Industrial Wastewater Pretreatment and Loading
What you must know
Industrial pretreatment protects biological treatment and publicly owned treatment works (POTWs). Key concepts: prohibited discharge standards, categorical pretreatment standards, local limits, and slug control. Common pretreatment technologies include pH neutralization, equalization, oil-water separation, chemical precipitation, coagulation/flocculation, dissolved air flotation, and metals removal. Toxicity reduction evaluations (TREs) identify inhibitory compounds.
Loading calculations are central: mass load = concentration × flow. Shock loads and batch discharges can overwhelm biomass; equalization and controlled feed rates mitigate this. Waste strength (high COD, low nutrients) may require nutrient addition. Salinity, temperature, and pH excursions can inhibit nitrifiers and floc-formers. Segregating high-strength or toxic streams is often more economical than end-of-pipe treatment.
Traps in questions
- Confusing concentration limits with mass-based limits.
- Forgetting to convert units (mg/L × m³/d → kg/d requires dividing by 1000).
- Assuming dilution is a legitimate compliance strategy - it is not.
- Overlooking slug discharge control requirements.
Worked example / rule of thumb
Flow 500 m³/d, COD 4000 mg/L → load = 4000 × 500 / 1000 = 2000 kg COD/d. If the biological system is rated for 1500 kg/d, equalization or pretreatment is needed. Rule of thumb: mass load (kg/d) = concentration (mg/L) × flow (m³/d) ÷ 1000.