Ocean salt is always in the atmosphere and returns quickly to sea.

One of the biggest questions I always get asked from potential clients wanting to incorporate enhanced evaporation equipment is the containment of salt drift from high total dissolved solids (TDS) wastestreams.

As technology improves and more studies evolve, one thing is for sure—salt is always in the atmosphere, mostly salt loading from the ocean due to nature’s design. Surprisingly, models and observations have proved tiny micron particles return to the sea in a short time frame.

HOW LONG SEA SALT STAYS IN ATMOSPHERE
In a 2002 study1 on sea-salt aerosols, many factors contribute to the time sea salt resides in the atmosphere. Sizing of the sea salt, height of the column and wind speeds are the three most important factors. Based on the study, here are some highlighted conclusions:

• Due to the large gravitational settling velocity and dry deposition velocity, large particles (r = 4–8 µm) will not participate in long-range transport and average ~30 minutes of hang time.
• About 98.5 percent of the total sea salt emitted from global oceans is returned to ocean surfaces by dry and wet removal processes.
• Only 1.5 percent of the total mass is deposited on continents.
• The mean residence time for 7.7 µm and 0.4 µm particles in the marine boundary layer were in the range of 0.3 to 10 hours and 80 to 360 hours, respectively.
• Thus, most of the sea salt deposition to land surfaces occurs along the coastal regions where the supermicron particles are able to penetrate. Assuming a dynamic balance of land surface NaCl and a closure of the sea salt budget, the runoff of sea salt from land to ocean is assumed to be equal to the amount deposited on land, 0.15 × 1012 kg/yr.

RAINFALL COLLECTION DATA
In following the sea-salt drift to onshore deposits, there is an agency in the U.S. established to monitor the annual depositions, the National Atmospheric Deposition Program (NADP).2 With specific monitoring locations across the country, NADP collects rainfalls on a weekly basis and runs tests for free acidity (H+ as pH), conductance, calcium (Ca2+), magnesium (Mg2+), sodium (Na+), potassium (K+), sulfate (SO42-), nitrate (NO3- ), chloride (Cl-) and ammonium (NH4+).

The map (Figure 1) is from the collected national data, which shows the most up-to-date deposition makeup from 2014. Please take notice of the location in Utah with a red circle and the number 854. This spot is where the Great Salt Lake is located along with the Bonneville Salt Flats, which is just west of the Great Salt Lake.

The 854 is in micrograms per liter of salt-ion deposits. The annual total salt deposits convert to 0.0000000083 pounds per gallon. As expected near many of the seaside locations, the salt deposits are higher than most other locations being monitored.

Since the Great Salt Lake shows higher concentrations of salt deposition farther inland, the typical thought is agriculture would suffer on the eastern side of the lake due to prevailing easterly winds with the salt drift causing harm.

PATTERNS OF CROP GROWTH
Zooming in on Google Earth, you will notice some intriguing patterns of crops growing right next to the lake's eastern edge. A mile further east from the side of the lake, you will observe a very green golf course (Figure 2).

Is salt harmful to the environment, or does salt carry more of a significant function in the hydrologic cycle and, therefore, a welcomed necessity?

Salt is everywhere, and the Great Salt Lake area seems to defy the current environmental logic of harmful effects. Even in the Bonneville Salt Flats, you will see patches of green agriculture growth surrounded by salt.

COOLING THE PLANET
Original design allows for salt particulate and other dust in the atmosphere for a couple of reasons. The first being cloud formation,3 and the second is to help block the sun’s direct rays, keeping our planet cooler. Volcanoes4 spew massive amounts of related sulfur gases and particulate into the atmosphere and have a proven cooling effect on the entire planet.

Geoengineers are performing studies and creating models5 of injecting even more salt into the atmosphere to combat so-called global warming/climate change. Furthermore, a 2011 study6 by Carnegie Institution researchers noted that water evaporated from trees and lakes could have a cooling effect on the entire planet.

The U.S. Environmental Protection Agency (EPA) method developed to regulate particulate from a stationary source was formulated in EPA’s North Carolina research lab. The EPA theorized that a 50-micron water droplet from high TDS water samples when dried could potentially create a 10-micron particulate.

The study also hypothesized that a 10-micron water droplet had the potential to develop a 2.5-micron particulate once the droplet dried. The University of North Carolina further theorized TDS water droplets up to 20 microns could create up to a 4-micron particulate when dried.

The EPA adopted this particulate theory and was codified in the Federal Register7 in 2010 with recommendations to use Method 5 for particulate matter created from wet scrubber stationary sources. Other methods involve using the fugitive dust opacity method, which is a visual inspection used to observe fugitive dust8 that is not harming neighboring properties.

Is salt harmful to the environment, or does salt carry more of a significant function in the hydrologic cycle and, therefore, a welcomed necessity?

spwm king2

 spwm king3The visual inspection method recommended by the EPA falls under Chapter 3745-179 Particulate Matter Standards. This is the primary method used to make sure any fugitive dust from within a property boundary stays within the property boundary. 

