Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid.

In light of industrial developments, water pollution by heavy metals as hazardous chemicals has garnered attention. Addressing the urgent need for efficient heavy metal removal from aqueous environments, this study delves into using poly-γ-glutamic acid (γ-PGA) for the bioflocculation of heavy metals. Utilizing γ-PGA variants from Bacillus subtilis with different molecular weights and salt forms (Na-bonded and Ca-bonded), the research evaluates their adsorption capacities for copper (Cu), lead (Pb), and cadmium (Cd) ions. It was found that Na-bonded γ-PGA with a high molecular weight showed the highest heavy metal adsorption (92.2-98.3%), particularly at a 0.5% concentration which exhibited the highest adsorption efficiency. Additionally, the study investigated the interaction of γ-PGA in mixed heavy metal environments, and it was discovered that Na-γ-PGA-HM at a 0.5% concentration showed a superior adsorption efficiency for Pb ions (85.4%), highlighting its selectivity as a potential effective biosorbent for wastewater treatment. This research not only enlightens the understanding of γ-PGA's role in heavy metal remediation but also underscores its potential as a biodegradable and non-toxic alternative for environmental cleanup. The findings pave the way for further exploration into the mechanisms and kinetics of γ-PGA's adsorption properties.

Isolation and characterization of novel cadmium-resistant Escherichia fergusonii ZSF-15 from industrial effluent for flocculant production and antioxidant enzyme activity.

Cadmium (Cd) is a highly toxic metal that frequently contaminates our environment. In this study, the bioflocculant-producing, cadmium-resistant Escherichia fergusonii ZSF-15 was characterized from Paharang drain, Bawa Chak, Faisalabad, Pakistan. The Cd-resistant E. fergusonii was used to determine the bioflocculant production using yeast-peptone-glycerol medium (pH 6.5) supplemented with 50 mg L-1 of Cd. The culture was incubated for 3 days at 37 °C in a rotary shaker at 120 rpm. The fermentation broth was centrifuged at 4000 g for 10 min after the incubation period. The maximum flocculating activity by isolate ZSF-15 was found to be 71.4% after 48 h of incubation. According to the Fourier transform infrared spectroscopy analysis, the bioflocculant produced by strain ZSF-15 was comprised of typical polysaccharide and protein, i.e. hydroxyl, carboxyl, and amino groups. The strain ZSF-15 exhibited bioflocculant activity at range of pH (6-8) and temperature (35-50℃). Maximum flocculation activity (i.e. 71%) was observed at 47℃, whereas 63% flocculation production was observed at pH 8. In the present study, antioxidant enzyme profile of ZSF-15 was also evaluated under cadmium stress. A significant increase in antioxidant enzymes including superoxide dismutase (118%) and ascorbate peroxidase (28%) was observed, whereas contents of catalase (86%), glutathione transferase (13%), and peroxidase (8%) were decreased as compared to control.

Microbial Interactions between Marine Microalgae and Fungi: From Chemical Ecology to Biotechnological Possible Applications.

Chemical interactions have been shown to regulate several marine life processes, including selection of food sources, defense, behavior, predation, and mate recognition. These chemical communication signals have effects not only at the individual scale, but also at population and community levels. This review focuses on chemical interactions between marine fungi and microalgae, summarizing studies on compounds synthetized when they are cultured together. In the current study, we also highlight possible biotechnological outcomes of the synthetized metabolites, mainly for human health applications. In addition, we discuss applications for bio-flocculation and bioremediation. Finally, we point out the necessity of further investigating microalgae-fungi chemical interactions because it is a field still less explored compared to microalga-bacteria communication and, considering the promising results obtained until now, it is worthy of further research for scientific advancement in both ecology and biotechnology fields.

N-Acyl-Homoserine Lactone (AHL)-Mediated Microalgal-Bacterial Communication Driving Chlorella-Activated Sludge Bacterial Biofloc Formation.

