- Email: [email protected]
A simple method to reduce discharge of sewage microorganisms from an Antarctic research station
Marine Pollution Bulletin 46 (2003) 353–357 www.elsevier.com/locate/marpolbul
Note
A simple method to reduce discharge of sewage microorganisms from an Antarctic research station Kevin A. Hughes *, Nigel Blenkharn British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
Abstract The majority of coastal Antarctic stations release untreated sewage into the near-shore marine environment. This study examined bacterial reproduction within the temporary sewage-holding tanks of Rothera Research Station (Adelaide Island, Antarctic Peninsula) and monitored sewage pollution in the local marine environment. By continuously flushing the sewage-holding tanks with cold seawater we inhibited microbial reproduction and decreased the numbers of bacteria subsequently released into the sea by >90%. The widespread use of this simple method could significantly reduce the numbers of faecal coliform and other non-native microorganisms introduced into the Antarctic marine environment. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Antarctica; Coliforms; Faecal pollution; Seawater; Sewage outfall
1. Introduction At present, most Antarctic research stations discharge untreated sewage waste directly into the marine environment. In order to protect the Antarctic environment, the Antarctic Treaty nations agreed the Protocol on Environmental Protection, which came into force in 1998 (Antarctic Treaty Consultative Parties, 1991). Annex III of the Environmental Protocol allows sewage and domestic liquid wastes to be discharged into the sea, provided that large quantities of waste (generated by 30 people or more) receive at least primary treatment such as maceration, and final discharge is located where conditions exist for initial dilution and rapid dispersal. Several studies describe the extent of sewage pollution released from Antarctic stations (Howington et al., 1992; McFeters et al., 1993; Bruni et al., 1997; Delille and Delille, 2000) and their ecological effects (Edwards et al., 1998; Smith, 2000). Lenihan et al. (1990) showed that sewage effluent from McMurdo station in the Ross Sea influenced marine benthic communities close to the sewage outfall. Sewage is a source of human-derived bacteria, yeasts and viruses that are not native to the Antarctic. Once released, enteric bacteria can remain *
Corresponding author. Fax: +44-1223-362616. E-mail address: [email protected] (K.A. Hughes).
viable in low temperature Antarctic waters (0 °C) for prolonged periods (Smith et al., 1994; Statham and McMeekin, 1994) and untreated sewage can affect biological oxygen demand (Howington et al., 1994). Several authors have recommended that sewage be fully treated before discharge into the polar environment (Halton and Nehlsen, 1968; Antarctic Treaty Consultative Parties, 1991; McFeters et al., 1993). However, logistic constraints mean that the release of untreated sewage into the marine environment is often the only option available––especially at smaller Antarctic stations. Given the requirements of the Environmental Protocol and the practical likelihood that release of untreated sewage will continue to be the preferred option for the majority of coastal Antarctic stations, a simple method to reduce the discharge of sewage-derived microbes would help protect the Antarctic marine environment. Rothera Research Station is a permanent British station situated on Rothera Point, Adelaide Island, Antarctic Peninsula (67°340 S, 68°080 W) (Fig. 1). It is the largest of the five bases maintained by the British Antarctic Survey with a population of 20–25 in the austral winter, which can rise to over 100 during peak periods in summer. Untreated sewage has been released into the sea since the base opened in 1976. An integrated sewage disposal system operates in all the inhabited buildings and carries human waste, grey water and food waste to
0025-326X/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0025-326X(02)00224-2
354
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
number of sewage microorganisms released into North Cove.
2. Materials and methods Throughout the austral winter of 1999 (April–October), 20 people lived on the station. The sewageholding tank in the main accommodation building was studied as it had the greatest level of sewage input. The seawater temperature around Rothera Point was 0 °C throughout the year and provided a readily available supply of cold water which was used routinely to flush toilets and was stored in large tanks in the building roof space. When required during this study, cold seawater was gravity fed to the sewage-holding tanks, which allowed continuous flow. No faecal coliforms were detected in the stored seawater. 2.1. Experiment 1. Effect of continuous salt water flushing on microbial numbers within a sewage-holding tank
Fig. 1. Map of Rothera Research Station, Rothera Point, showing the position of the sewage outfall (SO), main sewage pipe (SP), sewageholding tank (HT), seawater intake pipe (SWI) and Site of Special Scientific Interest (SSSI number 9). Crosses represent water sample sites.
