One of 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 – so there is created completely energy neutral catchment area for 200,000 people – just based on the energy which can be gained from these peoples’ household wastewater.
The Holy Grail: At a variety of points in 2017 the Seafield WWTP achieved full self-suffiency
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 (Fat Oil Grease) 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.
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, 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.
In helping to capture this potential, 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.
Renewable energy from biogas will also help drive the industry towards genuine carbon neutrality and energy self-sufficiency.
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.