Green Solvent Cleaning Removes Irrecoverable Foulants from End-of-Life Membranes in Membrane Bioreactors: Efficacy and Mechanisms.

Removal of irrecoverable foulants, which cannot be removed by conventional chemical cleaning, from end-of-life (EOL) membranes remains a substantial challenge due to the strong interaction between the foulants and membrane matrix. Herein, we developed a green solvent cleaning strategy based on Hansen solubility parameters to achieve the removal of irrecoverable foulants from the EOL polyvinylidene fluoride (PVDF) membranes serving for 6 years in a large-scale membrane bioreactor (MBR). We selected methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate (MDMO) as the green solvent due to its strong interaction with the PVDF material, which might enable the substitution of binding sites of irrecoverable foulants. After the MDMO cleaning, the water permeance of the EOL membrane recovered from 47.6 ± 4.7 to 390.9 ± 8.2 L m-2 h-1 bar-1 (with a flux recovery ratio of ∼100%), with its rejection ability and stability maintained. The main components of irrecoverable fouling were humic acid-like substances revealed by spectroscopic characterization. Molecular dynamic simulation further elucidated the cleaning mechanisms: the strong interaction of MDMO-PVDF enabled substitution of binding sites of irrecoverable foulants by MDMO, followed by desorption of the irrecoverable foulants from PVDF and diffusion of the irrecoverable foulants into the bulk phase of MDMO. Evaluation in a lab-scale MBR treating real municipal wastewater verified the reusability of green solvent cleaned-EOL membranes. This study provides a novel, effective, and green cleaning strategy to remove irrecoverable foulants and prolong the service life of membranes in MBRs, facilitating sustainable wastewater treatment using membrane-based processes.

Ocorrencia de micobacterias em aguas poluidas com residuos industriais e domesticos / Occurrence of mycobacteria in waters pollution with industrial and domestic residues

Foram isoladas 158 cepas de micobacterias a partir de amostras de agua poluida notadamente com residuos de petroleo apos a depuração com hidroxido de sodio 4 por cento (111 cepas) ou cloreto de benzalconio de 0,34 por cento (47 cepas) A maioria das micobacterias isoladas comportou se como pertencente ao grupo III de Runyon (78 cepas), seguindo-se as de crescimento rapido 61 cepas e as escotocromogenicas, de crescimento lento 19 cepas. Aproiximadamente 32 por cento das cepas foi caracterizada como micobacterias potencialmente patogenicas incluindo M avium intracelulare 3,8 por cento. M scrofulaceum 6,3 por cento e m fortutum 22,2 por cento. Conclui se que a agua do Rio de Jacare esta contaminada com micobacterias potencialmente patogenicas podendo servir como fonte de doença humana.