three sewage-holding tanks (1000 l) within the base buildings. The tanks store the sewage until full, after which the contents are simultaneously macerated and pumped into the main sewage pipe that empties into the sea at the high tide mark on North Cove beach (Fig. 1). The sewage does not undergo any secondary treatment. In 1987, a seawater desalination plant was installed to supply the station with potable water. The seawater intake pipe is situated 8 m below sea level on the opposite (southern) side of Rothera Point to the sewage outfall and it was determined that sewage contamination of the potable water supply was not taking place. Conditions favouring microbial reproduction were created within the sewage-holding tanks through addition of warm water from showers and other domestic equipment (increasing the temperature), macerated food waste from the kitchens (supplying nutrients) and human waste (inoculum). At night, liquid input to the storage tanks was minimal, therefore reducing the frequency of emptying and prolonging microbial residence time within the tanks. It was hypothesized that regularly flushing the sewage-holding tanks with cold seawater would limit microbial reproduction and reduce the
The initial study period was between 21:00 and 09:00 local time (00:00–12:00 GMT) during two successive nights (9–10 and 10–11 May 1999). During the night of 9–10 May, the sewage tank was allowed to fill with human waste and grey water as normal. No additional cold seawater flushing occurred. Liquid sewage samples were collected hourly in triplicate, 0.1 m from the base of the tank in sterile disposable Universal bottles and immediately transported to the station microbiology facility. During the next night (10–11 May), cold seawater was continuously added to the sewage-holding tank. Consequently, the tank was filled and emptied once every hour (900 l). This volume consisted of grey water and human waste collected in that hour, with the remainder being cold seawater. On each hour, after samples were collected, the tank was rapidly emptied to the minimum level of 100 l and then allowed to refill over the next 60 min period. Faecal coliforms were enumerated on membrane lauryl sulphate broth (MLSB) plus 1.5% agar (Oxoid, Basingstoke, UK) using the plate count technique according to established procedures (Anon, 1994). The volume of sewage in the holding tank was recorded from the tank control panel and sewage temperature was recorded within the tank. 2.2. Experiment 2. Daytime enumeration of faecal coliforms in the sewage-holding tank and North Cove After initial analysis of coliform numbers in the main building sewage-holding tank on 9–11 May, all three station sewage-holding tanks were steam-cleaned to remove any settled sewage sludge and sediment on 17 May. Continuous cold seawater flushing of the tanks
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
355
Changes in the sewage-holding tank volume during the two treatments are shown in Fig. 2. During the first night, when no salt water flushing occurred, the tank filled once within the 12 h study period. From 21:00 to 01:00 there was an increase in waste input due to clearing up after the evening meal and station personnel preparing to go to bed. After this there was a 6 h period where there was little input of waste into the tank. By
07:00 station personnel were rising and waste water levels increased again until 09:00 when the monitoring ceased. On the second night, 12 tank flushes were made of 900 l each. When cold water flushing was absent (9–10 May) there was a high initial temperature (33 °C) due to the hot water used to clear up after the evening meal. This was reduced to 25 °C within an hour and remained above 22 °C until 09:00. At 21:00 on the evening of 10– 11 May, just prior to cold water flushing, the initial temperature recorded was 25.5 °C. Once the seawater flow commenced, the temperature was reduced to 18 °C within the first hour. By 01:00 it was reduced to 6.5 °C and remained low until 09:00 when the experiment ended. As the sewage-holding tank could not empty to a level less than 100 l, a semi-solid sludge layer had formed on the base of the tank. This was overlaid by a fluid suspension of faecal material and food waste that was sampled throughout the experiment. Fig. 3 shows the number of faecal coliforms present in the liquid sewage within the tank during the sampling periods. This was estimated by multiplying the microbial count ml1 by the tank volume. During the night of 9–10 May, when no flushing occurred, the initial number of coliforms in the tank remained roughly constant at, on average, 1:70 1012 for the first four hours. Between 01:00 and 07:00 bacterial numbers increased 10-fold (1:87 1012 to 1:93 1013 ) although there was no additional sewage input. On 10–11 May, when seawater flushing commenced, there was an initial 6-fold decline in coliform number in the tank within the first two hours. By 09:00 this became a 25-fold decline (1:74 1012 to 7:00 1010 ). Faecal coliforms were lost from the tank during regular hourly emptying; by 04:00 this number was around 1% (1 1011 ) of the number in the tank when then there
Fig. 2. Volume of liquid in the sewage-holding tank: no flushing (dashed line), hourly flushing (solid line).
