Process Scheme for Reducing Colloidal Pollution in Coal Chemical Wastewater Using RO Membrane Technology
10 Jun 2025
Process Scheme for Reducing Colloidal Pollution in Coal Chemical Wastewater via RO Membrane Technology
This document outlines a specialized RO membrane process scheme designed to reduce colloidal pollution in coal chemical wastewater, targeting the characteristics of high suspended solids and high colloidal content (typical COD 2000-8000 mg/L, colloidal content>50 mg/L). The core of the process lies in enhancing colloidal interception and anti-fouling design.
Process Design Objectives
Core Issue: Coal powder, tar, and polycyclic aromatic hydrocarbons in coal chemical wastewater tend to cause irreversible fouling of RO membranes.
Solution Approach: Through a four-stage colloidal interception system + optimization of the anti-fouling RO system.
Expected Results: Extend the RO membrane cleaning cycle from 7 days to over 30 days, with a recovery rate of ≥75%.
Anti-Colloidal Pollution RO Process Flow
A[Equalization Tank] --> B[Hydrocyclone Oil Remover] --> C[Coagulation Reaction Tank] --> D[Magnetic Loading Sedimentation] --> E[Multi-Media Filter] --> F[Ultrafiltration (UF) System] --> G[Security Filter] --> H[Anti-Fouling RO Unit] --> I[RO Permeate Reuse] --> J[Concentrate Advanced Treatment] Four-stage colloidal interception B-->C-->D-->E-->F end
Key Process Unit Design Description
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Colloidal Targeted Removal System (Core of Pre-treatment)
Unit
Function and Technical Parameters
Hydrocyclone Oil Remover
Removes oil droplets and heavy particles larger than 50μm, with an oil removal rate of >90% (oil controlled at <10mg/L)
Compound Coagulation System
Adds PAC (100ppm) + PFS (50ppm) + anionic PAM (2ppm) to destabilize colloids
Magnetic Loading Sedimentation
Adds magnetic powder (2000GS), with a settling speed of 40m/h, SS removal >95%, effluent SS ≤10mg/L
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In-Depth Filtration Assurance
Multi-Media Filter:
Layers: anthracite (1.2mm) + quartz sand (0.6mm) + magnetite (0.3mm)
Filter velocity ≤10m/h, backwash expansion rate 30%
Ultrafiltration (UF) System:
PVDF hollow fiber membranes with an outer pressure design, pore size 0.03μm
Crossflow design (flow velocity 3m/s), controlling SDI15 ≤3
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Anti-Fouling RO System Design
Optimization Item
Technical Solution
Membrane Selection
Wide channel anti-fouling membrane (e.g., DOW FILMTEC™ BW30-365FR, channel width 34mil)
Channel Design
Single-stage two-section (7:3 arrangement), with a booster pump added between sections to balance flux
Anti-Fouling Operation Strategy
① Periodic pulse flushing (every 2h for 30s) ② Concentrate recycle ratio 20-30%
Chemical Protection
Combination of scale inhibitor (iminodiacetic acid) and non-oxidizing biocide (DBNPA) to control bio-colloidal growth
Core Technology for Colloidal Pollution Control
Magnetic loading + compound coagulation
A Fe₃O₄@PAC adsorption layer is formed on the surface of magnetic powder to specifically remove coal powder colloids
Destabilize the stability of tar-colloid complexes
Enhanced Ultrafiltration Pre-treatment
A 5μm bag filter is installed before the UF to protect the ultrafiltration membrane
The chemical cleaning cycle of UF is extended to 60 days (acid cleaning + alkali cleaning + surfactant)
Operation Parameter Control Standards
Parameter
Control Limit
Exceedance Response Measures
RO feed water SDI15
≤3.0
Check UF integrity or increase backwash frequency
Colloidal concentration
≤5 mg/L
Increase coagulant dosage by 10-20%
Turbidity
≤0.5 NTU
Check magnetic loading sedimentation effect
Transmembrane pressure difference
<1.5 MPa
Initiate chemical cleaning procedure
Recovery rate
75±5%
Adjust concentrate recycle valve
Expected Treatment Effect Comparison
Indicator
Raw Water Typical Value
RO Feed Water Before Improvement
RO Feed Water with This Process
Colloidal content
50-200 mg/L
15-30 mg/L
2-5 mg/L
Oil content
100-500 mg/L
20-50 mg/L
<5 mg/L
COD
5000±2000 mg/L
300±50 mg/L
150±30 mg/L
RO Membrane Life
1-1.5 years
≥3 years
Cost and Economics
Item
Before Improvement
This Process
Savings
Chemical cost per ton of water
2.8 yuan/ton
3.5 yuan/ton
-0.7 yuan/ton
Membrane replacement cost
320,000 yuan/year
120,000 yuan/year
200,000 yuan/year
Cleaning energy consumption
180,000 yuan/year
50,000 yuan/year
130,000 yuan/year
Comprehensive cost per ton of water
6.3 yuan/ton
5.1 yuan/ton
↓19%
Note: Based on a scale of 10,000 tons/day, the investment payback period is approximately 2.8 years.
Engineering Implementation Key Points
Coagulant Selection: Adjust the PAC/PFS ratio according to the differences in coal types (lignite/anthracite)
Magnetic Powder Recovery Rate: Must be >99.5% (using a matrix-type magnetic separator)
Zero Benchmark Installation: The RO membrane shell adopts a 180° rotation design to avoid installation stress damage
Smart Monitoring: Install a colloidal online monitor (Lumryz 3000) to link with the dosing system
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