τ = V / Qτ: hydraulic residence time in h; V: working tank volume in m³; Q: flow through the tank in m³/h.
Constant-volume, steady-flow approximation. Actual contact time depends on mixing, hydraulic short-circuiting and dead zones.
Chemistry · Course
Water treatment plant operation
Select a treatment train for a synthetic raw water, adjust operating settings, and compare water, pollutant, chemical and by-product balances.
← Back to the simulationScientific principles
Treatment selection depends on the source, contaminants and intended use. A turbid river, hard groundwater, saline water, municipal wastewater and acid mine drainage require different approaches. The six feed compositions are partial synthetic scenarios; they do not cover all real-world water conditions. Selecting a treatment train and obtaining favourable simulator indicators never certifies drinking-water safety or discharge compliance.
A conventional surface-water train combines screening, coagulation, flocculation, clarification, filtration and disinfection. Coagulant destabilises particles; gentle mixing promotes floc formation; clarification and filtration remove solids. Optimum dose depends on the water and is investigated experimentally, for example through jar testing. A higher dose is not necessarily better. Sludge and filter backwash water must appear in the balance.
Borehole water may require aeration or oxidation of iron and manganese followed by filtration, then softening where appropriate for the intended use. Ion exchange replaces ions such as calcium and magnesium; it does not mean that all salts have disappeared. An ordinary sand filter does not effectively remove dissolved salts. Hardness, total alkalinity and pH are different properties: pH alone cannot determine a neutralisation dose.
Reverse-osmosis desalination splits a feed into permeate and concentrate. Recovery is the fraction of feed water becoming permeate; rejection describes the reduction of a solute's concentration in permeate. Increasing recovery generally increases concentrate strength and operating constraints. Flow rates must be tracked and salt mass conserved. The model prescribes an educational rejection coefficient without reproducing osmotic pressure, fouling or real membrane design calculations.
A wastewater plant combines preliminary treatment, primary separation, an aerated biological process, clarification and, where needed, further treatment. Aeration supplies oxygen for some biological processes; clarification and sludge return/wasting control biomass. COD and BOD₅ are distinct indicators, while the permanganate index is another measure of oxidisability. Organic-matter removal alone does not demonstrate the absence of pathogens.
Acid mine water may require equalisation, neutralisation, metal precipitation, flocculation, clarification and filtration. Base dose depends on titratable acidity and metal reactions, not pH alone. Iron, manganese and copper behave differently; a single removal formula is not a complete chemical prediction. In every train, game efficiencies and coefficients remain educational assumptions. Disinfection, by-products, microbiology, variability and regulations require separate verification.
Equations, units and conditions
m = d × Q / 1000 ; L = C × Q / 1000m: chemical mass flow in kg/h; d: active chemical dose in mg/L; L: pollutant load in kg/h; C: concentration in mg/L; Q: m³/h.
Dose means active substance, not necessarily the mass of a commercial solution. A real balance must include purity, solution concentration and any additional streams.
η = 1 − C_out / C_inη: fractional removal efficiency, multiplied by 100 for a percentage; C_in and C_out: concentrations in the same unit.
Applies at equal flow rates with C_in > 0. If flows differ, compare Q × C loads; dilution alone is not mass removal.
Q_p = r × Q_f ; Q_c = (1 − r) × Q_f ; C_p = (1 − R) × C_f ; C_c = (Q_f × C_f − Q_p × C_p) / Q_cQ_f, Q_p, Q_c: feed, permeate and concentrate flows in m³/h; C_f, C_p, C_c: concentrations of the same solute in mg/L; r: water recovery; R: apparent rejection, both dimensionless fractions.
Steady-state reverse-osmosis model: 0 ≤ r < 1, 0 ≤ R ≤ 1, Q_c > 0, solute conservation and no accumulation. Assumes comparable density and a prescribed rejection; it does not calculate osmotic pressure, scaling or real membrane performance.
CT = C_res × tCT: simplified disinfectant exposure in mg·min/L; C_res: disinfectant residual in mg/L; t: contact time in min.
Educational indicator only: residual is not the applied dose. Actual efficacy depends on the organism, disinfectant, pH, temperature and hydraulics; no game CT value certifies disinfection.
Applications
Conventional surface-water treatment plant
Adjust flow, coagulant dose and residence times; track turbidity, chemicals, sludge and filter backwashing.
Borehole treatment and softening plant
Compare oxygenation, iron/manganese separation and hardness reduction; distinguish hardness from total salt concentration.
Desalination plant
Adjust recovery and rejection, compare permeate and concentrate, and check water and salt conservation.
Biological wastewater treatment plant
Track organic loading, aeration, hydraulic residence time, clarification and sludge production.
Mine-water treatment plant
Relate feed acidity, base dose, separated metals and sludge production while documenting model limitations.
What to observe in the simulation
Keep the feed water fixed and compare treatment trains, then keep the train fixed and change the source. With a constant tank volume, doubling flow halves hydraulic residence time. A dose of 20 mg/L at 100 m³/h requires 2 kg/h of active chemical. In reverse osmosis, a feed concentration of 35000 mg/L, 45% recovery and 99% rejection give 350 mg/L permeate and approximately 63350 mg/L concentrate in the ideal model. Check balances before writing the report.