November 11, 2010

3 Min Read
Bulk Handling Systems  Aid Desalination Plant

Sodimate has installed two bulk handling systems at the Aquaria desalination plant, by the Taunton River, a few miles from the mouth of Narragansett Bay, MA. The desalination plant supplies 4 million gallons of fresh water each day to the city of Brockton, 16 miles away. Using a reverse-osmosis process, it will filter salt and other impurities from brackish water flowing up the river from the ocean during high tide.


Big bag unloader feeding lime slurry tank

The first system is located at the head of the desalination plant by adding Powder Activated Carbon (PAC) to readily adsorb or capture the impurities/contaminants, and also naturally dissolved organic matter (much of which is harmless).

Therefore, monitoring is needed to ensure that carbon doses are high enough to absorb all contaminants. The desalination plant receives super sacks (1000 lb) of PAC and stores them on site. The system provided by Sodimate is a complete bulk bag unloader equipped with an agitator and accurate volumetric screw feeder.

To prevent dust and ease the insertion of the dry PAC into the water, a dry/wet slurry eductor is connected to the screw feeder outlet. The PAC feed rate is controlled by a Variation Frequency Drive (VFD) connected to the water supply flow rate. The supply water passes through the eductor creating a suction (Venturi effect) and mix of the PAC. Also, the desalination plant contains powerful pumps and systems that consume significant amounts of energy and water, hence influencing the plant’s water pressure and the flow rate.


Big bag unloader lime slurry system

For accurate PAC filtration, the feed rate and slurry concentration will remain homogenous and without fluctuation. Correlating the PAC screw feeder VFDs to the water supply flow meter prevents any variation on the PAC slurry. Hence the organic substances are properly filtered and no recirculation or post treatment will be required.

Using a reverse-osmosis process and other chemical treatments the treated water is ready to be transferred into a potable storage tank. However, prior to the transfer to a potable storage tank the desalinated water requires hydrated lime Ca(OH)2 to be re-mineralized. Lime increases the pH, re-mineralizes the water, and reduces corrosion of pipes and structures.

In this case Sodimate provided a complete bulk bag unloader similar to the PAC system with the difference of having a lime slurry tank and one skid pumps. The dry hydrated lime is fed simultaneously with supply water into the slurry tank when the “batch” level is activated. The volumetric screw feeder VFD is connected to the water supply flow meter to guarantee a precise slurry concentration in the mixing tank (here 4%). Such a low slurry concentration prevents from lime settlement, pipe clogging, reduces maintenance, and extends pump lives.

Dual peristaltic lime skid pumps

When the slurry tank is full, the slurry agitator continues to run suspending all lime particles in the water. A pH probe detects a low pH from the treated water and the pump (here peristaltic) starts to feed accordingly to the processed flow rate to reach the suitable potable water pH. This set up of precise lime slurry concentration and controlled pump rate reduces the installation complexity with excellent reading and adjustability.

For more information, call  773-665-8800 or visit

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