Multi-strain immobilization in extracellular polymeric substances for improving recalcitrant pollutants removal from wastewater

Abstract

The increasing discharge of industrial and household waste into wastewater collection systems introduces recalcitrant pollutants that resist treatment by indigenous microbial communities present in wastewater treatment plants (WWTP). These recalcitrant pollutants, such as endocrine disrupting compounds, fluorinated and chlorinated chemicals, and pharmaceuticals can adversely affect human health and aquatic life. A possible solution to eliminate the recalcitrant pollutants and protect humans and ecosystems could be the use specialized degrading microorganisms to bioaugment wastewater treatment system. In this study, extracellular polymeric substances (EPS) extracted from aerobic granular sludge (AGS) were used as a natural carrier material for the immobilization of three bacterial strains Labrys portucalensis F11, Rhodococcus sp. ED55, and Rhodococcus sp. S2, known for degrading fluorobenzene (FB), 17β-estradiol (E2), and 4-fluorocinnamic acid (4-FCA) respectively. Batch assays were performed to assess the efficiency of the multi-immobilized bacteria granules to remove a combination of FB (1 mM), 4-FCA (0.5 mM), and E2 (0.018 mM), and compare their performance with the ones obtained by using bacterial suspensions of the same strains. Gas chromatography and high-performance liquid chromatography were used to quantify the toxics. The co-immobilized bacterial granules were able to completely degrade E2 within 42.5 h, while 4-FCA and FB were completely degraded by the end of 66.2 h and 90 h, respectively. Although the toxics adsorbed onto the multi-immobilized bacteria granules to some extent (FB 3.16 ± 2.49 mM / g granules, 4-FCA 0.640 ± 0.073 mM / g granules, and E2 0.0048 ± 0.0003 mM / g granules), stoichiometric fluoride release was observed, which is indicative of complete biodegradation of fluorinated compounds. Bacterial suspensions exhibited a faster degradation of E2 (<20 h), but 4-FCA and FB required longer removal times of 90.1h and 231.5 h, respectively. These results highlight that the co-immobilization of strains in an EPS matrix can enhance the removal efficiency of fluorinated compounds in comparison to the bacterial suspensions. It also supports the potential use of extracted EPS as an immobilizing agent of degrading strains for bioaugmentation purposes, possibly improving wastewater treatment systems’ efficiency.

Date of Award	13 Nov 2024
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Ana Sofia Oliveira (Supervisor) & Catarina Leite Amorim (Co-Supervisor)