Water treatment is a series of physio-chemical processes to aid organic matter (OM)
removal, which helps to minimise the formation of potentially carcinogenic disinfection
by-products and microbial regrowth. Changes in OM character through the treatment
processes can provide insight into the treatment efficiency, but radiogenic isotopic characterisation
techniques have yet to be applied. Here, we show for the first time that
analysis of 13C and 14C of dissolved organic carbon (DOC) effectively characterises dissolved
OM through a water treatment works. At the sites investigated: post-clarification, DOC
becomes isotopically lighter, due to an increased proportion of relatively hydrophilic DOC.
Filtration adds ‘old’ 14C-DOC from abrasion of the filter media, whilst the use of activated
carbon adds ‘young’ 14C-DOC, most likely from the presence of biofilms. Overall, carbon
isotopes provide clear evidence for the first time that new sources of organic carbon are
added within the treatment processes, and that treated water is isotopically lighter and
typically younger in 14C-DOC age than untreated water. We anticipate our findings will
precipitate real-time monitoring of treatment performance using stable carbon isotopes,
with associated improvements in energy and carbon footprint (e.g. isotopic analysis used
as triggers for filter washing and activated carbon regeneration) and public health benefits
resulting from improved carbon removal.