Intracellular Organic Matter Research Articles

Microalgal-bacterial co-cultivation on novel bio-coated supports: Evaluation of growth performance in submerged and permeated biofilm cultivation system with cost-benefit assessment

In microalgae mass production, co-cultivation with bacteria and biofilm immobilization hold promise, yet challenges persist in biofilm-based cultivation due to weak cohesion under stress. Hence, a novel bio-coating derived from spent medium and cells (extra-/intra-cellular organic matter from Cylindrotheca fusiformis and Escherichia coli) was applied to microporous membrane in submerged and permeated biofilm systems. Results showed a minimum 25 % improvement in biomass productivity (up to 45 g m−2) on bio-coated membranes in permeated system. Mucopolysaccharides in bio-coating facilitated biofilm development and encouraged a 10-fold higher AOM yield (defense mechanism against shearing force) in submerged systems, but biomass productivity was 10 times lower than permeated system. In permeated system, cells on IOM-coated membranes exhibited the highest biomass growth and lipid yield, potentially addressing the biomass-lipid trade-off. Permeated system with low operating cost around 69 $ kg−1 was a viable cultivation approach, presenting an opportunity to optimize microalgae production facilities.

New insights into microalgal photobiological hydrogen production: Potential role of aggregation forms in modulating the hydrogenase activity and metabolic properties of microalgae during hydrogen production

Photobiological hydrogen production of microalgae is highly influenced by environmental conditions, and the appropriate microalgal aggregation form is conducive to microalgae overcome environmental limitations and increase their hydrogen production capacity. In this study, the effects of three aggregation methods including self-flocculation, biofilm attachment, and gel immobilization on the photobiological hydrogen production of both prokaryotic Synechocystis sp. and eukaryotic Chlamydomonas reinhardtii were investigated. The results indicated that microalgal aggregates formed via gel immobilization exhibited superior physicochemical properties such as porosity, integrity, and oxygen diffusion coefficients, creating favorable conditions for enhanced hydrogenase activity. Upon gel-immobilization, hydrogen production of Synechocystis sp. and C. reinhardtii exhibited an increase of 1.89 and 2.02-folds, respectively, compared with suspended microalgae. Concurrently, hydrogenase activities increased to 2.07 and 32.9 H2/(mg chlorophyll·h), respectively. The gel-immobilized aggregate form prompted the microalgae to maintain a relatively high photosynthetic activity, with the electron transfer rate reaching more than 1.58 folds of the control. Notably, three aggregated forms also accelerated oxygen consumption, and intracellular organic matter degradation, thereby optimizing electron utilization by microalgal hydrogenase. Furthermore, aggregation up-regulated hydrogenase gene expression in both species, particularly in gel-immobilized groups (2.34- and 4.14-folds increase compared with the control for Synechocystis sp. and C. reinhardtii, respectively). Subsequently, significantly upregulated gene expression related to oxidative phosphorylation and antioxidant systems was observed in C. reinhardtii aggregates, correlating with its relatively higher increase in hydrogen production compared with Synechocystis sp. aggregates. This study elucidated the mechanism by which aggregation strengthens microalgal hydrogen production and offers insights crucial for its industrialization.

Intracellular and extracellular organic matter removal by BT/C heterogeneous interface under visible light photodriven

Algae-derived organic matter (AOM) limits the effectiveness of conventional water treatment processes, affects the normal operation of water treatment plants, and causes water quality deterioration. Efficient elimination of AOM is an urgent issue in the advanced treatment of drinking water. In this study, A heterogeneous interface for AOM removal was established based on BT/C, which can be driven by visible light. The removal efficiencies of extracellular organic matter (EOM), intracellular organic matter (IOM), and AOM by BT/C reached the optimal levels at 30 min, 60 min, and 90 min, respectively, reaching 48.5 %, 81.8 %, and 74.0 %. BT/C can oxidize and break down a large amount of high-molecular-weight organic matter in EOM into medium- and low-molecular-weight organic substances, and effectively remove the low-molecular-weight organic matter in EOM. In addition, BT/C can efficiently remove humic acids(HS) and aromatic protein organic matter in IOM, directly mineralize or decompose high-molecular-weight biopolymers into small-molecular-weight acidic and neutral organic matter; electron paramagnetic resonance spectroscopy and reactive oxygen species trapping experiments verified that hydroxyl radical (·OH) have play most important role on the degradation of various molecular weight organic matters. Superoxide radical (·O2–) plays a dominant role in the oxidation process of soluble microbial metabolites and HS, and ·OH plays a significant role in the oxidation process of amino acid-like proteins. This study provides new ideas and technical support for the complete removal of algae-derived organic matter and the protection of drinking water safety.

