63 Integrated water management – squaring the circular economy

Last week I watched an excellent webinar on Integrated Water Management presented by George Warren of Anglian Water and hosted by the Pipeline Industries Guild.?You can find a recording here.

The problems

Growth and climate change are driving problems across the water cycle.?There is the risk of insufficient clean water for our needs and also the risk of increasing flooding and pollution from wastewater and drainage systems because of increasing rainfall intensity.

We can reduce demand for water through water efficient appliances and fitting and through customer education.?This is having an effect although possibly not as much as we had hoped.?We can also reduce runoff from rainfall through infiltration drainage features to reduce the volume of water and attenuation drainage features to reduce the peak flow rate.

However these reduction measures can only get us so far and at some point the pressures will require us to move to reuse of wastewater (I use wastewater in the widest sense here to include runoff from rainfall).?George thought that the pressure that would drive this would be shortage of water resources and that the tipping point would be to get below an average of 100 litres per head per day.

The categories

There are three aspect that we need to consider for the reuse of wastewater:

• The characteristics of the source of wastewater
• The characteristics of the reuse of the water
• The geographic scale at which reuse is implemented

The intersection of these defines what treatment is required and therefore the costs for construction, maintenance and operation.

George proposed that each of these three dimensions could be split into three bands.?Hence the Rubik cube at the head of the article.

Source

The three potential sources of water for reuse are:

• Runoff of rainfall is relatively unpolluted and may need only limited treatment for some uses.
• Greywater from showers, washbasins and washing machines contains more contaminants but (it is assumed) no faecal matter.
• Blackwater from toilets, kitchen sinks and dishwashers contains contaminants including fats oils and grease and faecal matter.

In practice, as with most things, there is more a spectrum of characteristics rather than three distinct categories.

Runoff from roofs is relatively unpolluted although it will contain nutrients and traces of faecal matter from birds.?However runoff from hard surfaces will potentially have a range of contaminants including; toxic herbicides at times of the year (even from within a property boundary), faecal matter from pets and wild animals on footpaths, through to the toxic cocktail of chemicals in the runoff from major roads.?There is therefore also a spectrum of treatment required for different uses although treatment through vegetated SuDS would be a good option.

Greywater will in fact contain some traces of faecal matter but not enough to be a health hazard for many uses.

It may be possible to find gradations in the classification of blackwater, but other than for toxic trade waste I don’t think that it is useful to do so.

Use

The three use categories are:

• Outside use for garden watering and washing down hard surfaces including cars.
• Inside use for toilet flushing and potentially for washing machines.
• Commercial and industrial use for cooling, washing, dilution of chemicals and transport of materials.

Again there is some gradation of uses with outside uses than involve the creation of aerosols potentially posing an extra hazard if there is bacterial or chemical contamination of the water.

Scale

The three categories of geographic scale within which the water is reused are:

• An individual property where the occupier of the property has control over the source and use of the water.?This does give the advantage of a closed loop of control but can also suffer from an imbalance of supply and demand either continuously or at certain times of the year.?A keen gardener could run out of stored rainfall in the summer whilst their neighbour has overflowing storage tanks.
• Neighbourhood.?(George used the word “development” focussing on new build, but I prefer “neighbourhood” to include retrofit.)?This could range from a block of flats, an infill development, all of the houses in a postcode or even large commercial sites.?This scale that there is some management structure in place to maintain and operate the drainage system, some form of contract defining service levels and some behavioural rules and a means of enforcing them.?If these systems were operated by the Suds Approval Body do they have adequate enforcement powers to have misconnected foul drains remedied or to prevent someone tipping waste pesticides down the surface water drain?
• Catchment.?This would be at the scale that we are used to for wastewater systems with the provision of water for reuse managed at the wastewater treatment works.?This can certainly help with the water resource position but requires investment in pipe networks to bring wastewater to the works and to distribute (partially) treated water for reuse.

Mix and match

Which are the best parts of the Rubik cube to focus on and which parts are no-go areas.?I consider, in particular, use in the UK as the situation will be different in other areas.

Property level blackwater reuse poses potential health risks and is probably not an appropriate technique, particularly in urban areas.?It also loses the recently discovered benefits of monitoring for pandemic pathogens at wastewater treatment works.

Neighbourhood level blackwater reuse could be implemented with small local treatment works and reuse by commercial sites or even by residential properties.?In the UK we used to have thousands of small treatment works but many were closed as they were too expensive to operate and maintain.?Perhaps with modern monitoring and control techniques it is time to revisit this.

Catchment level blackwater reuse is feasible and is already being used in the UK to feed industrial sites.?There could also be potential for other point uses including compensation flows for climate affected watercourses.??In hotter, drier climates blackwater reuse is used with distribution networks for garden watering throughout the catchment.?This requires an expensive second distribution system, but in locations where it is much more expensive to produce potable water through desalination than non-potable water from wastewater treatment then it is a sensible choice.?

At the other extreme, catchment level reuse of runoff makes little or no sense.?It requires that all of the runoff is conveyed to a central facility for reuse.?This just perpetuates the current problems of flooding and overflow discharge from the overloaded collection system.?

Dealing with greywater at catchment level is the current default but could potentially be changed, so this would be an interesting area to investigate.

We are already implementing reuse of runoff at property level with water butts, including smart water butts.?This is valuable for both water resources and overflow discharge and flood risk but there is more that could be done here.

Expanding the use at property level from garden watering to toilet flushing potentially makes more use of the captured water, even for properties without gardens (or gardeners).?However this does require some simple treatment of the water.?Where property level rainwater capture is still connected to the sewerage system, there is a concern that lack of maintenance and poor operation by householders could impact on the sewerage system.?The ideal would be complete disconnection from the sewer with any excess water (hopefully not much if it is used for toilet flushing) discharged to soakaway.?However we can make shorter term improvement with on-line monitoring of operation and better provision for maintenance (has anyone seen a water butt with a large valve to flush out sediment and debris?)?

Expanding rainwater reuse to neighbourhood level potentially gets even more efficiency and makes treatment easier, but does require management and enforcement of good behaviour.

Combining rainwater and greywater reuse at neighbourhood level would increase the amount of water available with little increase in the level of treatment required.?However this is probably only suitable for new build as it requires plumbing to be separated at individual fittings.

Future

There have been, are and will be pilot projects of different strategies of water reuse and these need to continue.?However at some point we need to make this mainstream, firstly by mandating it for new build and then incentivising it for retrofit.?The long delay in implementing Schedule 3 of the Flood and Water Management Act for sustainable drainage does not fill me with confidence that this will happen any time soon in England.?Step forward Wales, you have the opportunity to lead the way again.??