Water is an invaluable and essential resource for human life and for the environment, as well as an economic sector of growing importance for Europe. However, European water is under increasing pressure from the continuous growth in demand and from pollution derived from human activity. Moreover, fast emerging factors, such as the accelerating climate change, pose major challenges for water management across the EU.
In order to tackle these challenges several directives have been implemented within the European Union during the past decades, such as the Urban Wastewater Treatment Directive (UWTD, 91/271/EEC) or the more recent Water Framework Directive (WFD, 2000/60/EC), so as to manage and protect the European water heritage from any threat.
These directives require coordination of different EU policies and establish (amongst other things) the maximum level of pollutants allowed in wastewater discharged to natural water courses. Therefore most industries need to treat their wastewater residues prior to their discharge to the environment.
For industries generating vast amounts of wastewater, such as the food and beverage (F&B) industries, this management of their residues required to comply with the EU directives implies direct costs which can be very high. This is particularly critical for a subsector within the F&B industry devoted to the production of canned fish, meat processing, pickled vegetables, leather tanneries, aquaculture and all kind of brined products, as they generate saline wastewater.
This kind of wastewater, with high concentrations of biodegradable organic matter, suspended solids, nutrients (mainly nitrogen and phosphorus) and salt (concentrations up to 15%), is extremely difficult and expensive to treat, and its discharge represents a major threat to the environment e.g. salinity can cause eutrophication of water, and salinization and sodification of the soil. For SMEs within this subsector, which represents 5% of the total F&B industry (i.e. over 15,000 companies with a combined turnover of ~€63.7 billion), the treatment of their wastewater can represent up to 14% of their annual turnover (an estimated cost of ~€4.46 billion across the EC F&B sector).
The treatment of saline wastewater (>=2 g/L) in presence of organic content (BOD >=1 g/L) represents a challenge for many industrial sectors, such as food processing and leather industries, but also, for example, in land-based aquaculture. The discharge of such wastewater without prior treatment adversely affects the environment causing severe damage by contamination of soil, surface and groundwater. In this context, the variability in the physico-chemical properties of saline wastewater in presence of organic content represents one of the main challenges for their treatment, something which affects both feasibility and economic viability. The presence of micro-pollutants (e.g. pesticides) and heavy metals further complicates treatment, raises costs (i.e. downstream municipal operators may charge extra as EC legislation becomes stricter – e.g. Drinking Water Directive) and impacts on potential product streams that could otherwise result from the valorisation of the recovered substances (e.g. algae used as animal feed cannot have heavy metals in it).