Toxicological and mechanistic insights into organic contaminants released from on-line membrane cleaning during ultrafiltration of algal-containing waters

Eutrophication has significantly challenged the treatment of algae-contaminated water. Ultrafiltration has become an essential method for water purification, though frequent on-line chemical cleaning is necessary to maintain membrane permeability. This study aims to systematically investigate the impact of various chemical cleaning agents on the release of dissolved organic matters and toxic by-products, particularly from algal cells. Through a series of controlled experiments, Microcystis aeruginosa cells were exposed to different cleaning agents (HCl, NaOH, NaClO), and the resulting DOM and by-products were characterized. Special attention was paid to the release of intracellular organic matter (IOM) and extracellular organic matter (EOM). Results revealed that NaClO significantly oxidized IOM, leading to the formation of humic-like substances and halogenated organic compounds (TOX), including 15 types of halogenated by-products detected by UPLC/ESI-tqMS. Furthermore, the release of toxic microcystin LR (MC-LR) was traced primarily to IOM. The removability of these contaminants by UF and reverse osmosis (RO) membranes was analyzed, revealing that over 50% of the toxic by-products passed through UF membranes, and 10% still penetrated RO membranes, raising significant concerns for downstream water quality and drinking water safety.

Probing into the formation of brominated halonitromethanes from the intracellular organic matter of Anabaena during UV/chlorine disinfection

Eutrophication events in water bodies result in the release of algal organic matter, which is an essential precursor for halonitromethanes during disinfection, posing a significant threat to water quality. During UV/chlorine disinfection, the presence of Br− promotes the formation of brominated halonitromethanes (Br-HNMs), which exhibit higher toxicity compared to chlorinated halonitromethanes. Nevertheless, limited studies have been conducted on the Br-HNMs formation from algal precursors during UV/chlorine disinfection in the presence of Br−. Therefore, in this study, the formation pattern and toxicity variation of Br-HNMs from the intracellular organic matter (IOM) of anabaena during UV/chlorine disinfection was investigated. The results showed that monobromonitromethane, bromochloronitromethane, and bromodichloronitromethane could be detected during UV/chlorine disinfection. When the Br− concentration raised, the total concentration and toxicity of Br-HNMs exhibited an increase followed by a decline. Additionally, the concentration and toxicity of three Br-HNMs were promoted by increasing UV intensity, free chlorine dosage, and anabaena concentration but inhibited by increasing pH. Based on the experiment results, possible pathways for Br-HNMs formation from anabaena IOM in the presence of Br− were deduced. Moreover, anabaena IOM could also be converted to Br-HNMs during UV/chlorine disinfection of actual water, with a formation pattern similar to that found in distilled water. This research offers valuable insights into Br-HNMs formation from algal-containing waters.

Deciphering the Role of Microbial Extracellular and Intracellular Organic Matter in Antibiotic Photodissipation: Molecular and Fluorescent Profiling under Natural Radiation.

This study addresses existing gaps in understanding the specific involvement of dissolved organic matter (DOM) fractions in antibiotic photolysis, particularly under natural conditions and during DOM photobleaching. Employing fluorescent, chemical, and molecular analysis techniques, it explores the impact of extracellular and intracellular organic matter (EOM and IOM) on the photodissipation of multiclass antibiotics, coupled with DOM photobleaching under natural solar radiation. Key findings underscore the selective photobleaching of DOM fractions, propelled by distinct chemical profiles, influencing DOM-mediated antibiotic photolysis. Notably, lipid-like substances dominate in the IOM, while lignin-like substances prevail in the EOM, each uniquely responding to sunlight and exhibiting selective photobleaching. Sunlight primarily targets fulvic acid-like lignin components in EOM, contrasting the initial changes observed in tryptophan-like lipid substances in IOM. The lower photolability of EOM, attributed to its rich unsaturated compounds, contributes to an enhanced rate of indirect antibiotic photolysis (0.339-1.402 h-1) through reactive intermediates. Conversely, the abundance of aliphatic compounds in IOM, despite it being highly photolabile, exhibits a lower mediation of antibiotic photolysis (0.067-1.111 h-1). The triplet state excited 3DOM* plays a pivotal role in the phototransformation and toxicity decrease of antibiotics, highlighting microbial EOM's essential role as a natural aquatic photosensitizer for water self-purification. These findings enhance our understanding of DOM dynamics in aquatic systems, particularly in mitigating antibiotic risks, and introduce innovative strategies in environmental management and water treatment technologies.

