PhD Defence: Soil washing for mixed contamination of heavy metals and polycyclic aromatic hydrocarbons using sustainable washing agents – Københavns Universitet

PhD Defence: Soil washing for mixed contamination of heavy metals and polycyclic aromatic hydrocarbons using sustainable washing agents

Name of PhD student: Ms. Sarah Salah Mohammed Greish

Soil contaminated with mixtures of organic and inorganic contaminants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals is a worldwide problem and poses a threat to human health and ecosystems. Remediation of these soils is challenging as heavy metals and PAHs are persistent, have different physicochemical properties and behave differently in the soil. Only few remediation techniques have been tested for soil with mixed contamination.

The overall aim of this PhD study was to advance the current knowledge about remediating soil contaminated with mixtures of heavy metals and PAHs especially focusing on soil washing. Soil washing applying chemical extraction involves the use of an aqueous solution containing a washing agent to extract contaminants from the solid phase.

In this study, the following sub aims were addressed:

(1) testing the efficiency of five sustainable washing agents including two dissolved organic matter (F-DOM and CRC-DOM), two bio-based surfactants (BBE-1000 and Supersolv), and one bio-surfactant (Rhamnolipid)

(2) testing the most efficient washing agent on a number of soils with aged contamination

(3) investigating the effect of soil characteristics on the efficiency of the optimized soil washing procedure

(4) testing the optimized soil washing procedure on another group of organic contaminants (pesticides) and mercury

(5) investigating how PAHs interact with the least and the most effective soil washing agents to understand the factors affecting washing agents extraction capabilities.
 
Results showed that the two DOMs at the studied concentrations showed low efficiency for extracting heavy metals and PAHs. Rhamnolipid showed moderate efficiency and the bio-based surfactants showed high efficiencies at their highest concentrations. A soil washing method was developed for the simultaneous remediation of heavy metals and PAHs using Supersolv. The developed method showed potential for extracting heavy metals and PAHs from 13 soils with different soil characteristics. Soil washing efficiency decreased as the soil content of organic carbon, clay and CaCO3 increased. The developed method showed high efficiency for the extraction of organophosphate pesticides malathion and ethyl parathion, but low efficiency was observed for mercury. Furthermore, this PhD study highlighted the importance of nonpolar interactions between the PAHs and soil washing agents which could enhance PAHs desorption from the soil and micelles would increase PAHs solubility in the washing solution.

Supervisor
Professor, Peter Engelund Holm, Section of Environmental Chemistry and Physics, University of Copenhagen –PLEN

Co-supervisors
Associate professor, Helle Marcussen, Section of Environmental Chemistry and Physics, University of Copenhagen –PLEN
Professor, Jan H. Christensen, Section of Environmental Chemistry and Physics, University of Copenhagen –PLEN

Assessment committee
Hans Chr. Bruun Hansen, (Head of Committee), University of Copenhagen –PLEN
Professor, Dan Berggren Kleja, Sveriges Lantbruksuniversitet, Uppsala, Sweden
Senior researcher , Ulla Gro Nielsen , University of Aarhus, Roskilde