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Many of us have been disposing of our wash water by either pouring it out on the ground or down the sewer. The "Man" is likely to have a cow if he finds out you are doing that. If any gets into a stream or goes down a storm drain, then your in violation of the clean water act. If you pour it down the drain on a city sewer, you are probably overloading the system and causing the waste water treatment plant to get fined by the federal government for discharging untreated sewage.
The wash water contains both soap and biodiesel. The soaps are heavy in carbons, which demand large amounts of oxygen to biodegrade. The term to describe this is Biochemical Oxygen Demand (BOD). Typically the wash water from the first wash will usually kill your lawn. If you use NaOH, the second and third washes will also kill the lawn. One way to reduce the BOD is to let the wash water settle in a drum for a week or so. The biodiesel that was bound up in the soaps often rise to the top and can be used for fuel.
Neutralizing Wash Water
The most complete way to treat the water is to neutralize with acid. By adding enough acid to bring the pH to 7, you break down the soaps making FFAs and biodiesel. Run through a grease trap, to remove the oils and you can safely water your lawn with the water. The water will contain salts of some kind, depending on the acid used and the catalyst used.
If you use KOH as a catalyst and Sulfuric Acid to neutralize the water, then the salts that precipitate out will be potassium sulfate. After skimming off the biodiesel, oil, FFA layer (or running through a grease trap), the remaining water can be applied as a 0-0-50 fertilizer as needed. Be sure you don’t apply the water too fast or you will get runoff into either storm drains or streams and be in violation of the clean air and water act.
ION Exchange
There is a process called ION Exchange that can also be used to reduce the BOD. ION Exchange is the process of substituting one ion with another. In this case you’re substituting either the Sodium Ion or the Potassium Ion in the soap with a Magnesium Ion to form a soap that does not dissolve in either water or biodiesel. Do this by putting your wash water in a drum and dropping an aquarium air bubbler in to stir the water. Then add Epsom Salt and continue to bubble overnight. The biodiesel can be siphoned off the top. A layer of soap will be just below the biodiesel that can be scooped out and dried. The dried soap will be non-toxic and safe to put in your trash. The remaining water will contain either Sodium Sulfate or Potassium Sulfate depending on the catalyst you used originally. Potassium Sulfate is a 0-0-50 fertilizer often used on vegetable and flower gardens. It promotes the growth of flowers, fruits, and seeds.
Testing Wash Water
Steve Fugate (TDISteve) posted the following on infopop. It is testing he had performed on wash water to see how treatment effects the Waste Water Treatment Facilities' ability to accept the wash water.
Testing performed on wash water was performed on three samples.
• Sample #1 had the methanol recovered before washing
• Sample #2 had the methanol recovered before washing and was treated with 10 g/L of MgSO3 ION Exchange Treatment
• Sample #3 had no methanol recover and no ION exchange treatment
Sample #1 #2 #3
pH, s.u. 9.5 8.1 9.2
COD, mg/L 44,500 18,450 133,000
(Chemical Oxygen Demand)
CBOD, mg/L 24,800 10,100 81,300
(Carbonaceous Biochemical Oxygen Demand)
TS, % 0.9 1.0 4.0
(Total Solids)
TVS, % 100.0 20.0 88.9
(Total Volatile Solids)
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Wash Water Disposal
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