Wash water refers to the wastewater produced during industrial cleaning processes. These water streams typically contain dissolved and undissolved impurities originating from the cleaned surfaces, products or equipment. In industrial water treatment, the treatment of wash water plays a crucial role in minimizing environmental impact, complying with legal discharge limits and recycling the water for reuse.
Table of contents
Sources and composition of wash water
The composition of the wash water is highly dependent on the respective applications and industries:
Industrial sources
- Food and beverage industry:
Cleaning of production lines, containers and surfaces leads to wash water with high concentrations of organic substances, fats and oils. - Metalworking industry:
Wash water from the cleaning of workpieces contains oil, metal chips, cooling lubricants and heavy metals. - Chemical industry:
Residues of chemicals, surfactants and solvents are typical components. - Automotive industry:
Wash water from paint shops or body washing systems contains paint residues, surfactants and particles. - Textile industry:
High organic pollution from dyes, surfactants and fibers from washing processes.
Typical impurities
- Organic substances: oils, fats, protein and sugar.
- Particles: Sand, dust, fibers and metal shavings.
- Chemicals: surfactants, acids, alkalis, solvents and heavy metals.
- Biological contamination: Microorganisms from contaminated surfaces or raw materials.
Challenges in the treatment of wash water
Due to its heterogeneous composition, wash water places special demands on water treatment:
High variability:
The loads can vary greatly depending on the cleaning process and application sector.High content of dissolved and undissolved substances:
Particles, oils and chemical residues often require multi-stage treatment processes.Fluctuating pH value:
The use of acids or alkalis during cleaning results in acidic or alkaline wash water.Legal discharge limits:
Pollutants such as heavy metals, COD, BOD or surfactants must be reduced to a minimum in order to minimize environmental pollution.
Process for treating wash water
Washing water is treated in several steps that are tailored to the specific requirements of the wastewater.
1. mechanical pre-treatment
- Rakes and sieves:
Remove coarse particles such as fibers, metal chips or plastic residues. - Multi-layer filter:
Separates undissolved solids from the wash water. - Oil separator:
Separates free-floating oils and greases to reduce the load on downstream stages.
Photo: Our ALMA FIL multi-layer filters with downstream ALMA ION ion exchanger
2. chemical-physical treatment
- Neutralization:
Adjustment of the pH value by adding acids (e.g. sulphuric acid) or alkalis (e.g. caustic soda). - Precipitation and flocculation:
Use of chemicals such as iron or aluminum salts to remove heavy metals, phosphates or colloidal particles. - Dissolved air flotation (DAF):
Removal of fine suspended solids, COD, oils and fats by microbubbles.
Photo: Our ALMA NeoDAF flotation system with load-proportional dosing of precipitants and flocculants
3. biological treatment
- Activated sludge process:
Degradation of organic loads by aerobic microorganisms. - Biofiltration:
Use of bioactive filters to remove residual contamination, especially before membrane processes. - Anaerobic treatment:
Particularly suitable for wash water with high COD values, e.g. in the food industry, for methane production and COD reduction.
Photo: Our ALMA BioFil Compact biofiltration system for the treatment of organically contaminated wastewater
4. follow-up treatment
- Membrane process:
Use of ultrafiltration or reverse osmosis to remove residual substances and produce recycled water. - Activated carbon adsorption:
Reduction of organic trace substances and removal of surfactants or odorous substances. - UV disinfection:
Inactivation of germs and hygienic safety for reuse.
Photo: Our ALMA OSMO reverse osmosis system for in-house water recycling
Applications of the treated wash water streams
The reuse of wash water is becoming increasingly important in order to reduce costs and conserve resources:
- Circulating water for washing processes:
Reduction of fresh water consumption by recycling treated water. - Cooling water:
Use in cooling circuits after appropriate treatment. - Process water:
Use of the treated wash water for technical applications. - Discharge:
Ensure that the purified wash water complies with the legal discharge limits.
Future prospects for wash water treatment
Automation:
Advances in sensor and control technology enable more precise and efficient treatment.Modular system concepts:
Flexibility in adapting treatment capacities to different loads and volume flows.Combination of technologies:
Integrated approaches that combine chemical-physical, biological and membrane-based processes ensure maximum efficiency.Sustainability:
Increasing environmental requirements and water scarcity make the recycling and recirculation of wash water a central element of modern water treatment.
Conclusion
The treatment of wash water is a complex but indispensable part of modern water and wastewater technology. The targeted use of multi-stage processes allows pollutants to be removed efficiently, legal requirements to be met and valuable water resources to be recycled. The ongoing development of technologies offers industrial companies the opportunity to make their wash water flows more sustainable and cost-efficient.
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