N-acyl-homoserine lactones (AHLs) as autoinducers of Gram-negative bacteria for quorum sensing regulation have shown positive effects on the production of aromatic proteins in extracellular polymeric substances (EPSs) during bioflocculation. To investigate the role of AHLs in aromatic protein production, a Chlorella-bacteria system with great bioflocculation was established via fed-batch cultivation. Tryptophan and aromatic proteins as the main compounds in the EPS of bioflocs showed an increasing trend during fed-batch cultivation. The Chlorella cells only secreted tryptophan rather than aromatic proteins during axenic cultivation. N-dodecanoyl-l-homoserine lactone (C12-HSL) was correlated with the flocculation activity and extracellular protein content of bioflocs during fed-batch cultivation. The addition of exogenous C12-HSL enhanced the flocculation activity of the Chlorella-bacteria system and aromatic protein production in the EPS. Chlorella cells sensed exogenous C12-HSL and significantly upregulated the aromatic protein synthesis pathway during axenic cultivation. In addition, vanillin as a quorum-sensing inhibitor suppressed the positive effect of C12-HSL on flocculation activity and aromatic protein production and synthesis. This result indicated that vanillin intercepts the response of Chlorella cells to C12-HSL. Overall, C12-HSL is supposed to be an important signal molecule to achieve communication between Chlorella and Gram-negative bacteria and subsequently induce Chlorella cells to produce aromatic proteins for biofloc formation.

Effect of extracellular polymeric compositions on in-situ sludge minimization performance of upgraded activated sludge treatment for industrial wastewater.

The sludge yield minimization from advanced biological treatment for industrial wastewater could be considered a poorly explored area, therefore, seeks serious attention of the scientific community. Up to best of the knowledge, the extracellular polymeric substances (EPS) profile underlying an upgraded activated sludge treatment (as MANODOX system) for real tannery wastewater has not been addressed in a desired manner. This study covers the elucidation of EPS degradation mechanism and floc morphology underlying MANODOX system for the treatment of real tannery influent. For this purpose, a modified heat extraction method was followed for the estimation of EPS fractions like protein (PN), polysaccharides (PS) and humic contents from the sludge. For the present investigation, the variation in floc characteristics including PN/PS ratio, sludge hydrophobicity, sludge volume index, and facultative microbiota at corresponding change in hydrodynamic sludge retention time (SRT) of 08-40 days was emphasized. The strict maintenance of adapted operational strategies including favoring range of SRT (24 days) for MANODOX implementation succeeded an outstanding in-situ sludge yield minimization lowered up to 0.39 gMLSS/gTCOD that attributed to three times lowered accumulation of PN and PS, comparably lower PN/PS ratio, higher salinity of the mixed liquid, weakened cell-to-cell attachment compared with a parallel run identical aerobic treatment. Here, the reason for improved hydrophobicity and corresponding decline in floc aggregation was attributed to change in sludge PN/PS ratio, carbon to nitrogen ratio of feed influent. The observations confirmed that the sludge yield minimization from MANODOX like systems could be effectively controlled by maintaining aforementioned operational tactics.

Insights into bioflocculation of filamentous cyanobacteria, microalgae and their mixture for a low-cost biomass harvesting system.

Cyanobacteria and microalgae are considered as interesting feedstocks for either the production of high value bio-based compounds and biofuels or wastewater treatment. Nevertheless, the high costs of production, mainly due to the harvesting process, hamper a wide commercialization of industrial cyanobacteria and microalgae based products. Recent studies have found in autoflocculation and bioflocculation promising spontaneous processes for a low-cost and environmentally sustainable cyanobacteria and microalgae biomass harvesting process. In the present work, bioflocculation process has been studied for three different inocula: filamentous cyanobacteria, microalgae and their mixture. Their cultivation has been conducted in batch mode using two different cultivation media: synthetic aqueous solution and urban wastewater. The removal of nutrients and flocculation process performance were monitored during the entire cultivation time. Results have proved that bioflocculation and sedimentation processes occur efficiently for filamentous cyanobacteria cultivated in synthetic aqueous solution, whereas such processes are less efficient in urban wastewater due to the specific characteristics of this medium that prevent bioflocculation to occur. Besides different efficiencies associated to cultivation media, this work highlighted that bioflocculation of sole microalgae is not as effective as when they are cultivated together with filamentous cyanobacteria.

Bioflocculation and settling studies of native wastewater filamentous cyanobacteria using different cultivation systems for a low-cost and easy to control harvesting process.