Fig. 3. Faecal coliforms in the sewage-holding tank: no flushing (), hourly flushing (j).
commenced and continued for three months (17 May– 28 August). Faecal coliforms were then enumerated in the main building sewage-holding tank during the daytime (07:00–01:00) and also in the sea around the sewage outfall (27 and 24 August, respectively). The sewage tanks were then returned to their normal ‘no flushing’ state (28 August), and after roughly one month the faecal coliforms in the tank during the daytime and in the sea were enumerated again (1 October and 28 September, respectively). Seawater samples for microbial analysis were collected beneath winter sea ice from around North Cove (Fig. 1). The sea ice limited the input of faecal material by wildlife and microbial cell damage by solar radiation. The seawater samples were collected 1 m below the water surface and immediately taken to the laboratory for microbiological analysis. Faecal coliform bacteria were enumerated in triplicate by the membrane filtration (0.2 lm, Sartorius, Goettinger, Germany) and plate count techniques on MLSB agar (Anon, 1994). Maps of faecal coliform distribution in North Cove were created using ARC INFO version 7.2.
3. Results 3.1. Experiment 1
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K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
was no hourly flushing (1 1013 ). When the number of faecal coliforms released over the 12 flushes was added up, the total was only around 10% of the number released from the tank at the end of the 12 h without flushing.
when no flushing occurred (1 October). Faecal coliform concentrations in North Cove were also less when the tanks were flushed with cold water (24 August) compared to when there was no flushing (28 September) (Fig. 4).
3.2. Experiment 2 4. Discussion Calculation of the mean daytime faecal coliform number in the tank during each of the two treatments showed that flushing with cold seawater (27 August) reduced the coliform count by >24-fold compared to
Fig. 4. Distribution of faecal coliform bacteria in North Cove, Rothera Point during 24 August (seawater flushing of sewage tanks) and 28 September (seawater flushing ceased). Numbers represent the common log exponent of faecal coliform numbers 100 ml1 seawater.
Our study indicated that microbial reproduction within the sewage-holding tank, during periods of low liquid input, significantly increased the number of viable faecal coliform bacteria subsequently released into the Antarctic near-shore marine environment. However, continuous dilution of the waste with cold seawater caused a large decline in enteric bacterium reproduction within the tank, which subsequently reduced coliform concentrations in North Cove. When seawater flushing was initiated, our data showed that the number of faecal coliforms in the tank remained >7 1010 because the semi-solid sewage mass at the bottom of the holding tank was acting as a reservoir source of coliform bacteria. Due to the design of the holding tank, the sludge was not removed when the liquid was emptied, and served as a semi-permanent inoculum for microbial propagation. After this material had been removed by pressurized steam cleaning (17 May 1999), and the flushing resumed, bacterial numbers in the tank were routinely less than 5 109 . By 27 August the faecal coliform counts were again >7 1010 due to faecal sediment that had again settled in the tanks during the previous three months. This highlights the importance of tank design and initial sewage system planning in reducing sediment accumulation. Although a few Antarctic stations have sewage treatment plants, such as Rotating Biological Contractor Systems (el Naggar and Schoppe, 1994; Lori et al., 1996; Knox et al., 2001), most do not have any sewage treatment facilities. As a result the release of non-native microbes is widespread, yet permitted under Environmental Protocol regulations. In a wider context, other parts of the Environmental Protocol prohibit the import into the Antarctic of soil and other biological materials that may contain non-native microbes. Consequently, there is inconsistency in the regulations governing the anthropogenic spread of non-indigenous microorganisms in Antarctica. From this study, recommended methods to reduce microbial reproduction in Antarctic sewage-holding tanks include: (1) continuous flushing of tanks with a supply of cold water to reduce microbial reproduction, (2) selection of a sewage-holding tank design that limits build up of faecal sludge sediment, (3) regular cleaning of tanks to remove any highly contaminated sediment, thus ensuring that resident microbial numbers in the tank are limited.
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
The British Antarctic Survey has undertaken a range of sewage impact studies (Lohan et al., 2001; George, 2002) and as a result is installing a biological sewage treatment plant at Rothera Research Station to reduce pollution further.
