Wastewater and Sewage Treatment

• History

• Preliminary Treatment

• Primary Treatment

• Secondary Treatment

• Tertiary Treatment

• UV Treatment

• Other Treatments

The Methodology, Terminology and Results

There are many viable ways of treating human waste so as to render it safe to health and non-damaging to the environment. Indeed, methods exist to recycle it to form a valuable resource as a fertilizer and land conditioner. And then there are numerous ways to dispose of it that threaten human and animal health and the eco-system in general. Here is a brief summary of those means.

History

In the past, many communities were decimated due to washing in, bathing in and even drinking the water into which their excreta had been disposed. In the late 1940s a widespread epidemic of both typhoid fever and polio hit Britain. Both are ‘faecal-oral’ diseases, e.g. infections spread by ingestion or oral contact of the faeces by hosts. Many people died as a result of swimming in sewage-polluted waters, including Caroline, the daughter of Tony Wakefield, who formed the Coastal Anti-Pollution League, the very first group to oppose the bad practice. Most of Britain’s sewage was going totally untreated to rivers and to the sea, as it had been for many years. As a result of the evidenced serious health threat the government of the day set up a Royal Commission enquiry under the Chairmanship of Sir Richard Southwood. After studying the evidence they belatedly reported in 1959, concluding their report with the statement:-

“On the proviso that the bathing water is not so polluted as to be aesthetically revolting, there should be no danger to public health.”

In other words, if you can’t see it, you’re safe. But although seemingly banal and dismissive, it was in fact partly true, as one would easily have spotted the turds, condoms, sanitary towels and other sewage outfall debris littering the bathing water and the shoreline, and so decide not to enter unless one had called the Samaritans first. If the obvious indicators of faecal pollution were not obvious, then the chances are that it would be reasonably safe to enter that water. Sadly the Commission’s ambiguous conclusion was seized upon by the water authorities as an excuse to continue to pump untreated sewage to the sea. Anglian Water’s following criteria for marine sewage disposal stated:-

“Where effluent is discharged to the sea, the impact on the receiving water cannot be assessed in a manner used for works on inland waters. The criteria for the performance is then related to the visible effect of the discharge on the coastal water or the foreshore. A sea outfall is judged to be satisfactory if under normal operation it does not cause solid matter to be deposited on the shore …” i.e. if you can’t see it, you’re safe!

Here is a partial listing of those pathogenspathogens A virus, bacterium or parasite which causes disease is a pathogen. Disease causing pathogens live in the environment, and both humans and animals are hosts to them. Pathogenic viruses, bacteria and parasites are present in sewage, originating from humans and animals, and thus it is essential that sewage is given proper treatment in order to disable (kill) these pathogens before the end-products of sewage treatment (solids and water effluent) are returned to the environment. that we now know may be found to be present in untreated sewage, and the diseases that they can cause:-

1) Bacterial Pathogens

2) Viral Pathogens

Reference:- Memoranda from Pat Gowen, Norwich & Broadland Friends of the Earth to the House of Commons 1997-98 Environment, Transport and Regional Affairs Committee on ‘Sewage Treatment and Disposal’, pages 179 – 188, published 28th October 1997.Stationary Office, London, HC266-III.

Additional to these are parasites that too can damage health, such as: –

3) Parasites

Concern was expressed that laboratory experiments proved that HIV-3 (Aids) (that could arise from menstrual blood and semen in contraceptives going down sewage outfalls) can live in sea water for up to 1.6 days. It has also been conjectured if the BSE/CJD prion could be present due to effluents containing abattoir waste.

The net result was the ‘Long Sea Outfall’, in which disposal the effluent is chopped up and forced through a 6 to 8mm mesh to trap any items that would betray the evidence of the outgoing sewage. The soup is then pumped to the sea without any treatment whatsoever to destroy the pathogens. In fact the result is far worse than that of the predecessor, as the turbidity density produced by the sludge in the receiving water reduces light penetration. It further demands the available oxygen. Both of these are essential to enhance the decay of the bacteria and viruses. The viruses attach mainly to the sludge particles, and remain infective for very long periods. To increase profitability, Anglian Water closed down the sewage treatment plant at Caister-on-Sea in favour of a long sea outfall. To meet the Directive(s) they have since had to reinstate treatment and thus wasted a great deal of money.

