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Money down the drain….
When did you last take a hard look at what your water supplies and effluent disposal are really costing you? Steve Winpenny, md of consulting water engineers Fenland Hydrotech, suggests that it would be well worth your while.
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Water is one of the things in life you don't have to think much about - unless you are a production manager in a food processing factory, in which case water supply and effluent disposal are things you should think quite a lot about!
Industry is currently paying around £1 a ton for mains water and maybe £2 a ton or more for effluent disposal. The food processing industry uses huge amounts of water for operations such as product washing, cooling, sanitising and hosing down. Purchasing, pumping and disposing of water is a major cost, and figures can be mind-blowing. Water supply and effluent disposal used to cost one company in the snackfood business more than a million pounds a year; another was losing around £10,000 a year just from wasted energy in its pumping systems.
These substantial costs need to be monitored and minimised, and detailed survey by professional water engineering consultants often reveal areas where very worthwhile savings can be made - ongoing savings that well exceed the cost of the survey. A professional survey should save more than it costs.
Let's look at three areas where such a survey can produce worthwhile results; where the water comes from, how it is moved around the premises, and how waste water or effluent is disposed of.
Water supplies
The consultants will look at what happens to every litre of water used on the premises. What kind of water is needed, and where does it come from? Is it being used or is it leaking into the ground?
Most water for industrial use is taken from the mains supply. Yet for many heavy water uses - cooling, washing down or sanitising, for example - potable quality mains water at £1 a ton has been treated to an unnecessarily high standard. What about alternative sources such as wells or boreholes? The cost of the untreated water obtained from them under an abstraction licence is substantially cheaper; as much as 90 per cent less than mains water. Naturally it may involve sinking a well or borehole, but the consulting engineers will be able to advise on the feasibility and the cost compared with the possible benefits.
Another potential source of economy is the re-use of water. Take water that has already been used in a cooling process; it has not been contaminated, so maybe it could be re-used for purposes such as washing down, or flushing toilets. And if you have a process that generates quantities of hot water, could the heat be recycled or recovered by an exchanger? This would need careful handling because of potential hazards such as Legionnaire's Disease, yet careful hygiene procedures will eliminate risks to health and could produce worthwhile cost savings.
A lot of water in industry is wasted in many ways, not only by failure to re-use it. Leakage from pipes, valves and joints, for example - drips and leaks from valves and wash-down guns can add up to an unbelievable amount of wastage. Also, much water is wasted from over-use. For instance, to clean the interior of a tank, how long do you really need to keep water flowing through the spray bars?
Pumping systems
Water and effluent have to be moved around, and most pumping systems will be running well below their most cost-effective performance. A 15kW pump running for 24 hours a day costs at least £100 a week, and in one year its running costs will be greater than it cost to buy and install.
The general tendency is to use pumps that are bigger than necessary, and their output is often throttled back by the outlet valve. Pumps end up running off their peak efficiency point, with the motors underloaded and giving poor power factor. Many pumps are actually running at as low as 30 per cent efficiency against the ideal target of 80 per cent. Pumps need to be carefully tailored to individual requirements, and the two main critical factors are impeller size and pump speed. The flow rate from a pump varies with the squares of the impeller diameter and pump speed. Doubling the speed of the pump will thus double the flow, but increase head fourfold. Head losses through a pipe will tend to vary with the square of the velocity. Changing the pipe diameter has an even more dramatic effect, as halving the diameter increases head losses 32 fold. Pumping systems are therefore optimised by using variable speed drives or trimming impeller diameters to obtain peak efficiency and optimum power factors, together with pipework of the correct diameter to handle the required flow. Attention to all of these things can produce major savings.
It is not unknown for pumping and pipework systems to be left behind when changes are made to the plant around them, especially in older premises. One consultancy found his client was using pumps generating heads of 150ft to fill a water tower only 80ft high, just because no-one had thought to upgrade the connecting pipework.
Effluent disposal
The disposal of effluents from food processing plants is critical, particularly with today's strong regulatory emphasis on ecology and the environment. Disposal can also prove unnecessarily expensive, unless careful studies are carried out and procedures followed.
Disposal charges are calculated by the Mogden formula, where the charges are based on oxygen demand, suspended solids and treatability. Each water utility company sets its own Mogden charging parameters. There are two methods of testing the oxygen demand of effluent The one most commonly used by water companies for industrial effluent is the Chemical Oxygen Demand (COD) test. This is quite quick to complete compared to the five days needed for the Biological Oxygen Demand (BOD) test which is more commonly used for domestic sewage.
Industrial effluent is normally disposed of to the public foul sewer, and the water company will set limits on what can de discharged into the sewerage system, and some effluents may have to be tankered away to special disposal sites
The frequency and type of test depends upon how water companies assess risks from individual processors, but they are applied diligently because of the potentially devastating effects of pollution on sewage disposal plants. Levels of potential toxicity in effluent from food processing can be almost unbelievably high. For example, raw sewage has a BOD level of around 300 milligrams per litre (mg/l); spoilt beer from a brewery or milk waste can reach 100,000 mg/l.
If a large quantity of such an effluent got into a storm drain - especially if it had been stored for a while and had bred bacteria - it could actually put a local sewage works out of action. The same also applies to effluent water containing cleaning chemicals. Analytical chemists estimated that a 2-litre container of a certain industrial sterilising liquid poured down a public drain, could knock out a sewage works serving a medium-sized town!
A detailed knowledge and record of pipework layouts is important in the field of effluent disposal. For example, 'dirty' water is normally disposed of down metered foul drains and is charged for as such by the water company, whereas surface water goes down ordinary storm drains. However, in some older premises having a accumulation of partly uncharted pipework, it has been known for surface water to be accidentally routed into a metered foul drain, with expensive results. There is also the risk of the opposite happening - contaminated water going into a storm drain. The results could be both expensive and disastrous.
Busy factory managers and their staff, working flat out on keeping production going smoothly, often have little time - or even, dare we say it, expertise! - to make a holistic survey of water supplies and effluent disposal. Yet, as we have seen, the potential savings in these areas could make such a survey a worthwhile and cost-effective contribution to profitability - as any good water engineering consultant might soon discover for you…
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