Understanding water chemistry in biofilters using chemometric methods

Biological activated carbon filtration operating in slow flowing mode is a compromise between slow sand filtration and rapid-rate biological activated carbon filtration. It brings together the benefits of both systems: good control of microbial pathogens and dissolved organic matter removal. In this thesis the change in water chemistry in such biofilters was studied as a possible alternative for small-scale decentralised water treatment in Scotland. Change in chemical water quality was monitored in the influent, effluent, and pore water of labscale biofilters of varying lengths. Also, the effect of pore water chemistry on carbon processing by microbial communities from various filter depths was studied by batch experiment. Finally the effect of spatial and temporal water quality variation in Scotland on biofilter performance was studied via a metadata study. Results showed that dissolved organic matter was removed via multistage adsorption with filter length having a positive impact on the removal efficiency in apparent steady state. Applying the biofilters to other Scottish fresh waters with lower DOM concentrations will increase their performance. Within the filters, different ecological niches were formed. The community at the top processed the easily available low molecular weight acids, the community at the bottom was able to degrade the more recalcitrant humic substances. This indicates that specific microbes inhabit this bottom niche and are able to survive on the limited choice of DOM species. These research findings contribute to further optimisation of the biofilter design and for the scientific community to further understand biofilter stratification and its impact on DOM removal