Enhanced removing of cyanobacterium by NZVI coupled with H2O2: Influencing factors and removal mechanisms

AbstractAs advanced oxidation processes (AOPs) is considered to be a highly effective approach for degrading organic pollutants, the simultaneous coagulation and oxidation process by the Fenton‐like reaction of nanoscale zero‐valent iron (NZVI) and hydrogen peroxide (H2O2) is investigated to eliminate the harmful cyanobacterium Microcystis aeruginosa in this study, and the process conditions are optimized using the central composite design of response surface methodology (RSM); in addition, the removal efficiency of M. aeruginosa (in terms of chlorophyll a, Chl a) and the verifications of the antioxidant abilities, as well as extracellular organic matters (EOM) and intracellular organic matters (IOM) are investigated under the optimized conditions. Results indicate that H2O2 concentration is the key factor affecting the Chl a removal efficiency, and the maximum Chl a removal reaches 98.10% under the optimized conditions: NZVI concentration 62.82 mg L−1, H2O2 concentration 54.2 mmol L−1, pH 4.38 and rotating speed 67 rpm. The high correlation coefficient (R2 > 0.80) of analysis of variance (ANOVA) demonstrates the RSM model is extremely significant and suitable for experimental results. Moreover, the total organic carbon (TOC) and fluorescent substances (soluble cyanobacteria metabolic byproducts, aromatic proteins II, humic and fulvic acid‐like compounds) for both EOM and IOM are enhanced removal. It is speculated the removal mechanisms of the Fenton‐like process of NZVI/H2O2 for cyanobacterium belongs to the combined actions of the oxidation of Fe(II)/H2O2 and the coagulation of Fe(III), which destroy the defense system and result in the removal of M. aeruginosa.

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br−) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br−. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br−. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br−: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br− were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Suitability of inorganic coagulants for algae-laden water treatment: Trade-off between algae removal and cell viability, aggregate properties and coagulant residue

Inorganic coagulants could effectively precipitate algae cells but might increase the potential risks of cell damage and coagulant residue. This study was conducted to critically investigate the suitability of polyaluminum (PAC), FeCl3 and TiCl4 for algae-laden water treatment in terms of the trade-off between algal substance removal, cell viability, and coagulant residue. The results showed that an appropriate increase in coagulant dosage contributed to better coagulation performance but severe cell damage and a higher risk of intracellular organic matter (IOM) release. TiCl4 was the most destructive, resulting in 60.85% of the algal cells presenting membrane damage after coagulation. Intense hydrolysis reaction of Ti salts was favorable for the formation of larger and more elongated, dendritic structured flocs than Al and Fe coagulants. TiCl4 exhibited the lowest residue level and remained in the effluents mainly in colloidal form. The study also identified charge neutralization, chemisorption, enmeshment, and complexation as the dominant mechanisms for algae water coagulation by metal coagulants. Overall, this study provides the trade-off analyses between maximizing algae substance removal and minimizing potential damage to cell integrity and is practically valuable to develop the most suitable and feasible technique for algae-laden water treatment.

