Coming into the galley alone, I plunked down at a table with another guy who was sitting by himself. A retired schoolteacher from Montezuma, Iowa, my table mate Paul had first come down ten or fifteen years ago in a "teacher experience" program. After his retirement from teaching, he returned to work in the McMurdo municipal utilities--fresh water, power, and wastewater treatment.
After dinner, we headed down to a row of structures along the waterfront to tour the utility buildings.
All fresh water in McMurdo is generated through desalination. In the past, sea water was evaporated, and the resulting steam condensed to create fresh water--an energy-intensive process. Now, fresh water is created through reverse-osmosis. Seawater enters the plant through an intake in front of town, and is run through a coarse filter to remove jellyfish, sea stars, or small fish that were drawn into the intake. At -2°C, the salty sea water would freeze were the salt removed, so the seawater is pre-heated using waste heat from the diesel power generators. The warmed seawater is filtered through several stages of sand and fiber batting in a sequence similar to normal municipal water treatment.
Desalination is the real challenge. Fresh water is extracted from a larger volume of salt water through reverse osmosis, a process by which water at high pressure is forced through a membrane and leaves behind salt molecules. Water runs through the system 700 psi, and the welded stainless plumbing that carries the high pressure water is beautiful. Pressures are generated by a multi-cylinder pump driven by a huge 50-hp motor. The pump looks an awful lot like an engine block. About 80 gallons per minute of sea water passes through the system: 30 gallons of fresh water is extracted and a very salty 50 gallons is expelled back to the sea. The fresh water is then treated with calcium carbonate to restore the calcium ions desirable for water taste, the PH is adjusted to 8, and a small amount of chlorine is added. The in-town water plumbing runs through above-ground culverts that are packed with insulation and warmed with heat tape.
We crossed a steel platform to the power plant, where several diesel generators create electricity to power McMurdo base and the New Zealand Scott Base (when their wind turbines aren't spinning). Inside the plant, we checked in with the operator, who sits in a sound-insulated booth and monitors the engines. We inserted ear plugs, then put on ear muffs, and stepped into the loudest room I have ever experienced. Lit by overhead mercury vapor lamps, several 12-cylinder Cat diesels were thundering side-by-side in a concrete room. The very air of the room shook with noise and my torso rattled in sync. We didn't stick around for long.
We exited the power plant, and stepped out across a catwalk to the upper story of the wastewater treatment plant. The wastewater plant is on the lowest tier of town, sitting just 10-20' above the ocean. Raw sewage enters the plant and runs through a macerator, which turns the effluent into a thin homogeneous liquid. Foreign debris is filtered out, and the sewage is fed into an large array of open, circulating pools. Like an 'endless swimming pool', the sewage is released from pumps at end of the pool, flows rapidly across the pool, and disappears back into a pump intake. It looked like a 30' long cross section of a muddy springtime river had been diverted through an industrial scaffolding. It was hard to gauge the depth, but I would estimate about 10 feet. Roughly 2000 cfs, and probably Class II if the catwalks were pulled off.
The water is constantly circulated to maintain adequate oxygenation and encourage microbial growth. An ecosystem of microbes consumes one another and digests nutrients in the sewage. The tanks taper at the bottom, and heavier material settles and is pumped out. The heavy, decomposed solids are dried in a large press, and the resulting bins of dark organic soil are shipped back to the US. Treated liquid waste is expelled to the ocean. There was no sewage smell or bad odors whatsoever in the facility.
Because there are no storm drains, water sprinklers, or other major losses from the water system, the volume of wastewater treated at the plant is roughly equal to the volume of fresh water supplied to town. This is in contrast to most municipal utilities, where perhaps half of the supplied water makes it back to be treated as wastewater. I really appreciated the great opportunity for a tour of some of the basic municipal services that keep town running!