particular obligation to share our know-how since issues such as resource scarcity, climate adaptation 
and mitigation of climate change all constitute global challenges….which we believe are essential 
elements of a Utility of the Future. 

Finding ways to improve our energy profile and reduce our carbon footprint 

Our journey towards recovering energy resources in the wastewater began in 2010. At that point, VCS 
Denmark decided to challenge the paradigm of major wastewater treatment plants by becoming energy 
neutral by 2014, and we put out an international tender asking for inspiration to achieve this goal. Our 
collaborative project with a global consultancy led to a quantified catalogue of potential energy savings, 
and more importantly - a number of potential improvements in energy production. The Ejby Mølle 
WWTP (our largest facility with a capacity of 385,000 population equivalents) already had biogas driven 
combined heat power (CHP) facilities producing electricity and heating for our district heating system, 
but we wanted to go further. Our improvement program was in line with a general approach in 
Denmark and in our local community that green solutions are considered to be of high value. 

Focusing on recovering energy resources 

The basic approach was to identify energy resources in the wastewater. The more carbon that goes into 
the digester the higher the production of biogas. We evaluated the carbon-balance throughout the 
treatment processes with the objective of optimizing the utilization of the received organic material, 
while reducing its impact to the existing biological nutrient removal process in the liquid stream.  By 
concentrating in carbon redirection, we were able to go from 75% energy self-sufficiency in 2011 to 
energy neutral by the end of 2014. 

In addition to our process optimization program, one of innovative concepts we adopted was the 
treatment of the sidestream from digested sludge dewatering with the deammonification process, and 
its configuration to allow its implementation in the mainstream of our biological nutrient removal 
process as well.  The general idea is to focus on elements such as carbon and ammonia, and make sure 
that they are handled in the most optimal way - whether for the purpose of removal or utilization. The 
result has been a process optimization containing many elements of improvement – many of them 
interrelated. By 2015 the Ejby Mølle WWTP became net energy producing by producing in terms of 
electrical and heat energy over 150% of what it requires to operate meeting very stringent nutrient 
removal requirements (TN< 5 mg/L; TP < 0.5 mg/L). 

Holistic approach towards system-wide optimization  

Our results are the sum of many initiatives – major as well as minor. E.g. we reduced the amount of 
oxygen used in the aeration process substantially through online measuring – thereby saving both 
energy and maintenance of our equipment. We also found that the mixing of the digester could be 
reduced to 6 hours daily – instead of having the mixer equipment operating 24 hours a day to produce 
the same amount of biogas.  

For VCS Denmark, acting sustainably in a broader sense is an important part of the reason that we 
perceive wastewater as a resource. Many of the minor improvements in producing biogas are – as yet – 
mainly important from an environmental perspective. However, we choose to implement them