Bioflocculation phenomena for filamentous cyanobacteria were studied and analysed in two different cultivation systems (i.e. based on air-bubbling and on shaking) and for different initial biomass concentrations. Floc formation and biomass settling were monitored during batch cultivation tests according to an innovative protocol. Results showed that the two cultivation systems enhanced two different flocculation behaviours: air bubbling led to the formation of small and dense flocs, while the shaking table resulted in larger (14 mm2 vs 4 mm2) but mechanically weaker flocs. Floc analysis evidenced that the different mixing systems also affected the speciation of biomass. A mathematical model was developed to simulate and predict the settling performance during the bioflocculation process of filamentous cyanobacteria. Natural settling was examined at different phases of biomass growth. Optimal conditions were obtained at the end of the exponential growth phase, when 70% of the total cultivated biomass could be recovered.

Culture optimization for production and characterization of bioflocculant by Aspergillus flavus grown on chicken viscera hydrolysate.

The economics of bioflocculant production is coupled with the use of a low-cost substrate at appropriate culture conditions. The use of a waste substrate for this purpose offers an additional treatment measure to mitigate environmental pollution. We investigated the growth of Aspergillus flavus and its bioflocculant yield using chicken viscera hydrolysate as the sole media. The effects of culture conditions including time, pH, shaker speed, temperature and inoculum size on bioflocculant production were all investigated and optimised through response surface method based on the central component design (CCD) package of Design Expert. Next, the purified bioflocculant was physically and chemically characterised. Under optimised culture conditions (incubation time 72 h, pH 7, shaker speed 150 rpm, temperature 35 °C and inoculum 4%), 6.75 g/L yield of crude bioflocculant was recorded. The bioflocculant activity was mostly distributed in the cell-free supernatant with optimum efficiency of 91.8% at a dose of 4 mL/100 mL Kaolin suspension. The purified bioflocculant was a glycoprotein consisting of 23.46% protein and 74.5% sugar, including 46% neutral sugar and 2.01% uronic acid. The X-ray photoelectron spectroscopy fundamental analysis of the purified bioflocculant indicated that the mass proportion of C, O and N, were 63.46%, 27.87% and 8.86%, respectively. The bioflocculant is mainly composed of carbonyl, amino, hydroxyl, and amide functional groups. This study for the first time indicates a high potential of bioflocculant yield from chicken viscera at the appropriate culture conditions.

Bioflocculation in natural and engineered systems: current perspectives.

Microorganisms have the tendency to accumulate at interfaces through the release of extracellular polymeric substances to form aggregates such as films or flocs. This physical association leads to different modes of interactions among cells and the subsequent development of functionally and metabolically diverse consortia. Aggregation of cells in aqueous suspensions often results in the formation of flocs, which are hotspots of enhanced microbial processes. This has important implications for the dynamics of organic and inorganic matter in varied ecosystems. These microbial flocs are not only important components in nutrient turnover, decomposition, and sinking flux but also facilitate contaminant removal and treatment of wastewater and biomass harvesting. Greater insight into the multitude of interactions between microorganisms in flocs would be useful to enhance the efficiency of bioflocculation processes. This review covers the fundamental aspects and outlines the role of bioflocculation in controlled industrial processes and in nature.

Use of activated sludge biomass as an agent for advanced primary separation.

Conventional primary settling is a physical process of solid-liquid separation, normally presenting low removal efficiencies. Improvement of this separation process would result in energetic advantages: lower aeration requirements and higher biogas production form primary and secondary sludges. Secondary sludge has been proposed as a potential agent promoting an increase in primary separation efficiency. Few processes have been proposed, based on the cultivation of sludge under special conditions. However, one can speculate that regular sludge may have a similar effect. The aim of this research was to study that possibility. Sludges from different activated sludge reactors were tested. Results showed that COD removals were up to 55%, 2 times higher than that for simple settling. Under that condition, COD balances showed that aeration requirements would reduce 40%, and biogas production from primary and secondary sludges would increase 50%. It is inferred then that the application of activated sludge as an external agent represents an interesting alternative that have the potential to significantly improve energetic efficiency of sewage treatment plants.

Efficacy of exopolysaccharide in dye-laden wastewater treatment: A comprehensive review.

