The Wastewater Holy Grail: Energy Self-Sufficiency

March 1, 2018
A growing number of wastewater facilities around the world have taken steps to install novel wastewater to energy technology - with some even achieving complete energy self-sufficiency. So, what have been the most recent trends and developments in this area?

A growing number of wastewater facilities around the world have taken steps to install novel wastewater to energy technology - with some even achieving complete energy self-sufficiency. So, what have been the most recent trends and developments in this area?

By Andrew Williams

One of the most interesting ongoing initiatives in this area is a ground-breaking project by the UK utility Scottish Water, which has set itself the target of achieving total energy at its Seafield Wastewater Treatment Works - the largest wastewater treatment facility in the east of Scotland.

Since 2015, a team from the leading resource management company Veolia has been working to ramp up the capacity of the Seafield site’s capability to generate its own energy. Last year the firm reported an impressive increase in the amount produced, from 55 percent to around 85 percent of the total requirement. This was achieved by bolstering the renewable energy generated from a combination of anaerobic digestion of sludge and biogas fired combined heat and power (CHP) plants. At a variety of separate points throughout 2017, the company even reports that ‘full self-sufficiency’ was achieved - described as instances when the Seafield facility required no electricity from the local grid whatsoever.

These impressive results have been made possible via the introduction of a number of innovative measures, including the installation of a cutting edge thermal hydrolysis process - that the company claims has increased biogas production by around 10 percent. This is as well as investment in an additional CHP unit to “provide greater energy generation and to take advantage of the additional biogas, and a further 3 percent increase in the yield of biogas”.

The Seafield scheme forms a central part of the AVSE (Almond Valley, Seafield and Esk) project - a 30 year performance based contract, awarded in 1999 to Stirling Water Seafield under the UK Government’s Private Finance Initiative (PFI) for the operation of a number of Wastewater Treatment Works in Edinburgh and the broader Lothian region. In all, these facilities treat a total of 125 million cubic metres of wastewater treated each year - and recycle some 60,000 tonnes of waste sludge per annum.

As Mark Keast, general manager of the AVSE (Almond Valley, Seafield and Esk) PFI at Veolia, explains, although the assets themselves are owned by Stirling Water Seafield over the contract period for Scottish Water, Veolia is responsible for the operation of a total of 15 sites across Edinburgh and the Lothians. This includes five treatment works, 11 storm water sites, one trunk sewer, one pumping station, two combined heat (CHP) and power plants and two advanced digestion plants.

“Taken together, the AVSE project area is equivalent to a population of 907,000 and involves treating over 125 million cubic metres of wastewater of wastewater each year. In addition to operating the 15 sites, Veolia was also required to improve operational efficiency including regulatory and health and safety performance, communication and stakeholder engagement and financial and asset performance,” says Keast.

Advanced digestion plant

In facing up to the perhaps considerable challenge of managing such a wide range of key objectives, Keast reveals that the Veolia strategy was to move operations forward on a number of fronts. In the first instance, he explains that this strategy entailed the full utilisation of all the sites at its disposal and the enhancement of a combined heat and power plant (CHP), as well as the construction of an advanced digestion plant - developments which, taken together, have “provided AVSE with valuable income streams.”

Large scale: A total of 125 million cubic metres of wastewater is treated each year at Seafield, with 60,000 tonnes of sludge recycled

“Electricity is sold to the National Grid and reducing the disposal of sludge has made significant savings of £2 million per year,” he says.

“Minimising asset management costs was also crucial. The process is now proactive to ensure regulatory limits are not exceeded, thereby reducing contract deductions. A focus on operational excellence has also lowered costs by reducing downtime and lost man hours, with an increase in productivity contributing around £1 million in efficiency savings,” he adds.

In addition to these achievements, Keast reveals that Veolia has also identified a wide range of key stakeholders in the project and “actively engaged with them to build stronger community relationships and to operate in a more transparent manner.” As part of this process, a number of environmental initiatives have also been implemented - with participation in the Carbon Reduction Commitment (CRC) also resulting in improved carbon emissions reporting, as well as “the best ever performance of the CHP plant, the construction of an advanced digestion plant at Seafield, a review of alternative means of power and the establishment of the East Calder Biodiversity Project.”

“Converting waste sludge into a marketable product has enabled Veolia to recycle 60,000 tonnes of waste sludge per year and provide 30,000 tonnes of treated sludge for agriculture. Creative use of waste products also maximises the project’s financial opportunities and, thanks to the increased efficiency of the CHP plant, it is now 85 percent self-sufficient in electricity,” says Keast.

“The AVSE carbon footprint was analysed to understand the sources of its greenhouse gas emissions. As a result, a significant number of environmental improvements have been made including recycling aggregate from the transportation of materials, which has reduced by 75 percent,” he adds.

Expansion: The investment at Seafield into an additional CHP unit provided a 3 percent increase in the biogas yield

Excess power

Elsewhere, the Dutch EPC outfit Nijhuis Industries has recently been given the green light to install a turnkey wastewater treatment plant for the South Port Said Industrial Zone (SPIZ) in Port Said, Egypt. In light of a compositional analysis of the wastewater collected from upwards of 250 companies in the Zone, the facility, to be constructed on behalf of Green Valley Oil Services (GVOS), is being designed to be completely self-sufficient in terms of its energy demand - and there are even plans to sell any excess power to the local grid.

