SEWAGE DISPOSAL AT SEA (Pipeline Discharges)
Part 3: The Health Risk
by Andy Horton 1993
Previous reports on sewage in the sea in Glaucus have been couched in relatively simple terms because they have only investigated the effects of sewage outfalls on the marine fauna.
The articles concluded that even raw sewage discharges into the sea would not be detrimental, except in special wildlife areas or marine reserves. The increase in turbidity could possible cause some impoverishment but this would be small in comparison to the damage caused by scallop dredgers.
However, it is recognised that in the course of the study and investigation of marine life, members will snorkel, dive, and fish in contaminated waters, and will frequently collect and consume seafood, including bivalve molluscs (mussels, cockles etc.) that could prove harmful to their health.
Legal Directives
The E.C. Bathing Water Directive 76/160/EEC obliged the U.K. government to bring in laws to achieve the following levels:
95% of samples should contain these levels.
Guide (G)Mandatory (I)
Total coliforms/100ml50010,000
Faecal coliforms/100ml100 2,000
In order to comply with the Directive 80% of the samples must meet the G-levels and 95% of the samples must meet the I-levels.
The Directive 91/492/EEC applies to shellfish.
------
Health Risk Surveys
"Establishing a link between minor illnesses such as gastroenteritis and ear, nose and throat infections is extremely difficult because these conditions are so common and may have various causes. Some headway has been made from large epidemiological studies which have compared the symptoms of swimmers with those of people who stayed out of the water" (Alison Walker, British Medical Journal).
All surveys have concluded that there is a significant statistical risk in contracting a minor illness e.g. gastroenteritis, upper respiratory infections after bathing in contaminated seas1. However, although the numbers tested run in many thousands, the controls were not rigorous enough to become convincing. The results of a four year research project coordinated by the Department of the Environment will be available later this year1.
Local opinion that I have been able to ascertain from Sussex where the beaches regularly exceed the mandatory coliform levels indicate that bathers, divers, shellfish collectors could expect to have abrasions infected, and these may take along time to clear up. There is at least one report from a regular swimmer who has contracted an unpleasant stomach complaint (gastroenteritis) after swimming for long periods (over 15 minutes) on a regular basis. Illness from eating prawns or fish caught in contaminated seas is fortunately non- existent, which was surprising because shrimps, prawns, and even mussels and cockles have been eaten from contaminated waters near the coast.
Controversy
The biggest discrepancy of information occurs in an area where it could be expected to obtain accurate information. This is on the efficiency of the secondary biological treatment process in removing bacteria, viruses, and other pathogens.
It must be remembered that the bacteriological (or biological) treatment has a principal function of reducing the organic load and biological oxygen demand, and the removal of solid material. (See Part 2).
Campaigners against sewage pollution in the sea have claimed that that secondary treatment is necessary to make the seas safe to swim in, and to comply with the EEC Directives. Southern Water (and other water companies) have maintained that secondary treatment is not necessary and that the various alternative methods, usually primary treatment with a long sea outfall will ensure that the bathing waters are clean enough to swim in.
The difficulty that arises is the definition of what constitutes secondary treatment. The degree of reduction will vary depending on the type of secondary treatment employed, for example activated sludge or trickling filtration. Published data indicates that bacterial removal during secondary filtration varies between approximately 40% and 90%. This does not take into account the percentage removed during primary treatment, which again varies with the process employed2.
1Information supplied by Steve England from 'Surfers Against Sewage'.
2Information supplied by Michael Stephen M.P. (Shoreham) from a letter by Lord Strathclyde (DOE Marsham Street).
------
PREVIOUS ARTICLES
Sewage Pollution
Part 1:
Introduction: Sewage Disposal at Sea
(02.02.24-25,29)
Part 2:
Effects on Marine Fauna
(02.04.27-29)
------
Part 4: Bathing Water Testing
Coliform Counts
The bacteria measured by the coliform count is Echerichia coli. It is a natural occurring bacteria always present in the intestine, and because of this it is used as a rough and ready indicator as to the extent of sewage contamination.
