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Standardized Dosing Guidelines for Wastewater Treatment Chemicals: Optimize Proportioning for Stable Compliance & Cost Efficiency
2026-06-06
Standard Dosing Sequence
pH Adjustment → PAC Inorganic Coagulant → PAM Organic Flocculant → Functional Agents (Decolorization, COD Removal, Heavy Metal Capturing)
1. Core Coagulation & Flocculant Specifications
1.1 PAC (Polyaluminum Chloride)
Application: Municipal sewage, sand washing, textile and general industrial wastewater for removing suspended solids and colloids.
Preparation: Solid PAC diluted to 5%–10% (15–30 min stirring); liquid PAC diluted to 3%–5%.
Optimal pH: 6.5–8.5.
Dosage: 50–200 g/ton raw water; increase for high-turbidity water based on jar tests.
Dosing interval: 30 seconds to 3 minutes after PAC before adding PAM for full floc formation.
1.2 PAM (Polyacrylamide)
Concentration & Application
Anionic / Nonionic PAM (0.1%–0.3%): Sedimentation for sand washing and dyeing wastewater. Cationic PAM (0.05%–0.1%): Organic wastewater treatment and sludge dewatering.
Operation notes: Slowly dissolve PAM in room-temperature water (≤60℃) to avoid agglomeration and molecular chain damage.
Optimal ratio: PAC : PAM = 30–50:1 (excess PAM causes residual turbidity).
Shelf life: Anionic ≤24h; Cationic ≤12h.
2. Functional Agent Operation Standards
2.1 pH Regulators (Soda Flakes / Dilute Sulfuric Acid)
Preparation: Prepare 20%–25% soda flake solution with slow batch dissolution to prevent splashing.
Standard pH range: 7.0–8.0 for general wastewater; 8.5–10.5 for heavy metal wastewater for precipitation treatment.
Alkaline water adjustment: Gradually add dilute sulfuric acid to lower over-alkaline water to pH 6.5–8.5 before PAC dosing. Avoid sharp pH drops. Increase PAC dosage by 5%–15% to offset reduced coagulation efficiency in high-alkaline conditions.
Chelating anti-scaling & stubborn scale solution: High-hardness and alkaline circulating water easily forms calcium/magnesium scale that blocks pipelines and weakens treatment performance. Relying only on acid cleaning cannot prevent re-scaling. Add chelating scale inhibitors in advance (pH 6.0–9.0) to stabilize metal ions, suppress crystallization, and achieve long-term anti-scaling protection via continuous trace dosing.
2.2 Heavy Metal Capturing Agent
Application: Electroplating and surface treatment wastewater containing nickel, copper, zinc and chromium.
Preparation: Solid agent diluted to 10%; liquid agent used directly.
Process: Adjust pH to 8.5–10.5 → Add capturing agent and stir 5–10 min → Dose PAC & PAM for sedimentation.
2.3 Decolorizing, COD & Ammonia Nitrogen Removal Agents
Oxidative decolorization: For common reactive dyes. Prepare 5%–10% solution, break chromophores first, then apply PAC/PAM flocculation.
Reductive decolorization (refractory color): For stable vat and sulfur dyes. React at pH 6.0–8.0 for 10–15 minutes to decompose macromolecular colored structures into colorless small molecules. Use staged dosing for heavily colored wastewater to eliminate residual chroma.
COD & Ammonia Nitrogen removal: 10% solution for solid agents; liquid agents direct dosing. Optimal pH 7–9, reaction time 10–15 minutes. Fine-tune dosage by water sample testing.
3. Sludge Dewatering & Special Working Condition Adjustments
Sludge dewatering: Use 0.08% cationic PAM at 0.1%–0.5% of sludge dry weight for screw and plate-frame filter presses to improve sludge dryness.
Low-temperature adjustment: Below 10℃, slow hydrolysis and flocculation require a 20% increase in total chemical dosage.
Biochemical phosphorus supplementation & bacteria cultivation: Maintain microbial C:N:P = 100:5:1 for low-phosphorus wastewater and inactive sludge systems. Prepare 10%–15% phosphate solution for continuous dosing to balance nutrients. For new startup or sludge collapse systems, supplement carbon and phosphorus, stabilize DO and pH 7.0–8.0, and avoid impact load to restore bioactivity. Avoid over-dosing to prevent total phosphorus exceedance.
General principle: All dosing must follow lab test → pilot test → formal dosing, with dynamic adjustment according to fluctuating raw water quality to save chemical costs.
4. Conclusion
Standardized and refined chemical dosing ensures efficient removal of suspended solids, chroma, COD, ammonia nitrogen and heavy metals, enabling long-term stable effluent compliance while reducing operational costs. Customized water treatment solutions and professional on-site commissioning help industrial enterprises achieve stable, low-cost and environmentally compliant wastewater operation.