Salinity refers to the total amount of dissolved inorganic salts in process water. Salts include the ions of sodium, magnesium, calcium, potassium, chloride, sulfate, bicarbonate and carbonate.
Accumulations of salts in water and soil can impact plant growth and damage soil biota, limiting wastewater reuse options such as irrigation. Salts can also migrate to groundwater or degrade waterways, damaging human water supplies and impacting aquatic life. Across California, and especially in areas where groundwater aquifers are salt-impaired, regulatory agencies are asking for even greater salt reductions in winery wastewater.
Three Ways to Measure Salinity in Winery Wastewater
Total Dissolved Solids (TDS) is the amount of residue left by a filtered liquid sample that has been evaporated to dryness at 180˚C. TDS is often used to approximate salt content in natural waters, but in winery process waters this analysis can be greatly affected by the organic content of the water. Usually expressed as mg/L.
Fixed Dissolved Solids (FDS) is the amount of residue left by a filtered liquid sample that has been evaporated to dryness at 550˚C. In winery wastewater, it is usually considered a more accurate measurement of inorganic ions (e.g. salts) than TDS. Usually expressed at mg/L.
Electrical Conductivity (EC) is an indicator of the concentration of dissolved salts in a water sample. When salts dissolve in water, they give off charged ions that conduct electricity. Often measured in microSiemens/centimeter (uS/cm) or millimhos/centimeter (mmho/cm).
Sources of added salinity in winery wastewater, other than naturally occurring salt concentrations in grapes, include:
Chemical inputs used in cleaning and sanitation (e.g. sodium hydroxide, soda ash, chlorine, sulfur dioxide)
Water softeners, which function by using salt to remove hardness from the water supply by ion exchange
Blowdown water produced by boilers, cooling towers, evaporative condensers and some refrigeration activities
Salts typically cannot be treated by biological wastewater treatment methods (e.g., aeration), making them significantly more difficult to remove than organic matter and nutrients. Effective source control methods to prevent salts from entering the wastewater stream include:
Reduce the use of cleaning and sanitation chemicals where possible, e.g., by implementing and optimizing Standard Operating Procedures (SOPs)
Substitute cleaning chemicals with lower salt content, and/or consider switching from sodium-based to potassium-based cleaners
Optimize and reduce (where possible) the operation of water softeners in the facility, and consider switching from sodium chloride to potassium chloride
Given the costs and complexity of treating winery wastewater for salinity, cleaning and sanitation source controls are a key area to focus on.
[Adapted from the Comprehensive Guide.]
KEY QUESTIONS TO CONSIDER
Use these guiding questions as you begin to evaluate opportunities for additional water quality actions in the winery.
Which activities in your winery have the potential to generate salinity?
Do you measure salinity in the winery’s source water or wastewater stream (for example, by measuring Electrical Conductivity)? If wastewater is discharged to land, have salt loadings been calculated?
Has the winery completed an inventory of chemical inputs used at the winery to quantify the total volume used and their costs?
Are there additional opportunities to reduce the use of chemical cleaners and sanitizers, for example by substituting ozone, steam or hot water?
Visit the Resources page for more Key Questions.