Acknowledgements This work was supported by the British Antarctic Survey’s ‘Biomolecular Responses to Environmental Stresses in Antarctica’ project and the Environment and Information Division. We thank C. Thompson, P. Wickens, G. Fell, M. Annat and C. Day for assistance during sampling and N. McWilliam for map production. K. Jones is acknowledged for advice on methodology and P. Convey, D. Walton and J. Shears are thanked for their advice and comments on the manuscript.
References Anon, 1994. The microbiology of water 1994. Part 1––drinking water. Methods for the examination of waters and associated materials. Report on public health and medical subjects no. 71. Her Majesty’s Stationery Office, London. Antarctic Treaty Consultative Parties, 1991. Protocol on Environmental Protection to the Antarctic Treaty. CM 1960. Her Majesty’s Stationery Office, London. Bruni, V., Maugeri, T.L., Monticelli, L., 1997. Faecal pollution indicators in the Terra Nova Bay (Ross Sea, Antarctica). Marine Pollution Bulletin 34, 908–912. Delille, D., Delille, E., 2000. Distribution of enteric bacteria in Antarctic seawater surrounding the Dumont d’Urville permanent station (Adelie Land). Marine Pollution Bulletin 40, 869–872. Edwards, D., McFeters, G., Venkatesan, M.I., 1998. Distribution of Clostridium perfringens and fecal sterols in a benthic coastal marine environment influenced by the sewage outfall from McMurdo station, Antarctica. Applied and Environmental Microbiology 64, 2596–2600.
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el Naggar, S., Schoppe, S., 1994. Waste management concept at the German winter station Neumayer. In: Giuliani, P. (Ed.), Proceedings of the Sixth Symposium on Antarctic Logistics and Operations. Italian ENEA Antarctic Project, Rome, Italy, pp. 13–23. George, A.L., 2002. Seasonal factors affecting surfactant biodegradation in Antarctic coastal waters: comparison of a polluted and pristine site. Marine Environmental Research 53, 403–415. Halton, J.E., Nehlsen, W.R., 1968. Survival of Escherichia coli in zero degree centigrade sea water. Journal of the Water Pollution Control Federation 40, 865–868. Howington, J.P., McFeters, G.A., Barry, J.P., Smith, J.J., 1992. Distribution of the McMurdo station sewage plume. Marine Pollution Bulletin 25, 324–327. Howington, J.P., McFeters, G.A., Jones, W.L., Smith, J.J., 1994. The effects of low temperature on BOD in Antarctic seawater. Water Research 28, 2585–2587. Knox, G., Ling, N., Patrick, M., Wilson, P., 2001. State of the Ross Sea region marine environment. In: Waterhouse, E.J. (Ed.), Ross Sea Region––a State of the Environment Report for the Ross Sea region of the Antarctic. New Zealand Antarctic Institute, Christchurch, New Zealand, pp. 5.1–5.52. Lenihan, H.S., Oliver, J.S., Oakenden, M.D., Stephenson, M.D., 1990. Intense and localized benthic marine pollution around McMurdo station, Antarctica. Marine Pollution Bulletin 21, 422–430. Lohan, M.C., Statham, P.J., Peck, L., 2001. Trace metals in the Antarctic soft-shelled clam Laternula elliptica: implications for metal pollution from Antarctic research stations. Polar Biology 24, 808–817. Lori, A., Ponzo, U., Indulti, M., Stefanoni, M., 1996. A new waste water treatment plant installed at the Italian Antarctic station of Terra Nova Bay. In: Hall, J. (Ed.), Proceedings of the Seventh Symposium on Antarctic Logistics and Operations. British Antarctic Survey, Cambridge, pp. 263–278. McFeters, G.A., Barry, J.P., Howington, J.P., 1993. Distribution of enteric bacteria in Antarctic seawater surrounding a sewage outfall. Water Research 27, 645–650. Smith, J.J., Howington, J.P., McFeters, G.A., 1994. Survival, physiological response and recovery of enteric bacteria exposed to a polar marine environment. Applied and Environmental Microbiology 60, 2977–2984. Smith, S., 2000. The effects of a small sewage outfall on an algal epifaunal community at Macquarie Island (sub-Antarctic): a drop in the Southern Ocean? Marine Pollution Bulletin 40, 873–878. Statham, J.A., McMeekin, T.A., 1994. Survival of faecal bacteria in Antarctic coastal waters. Antarctic Science 6, 333–358.
