Immobilization of activated sludge using improved polyvinyl alcohol (PVA) gel

Wastewater treatment optimization utilizing polyvinyl alcohol cryogel immobilized microalgae for nutrient removal

This study investigated the use of polyvinyl alcohol (PVA) cryogels to immobilize microalgae for wastewater treatment. Chlorella sorokiniana was successfully entrapped in PVA cryogels via repeated freeze/thaw cycles. The nutrient removal efficiency of these cryogels was tested in a continuously stirred photobioreactor under varying conditions, both with and without the addition of an organic carbon source (sodium acetate). The presence of organic carbon significantly enhanced nutrient removal. Specifically, PVA cryogels with immobilized C. sorokiniana achieved 100% nitrogen removal and 97.2% phosphorus removal under mixotrophic conditions. Furthermore, the maximum nutrient removal capacities of the PVA cryogels were found to be 0.033 mg-N/cube·day for nitrogen and 0.0047 mg-P/cube·day for phosphorus. As the inorganic carbon (bicarbonate) concentration increased from 5 to 100 mg/L, the N/P ratio rose from 6 to 8, with a higher N/P ratio of 10 observed when nitrate nitrogen was used as the nitrogen source, compared to ammonia nitrogen, at 100 mg/L bicarbonate. This study offers an effective method for using microalgae immobilized in PVA cryogels for wastewater treatment. The findings highlight the potential for PVA cryogels to significantly improve nutrient removal efficiency, particularly in the presence of organic carbon sources, thereby enhancing bioreactor performance. High nitrogen and phosphorus removal efficiencies can help reduce eutrophication in water bodies, protect aquatic ecosystems, and enable nutrient recovery and reuse, supporting a circular economy in wastewater treatment practices.

Adsorption and biodegradation of the azo dye methyl orange using Ralstonia pickettii immobilized in polyvinyl alcohol (PVA)-alginate-hectorite beads (BHec-RP)

Biological methods are widely used to treat dye waste, particularly methyl orange (MO) dye. The importance of MO degradation stems from its classification as a toxic dye. Within the scope of this research, successful bio-decolorization of MO was achieved through the use of Ralstonia pickettii bacteria immobilized in a PVA-alginate-hectorite matrix (BHec-RP). The optimum conditions for the degradation were observed at a composition of PVA (10%), hectorite (1%), static incubation, 40 °C, and pH 7. Subsequently, the adsorption kinetics of BHec-RP (dead cells) as well as the degradation kinetics of BHec-RP (live cells) and MO using free R. pickettii cells were evaluated. The decolorization of MO using BHec-RP (dead cells) is an adsorption process following pseudo-first-order kinetics (0.6918 mg g-1 beads) and occurs in a monolayer or physical process. Meanwhile, the adoption of BHec-RP (live cells) and free R. pickettii cells shows a degradation process under pseudo-first-order kinetics, with the highest rates at an initial MO concentration of 50 mg L-1 being 0.025 mg L-1 h-1 and 0.015 mg L-1 h-1, respectively. These results show that the immobilization system is superior compared to free R. pickettii cells. Furthermore, the degradation process shows the inclusion of several enzymes, such as azoreductase, NADH-DCIP reductase, and laccase, presumed to be included in the fragmentation of molecules. This results in five fragments based on LC-QTOF/MS analysis, with m/z values of 267.12; 189.09; 179.07; 169.09; and 165.05.

Advanced treatment of coking wastewater: Recent advances and prospects

Advanced treatment of refractory industrial wastewater is still a challenge. Coking wastewater is one of coal chemical wastewater, which contains various refractory organic pollutants. To meet the more and more rigorous discharge standard and increase the reuse ratio of coking wastewater, advanced treatment process must be set for treating the biologically treated coking wastewater. To date, several advanced oxidation processes (AOPs), including Fenton, ozone, persulfate-based oxidation, and iron-carbon micro-electrolysis, have been applied for the advanced treatment of coking wastewater. However, the performance of different advanced treatment processes changed greatly, depending on the components of coking wastewater and the unique characteristics of advanced treatment processes. In this review article, the state-of-the-art advanced treatment process of coking wastewater was systematically summarized and analyzed. Firstly, the major organic pollutants in the secondary effluents of coking wastewater was briefly introduced, to better understand the characteristics of the biologically treated coking wastewater. Then, the performance of various advanced treatment processes, including physiochemical methods, biological methods, advanced oxidation methods and combined methods were discussed for the advanced treatment of coking wastewater in detail. Finally, the conclusions and remarks were provided. This review will be helpful for the proper selection of advanced treatment processes and promote the development of advanced treatment processes for coking wastewater.