Effects of clarithromycin exposure on the growth of Microcystis aeruginosa and the production of algal dissolved organic matter

Antibiotics are commonly found in the aquatic environment, which can affect microbial community compositions and activities, and even have potential adverse impacts on human and ecosystem health. The current understanding of the effects of antibiotics on microalgae growth and algal dissolved organic matter (DOM) remains indistinct. To understand the toxic effects of antibiotics on the microalgae, Microcystis aeruginosa was exposed to clarithromycin (CLA) in this study. Cell density determination, chlorophyll content determination, and organic spectrum analysis were conducted to show the effect of CLA exposure on the growth, photosynthetic activity, and organic metabolic processes of Microcystis aeruginosa. The findings revealed that the physiological status of algae could be significantly influenced by CLA exposure in aquatic environments. Specifically, exposure to 1 μg/L CLA stimulated the growth and photosynthetic activity of algal cells. Conversely, CLA above 10 μg/L led to the inhibition of algal cell growth and photosynthesis. Notably, the inhibitory effects intensified with the increasing concentration of CLA. The molecular weight of DOM produced by Microcystis aeruginosa increased when exposed to CLA. Under the exposure of 60 μg/L CLA, a large number of algal cells ruptured and died, and the intracellular organic matter was released into the algal liquid. This resulted in an increase in high molecular weight substances and soluble microbial-like products in the DOM. Exposure to 1 and 10 μg/L CLA stimulated Microcystis aeruginosa to produce more humic acid-like substances, which may be a defense mechanism against CLA. The results were useful for assessing the effects of antibiotic pollution on the stability of the microalgae population and endogenous DOM characteristics in aquatic ecosystems.

Changes of characteristics and disinfection by-products formation potential of intracellular organic matter with different molecular weight in metalimnetic oxygen minimum

Metalimnetic oxygen minimum (MOM) occurs in reservoirs or lakes due to stratification and algal blooms, which has low dissolved oxygen (DO) levels and leads to the deterioration of water quality. The transformation mechanism and the impact on the water quality of intracellular organic matter (IOM) derived from algae are poorly understood under MOM conditions. In this study, IOM extracted by Microcystis aeruginosa was divided into five components according to molecular weight (MW), and the changes of characteristics and correlated disinfection by-products formation potential (DBPFP) were analyzed and compared under MOM conditions. The removal efficiency of dissolved organic carbon (DOC) in the <5 kDa fraction (66.6%) was higher than that in the >100 kDa fraction (41.8%) after a 14-day incubation under MOM conditions. The same tendency also occurred in Fmax and DBPFP. The decrease in Fmax was mainly due to the decline in tryptophan-like and tyrosine-like for all IOM fractions. The diversity of microorganisms degrading the MW > 100 kDa fraction was lower than others. Besides low MW fractions, these findings indicated that more attention should be paid to high MW fractions which were resistant to biodegradation under MOM conditions during water treatment.

Stress response of Microcystis aeruginosa to chlorine during transportation: The significance of surface-adsorbed organic matter

The desorption of surface-adsorbed organic matter (S-AOM) without damaging algal cells was reported to be the key to destabilizing Microcystis aeruginosa (M. aeruginosa) cells while avoiding intracellular organic matter (IOM) release in our previous study. However, a temporal effect was found from spontaneous and continuous damage to algal cells even after quenching. This study aims to demonstrate the mechanism of the temporal inactivation effect and the stress response exhibited by chlorine-oxidized algal cells, and finally guide the prechlorination process for algae-laden water at water sources. Chlorine was proved to cause oxidative stress to M. aeruginosa cells, and result in a rapid increase in intracellular reactive oxygen species (ROS) levels. S-AOM appeared to have a protective effect on algal cells against oxidative damage, as evidenced by the maintenance of algal cell integrity and activated antioxidant enzymes. In addition, the activity of Caspase 3, a key protease for the execution of programmed cell death (PCD), was significantly enhanced during prechlorination. Cellular chromatin condensation and DNA fragmentation occurred in the early stages of PCD in algal cells. Therefore, the pre-treatment of algae-laden water at water sources, even with low chlorine doses, can induce a risk of significant algal cell death during the water transfer process due to activation of the PCD process, resulting in a higher health risk for drinking water. These findings indicate that both the dosage of chlorine and the duration of the transportation process should be considered during the prechlorination of algae-laden water, which can provide an important basis for avoiding increasing the risk to drinking water safety.

