Acute effects of acrylamide and its biodegradation products on microbes from SBR wastewater treatment systems were revealed by respirometric activities.

This study evaluated the kinetics of acrylamide (AM) biodegradation by mixed culture bacteria and Enterobacter aerogenes (E. aerogenes) in sequencing batch reactor (SBR) systems with AQUASIM and linear regression. The zero-order, first-order, and Monod kinetic models were used to evaluate the kinetic parameters of both autotrophic and heterotrophic nitrifications and both AM and chemical oxygen demand (COD) removals at different AM concentrations of 100, 200, 300, and 400 mg AM/L. The results revealed that both autotrophic and heterotrophic nitrifications and both AM and COD removals followed the Monod kinetics. High AM loadings resulted in the transformation of Monod kinetics to the first-order reaction for AM and COD removals as the results of the compositions of mixed substrates and the inhibition of the free ammonia nitrogen (FAN). The kinetic parameters indicated that E. aerogenes degraded AM and COD at higher rates than mixed culture bacteria. The FAN from the AM biodegradation increased both heterotrophic and autotrophic nitrification rates at the AM concentrations of 100-300 mg AM/L. At higher AM concentrations, the FAN accumulated in the SBR system inhibited the autotrophic nitrification of mixed culture bacteria. The accumulation of intracellular polyphosphate caused the heterotrophic nitrification of E. aerogenes to follow the first-order approximation.

Enterobacter aerogenes was reported as a bacterium capable of heterotrophic nitrification. It is typically found that autotrophic nitrification is greater in rate than the heterotrophic nitrification. However, heterotrophs are faster growing and lesser sensitive than the autotrophic nitrification bacteria. In this study, the heterotrophic nitrification of E. aerogenes was enhanced with IFAS technology using BioPortz moving media operated at the suspended-growth solids retention time (SRT) of 9 days and temperature of about 28 o C. The experiments were conducted comparatively in the conventional activated sludge (AS) and IFAS systems containing either mixed culture bacteria or E. aerogenes for autotrophic and heterotrophic nitrifications, respectively. The results revealed that E. aerogenes could be enhanced with IFAS technology to complete heterotrophic nitrification with the removal efficiency of 100%. There was no significant difference in nitrification between AS and IFAS systems of two microbes if the systems were properly operated. Ammonia stripping was found in the AS systems whenever nitrification was failed and CO2 was stripped out, resulting in the increase of pH. The clogging of BioPortz media with calcium carbonate precipitates, reducing the IFAS performances, was firstly reported as a result of operating the IFAS systems at the moderate temperature and hardness.

Salinity or saltiness is dissolved in water by the relative proportion of salt in a solution. All organisms have to keep their cells alive a water balance in their bodies. The activated sludge process (ASP) containing aerobic microorganisms located nearby the coastal area may be faced the problems of salinity from sea water. In this research, the effects of salinity on the respirometric activities of mixed culture bacteria from activated sludge process were evaluated at different levels of NaCl concentrations ranging between 0-25 g/L in the OxiTop system at the temperature of 20 °C. The oxygen uptake rate (OUR) was used to reveal the effects of salinity. The experiments results indicated that the OURs decreased as the NaCl concentrations increased, resulting in the failures of bacterial osmotic pressure systems and causing the lysis of bacteria. The COD and nitrification were failed because the nitrogen and COD loadings to the systems were increased by the lysis of bacteria.