Sir Hugh Rossi, Chairman of the House of Commons 1989-90 Environmental Committee Enquiry into the Pollution of Beaches likened Long Sea Outfalls to the earlier British practice of building higher chimneys that whilst reducing the level of local pollution exported the problem to far wider areas to decimate the trees and lakes in northern Europe.

By the time that the danger of Long Sea Outfalls was recognised, despite the early warning and advice of environmental and health organisations, water companies had wasted many millions of water-ratepayers money by destroying sewage treatment plants and building many Long Sea Outfalls, only to find that what they had been warned of, i.e. more pollution dispersed over a far wider coastline, was true. To conform to the requirements of the Urban Waste Water Directive and to be able to comply with the demands of the Bathing Waters and Shellfisheries Directives, proper treatment of all marine outfalls is essential.

Ancient History and Necessity

It has long been known that contact with sewage poses the greatest single known threat to health. The ancient Chinese dynasties, the Egyptians under the Pharaohs, the Saxons and the Romans all recognised this, and took steps to prevent the faecal related diseases which they well recognised could wipe out entire communities. They knew nothing about pathology, bacteria or viruses, but they were fully aware of cause and effect, so practised simple but effective means of sewage disposal. Dogs and other carnivores attempt to cover and bury their own excreta, yet few of these creatures have studied pathology. Such methods of safe disposal come from inherited instinctive behaviour, because species that followed this practice survived whilst those who failed to do so became extinct. Every nursing mother knows of faecal dangers. Children are taught to thoroughly wash their hands after visiting the toilet. You know the basic hygiene required, I know it, and every little child knows it, but it appears that our water companies and the British government remained blissfully unaware, as they continued to permit the dumping and pumping of millions of gallons of untreated sewage into the sea every day.

Sewage is a valuable product, which, on the proviso that it is free from heavy metals and dangerous industrial and chemical inputs, and has been sterilized and properly treated so as to kill off infective pathogens, can be used as a basis for many things valuable to the community. Indeed, in most civilized countries sewage is so dealt with, normally composted and used for the land, which also reduces the need for damaging artificial chemical fertilizers. Here are some of the many means of treating sewage – the good, the bad and the ugly.

Treatment Methodologies

There are many specific ways of treating sewage to render it safe to human health and the environment. Here follow the main.

Preliminary Treatment.

Already mentioned above when used in conjunction with Long Sea Outfalls, this is not actual treatment as such although claimed to be. It is more of a disguising process in which the effluent is chopped up and forced through a 6 to 8mm mesh to trap any items that would betray the evidence of the outgoing sewage. The soup is then pumped to the sea without any treatment whatsoever to destroy the pathogens. Many millions of pounds were wasted by the water companies in closing down treatment plants and substituting them with preliminary treatment to long sea outfalls. Now that the Urban Waste Water Directive is in force, this highly polluting practice is illegal, and primary and secondary treatment must be applied as a minimum.

Primary Treatment

This treatment removes the sludge, the solid content of sewage. It may take the form of either filtration or by settling the sludge by sinking it in large holding tanks. The bacterial reduction is normally 90%, and the viral reduction even greater, as the viruses mainly attach to the solids. As it is mainly the sludge that demands the oxygen and is also responsible for the turbidity, any following secondary treatment then becomes effective. The sludge removed by the primary process may be digested, sterilized, or otherwise treated, and if free of heavy metals or other toxic content, may be safely used as a soil conditioner and fertilizer or other uses. When dried by the heat sterilization process it is known as ‘Basic Sludge’ and widely used as compost. Sadly, certain Water Companies provided the primary solids completely untreated to farmers under the heading of ‘Soil Conditioner’ so risking pathogen contamination of vegetables and stock. This practice is now banned. But still much of the sludge is wasted by disposal to landfill tips.