Removal of Anabaena by ultrasonic pretreatment enhancing-coagulation and water treatment processes

Cyanobacteria bloom brings great challenges to the safety of the drinking water process. Ultrasonic pretreatment can effectively enhance coagulation to remove algae cells from algae-laden water. However, due to the special chain-like structure of Anabaena, the removal characteristics of Anabaena in water treatment process are quite different from those of unicellular cyanobacteria. No study has yet systematic studied on the enhancement effect of ultrasonic enhanced water treatment process on Anabaena. Therefore, this paper studied the characteristics and mechanism of ultrasonic pretreatment to enhance the removal of Anabaena, and carried out pilot experiments. The results showed that ultrasound irradiation at 740 kHz and 1.12 MHz had a great effect on the destruction of the chain-like structure and cell structure of Anabaena. After 15 min, the removal rate of Anabaena cells reached 16.0% and 30.4%, respectively, and the release of intracellular organic matter (IOM) reached 4.3 and 6.0 mg/L, in which phycocyanin released more. The damage of dynamic ultrasound irradiation on algae cells is weak, which can avoid the influence of uneven ultrasound irradiation on algae cells. The enhanced coagulation effect was better after 740 kHz ultrasonic pretreatment for 1 min, and the removal rates of algal cells, turbidity and dissolved organic carbon (DOC) increased by 7%, 9.4% and 12.6%, respectively. Pilot scale experiments demonstrate that ultrasonic pretreatment leads to a notable enhancement in the removal efficiency during the coagulation and sedimentation stages. After 4 h of operation, the turbidity and algal cell removal in the sedimentation stage increased by 6.1% and 14.0%, respectively. In addition, the removal of DOC in the final treated water increased by 6.7%. Furthermore, the disinfection by-products (DBPs) concentration experiences a reduction exceeding 200 μg per liter. Together, these results show a substantial improvement in filtration efficiency and effluent quality. This study provides guidance for the ongoing study of ultrasonic pretreatment to remove chain-like cyanobacteria.

Impact of harmful algal bloom severity on bacterial communities in a full-scale biological filtration system for drinking water treatment

The occurrence of harmful algal blooms (HABs) in freshwater environments has been expanded worldwide with growing frequency and severity. HABs can pose a threat to public water supplies, raising concerns about safety of treated water. Many studies have provided valuable information about the impacts of HABs and management strategies on the early-stage treatment processes (e.g., pre-oxidation and coagulation/flocculation) in conventional drinking water treatment plants (DWTPs). However, the potential effect of HAB-impacted water in the granular media filtration has not been well studied. Biologically-active filters (BAFs), which are used in drinking water treatment and rely largely on bacterial community interactions, have not been examined during HABs in full-scale DWTPs. In this study, we assessed the bacterial community structure of BAFs, functional profiles, assembly processes, and bio-interactions in the community during both severe and mild HABs. Our findings indicate that bacterial diversity in BAFs significantly decreases during severe HABs due to the predominance of bloom-associated bacteria (e.g., Spingopyxis, Porphyrobacter, and Sphingomonas). The excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) confirmed that filter influent affected by the severe HAB contained a higher portion of protein-like substances than filter influent samples during a mild bloom. In addition, BAF community functions showed increases in metabolisms associated with intracellular algal organic matter (AOM), such as lipids and amino acids, during severe HABs. Further ecological process and network analyses revealed that severe HAB, accompanied by the abundance of bloom-associated taxa and increased nutrient availability, led to not only strong stochastic processes in the assembly process, but also a bacterial community with lower complexity in BAFs. Overall, this study provides deeper insights into BAF bacterial community structure, function, and assembly in response to HABs.

Flocculation-enhanced photobiological hydrogen production by microalgae: Flocculant composition, hydrogenase activity and response mechanism

