Washwater Treatment Targets

Keeping Your Eye on Reasonable Washwater Treatment Targets

Maintaining optimal water quality throughout the recycling process is crucial for effective cleaning, equipment longevity, and environmental compliance. The following washwater treatment targets are parameters at various stages of the water recycling process for wash racks. It is meant as a rough guide only.

pH Levels

pH is a critical parameter throughout the recycling process due to its impact on chemical reactions, equipment corrosion, and cleaning efficacy.

1. Initial Wash Water:
– Typical range: 6.0 – 9.0
– Influenced by detergents and contaminants from vehicles

2. After pH Adjustment:
– Target range: 6.5 – 8.5
– Adjusted using sodium hydroxide (to increase pH) or hydrochloric acid (to decrease pH)

3. Final Recycled Water:
– Ideal range: 7.0 – 8.0
– Ensures optimal cleaning performance and minimizes equipment wear

Importance: Maintaining proper pH prevents corrosion of metal components in both the recycling system and the vehicles being washed. It also ensures optimal performance of cleaning agents and supports effective disinfection.

Total Suspended Solids (TSS)

TSS refers to particles that are larger than 2 microns found in the water column.

1. Raw Wash Water:
– Typical range: 100 – 1000 mg/L
– Varies greatly depending on the type of vehicles being washed

2. After Sedimentation and Coarse Filtration:
– Target: < 100 mg/L

3. After Advanced Filtration:
– Target: < 20 mg/L

4. Final Recycled Water:
– Ideal: < 5 mg/L

Importance: Reducing TSS improves water clarity, reduces wear on pumps and nozzles, and enhances the effectiveness of disinfection processes.

Total Dissolved Solids (TDS)

TDS includes all inorganic and organic substances dissolved in the water.

1. Initial Wash Water:
– Typical range: 500 – 2000 mg/L
– Higher in areas with hard water or when salt-laden vehicles are washed

2. After Ion Exchange or Reverse Osmosis:
– Target: < 500 mg/L

3. Final Recycled Water:
– Ideal: < 200 mg/L for general washing
– < 50 mg/L for spot-free rinsing applications

Importance: Controlling TDS prevents scale formation in the recycling system and on washed vehicles. Low TDS levels are crucial for spot-free drying and preventing mineral deposits on vehicles.

Chemical Oxygen Demand (COD)

COD indicates the amount of organic compounds in water.

1. Raw Wash Water:
– Typical range: 300 – 1000 mg/L

2. After Biological Treatment (if applicable):
– Target: < 150 mg/L

3. Final Recycled Water:
– Ideal: < 100 mg/L

Importance: Reducing COD prevents bacterial growth, odors, and foaming in the recycled water.

Oil and Grease

1. Initial Wash Water:
– Can range from 50 – 500 mg/L depending on vehicles washed

2. After Oil/Water Separation:
– Target: < 50 mg/L

3. Final Recycled Water:
– Ideal: < 10 mg/L Importance: Removing oil and grease improves water clarity, prevents clogging of filters, and ensures effective cleaning.

 Microbiological Parameters

1. Total Coliform Bacteria: – Raw water: Can be > 1000 CFU/100mL
– After disinfection: < 1 CFU/100mL 2. Legionella: – Must be non-detectable in recycled water Importance: Controlling microbial growth prevents health hazards, odors, and biofilm formation in the recycling system. Dissolved Oxygen (DO) 1. Target in aeration tank: > 2 mg/L

2. Ideal in final recycled water: 4 – 6 mg/L

Importance: Adequate DO levels prevent anaerobic conditions, reduce odors, and support aerobic biological processes that break down contaminants.

Turbidity

1. Raw Wash Water:
– Can exceed 100 NTU

2. After Filtration:
– Target: < 5 NTU

3. Final Recycled Water:
– Ideal: < 1 NTU for optimal clarity

Importance: Low turbidity improves the visual quality of the wash, enhances disinfection effectiveness, and reduces wear on system components.

Conclusion

Maintaining these water quality parameters within their target ranges is essential for the effective operation of a water recycling system in industrial wash racks. Regular monitoring and adjustment of these parameters ensure optimal cleaning performance, system longevity, and environmental compliance. The specific targets may vary based on local regulations and the particular requirements of the wash rack operation.