NONATTAINMENT AREA MAPS
The EPA has created a website10 specifically covering nonattainment areas in the United States for PM-2.5 & PM-10 standards. Based upon the maps located on this website, the majority of nonattainment areas are located in the Central and Southern California regions with a majority being located in the San Joaquin Valley.11

The EPA suggests the major influences on the San Joaquin Valley are related to emissions from diesel-related transportation and wood-burning fireplaces. While research, regulation and technology advance in assuring clean air, Figure 3 is an EPA graph12 that reflects the advancement of clean air since 1970.

DUST DEVIL PARTICLE LOADS
Another related dust-particle study,13 released in 2016, details an in-situ samplings of particle loads during dust devil events in the Sahara Desert. The dust particles were collected at heights up to 4 meters. The particles inside the vortex of the dust devil were weighed, sized and labeled.

For comparison purposes to the salt-drift study noted earlier, the particle size ranged from less than 2 microns to more than 500 microns. In section 5.2, the authors describe particle load sizing and hang time, with the relationship of longer hang times occurring between particle sizes of 0.1 microns up to 31 microns with low weight percentages. The overall agreement is the bigger and heavier the particle, the quicker the return to the ground.

For comparison reasons, table salt (sodium chloride) measures ~100 microns and is not inhalable. The complexity of nature’s design that loads the atmosphere with particulate of all types by wind or dust devils opens up the conversation to what happens if we continue to regulate the removal of these naturally occurring atmospheric particle loading.

NEED TO UNDERSTAND SALT DRIFT
When deciding on wastewater-treatment methods using enhanced evaporation equipment like the E3 Solutions technology, understanding the salt drift and salt in the surrounding environment can help guide the discussion during the environmental permitting phase of your project.

Varimax atomizers have an average micron spectrum between 70 and 120 microns, which is a sweet spot for higher evaporation rates and also for staying above the 50-micron14 droplet threshold from creating PM10 and PM2.5.

In addition to meeting permittable micron water droplet spectrums above 50 microns,15 E3's patented atomizer allows users custom site-specific inputs to control water droplet size based on wind speeds to control potential drift. Any drift associated with the E3's system will enable the user ultimate control of keeping particulate drift within containment areas.

Fencing material can allow the wind to pass through easily yet still capture any particulate that hasn't already fallen back into the evaporation pond.

Since salt and chloride influences are always in the surrounding atmosphere naturally, incorporating salt-tolerant16 grasses, plants and trees around and near your industrial ponds and property boundaries will help maintain a sustainable environment for the future of our planet. Another option is fencing material that allows the wind to pass through easily yet still capture any particulate that hasn't already fallen back into the evaporation pond.

PERMITTING SALT PARTICULATES
An example of permitting salt particulates from an industrial power-plant cooling tower was published by the New Mexico Environment Department Air Quality Bureau17 in 2013. In the environmental technical discussion, you will see reference tables regarding droplet sizing to particulate creation and how they are used to determine potential PM10 and PM2.5 from the cooling-tower operation.

In the past, several long-term cooling-tower salt-drift studies have been performed and were canceled by the EPA when negligible salt loading within property boundaries was unfounded. See the letter request for the scrapping of the 13-year Crystal River salt drift study.18

E3 Solutions highly recommends using qualified permitting experts when discussing emissions from industrial evaporation ponds. E3's industry-leading systems have proven permittable in most applications.

Please enjoy E3's Varimax atomizers video displaying the use of water droplet sizing control during overspray conditions. (https://youtu.be/1t4N00F1HRY)

 

References
1. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2001JD002004
2. http://nadp.slh.wisc.edu/
3. https://earthobservatory.nasa.gov/features/Aerosols/page4.php
4. https://www.scientificamerican.com/article/how-dovolcanoes-affect-w/
5. https://www.scientificamerican.com/article/salt-spray-mayprove-most-feasible-geoengineering/
6. https://iopscience.iop.org/article/10.1088/1748-9326/6/3/034032
7. https://www.federalregister.gov/documents/2010/12/21/2010-30847/methods-for-measurement-of-filterable-pm10
8. https://www.epa.gov/sites/production/files/2017-12/documents/chapt-08-2017.pdf
9. https://www.epa.gov/sites/production/files/2018-07/documents/chapter_3745-17.pdf
10. https://www.epa.gov/green-book
11. https://www.epa.gov/sanjoaquinvalley/epa-activities-cleaner-air
12. https://www.epa.gov/sites/production/files/2019-07/2018_baby_graphic_1970-2018.png
13. https://www.liebertpub.com/doi/pdf/10.1089/ast.2016.1544
14. https://www3.epa.gov/ttnemc01/methods/comments201a202.pdf
15. https://evaporationworks.com/droplet-test-enhanced-evaporation/
16. http://www.fao.org/3/ag127e/ag127e08.htm
17. https://www.env.nm.gov/aqb/permit/documents/PermittingGuidanceforCoolingTowerParticulateEmissions.pdf
18. http://pbadupws.nrc.gov/docs/ML0913/ML091320177.pdf

Authored by Kevin King, E3 Solutions CEO