Determination of biodegradable dissolved organic carbon in waters: comparison of batch methods

An effect of different types of bacterial inocula upon the final biodegradable dissolved organic carbon (BDOC) result was investigated in samples of both low and high BDOC concentrations. Stream water and leaf leachate samples were incubated either with free, suspended bacteria or with bacteria attached to the stream sediment particles or attached to artificial substrata. The time course of dissolved organic carbon (DOC) decomposition was observed using absorbance analysis of DOC. BDOC determination by means of commonly used suspended bacteria as the inoculum made for an underestimation of BDOC between 5% and 25%, compared with attached bacterial community (biofilm). The reason for these findings could be the higher microbial diversity, higher metabolic activity of attached bacteria and abiotic adsorption of organic molecules to inorganic support and biofilm matrix surfaces. Adsorbed DOC is easily hydrolyzed and utilized by biofilm bacteria.