Difficult Digestable Materials Digestion

Difficult Digestable Materials Digestion

HoSt is one of the largest suppliers of bio-energy installations in Europe. HoSt focuses on the technological development of the processing of biomass flows and the supply of systems for sustainable energy generation from biomass. HoSt has a laboratory where various tests can be performed, such as ‘batch tests’, to determine the biogas potential of a power supply, or continuous tests, where a digestor is simulated.

It is known that an excessive amount of NH3 in the digestor leads to ‘nitrogen inhibition’, the digestion will then proceed less quickly and less completely. It may be desirable to use waste streams with a high nitrogen content in a digester. An applied technique to reduce the nitrogen content in a digester is to remove nitrogen from the digestate coming out of the digester, and to recirculate this low-nitrogen digestate back to the digester. The removal of nitrogen can be done in various ways, for example with a nitrogen stripper, however here the pH and/or temperature is increased, which can influence the digestion process when this material is recycled.

The research focuses on the influence of nitrogen in a digester, and on the influence of recirculating digestate with an increased pH and/or temperature. You will answer the following questions:

What is the influence of organically bound nitrogen in relation to ammonium (NH4)? How does the conversion of organic nitrogen to ammonium proceed? At what concentrations does nitrogen lead to nitrogen inhibition, and how does this depend on pH and temperature? Are there other parameters when recycling digestate that can influence the digestion (eg salting)?


  • Literature study into the inhibitory effect of nitrogen on digestion;
  • Collection of test results for nitrogen inhibition and nitrogen stripping;
  • Collecting data from running digesters with different nitrogen concentrations;
  • Conducting lab tests to simulate the gas production of a digester;
  • Estimating and performing lab scale tests for digestion with difficult waste streams.


  • Chemical Technology, Process Technology, Mechanical Engineering, Agrotechnology (hbo/wo).


  • Monthly fixed fee of €400 based on 40 hours per week;
  • Lots of responsibility and room for own initiatives;
  • Professional support, guidance and insights;
  • An internship in the renewable energy sector;
  • Interesting international environment which is only a 5-minute walk from the ‘Kennispark’ train station in Enschede;
  • Nice welcome package;
  • A dynamic, flexible and passionate team.


HoSt is one of the world market leaders in the field of energy installations to convert biomass and waste into renewable energy and other valuable end-products. With over 200 employees, HoSt has been developing, designing, manufacturing and maintaining innovative energy plants for the production of renewable energy from biomass and waste since 1991. HoSt bioenergy plants contribute to the success of a circular economy by producing renewable energy, solving the waste problem and creating valuable end products from organic waste.

In addition to its headquarters in the Netherlands, HoSt has offices in the US, France, Latvia, England, Poland and Germany and more than 280 installations in over 30 countries across four continents. For the biogas plants, boilers and combined heat and power plants supplied by HoSt, HoSt has 24/7 maintenance teams in several countries.


Mail your resume and motivation to [email protected]. General questions can be addressed to Mariëtte Huis in `t Veld, internship coordinator. For questions and more details about the internship please contact Gijs Olde Loohuis via +31 (0) 53 – 460 90 80.

Please do not make use of this vacancy as an acquisition opportunity.