My research has been based on waste valorisation by assessing different thermal technologies as alternative route for further treatment of digestate. Same crop digestate, has been already processed in conventional pyrolysis, slow at University of Nottingham in United Kingdom and fast VTT in Finland. Further experiments will be also carried out with microwave pyrolysis to identify which compounds are potential for further valuable product generation, such as chemicals, biofuels and others. My investigation has undertaken these experimental approaches of product composition and heating conditions to develop a kinetic model to predict pyrolysis behaviour. This model is based on the decomposition of cellulose, hemicellulose and lining content in biomass to project yields of bio-oil, gas and char. My current investigations can be summarised in the Figure 1 which is a general diagram of the main inputs for the kinetic model and the possible projections of yield product, mass balance and product composition. 

Some methods have been implemented to obtain an approximation of lignocellulose composition, such as a thermogravimetric analysis (TGA). However, it is important to compare this with more accurate methods, in which the characterisation is based on extraction of lignocellulose components in order to have a better characterisation of digestate due to being a crucial kinetic model input.

Cellulose and Hemicellulose are formed from a combination of sugars: cellulose is mainly composed of glucose and hemicellulose is a structure of xylose, arabinose, galactose and others. Wageningen Food & Biobased Research has performed analyses of these carbohydrates for many years, and has had the experience and facilities to quantify the amount of sugars in this waste. This institute mainly uses an ICS-5000 for this quantification, which includes a CarboPacTM PA1 column that can easily separate the saccharides through a high-performance anion-exchange (HPAE), using NaOH as eluent. It has the advantage of obtaining high-resolution separations for better results. This is why I applied to work at here to get more precise crop digestate composition I have been used in different pyrolysis systems.

Eight samples were analysed, and one important step of this analysis was to differentiate between the glucose that could possible coming from starch and the glucose from cellulose, which will help to know if the digestate still has some remaining starch after anaerobic digestion processing.

For this differentiation, the eight samples were processed in two ways:

  • Glucose in cellulose. For this, strong hydrolysis is needed. The samples were treated with 72% (w/w) H2SO4 at 30 °C for 1h. Then deionised water was added to get a 1M H2SO4 solution to be incubated for 3h at 100oC
  • Glucose in starch. This glucose chain is easier to break down. The samples were just hydrolysed in a solution of 1M H2SO4 and incubated for 3h at 100oC

These procedures were carried out by duplicate for each sample, having in total 32 samples.

Picture 2 shows the same crop digestate treated with both hydrolysis, resulting the darker brown colour the one went through strong hydrolysis. 

After hydrolysis, samples needed to be neutralised with barium carbonate and filtered to be injected in the Dionex as it shown in Picture 3. 

The next steps are to quantify the sugar content in each sample processed, based on calibration curves obtained from the sugar contents in the standards.  Examples of glucose and galactose calibration curves are shown in Figure 2. Additionally, the amount of moisture and ash in the samples were also obtained to calculate how much of the biomass has lignocellulose material. 

Some components found in bio-oil pyrolysis can be directly related to the decomposition of cellulose, hemicellulose and lignin at different temperatures. This whole characterisation performed in Wageningen Food & Biobased Research of the crop digestate employed for my experimental work will help not only to improve the current kinetic model developed to predict the pyrolysis of crop digestate using a range of processing conditions, but also to evaluate possible alternatives of how these technologies can be implemented, and the possibility to respond some questions such as: is pyrolysis suitable for this waste? or is there another scenario to integrate pyrolysis: Pre or post Anaerobic digestion?. 

 Figure 3 shows a general diagram of how knowing lignocellulose composition of waste, pyrolysis can be evaluated as an alternative treatment to increase the value of waste in different scenarios, and how some components can be used for further valuable products. 

Acknowledgments 

My time at Wageningen Food & Biobased Research was such a great experience, not only because I have the opportunity to meet exceptional staff and experts in biomass valorisation, but also because I was able to work in such astounding facilities.

I want to express thanks to some of the people who helped make this opportunity happen: 

Rene van Ree, Carl Safi and Peter Geerdink not only for accepting me, but also for ensuring that I had everything I required for my stay. 

Thank you to Ben van den Broek, who was in charge during my stay. He not only supervised me and introduced me to all the staff and experts that I would be working with, but he also ensured I was learning everything I needed in order to carry out these assays and to analyse further data. He did everything he could to make this visit successful and fruitful.  

Ingrid Haaksman and Jacinta van der Putten for all the support when I was in the laboratories, for answering my questions and ensuring my safety, and for pushing me to do further analysis of the samples in order to obtain more useful data for my research project. They were fundamental in helping me understand the starch and lignin content in this waste.  

Willem Drost for ensuring that the determination of moisture and ash occurred. 

Thank you to all of the staff at Wageningen Food & Biobased Research for making me feel so welcome. It has such a great research environment. 

Thank you to my main supervisor at the University Of Nottingham, John Robinson, who has supported me throughout this other opportunity. 

BRISK2 has been one of the best organisations I have ever known. The opportunities offered to me have been crucial for my progress as a researcher and international student. Beyond visiting the facilities, the quality of experts I have met and the knowledge they have shared with me have had a great impact on me.