Characterisation and functionality of soil treatment units microbial mats (“Biomats”) in on-site wastewater treatment systems
Near half a million households in Ireland are served by some form of on-site wastewater treatment system. Mainly located in rural areas, these systems are composed of a settling or septic tank, ideally combined to a network of percolation trenches (see fig 1) permitting the dissemination and passive treatment of domestic wastewater. If properly installed, these systems should bioremediate domestic wastewater, preventing the contamination of ground water and nearby surface water of nutrients and potential pathogens.
Figure 1. (source EPA ireland) Is a basic illustration of the on-site wastewater treatment system including a water pathway profile.
The aim of this research is to better characterise the functionality of soil treatment units in on-site treatment units. Four septic tank systems, employing different secondary treatments will be monitored for biotic and abiotic parameters to characterise the functionality of soil treatment units over time. There is limited research available on the impact of microbial composition on the functionality of soil treatment units. Microbial analysis will be critical component of this investigation as it will allow for microbial characterisation of biomat development and subsequent bioclogging, and greenhouse gas production (GHG) nearer to the subsrface.
The research techniques will employ both on-line monitoring system applying moisture and flow sensors (see fig 2), including Licor long term gas chambers for GHG fluxes. Regular sampling campaigns will be conducted to temporally and spatially characterise the treatment systems extracting water, biomat, and gas samples. Water samples will be analysed for several parameters such as Nitrogen, Phosphorous, TOC, fecal coliforms and E.coli. Gas samples will be analysed on Gas Chromatography mass spectrometry for Nitrous oxide and Methane. Soil samples will be molecularly analysed for microbial species. Targeted biomarkers will be employed to analysed samples for species involved with green-house gas production, samples of interest will be subsequently sequenced to further analyse the microbial composition.
Figure 2. Shows some of the instruments installed on site, these include lysimeters, moisture sensors, gas probes and biological access ports (BIOPORTs) for microbial sampling.
Project Supervisor: Prof. Laurence Gill
Funding was granted by the Science Foundation Ireland