Chris Woodhams, Managing Director at Argenta, commented that "this is a really interesting article relating to an energy source that many of us are unaware of, sewage. If the benefits of converting sewage to a material for use as a fuel for power stations can be realised, then there is massive potential. Power from the oceans is another key source for reducing our carbon footprint and again there is significant potential here too."
Patrick Potter looks at how sewage energy can be harnessed in order to combat climate change.
The possibility of climate change has been with us for many years and even now many people do not believe it is happening. However, its arrival is now inevitable and it is already making a big difference in our lives.
You could well ask “what has brought about climate change”? The answer is atmospheric pollution which is brought about in the main by the combustion of carbon. Combustion gases of carbon have increased steadily over the past 100 years with the advent of the internal combustion engine. With its continuing demand for the likes of transport, including private cars, buses, heavy vehicles, aeroplanes, ships, and practically everything that moves, no thought has been given to the effects on our atmosphere caused by these exhaust gases, which have steadily increased to the extent whereby they are causing an insulating blanket between the earth and sun.
The problem is that all carbon, when combusted by fossil fuels, produces carbon dioxide (CO2). Nature cleans our atmosphere of carbon products by absorbing them into plant life, which utilises the carbon for plant growth. The clean oxygen is passed back into the atmosphere. Plant growth however, has steadily been reduced by cutting down the trees in the Amazon and deforestation in other areas of the planet.
It is almost an impossibility to eliminate the combustion of carbon in our modern world, however, now that it has been recognised that the main cause of earth warming is the combustion of carbon, attempts are now being made to reduce the amount of carbon being burned. The internal combustion engine has made far greater inroads into our society than could ever have been imagined. In fact, the only energy available other than that obtained from carbon is electrical energy. Electrical energy is mainly produced out of the combustion of carbon. Although great strides have been made in the use of producing electricity by natural means such as Hydro and Solar, it would not be possible as matters stand today to produce all electricity required without the use of carbon.
By far the greatest source of energy available to the world would be the harnessing of the almost limitless supply of energy available from the world’s oceans, and this can cause some big problems. All energy produced by mechanical means has been produced by the burning of coal, oil, gas, wood, all of which produce large quantities of carbon dioxide. There is one source of the production of carbon dioxide which cannot be reduced and that is the gases created by sewage. Every living person produces some 70 grams per day of solid sewage waste. Once it is discharged from the body, oxidation immediately commences and automatically proceeds to completion. When we consider the world has now a population of over eight billion people, a total sewage load of BOD would produce some 560,000 tonnes per day.
Very little use is being made of sewage as a fuel, and this valuable source of energy must be exploited in the interest of reducing its effect on atmospheric pollution. It is also a fact that for every tonne of sewage burned, it reduces the necessity to burn other fossil fuels which can be replaced by sewage combustion. This requirement has now become an absolute necessity as a good deal of exhaust gases from sewage are in its water content as it is very high in hydrogen, and at least 60% of sewage produces volatile combustion which has no carbon whatsoever.
The world is at present aware of the effects of fossil fuels on our climate. Power stations are being closed down, and are much reduced in output in an attempt to control carbon dioxide emissions. However, if we are to look for the answer to reduce the combustion of carbon to a controllable level, then we must harness the energy available from the world’s oceans. All power stations have been installed on land and are easily accessible for the control of solid fuel supply and for the removal of waste combustion products such as clinker. Ocean power will be generated under water and will require far more stringent facilities than that required for surface generation.
The source of power obtained from the oceans can be harnessed by taking advantage of the world’s tides. All the world’s coastlines are subjected to two tides per day, which contain a good deal of energy. Most tides can produce a maximum velocity of eight to 12 feet per second which is an average velocity of 160 metres per minute. Thus, a square metre of tide will move an average velocity of six knots, which amounts to 160 metres per minute.
With this in mind, the tidal power station may be produced in module form and placed in relatively shallow water off shore in a minimum depth of six metres. For instance, the modules require one square metre of tidal water at six knots which can produce 500 hp per minute. Tidal modules will need to be constructed so the water enters at their base and flows upwards in the module so that whichever direction the tide is moving, it can operate on a continuous basis even at ebb tide. This will enable the module to be permanently located and will ensure that generation of electrical energy will be consistent and permanent in all directions of the tidal movement.
These small modules can be factory produced on a large scale in selective sizes, which can be made adaptable to selected coastal requirements. They can be easily lowered into the water by a large floating crane, and hence easily lifted clear of the water and placed on land for maintenance, so that replacement would be quick and efficient.
There will be sufficient generating capacity in tidal currents to satisfy the world’s problem for the quantity of electricity required. There are thousands of miles of coastal tidal areas which can accommodate these modules and their installation would require little, if any, demand on the human population. Its operation would be automatic and continuous at all times.
This system of construction would be a preferable approach to that of large underwater generating plants which will always be subject to movements of the ocean floor; in fact, one earthquake could completely destroy them. This a risk the world could not accept because it would not generate the consistent quantity of electrical energy the world is dependent upon.
Use of fossil fuels cannot be completely eliminated because of the effect of sewage, which is impossible to eliminate. However, sewage, which is at present producing no energy, can be organised to collect the maximum sewage solids from existing systems. This will mean that the maximum energy can be made available to convert to powder fuel suitable for use for firing existing boiler plants, which is at present fired by pulverised coal or oil. Such conversion would require minimum modification to present firing systems and there are sufficient systems available in the world today to burn all the sewage energy we can collect. The collection of sewage energy would be no simple matter and will require construction of drying systems which would be best installed in present operating Sewage Treatment Plants.
The present electrical requirements are computerised to produce sewage fuel, and with good management some 20% of the energy available in sewage could be converted to powder fuel. This could then be combusted in modern boiler plants which are at present being utilised for the combustion of powdered coal and oil applications.
The remaining electrical requirements would be to utilise the energy available from the world’s rivers, solid energy and wind energy all of which will be free from producing CO2. Electrical companies which are producing electrical power will continue to produce and operate plants with the minimum use of fossil fuels for the combustion of maximum sewage sludge. If this is done on a worldwide basis it would be possible to produce the world’s electrical power requirements by controlling the use of fossil fuels within safe limits, while at the same time utilising the maximum accessible requirements to provide the world’s energy from the enormous potential available from tidal energy accessible from the world’s coastlines.
This whole problem of earth warming could be solved by utilising knowledge already available, and with maximum co-operation throughout the world, smaller engineering companies could be organised to supply the requirements on a global scale.
Accreditation: Institution of Mechanical Engineers, Patrick Potter, 2016. The original article can be located here.