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Purpose and Nature of Wastewater Collection and Treatment Systems
By Bert Gray, Principal Training Consultant, Opus Environmental Training Centre.
In essence the purpose of a wastewater collection/treatment system is to protect our environment and public health by ensuring that the wastewater is collected and treated to a specified level prior to discharge back to the environment.
A wastewater collection system or sewerage system is a network of pipes connected together which allow human and industrial wastewaters to flow, underground, from individual properties through to a central collection point where the wastewater is normally treated at a wastewater treatment plant and then discharged.
A Bit of History
This idea dates from ancient times, and such systems have been found in the ruins of the prehistoric cities of Crete and the ancient Assyrian cities. Storm-water sewers built by the Romans are still in service today. Although the main purpose of these was drainage, the Roman practice of dumping rubbish in the streets allowed the rubbish to be carried along with the rainwater runoff.
In many European cities, however, wastewater collection systems really only started to be developed in the 1800’s. Before that, people used to discharge their own wastewaters on land on or next to their own properties. If the people lived in large cities such as London, there was not enough room to do this in a sanitary manner and the streets became covered in filth.
A famous event occurred about this time in London, which was to show people the link between poor sewage disposal and disease. During the 1830s and 1840s, when severe cholera epidemics threatened London, a doctor named John Snow had become interested in what caused the disease and how it was spread. In 1849, he published a brief pamphlet, “On the Mode of Communication of Cholera”, suggesting that cholera “is a disease caused by a”poison” that reproduces in the human body and is found in the vomitus and stools of cholera patients”, (in those days, people did not know about microscopic organisms like bacteria, viruses, worms and protozoa that we now know can cause disease). He believed that the main means of passing disease from one person to another was water contaminated with this “poison”. This differed from what most people believed, which was that such diseases are caught by breathing in vapours, (smelly gases). The pamphlet caused no great stir, and Snow's argument was only one of many hopeful ideas about how cholera was spread, at a time when it was causing high levels of illness and death.
Snow was, however, able to prove his theory in 1854, when another severe epidemic of cholera occurred in London. Through finding out where the cases occurred and comparing that to which of the cities two water companies’ people got their drinking water from, he showed that cholera occurred much more frequently in customers of one water company, the Southwark and Vauxhall. This company drew its water from the lower Thames, where it was badly polluted with London sewage, whereas the other water company obtained water from the upper Thames, where the pollution was much less.
People started to believe Snow, but a later event gave even more support to his theory.
In one particular neighbourhood, the intersection of Cambridge Street and Broad Street, the concentration of cholera cases was so great that the number of deaths reached over 500 in 10 days. Snow investigated the situation and concluded that the cause was centred on the Broad Street pump, (a simple hand operated stand pipe pump which drew polluted water from the ground). He told the city officials to simply remove the pump handle, and when they did, people stopped becoming ill.
A Bit of New Zealand History
Although large towns and cities in New Zealand have not been around for as long as overseas, we do have records from the late 1800’s and early 1900’s which show that in many areas things were not much better.
By the late 1800’s, a number of large towns had sprung up around New Zealand. Yet for quite some time there was no facilities installed for providing safe water or taking wastewater from the populated areas. This resulted in high levels of disease and death for both adults and infants.
Auckland for example, in 1900 was still controlled by some 19 Borough Councils. There was no large scale waste water collection system, and most human effluent was a collected by night carts which drove along each street, and the householder would come out and empty their wastes from a bucket into the cart. Each of the 19 Councils then allowed their night cart contractor to deposit his collected night soil and refuse into the territory of a neighbouring Council, which made friction between these authorities very common.
The City of Wellington was somewhat quicker than Auckland to install a limited wastewater collection system however that simply discharged to the nearest stream or direct to the harbour and caused considerable pollution at the point of discharge. In a report to the council in 1889 the City Health Inspector stated:
“one of the causes of the death-rate in the city being large is that numbers of children are to be seen, particularly on fine sunny days, congregated around the mouths of the main sewers of the city, just where the contents flow into the bay, amusing themselves with fishing, and seated in many cases right in the midst of the odours that arise from the drains”.
Just so South Islander’s do not feel excluded; Dunedin City was as bad if not worse. In the first six months of 1864 the death rate from infectious disease in Dunedin was 34 people per 1000. The Otago Daily Times newspaper in that year was moved to write;
“Dunedin is allowed to remain a city which invites pestilence. Every sanitary precaution is neglected; its streets and the surroundings of its dwelling-houses reek with impurity and filth - its inhabitants imbibe poison in the water they drink. The grim Phantom of the inexorable destroyer, (death), stalks through the streets ready to commence his work of destruction”.
Some people may think that we do not face these problems in the 21st century because “modern medicine can treat any micro organism which causes illness”. This is not true. Although doctors have a range of antibiotics they can prescribe, they don’t work on all micro organisms, and some micro organisms are constantly becoming resistant to them. Consider the following cases;
- Queenstown, NZ, 1984. A blocked sewer overflows into the lake near the water supply intake. Over the next two weeks, around 3500 people become ill. The microbe causes gastroenteritis.
- Cabool, USA, 1990. A water main repair carried out without good hygiene precautions causes about 240 people to become ill. Of these, 4, all over 60 years old, die. 11 others develop serious and life threatening complications. The organism responsible was pathogenic strain of E.coli (VTEC/STEC).
- Walkertown, Canada, 2000. Run off containing animal faeces contaminates a drinking water supply. 2300 become ill, 7 die. The organisms responsible were E.coli and Campylobacter jejuni.
- Milwaukee, USA, 1993. The water supply is contaminated with runoff containing animal faeces, 403,000 people become ill, and estimated 140 die. The microbe responsible was Cryptosporidium, a protozoan cyst.
These all happened recently, in first world countries, and modern medicine could not prevent many becoming ill and some dying.
In the early years of this country’s development, we found that we could stop people dying from water borne disease by two simple services;
- The building of a wastewater collection system, and
- The supply of safe potable water.
Conclusion
In these days of worrying about the cost of services and trying to reduce this cost and, in some cases allowing people who don’t understand the importance of these services in preventing disease to make decisions which limit their effectiveness, it is worth remembering what happened in the past, and how we could easily return to those conditions if we allow our standards to slip.
Bert Gray has 42 years experience in wastewater treatment, operation and management and provides training in wastewater treatment and all areas of reticulation. A "father figure" of water industry training, he is well known for his support of operational personnel throughout New Zealand.
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