Can greywater recycling snatch life from the “Jaws of Death”?

Sam Burgess
Sam Burgess

Sam Burgess, Water Reuse Manager at SDS, says wasting water should be as socially unacceptable as blowing smoke in the face of a baby. That was the urgent appeal of Environment Agency Chief Executive Sir James Bevan in his famous “jaws of death” speech back in 20191

Despite that warning, England is still on a trajectory to start running out of treated mains water within 20 years. By 2050, the deficit is predicted to reach 3,500 million litres per day. Yet up to 60%  of the drinking water supplied to commercial buildings, such as office blocks or hotels, is used where high-level treatment is simply not needed.

Water UK – the body that represents Water Companies – has told the Government that a maximum 2050 target of 85 litres per person per day is feasible by 205022. But how? Current planning regulations for England and Wales require a 125 litres per person daily limit for new developments, but Environment Secretary George Eustice has said he will encourage local authorities in the 14 most water-stressed Water Company regions to adopt an optional 110 litres per person daily3. This lower limit is already applied through The London Plan, leading to a much greater take-up of grey water schemes in new buildings in the capital.  

Better understanding and evidence of what grey water systems can achieve is, therefore, essential to driving informed policy decision-making, as well as encouraging adoption by architects, engineers, developers, and planners.

Recent innovations in grey water recycling technologies promise to help meet these challenges. Grey water is usually wastewater harvested from baths, showers, and hand basins, which is filtered, treated, and then reused for non-drinking purposes such as toilet flushing, laundry, or garden irrigation.

On-demand technology

Advances in grey water technology using a new ‘on-demand’ process are providing a more responsive and cost-efficient process that makes the return on Investment more favourable. The new technology is also offering early adopters of grey water systems the opportunity to replace legacy high-maintenance Membrane Bioreactor (MBR) systems with more efficient and cost-effective treatment systems. 

SDS’s Grey Water Recycling systems are supplied as package treatment plants. Larger scale systems use a sequence of leading-edge disk filtration and ultrafiltration processes.

In one of the first residential installations in the UK, this system was successfully installed in a high-class apartment development in Holland Park, Kensington, one of London’s most exclusive addresses. Despite the extremely high-specification bathrooms, the building’s water usage was calculated to reduce by at least 15% to an average of 90 litres per person per day, more than meeting the planning requirements.

The technology is also being adopted in new commercial and mixed-use developments in London; and seeing take-up in hotels both in, and outside of, the capital. Grey water systems are of course best suited for installation in new buildings because a separate network of additional pipework is required through the building.

Earlier this year, we introduced a ground-breaking, smaller-scale rapid greywater treatment system that is especially suitable for buildings with lower usage, for example, hotels with between 50 and 150 bedrooms. Its first installation has been completed at the new 84-bed Premier Inn development in Faversham, Kent.

 MBR systems

In the past, MBR systems have been the technology of choice for grey water reuse. However, the smaller footprint of on-demand systems, together with their ability to provide quality recycled water whenever needed, makes them capable of significantly improved investment payback.

MBR systems use a biological treatment process and a flat membrane that filters water at a much lower pressure than the new on-demand technology. For example, an on-demand Grey Water Recycling systems treat grey water at 1m3 per hour, compared to 0.5m3 per day for a traditional MBR reactor.

Because it can be so quickly replenished, only about a quarter of a day’s supply of treated water needs to be stored at any one time. So, an on-demand system requires a much smaller footprint and can be more easily scaled up to match an expansion in requested supply. The only way to expand an MBR system is to add more reactor tanks.

Because an on-demand system has a much quicker start-up and shut-down procedure compared to MBR, it can be easily switched off during periods of low demand, for example in a commercial building at the weekend. It can then be restarted immediately when required by the building services operator or a facilities management contractor.

Gray Water cycle

Furthermore, as MBR systems depend on building up biomass of live bacteria, if grey water is not used at a sufficient rate, the bacteria can die, stopping the treatment process. MBR systems need a coarse filter before the water enters the first collection tank, which the on-demand system does not. The MBR membranes can clog, also leading to smells, and may require more frequent replacing. So MBR systems require more maintenance and, if they have to be shut down, then it would be necessary for the supplier or manufacturer to reintroduce the bacteria and recommission the biological operation before the system could be brought back into use.

How the on-demand system works

In larger-scale Grey Water Recycling systems, wastewater is directed into a collection tank. A submersible macerator pump feeds the water at high pressure to a disc filter, which uses a patented process to pass water through a disc stack with a centrifugal action to remove particulates > 100 microns. The disc filter provides a highly efficient filtration process that avoids clogging. An automatic self-cleaning backwash process periodically cleans the discs to keep the filter running at optimum efficiency.

In the second stage of the process, the water is fed to a state-of-the-art ultrafilter. This is packed with hollow polymer fibres which ensure all contaminates > 0.05 microns are consistently removed. This is small enough to include bacteria and viruses and achieve near-potable water quality. The ultrafiltration membranes are also automatically cleaned using pressurised air and water.

The addition of sodium hypochlorite for chlorination and oxidation is kept to a minimum throughout the fast-moving process, before the water is given a final dose to ensure high-quality water is ready for onward distribution around the building.

The complete system is supplied with a control cabinet and HMI screen. In addition, the inclusion of a “SYMBiotIC™” data-logging and uplink device enables values from a wide range of input sensors to be recorded and visualised with a cloud-based dashboard. Data collected could include flow rates, temperature, and level information. Alarms can be set up to alert if the data goes outside of predetermined limits, so that any discrepancies or anomalies can be quickly identified for action. Remote monitoring of the on-demand system not only assists system maintenance by operators, but our service team can also identify any requirement for maintenance visits in real time, so continued supply is assured.

In smaller scale Grey Water Recycling systems are designed along very similar treatment principles, except that the two-stage treatment process uses cartridge filters followed by nanofiltration, alongside intelligent chlorine dosing using dry block calcium hypochlorite.

Rapid payback with low maintenance

These Grey Water Recycling systems can pay back in as little as seven years, although the actual return on investment will depend on the size of the system and the local Water Company charges. The system continues to deliver reliable, treated water throughout a long design life with minimal maintenance.  

Increasingly I see grey water recycling systems being specified alongside rainwater harvesting systems as part of a wider water reuse strategy that targets objectives in water, carbon, neutrality, and delivers benefits to the environment.

Reliance upon mains water, particularly in our changing climate of weather extremes, exposes businesses to supply shortfalls which grey- and rainwater recycling technologies can play a significant part in addressing. Amidst growing recognition that water has to date been severely undervalued, decisions to introduce alternative supply sources will almost certainly prove to be financially astute.

Sources:

  1. www.gov.uk/government/speeches/escaping-the-jaws-of-death-ensuring-enough-water-in-2050
  2. www.gov.uk/government/consultations/water-conservation-measures-to-reduce-personal-water-use
  3. https://tinyurl.com/2p9ajjvs

Sam Burgwess is Water Reuse Manager at SDS

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