Secondary Treatment

This involves aeration of the clear effluent produced following primary treatment solids removal. The liquid phase may be aerated in daylight in large storage tanks, or it may be trickled or sprayed over banks of stones open to the air and daylight. Both are effective. The pathogen reduction is a further 90%, giving now 99% total reduction in infectivity. As the biological oxygen demand is now substantially reduced and the transparency to natural UV light penetration much enhanced, if now placed into the sea, a further rapid die-off of organisms will come about. The Urban Waste Water Directive, implemented in December 2000, requires that no sludge shall enter the sea, i.e. primary treatment, and that secondary treatment must be applied as a minimum.

Tertiary Treatment

This just means ‘Third Degree Treatment’, but not that sort seen in the Hollywood gangster and police movies. It may take the form of passing the primary and secondary treated liquid phase through clear quartz tubes exposed to intense ultra-violet light. With fully transparent and well-oxygenated liquid phase effluent, this can totally destroy all known pathogens, and so be employed to provide safe discharges to bathing waters and to shellfish areas. Such has been used for all of Jersey’s outfalls since 1995, where the direct output of the sea going sewage plants produce pathogen levels far lower than in any British bathing water. But ‘Tertiary Treatment’ may also include chemically stripping off the phosphate and nitrate levels found in the outfall. The phosphates emanate from detergents and from human urine in the effluent, whilst nitrogen as ammonia from urea in urine come from both sewage and agricultural sources. Such nutrient stripping treatment may be essential in waters where eutrophicationeutrophic Water (freshwater or saline) is said to be eutrophic when all normal life in it has died due to oxygen starvation. The process is usually caused by excess nutrients present in the water which causes an explosion in algal species (known as an algal bloom). As this algal bloom dies the decaying plant material (algae) falls to the bed of the watercourse where it is consumed by bacteria. This abundance of decaying material in turn causes a population explosion in the bacteria. However, bacteria (unlike plants) consume oxygen and the population explosion of bacteria strips all the dissolved oxygen out of the water with the result that all other aquatic species who are reliant on the dissolved oxygen for breathing (e.g. fish, larvae, insects) are asphyxiated and die. When this process occurs, a body of water is said to eutrophic. A body of water that is partially eutrophic is where this process (oxygen starvation) has fallen short and/or not yet reached its fullest extent. is likely to produce dangerous levels of toxic algae, such as brought about the shellfish ban some five years ago. The Urban Waste Water Directive requires that tertiary treatment may be necessary in ‘environmentally sensitive areas’. Surely the entirety of the North Sea is such? Denmark provided full tertiary treatment to all of its sea outfalls in 1995. Britain has but a tiny handful to this day.

Ultra-Violet Treatment

As stated under Tertiary Treatment, in UV treatment the clear effluent resulting following primary and secondary treatment is passed through transparent tubes and irradiated with powerful UV light. If fully efficient, the remaining viruses and bacteria can be killed to give an output that could virtually be drunk, even the undiluted output straight from the effluent pipe being far less infective than the sea of most of the British coastline. Such treatment, if correctly run, gives bathing beaches that easily meet the EC Guideline standard. UV is already in use in many countries, but despite promises to adopt for the Welsh and South Western UK areas, few have yet to come about in practice. This method is quite one of the very best methods possible, and is much to be recommended. Unfortunately is does not sterilize the sludge, as the UV is unable to penetrate the turbidity.

Natural Treatments

In east and southeast Europe, and indeed in most non-western countries, sewage is regarded as a resource rather than a problem. It is composted with animal waste, straw, seaweed, or any natural organic material to provide a totally safe valuable moisture retaining agricultural product. Pathogen destruction is brought about by the heating provided in the composting cycle. On the proviso that no toxic chemical or industrial contents are present, the product makes a remarkably good fertilizer. Wye College in Kent have a rapid method of composting the primary recovered sludge with waste straw and seaweed recovered from the beaches to provide a superb potting compost used by many plant providers. It is an excellent alternative to peat.

