Hardware Processing Wastewater Treatment
1. Typical Water Quality and Diversion Recommendations
Common Sources and Pollutants:
Cutting/Grinding Fluids: Emulsified Oil, Surfactants, COD (800–4000 mg/L), SS, and Trace Metal Ions.
Cleaning/Degreasing: Grease, Phosphate/Silicate Additives, COD, and Surfactants.
Acid/Alkaline Cleaning: Extreme pH, Fe²⁺/Fe³⁺, Zn²⁺/Ni²⁺/Cu²⁺, and Cr⁶⁺ (if electroplating/passivation is performed).
Polishing/Grinding: High SS, Metal Powder.
Cooling Circulating Water Wastewater: SS, Small Amounts of Oil and Chemicals.
Strong diversion:
① Chromium (Cr⁶⁺) → Dedicated reduction line followed by co-flow; ② High-oil emulsion → First oil-water/demulsification; ③ High-metal content → First precipitation/capture; ④ Normal organic wastewater → Can proceed to biochemical treatment.
2. Typical Process Combinations
A. Primarily “emulsified oil + COD” (no or trace heavy metals)
Process:
Homogenization → Demulsification (acid adjustment/inorganic polymer) → Flocculation → Air flotation (DAF) / Ultrafiltration (UF) → A/O or MBR → Sand filtration + activated carbon → Compliance/reuse
Key Parameters:
Equalization tank HRT 6–12 hours, pH 6.5–7.5 (can be lowered to 4–5 before demulsification and then adjusted back).
Flocculation: PAC/FeCl₃ 80–600 mg/L + anion PAM 1–5 mg/L; Agitation G·t: Fast 300 s⁻¹ × 1–2 min, Slow 40 s⁻¹ × 10–20 min.
DAF: Reflux ratio 30–50%, Dissolved air pressure 0.4–0.6 MPa, Air-to-water ratio 0.03–0.06.
UF (for emulsified oil treatment): Cutoff 10–100 kDa, Design flux 20–60 L·m⁻²·h⁻¹.
Biochemical: A/O or MBR, MLSS 6–10 g/L (MBR), SRT 20–40 d, Dissolved oxygen 1.5–2.5 mg/L.
Expected: Oil <10 mg/L, SS <20–30 mg/L, COD 60–100 mg/L (depending on the reference point).
B. Focus on “heavy metals + a small amount of oil” (before and after polishing/cleaning/partial electroplating)
Process:
Diversion → pH adjustment (hydroxide precipitation) → flocculation and precipitation → metal scavenger (DTC/TMT/sulfide) fine reduction → filtration (sand filtration/cartridge filtration) → activated carbon → meet standards
(If high levels of organic matter are present, add Fenton filter at the front end or biochemical/activated carbon at the back end.)
Key Parameters:
Hydroxide precipitation: For common metals (Cu/Ni/Zn), control the pH at 9.5–10.5; settle for 60–120 minutes.
Hexavalent chromium: First reduce (NaHSO₃/ferrous salt, pH 2–3), then adjust the pH to 7.5–8.5 for precipitation.
Complexed metals: Preferentially decompose the complex (UV-Fenton/pH swing/oxidation), or directly polish to trace levels with DTC/TMT (pH 7–9).
Expected: Cr⁶⁺ <0.1 mg/L; total Cr, Cu, Ni, and Zn typically <0.5–1.0 mg/L (depending on the standard).
C. High Difficulty (High COD, Strong Emulsification, Complex Complexation)
Combined Enhancement:
Pretreatment (Emulsion Demulsification + DAF/UF) → Fenton (·OH) (pH 2.5–3.5, 30–60 min, H₂O₂:Fe²⁺ molar ratio 10–20:1) → Neutralization and Flocculation → Biochemical (MBR/MBBR) → Deep (Activated Carbon/RO) → Reuse/Zero Discharge
3. Key Units and Design Cheat Sheet
Oil-Water Separation: Gravity/API is effective for free oil; emulsified oil requires “acidification + salting out + DAF/UF.”
Coagulant Selection: Phosphorus-containing/high-surfactant → Fe-based systems are more stable; pH 6.5–8.0 PAC is generally suitable.
Biochemical Feasibility: The cutting fluid must be fully demulsified and detoxified (B/C ≥ 0.3 for greater stability).
Deep metal removal: First, perform extensive precipitation, then “collector polishing” to avoid relying solely on collectors, which results in high chemical consumption and large sludge volumes.
Sludge disposal: Oily/metal-containing sludge is often hazardous waste; filter press moisture content is 70–80%, and the cost per ton of sludge is calculated with the disposal company.
Online control: pH, ORP (Cr⁶⁺ reduction/sulfide precipitation), turbidity/SS, COD (rapid method), and heavy metals (XRF/weekly laboratory testing).
4. Two typical process diagrams
(1) Emulsified oil as the main process:
Homogenization adjustment → Demulsification/coagulation → DAF/UF → A/O or MBR → Sand filtration → Activated carbon → Compliance/reuse
(2) Heavy metals as the main process (including Cr⁶⁺):
Diversion → Cr⁶⁺ reduction → pH↑ hydroxide precipitation → flocculation precipitation → deep removal of collector → filtration → activated carbon → discharge
5. Minimum information required for project approval/quotation
Daily average/peak flow rate (m³/d, m³/h), available floor space and floor height;
Influent index range (COD, BOD₅, SS, dynamic/static oil, pH, Cu/Ni/Zn/Cr⁶⁺, etc.), presence of chelating agents/surfactants;
Whether discharge or reuse is required (recycled water quality targets);
Automation and O&M preferences (chemical dosing, offline/online monitoring).