Dilution is the Solution to Pollution – Or is it?

A little history to explain why we are still in a mess

We all complain about pollution and think that it should be avoided. In earlier times this was simply done by dilution, however some form of waste disposal becomes more important as population and industrial enterprise increases. Here is a little history which may explain the dilemmas faced by the various agencies involved, and ultimately by Society.

The Romans built sewers in their city but there was no treatment system so it was basically a means of removing the pollution from the city where it was diluted. Until the 1800’s there were few places where there was an organised sewerage treatment system.

As cities grew as part of the industrial revolution, sewers, initially open drains then piped systems, were constructed in a haphazard way and living conditions, particularly for the poor, became very unsanitary. There were numerous outbreaks of Cholera and following a serious outbreak in London in 1831, Dr Jon Snow demonstrated that this was caused by pollution of drinking water from sewage.

Before 1857 there was little requirement for anyone to take responsibility for the pollution of rivers or the sea in Britain, and they were simply used to dump any waste. The Public Health Act 1875 was passed which made Local Authorities responsible for sewers and drainage within their Areas.

There followed legislation and engineering works that are still the basis of much of the present day system. In London the “Great Stink” of 1858 resulted in Joseph Bazalgette’s construction of the London Sewers many of which are still in use today. Although a major achievement for the time, they simply took the problem downstream, outside the Metropolitan boundary, where raw sewage was discharged to be diluted in the Thames Estuary.

Similarly, locally in Portsmouth in 1865, council sewers were constructed and as the land is low-lying a steam pumping station was built at Eastney to pump essentially raw sewage into Langstone Harbour.

At this time the words “Sewer” and “Drain” were almost interchangeable and the system was designed to dispose of all “waste water” – rainwater, domestic and industrial effluent, and so they were all mixed in a single system. It didn’t really matter which as it would all end up in the sea or river to be diluted rather than treated. As in England the prevailing wind is from the West, the outfalls of the sewers for coastal towns were usually constructed downwind in the East, which is why for many towns the West End is the wealthy area and the East End the poorer sector, this can be seen in Southampton and even in Cowes.

However this combined sewer system has severe disadvantages – in dry conditions the flow (Dry weather flow – DWF) is only waste water, mainly domestic, but when it rains, particularly sudden heavy showers, the volume can increase sometimes a hundred fold in a matter of minutes. This means that the pipework must be designed for the rainwater flows and this makes treatment very difficult.

In older residential developments most are combined systems, in which the rainwater and wastewater are mixed, further adding to the difficulty of separation. In the last 50 years or so new developments have separate systems but often have to become combined once they meet the main sewer.

In 1898 a Royal Commission was set up to investigate methods of treating sewage consistent with public health. The commission continued to meet until 1912 and its findings formed the basis of legislation until the 1974 Water Act. One of the main findings was for sewage works to meet “Royal Commission Standard” (i.e. 20mg/l Biochemical Oxygen Demand (BOD) and 30mg/l for suspended solids – known as “30:20”). However, this standard, which was set to avoid unreasonable cost, only applies to a flow of 3 x DWF. In excess of this flow it is permitted to discharge diluted sewage directly to the watercourse, either from the works or from a Combined Sewer Outfall (CSO) – in effect an overflow system before the sewage gets to the treatment works.

Things didn’t change significantly until two further Acts, the 1973 Water Act, which transferred responsibility for sewage disposal from more than 1300 councils to the 10 newly formed Water Authorities. The 1974 Control of Pollution Act which made the
“30:20” standard a minimum and introduced the concept that the standard should be set according to the environmental requirements of the receiving watercourses.

During this time, it was still normal practice for Coastal Towns to discharge raw untreated sewage directly to the sea via “Short Sea Outfalls” – generally just below low water. However, in the 1970’s a new concept of “marine treatment” became common – this is not exactly treatment in any meaningful way but taking the sewage further off-shore by means of “Long-Sea Outfalls”. These were built in many locations and locally at Eastney and Sandown, so the sewage was diluted by the sea before it reached bathing beaches.

Although not an effective solution, as standards increased due to improved environmental understanding and European directives, these Long Sea Outfalls have continued to be used now to discharge treated sewage from new works built inland.

The next major change came in 1989 with Water privatisation when the ten Regional Water Authorities were sold off to become the private Water Companies we know today (actually they are mainly Sewage Companies, but perhaps that would have made it more difficult to sell shares), and the regulatory and river management agency became the National Rivers Authority (NRA).

The Environment Act 1995 merged the NRA with other environmental regulators to become the Environment Agency but made little change to the regulatory regime for discharge to rivers and the sea.

So under the current system the (privatised) Water Companies have a duty to follow all the Environmental Regulations, which are mainly European Directives brought into English law but are constrained in how much they can spend by OFWAT, who have to balance the cost to the customer, via our water bills, with the environmental improvements.

So rather sadly we conclude that Legislation and Money are the only Solution to Pollution.