Environment, Coasts, Oceans, & Infrastructure

Hello EWRI Colleagues:  I'm working on a project and would like your input on how to design an evaporation pond for brine/saline water conducted from desalination plants. Is it possible to calculate the amount of salts after evaporation? Your prompt feedback guys is highly appreciated.

Many Thanks,

Zayat

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Mohamed El Zayat
Student
Cairo
20106097641
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Hi Mohamed, This is an interesting problem. If I were solving it, I would model it as a simple mass balance problem with balanced inflow and evaporation rates. Assuming it is a lined pond, your inflow rate will equal your evaporation rate, so you need to design a surface area that will evaporate at least as much inflow you plan to handle. Evaporation rate can be estimated from local pan evaporation data, or calculated based on weather averages using accepted formulations, for instance the Penman-Monteith or Priestley-Taylor relationships. You have a mass loading rate that is simply concentration of salinity times the inflow rate, and a fixed volume of pond, so your concentration (mass per volume) will continue to increase over time until it reaches saturation, and then precipitation will begin occurring at the inflow mass loading rate. Evaporation rate may vary with salinity - I think the pond will absorb more solar energy as salinity increases - so look into that and take it into account in your calculations. Hope that helps. -Steve ------------------------------------------- Stephen Farrington, P.E. Gaysville VT -------------------------------------------

------------------------------------------- Joseph Reichenberger Professor of Civil Engineering Monterey Park CA (626) 288-5046 ------------------------------------------- It is a simple mass balance. Assume all of the dissolved minerals are "left behind". You need to do a liquid volume mass balance and a salt mass balance. The liquid will become more concentrated over time. At some point you will begin to reach the solubility product of some of the ions and they will precipitate. The real issue you face is the decrease in evaporation rate as the water becomes more salty. You will also need to make a determination of what evaporation rate to use: pan evaporation or reservoir evaporation (deep lake) or something in between.
Original Message: Sent: 06-05-2014 15:18 From: Mohamed El Zayat Subject: Evaporation Pond Hello EWRI Colleagues: I'm working on a project and would like your input on how to design an evaporation pond for brine/saline water conducted from desalination plants. Is it possible to calculate the amount of salts after evaporation? Your prompt feedback guys is highly appreciated. Many Thanks, Zayat ------------------------------------------- Mohamed El Zayat Student Cairo 20106097641 -------------------------------------------

Zayat, I don't have experience designing evaporation ponds, but it seems like a fairly simple thing to design for. Working out the size of the ponds to accommodate the amount of influent coming in would be the most critical part. And to calculate the amount of salts left over in the ponds after the water has evaporated, seems like all you would need to do is determine the concentration of the salt in the water, and then just multiply the concentration by the volume of water (making sure your units match up of course). Hope this is helpful, but as I said before I've never worked with designing evaporation ponds. These are just some insights I learned in school while specializing in Water Resources and Environmental. ------------------------------------------- Matthew Hosey Engineer Intern Baston and Brown, Inc Gautier, MS, USA -------------------------------------------
Original Message: Sent: 06-05-2014 15:18 From: Mohamed El Zayat Subject: Evaporation Pond Hello EWRI Colleagues: I'm working on a project and would like your input on how to design an evaporation pond for brine/saline water conducted from desalination plants. Is it possible to calculate the amount of salts after evaporation? Your prompt feedback guys is highly appreciated. Many Thanks, Zayat ------------------------------------------- Mohamed El Zayat Student Cairo 20106097641 -------------------------------------------

Mohamed and others,

The other discussions have hit on how to design the system.  But to figure out how much salt will remain does not require that much analysis. Assuming the system is closed and salt does not exit, then the simple salt balance is:

Salt Remaining = Salt Added

To estimate the amount of salt applied:

Given:
TDS of brine (ppm) - assuming you have a water quality analysis
Weight of water = 62.4lbs/ft^3

Sol'n:
Lbs of salt = TDS* (1lb salt/1,000,000lbs water)*(62.4lb/ft^3)*(total brine applied (ft^3))

Sorry for not using SI units but you can replace lbs with metric-tons and ft^3 with m^3 (or whichever units you prefer)

Good luck,

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Daniel Howes
Assistant Professor/Sr Engineer
San Luis Obispo CA
(858) 354-0504
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