Making the case for an energy-neutral water sector: allowing for health, energy efficiency and environmental gains

Wednesday, 13 October 2021

Expanding water treatment globally is not only a key enabler for creating a better world for humankind, but it can also contribute to fighting climate change and reducing carbon dioxide (CO2) and greenhouse gas (GHG) emissions.

So said Mads Warming, Global Head: Water & Wastewater, Danfoss Drives, who spoke at the 11th annual Sustainability Summit, a live virtual event held recently in South Africa. Warming explained that currently, approximately just 20 percent of all wastewater globally is treated, meaning that around six billion people only have access to untreated water.

The United Nation’s (UN) Sustainable Development Goal (SDG) 6 defines improvement targets for clean water and sanitation. SDG 6.2 aims at improving the 20 percent of wastewater treated globally to 60 percent, by latest 2030.

Achieving this objective would bring with it a multitude of health improvements, and in addition would play an important role in reducing the greenhouse gas (GHG) load.

Typically, the key components in water treatment emissions are methane (CH4), nitrous oxide (N2O) and CO2. CO2 results from the energy consumed, while the term ‘greenhouse gases’ refers to all three components.

“Perhaps unexpectedly for many, the GHG effect of letting the wastewater escape untreated into the surrounding environment is far more detrimental than that of additional energy consumption due to new wastewater facilities,” Warming stated.

According to the International Water Association (IWA), untreated wastewater running directly into the environment generates a GHG footprint roughly three times higher than when the same wastewater is dealt with in a traditional wastewater facility.

“The good news, though, is that we already have the right technology needed to move forward to achieve energy neutrality, and an additional one-third reduction in GHG emission can be gained by using digitalisation and applying variable speed drive (VSD) control.

“Furthermore, VSDs are playing a critical role in helping the water sector to reduce energy use. And there is an excellent reason for this, as water and wastewater facilities are extremely energy intensive. In fact, the International Energy Agency (IEA) states that four percent of all electricity used globally goes towards water and wastewater handling facilities alone. The IEA also says that between 30 and 50 percent of a local government’s electricity bill is typically related to these operations.”

Save Water and Energy — How Aarhus Water went energy-neutral

Together with Danfoss, Aarhus Water, the second largest water service company in Denmark, has succeeded in bringing the entire water cycle (drinking water and wastewater) into energy neutrality.

The world’s first energy-neutral catchment area

Together with Danfoss, Aarhus Water, the second largest water service company in Denmark, has succeeded in bringing the entire water cycle (drinking water and wastewater) into energy neutrality.

Aarhus Water’s aim was to transform the water treatment facility of a catchment area in the centre of Aarhus named Marselisborg, a small borough with a population of 200,000 people, into an energy producer, while also achieving energy neutrality for the drinking water supply, wastewater pumping and wastewater treatment.

Marselisborg is a traditional city area in a relatively flat geographic region, where water supply is based on groundwater supply, which is on average pumped from 35m depths, and traditional household wastewater.

It has now become the world’s first energy-neutral catchment area.

  • The concept used by the utility and Danfoss was based on a two-step strategy, covering:
    Reducing energy consumption throughout the water and wastewater facilities to the lowest possible sensible level; and
  • Increasing energy production from the wastewater facility.

On the water supply side, energy savings have been obtained by splitting the city into pressure zones, which then, based on pressure transmitters and VSDs, regulate pressure to optimal levels in each zone. This offers an energy reduction and has also brought leakage down to between only six and eight percent.

The Marselisborg wastewater facility has been upgraded with more energy efficient equipment, and, in particular, with advanced real-time process control based on online sensors. Other key elements include VSD drives on all rotating equipment; carbon harvesting; highly efficient components (such as bottom aeration and high-speed blowers); and a CHP installation (electricity and heat).

The experience from this and other facilities indicates that of all improvements obtained over the years, more than 70 percent of the energy reduction/improvement is obtained from better process control, also known as digitalisation, where the VSDs play a key roll.

New advanced VSD with edge computing technologies supports digitalisation

With its newest water-dedicated VSD, Danfoss has placed even greater support behind digitalisation.

Edge computing technologies integrated in the VSD provide intelligent, condition-based monitoring of equipment such as pumps and fans, based on both vibration and load-envelope detection.

How does it work? Using the example of a pump, the VSD creates a baseline for power consumption and vibration as a function of the pump speed, based on one day, for example, or one week’s operation.

Having established the baseline, the VSD then detects anomalies and reports them. Besides monitoring power consumption patterns, it also monitors motor windings. The condition monitoring functionality helps water facilities run more cost effectively, as well as reducing energy consumption.

The VSD also offers other digital functions which contribute towards running efficiently with a lower GHG footprint, for example a standard integrated deragging function which automatically prevents unnecessary pump clogging.

“Digitalisation and control using VSDs have been proven as key enablers in achieving the goals of reducing water loss, cutting energy consumption and delivering better quality of water. Danfoss is ready to help by replicating the success of Marselisborg in other cities across the world.”