PhD defence by Yinqi Tang: Biochar assisted soil quality recovery in chromated copper arsenate contaminated soil

Soil pollution with heavy metals and metalloids is considered as one of the major threats to human and ecosystem health. Chromated copper arsenate (CCA) polluted sites globally spread due to the intensive usage of CCA compound for protecting wood products from decay. In order to improve soil quality and ecosystem health, the development of cost-effective remediation technologies are highly required. Biochar has become a popular remediation technology because of its environmental benefits such as pollution control, greenhouse gas regulation, and fertilizer supply. Biochar is a carbon material by pyrolysis of organic wastes such as wheat straw, bone meal, food wastes, sewage sludge, and manure. To enhance the biochar ability of decreasing the toxicity of metalloids like arsenic, combination of biochar and zero-valent iron (ZVI) is developed and applied for remediating polluted soils. However, soil microbial community recovery during the remediation of polluted soils, particularly by biochar and its combination with ZVI, is not well studied, although soil microbial communities play a key role in ecosystem functions.

Therefore, this PhD thesis aimed to evaluate soil quality recovery during the remediation of CCA polluted soil according to chemical, ecotoxicological, and ecological lines of evidence. This thesis focused on soil microbial community recovery and explored determinant factors for increasing the speed and degree of soil ecological recovery. To this end, this study first tested 14 types of contrasting biochars for their performance on reducing soil toxicity, decreasing copper (Cu) bioavailability, and recovering soil bacterial communities including function, tolerance, and composition. Furthermore, this study tested bone biochar combined with ZVI for their ability of decreasing soil toxicity and pollutant availability and recovering soil microbial communities including bacteria and fungi.

This thesis suggests that ZVI-modified biochar (biochar raw material: pig bone meal powder; pyrolysis temperature: 950°C) shows a great potential for improving soil quality in CCA polluted soils. This study demonstrates the importance of including bacterial growth, bacterial community tolerance and composition as soil ecological indicators in ecological risk assessment of contaminated soils. This study also provides new insights into the underlying mechanisms and influencing factors of soil microbial community recovery.

Assessment Committee

Professor Anne Winding, Aarhus University, Denmark
Senior Lecturer Olof Berglund, Lund University, Sweden
Associate Professor Mette H. Nicolaisen, (Chairman), PLEN, University of Copenhagen, DK


Associate Professor Kristian Koefoed Brandt, PLEN, University of Copenhagen, Denmark
Professor Peter Engelund Holm, PLEN, University of Copenhagen, Denmark

The defence is followed by a reception in meeting room B212 on 2nd floor.