In normal circumstances it will not make humans ill. However, after prolonged swimming, or diving, over an hour, these bacteria can cause a secondary infection in cuts and grazes, and had been positively identified from pus, by cultures (Dr P. Glanvill M.D.). There are several different strains of Echerichia coli and strains different from those normally present in the population can cause illness of the 'gippy tummy' variety encountered on trips abroad. Extensive intake of Echerichia coli can also cause illness although this is unlikely.
National River Authority Readings
Twenty sea tests are meant to be undertaken on a random basis between the months of May and October when bathing is thought likely to take place. The NRA take tests for total coliforms, and faecal coliforms regularly with other information collected that would effect the readings, including the visual appearance of the water3. Pressure group organisations have criticised the information obtained by the NRA for not being good enough, because there are no readings taken for the various pathogens known to be present in sewage including Listeria and Salmonella. The best part about the readings is that are easy to take, and samples have been taken by local councils, pressure groups, and by Coastwatch U.K.
Exactly how indicative that the coliform readings are of the amount of sewage I would have thought it was quite a good method - nobody seems to agree - but I have reservations about the randomness of the tests.
In Sussex, they are always taken at high water, or at least not at low water, and never at low spring tides. Because of the frequency of the waves and the topography of the shore - a shallow sand gradient, almost level from neap low water downwards, any rubbish in the sea, including sewage, is deposited on the low springs and not dragged back out to sea again. Bathing, paddling, shrimping, takes place in greater numbers than at high tide. I would estimate that the current tests would miss peak times for coliform counts and therefore underestimate the contamination.
3 Information from John Foster, Pollution Prevention Officer, National Rivers Authority (NRA), Worthing.
------
Independent Monitoring
The SBRA undertook samples for the 1991 season using the Coastwatch method. The National Rivers Authority and Adur District Council took other readings. We measured peaks of bacterial counts not measured by the other two organisations.
SUMMARY OF EARLIER ARTICLES
Faunistic Implications
1) Deoxygenation can occur when untreated sewage is pumped into the seas and rivers. Aerobic bacteria feed on the rich organic load in the sewage reducing the amount of dissolved oxygen in the vicinity of the outfall.
This is unlikely in the open sea, and secondary biological filtration is used to prevent anoxic conditions in rivers.
2) Particulate matter is a natural feature of many seas when storms stir up the sediments. Sewage contains a large amount of solids and particles. Some invertebrate animals are unable to survive in turbid conditions.
3) An eutrophic habitat is one that is high in mineral salts that are needed for primary productivity in the food chain. Even treated sewage is high in phosphates and nitrates, which in rivers can create eutrophic conditions in rivers. If the river is overnutrified the correct term should be 'hypertrophic'.
4) Toxic wastes can be introduced into the seas through the sewage system. Industrial pollutants, metals, pesticides, hydrocarbons are direct poisons in excessive quantities.
5) Sewage is termed 'wastewater'. The proportion of solid matter is 1 ppt (0.01%). The salinity is reduced over a small area of the sea.
Human Health Implications
Pathogens, including viruses and natural occurring human bacteria can survive for varying amounts of time in seawater. They can be ingested by swimmers and surfers, people eating seaweed, or infect wounds, including small cuts.
Aesthetics
A screen is usually, but not always, used to prevent large items like toilet paper giving obvious visible evidence of sewage discharges. With the screen affixed the wastewater is just a milky white colour variously diluted. Scum on the surface of the sea is often correctly attributed to various natural occurrences, including the presence of phytoplankton blooms.
------
European Standards
The EC Report 'Quality of Bathing Water 1992' lists the bathing waters of each EEC nation and the numbers which complied with and those that failed mandatory and guideline levels.
Mr Steen asked for this information in a Parliamentary Question on 21 July 1993, and an abbreviated text was included in the Water Bulletin.
(No. 569 Ref: B02 Contact Joyce Poynter Tel :071 957 4516).
