca, alkalinity | Langelier, 1936; APHA Std Methods 2330; BS EN 12502 |
| Langelier LSI | LSI = pH − pHs | Langelier, 1936 |
| Ryznar RSI | RSI = 2·pHs − pH | Ryznar, 1944 |
| Aggressiveness AI | AI = pH + log₁₀(Alk × Ca) (both as CaCO₃) | BS EN 12502; APHA Std Methods 2330B |
6 · Carbonate system & physical properties
| Free CO₂ | [CO₂] = [HCO₃⁻][H⁺]/K₁, pK₁ = 6.35 (25 °C); [HCO₃⁻] ≈ Alk/50000 | Stumm & Morgan; Plummer & Busenberg, GCA 46:1011, 1982 |
| Conductivity | EC (µS/cm) ≈ TDS / 0.64 | APHA Std Methods 2510; Hem, USGS WSP 2254, 1985 |
| Ionic strength | I (mol/L) ≈ 2.5×10⁻⁵ × TDS | Langelier, 1936; Russell, 1976 (Langelier–Russell) |
7 · Clarifier & DAF design
| Acid demand (pH 12→7) | neutralise alkalinity (meq balance) → ≈1 L of 50% H₂SO₄ per m³ at 800 mg/L CaCO₃ | Std Methods 2310/2320; mass balance |
| Lamella overflow rate | v_o = Q / (N · A_proj); laminar capture (Re < 800) | Hazen, Trans. ASCE 53:45, 1904; Yao, JWPCF 42:218, 1970 |
| Static-mixer G-value | G = √(ρ·g·h_L / (μ·θ)) | Crittenden/MWH; Camp & Stein, 1943 |
| Scenario library | municipal surface-water clarification, food & beverage DAF, heavy-metals precipitation, cooling-water softening — indicative, jar-test-calibrated doses | Twort's Water Supply; APHA Std Methods |
Screening-level methods. Simplifications: full pH from the carbonate buffer, temperature-dependence of equilibrium constants, reaction kinetics/decay, and floc settling dynamics are not solved here — confirm with jar tests, a full ionic balance and the cited standards for detailed design.