Note
A simple method to reduce discharge of sewage microorganisms from an Antarctic research station Kevin A. Hughes *, Nigel Blenkharn British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
Abstract The majority of coastal Antarctic stations release untreated sewage into the near-shore marine environment. This study examined bacterial reproduction within the temporary sewage-holding tanks of Rothera Research Station (Adelaide Island, Antarctic Peninsula) and monitored sewage pollution in the local marine environment. By continuously flushing the sewage-holding tanks with cold seawater we inhibited microbial reproduction and decreased the numbers of bacteria subsequently released into the sea by >90%. The widespread use of this simple method could significantly reduce the numbers of faecal coliform and other non-native microorganisms introduced into the Antarctic marine environment. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Antarctica; Coliforms; Faecal pollution; Seawater; Sewage outfall
1. Introduction At present, most Antarctic research stations discharge untreated sewage waste directly into the marine environment. In order to protect the Antarctic environment, the Antarctic Treaty nations agreed the Protocol on Environmental Protection, which came into force in 1998 (Antarctic Treaty Consultative Parties, 1991). Annex III of the Environmental Protocol allows sewage and domestic liquid wastes to be discharged into the sea, provided that large quantities of waste (generated by 30 people or more) receive at least primary treatment such as maceration, and final discharge is located where conditions exist for initial dilution and rapid dispersal. Several studies describe the extent of sewage pollution released from Antarctic stations (Howington et al., 1992; McFeters et al., 1993; Bruni et al., 1997; Delille and Delille, 2000) and their ecological effects (Edwards et al., 1998; Smith, 2000). Lenihan et al. (1990) showed that sewage effluent from McMurdo station in the Ross Sea influenced marine benthic communities close to the sewage outfall. Sewage is a source of human-derived bacteria, yeasts and viruses that are not native to the Antarctic. Once released, enteric bacteria can remain *
Corresponding author. Fax: +44-1223-362616. E-mail address: [email protected] (K.A. Hughes).
viable in low temperature Antarctic waters (0 °C) for prolonged periods (Smith et al., 1994; Statham and McMeekin, 1994) and untreated sewage can affect biological oxygen demand (Howington et al., 1994). Several authors have recommended that sewage be fully treated before discharge into the polar environment (Halton and Nehlsen, 1968; Antarctic Treaty Consultative Parties, 1991; McFeters et al., 1993). However, logistic constraints mean that the release of untreated sewage into the marine environment is often the only option available––especially at smaller Antarctic stations. Given the requirements of the Environmental Protocol and the practical likelihood that release of untreated sewage will continue to be the preferred option for the majority of coastal Antarctic stations, a simple method to reduce the discharge of sewage-derived microbes would help protect the Antarctic marine environment. Rothera Research Station is a permanent British station situated on Rothera Point, Adelaide Island, Antarctic Peninsula (67°340 S, 68°080 W) (Fig. 1). It is the largest of the five bases maintained by the British Antarctic Survey with a population of 20–25 in the austral winter, which can rise to over 100 during peak periods in summer. Untreated sewage has been released into the sea since the base opened in 1976. An integrated sewage disposal system operates in all the inhabited buildings and carries human waste, grey water and food waste to
0025-326X/03/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0025-326X(02)00224-2
354
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
number of sewage microorganisms released into North Cove.
2. Materials and methods Throughout the austral winter of 1999 (April–October), 20 people lived on the station. The sewageholding tank in the main accommodation building was studied as it had the greatest level of sewage input. The seawater temperature around Rothera Point was 0 °C throughout the year and provided a readily available supply of cold water which was used routinely to flush toilets and was stored in large tanks in the building roof space. When required during this study, cold seawater was gravity fed to the sewage-holding tanks, which allowed continuous flow. No faecal coliforms were detected in the stored seawater. 2.1. Experiment 1. Effect of continuous salt water flushing on microbial numbers within a sewage-holding tank
Fig. 1. Map of Rothera Research Station, Rothera Point, showing the position of the sewage outfall (SO), main sewage pipe (SP), sewageholding tank (HT), seawater intake pipe (SWI) and Site of Special Scientific Interest (SSSI number 9). Crosses represent water sample sites.
