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Squaring up to the challenge of cutting water sector carbon

Andrew Heather

Revolution, not just evolution, is needed if the water industry is to play its part in achieving the government’s 80% carbon reduction commitment by 2050.

The 31 March 2014 IPCC report on climate change states that while major climate change is now unstoppable, the worst extremes can be averted if fast, decisive action is taken to curb greenhouse gas emissions. But meeting UK carbon reduction targets looks a tough challenge for the water and wastewater industry: To help slow the pace of climate change, the government has pledged that emissions of greenhouse gases will be cut by 80% CO2 equivalent, measured against 1990 levels, within the next 35 years. Over the same time Britain’s population is expected to grow by anywhere from 15­-30%, per capita water use is rising, and it is likely the industry will be required to meet higher quality and environmental standards, all driving up energy consumption. How are companies going to square the circle?

Water sector carbon at a glance

  • Current UK per capita water consumption: 150 litres/day
  • Anticipated consumption in 2050, based on trends: 165 litres/day (+10%)
  • Government’s 2030 per capita consumption target: 130 litres/day (-13%)
  • Current annual operational carbon emissions: 4.5Mt CO2e
  • Estimated increase in emissions since 2000: 10%

Carbon reduction hurdles

The European Union’s Water Framework Directive drove major investment in wastewater treatment, which significantly increased the energy intensity of the water consumption cycle during the 2005-10 and 2010-15 investment cycles (AMPs 4 and 5). Additional quality legislation is not currently on the cards but is possible in future.

Meanwhile, rising water consumption will be accompanied by growing volumes of wastewater requiring treatment and return to the environment. Higher volumes of sewage effluent relative to the receiving water flow will mean that more nutrients must be removed to maintain river quality. In areas where climate-change will reduce dry-weather flows the most, this problem will be acute.

The increase in power and chemical consumption with increasing effluent quality is non-linear. Emissions have increased significantly in recent years as result of quality drivers. An increase in treated water volumes, especially in water stressed areas, is likely to lead to a proportionately greater increase in greenhouse gas emissions.

Emissions will be further increased as waste water companies build more interconnected and robust water distribution grids to deal with security of supply and low flow rivers.

Step change required

The water industry is already ahead of most UK infrastructure sectors in using innovation to drive down carbon emissions. Some within the sector have demonstrated unequivocally that cutting carbon reduces capital and operational costs, which is good for shareholders and customers.

Within the next decade, technical revolution resulting in a huge step change is unlikely. However, advancing into the 2030s it’s quite possible there will be major breakthroughs as research and development bears fruit and new technologies come to maturity.

In the near-term, implementing the following steps would yield 30-45% energy and carbon savings:

  • Improving efficiency of water company assets: 6-10%
  • Additional energy recovery: 10-15%
  • More efficient designs of common processes: 5-10%
  • Per capita demand reduction of 20%: 13-20%
  • Per capita consumption-related sewage savings: 13-20%

Strategies for cutting carbon

Demand reduction

Reducing consumer demand offers the greatest opportunity for carbon saving. Though the relationship between water volume and energy consumption isn’t linear, if you can cut the volume by half you’ve got a lot less clean water to treat and distribute, and you also get a large scale reduction in dirty water.

Can a 50% demand reduction be achieved? Water saving devices such as low water shower heads and taps are up to 80% more efficient than their standard counterparts, but they are difficult to find on the high street. People don’t know they exist and there is no incentive at present to have them. Click taps, which increase flow in measured increments, cost a good deal more than conventional taps – they are not going to appeal to someone doing DIY. And even though they are now standard in new social housing, they are not in private sector houses.

Education has a vital role to play in changing water use attitudes and habits. Droughts prove that demand can be reduced by appealing directly to clients. The challenge is to extend reductions from, say, 15% and sustain it. Part of the problem is that, as part of society, we're all geared to take the maximum we can for our money. Water customers pay for an unlimited service and most of us see it as a right to use as much water as we want. Changing that requires companies to explain the carbon emissions and environmental impacts of abstraction and discharge on watercourses, groundwater and coastal waters, and their ecosystems. For example, in south-east England, some rivers that aren’t replenished by treated wastewater effluent dry up in summer, and that’s likely to become more widespread in future. Do people know? Do they mind?

