How to minimise water consumption9 February 2021
Water conservation is becoming ever more important globally. Richard Neale of LTC worldwide looks at what can be done immediately to address this in a cost-effective way, without significant investment
Despite its relative abundance of rainfall, even the UK has occasional water shortages and hosepipe bans. Water is getting into shorter supply worldwide and launderers and textile renters are learning to cope with this and the inevitable cost pressures which higher water charges bring. This month we look at what can be done immediately to address this in a cost-effective way, without significant investment. All that is needed is modern laundry technology and management leadership. If you are not yet back up to full output, then now is the time to tackle this, to improve productivity and reduce operating costs permanently at a single stroke. It does not require much, if any, investment, but it does need careful application of some basic principles.
Washer extractor operation
Washer extractors are greedy consumers of water by their very design. It seems amazing now that when the washer extractor was first introduced, in the 1950s, it reduced water consumption from around 45 litres per kg of dry textiles down to around 25 litre/kg. Now it struggles to compete with tunnel washers which can achieve under 12 litre/kg for workwear and 4.5 litre/kg for flatwork. Indeed, the latest detergent systems can reportedly get down to below 2 litre/kg!
But there is much that can still be done to make the washer extractor-based operation more competitive. Modern computercontrolled machines offer the ability to fix the dip levels at the optimum depth for every stage of every classification but, surprisingly, not everyone has yet taken advantage of this feature. The running dip (that is the average dip when the cage is rotating) is normally shown in cm measured from the inside of the cage in the lowest position. It should be adjustable in the ‘programming’ mode of the machine controller, usually in steps of 0.5 cm or 1.0cm.
The generalised optimum settings were developed by the British Launderers Research Association (BLRA) many decades ago, as pre-wash 12.5cm, main wash 7.5cm and rinses 37.5cm. These varied slightly with machine capacity, but they were derived in the days when water was free or virtually so and dip controls were hardware, so there were just three or four pre-settable levels and the laundry programmer had to make these work for every classification. Modern laundries still use some of these old machines and if you have one, it is only necessary to tune the dips for the dirtiest classification (because that is the one which will need the highest rinse dips).
With modern microprocessor-controlled machines, the more classifications you use, the longer the time needed to optimise the dip for each stage of every programme. Perhaps this is why there are so many washhouses still operating on the original BLRA settings for every programme! However, there is much to be gained from carrying out the optimisation exercise, because once the savings in water are established, they accrue every day going forward.
The pre-wash dip needs to be sufficient to sluice loose debris from the textiles, so 12.5cm is usually correct. If the classification is lightly soiled and carries little or no debris, then the pre-wash dip can be set to be the same as the main wash at around 7.5cm and there might be no need to drain the pre-wash at all. This is known as a ‘stepped’ wash and it saves time, energy, detergent, water charges and effluent costs, so it should be employed whenever possible.
The major savings come with minimising the rinse dips. These depend on the quality of the local water, especially with regard to the amount of alkali it contains. The alkali in the raw water is not removed by the water softener and the higher the alkali content, the more rinse water is required to remove the detergent and soiling residues. When a new washer extractor is delivered it will probably have its rinse dips set so that in can cope with the poorest quality water in the country. This means it will work anywhere. It also means that in every area where the water is lower in alkali, there are savings to be made.
The minimum amount of rinse water for any classification is that which gives an alkalinity in the final rinse of no more than 0.04 gram/litre above the alkalinity of the incoming raw water after softening. This means that in order to minimise the final rinse dip safely, you need to get your detergent suppler to titrate the final rinse as you reduce the dip in 1cm steps. This will probably need more than one visit by the detergent supplier, and this should be planned in conjunction with them. If you get any problem with yellowing in drying, then a calculated amount of an acid sour (such as sodium metabisulphite) should be added to the final rinse, to neutralise the excess. This begs the question as to whether the result is likely to be worth the effort. The answer is quite definitely ‘yes!’ and the final value of the savings will be greatest in areas of the best water quality. One launderer has reduced every rinse dip by 5cm and is still not at the optimum yet! Meanwhile, the savings mount up.
Once the optimum dips have been identified and set in each programme, the next step is to plan for ‘last rinse recycling’. This does require some investment in a recycle tank, piping and pump, but this can be minimised by doing the work in-house. The diagram shows schematically now to convert a standard three washer-extractor installation to last rinse recovery, to reduce water consumption by about 30%. It only makes commercial sense to undertake this after work to minimise the dips, because this minimisation is generally without cost and it will reduce the size of the recycled water tank needed. The size to be specified should be sufficient to give about 30 minutes residence time with all washer extractors in operation.
Tunnel washer operation
In a tunnel washer, the rinse water flow is often counter-current to the flow of work, so it enters at the penultimate compartment and flows towards the front of the machine. This leaves the final compartment available for special treatments such as textile softening or starching. Exactly the same principle applies as for the washer-extractor. The final rinse liquor in the press tank must not be allowed to increase in alkalinity by more than 0.04 gram/litre above that of the incoming soft water. Again, this favours laundries in areas with the best quality, low-alkali water, which should always give an optimum rinse water flow which is significantly below that in areas that are less well served.
Assistance from the detergent supplier will again be needed with the titration of the press tank liquor, but this ought to be achievable on a single visit. If some of the classifications being fed into the tunnel involve higher detergent doses, then it is important to set up the optimum rinse water flow with the normal proportion of these classifications going through.
If the tunnel washer has a double skinned rinse zone (or at least a double skin in the centre of the rinse zone) then it is possible to achieve a further significant reduction in rinse flow using a technique termed ‘split rinsing’. This involves fitting an extra recycle onto the tunnel, which takes a pumped flow from the press tank and injects this into the centre of the rinse zone (hence the need for a double skin to accommodate this). Some of this extra flow will come forward to the middle of the machine and increase the exit flow from the rinse. Some will flow back to the end of the machine and increase the flow into the press tank. The net effect will be to reduce the optimum rinse water flow by up to 2 litre/kg, which could be 20 – 40% of the tunnel demand. There will be a corresponding reduction in the volume component of the effluent charge.
It can be seen that there are likely to be significant and achievable reductions in water demand in a great many laundries (and quite possibly in every laundry). This does not demand massive capital outlay, but it will require management leadership and sound application of laundry technology. This will take time on the part of the General Manager, the Washhouse Supervisor and the Laundry Engineering team, with the cooperation of the detergent supplier, but it is all achievable. The detergent supplier should have the necessary chemical knowledge and kit to handle the last rinse or press tank titrations. It makes little or no difference whether the laundry is based on washer-extractors or on tunnel washers – they both offer useful opportunities.
If you have any queries about the application of these water saving ideas in your laundry, please email the editor and we will do our best to answer them in a future issue. In these difficult times, when capital is tight and profits elusive, economising on water makes sound sense, both as regards costs and productivity.
Please tell us about your successes and achievements. Email [email protected]