Part 5: Methods of Treatment
Primary Treatment
Primary treatment consists of a screen to remove solids and settlement tanks to remove more particles. The discharge has a high organic content and biological oxygen demand (BOD). The effluent will still contain a large visible proportion of small particles at 0.01%.
The new chemical method uses 'ferric sulphide' at the settlement tank stage, which has the effect of binding together solid particles on plates. The effluent is only slightly discoloured.
Secondary Treatment
Secondary treatment involves passing water through filter beds, where the organic matter is trapped and consumed by aerobic bacteria. The discharge is clearer with a very low Biological Oxygen Demand (BOD).
Bacteria are adsorbed on to particles4. Different materials and methods can be used. The Activated Sludge method and the Percolating Filter are two examples.
In drinking water, chlorine (it forms hypochlorous acid) is added to achieve a bacterial kill rate of over 99%. Chlorine is toxic to marine life is small amounts although because it is a gas, it will quickly diffuses into the air. However, chlorine can combine with ammonia to form chloramine, which is more stable and just as toxic as chlorine to marine life.
Tertiary Treatment
This is method is only used when exceptionally high quality discharges are required. Algal ponds can utilize high levels of nitrates and phosphates in the water.
Ultra-violet Disinfection
This is an expensive and slow treatment that is only feasible after secondary bacteriological treatment, and even after tertiary treatment when the UV lights kill bacteria, including the minority of pathogens. It is only likely to used in areas where Grade 'A' shellfish seas are demanded5.
Natural Degradation
There are figures to state that in bright sunshine that 90% of bacteria in the sewage is destroyed by natural ultra-violet light for each hour in the sea6. In a normal British summer this hour should be extended to four hours.
4 Method deduced by the writer Andy Horton (unconfirmed).
5 Plant at Bellozane, Jersey, Channel Islands. (Source: Water Bulletin).
6 Royal Commission on Environmental Pollution 10th Report. (Information supplied by Graham Amy of Southern Water plc).
TREATMENT BOD % SOLIDS BACTERIA
------
1.Fine Screening2 - 20 25 - 20 10 - 20
2.Chlorination of Raw15 - 30 90 - 95
3.Plain Sedimentation25 - 40 40 - 70 25 - 75
4.Chemical Precipitation50 - 85 70 - 90 40 - 80
5.3 + Rapid Filtration35 - 65 50 - 80
6.4 + Rapid Filtration50 - 90 80 - 95
7.Trickle Filter + 380 - 95 70 - 92 90 - 95
8.Activated Sludge + 385 - 95 85 - 95 90 - 98
9.Intermittent Sand 90 - 95 85 - 95 95 - 98
10.Chlorination of
Biologically Treated 98 - 99
------
These figures were supplied by Graham Amy (Southern Water) from an old text. More comprehensive figures were supplied by K.M. Jury and John Foster of the NRA (Southern Region). The above figures are easier to understand at a glance. Chemically enhanced ('ferric sulphide') treatment will give a figure on all three counts between Primary Treatment and Secondary Treatment.
Part 6: Sussex
In common with most British seaside towns, the towns of Sussex discharge almost raw sewage directly into the sea, in 22 short outfalls just below low water mark. In most cases screens have been installed to prevent large items being discharged. At least 5 of the outfalls regularly fail the EEC mandatory level for coliforms.
Southern Water plc are beginning expensive (£100 million+) improvements to install improved Primary Treatment plants with settlement tanks.
SHOREHAM HARBOUR OUTFALL
I will examine the Shoreham Harbour outfall as a test case and try to examine what difference the improvements will make.
Graham Amy of Southern Water (Sussex Division) provided the information on the plans.
Current Situation:
Raw sewage is discharged directly into the sea about 800 metres offshore, which is just beyond the harbour arms, and not very far below Chart Datum (Extreme Low Water). A screen removes some of the larger items, but shredded toilet paper is clearly visible welling up to the surface. Discharge is only meant to occur two hours each side of high water. The pipe sometimes leaks and the sewage is then discharged nearer to the shore. Bacterial counts tested nearby frequently exceed the mandatory levels*.