Nitrogen removal by a strengthened comprehensive floating bed with embedded pellets made by a newly isolated Pseudomonas sp. Y1

A newly heterotrophic nitrification aerobic denitrification(HN-AD) bacterium Pseudomonas sp. Y1 with highly nitrogen removal ability was isolated from the activated sludge, TN removal rate of which was 99.73%. In this study, two types of different ecology floating bed systems were designed to achieve efficient nitrogen removal in the urban eutrophic landscape water body, one is the comprehensive ecological floating bed(CEFB) system with only Lythrum salicari and the other is the strengthened comprehensive ecological floating bed (SCEFB) system with both Lythrum and embedded pellets made by Y1. The TN removal rates of the CEFB system were 33.82%, 83.84% and 88.91% at 8±1℃, 15±1℃ and 25±1℃, respectively, while the TN removal rates of the SCEFB system increased by nearly 40%, 16% and 11% at the same environment, respectively. The result shows that the SCEFB system can purify the simulated water from surface water body class V to class IV. Thus it has a broad application prospect in the urban eutrophic landscape water body.

Enhanced sludge settlement of two stage PN/Anammox for reject water treatment with respective diatomite addition

The present study investigated the potential of diatomite addition in enhancing sludge settlement of two-stage PN/Anammox for real reject water treatment, with a focus on sludge settling velocity, nitrogen removal capacity, sludge morphological features, and microbial community changes. The study found that diatomite addition significantly improved the sludge settleability of the two-stage PN/A process, resulting in a decrease in sludge volume index (SVI) from 70 to 80 mL/g to about 20-30 mL/g for both PN and Anammox sludge, although the sludge-diatomite interaction differed between the two types of sludge. In the PN sludge, diatomite acted as a carrier, while in the Anammox sludge, it acted as micro-nuclei. The addition of diatomite also increased the biomass amounts in the PN reactor, with a 5-29 % improvement attributed to its role as a biofilm carrier. The effects of diatomite addition on sludge settleability were more prominent at high mixed liquor suspended solids (MLSS), where sludge characteristics were deteriorated. Furthermore, the settling rate of the experimental group consistently exceeded that of the blank group after diatomite addition, with a significant decrease in SV. The relative abundance of Anammox bacteria was improved, and sludge particle size decreased in the diatomite-added Anammox reactor. Diatomite was effectively retained in both reactors, with less loss observed for Anammox than PN due to its more tightly wrapped structure, resulting in a stronger sludge-diatomite interaction. Overall, the results of this study suggest that diatomite addition has potential in enhancing the settling properties and performance of two-stage PN/Anammox for real reject water treatment.

Comparative investigation on heterotrophic denitrification driven by different biodegradable polymers for nitrate removal in mariculture wastewater: Organic carbon release, denitrification performance, and microbial community

