Periodic chemical cleaning with urea: disintegration of biofilms and reduction of key biofilm-forming bacteria from reverse osmosis membranes

Alleviation of RO membrane fouling in wastewater reclamation plants using an enhanced acid-base chemical cleaning method

Membrane fouling has always been a critical constraint in the operation of the reverse osmosis (RO) process, and chemical cleaning is essential for mitigating membrane fouling and ensuring smooth operation of the membrane system. This paper presents an optimized chemical cleaning method for the efficient cleaning of RO membranes in full-scale applications. Compared to the regular cleaning method (cleaning with 0.1 % NaOH + 1 % ethylenediaminetetraacetic acid + 0.025 % sodium dodecyl benzene sulfonate followed by 0.2 % HCl), the optimized cleaning method improves the cleaning efficiency by adding sodium chloride to the alkaline cleaning solution and citric acid to the acid cleaning solution. Notably, the membrane flux recovery rate with the optimized cleaning method is 45.74 %, and it improves the cleaning efficiency by 1.65 times compared to the regular cleaning method. Additionally, the optimized cleaning method removes 30.46 % of total foulants (organic and inorganic), which is 2.11 times higher than the regular cleaning method. The removal of inorganic ions such as Fe, Ca, and Mg is significantly improved with the optimized cleaning method. For organic matter removal, the optimized cleaning method effectively removes more polysaccharides, proteins, and microbial metabolites by disrupting the complex structures of organic matter. Furthermore, it also changes the microbial community structure on the RO membrane surface by eliminating microorganisms that cannot withstand strong acids, bases, and high salt environments. However, Mycobacterium can adapt to these harsh conditions, showing a relative abundance of up to 84.13 % after cleaning. Overall, our results provide a new chemical cleaning method for RO membranes in full-scale applications. This method effectively removes membrane foulants and enhances the understanding of the removal characteristics of foulants on RO membrane surfaces by chemical cleaning.

Variations in bacterial community succession and assembly mechanisms with mine age across various habitats in coal mining subsidence water areas

Microorganisms play a pivotal role as catalysts in the biogeochemical cycles of aquatic ecosystems within coal mining subsidence areas. Despite their importance, the succession of microbial communities with increasing mine age, particularly across different habitats, and variations in phylogenetically-based community assembly mechanisms are not well understood. To address this knowledge gap, we collected 72 samples from lake sediments, water, and surrounding topsoil (0-20 cm) at various mining stages (early: 16 years, middle: 31 years, late: 40 years). We analyzed these samples using 16S rRNA gene sequencing and multivariate statistical methods to explore the dynamics and assembly mechanisms of bacterial communities. Our findings reveal that increases in phosphorus and organic matter in sediments, correlating with mining age, significantly enhance bacterial alpha diversity while reducing species richness (P < 0.001). Homogenizing selection (49.9 %) promotes species asynchrony-complementarity, augmenting the bacterial community's ability to metabolize sulfur, phosphorus, and organic matter, resulting in more complex-stable co-occurrence networks. In soil, elevated nitrogen and organic carbon levels markedly influence bacterial community composition (Adonis R2 = 0.761), yet do not significantly alter richness or diversity (P > 0.05). The lake's high connectivity with surrounding soil leads to substantial species drift and organic matter accumulation, thereby increasing bacterial richness in later stages (P < 0.05) and enhancing the ability to metabolize dissolved organic matter, including humic-like substances, fulvic acids, and protein-like materials. The assembly of soil bacterial communities is largely governed by stochastic processes (79.0 %) with species drift (35.8 %) significantly shaping these communities over a broad spatial scale, also affecting water bacterial communities. However, water bacterial community assembly is primarily driven by stochastic processes (51.2 %), with a substantial influence from habitat quality (47.6 %). This study offers comprehensive insights into the evolution of microbial community diversity within coal mining subsidence water areas, with significant implications for enhancing environmental management and protection strategies for these ecosystems.

Insight into key interactions between diverse factors and membrane fouling mitigation in anaerobic membrane bioreactor

Anaerobic membrane bioreactors (AnMBRs) have garnered considerable attention as a low-energy and low-carbon footprint treatment technology. With an increasing number of scholars focusing on AnMBR research, its outstanding performance in the field of water treatment has gradually become evident. However, the primary obstacle to the widespread application of AnMBR technology lies in membrane fouling, which leads to reduced membrane flux and increased energy demand. To ensure the efficient and long-term operation of AnMBRs, effective control of membrane fouling is imperative. Nevertheless, the interactions between various fouling factors are complex, making it challenging to predict the changes in membrane fouling. Therefore, a comprehensive analysis of the fouling factors in AnMBRs is necessary to establish a theoretical basis for subsequent membrane fouling control in AnMBR applications. This review aims to provide a thorough analysis of membrane fouling issues in AnMBR applications, particularly focusing on fouling factors and fouling control. By delving into the mechanisms behind membrane fouling in AnMBRs, this review offers valuable insights into mitigating membrane fouling, thus enhancing the lifespan of membrane components in AnMBRs and identifying potential directions for future AnMBR research.

