How can more water treatment cut CO2 emissions?
Expanding water treatment globally is not only a key enabler for creating a better world for humankind. Water treatment can also contribute to fighting climate change and reduced CO2/GHG emission; the term ‘greenhouse gases’ (GHG) in this blog refers to all 3 components. Typically, the key components in water treatment emissions are methane (CH4), nitrous oxide (N2O) and CO2. CO2 results from the energy consumed.
Only about 20% of all wastewater globally is treated. In other words, wastewater for 6 billion people remains untreated. Untreated wastewater released into the environment generates a GHG footprint roughly 3 times that of the GHG footprint when the same wastewater is treated in a traditional wastewater treatment plant (WWTP).
The UN Sustainable Development Goal 6.2 aims to increase the level of wastewater treatment from today’s level of 20% of all wastewater generated globally, to 60% in 2030. Achieving this would bring vast health improvements. Additionally, it would reduce the GHG load, since the GHG effect of releasing untreated wastewater into the surrounding environment is far more detrimental than the GHG effect of additional energy consumption due to new WWTPs.
According to IWA, treating wastewater cuts its GHG emission to about one-third. The final one-third of GHG emissions can also be eliminated using digitalisation and variable speed drive (VSD) control.
Decarbonisation of the wastewater industry:
One of the world’s most energy efficient WWTP facilities is operated by Aarhus Vand, a water utility operating in Denmark’s second largest city, Aarhus. The Marselisborg WWTP is a traditional, rather old, activated sludge wastewater facility handling household wastewater from about 200,000 people.
The facility receives no external carbon – for example, no FOG (fat, oil and grease), and no external sludge. Neither is it powered by wind power, nor solar power, nor burning of sludge, nor heat pumps. It treats water very close to plain household wastewater supplied from a combined sewage collection system. Still it generates twice the energy needed for cleaning the wastewater to very low outlet values (BOD5 = 2.4/TN= 6.0/TP = 0.2). Here, digitalisation and Danfoss VSDs are absolutely key components in obtaining this impressive result.
IEA’s World Energy Outlook 2018 states that by achieving SDG 6.2 either by controlling the wastewater facilities the traditional way alone, or by applying Aarhus/Danfoss-type strategies, the reduction in energy consumption would equate to approximately 650 TWh. A value equivalent to the total annual energy output of all coal-fired power plants in Europe.
It’s one thing to transform a WWTP into an energy producer, another matter entirely to make it climate neutral. This is due to nitrous oxide (N2O) and methane (CH4) emissions. Respectively, these gases have global warming potentials up to 300 times and 30 times that of CO2. Calculations show that Marselisborg WWTP is climate neutral, despite the GHGs and sludge handling – clearly demonstrating that decarbonisation of the WWTP industry is possible.
Digitalisation in practice:
The Marselisborg WWTP is upgraded with more energy efficient equipment, and importantly, with advanced real-time process control based on a much wider use of real-time online sensors and Danfoss VSDs, than is common. The key strategy is twofold:
- Save energy
- Increase energy production
The experience from this and other facilities in Denmark indicates that of all the improvements obtained over the years, over 70 % of savings is due to process control/digitalisation improvements.
The newest water-dedicated Danfoss VSD supports digitalisation even more. Edge computing technologies integrated in the VSD provide two-dimensional supervision of equipment such as pumps, based on both vibration and load-envelope detection.
In the specific installation, the VSD creates a baseline for power consumption and vibration as a function of the pump speed, based on one day, or one week’s operation. Having established the baseline, the VSD then detects anomalies and reports them. It also monitors motor windings and has a deragging function to automatically prevent unnecessary pump clogging.
The future of WWTPs is therefore not only to achieve the primary aim of improved health for humankind, but also to integrate into future energy networks and contribute to reduced CO2/GHG emission.
Digitalisation and VSDs have proven to be key enablers in this integration.