Activated sludge biochar as an adsorbent for organic micropollutants – a first attempt
On May 30, Veronika Jörntell presented her Master´s degree project "Sludge biochar as an adsorbent for pharmaceutical residues in wastewater" at Lund University.
Several combinations of different sludge biochars, particle sizes as well as activation temperatures and residence times were tested in the degree project
Veronika activated four different sludge biochars in a pyrolysis furnace at the laboratory at Lund University. An activation is carried out to try to increase the sludge biochar’s ability to adsorb organic substances. The activation took place at high temperature in an atmosphere filled with carbon dioxide. Different activation temperatures (700, 800 and 900 ˚C) and different activation times (15 min, 30 min, 1 h, 2 h, 4 h) were tested in a series of combinations to be able to draw conclusions about which conditions give the highest degree of activation. In addition, the sludge biochar was sieved, and the tests were carried out for different particle sizes.
Since the pilot within the Testbed Ellinge project could not be put into operation in the spring, the degree projects this spring had to be carried out with sludge biochar from four Danish wastewater treatment plants (Søndersø, Højby, Nykøbing and Fårevejle) whose sludge is pyrolysed in full-scale at Søndersø’s and Fårevejle’s wastewater treatment plants, respectively. None of these sludges undergo anaerobic digestion before pyrolysis.
To measure the degree of activation, the adsorption of various organic substances was measured and the level of adsorption was directly linked to the degree of activation. A higher adsorbance indicated that the activation was of a higher degree. The adsorption of organic compounds was measured by UV absorption and radioactivity from 14C isotopes.
In the experiments, it was found that smaller particle sizes, <0.425 mm, reached a higher degree of activation and that an activation of 800 ˚C for 30 min contributed to the most increased adsorption. A comparison with commercial particulate activated carbon (PAC) showed that the best activated sludge biochar had a significantly lower adsorption capacity at low concentrations of organic substances, but approached about 50% lower at high concentrations. However, the comparison is probably misleading as PAC had a particle size of less than 0.1 mm.
Veronika thinks that the results are promising, but that there is development potential to find activated sludge biochars whose adsorption capacity is more similar to commercial activated carbon.
You can find the thesis in its entirety here.
Veronika Jörntell has now got her Degree of Master of Science in Biotechnology Engineering