Figure 1. The McMurdo wastewater treatment plant is a substantial facility to serve a population that can exceed 1000 people and carries a higher than average solids load which requires substantial macerators on line.
Wastewater on Antarctic stations includes domestic (kitchens, showers, toilets) and light industrial sources wastewater from laboratories and mechanical workshops. Station wastewater has some similarities to standard municipal wastewater, for example, high microbiological loads , however, several properties can differ: wastewater may be more concentrated (as there is no stormwater or runoff inputs and water use is generally restricted) while nutrients, Biological Oxygen Demand (BOD) and settleable solid levels may be higher  and environmental degradation rates lower . Wastewater quantity may also be highly variable due to seasonal cycles in station populations; however, volumes are generally small in comparison to domestic outfalls, ranging from several hundred to tens of thousands of litres per day, with notably higher volumes at larger stations (e.g. McMurdo Station ). The large variability in wastewater parameters may cause technical difficulties for those operating treatment plants year-round. Contaminants detected in wastewater and around Antarctic stations include metals, persistent organic compounds (POPs), (such as polybrominated diphenyl ethers (PBDEs) [7, 8]) surfactants, hydrocarbons, endocrine disrupting compounds , pharmaceutical compounds  and microplastics .
Figure 2. Clarity of the water discharged from the McMurdo wastewater treatment plant.
Antarctic wastewater studies have focused on measuring the distribution and extent of wastewater discharged into the marine environment. Five categories of wastewater dispersal tracers have been identified: human-associated enteric bacteria e.g. Escherichia coli, Enterococci, Clostridum perfringens and total coliforms [3, 11-13]; human biomarkers e.g. faecal sterols [14-16]; contaminants and sewage molecular markers e.g. hydrocarbons , linear alkylbenzenes , trace metals , polybrominated diphenyl ethers (PBDEs) [7, 8, 12]; stable isotopes ; and pharmaceutical compounds and drugs [9, 10]. Wastewater tracers have been detected in seawater, marine sediments and biota, including fish and invertebrates , up to 2 km from stations. Studies have been undertaken predominantly during the summer; however, during winter when coastal areas are covered by sea ice the dispersal conditions may be different . In general, wastewater discharged from Antarctic outfalls predominantly flows along the shore, with less evidence for dispersal out to sea [12, 17]. Exceptions are for offshore disposal sites on ice shelves or permanent sea ice such as the airfields at McMurdo Station .The detection of tracers in the environment, however, does not indicate whether any environmental impacts result from the discharge.
The Protocol states that precautions should be taken to prevent the introduction of non-native micro-organisms to Antarctica, although it does not specifically mention risks posed by wastewater. Wastewater discharge results in the release of large numbers of non-native micro-organisms, viruses and pathogens  to the environment that may remain viable for extended periods [2, 19], and may also present a substantial threat to indigenous microbial and macrofaunal species . Wastewater may also contain mobile genetic elements, such as those encoding for antibiotic resistance [21, 22], which have been found established in local bacterial and animal populations [20, 21] and have been termed “genetic pollution”. Beyond establishing the presence of non-native microorganisms, there has been little research to determine their potential impacts. There are many records of disease associated pathogens (e.g. Salmonella) present in Antarctic wildlife including Adélie and macaroni penguins, skuas, fur seals, albatross and gulls , although evidence of an anthropogenic source or any subsequent disease outbreaks is lacking. Human faecal bacteria have been found in Antarctic wildlife, (e.g. clams, fish, sea urchins and starfish) with a higher incidence closer to outfalls, indicating ingestion of wastewater, further confirmed by stable isotopes . No disease symptoms have been reported  but an increased incidence of internal organ abnormalities were reported for fish around an outfall .
Our understanding of the environmental impacts of wastewater discharged into Antarctic ecosystems is relatively limited, but a comprehensive study at Australia’s Davis Station indicated a potentially wide range of significant impacts resulting from practices currently regarded as acceptable under the Protocol . Marine benthic communities have been studied at McMurdo, Casey and Davis Stations as indicators of wastewater pollution. In general, impacts on the communities were correlated with scale of the wastewater discharge, with reduced species diversity and abundance and dominance by some opportunistic species [25, 26]. Ecotoxicological studies of wastewater are rare but indicate toxicity to Antarctic marine invertebrates at low concentrations, over exposures of several weeks . Very little is known regarding the impacts of wastewater disposed to inland areas such as ice pits, freshwater lakes and streams or ice-free areas. Extremely low degradation rates and recent climate change may lead to exposure of historical wastes and long term pollution problems .
The effectiveness of wastewater treatment facilities depends on the type and level of treatment. Traditional wastewater treatment removes nutrients (to prevent eutrophication) and reduces microorganism/pathogen concentrations. Antarctic marine waters are generally not nutrient limited but significant risks to the environment may be caused by contaminants and microorganisms . Most station treatment systems remove nutrients and lower BOD, thereby reflecting secondary treatment processes described in the Protocol, (i.e. Rotary Biological Contactors). However, the removal of sewage microorganisms becomes more effective when employing more sophisticated treatment processes, with advanced tertiary treatment almost eliminating micro-organism/pathogen release and removing all contaminants [3, 5].
Currently, no specific guidelines for wastewater disposal or allowable levels of bacteria in discharges from outfalls have been agreed upon under the Protocol. Technologies for wastewater treatment, however, have improved markedly since the Protocol was signed in 1991, and advanced tertiary treatment is now the best procedure to minimize the full range of potential risks from wastewater discharge. The release of untreated sewage, with the associated non-native microorganisms, genetic elements, chemical contaminants and nutrients, remains a cause for substantial concern. Monitoring of existing outfalls/disposal areas and further research on their potential impacts, particularly those related to harmful contaminants (such as POPs), microbiological impacts, genetic pollution and wildlife health may help to quantify the risk and their potential impacts, along with more sensitive analytical techniques to detect low levels of sewage input in the Antarctic environment (e.g. . 'Sufficient “initial dilution and rapid dispersal” to prevent impacts may not be achievable in Antarctic nearshore marine environments, but advanced treatment methodologies represent the best possible solution to mitigate the environmental risks associated with discharge.
Figure 3. This sectional view of the wastewater treatment plant for Davis Station indicates the complexity of the engineering needed for treatment.
Figure 4. Inside the Davis Station treatment plant.
Figure 5. The Davis Station wastewater outfall when the sea ice is in.