Laundry wastewater treatment plant
Target
During the cleaning of laundry, a highly polluted wastewater is discharged into municipal sewer network. Wile the polluted water is mixed with a large amount of conventional wastewater in case of domestic user, for commercial or industrial cleaning the effluent is concentrated at a single point and it exceeds the legislation limits. For this reason, wastewater con not to be discharged directly into the municipal wastewater treatment plant.
When the system does not discharge into the public sewer a high performance wastewater treatment is high recommended.
Pollutants
Effluent characteristics depend on washing machine and its use.
Except for domestic users, there are two principal kind of laundries type : commercial and industrial.
Commercial laundries often work in self-service mode (no personal needed) wile industrial laundries are specialized in large users service such as hotels, restaurants, canteens, hospitals, nursing homes etc. for washing table linen (tablecloths and napkins), linen, working clothes or hospital.
Laundries in the textile sector are very special and difficult to treat because they produce different types of pollutants depending on the production process.
Water consumption depends on laundry machine and washing process and it can be calculated considering the quantity of water (litres) used to wash each kilogram (or cubic meters) of laundry.
Effluent often has different characteristics depending on the industrial process, products for cleaning and washing machine. Typical values are shown as follows:
Commercial laundry
- Temperature: 38°C
- pH: 7 – 8
- COD: 5000-1000 mg/l
- BOD: 250-500 mg/l
- Suspended solids: 400-1200 mg/l
- Grease: 400-600 mg/l
- Surfactants: 50-80 mg/l
- Phosphate (PO4): 250-300 mg/l
- Water consumption: 15 litre per kg of cloth.
Industrial laundry
- Temperature: 45°C
- pH: 10
- COD: 8000-12000 mg/l
- BOD: 5000-7000 mg/l
- Suspended solids: 1500-2000 mg/l
- Grease: 1500-32000 mg/l
- Tensioattivi: 100-600 mg/l
- Phosphate (PO4): 300-200 mg/l
- Water consumption: 20-30 litre per kg of cloth
Wastewater produced by an industrial washers contains sand and grit, lint, free and emulsified oil and grease, heavy metals and volatile organic compounds (VOC’s)
Laundry effluent has in the past, low biodegradability because of the extensive use of synthetic detergents.
Recently, however, biodegradable products are widely used due to legislation and to an increased environmental awareness.
These new bio detergents preserve environment and allow a successful use of biological methods for the laundry effluent treatment.
System layout
Biological treatment is the most complete method and it gets a good quality of the effluent.
Normal activated sludge system or biological filtration are used.
Trickling filters give good results for industrial effluent while the activated sludge process is better for mixed wastewater with a significant percentage of domestic wastewater.
The systems can be combined with a lifting/equalisation compartment to get the best results to obtain a higher resistance to load and flow peaks.
Laundry wastewater treatment layout nitro-denitro
The increasing use of detergents and biodegradable products makes possible the extended use of biological wastewater treatment systems as activated sludge plant, MBR.
The typical configuration is made up by a primary treatment (as screen), primary sedimentation, equalization chamber, biological denitrification, activated sludge reactor and a secondary sedimentation. Tertiary treatment, as disinfection, can follow depending on the requested of effluent’s quality.
Laundry wastewater treatment layout Membrane bioreactor MBR and nitro-denitro
Biological section can be a conventional activated sludge (constant flow), sequencing batch reactor (SBR) or a bio membrane reactor (MBR). MBR process allows to reuse water with a considerable reduction of drinking water consumption that allows a substantial saving of money and environmental protection.
Laundry wastewater treatment layout tricking filter and activated sludge.
Physical chemical treatments often provide good results for laundry effluent not mixed with domestic wastewater.
Most common process is the coagulation by means of aluminium salts, such as aluminium sulphate and lime, after neutralization reaction with sulphuric acid.
A well-functioning system can get a COD removal efficiency about 85% and suspended solids reduction of about 94%.
Good results can be achieved by activated carbon adsorption or by the separation of the foam (foam fraction), also in combined with biomass with immobilized biomass systems (biofiltration).
Note
The right choice depends on effluent characteristics and user size.
Physical-chemical plants has a high efficiency but even high operating and maintenance costs (reagent). Purification in biological treatment is carried out by microorganism but it requires higher volume and constant monitoring of the biological parameters.
