In the present study the time of adaptation of fixed biomass for biodegradation of natural organic matter was investigated. The experiments were done in columns that are usually used for rapid determination of biodegradable dissolved organic carbon (BDOC). The biomass was adapted to samples with different concentrations of organic substances before measurements by pumping water to be investigated through the columns for several days. The time of adaptation was dependent on the initial concentration of the organic matter in the water sample. The adaptation time increased from 6 to 24 h with increase of concentration of acetate solution from 2 to 10 mg/l, thus adaptation rate decreased simultaneously from 0.28 to 0.11 min(-1). In natural water samples with the initial concentration in the range from 4.61-10.82 mg/l of dissolved organic carbon (DOC) the maximal adaptation time was less than 24 h. During the adaptation period the increase in reproducibility and decrease in the standard deviation was observed. The study showed that adaptation of column to the different concentration of organic matter in water sample is necessary in order to decrease the bias in BDOC measurements when using columns tests.

A B S T R A C TFor many years, electrochemical treatment has been proposed as a potential alternative to conventional drinking water chlorination due to its simplicity, ease of use and ability to generate active disinfectant from ions naturally found in the drinking water The aim of this study was to evaluate the survival of Escherichia coli on the surfaces of water distribution system after exposure to in situ electrochemically generated chlorine. To analyse the effect of chlorine and its reaction intermediates, completely mixed reactor with or without ingenuous biofilm was supplied with natural drinking water containing low amount of chloride ions (<10 mg/L) and treated with non-stoichiometric titanium oxide electrodes (TiO 2−x ) at low current density (4.1-8 mA/cm 2 ) which generate predominantly chlorine species. Various cell viability markers (cultivability, ability to divide as such and respiratory activity) were assessed in this study. The results showed that electrochemical disinfection was very effective to neutralize the suspended E. coli (>5 log decrease in cultivability and 2 log decrease in respiratory activity was obtained after 1 h of treatment). However, surface and biofilm analyses showed significantly lower inactivation rates (1.49-1.79 log after 1 h of treatment). Moreover, after 24 h, biofilm still contained 16% ability to divide E. coli. The study clearly showed that surface-or biofilm-attached E. coli is more resistant towards electrochemically generated chlorine than the suspended ones, and this should be taken into account when choosing optimal doses for electrochemical disinfection.

Abstract. The addition of labile organic carbon (LOC) to enhance the biodegradation rate of dissolved organic carbon (DOC) in biological columns was studied. Acetate standard solution (NaAc) and LB (Luria Bertrani) medium were used as LOC as biostimulants in glass column system used for measurements of biodegradable dissolved organic carbon (BDOC). The addition of LOC related with the increase of total DOC in sample. The concentration of BDOC increased up to 7 and 5 times and was utilized after 24 min. contact time. The biodegradation rate constant was increased at least 8 times during adaptation-biostimulation period. There was a strong positive correlation between the biodegradation rate constant and the concentration of BDOC. Biostimulation period ranged from 24 to 53 h for NaAc biostimulant and from 20 to 168 h for LB. The study has shown that LOC could be used as stimulator to enhance the biodegradation rate of DOC during biofiltration.

Abstract. The addition of labile organic carbon (LOC) to enhance the biodegradation rate of dissolved organic carbon (DOC) in biological columns was studied. Acetate standard solution (NaAc) and Luria Bertrani (LB) medium were used as LOC as biostimulants in glass column system used for measurements of biodegradable dissolved organic carbon (BDOC). The addition of LOC related with the increase of total DOC in sample. The concentration of BDOC increased up to 7 and 5 times and was utilized after 24 min. contact time. The biodegradation rate constant was increased at least 26 times during adaptation-biostimulation period. There was a strong positive correlation between the biodegradation rate constant and the concentration of BDOC. Biostimulation period ranged from 24 to 53 h for NaAc biostimulant and from 20 to 168 h for LB. The study has shown that LOC could be used as stimulator to enhance the biodegradation rate of DOC during biofiltration.