After more than four decades of operation, New Zealand's Antarctic research station, Scott Base, is installing a sewage treatment plant. Scott Base houses around 80 scientists and staff during summer, and a crew of 10 during the winter. It consists of a complex of lime-green buildings which open on to the frozen continent through fridge-style doors. The base is set on crunchy black volcanic gravel at the tip of Ross Island's Hut Point Peninsula and is surrounded for most of the year by sea ice. For the past 45 years, the biological wastes from the base have simply been macerated and discharged into the sea under the ice near the shore. Scott Base discharges up to 17,000 litres of this raw sewage and wastewater daily, while neighbouring US McMurdo Station discharges up to 270,000 litres. Changing attitudes mean that crude discharge is no longer acceptable. Italy included a treatment plant in its new base constructed in 1987. And now, after the adoption of the 1991 Protocol on Environmental Protection to the Antarctic Treaty and the restructuring of Antarctica New Zealand in 1996, the Scott Base sewage question is being addressed. As part of the project justification process, expert monitoring teams were flown to Scott Base to investigate the fate of the discharged sewage and sediment in the environment. The job was difficult—like trying to observe the condition on a rugby pitch with the rain covers on, except it was a lot colder. Researchers drilled holes through the 2 m-thick sea ice, then tried to plot the movement of currents carrying the wastewater and also to sample seafloor organisms for signs of sewage assimilation. They concluded that the effect of the discharge was almost undetectable beyond 50-60 m from shore, but that there was a cumulative effect on inshore communities. A second concern was for human health. The clash of shelf and sea ice at land's edge causes pressure ridges of ice to form, and some of these ground in shallow water. The ridges impound discharged effluent, keeping it close to the base's drinking water intake pipe. A third concern was about consequences of possible introduction of foreign genetic material into local organisms. Some scientists believe that seals near McMurdo Sound are being infected by the human enteric bacterium Clostridium perfringens during summer. Infection of invertebrates in the area could lead to the transfer of human bacteria to other marine life as well. The Antarctic seawater remains at around –1.8° C throughout the year. At this temperature, anthropogenic organic matter decomposes a third as quickly as at 20° C. Organisms such as Clostridium perfringens are able to persist in these conditions, even surviving beneath 5 cm of sediment, suggesting that at least elements of the sewage may persist for a long time. Several other issues were also considered, in the areas of human health, environmental contamination, environmental dynamics and ethical and moral issues. In view of the fact little is known of the effects (both immediate and cumulative) of exposing Antarctic marine environments to human pathogens, the precautionary principle was adopted and the decision made to spend almost $500,000 on a treatment plant. The final environmental assessment report cited the need to reduce the disposal of wastes as far as practicable, in order to minimise the impact on the Antarctic environment, and to reduce or remove pathogens as a precautionary measure. "But in the end," says Emma Waterhouse, environmental manager of the New Zealand Antarctic Institute, "there was a large ethical component to the decision. There is no longer any reason for New Zealand to be making these discharges. We want to be leading by example." The selection of the most suitable sewage plant for the base was a complex process involving consideration of treatment performance, maintenance needs, environmental "footprint," logistics and cost. Among the design challenges, extreme cold was not a major problem, as the plant is to be housed inside a building heated partially by the temperature of the waste itself and partially by recycled warm air. Several types of plant were considered. Some, such as composting or high-pH systems, were rejected as they would require bulk shipments of sawdust or lime to Scott Base. Another system was rejected because it required a 7 m-high building, which was considered to have too great a visual impact on the landscape. Finally, a fixed-bed aeration process with UV disinfection was chosen. This system must cope with several inherent features of the base wastewater: the high salinity of the seawater flowing through the flush toilet system, (water produced by reverse osmosis—used for drinking—is too "energetically expensive" to use in toilets) and the fluctuation in numbers of people on base. With the decrease from up to 100 summer personnel to 10 in winter, the system will have parts of its surface area phased in and out of action. In other seasonally run systems, such as skifields, the sudden decline in nutrients is remedied by feeding the system dog food to keep the bacteria thriving. After filtering and UV treatment, the water will be piped into the bay, while solid sludge will be dewatered to 20 per cent dry solids (the consistency of moist cake) and returned to New Zealand for disposal. An estimated 5.5 tonnes will 0 enter the Christchurch City wastewater treatment plant each year. The foundations for the new plant have been laid and the parts shipped to Ross Island in several containers, all pre-prepared for erection on site. The plant will be phased in over the coming winter, when only a few personnel are present. Waste disposal of any sort is a serious matter in Antarctica. Chefs at Scott Base, cognisant of the fact that a cosmopolitan poultry virus has reached and infected Antarctic birdlife, are careful to collect all water dripping from thawing chickens for return to New Zealand. Field researchers who camp out are required to collect their waste and return it to base. The United States' Amundsen–Scott South Pole Station is too far from anywhere to freight out waste. It simply creates chasms in the ice to be filled with waste. These are calculated to reach the oceans below on geological, rather than human, timescales. But for Scott Base the news is good. By next season, New Zealanders working at the base will be able to relax when they spend a penny, confident their waste is not going to damage the fragile Antarctic environment.