For small non-rural communities with the required land space available, the sewage can be trickled through reed-beds, which take out most of the organics and nutrients whilst the oxygen in the air and the ultra-violet light from the sun kills the pathogens. Although excellent, such is not really viable for large urban communities with considerable loadings and high land costs. A visit to www.rockbourne.net/waste_water_treatment.html offers a path to further detail.

Individual ‘dry’ toilets work well as pollution preventers, as indeed do the cesspools still used in many country areas. It could be said that the flush toilet, thought once claimed to be the very pinnacle of hygiene, has in fact been the basic cause of most of the faecal pollution and eutrophication of our rivers and seas that we have today.

Filtration

The ‘Memcor’ micro filtration process, whilst not addressing the primary sludge problem, is an excellent process for purifying the liquid effluent before disposal to river, estuary or sea. The liquid phase is passed through a very fine electronically created membrane with pores so fine that they filter out all the sludge, bacteria and viruses. Backpressure cycles are incorporated to prevent clogging. Similar systems were used on the MIR Space station, where all the wastewater goes in one end to provide fresh water at the output. Such a system provides excellent recycling and complete safety. It is much to be recommended.

Oxy-ozo-synthesis

Here the sewage is acidified and injected with ozone created by passing oxygen through an electric arc. It not only sterilizes the sludge, but bleaches it too, permitting its re-use as insulation material, for newsprint, as packaging or as fuel, which sells at £50 per ton. The supernatant liquid too can be ozonised in the outgoing pipeline to render it free of all pathogens prior to discharge to water. An excellent process although possibly more expensive than some. It was successfully used for the treatment of New York’s and New Jersey’s sewage until the Union bosses objected to the loss of employment of those who took the sludge out in barges to dump in the Atlantic Ocean!

Chlorination

Chlorine treatment, as with ICI’s ‘Coastguard’ system, whilst effectively destroying the pathogens, is not to be recommended. The large number of organochlorines and organic bromines formed can be highly toxic to the marine environment as they are both mutagenic and carcinogenic. Another method involving chlorination is by the addition of sodium hypochlorite into the sewage. The same environmental hazard results as with direct chlorination.

Electrolysis

This is simply passing a high electrical current through the effluent, producing by electrolysis hydrogen, oxygen and heat. This method certainly sterilizes very well, partly so because of the chlorine produced from saline water. It is not to be advised because this methodology produces chlorine hence organochlorines like direct chlorination.

Peracetic Acid

As used by the ‘Oxymaster’ system, this process relies on the addition of acetic acid and hydrogen peroxide to the sewage. Whilst this effectively kills off the coliform indicator bacteria, it may be seen as merely cosmetic, as it is far less effective against other bacterial pathogens and viruses. Thus whilst bathing waters may be brought to meet the EC Directive standards by its use, the most infective pathogens may remain infective. It can also oxidise the urea in urine to give rise to free chlorine.

Other Methods of Treatment

Yes, there are many more, and no doubt many more still will be many more evolving in the future. But this treatise is not intended to be exhaustive nor even comprehensive. It is merely to show that human effluent can be treated to render it not only benign but also actually beneficial to mankind and the environment. Whatever treatment is selected, it just has to be superior to dumping such hazardous untreated material into the marine or estuarine environment to give health problems to people, marine mammals and all the sea creatures upon which we depend.

Current Status

Although much improved, Britain still has many sewage polluted resorts that fail to meet the imperative 1975 Bathing Water Directive mandatory demands. In January 2005, it has yet to meet the requirements of the 2000 Urban Wastewater Directive. European Court action is now imminent because of this failure of the British government to meet its obligations.

Pat Gowen, North Sea Action Group, first written 27th September 2000, updated 23rd January 2005.

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