E ffective management of water and effluent can bring considerable savings and help increase profitability.

Technological development has made dramatic savings in water consumption possible, but this also has implications for effluent costs.

When conventional rotary washing machines and washer-extractors were the most common type of washing machinery available, typical water usage rates were around 29-33litres of water per kilogram of work processed.

Some forward-thinking launderers installed single or double water recovery systems and have reaped progressively increased annual savings.

A single recovery system might use the final-rinse water and some of the cleaner second-rinse water for the first two washes. A double recovery system might use the final rinse on the first rinse, and use the second-rinse (plus some of the cleaner first-rinse) for the first two washes.

In both systems, this involved installing not only large holding tanks that needed to be routinely treated to prevent bacteria growth, but also extra water inlet and drain valves. The drains were divided to ensure the water draining from the washing machinery was diverted into the correct holding tank.

Although these systems worked well, they could be a nightmare to manage and control and required extra care when preparing the process card controls.

Significant development

While the introduction of the “Carousel” washing machinery went some way to helping to reduce water and energy consumption by using a water contra-flow system, the most significant development was the introduction of the continuous tunnel washer in the mid-1970s.

One of the first of these in commercial laundries was the Baker Perkins Streamline. Water consumption was reduced to less than 12litres per kg. The Streamline’s development resulted in the introduction of compartments which separated the work into batches and enabled a standard water consumption of 8litres per kg to be uniformly achieved.

Many believed that this was the optimum until improvements at the transfer point from the wash zone into the rinse zone reduced this further to 4-5litres/kg.

Advances in detergent systems drove consumption ratios down to 2.5 litres/kg. This can now be achieved with integrated water purification systems using standard detergent chemistry, and 2.5 litre/kg consumption has become the benchmark for the textile rental sector serving the hospitality industry.

There are strong financial motivations, over and above the environmental concerns, for keeping water usage as low as possible – the obvious ones being the volume cost of the water supply and the volume cost of disposal.

However, because the water is contaminated with detergents, alkalis and a wide range of soiling, and all of this contamination is concentrated into a much smaller volume of water, the unit cost per cubic metre (1,000litres) of water disposed of into the sewer will increase. It therefore is important that the water company inspector uses the correct sampling procedure and that the laundry recieves the correct “evaporation rate” entitlement.

Most water authorities use the Mogden Formula to assess just how much they are going to charge laundries to discharge the waste-water down the drain. However, I feel that the charge the laundry industry is levied may be somewhat unfair.

As the majority of waste sent down the sewer is acidic and laundries discharge high volumes of alkaline waste, this reduces the cost of the effluent treatment, because one neutralises the other.

Some authorities may (reluctantly) be willing to admit that sewerage maintenance levels are significantly reduced in the vicinity of any laundry.

Laundries must pay to dispose of waste – and the formula is based on the following components:

Reception: The charge levied for handling the total volume discharged in a quarter via the sewer pipe system;

Volume: The charge for settlement and treatment of the total volume of laundry effluent within the sewage works;

Chemical Oxygen Demand (COD): The cost of the biological treatment of the effluent; the cost is actually based on the Biological Oxygen Demand (BOD) but COD is quicker and cheaper to measure.

Settleable Solids: The amount of sludge that accumulates from laundry effluent in the settlement tanks, which must be removed periodically by mechanical digger.

Consent limits

In addition to the measurements made for charging, the water company will also check that the laundry is not violating consent limits. These govern features of laundry effluent with which the water company cannot cope at any price. Typically they could include:

Alkalinity: Very highly alkaline effluent will cause accelerated erosive corrosion of Portland cement sewer pipes. This can be a problem for workwear rental plants washing garments with heavy engineering soiling. The more efficient their water consumption the greater the problem, because the alkali from the detergent is concentrated in a smaller volume of waste-water.

Temperature: High discharge temperatures pose a problem with water vapour and scalding hazards and encourage bacterial growth in the sewers. They also accelerate any effect of high alkalinity as well as increasing the COD/BOD due to de-aeration.

Oils and greases: Most sewage plants are not designed to handle these, even in small quantities.

Heavy metals: Cadmium, lead and mercury compounds are three common groups of poisons which the water company cannot discharge safely into rivers or the sea. They can be a problem for laundries processing chemical industry garments.

Each of the first four components (Reception, Volume, COD and Solids) will incur a separate charge – and, because the method of calculation can be complex, many launderers merely accept this charge without question and without understanding how the charge is made up.

There are now several websites where an effluent cost calculator can be downloaded free of charge and allow you to check whether you are being charged correctly.

The next thing is to ensure the laundry’s “evaporation rate” is correct. The water authorities will normally base the volume of effluent discharge on the amount of water taken into the plant from the water meter.

However, some of the water used is evaporated into the atmosphere during the finishing processes and so never goes down the drain.

As a general guide, work leaving the washroom will have about a 50% moisture retention level (this will vary to some extent depending upon how well tuned your moisture extraction system is), all of which will be evaporated during the tumble drying and ironing processes.

For a plant processing 150,000 pieces/week at an average 400g per piece the laundry will be evaporating 150,000 x 0.4 x 50kg ( or litres) water /week. so the evaporation rate should be 20%. A laundry using conventional washer extractors should expect a much lower evaporation rate percentage.

It is also important to ensure that when the water company visits the laundry to take a water sample it is taken at the right place for an appropriate time to obtain a representative sample.

For example, taking a sample from a washing machine that was draining from the main wash stage and using it as representative is clearly inappropriate. It is essential that the sample is taken from the point where the effluent enters the main sewerage system.

The inspector should then leave the collection container down the drain for at least 20 minutes to ensure that the sample represents the average quality of waste-water.

The inspector should then divide the sample in half, give one to the laundry and take the other away for analysis to calculate charges.

Independent checks

All launderers are strongly urged to have their water sample checked independently to ensure the results obtained on the sample are the same as those produced by the water authority. The costs for this analysis could well be saved many times over if any errors have occurred in the water sample analysis.

It is well worth remembering that the amount of soiling and chemicals contained in your effluent will have a serious impact on the final charge made for your effluent.

Greasy engineers’ overalls, for example, will cause a significantly higher effluent charge than say lightly soiled hotel bedlinen.

There are several methods available to help reduce the level of contamination, ranging from micro-pore filtration up to reverse osmosis or even chemical treatment of waste streams.

There many systems available, some more sophisticated than others, and some that incorporate heat recovery as well as permitting the re-use of some of the water to further reduce your consumption.

Depending upon how much a laundry is paying for its effluent and heating, the cost of investment in a water and heat recovery system may be recovered in a few months and is worth investigating.

This year is likely to be the year of maintaining profit by cost management. Water and effluent make an excellent starting point because there are so many opportunities.

Read Ian Harris’s article on water quality on this website