Alongside developing awareness of the environmental cost of water, the price of water should be adjusted to reflect it. Seasonally variable tariffs, rising when water’s scarce and demand is greatest, then falling during wetter months, might make people think more about the way they use water and its wider environmental and social impact. Some companies are already trialling ‘rising block’ tariffs, with water becoming increasingly expensive as more of it is used. To make tariffs an effective tool in water companies’ carbon reduction armoury universal metering will be required.

Catchment management

Water companies are increasingly involved in catchment management. Simple in concept but difficult to implement comprehensively, catchment management involves acting to control and reduce water pollution at source.

If you can reduce the chemical, organic and sedimentary pollution load in water abstracted for drinking water distribution, you need less resources to treat it.

This involves liaising with land owners and users, principally in the farming and forestry sectors, to change the way they apply fertilisers and pesticides, graze livestock and plough fields, for example, and stabilising land that is being eroded. Effective catchment management often involves looking at land use on a field by field basis to determine the sources of different pollution types. Challenges include resourcing, gaining support of stakeholders, and enforcement.

Sustainable drainage

Sustainable drainage solutions – SUDS – offer a means of reducing the volume of wastewater needing treatment. By holding back rainwater run-off and allowing it to soak into the ground, storing it for use, or releasing it slowly, SUDS reduce the volume of water that ends up in sewers. Wider use of SUDS has been limited by lack of clarity over who is responsible for their ownership and maintenance – water authorities or local authorities. The UK’s Flood and Water Management Act, 2010, made SUDS mandatory on all new developments, assigning responsibility for their upkeep and performance to local authorities – but has yet to make a significant impact.

Operational efficiencies

A review of wastewater treatment plants carried out by Mott MacDonald has revealed opportunities for cuts in energy and carbon emissions of up to 15%. These include installing real time monitoring, enabling treatment intensity to be adjusted according to pollution loads. Pumping efficiency can be gained by improving maintenance, replacing worn or poorly fitting impellers, selectively upgrading equipment, taking full advantage of gravity where opportunity exists, reducing pressure in pumping systems when practicable and scheduling pumping to match demand.

Variable discharge standards

Some companies have been allowed to vary the quality of the treated wastewater they discharge. During summer and dry weather periods, when flow rates in receiving rivers are low and people are swimming in the sea, maximum treatment standards have to be met. However, standards are relaxed when rivers are in full flow, providing greater dilution, or when coastal bathing has ceased. Environment Agency guidance for the water industry on reducing carbon emissions was published in 2010. The Agency considers applications for variable discharge on condition that companies are able to demonstrate that agreed seasonal quality standards can be met.

Low energy solutions

Where land is available and planning authorities permit, water companies should consider reverting to low energy traditional treatment technologies such as trickling filter beds or facultative ponds – lagoons with large surface area that enable oxygenation through surface exchange rather than forced aeration.

Adoption of small scale, low energy treatment would be aided by disaggregating water company activities. Much investment to date has been driven by the desire to realise scale economies measured in terms of asset numbers and manpower, resulting in large-scale, centralised treatment operations. Taking carbon and energy as the measures of economy could reverse the trend. Opening up wastewater treatment to competition could help to move this forward.

New technologies

In the current 2010-15 investment period UK water companies have seized on the opportunities offered by enhanced sewage sludge digestion technologies to generate calorific biogas and reduce the final volume of biosolids waste for disposal. By using biogas to drive combined heat and power engines, enhanced biodigestion offers potential to make sewage treatment works energy self-sufficient. Some are ‘cleaning up’ biogas so that it can be used as a vehicle fuel or sold into the national gas grid. Some companies are looking to increase energy from biodigestion by supplementing sewage sludge with food and industrial waste. Sludge pyrolysis also offers potential to generate both heat and power.

Water companies are looking for opportunities to diversify into other renewable power technologies. And small scale generating technologies, are becoming steadily cheaper, opening up potential for energy to be recovered in the clean and dirty water treatment and distribution processes. Low head turbines can generate electricity using the pressure created by small gravity runs. Mini hydropower generators can replace pressure reducing valves.

Curbing construction

Research carried out by Mott MacDonald shows that embodied carbon accounts for a third of water industry carbon emissions and sometimes more. The water sector’s leading clients recognise this and have been very proactive in planning investment to reduce their carbon emissions. Gains have been made by challenging assumptions and questioning need to eliminate capital works or scale them back; making better use of existing assets to meet capacity and resilience requirements; and using competition to drive design and construction innovations. New assets may well reduce carbon emissions long-term by reducing power consumption. But it is increasingly recognised that companies must put embodied carbon into the equation and minimise the impact of the construction they do.

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