* NRA figures, plus readings taken by Adur District Council (available to enquirers) and the SBRA (see page 19).
Proposed Improvements:
Primary Treatment is proposed using settlement tanks, fine screens, and a 3,100 metre long outfall. Discharges into 7.6 metres of water will occur at all states of the tide. The small proportion of solid particles will be reduced by 50% (see diagram on page 15).
There is no provision for storage of the sewage or cessation of pumping if the tides and weather are unfavourable. Southern Water considers that the tides and currents will disperse and dilute the sewage.
The discharge will still be visible from a boat in calm weather. Southern Water ensures the public that the beaches will be safe to swim on, and the bacterial counts will register at very low levels.
Southern Science Ltd EMU, Winchester, has published an Environmental Impact Assessment. Southern Water plc have also acquired sufficient land for any improvements in the treatment to be introduced in the future.
Current:
Faunistic:
Dissolved oxygen levels near saturation level, and Mackerel have been caught in the middle of the sewage outflow.
Small impoverishment because of turbidity, just as likely to have been caused by dredging operations.
Slightly eutrophic, but no fauna reductions.
Copper levels possibly too high.
Salinity alteration insignificant - at entrance to estuary.
Human Health:
Minor ailments and infections recorded. Mandatory bacterial counts regularly exceeded.
Aesthetics:
Visible sewage at sea, and often on the shore. Smells at low springs.
Proposed (now in operation):
Faunistic:
Dissolved oxygen levels at saturation level.
Particles dispersed over a large area and in naturally turbid waters will not have an environmental impact.
Primary productivity unlikely to be increased.
Copper will be adsorbed on to settled particles and discharge may comply with legal standards. Local sea around this discharge is polluted by tributyltin from commercial shipping.
Salinity change insignificant.
Human Health:
Bathers unlikely to suffer minor ailments in most years, but still could be encountered by surfers and divers. Whether the bacterial levels inshore can be complied is debatable, with a forecast of once every 10 years - instead of every year - that the levels are exceeded, largely dependent on the weather, with prolonged periods of light southerly winds and overcast skies producing bad conditions. It is difficult to envisage a longer outfall solving this problem.
In 2002, a similar sewage outfall resulted in 2 failures on the mandatory coliform counts, 2 that only passed, and 16 readings that complied with the stringent conditions.
Aesthetics:
Discharge will be clearly visible by yachtsmen in important leisure boating centre, but it will be less visible than before. Smells will disappear.
Other Possibilities
Introduction of the 'ferric sulphide' chemical addition to the Primary Treatment system will further improve the visible signs to acceptable levels, and reduce the incidence of sewage pollution in bathing waters to freak weather and tide conditions, and well within the EEC limits under the strictest interpretation of the tests.
Secondary Treatment will satisfy all likely bacterial counts, and water clarity at the expense of higher water bills, and air pollution caused by the transport of the sludge, although conceivably this could be shipped out.
SHOREHAM HARBOUR SEWAGE OUTFALL
Investigations by F. G. Evelein
Shoreham Beach Residents Association (SBRA).
In 1976 the European Community published a Directive 76/160/EEC outlining the allowable of bacteria coliforms, and faecal bacterial coliforms in seawater. There are two levels. The lower G-level is a guide for safe bathing, and the higher I-level, the mandatory level, should never be exceeded during the bathing season. This Directive has been accepted by the Dept. of the Environment in 1989.
The occurrence of sea pollution during one season (May to October) must be subjected to a statistical approach. At present, this approach leaves too much room for short term exceedances of the mentioned levels. The SBRA does not agree with the statistical approach and does not agree with the high G-level allowed. The latter is because a number of bathers have attributed illnesses to swimming in the sea below the I-level.
At present, in Great Britain, the Government guide is that when a sewage outlet serves at least 150,000 inhabitants, the secondary treatment should be installed.