Tensammetric studies of biodegradation of Marlipal 1618/25 in the river water die-away test

Biodegradation of Marlipal 1618/25 (Marlipal) under the river water die-away test was studied. Marlipal was a representative surfactant of the group of oxyethylated alcohols. The Warta River (Poznan) water, containing no additional organic nutrients, was used as inoculum. The indirect tensammetric method (ITM) was used for the measurement of total concentration of non-ionic surfactants (NS), i.e. for primary biodegradation control and the adsorptive stripping tensammetry (AdST) as a supplementary technique. The manometric respirometry method (MRM) measuring the total biodegradation was used as comparative method. Marlipal was completely degraded within the period of 5–10 days, depending on the surfactant spike, but in two distinctly separated stages, evidenced both by the ITM and AdST. The time of both steps was dependent on the spike of Marlipal: with the higher spike the steps appeared later. The results of MRM differed from the results of the ITM within the initial period of the experiment. The MRM showed distinct biodegradation within this period while the total concentration of NS, as measured by the ITM, was equal to the initial value, showing lack of biodegradation of Marlipal. The biodegradation of the river water organic matter induced by the spike of surfactant, at sufficiently high concentration can be the explanation of this effect. High sensitivity of the ITM enabled to measure the biodegradation of “native” NS of the river water in non-spiked samples.