Effect of Magnetic Field Enrichment Conditions on the Synthesis of Polyhydroxyalkanoates by Activated Sludge

It has been demonstrated that magnetic fields can increase the yield of activated sludge for synthesizing polyhydroxyalkanoates (PHAs) under the aerobic-dynamic feed process (ADF). However, studies on other processes are lacking, and research on the effects of magnetic fields on microbial community structure and function is limited. Therefore, this study investigated the effect of an applied magnetic field (magnetic field strength of about 20 mT) on the yield of PHAs by activated sludge and changes in microbial communities during the enrichment phase of PHAs bacteria under the anaerobic-oxygen limiting process. The results demonstrated that the magnetic field applied profoundly affected the accumulation of PHAs in activated sludge. At an influent chemical oxygen demand (COD) of 800 mg/L and carbon/nitrogen (C/N) = 150, the maximum accumulation of PHAs was 46.85% cell dry weight (DCW) and 57.38% DCW for the blank group (R1) and the group with applied magnetic field (R2), respectively. Microbiological analyses showed that Candidatus_Competibacter (29.19%) and Ignavibacterium (10.75%) were the dominant genera of PHAs under the applied magnetic field. Both are denitrification-functioning genera, meaning the activated sludge system transformed from a phosphorus-removing system to a denitrification system.

To reduce the energy cost caused by high aeration, an anaerobic-oxygen-limited process (DO less than 2 mg/L) was used in this experiment. The maximum PHAs synthesis capacity of the dominant PHAs bacteria under magnetic field conditions, as well as the succession pattern and functional changes of microbial communities, were investigated, which provided a certain basis for the subsequent improvement of the synthesis efficiency of PHAs from the microbial point of view.