Wastewater Reuse in Industry

Industrial water consumption makes up 22% of global water use (UNWATER 2012). In 2009, European and North American industrial water use accounted for half of their total water use, whereas in developing nations industrial water use ranges from 4-12% of national water use. As industrialisation in developing nations increases, industrial water use could potentially increase by a factor of five, strongly increasing pressure on water resources (WWAP 2009).

One method of curbing water consumption in industry is through the reuse of wastewater. Reducing the amount of water use by industries can lower water withdrawals from local water sources thus increasing water availability and improving community relations, increasing productivity per water input, lowering waste water discharges and their pollutant load, reducing thermal energy consumption and potentially processing cost.

Wastewater reuse in industry can take place within a business or between businesses and has the potential to reduce costs for businesses both on water bills as well as wastewater treatment. Depending on the contaminants present in wastewater and its future reuse, it can either be directly reused, or treated and reused (recycled).

Direct Reuse within a Business

A business can directly reuse wastewater that is clean enough for the purpose for which it is being reused. Process water is produced by industrial processes such as cooling and heating, and often contains few contaminants after use. In industry, both rainwater and process water can be reused for purposes such as:

• Irrigation (see also WHO guidelines on reuse of wastewater in agriculture)
• Washing
• pH adjustment
• Fire protection

For more information about directly reusing water within a business, see reuse within a business.

Direct Reuse between Businesses

Direct wastewater reuse can also be practiced between businesses. The exchange of waste products for the mutual benefit of two or more businesses is also known as “industrial symbiosis.” In industrial symbiosis, all members profit from the arrangement by either reducing the inputs necessary in their production process (i.e. water, organic material) or by reducing the costs of wastewater treatment.

Industrial symbiosis can take place in three ways:

• Exchange of by-products,
• Sharing the management of utilities, and
• Sharing ancillary services.

Some examples of direct reuse of wastewater in industrial symbiosis include:

• Exchange of process water from one business to another andsubsequent direct reuse as described above (such as irrigation, washing pH adjustment, fire protection, etc.)
• Reuse of organic waste or wastewater for largescale biogas production through anaerobic digestion, which can then be used to generate electricity)
• Reuse of wastewater for aquaculture of plants or animals
• Short rotation plantations
• Etc.

For more information on industrial symbiosis, see reuse between businesses.

Treat and Reuse (Recycling)

If wastewater is not suitable for direct reuse, decentralised wastewater treatment systems may be employed to reduce the level of contaminants to a level that is safe for reuse. This can be done within a business for its own reuse, or between businesses. Wastewater treatment and reuse between businesses can lower the costs of treatment for all businesses, thus making reuse options more economical.

Some possibilities for decentralised wastewater treatment systems include:

• Waste stabilisation ponds
• Aerated ponds
• Constructed wetlands (see free-surface, horizontal, vertical, and hybrid constructed wetlands)
• Non planted filters
• Technologies making use of anaerobic digestion such as: anaerobic baffled reactors, biogas settlers, and anaerobic digestion
• More high-tech options: activated sludge, membrane bioreactors, advanced oxidation processes, ozonation, activated carbon, rotating biological contactors, and anammox

The choice for the specific treatment option depends on the quality required at the end. If water is to be used for gardening, a natural treatment such as a free surface constructed wetland where some nutrients remain in the water may be suitable, if space is available and loss of water through evapotranspiration is not important.

Some advanced options like membrane filtration and activated carbon may even produce treated wastewater of a better quality than freshwater, so that the treated wastewater can even be reused as process water where high water quality is required.

To ensure that the quality of the (pre-treated) wastewater or greywater is appropriate for reuse, the water quality should be tested for chemical composition, including pH, nutrient concentrations, pathogens, etc.

• Businesses can save money on water bills and wastewater treatment by reusing process water.
• Industrial symbiosis is mutually beneficial to all businesses involved by reducing input costs or wastewater treatment costs.
• Implementing reuse or treat-and-reuse measures requires initial investment which may be costly (depending on modifications required and technology).