The practical application of microalgal photobiological hydrogen was limited by its low yield and short production time. In this study, the promotion of inorganic flocculants (polymeric aluminum chloride, PAC) and organic flocculants (cationic polyacrylamide, CPAM) to the aggregate formation and photobiological hydrogen production of prokaryotic microalgae (Synechocystis sp.) and eukaryotic microalgae (Chlamydomonas reinhardtii) were investigated. The effectiveness of PAC-CPAM composite flocculants in promoting aggregation was compared to single PAC or CPAM, with flocculation efficiencies exceeding 92.2 % for both microalgal strains. After aggregate formation, hydrogen production in Synechocystis and C. reinhardtii increased by 65.9 % and 80.2 %, respectively, compared with the control (without flocculation). Their hydrogenase activity rose to 1.14 and 28.2 μmol H2/(mg chlorophyll·h), respectively. Aggregation sustained the photosynthetic activity of both Synechocystis and C. reinhardtii, with the photosynthetic system electron transfer rate (ETR) 1.54–1.72 times higher than that of the control. The formation of aggregates enhanced microalgal respiration, accelerating the reduction of oxygen content, and increasing hydrogenase activity. Notably, the increased respiration in Synechocystis and C. reinhardtii aggregates supplied more electrons, enhancing hydrogen production by consuming intracellular organic matter. Aggregate formation upregulated the expression of Synechocystis and C. reinhardtii hydrogenase genes by average 2.1-fold and 2.5-fold, respectively. Simultaneously, the expression of genes related to photosynthetic system Ⅱ, ferredoxin, pyruvate ferredoxin-oxidoreductase, and oxidative phosphorylation were upregulated, with a significant effect observed in C. reinhardtii aggregates. The results of this study advanced the utilization and industrialization of microalgae-based green hydrogen production, contributing to carbon neutrality.

Z-scheme Ag2MoO4/BiVO4 photocatalyst using Ag as charge transfer mediator: Performance optimization and Microcystis aeruginosa inactivation application

Eutrophication in water bodies has caused harmful algal blooms (HABs) to occur worldwide, resulting in significant impacts on both the environment and human well-being. In this work, a Z-scheme Ag2MoO4/BiVO4 (AMB) photocatalyst with Ag as the charge transfer mediator was constructed by depositing Ag2MoO4 on BiVO4 through a simple in-situ generation method and characterized by various techniques. In addition, AMB-30% has the best photocatalytic performance, removing 99% of chlorophyll a within 3 h and performing well under different conditions. The physiological characteristics of algal cells were also investigated. The results showed that AMB-30% could not only destabilize the stability, membrane permeability and physiological function of algal cells, but also degrade the intracellular organic matter leaked out from the algal cells, effectively avoiding the secondary pollution of the water body while inactivating algae. Based on the identification of the active substance, the possible algal removal mechanism of Ag2MoO4/BiVO4 under the photocatalytic system was further proposed. Finally, the results of the five-cycle experiments and XRD characterization of AMB-30% demonstrated that it has great recyclability and stability, thus offering a favorable prospect in mitigating HABs.

The pre-coated photocatalytic ceramic membrane with Bi2O3–TiO2/powdered activated carbon nanoparticles to alleviate ultrafiltration fouling caused by intracellular organic matter of Microcystis aeruginosa

Algal intracellular organic matter (IOM), released during algae's normal growth phase and water treatment processes, has long been a source of significant membrane fouling, considerably limiting the effective use of ultrafiltration(UF) technology. In this study, a Bi-doped TiO2 composite with powdered activated carbon (Bi2O3–TiO2/PAC) was loaded on ceramic UF membranes by vacuum filtration, and the prepared photocatalytic modified ceramic membranes (MCMs) were investigated for the removal of IOM and the mitigation of membrane fouling at different loading levels and under three operating conditions: Dark, Dark-UV, and UV. The results showed that the photocatalytic MCMs were able to remove the protein and humic acid fluorescent components of IOM and decompose or mineralize organic matter with molecular weights of 10–50 kDa. Under the Dark, Dark-UV, and UV conditions, the final normalized flux of MCM-2.88 was significantly increased by 22.6 %, 82.1 %, and 108.0 %, respectively. The hydrophilicity of MCMs not only transformed the interactions between IOM and the membrane into repulsive forces, but also the composite material on the membrane surface transforms the membrane fouling mechanism from intermediate blocking model to cake layer formation. Furthermore, the application of photocatalytic oxidation under the Dark-UV and UV conditions yielded a reduction in both reversible and irreversible fouling. This action led to an increased hydrophilicity and elevated free energy of adhesion with IOM during the filtration process. Moreover, the main fouling mechanism changed into complete or intermediate blocking. These outcomes collectively underscore the capability of MCMs to alleviate membrane fouling induced by IOM. This advancement holds substantial promise for the advancement and widespread implementation of photocatalytic ceramic membrane filtration techniques.