The discharge of dye-laden wastewater into the water streams causes severe water and soil pollution, which poses a global threat to aquatic ecosystems and humans. A diverse array of microorganisms such as bacteria, fungi, and algae produce exopolysaccharides (EPS) of different compositions and exhibit great bioflocculation potency to sustainably eradicate dyes from water bodies. Nanomodified chemical composites of EPS enable their recyclability during dye-laden wastewater treatment. Nevertheless, the selection of potent EPS-producing strains and physiological parameters of microbial growth and the remediation process could influence the removal efficiency of EPS. This review will intrinsically discuss the fundamental importance of EPS from diverse microbial origins and their nanomodified chemical composites, the mechanisms in EPS-mediated bioremediation of dyes, and the parametric influences on EPS-mediated dye removal through sorption/bioflocculation. This review will pave the way for designing and adopting futuristic green and sustainable EPS-based bioremediation strategies for dye-laden wastewater in situ and ex situ.

Cultivation of Arthrospira platensis and harvesting using edible fungi isolated from mould soybean cake.

In this study, the cultivation and harvesting of Arthrospira platensis biomass were proposed via simple, safe, and efficient techniques for direct consumption. Cultivation of microalgae in a covered macrobubble column under outdoor conditions resulted in significant differences (p < 0.05) with a maximum dry cell weight (Xm) of 0.959 ± 0.046 g/L. Notably, outdoor cultures resulted in approximately twofold biomass compared to indoor cultures. This outcome shows that the developed outdoor setup integrated with solar panels while utilising Malaysia's weather and atmospheric air as carbon sources is viable. Meanwhile, for harvesting, the screening showed that the fungus isolated from mould soybean cake (tempeh) starter indicated the highest harvesting efficiency, which was then further identified as Rhizopus microsporus, microscopically and molecularly. Overall, the economical and portable setup of outdoor cultivation coupled with safe harvesting via locally isolated fungus from tempeh as a bioflocculant would provide sustainability to produce A. platensis biomass.

Strategy for the formation of microalgae-bacteria aggregates in high-rate algal ponds.

This work studied the formation of aggregates used for wastewater treatment in high-rate algal ponds (HRAP). For this, the establishment of microalgae-bacteria aggregates in these systems was evaluated, considering strategies for the inoculation and start-up. Two HRAP were operated in parallel, at first in batch mode and then in continuous flow. The wastewater treatment was efficient, with removal rates around 80% for COD and N-ammoniacal. Volatile suspended solids and chlorophyll for the culture grew continuously reached a concentration of 548 ± 11 mg L-1 and 7.8 mg L-1, respectively. Larger photogranules were observed when the system was placed in a continuous regime. The protein fraction of extracellular polymeric substances was identified as a determinant in photogranules formation. During the continuous regime, more than 50% of the biomass was higher than 0.2 mm, flocculation efficiency of 78 ± 6%, and the volumetric sludge index of 32 ± 5 mL g-1. The genetic sequencing showed the growth of cyanobacteria in the aggregate and the presence of microalgae from the chlorophytes and diatoms groups in the final biomass.

Cultivation of carbohydrate-rich microalgae with great settling properties using cooling tower wastewater.

Wastewater treatment and simultaneous production of value-added products with microalgae represent a sustainable alternative. Industrial wastewater, characterized by high C/N molar ratios, can naturally improve the carbohydrate content in microalgae without the need for any external source of carbon while degrading the organic matter, macro-nutrients, and micro-nutrients. This study aimed to understand the treatment, reuse, and valorization mechanisms of real cooling tower wastewater (CWW) from a cement-processing industry mixed with domestic wastewater (DW) to produce microalgal biomass with potential for synthesis of biofuels or other value-added products. For this purpose, three photobioreactors with different hydraulic retention times (HRT) were inoculated simultaneously using the CWW-DW mixture. Macro- and micro-nutrient consumption and accumulation, organic matter removal, algae growth, and carbohydrate content were monitored for 55 days. High COD (> 80%) and macronutrient removals (> 80% of N and P) were achieved in all the photoreactors, with heavy metals below the limits established by local standards. The best results showed maximum algal growth of 1.02 g SSV L-1 and 54% carbohydrate accumulation with a C/N ratio of 31.24 mol mol-1. Additionally, the harvested biomass presented a high Ca and Si content, ranging from 11 to 26% and 2 to 4%, respectively. Remarkably, big flocs were produced during microalgae growth, which enhanced natural settling for easy biomass harvesting. Overall, this process represents a sustainable alternative for CWW treatment and valorization, as well as a green tool for generating carbohydrate-rich biomass with the potential to produce biofuels and fertilizers.

