有機汚濁化水域の嫌気的条件下での水質動態に関する実験的研究

抄録

  When considering the aquatic environmental conservation of a closed water body in which organic contamination is ongoing, it is important to study the occurrence mechanism of anaerobic organic matter decomposition such as denitrification in addition to both iron and sulfate reduction due to increasingly anoxic conditions in the aquatic environment. From the perspective of oxidation-reduction potential (ORP), nitrate nitrogen (NO₃-N), ammonia nitrogen (NH₄-N), phosphate phosphorus (PO₄-P), sulfides, and dissolved organic carbon (DOC), we herein present a quantitative evaluation of water quality dynamics near the water bottom under the anaerobic state in a laboratory environment. We modeled the ORP behavior at the bottom of the aquatic environment under anaerobic conditions by using a regression equation that applies a logistic curve and uses the number of days of continuous anoxic condition as the time axis. Specifically, the rate of ORP decrease was shown to be dependent on the concentration of NO₃-N at the time of anoxic condition development. In addition, temporal changes in the decrease of NO₃-N and increases of NH₄-N, PO₄-P, and sulfide were modeled with either linear or non-linear regressions. In particular, the properties of organic matter such as the ease and difficulty of degradation are shown to have a strong impact on the rate of PO₄-P increase, whereas the production of sulfides increased with a higher concentration of TOC. Furthermore, the laboratory experiment showed that, in an actual aquatic environment with various coexisting redox reactions, the following reduction reactions take place under anaerobic conditions: denitrification, followed by iron reduction and then sulfate reduction. Each reaction is completed before the next one begins. In addition, when the concentration of DOC derived from humic acid is extremely high, even under an anoxic environment, ORP becomes positive and may lead to an oxidative state. Thus, we were able to incorporate the resultant measurements of PO₄-P, sulfides and DOC to explain these mechanisms based on the experiment results.