Brine Co-Disposal with Wastewater Effluent

Potential Environmental Impacts
Impact on Wastewater Treatment Plant Operations
Effect on Water Reuse
Costs for Brine Sewer Discharge

Brine discharge to the nearest wastewater system is only suitable for small volumes into large-capacity WWTPs, due to the potential impact of the brine’s high TDS to the WWTP operations. In most countries, brine discharge to a WWTP is regulated by the requirements applicable to industrial discharges of the responsible authority.

Potential Environmental Impacts

Desalination plant discharge to a sanitary sewer could potentially have environmental impacts similar to those of co-discharge of concentrate and WWTP effluent.

Impact on Wastewater Treatment Plant Operations

This brine disposal method is limited by the hydraulic capacity of the WW collection system and the capacity of the WWTP processes.

A WWTP biological treatment process is usually constricted by high salinity (TDS > 3000 mg/L). So the WWTP’s salinity tolerance must be assessed before discharging the desalination plant brine to the sewer. Accounting for the influent TDS being ≥ 1000 mg/L in many facilities located

along the ocean coast, and that the SWRO brine TDS is ≥ 65,000 mg/L, the WWTP’s capacity has to be 30 to 35 times higher than the daily volume of brine discharge so as to maintain the influent TDS concentration

Effect on Water Reuse

If there’s reuse of the WWTP’s effluent, the brine intake is limited by,

its salinity
the concentrations of sodium, chlorides, and boron

These constituents could severely impact the reuse of the WWTP effluent especially if it is used for irrigation due to the treatment processes of a typical WWTP not removing a sizeable amount of these contaminants. Although there are crops and plants that have >1,000 mg/L TDS tolerance, most plants cannot tolerate chloride levels > 250 mg/L. Typical WWTP effluent has chloride levels ≤ 150 mg/L, while SW brine could have > 40,000 mg/L.

Costs for Brine Sewer Discharge

Brine sewer discharge is typically the lowest-cost disposal method, especially if there’s already a wastewater collection system is available near the desalination plant site, and the WWTP can manage the brine intake.

Conditions and therefore costs are site-specific, and the main costs are for the discharge conveyance (pump station and pipeline) and the fees for connecting to the sewer and for the treatment/disposal (can vary from very low to several orders of magnitude larger than the conveyance costs).

Brine Co-Disposal with Wastewater Effluent