The overlooked role of the association between 2-methylisoborneol and natural organic matters in the nanofiltration treatment of authentic water

The presence of natural organic matter (NOM) in surface water and its significance for removing pollutants during nanofiltration (NF) are overlooked since most previous studies were conducted in synthetic water rather than real water. In this paper, using raw water collected from Lake Tai (the third largest lake in China), we investigate the removal of 2-methylisoborneol (2-MIB, one of the most concerned off-flavor compounds in raw water) by NF and analyze the binding behaviors between 2-MIB and NOM, which affect their corresponding migration and removal behaviors of 2-MIB during NF. The results show that the removal of 2-MIB in real raw water is 12.2 ∼ 22.0 % higher than that in pure water (PW). Additionally, we evaluate the increment of the removal of 2-MIB under different backgrounds, which follow the order NOM (17.2 %∼22.0 %) > bovine serum albumin (BSA 16.0 %∼19.1 %) > intracellular organic matter (IOM) of M. aeruginosa (8.3 %∼9.4 %) > sodium carboxymethyl cellulose (CMC 3.9 %∼6.5 %) > humic acid (HA 0.28 %∼0.31 %). These findings demonstrate that the protein-like components in raw water play a major role in binding to 2-MIB, while humic-like components exhibit a weak association with 2-MIB. Overall, the conclusion and findings in this study provide a new perspective on the NOM effect on micropollutant removal during water treatment.

Two wastes into one resource: Carbide slag-driven anaerobic fermentation of excess sludge towards short-chain fatty acids recovery

The anaerobic fermentation has been regarded as promising technology for short-chain fatty acids (SCFAs) recovery from excess sludge. Despite that various treatment approaches have been developed, the sustainable waste utilization of carbide slag in enhancing anaerobic fermentation has rarely been reported. It demonstrated that the carbide slag-derived alkaline condition dominantly contributed to triggering extracellular polymeric substance disruption and microbial cell lysis by protein molecule deconstruction. Considerable sludge hydrolysis was facilitated owing to extracellular and intracellular organic matter release, solubilizing 14.73 % of total solid organic matters in 4-h treatment. Correspondingly, massive SCFAs of 2219.70 mg COD/L (mainly acetate) were produced through 8-day anaerobic fermentation, with the improved acidification and the inhibited methanogenesis. Approximately 83.03–96.21 % of the recoverable SCFAs were extracted after sludge conditioning and solid–liquid separation, providing remarkable economic benefit of 196.23 CNY/ton VSS and carbon-emission reduction of 0.069–0.347 ton CO2/ton VSS. The findings proposed an innovative and sustainable carbide slag-driven anaerobic fermentation strategy for SCFAs recovery and waste stabilization, with low heavy metal residual and negligible environmental risks in “two wastes into one resource” pattern.

Biological effects of hydroxyl radical inactivation for typical red tide algae Alexandrium tamarense

Dinoflagellates are responsible for harmful algal blooms (HABs) worldwide and cause serious ecological security crises and economic losses to the aquaculture industry. In this study, hydroxyl radicals (•OH) were generated by the synergistic effect of strong ionization discharge and hydrodynamic cavitation and were injected into cells to inactivate Alexandrium tamarense within 9 s at a total reactive oxidant (TRO) concentration of 1.0 mg/L. The concentration and time (CT) value of •OH inactivating A. tamarense was 0.153 mg•min/L, which is 1/100 that of ClO2 inactivation. Scanning electron microscopy results demonstrated that the integrity of the algal cells remained without any leakage of intracellular organic matter post •OH inactivation. Furthermore, the chromosomes in the nucleus unwound and broke into fragments under a transmission electron microscope, indicating that the DNA was damaged. In comparison, ClO2 contributed to the severe destruction of cell membranes and walls, resulting in massive intracellular organic matter (IOM) leakage. Based on the single cell gel electrophoresis results, DNA comet length increased 329 % post •OH inactivation, demonstrating that •OH induced DNA fragmentation. Additionally, based on the transcriptomic analysis of A. tamarense, •OH induced a DNA repair response, indicating that DNA strand breakage occurred. In summary, DNA strand breakage and fragmentation were the major reasons for •OH rapidly inactivating A. tamarense with cell integrity retained, which provided critical advancements in controlling HAB safely and efficiently. This method avoids the risk of A. tamarense lysis and IOM release, while guaranteeing marine water security.