ETP Chemical Supplier Guide India | Dosing by Treatment Stage

Coagulation is the first chemical treatment stage in most Indian ETPs. Raw effluent enters a flash mixer or rapid mix chamber where coagulant is dosed to destabilise colloidal particles and colour molecules. Poly Aluminium Chloride (PAC) powder has become the dominant coagulant in modern ETPs, replacing alum in textile, paper and chemical industry plants due to lower dosing rates and broader pH tolerance. Ferric alum and non-ferric alum remain widely used in cost-sensitive applications and municipal-style clarifiers.

Ferric chloride serves as an alternative coagulant particularly effective for phosphorus removal, heavy metal precipitation and high-colour effluent where dual coagulation (PAC followed by ferric chloride) achieves compliance limits that single coagulant dosing cannot. Ferric chloride also performs well in low-alkalinity effluent where alum would require excessive lime addition.

After coagulation, flocculants (polyelectrolytes) are dosed in the flocculation chamber to agglomerate micro-flocs into larger, settleable flocs. Anionic polyelectrolytes are used for most industrial effluent with negative surface charge — typical in textile dyeing, paper and food processing wastewater. Cationic polyelectrolytes are preferred for oily effluent, sludge dewatering and effluent with positively charged organic matter. Polyelectrolyte doses are typically 1–5 mg/L — a small volume but critical for clarifier performance and final water clarity.

pH control is fundamental to ETP operation. Most coagulants perform optimally at pH 6.5–8.0, but raw industrial effluent often arrives at pH 2–4 (acidic from dyeing, pickling, chemical synthesis) or pH 10–12 (alkaline from scouring, bleaching, caustic cleaning). Caustic soda (NaOH) lye and flakes raise pH efficiently and are the most common alkali used in Indian ETPs. Hydrated lime (calcium hydroxide) is an economical alternative that also adds calcium hardness, aiding coagulation in soft-water effluent.

For effluent that is too alkaline, sulphuric acid or hydrochloric acid lowers pH before coagulation. Acid dosing must be controlled carefully — over-acidification wastes acid, under-dosing leaves coagulant ineffective. Automated pH controllers with acid/alkali metering pumps are standard in well-designed ETPs. Biological treatment stages (activated sludge, trickling filters) require pH 6.5–8.5 for microbial activity, making pH adjustment chemicals essential for both primary and secondary treatment.

Soda ash (sodium carbonate) is occasionally used where both pH elevation and alkalinity addition are needed to buffer against acid coagulant consumption. Potassium hydroxide (caustic potash) serves niche applications in food and pharma ETPs where sodium ion addition is undesirable.

Biological treatment in activated sludge systems requires nutrient supplementation when effluent BOD is high but nitrogen and phosphorus are insufficient for microbial growth. Urea and DAP (diammonium phosphate) are dosed to maintain C:N:P ratios of approximately 100:5:1. Bacterial culture powders and liquids seed new aeration tanks or recover systems after shock loads, toxic events or seasonal shutdowns.

Tertiary treatment chemicals address residual colour, odour, trace organics and disinfection. Activated carbon (granular and powder) adsorbs residual dye molecules, phenols and organic compounds that pass through primary and biological stages. Sodium hypochlorite provides effluent disinfection before discharge or reuse, particularly for effluent directed to horticulture, toilet flushing or cooling tower make-up.

Defoamers control foam in aeration tanks, clarifiers and equalisation tanks — common in textile scouring effluent, food processing wastewater and chemical plant discharge. Silicone and non-silicone defoamer formulations are selected based on compatibility with downstream biological treatment. Filter sand and media support tertiary filtration where TSS limits require polishing beyond clarifier settling.

CPCB general standards for inland surface water discharge require pH 5.5–9.0, BOD ≤ 30 mg/L, COD ≤ 250 mg/L, TSS ≤ 100 mg/L and colour ≤ 100 Pt-Co (for textile effluent). State boards in Gujarat, Maharashtra, Tamil Nadu and Karnataka may impose stricter limits, particularly for CETP member industries. Chemical dosing must be optimised to meet these limits at minimum cost — over-dosing wastes chemicals and generates excess sludge, while under-dosing causes compliance failures and penalty notices.

Jar testing is the gold standard for dose optimisation. Collect a representative effluent sample, test five or more coagulant dose levels in graduated jars, stir to simulate plant mixing conditions, settle for 30–60 minutes and measure supernatant turbidity, colour and pH. Repeat monthly or whenever raw effluent characteristics change — which happens frequently in textile mills when dye recipes change between production batches.

Maintain 2–4 weeks of coagulant and polyelectrolyte inventory as these are the highest-volume ETP chemicals. pH adjusters (caustic soda, lime, acid) should be stocked based on daily consumption logs. Specialty chemicals (activated carbon, defoamer, bacterial culture) can be ordered on shorter lead times. Consolidate procurement with a single supplier like Drashti Chemicals to simplify GST invoicing, COA traceability and technical support.

Verify every batch comes with Certificate of Analysis (COA) showing key parameters — for PAC: Al2O3 content, basicity, iron content and insolubles; for alum: Al2O3, iron content and pH of 1% solution; for polyelectrolytes: charge type, molecular weight and viscosity. Request MSDS for all chemicals and ensure your plant has appropriate storage, PPE and spill response equipment.

Evaluate packaging options against your handling capacity. Coagulants and lime are typically supplied in 25–50 kg HDPE bags. Caustic soda is available as lye in HDPE drums (50–200 kg) or as flakes/prills in bags. Liquid chemicals (ferric chloride, sodium hypochlorite, sulphuric acid) come in HDPE drums or tanker loads for large consumers. Minimum order quantity at Drashti Chemicals is 50 kg for most products.

Choose suppliers with pan-India delivery capability, responsive technical support for jar testing and dose optimisation, and experience in your industry segment. A Gujarat-based supplier with proximity to Surat, Ahmedabad, Vapi and Vadodara industrial clusters offers logistics advantages and faster on-site support for CETP and standalone ETP operators across western India.

ETP chemical demand and dosing requirements change seasonally in many parts of India. Monsoon runoff dilutes effluent but increases inlet flow volume, requiring higher absolute chemical consumption even if mg/L dose stays constant. Summer heat increases biological activity in aeration tanks but can degrade chlorine-based disinfectants faster in storage. Winter cold reduces alum coagulation efficiency in northern plants — PAC powder is less affected by temperature and may be preferred for year-round consistency.

Industry-specific effluent profiles dictate chemical program design. Textile ETPs prioritise colour removal coagulants (PAC, ferric chloride) and anionic polyelectrolytes. Food and dairy ETPs focus on BOD reduction with nutrient supplementation and defoamers for high-fat waste streams. Pharmaceutical ETPs require careful coagulant selection to avoid interfering with active pharmaceutical ingredient (API) discharge limits. Metal finishing ETPs need ferric chloride or lime for heavy metal precipitation alongside standard coagulation chemicals.

Document your chemical consumption monthly and correlate with discharge quality test results. Trends in rising coagulant dose without worsening inlet quality may indicate coagulant batch quality variation, equipment calibration drift or changing effluent composition from production changes. Regular supplier review meetings with documented COA comparison help catch quality issues before they cause compliance failures.