Heterotrophic denitrification is widely studied to purify freshwater wastewater, but its application to seawater wastewater is rarely reported. In this study, two types of agricultural wastes and two types of synthetic polymers were selected as solid carbon sources in denitrification process to explore their effects on the purification capacity of low-C/N marine recirculating aquaculture wastewater (NO3 --N 30 mg/L, salinity 32‰). The surface properties of reed straw (RS), corn cob (CC), polycaprolactone (PCL) and poly3-hydroxybutyrate-hydroxypropionate (PHBV) were evaluated by Brunauer-Emmett-Teller, Scanning electron microscope and Fourier-transform infrared spectroscopy. Short-chain fatty acids, dissolved organic carbon (DOC), and chemical oxygen demand (COD) equivalents were used to analyze the carbon release capacity. Results showed that agricultural waste had higher carbon release capacity than PCL and PHBV. The cumulative DOC and COD of agricultural waste were 0.56-12.65 and 1.15-18.75 mg/g, respectively, while those for synthetic polymers were 0.07-1.473 and 0.045-1.425 mg/g, respectively. The removal efficiency of nitrate nitrogen (NO3 --N) was CC 70.80%, PCL 53.64%, RS 42.51%, and PHBV 41.35%. Microbial community analysis showed that Proteobacteria and Firmicutes were the most abundant phyla in agricultural wastes and biodegradable natural or synthetic polymers. Quantitative real-time PCR indicated the conversion from nitrate to nitrogen was achieved in all four carbon source systems, and all six genes had the highest copy number in CC. The contents of medium nitrate reductase, nitrite reductase and nitrous oxide reductase genes in agricultural wastes were higher than those in synthetic polymers. In summary, CC is an ideal carbon source for denitrification technology to purify low C/N recirculating mariculture wastewater.

Biological production of medium-chain carboxylates through chain elongation: An overview

Medium chain carboxylates (MCCs) have wide applications in various industries, but the traditional MCCs production methods are costly and unsustainable. Anaerobic fermentation offers a more scalable, economical and eco-friendly platform for producing MCCs through chain elongation which converts short chain carboxylates and electron donor into more valuable MCCs. However, the underlying microbial pathways are not well understood. In this review, biological production of MCCs through chain elongation is introduced elaborately, including the metabolic pathways, electron donor and substrates, microorganisms and influencing factors. Then, the strategies for enhancing MCCs production are extensively analyzed and summarized, along with the technologies for MCCs separation from the fermentation broth. Finally, challenges and perspectives concerning the large-scale MCCs production are proposed, providing suggestions for the future research. Extensive review demonstrated that anaerobic fermentation has great potential in achieving economical and sustainable MCCs production from complex organic substrates, including organic waste streams, which would significantly broaden the application of MCCs, especially in the renewable energy field. An interdisciplinary approach with knowledge from microbiology and biochemistry to chemical separations and environmental engineering is required to use this promising technology as a valorization method for converting organic biomass or organic wastes into valuable MCCs.

Living Bacteria Directly Embedded into Electrospun Nanofibers: Design of New Anode for Bio-Electrochemical Systems

The aim of this work is the optimization of electrospun polymeric nanofibers as an ideal reservoir of mixed electroactive consortia suitable to be used as anodes in Single Chamber Microbial Fuel Cells (SCMFCs). To reach this goal the microorganisms are directly embedded into properly designed nanofibers during the electrospinning process, obtaining so called nanofiber-based bio-composite (bio-NFs). This research approach allowed for the designing of an advanced nanostructured scaffold, able to block and store the living microorganisms inside the nanofibers and release them only after exposure to water-based solutions and electrolytes. To reach this goal, a water-based polymeric solution, containing 5 wt% of polyethylene oxide (PEO) and 10 wt% of environmental microorganisms, is used as the initial polymeric solution for the electrospinning process. PEO is selected as the water-soluble polymer to ensure the formation of nanofiber mats offering features of biocompatibility for bacteria proliferation, environment-friendliness and, high ionic conductivity. In the present work, bio-NFs, based on living microorganisms directly encapsulated into the PEO nanofiber mats, were analyzed and compared to PEO-NFs made of PEO only. Scanning electron microscopy allowed researchers to confirm the rise of a typical morphology for bio-NFs, evidencing the microorganisms’ distribution inside them, as confirmed by fluorescence optical microscopy. Moreover, the latter technique, combined with optical density measurements, allowed for demonstrating that after electrospinning, the processed microorganisms preserved their proliferation capability, and their metabolic activity after exposure to the water-based electrolyte. To demonstrate that the energy-production functionality of exo-electrogenic microorganisms was preserved after the electrospinning process, the novel designed nanomaterials, were directly deposited onto carbon paper (CP), and were applied as anode electrodes in Single Chamber Microbial Fuel Cells (SCMFCs). It was possible to appreciate that the maximum power density reached by bio-NFs, which resulted in being double of the ones achieved with PEO-NFs and bare CP. SCMFCs with bio-NFs applied as anodic electrodes reached a current density value, close to (250 ± 5.2) mA m⁻², which resulted in being stable over time and was comparable with the one obtained with carbon-based electrode, thus confirming the good performance of the whole device.

