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Jan Knappe

Postdoctoral Researcher
Dept. of Civil, Structural & Environmental Engineering




The influence of the biomat on on-site wastewater contaminant transport and attenuation

Keywords: biomat; domestic wastewater treatment; sustainable sanitation; soil treatment unit; vadose zone.

With circa 500,000 septic tank systems currently installed, approximately one third of the domestic wastewater generated in Ireland is treated in on-site wastewater treatment systems consisting most commonly of a septic tank and a soil treatment unit (STU). In the soil, a microbial biomat at the infiltrative surface plays a critical role with regards to effluent distribution and pollutant attenuation due to its control on the underlying soil moisture conditions as well as the nature of organics which percolate from it.

In field studies, we proved that the development and characteristics of such a biomat is dependent on the subsoil and the level of effluent pre-treatment. We are now trying to improve our understanding of the physical and biogeochemical implications of biomats in STUs on pollutant transformation pathways, with a specific focus on:

  • metagenomic approaches to identify microbial communities in the biomat;
  • identifying physical properties and hotspots of microbial activity using non-invasive probing and imaging techniques;
  • numerical modelling of the development and the nature of biomats using finite element models (e.g. HYDRUS) and analytic solutions;
  • the nature of dissolved organic material that percolates into the unsaturated zone beneath the biomat from full-scale field studies;
  • the nature of nitrogen removal pathways through the biomat and in the underlying unsaturated subsoil under different effluent loadings from both field and controlled column studies;
  • pathogen transport and attenuation processes through the unsaturated subsoil from the analysis of enteric bacteria and phages from both field and controlled column studies;
  • and the risk of engineered nanoparticles as an emerging contaminant of groundwater from on-site wastewater treatment systems.





Principal Investigator: Prof. Laurence Gill