Exploring bisphenol S removal mechanism with multi-enzymes extracted from waste sludge and reed sediment.

4,4'-Sulfonyl-diphenol (BPS), as a widespread environmental hormone-like micropollutant, is difficult to be degraded in the environment. In this study, the removal of BPS with multi-enzymes extracted from waste sludge and reed sediment was studied at 298 K, 310 K, and 328 K. Results show that BPS could be removed efficiently and was time-temperature dependent, which could involve enzymolysis and bio-flocculation. The mechanism and pathways of the enzymolysis were identified with ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Polymerization of BPS with enzymolysis further improved the removal by bio-flocculation due to the production of BPS oligomers. Furthermore, the interaction mechanism between BPS and multi-enzyme was explored through a series of spectroscopic experiments. Results show that more loose skeletal structure of the multi-enzymes and more hydrophobic microenvironment of the amino acid residues are responsible for the removal of BPS. This research not only provided a method for refractory micropollutants removal but also a way for the utilization of waste sludge and reed sediment.

A comprehensive study on flocculation of anionic dyes using the bioflocculant produced by Bacillus thuringiensis: Kinetics, affecting factors, and perspectives.

Bioflocculants have received more and more attention as alternatives to chemical flocculants because of their innocuousness, environmental friendliness, and high effectiveness. This study aims to investigate various factors that influence the performance of the novel bioflocculant produced by Bacillus thuringiensis (BF-TWB10) and analyze its adsorption kinetics to optimize its flocculation performance for real applications. The best-fit kinetic model was pseudo-second order with R2 = 0.999. The effects of pretreatment temperature, pH, and the presence of cations on flocculation were assessed. Further investigations of flocculation, including zeta potential analysis and particle size analysis, were also conducted. Thermal pretreatment of BF-TWB10 or the presence of divalent cations could stimulate the decolorization efficiency of the bioflocculant. BF-TWB10 manifested outstanding dye removal performances with over 90% for all tested anionic dyes at pH 2 and 3. Its decolorization efficiency on anionic dyes decreased with the increase of pH values. Zeta potential analysis revealed that the electrostatic repulsion between anionic dyes decreased after the addition of BT-TWB10 and further diminished by adjusting the reaction mixture to pH 2 before flocculation, suggesting the occurrence of adsorption bridging and charge neutralization. These findings proposed that BF-TWB10 might be a promising bioflocculant for the removal of dyes in textile wastewater. PRACTITIONER POINTS: Bioflocculant BF-TWB10 shows outstanding performance in flocculation. Adsorption process follows pseudo-second-order kinetic model. Flocculation process is pH-responsive. High-temperature pretreatment or divalent cations enhance its flocculation performance. The analyses suggest the occurrence of charge neutralization and adsorption bridging.

Microplastics in water: types, detection, and removal strategies.

Microplastics are one of the most concerning groups of contaminants that pollute most of the surroundings of the Earth. The abundance of plastic materials available in the environment moved the scientific community in defining a new historical era known as Plasticene. Regardless of their minuscule size, microplastics have posed severe threats to the life forms like animals, plants, and other species present in the ecosystem. Ingestion of microplastics could lead to harmful health effects like teratogenic and mutagenic abnormalities. The source of microplastics could be either primary or secondary in which the components of microplastics are directly released into the atmosphere and the breakdown of larger units to generate the smaller molecules. Though numerous physical and chemical techniques are reported for the removal of microplastics, their increased cost prevents the large-scale applicability of the process. Coagulation, flocculation, sedimentation, and ultrafiltration are some of the methods used for the removal of microplastics. Certain species of microalgae are known to remove microplastics by their inherent nature. One of the biological treatment strategies for microplastic removal is the activated sludge strategy that is used for the separation of microplastic. The overall microplastic removal efficiency is significantly high compared to conventional techniques. Thus, the reported biological avenues like the bio-flocculant for microplastic removal are discussed in this review article.

