Water finally flows at Davis
When the Australian National Antarctic Research Expeditions established its second Antarctic station at Davis in 1957, there was just one problem…no water. Water issues have continued to dog engineers and expeditioners, but a new reverse osmosis plant, installed in 2009, heralds a new level of luxury; as Australian Antarctic Division engineer, Mark Pekin, explains.The initial approach to a water supply at Davis – as with all the original Australian stations – was to install a snow melter. Filling the melter with snow for daily water needs was one of the station duties and over time, as the population on station grew, this began to involve days of effort using loaders and trucks.
To improve the reliability of the water supply a nearby natural depression was modified in 1982-83 to form two tarns, with a total storage capacity of some 4.5 million litres. In years of average to high snow falls this system yielded adequate water volumes (estimated at 3 million litres). But in low snowfall seasons little water was produced and the water quality deteriorated due to increased salinity.
A desalination unit was subsequently installed. However, the unit failed to function effectively due to the lack of available expertise for commissioning and ongoing maintenance.
In 1990, drinking water was obtained from a new snow melter, and snow collection sometimes required taking heavy earth-moving equipment beyond the station limits in search of suitable snow. Tarn water was used for ablutions and washing, while high quality water for laboratory work was taken from inland lakes, using either helicopters in summer or over-snow vehicles in winter. Water conservation measures were strictly employed, including restricting showers to two per week.In 1994-95 two reverse osmosis (RO) units (which purify water) were installed, each producing 12 000 litres per day, along with two 600 000 litre storage tanks. Despite these additions water shortages continued, with expeditioners restricted to about 50 litres per person per day, compared to 170 litres on other stations. Two three-minute showers a week became the norm. The crunch came when the RO units exceeded their design life and required constant attention to coax them to produce less and less water each year. For the past three years, during the resupply of the station, water had to be carted from the ship to augment station supplies.
A new RO unit was purchased from the United States in 2007, capable of producing 100 000 litres per day. However, during transport to Davis it was badly damaged during a 40 degree roll of the ship and was found to be unserviceable once on station. The old RO unit was coaxed out of retirement and produced enough water to get the station through winter.
A replacement RO unit made it to Davis intact and after 10 weeks of installing the machine and kilometres of wiring, piping and brackets, it started producing water in January 2009. However, the machine could only run for short periods of time before shutting down, due to over-pressure faults. The fault was found when the manufacturer finally approved dismantling of the pressure exchanger. This unit is like a turbo-charger on a vehicle, with the outlet pressure being used to assist in providing inlet pressure. The rotor within the pressure exchanger had a large crack in the external wall, which caused a tiny (200-300 micron) displacement that, as a result of the fine tolerance between the rotor and its sleeve, prevented the rotor from spinning.A new rotor was ordered and appeared in time to catch a flight to Wilkins aerodrome. It then made its way by oversnow transport to Casey station and on to the last resupply ship, waiting to depart for Davis.
Since the new rotor was installed the RO unit has been operating flawlessly, producing 75 000 litres of water per day. Every storage tank on station is full, holding more than 1.4 ML of water. More than 50 years since the station was established, Davis expeditioners can finally enjoy what most people take for granted… daily showers.