Biomass energy describes heat and power produced from wood, forest and agricultural residues and wastes, and a wide range of organic wastes such as animal slurry and kitchen waste.
Precipation is the main source of water for drinking purposes. A percentage of rainfall evaporates soon after it falls, a percentage runs off the ground to join streams and rivers and a percentage seeps through the ground to join underground supplies.
Sources of water supply consist of surface water and underground water.
This includes water collected from roofs and paved areas as well as streams, rivers, lakes and reservoirs. This water is liable to contamination by vegetation and farm pollutants. Sewage and industrial waste are sometimes fed into rivers without any purification treatment.
These same rivers are usually expected to supply fresh water for towns and villages. Rivers have the ability to purify themselves, especially if they are fast flowing and shallow. Despite this ability water taken from a river for public use should be treated before consumption.
Rain that seeps through the ground may eventually reach an impervious layer, where it may be held as in a reservoir or it may flow like an underground stream on top of the impervious layer. Layers of ‘water’ are called aquifers.
There are two types of springs. A main spring which is usually deep and connects to the aquifer layer and a shallow or simple spring which connects to underground surface water.
The latter is likely to be intermittent. Spring water is usually pure resulting from the natural purification that occurs as the water permeates through the ground.
Wells are different to springs as the ground has to be bored to reach the water. Springs occur naturally. The upper part of a well must be lined to exclude surface water entering it as it may be polluted.
Water to be used in a public water supply is required to be fit for drinking. This implies that it poses no danger to health, and it should be colourless, clear, odourless, sparkling and pleasant to taste.
There are four main techniques used for the treatment of water. They are:
Water is stored in reservoirs where contaminants/impurities settle to the bottom (sedimentation). Pathogenic bacteria (disease producing) find it difficult to survive in storage due to the lack of food, low temperatures and the effect of sunlight.
If water is stored for long periods, algae tend to grow. The growth of algae can be controlled using chemicals such as copper sulphate.
Water is passed through sand or a fine wire mesh to remove particles. Rapid sand filters act as a physical filter, leaving the water in need of chemical treatment. Slow sand filters provide physical and chemical action. In a slow sand filter water slowly percolates down through the sand.
Fine particles, micro-organisms, and microscopic plant life are retained in the sand bed. The bed must be emptied for cleaning after a number of weeks. The slow sand filter produces high quality water, which needs little further processing.
Water must be sterilised before it can be consumed by humans. Chlorine is added to the water for public supply, but this isn’t always feasible for small installations. Chlorine kills bacteria making the water safe to drink. After sterilisation ammonia is sometimes added to the water to reduce the offensive taste left by the chlorine.
For smaller installations water is passed through a very fine filter capable of removing the bacteria.
Hard water is recommended for drinking but it has disadvantages. Scale may be deposited in hot water pipes and boilers, and soap does not make a lather.
There are a number of ways to soften water:
- Base exchange methods change hardness compounds into compounds which do not cause hardness.
- Demineralisation is a process to remove all chemicals dissolved in the water.
- Lime-Soda treatment depends on chemical reactions to make the calcium and magnesium in the hard water insoluble and they are then removed.
Mains Water Supply
Most dwellings and buildings, including those in rural areas are supplied with water from a public water supply, otherwise known as the mains supply. The design of a mains water supply needs to consider present demand and anticipated future demand, the size of the water mains, and the pressure of water in the mains (this is known as the ‘head’, the height to which the water would rise in a vertical pipe.
The standard size for a water mains is 75 mm diameter if it is supplied from both ends and 100 mm if it is supplied from one end only. 30 m is the minimum head of water recommended for firefighting purposes, while a head of 70 m is recommended to minimise waste and reduce noise in pipes.
The head is achieved by locating reservoirs at appropriate heights above the buildings being served. Full pressure (head) from the reservoir is seldom available as flow in the mains will be taking place at most times. Pressure is further reduced by friction due to flow.
The water mains is usually sited along the edge of a roadway. Permission must be obtained to connect to the mains and to cut the road if this is necessary. A domestic connection consists of a 12 mm diameter pipe with a minimum cover of 750 mm below ground as protection from frost.
Cold Water Storage & Distribution
The connection to the mains water supply is usually taken to the boundary of the site and finished with a stop valve or stop cock, housed in a suitable box or purpose chamber. This chamber may be fitted with a hinged cast iron cover. The cold water supply for the dwelling is taken from the stop valve to the building, 750 mm below ground level. stop valve.
A second stop valve should be fitted on the service pipe where it enters the building. Where possible this should be at the kitchen sink, although the location is not critical. Inside the house a drain cock should be fitted above the stop valve to allow the cold water system to be drained down.
There are two main types of cold water supply systems within the house. These are known as ‘direct’ and ‘indirect’.
Indirect Cold Water Supply System
In this system all cold water outlets with the exception of one drinking water outlet are supplied indirectly from a cold water storage cistern, usually located in the roof space. ‘Indirect’ means the water is not coming directly from the mains to the outlets, it is piped to and stored in the cistern in the attic.
Advantages of This System:
- A reserve supply in case of mains failure.
- Less pressure on the taps and valves resulting in less wear.
Disadvantages of This System:
- More pipework required.
- Provision and installation of a storage cistern in the attic.
This is the most common system used.