Anlæg på DTU Aqua, Hirtshals til forsøg med næringsstofbalance i akvakultur

PhD defence about transforming waste from aquaculture into new resources

Sunday 05 Feb 17


Carlos Octavio Letelier-Gordo
Research Assistant
DTU Aqua
+45 35 88 32 99

Time & Place


Friday, 10 February 2017, 11:00 a.m.


DTU Aqua
Nordsøen Forskerpark
Willemoesvej 2
9850 Hirtshals 

The thesis

A copy of the PhD thesis is available for reading at the Institute. Contact Christine Hastrup,

On 10 February 2017 PhD student Carlos Letelier Gordo will defend his thesis about optimizing sludge hydrolysis to improve nitrogen removal in aquaculture

PhD student Carlos Octavio Letelier Gordo will defend his thesis "Transforming waste into new resources: Optimizing sludge hydrolysis to improve nitrogen removal in aquaculture through denitrification" on Friday, 10 February 2017, 11:00 a.m. at  DTU Aqua, Nordsøen Forskerpark, Willemoesvej 2, 9850 Hirtshals. 


  • Principal supervisor: Head of Section Per Bovbjerg Pedersen
  • Co-supervisor: Senior Researcher Anne Johanne Tang Dalsgaard


  • Senior Researcher Ivar Lund, DTU Aqua
  • Lecturer Natella Mirzoyan, American University of Armenia
  • Professor Jaap van Rijn, Hebrew University of Jerusalem

Chairperson at defence

  • Senior Researcher Dr. Lars-Flemming Pedersen


Intro to the thesis

This PhD thesis focuses on enhancing the use of organic waste produced by the fish as an internal carbon source for on-farm denitrification, i.e., transforming the organic waste into a new resource following the “Residual Resource” approach.

In Denmark, the implementation of stricter environmental policies has forced the aquaculture sector to improve its practices and water treatment technologies, thus becoming progressively more environmentally sustainable and competitive. Even though the industry has managed to reduce the discharge of organic matter and phosphorous, the major challenge is now the removal of total nitrogen, where only 15-50% can be removed with the best available current technology.

From the nitrogenous compounds found in recirculating aquaculture system (RAS) effluent nitrate-N constitutes by far the major fraction of total nitrogen deriving from biological oxidation of ammonium, the major nitrogen compound excreted by the fish. Therefore, removing the content of nitrate-N from effluent water is an important step to take. In this respect, heterotrophic denitrification—a biological process where bacteria reduce nitrate into gas with the use of organic carbon as electron donor— is central.

The organic waste produced by the fish in RAS can be used as an internal carbon source for on-farm denitrification. In this way, two waste types (organic waste and nitrate) are treated simultaneously, reducing the associated costs for purchasing external carbon sources and the cost for disposing the organic waste.

Feed is indirectly the major source of the waste produced in RAS, with the digestibility of the feed ingredients along with the macro and micronutrient composition of the feed dictating the amounts and characteristics of the waste produced. Thus, coupling feeding with waste production allows influence on and an estimation of the masses of waste to be treated, including the availability of organic waste that may be used as a resource.