three sewage-holding tanks (1000 l) within the base buildings. The tanks store the sewage until full, after which the contents are simultaneously macerated and pumped into the main sewage pipe that empties into the sea at the high tide mark on North Cove beach (Fig. 1). The sewage does not undergo any secondary treatment. In 1987, a seawater desalination plant was installed to supply the station with potable water. The seawater intake pipe is situated 8 m below sea level on the opposite (southern) side of Rothera Point to the sewage outfall and it was determined that sewage contamination of the potable water supply was not taking place. Conditions favouring microbial reproduction were created within the sewage-holding tanks through addition of warm water from showers and other domestic equipment (increasing the temperature), macerated food waste from the kitchens (supplying nutrients) and human waste (inoculum). At night, liquid input to the storage tanks was minimal, therefore reducing the frequency of emptying and prolonging microbial residence time within the tanks. It was hypothesized that regularly flushing the sewage-holding tanks with cold seawater would limit microbial reproduction and reduce the
The initial study period was between 21:00 and 09:00 local time (00:00–12:00 GMT) during two successive nights (9–10 and 10–11 May 1999). During the night of 9–10 May, the sewage tank was allowed to fill with human waste and grey water as normal. No additional cold seawater flushing occurred. Liquid sewage samples were collected hourly in triplicate, 0.1 m from the base of the tank in sterile disposable Universal bottles and immediately transported to the station microbiology facility. During the next night (10–11 May), cold seawater was continuously added to the sewage-holding tank. Consequently, the tank was filled and emptied once every hour (900 l). This volume consisted of grey water and human waste collected in that hour, with the remainder being cold seawater. On each hour, after samples were collected, the tank was rapidly emptied to the minimum level of 100 l and then allowed to refill over the next 60 min period. Faecal coliforms were enumerated on membrane lauryl sulphate broth (MLSB) plus 1.5% agar (Oxoid, Basingstoke, UK) using the plate count technique according to established procedures (Anon, 1994). The volume of sewage in the holding tank was recorded from the tank control panel and sewage temperature was recorded within the tank. 2.2. Experiment 2. Daytime enumeration of faecal coliforms in the sewage-holding tank and North Cove After initial analysis of coliform numbers in the main building sewage-holding tank on 9–11 May, all three station sewage-holding tanks were steam-cleaned to remove any settled sewage sludge and sediment on 17 May. Continuous cold seawater flushing of the tanks
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
355
Changes in the sewage-holding tank volume during the two treatments are shown in Fig. 2. During the first night, when no salt water flushing occurred, the tank filled once within the 12 h study period. From 21:00 to 01:00 there was an increase in waste input due to clearing up after the evening meal and station personnel preparing to go to bed. After this there was a 6 h period where there was little input of waste into the tank. By
07:00 station personnel were rising and waste water levels increased again until 09:00 when the monitoring ceased. On the second night, 12 tank flushes were made of 900 l each. When cold water flushing was absent (9–10 May) there was a high initial temperature (33 °C) due to the hot water used to clear up after the evening meal. This was reduced to 25 °C within an hour and remained above 22 °C until 09:00. At 21:00 on the evening of 10– 11 May, just prior to cold water flushing, the initial temperature recorded was 25.5 °C. Once the seawater flow commenced, the temperature was reduced to 18 °C within the first hour. By 01:00 it was reduced to 6.5 °C and remained low until 09:00 when the experiment ended. As the sewage-holding tank could not empty to a level less than 100 l, a semi-solid sludge layer had formed on the base of the tank. This was overlaid by a fluid suspension of faecal material and food waste that was sampled throughout the experiment. Fig. 3 shows the number of faecal coliforms present in the liquid sewage within the tank during the sampling periods. This was estimated by multiplying the microbial count ml1 by the tank volume. During the night of 9–10 May, when no flushing occurred, the initial number of coliforms in the tank remained roughly constant at, on average, 1:70 1012 for the first four hours. Between 01:00 and 07:00 bacterial numbers increased 10-fold (1:87 1012 to 1:93 1013 ) although there was no additional sewage input. On 10–11 May, when seawater flushing commenced, there was an initial 6-fold decline in coliform number in the tank within the first two hours. By 09:00 this became a 25-fold decline (1:74 1012 to 7:00 1010 ). Faecal coliforms were lost from the tank during regular hourly emptying; by 04:00 this number was around 1% (1 1011 ) of the number in the tank when then there
Fig. 2. Volume of liquid in the sewage-holding tank: no flushing (dashed line), hourly flushing (solid line).