Reinforcement of Different Sands by Low-pH Bio-Mineralization.

Different sands have significant influences on MICP reinforcement effects. Using calcium carbonate production and bioflocculation lag period as evaluation criteria, this study investigates the optimal theoretical pH values of bacterial solutions with different concentrations. We reinforced four different sands using MICP at the optimal theoretical pH, and based on permeability, moisture retention, raindrop erosion, wind erosion, penetration, and SEM tests, the influence of sand properties on low-pH MICP reinforcement was analyzed and the low-pH MICP mechanism was revealed. The results indicate the following: (1) The optimal theoretical pH values for bacterial solutions with concentrations of 0.67 × 108 cells/mL, 3 × 108 cells/mL, and 10 × 108 cells/mL are 4.5, 3, and 4, respectively. (2) With 0.67 × 108, 3 × 108, and 10 × 108 cells/mL bacterial solutions, the strength of tailings sand containing calcium salt was 21.15%, 44.42%, and 13.61% higher than that of quartz sand, respectively. The effective reinforcement depth of alkaline reclaimed sand was 10, 8, and 6 mm lower than that of neutral calcareous sand, respectively. The strength of fine tailings sand was 70.41%, 58.04%, and 22.6% higher than that of coarse reclaimed sand. The effective reinforcement depth of fine quartz sand was 6, 4, and 4 mm lower than that of coarse calcareous sand. (3) Low pH temporarily suppresses urease activity, delaying calcium carbonate flocculation and enhancing reinforcement uniformity. To achieve optimal reinforcement effects, adjusting the actual optimal pH values of bacterial solution based on sand properties is essential in engineering applications.

Insights into differences between spore-assisted and pellet-assisted microalgae harvesting using a highly efficient fungus: Efficiency, high-value substances, and mechanisms.

To achieve efficient and low-cost microalgae harvesting, investigations were conducted on the harvesting efficiency and potential mechanisms of Chlorella sp. HQ by filamentous fungi using two strategies, fungal spore-assisted harvesting (FSH) and fungal pellet-assisted harvesting (FPH). Five of the 19 fungal species isolated from domestic sewage could form pellets, and Aspergillus niger HW8-1 comprised the highest harvesting efficiencies of 99.17 % and 88.70 % for FPH and FSH, respectively. FSH had 2-3 times more lipids and polysaccharides in fungus-alga pellets and caused richer saturated and monounsaturated fatty acids compared with FPH. Moreover, by optimizing the microalgae preculture time, glucose concentration, and microalgae initial density, the contents of high-value substances, such as lipids, polysaccharides, and proteins of fungus-alga pellets after FPH were improved from 5.96 %, 5.67 %, and 7.27 % to 20.18 %, 24.34 % and 10.48 %, respectively. Furthermore, fungal pellets secreted more extracellular polymeric substances (EPS) during FPH than those by FSH, which could chemisorb algal cells by lowering the surface potential of fungal pellets. FPH caused algal cells to cover the outside, which increased the light exposure area of algae, thereby increasing the photosynthesis rate, whereas FSH mainly captured microalgae physically through mycelium entanglement.

Chitosan as an Outstanding Polysaccharide Improving Health-Commodities of Humans and Environmental Protection.

Public health, production and preservation of food, development of environmentally friendly (cosmeto-)textiles and plastics, synthesis processes using green technology, and improvement of water quality, among other domains, can be controlled with the help of chitosan. It has been demonstrated that this biopolymer exhibits advantageous properties, such as biocompatibility, biodegradability, antimicrobial effect, mucoadhesive properties, film-forming capacity, elicitor of plant defenses, coagulant-flocculant ability, synergistic effect and adjuvant along with other substances and materials. In part, its versatility is attributed to the presence of ionizable and reactive primary amino groups that provide strong chemical interactions with small inorganic and organic substances, macromolecules, ions, and cell membranes/walls. Hence, chitosan has been used either to create new materials or to modify the properties of conventional materials applied on an industrial scale. Considering the relevance of strategic topics around the world, this review integrates recent studies and key background information constructed by different researchers designing chitosan-based materials with potential applications in the aforementioned concerns.