Piperine, a phytochemical prevents the biofilm city of methicillin-resistant Staphylococcus aureus: A biochemical approach to understand the underlying mechanism

Methicillin-resistant Staphylococcus aureus (MRSA), a drug-resistant human pathogen causes several nosocomial as well as community-acquired infections involving biofilm machinery. Hence, it has gained a wide interest within the scientific community to impede biofilm-induced MRSA-associated health complications. The current study focuses on the utilization of a natural bioactive compound called piperine to control the biofilm development of MRSA. Quantitative assessments like crystal violet, total protein recovery, and fluorescein-di-acetate (FDA) hydrolysis assays, demonstrated that piperine (8 and 16 μg/mL) could effectively compromise the biofilm formation of MRSA. Light and scanning electron microscopic image analysis confirmed the same. Further investigation revealed that piperine could reduce extracellular polysaccharide production by down-regulating the expression of icaA gene. Besides, piperine could reduce the cell-surface hydrophobicity of MRSA, a crucial factor of biofilm formation. Moreover, the introduction of piperine could interfere with microbial motility indicating the interaction of piperine with the quorum-sensing components. A molecular dynamics study showed a stable binding between piperine and AgrA protein (regulator of quorum sensing) suggesting the possible meddling of piperine in quorum-sensing of MRSA. Additionally, the exposure to piperine led to the accumulation of intracellular reactive oxygen species (ROS) and potentially heightened cell membrane permeability in inhibiting microbial biofilm formation. Besides, piperine could reduce the secretion of diverse virulence factors from MRSA. Further exploration revealed that piperine interacted with extracellular DNA (e-DNA), causing disintegration by weakening the biofilm architecture. Conclusively, this study suggests that piperine could be a potential antibiofilm molecule against MRSA-associated biofilm infections.

Base type determines the effects of nucleoside monophosphates on microalgae-bacteria symbiotic systems

Microalgae are promising sources of clean energy. Bioflocculation by cocultured bacteria is an effective way to harvest microalgae. As a key foundation for microorganisms, phosphorus is theoretically effective in shaping microalgae production and flocculation. In this study, the impacts of 23 nucleoside monophosphates on Auxenochlorella pyrenoidosa growth, lipid synthesis, and self-settlement and on the symbiotic bacterial system were investigated. Adenosine monophosphate was the most effective in enhancing microalgae development (2.14-3.16 × 10⁸ cells/mL) and lipid production (average 10.48%) and resulted in a low settling velocity. Samples were divided into two groups, purine and pyrimidine feeding, according to a random forest analysis (OOB = 0%, p < 0.001). Purine feeding resulted in the highest soluble extracellular protein and polysaccharide secretion (p < 0.01). KEGG ortholog count prediction of functional genes related to biofilm formation was conducted using PICRUSt2, and significant upregulation (FC ≥ 1.77, p < 0.05) of the extracellular polymeric substance formation functional group was observed in the adenosine and guanosine treatments. The symbiotic bacterial community structure differed substantially between purine- and pyrimidine-feeding systems. In summary, these results indicated that the effect of nucleoside monophosphates on the microalgae-bacteria system is determined by the base type (purine or pyrimidine) rather than the molecular structure (cyclic or noncyclic).

Ionic fluid as a novel cleaning agent for the control of irreversible fouling in reverse osmosis membrane processes

While a variety of chemical cleaning strategies has been studied to control fouling in membrane-based water treatment processes, the removal of irreversible foulants strongly bound on membrane surfaces has not been successful. In this study, we firstly investigated the diluted aqueous solutions of ionic fluid (IF, 1-ethyl-3-methylimidazolium acetate) as a cleaning agent for three model organic foulants (humic acid, HA; bovine serum albumin, BSA; sodium alginate, SA). The real-time monitoring of cleaning progress by optical coherence tomography (OCT) showed that fouling layer was dramatically swelled by introducing IF solution and removed by shear force exerted during cleaning. This phenomenon was induced due to the pre-existing interactions between organic foulants were weakened by the intrusion of IF into the fouling layer, which was analyzed by the measurement of adhesion forces using atomic force microscopy (AFM). In the experiments with model foulants and wastewater effluent, IF was added to alkaline cleaning agents (NaOH) to verify the applicability to be supplemented in commercial cleaning agents, and resulted in the significantly enhanced control of irreversible membrane fouling. Implication of utilizing recyclable IF with negligible volatility is that environmental effects of membrane cleaning solutions could be minimized by decreasing usage of cleaning chemicals, while increasing the cleaning efficiency.