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The impacts of biodegradable and non-biodegradable microplastic on the performance and microbial community characterization of aerobic granular sludge
Summary
Researchers compared the effects of biodegradable polylactic acid microplastics and non-biodegradable polyethylene microplastics on aerobic granular sludge used in wastewater treatment. They found that high concentrations of both types impaired the sludge's ability to remove organic pollutants, but both actually enhanced nitrogen and phosphorus removal at moderate levels. The study reveals that even biodegradable microplastics can disrupt wastewater treatment processes in unexpected ways.
It was discovered that low and medium concentration of MPs (10 and 50 mg/L) showed no significant effects on COD removal by AGS, but high concentration (100 mg/L) of MPs markedly diminished the ability to remove COD of AGS, by blocking most of the nutrient transport channels of AGS. However, both PLA and PE promoted the nitrogen and phosphorus removal ability of AGS, and significantly increased the removal efficiency of total inorganic nitrogen (TIN) and total phosphorus (TP) at stages II and III (P < 0.05). High concentration of MPs inhibited the growth of sludge. PET noticeably deteriorate the sedimentation performance of AGS, while 50 mg/L PLA proved to be beneficial to sludge sedimentation at stage II. The addition of MPs promoted the abundance of Candidatus_Competibacter and Acinetobacter in AGS, thereby promoting the phosphorus removal capacity of AGS. Both 50 mg/L PET and 100 mg/L PLA caused large amount of white Thiothrix filamentous bacteria forming on the surface of AGS, leading to deterioration of the sludge settling performance and affecting the normal operation of the reactor. Comparing with PET, AGS proved to be more resistant to PLA, so more attention should be paid to the effect of non-biodegradable MPs on AGS in the future.
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