Fig. 3. Faecal coliforms in the sewage-holding tank: no flushing (), hourly flushing (j).
commenced and continued for three months (17 May– 28 August). Faecal coliforms were then enumerated in the main building sewage-holding tank during the daytime (07:00–01:00) and also in the sea around the sewage outfall (27 and 24 August, respectively). The sewage tanks were then returned to their normal ‘no flushing’ state (28 August), and after roughly one month the faecal coliforms in the tank during the daytime and in the sea were enumerated again (1 October and 28 September, respectively). Seawater samples for microbial analysis were collected beneath winter sea ice from around North Cove (Fig. 1). The sea ice limited the input of faecal material by wildlife and microbial cell damage by solar radiation. The seawater samples were collected 1 m below the water surface and immediately taken to the laboratory for microbiological analysis. Faecal coliform bacteria were enumerated in triplicate by the membrane filtration (0.2 lm, Sartorius, Goettinger, Germany) and plate count techniques on MLSB agar (Anon, 1994). Maps of faecal coliform distribution in North Cove were created using ARC INFO version 7.2.
3. Results 3.1. Experiment 1
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K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
was no hourly flushing (1 1013 ). When the number of faecal coliforms released over the 12 flushes was added up, the total was only around 10% of the number released from the tank at the end of the 12 h without flushing.
when no flushing occurred (1 October). Faecal coliform concentrations in North Cove were also less when the tanks were flushed with cold water (24 August) compared to when there was no flushing (28 September) (Fig. 4).
3.2. Experiment 2 4. Discussion Calculation of the mean daytime faecal coliform number in the tank during each of the two treatments showed that flushing with cold seawater (27 August) reduced the coliform count by >24-fold compared to
Fig. 4. Distribution of faecal coliform bacteria in North Cove, Rothera Point during 24 August (seawater flushing of sewage tanks) and 28 September (seawater flushing ceased). Numbers represent the common log exponent of faecal coliform numbers 100 ml1 seawater.
Our study indicated that microbial reproduction within the sewage-holding tank, during periods of low liquid input, significantly increased the number of viable faecal coliform bacteria subsequently released into the Antarctic near-shore marine environment. However, continuous dilution of the waste with cold seawater caused a large decline in enteric bacterium reproduction within the tank, which subsequently reduced coliform concentrations in North Cove. When seawater flushing was initiated, our data showed that the number of faecal coliforms in the tank remained >7 1010 because the semi-solid sewage mass at the bottom of the holding tank was acting as a reservoir source of coliform bacteria. Due to the design of the holding tank, the sludge was not removed when the liquid was emptied, and served as a semi-permanent inoculum for microbial propagation. After this material had been removed by pressurized steam cleaning (17 May 1999), and the flushing resumed, bacterial numbers in the tank were routinely less than 5 109 . By 27 August the faecal coliform counts were again >7 1010 due to faecal sediment that had again settled in the tanks during the previous three months. This highlights the importance of tank design and initial sewage system planning in reducing sediment accumulation. Although a few Antarctic stations have sewage treatment plants, such as Rotating Biological Contractor Systems (el Naggar and Schoppe, 1994; Lori et al., 1996; Knox et al., 2001), most do not have any sewage treatment facilities. As a result the release of non-native microbes is widespread, yet permitted under Environmental Protocol regulations. In a wider context, other parts of the Environmental Protocol prohibit the import into the Antarctic of soil and other biological materials that may contain non-native microbes. Consequently, there is inconsistency in the regulations governing the anthropogenic spread of non-indigenous microorganisms in Antarctica. From this study, recommended methods to reduce microbial reproduction in Antarctic sewage-holding tanks include: (1) continuous flushing of tanks with a supply of cold water to reduce microbial reproduction, (2) selection of a sewage-holding tank design that limits build up of faecal sludge sediment, (3) regular cleaning of tanks to remove any highly contaminated sediment, thus ensuring that resident microbial numbers in the tank are limited.
K.A. Hughes, N. Blenkharn / Marine Pollution Bulletin 46 (2003) 353–357
The British Antarctic Survey has undertaken a range of sewage impact studies (Lohan et al., 2001; George, 2002) and as a result is installing a biological sewage treatment plant at Rothera Research Station to reduce pollution further.
