An application of algae that consumes bacteria and other pathogens without the need for sunlight to cut operating costs in sludge digestion.
The Afulilo Dam in Upolu, Samoa, was built in the 1990s to harness hydroelectric power, particularly during the dry season (May through October), with the goal of making the island less reliant on foreign oil. Like many islands, Upolu imports almost everything, including energy. Developing indigenous renewable energy and minimizing over-reliance on fossil fuels was identified as a significant barrier to long-term growth and environmental stewardship. The Afulilo Dam was built as a step in a better, more-sustainable direction.
The dam produces 30% of Samoa’s total energy demand, supplying up to 10,000 residences and businesses. It also supplies Samoa’s Ta’elefaga Power Station, which provides a significant amount of the island’s power. But trouble in paradise began with when hydrogen sulfide concentrations surged in the dam’s reservoir, Lake Afulilo.
High concentrations of hydrogen sulfides not only create a corrosion problem at the face of the dam, but also produce a “rotten egg” smell, which has hounded residents of nearby villages for years. It also depleted marine life in Fagaloa Bay, a water body from which many residents make their livelihood.
One potential solution Afulilo considered was to funnel water to the ocean via a pipe, where it could disperse. But government officials determined that this was too expensive; moreover, unless ocean currents were studied, there was potential for waste and noxious gases to be blown back to the villages anyway.
After a yearlong investigation by Electric Power Corp. (EPC) and the Scientific Research Organization of Samoa, EPC concluded that aeration and bubble technology was a viable solution for improving Lake Afulilo’s water quality.
Air Diffusion Systems (ADS) of Gurnee, Ill., supplied 44 Model “LTC” ADS Diffusers, 82,200 ft of self-sink feeder tubing from the compressor manifold to the diffusers, and two BSD 65 40 hp Kaeser Compressors to deliver 199 cfm at 123 psi to the dam’s 640 acre, 2.6-billion-gal reservoir. The diffusers add oxygen to the water column, facilitating a reaction between oxygen and hydrogen sulfide to produce odorless sulfate.
John Hinde, ADS president and owner, traveled to Samoa to personally oversee the installation of the diffusers and train the dam’s engineer on maintaining and operating the equipment. The company partnered with King Construction Ltd. in Apia, Samoa, to design, install and maintain the system.
The $375,000 project was completed in July of 2016. After several weeks of ADS fine bubble operation in Lake Afulilo, bottom oxygen concentrations had significantly increased, helping to eliminate odor and prevent fish kill. The system is expected to last 20 years, but other, similar aeration systems have lasted more than 40 years.