Portable Sanitation Association International

Association Insight Dec 01 2021

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2 I PSAI Association Insight, December 1, 2021 On Mulan, we initially tried dropping the salt straight into the toilets before pouring in fresh water, but the salt didn't dissolve. The other problems we encountered while dosing that way were: 1. The drivers weren't consistent. They forgot the salt, they added too much, or they didn't use enough. 2. The salt spilled everywhere, usually in the cab where the driver carried it to keep the bag dry. 3. The salt didn't dissolve, so it didn't do its job. 4. The fresh water we carried on the truck was often frozen, so we couldn't fill the toilets anyway. In the end, we learned to pre-mix our brine in another tank in the yard, added blue and carried that on the truck. We set up a 260 gallon (1000L) Intermediate Bulk Container (IBC) used to transport bulk liquids and often used as water butts on ranches and farms. We'd add the salt, fill the IBC with water in the yard, and carry it on the truck. If you do this, it's important to strap the container down tightly and to find — and use — a screw- on lid. Mixing brine in advance ensures that the salt is fully dissolved and has some other benefits, too. It saves you having to measure out the salt at every toilet and means you don't Salt brine is made by simply dissolving salt in water. When technicians visit sites to service their restrooms, they simply add the brine instead of fresh water to prepare the toilets for use. On Mulan, we used swimming pool salt because it was cheap, dissolved quickly, and was readily available from the local hardware store. Alternatively, water softener salt, rock salt, road salt, and pretty much any other bulk salt may be used. At Home Depot, a 40 lb (18kg) bag of water softener salt currently costs $7.50. Swimming pool salt is a little more expensive at $9, although it is essentially the same product. Operators may secure a better price if they buy in bulk and shop around. Operators can lower the freezing point of salt brine by adding extra salt to create a stronger solution, but only up to a point. At 2 lbs of salt per gallon of water (240g per litre), salt brine reaches maximum density, known as the Eutectic Point, and no more salt can be absorbed. You can add more salt, but it won't dissolve. The freezing point of different concentrations of salt brine are shown in Table 1. Winterization: How to Prepare Restrooms and Equipment for Extremely Cold Weather (Part 2) (continued from page 1) (continued on page 4) CONCENTRATION OF SOLUTION SALT DOSE (PER GAL) SALT DOSE (PER LITRE) FREEZING POINT OF SOLUTION 5% 0.5lb 60g 25°F (-3°C) 10% 1lb 120g 19 °F (-7°C) 15% 1.5lbs 180g 11°F (-11°C) 20% 2lbs 240g 0°F (-18°C) Table 1. Mixing Guide: Salt Brine NOTE 1: Contact with bare skin at very cold temperatures can lead to serious injury and harm. Correct PPE must be worn when handling these solutions. NOTE 2: Salt brine reaches maximum density at 2 lbs per gallon or 240g per litre. Beyond that, any salt added will not dissolve.

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