Acknowledgements This work was supported by the British Antarctic Survey’s ‘Biomolecular Responses to Environmental Stresses in Antarctica’ project and the Environment and Information Division. We thank C. Thompson, P. Wickens, G. Fell, M. Annat and C. Day for assistance during sampling and N. McWilliam for map production. K. Jones is acknowledged for advice on methodology and P. Convey, D. Walton and J. Shears are thanked for their advice and comments on the manuscript.
References Anon, 1994. The microbiology of water 1994. Part 1––drinking water. Methods for the examination of waters and associated materials. Report on public health and medical subjects no. 71. Her Majesty’s Stationery Office, London. Antarctic Treaty Consultative Parties, 1991. Protocol on Environmental Protection to the Antarctic Treaty. CM 1960. Her Majesty’s Stationery Office, London. Bruni, V., Maugeri, T.L., Monticelli, L., 1997. Faecal pollution indicators in the Terra Nova Bay (Ross Sea, Antarctica). Marine Pollution Bulletin 34, 908–912. Delille, D., Delille, E., 2000. Distribution of enteric bacteria in Antarctic seawater surrounding the Dumont d’Urville permanent station (Adelie Land). Marine Pollution Bulletin 40, 869–872. Edwards, D., McFeters, G., Venkatesan, M.I., 1998. Distribution of Clostridium perfringens and fecal sterols in a benthic coastal marine environment influenced by the sewage outfall from McMurdo station, Antarctica. Applied and Environmental Microbiology 64, 2596–2600.
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el Naggar, S., Schoppe, S., 1994. Waste management concept at the German winter station Neumayer. In: Giuliani, P. (Ed.), Proceedings of the Sixth Symposium on Antarctic Logistics and Operations. Italian ENEA Antarctic Project, Rome, Italy, pp. 13–23. George, A.L., 2002. Seasonal factors affecting surfactant biodegradation in Antarctic coastal waters: comparison of a polluted and pristine site. Marine Environmental Research 53, 403–415. Halton, J.E., Nehlsen, W.R., 1968. Survival of Escherichia coli in zero degree centigrade sea water. Journal of the Water Pollution Control Federation 40, 865–868. Howington, J.P., McFeters, G.A., Barry, J.P., Smith, J.J., 1992. Distribution of the McMurdo station sewage plume. Marine Pollution Bulletin 25, 324–327. Howington, J.P., McFeters, G.A., Jones, W.L., Smith, J.J., 1994. The effects of low temperature on BOD in Antarctic seawater. Water Research 28, 2585–2587. Knox, G., Ling, N., Patrick, M., Wilson, P., 2001. State of the Ross Sea region marine environment. In: Waterhouse, E.J. (Ed.), Ross Sea Region––a State of the Environment Report for the Ross Sea region of the Antarctic. New Zealand Antarctic Institute, Christchurch, New Zealand, pp. 5.1–5.52. Lenihan, H.S., Oliver, J.S., Oakenden, M.D., Stephenson, M.D., 1990. Intense and localized benthic marine pollution around McMurdo station, Antarctica. Marine Pollution Bulletin 21, 422–430. Lohan, M.C., Statham, P.J., Peck, L., 2001. Trace metals in the Antarctic soft-shelled clam Laternula elliptica: implications for metal pollution from Antarctic research stations. Polar Biology 24, 808–817. Lori, A., Ponzo, U., Indulti, M., Stefanoni, M., 1996. A new waste water treatment plant installed at the Italian Antarctic station of Terra Nova Bay. In: Hall, J. (Ed.), Proceedings of the Seventh Symposium on Antarctic Logistics and Operations. British Antarctic Survey, Cambridge, pp. 263–278. McFeters, G.A., Barry, J.P., Howington, J.P., 1993. Distribution of enteric bacteria in Antarctic seawater surrounding a sewage outfall. Water Research 27, 645–650. Smith, J.J., Howington, J.P., McFeters, G.A., 1994. Survival, physiological response and recovery of enteric bacteria exposed to a polar marine environment. Applied and Environmental Microbiology 60, 2977–2984. Smith, S., 2000. The effects of a small sewage outfall on an algal epifaunal community at Macquarie Island (sub-Antarctic): a drop in the Southern Ocean? Marine Pollution Bulletin 40, 873–878. Statham, J.A., McMeekin, T.A., 1994. Survival of faecal bacteria in Antarctic coastal waters. Antarctic Science 6, 333–358.