The main purpose of the visit was to study the N transformation pathways during single particle pyrolysis of dried dairy sludge. Dairy sludge (biological sludge from wastewater treatment plants in milk processing factories) contains valuable nutrients and is usually used a fertilizer. Increasing volumes of dairy sludge create the need for new applications. Pyrolysis of dairy sludge is considered as an alternative way of utilisation of its value by producing bio-char while recovering of energy in the form of a high calorific value pyrolysis gas. Due to the high N content of dairy sludge, NOx emissions are considered to be problematic for final application of pyrolysis gas. Therefore, a thorough understanding of N partitioning during thermal conversion is of particular importance. 

The single particle pyrolysis reactor was used to carry out tests at 5 different temperatures in the range from 400 to 900°C. The reactor enables for an on-line measurements of particle mass as well as temperature inside the particle as pyrolysis progresses. At each process temperature, three different series of experiments were conducted in order to measure the N-containing species: 1) for measuring gaseous compounds released during pyrolysis; 2) for collecting tar compounds and 3) for measuring NH3 and HCN using the wet chemistry methods. After each pyrolysis test the char samples were collected for further determination of an elemental composition. The N-containing compounds NH3, HCN, NO, N2O, NO2, were the main focus of the study. In addition, to the on-line measurements of NH3 and HCN by means of FTIR, accumulative sampling in impingers containing absorption solution of H2SO4 or NaOH was carried out. The tar measurements were conducted according to the tar protocol, and the N-containing tar species will be identify and quantified.  

The results of the experimental tests and all the measurements will allow to close the N balance, and to understand N transformation pathways under pyrolysis conditions for dairy sludge.  

The Bioenergy 2020+ had excellent preparation for carrying out experiments at the single particle reactor. The facilities were very well equipped and highly organised. The scientists and staff were really helpful and supportive in the experiments. This project was a very fruitful continuation of study we had started at the University of Limerick. It was a nice experience and great opportunity to follow the transitional access to Bioenergy 2020+ via BRISK2, for exchanging ideas and a potential continuation of collaboration on topics of interests for both institutions.