Limits to Growth: Sewage in Jersey

When I was a youngster, Jersey had a Sewage Board Committee, which later changed its name (and some of its functions) and became the more euphemistic Public Works, and then Public Services, and now TTS.

All the recent talk about the incinerator has meant attention has been diverted from the Medical Officer of Health's recent report, which actually is giving us some facts and figures about sewage, which are rather worrying.

Liquid waste disposal

The sewage treatment plant at Bellozanne is ageing and has been in operation since 1959. Over the years, treatment processes have been updated as the population has grown and as more stringent effluent standards have been required. The plant was initially built to deal with a lower total volume of liquid waste than it does today. It currently receives on average 33,000 cubic metres per day - a 36% increase since 1977.

This increase has occurred despite the many surface water separation schemes undertaken during that time which should have reduced flows. The mains drainage systems work well in general, although in extended periods of inclement weather, the network becomes overburdened with surface water from combined drainage systems (where foul and surface waters are mixed together) and from ingress through leaking pipe work. The cavern under Fort Regent is designed to take up the excess from the town area and, when flows in the system return to normal, to pump back collected sewage into the works.

The report recommends:

the early formulation of an Islandwide liquid waste strategy to determine the appropriate level of improvement and extension to the mains drainage network, along with an appropriately sized and located replacement for the Bellozanne sewage treatment plant

What is missing from the report, and perhaps may become available from TTS, is the capacity of the sewage treatment plant in tons per day, and how close it is to reaching that capacity, and how much plant is needed per head of population to sustain that capacity.

This is what I call "real joined up thinking", and there seems to be precious little of it around. Population growth always looks at housing, roads, sometimes schools, but never at the distant end of the infrastructure needed to support it. Until, as with the incinerator, it has to be done hurriedly out of necessity, because when firefighting, it is the wrong time to stop and assess the merits of different engines.

In the University of London Study "Determining Sustainable Development Density using the Urban Carrying Capacity Assessment", the authors note that "The determination of the capacity of a system is fairly straightforward when managing suburban facilities as water supply, sewage treatment, and transportation."

There is also an energy cost to sewage treatment. The UK Parliamentary Office of Science and Technology, has produced a paper on "Energy and Sewage" in which they note:

Over 10 billion litres of sewage are produced every day in England and Wales. It takes approximately 6.34 gigawatt hours of energy to treat this volume of sewage, almost 1% of the average daily electricity consumption of England and Wales. The actual energy used will depend on the quality of sewage and intensity of treatment required. Typically, there are three stages of treatment:
. Primary. Solids are physically settled out.
. Secondary. Bacteria convert organic matter to a carbon-rich sludge.
. Tertiary. Further treatment may be used to remove more organic matter and/or disinfect the water.

Effluent is discharged to fresh, ground or coastal water.

Sludge is applied to agricultural land (62%), incinerated (19%), used for land reclamation (11%) or used for other purposes, such as composting or landfill (8%)

It would be interesting to note the statistics regarding Jersey's use of sludge.

The report also notes that:

There are mature, widely-practised technologies for generating fuels from sewage treatment and research has
identified future methods for exploiting sewage as an energy resource . In 2005 - 2006, the amount of
renewable energy generated on water industry sites was 493 gigawatt hours - 6.4% of the total energy used to
treat water and wastewater.

Regarding sustainable energy, it is also worth noting that biogas can be generated from the system, and this can offset against the energy consumption. Whether this would be viable in Jersey is another matter, considering the small size of the Island, but it is worth considering.

Biogas production from sewage sludge treatment, via a process called anaerobic digestion, is already a well established means of generating energy in the UK. Bacteria use organic matter in sludge to produce a mixture of methane (60 - 65%), CO2 (35 - 40%) and trace gases. Impurities, such as hydrogen sulphide and water, are removed and the resulting biogas is then commonly used in boilers or combined heat and power (CHP) systems. For example, anaerobic digestion facilities are being developed at United Utilities' Davyhulme sewage treatment plant that will provide 90% of the site's power via CHP. Biogas may also be used for other applications, such as vehicle fuel, if CO2 is also removed. In Linköping in Sweden, trains, buses,
taxis and some private cars run on biogas.


Links:
Report on Energy and Sewage
http://www.alphagalileo.org/images/pdf.pdf

Determining Sustainable Development Density using the Urban Carrying Capacity Assessment
http://eprints.ucl.ac.uk/208/1/paper78.pdf.

Medical Officer of Health report
http://www.gov.je/Health/public_health/OurIslandOurHealth2008.htm

Limits to Growth: The Water Supply

I've been looking though the old States Minutes from 1985, and some quite interesting figures emerge.

The yield per annum of the main water supply, factoring both Queen's Valley and the Desalination plant is:

Val de La Mare etc 929,000,000 gallons per annum
Desalination 300,000,000.00 gallons per annum
Queen's Valley 475,000,000.00

Total 1,704,000,000 gallons per annum

Now back in 1985, when they were making assumptions for the year 2000 - which is why they argued for flooding Queen's Valley - the considered the following:

a) A maximum demand per head of 40 gallons per day, which is also supported by current supply figures.
b) No expansion in tourism demand - the industry has in fact been able to maintain its demand for treated water at a more or less constant figure by restraining use and investing in borehole facilities in a number of places.
c) Industrial demand increasing by 10 per cent - this trend is confirmed.
d) 0 per cent saved by metering. The States subsequently decided against domestic metering.
e) Unaccounted for use limited to 16 per cent.

For a population of 90,000, this means a demand of 40 x 90,000 x 365 = 1,314,000,000 gallons per annum

Even allowing for the cancelling out of some of b) to e), this means we are below the total of 1,704,000,000.00

But - just accounting for the population - ignoring all the other uses, this means that when the population reaches 116,712, we will have run out of capacity. In fact, because of other demands this may well happen before this limit.

It also does not take into account how soon the reservoirs will take to run dry in a drought. But it does give us a maximum figure beyond which the population cannot easily expand.

Now if you take out the Desalination plant, it reduces to a maximum of 96,164 before the population consumption per annum exceeds that of the reservoirs. Not far off the present!

I'm sure there must be similar limiting factors with (1) sewage treatment (2) electricity capacity.

Even despite the French link, only so much power can be pulled over from France. And as far as sewage treatment goes, there must be a limit on the speed at which the existing system can cope with sewage, and the amount generated per head of the population. If anyone has any figures, I'd be pleased to work on them. This kind of calculation is rough and ready, but it certainly can provide a warning note which we would do well not to ignore.