Quick answer: Reverse osmosis brine disposal manages the concentrated reject stream from RO systems. The main routes are surface water discharge, sewer discharge, deep well injection, evaporation ponds and further concentration toward zero liquid discharge. Selection depends on brine volume and chemistry, site location, discharge permits and cost, and in the Netherlands and EU discharge is tightly regulated.
Frequently asked questions
What are the disposal options for RO concentrate?
The main options are surface water discharge, sewer discharge, deep well injection, evaporation ponds and further concentration toward zero liquid discharge. Discharge routes are usually cheapest where capacity and permits allow, while evaporation and ZLD suit sites where discharge is unavailable or capped, at higher cost.
Can RO brine be discharged to the sewer?
Sometimes, for small volumes near a municipal sewer, but salinity passes largely untreated through the works and can breach its own permit. Utilities therefore cap the volume and strength accepted and charge tariffs. You must confirm the works has salinity headroom before relying on this route.
Is deep well injection used for RO brine in the Netherlands?
Rarely. Deep well injection needs a suitable, isolated deep formation and carries induced-seismicity and groundwater risks. In the Netherlands and EU its applicability is very limited by subsurface protection rules and public sensitivity to induced earthquakes, so discharge or concentration routes are generally preferred.
What is zero liquid discharge and when is it needed?
Zero liquid discharge further concentrates brine with membrane and thermal steps until only solids and recovered water remain, eliminating liquid disposal. It is needed where discharge is impossible or capped, water is scarce, or corporate targets demand it. It offers the lowest discharge but the highest energy and capital cost.
How is RO brine disposal permitted in the EU?
Under the EU Water Framework Directive and, for larger plants, the Industrial Emissions Directive with BAT-BREF. In the Netherlands, direct discharge to surface water is permitted by the relevant Waterschap or Rijkswaterstaat, indirect discharge to sewer is regulated separately, and substances of very high concern fall under the ZZS framework. Chloride is often the binding local limit.
Sources and further reading
- European Commission, EU Water Framework Directive (Directive 2000/60/EC)
- European Commission, Industrial Emissions Directive and BAT reference documents (BREF)
- Rijkswaterstaat, guidance on discharges to state waters
- Unie van Waterschappen, information on discharge permits
- Rijksoverheid, ZZS (Zeer Zorgwekkende Stoffen) framework
Talk to Brine Consulting for an independent, vendor-neutral review of your RO concentrate disposal options.
Written by the Brine Consulting advisory team. The Brine Consulting advisory practice includes Prof. Basel Abusharkh, a specialist in brine valorization, ZLD and high-recovery desalination, and Osis G. Kalache, P.Eng., a senior wastewater process engineer with over 17 years in industrial treatment and process optimization. Meet our experts.