Feasibility study of microplastic biodegradation in effluents from South Tehran WWTP after quantitative and qualitative measurement of the particles

Abstract

Microplastics are currently known to be among the most detrimental environmental. The research on ways to counteract these pollutions and the use of microorganisms for the biological decomposition of various plastic polymers have evolved over the recent years. In this regard, the present study collected effluents from the southern Tehran treatment plant and separated and counted the microplastics present in them, it was found that the least number of microplastics was found in the samples of the summer season and the highest number of microplastics was found in the samples of the spring season. In these samples, particles could be identified in three forms: fiber, fragment, and film, which revealed that the most frequently observed microplastics were polypropylene and then polyethylene. These microplastics combine with the microbes in the culture medium. Three microbial colonies that survived were then separated and identified, which revealed that these bacteria included Achromobacter denitrificans (sample B), Bacillus amyloliquefaciens (sample C), and Pseudomonas aestusnigri (sample E). Moreover, the decomposition of polypropylene and polyethylene microplastics exposed to isolates was examined through various methods. Results of cellular gravity examination indicated that the average weight reduction in the PP sample exposed to B and E bacterial isolates was 38.2% and 58.9%, respectively. In the SEM images, the surface of the polymers of these two isolates is more uneven. Moreover, the mean cellular weight reduction for PE-based microplastic exposed to isolate C was 13.3%, the results of FT-IR tests showed that the peaks in the samples exposed to strains B and E were accompanied by changes compared to the control sample (G). The results of the TGA test also confirm the greater effectiveness of the bacterial strain E. It was based on the polymer structure. In the Raman spectrum of sample E, some peaks have been removed and new peaks with other shifts have appeared in their place. Results were confirmed by carbon dioxide emission tests and the produced protein amount.