Evaluation of seasonal activity of various bacteria in a constructed wetland using AT4 and TTC tests

The article presents the results of research studies aimed at the application of AT4 (respiration activity) and TTC (dehydrogenase activity) tests to assess the seasonal variability of the efficiency of a constructed wetland wastewater treatment plant. The research was carried out on the site, serving a single-family house inhabited by three people. The test results clearly showed that the wastewater treatment plant complies with the legally required quality requirements for discharged treated waste-water, yielding an average of 98% removal efficiency of organic biodegradable compounds (BOD 5 ) and 93% of organic pollutants expressed in the COD parameter. The efficiency of biogen removal was relatively low, in the range characteristic for this type of systems 13%, respectively, for total nitrogen and total phosphorus. The use of the polishing pond allowed in summer to reduce the total nitrogen content in treated sewage by nearly 50%. In the winter, the polishing pond played mainly a retention role, not contributing to increasing the efficiency of the entire system. The microbiological activity tests in relation to the system effectiveness were based on respiration (AT4) and dehydrogenase activity (TTC). A proprietary solution was used to enable non-invasive sampling of soil samples from the interior of the filtering filtration material, which allowed the obtention of an image of the stratification of microbial activity. The oxygen demand of the filtration material in the summer was about 50% higher than in the autumn and winter period. The obtained results showed a seasonal change in the distribution of microbial activity inside the filtration material, reflecting the adaptive abilities of the filtration material’s microfauna to the variability of thermal conditions. It was found that in the winter period, the wetland filtration material, which was originally a system implementing oxygen processes, goes into anaerobic state, without reducing the efficiency of organic compound removal.