According to Menno Holterman, chief executive officer at Nijhuis Industries: “The plant consists of Nijhuis proven technologies for physical-chemical, aerobic and anaerobic biological treatment, active sludge and tertiary treatment, to meet strict effluent requirements, and will optimise the recovery of biogas and energy from the effluent.

“This is of critical importance, due to the limited availability of power from the grid, and hence why the wastewater treatment plant is designed to become self-sufficient and energy neutral,” he adds.

The Seafield WWTP is the largest of its kind in the East of Scotland

Variable speed drives

Another very interesting ongoing initiative is the wastewater to energy system installed at Aarhus Water’s Marselisborg Wastewater Treatment Plant in Aarhus, Denmark - a traditional activated sludge treatment plant with mesophilic digestion based on household wastewater.

Over the course of around five years, a variety of energy efficient equipment has been installed at the facility, including high speed turbo blowers, variable-speed alternating current (VSD/AC) drives on all rotating equipment, a highly efficient CHP (Combined Heat & Power) station - and energy efficient bottom aeration via regular maintenance of the entire aeration system.

The facility, which operates unmanned for 15 hours each day is also completely computer controlled via online sensors, enabling real-time control of the biological stage by operating blowers based on precise load-estimates - calculated using a combination of the on-line ammonium sensors and the incoming flow. The key net result of all these improvements is that Aarhus has been able to get the wastewater facility to produce 134 percent more energy than is needed for wastewater treatment at the facility.

“This surplus energy is enough to cover the need related to producing drinking water, distributing water and pumping wastewater back to the wastewater facility – and so the company has created the world’s first energy neutral catchment area for 200,000 people – just based on the energy which can be gained from these peoples’ household wastewater,” says Mads Warming, global director & GKAM water & wastewater at Danish company Danfoss Drives, which was heavily involved in the installation of energy efficient equipment at the facility.

The Holy Grail: At a variety of points in 2017 the Seafield WWTP achieved full self-suffiency

Energy neutral

In Warming’s view, the most interesting thing about the Marselisborg initiative is that the utility has approached the project with the twin aims of achieving energy savings - both in drinking water production and distribution, as well as wastewater pumping and treatment - and secondly increasing energy production at the wastewater facility.

“This was also achieved with only the household wastewater they receive from the 200,000 people - meaning that no wind, solar, heat pump or sludge burning energy is produced and no external sludge, FOG or carbon is added to improve production,” he says. Aarhus Water is currently also in the process of upgrading facilities at Egaa, another of its catchment areas containing some 120,000 people. Interestingly, the company expects the same performance levels it achieved at Marselisborg, even though the Egaa facility is only half the size.

Over the next few years, Warming predicts that successful examples like these will prompt the broader wastewater sector to realise the “huge energy savings potential in using a lot more online sensors combine with VSD’s on all pumps and blowers’ - combined with the help of smart process control ‘to obtain energy neutrality for the whole water business.”

“The Danish government is aiming at making the whole water sector in Denmark completely energy neutral. We have seen great interest both in EU but also in the US, especially Chicago and California, and are introducing the concept globally,” he adds.

‘Step change’

Looking ahead, Keast is confident that the commercial prospects of wastewater to energy initiatives of the type already underway at Seafield and elsewhere will continue to improve. In his view, this is particularly the case because the water industry is currently the fourth most energy-intensive industry in the UK - using approximately 3 percent of UK generated electricity for pumping, water treatment and waste management and responsible for around 1 percent of the country’s greenhouse gas emissions.’

Against the background of such high levels of consumption, he believes that the challenge for the next decade or so will be to ‘move towards energy self-sufficiency, cut carbon and exploit all the opportunities for customer-controlled energy.’

“Harnessing the potential of seven million tonnes of human waste each year will become a vital strategy to meeting these challenges,” he says.

In helping to capture this potential, he highlights the fact that Anaerobic Digestion (AD) and Combined Heat and Power (CHP) technology is “advancing rapidly” - with gas cleaning systems, lean-burn engine-based CHPs and thermal hydrolysis “already creating the potential to double renewable generation capacity by 1,697 gigawatt hours – enough to power half a million homes.”

Keast also points out that low-energy devices, controls and the use of consumption data will enable the industry to cut water consumption - and, at the same time, innovations like the recovery of low-grade heat from sewers “could become a source of additional revenue in the future and boost sustainability.”

Eventually, he predicts that renewable energy from biogas will also help drive the industry towards what he describes as “genuine carbon neutrality and energy self-sufficiency.”

Mads Warming at the Marselisborg WWTP that produces 134 percent more energy than is needed

“As populations grow, more sludge will be available and this in turn will allow expansion in the ability to capture renewable biogas and generate renewable electricity. As treatment processes are further optimised and AD and CHP technology advances, the opportunity for greater energy self-sufficiency and renewable energy export will rise. This would be further increased if any spare - or headroom - capacity could be used for the co-digestion of energy crops or other liquid organic wastes,” he says.

“To lower energy demand and use optimised energy management, based on implementation of low energy devices, controls and the use of consumption data will enable the industry to make a step change in reducing demand side consumption,” he adds.

Andrew Williams is a freelance contributor to WWi magazine.

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