Research progress on enhancing the performance of autotrophic nitrogen removal systems using microbial immobilization technology

The autotrophic nitrogen removal process has great potential to be applied to the biological removal of nitrogen from wastewater, but its application is hindered by its unstable operation under adverse environmental conditions, such as those presented by low temperatures, high organic matter concentrations, or the presence of toxic substances. Granules and microbial entrapment technology can effectively retain and enrich microbial assemblages in reactors to improve operating efficiency and reactor stability. The carriers can also protect the reactor's internal microorganisms from interference from the external environment. This article critically reviews the existing literature on autotrophic nitrogen removal systems using immobilization technology. We focus our discussion on the natural aggregation process (granulation) and entrapment technology. The selection of carrier materials and entrapment methods are identified and described in detail and the mechanisms through which entrapment technology protects microorganisms are analyzed. This review will provide a better understanding of the mechanisms through which immobilization operates and the prospects for immobilization technology to be applied in autotrophic nitrogen removal systems.

Coral Probiotics: Premise, Promise, Prospects

The use of Beneficial Microorganisms for Corals (BMCs) has been proposed recently as a tool for the improvement of coral health, with knowledge in this research topic advancing rapidly. BMCs are defined as consortia of microorganisms that contribute to coral health through mechanisms that include (a) promoting coral nutrition and growth, (b) mitigating stress and impacts of toxic compounds, (c) deterring pathogens, and (d) benefiting early life-stage development. Here, we review the current proposed BMC approach and outline the studies that have proven its potential to increase coral resilience to stress. We revisit and expand the list of putative beneficial microorganisms associated with corals and their proposed mechanismsthat facilitate improved host performance. Further, we discuss the caveats and bottlenecks affecting the efficacy of BMCs and close by focusing on the next steps to facilitate application at larger scales that can improve outcomes for corals and reefs globally.

Kinetics of a fixed bed reactor with immobilized microorganisms for the removal of organic matter and phosphorous

The biodegradation of domestic wastewater contaminants has been carried out using microorganisms immobilized in sodium alginate gel (Alg-Na). A fixed bed reactor with immobilized microorganisms was used for the treatment of domestic wastewater. A wastewater pretreatment was carried out to remove the larger particulate matter, which consisted of a reactor packed with different materials (anthracite, zeolite, and activated carbon). Later, a second reactor packed with balls with immobilized microorganisms was used to eliminate organic matter and nutrients. 2.5% w/v of Alg-Na was used as a support to immobilize the microorganisms. According to the results, a total phosphorus (TP) and chemical oxygen demand (COD) removal of 94.26% and 78.25% was obtained, respectively. In addition, the degradation rate for both organic matter and phosphorous was studied by using the kinetic model for fix bed reactor. © 2020 Water Environment Federation PRACTITIONER POINTS: Phosphorous and organic matter removal by adsorption and immobilized microorganisms. High removal efficiency of phosphorous and organic matter was found. An innovative wastewater treatment alternative is proposed. Kinetic model for fixed bed reactor is also proposed for scaling-up purposes.

Comparison of agricultural wastes and synthetic macromolecules as solid carbon source in treating low carbon nitrogen wastewater

This paper investigated the feasibility of using agricultural wastes and synthetic macromolecules as solid carbon sources and studied the effects of improvement of denitrification by the selected agricultural wastes. The carbon release capacity and denitrification performance of corncob (CC), peanut shell (PS), obsolescent rice (OR) and polycaprolactone (PCL), poly butylene succinate (PBS), polyvinyl alcohol sodium alginate (PVA-SA) were systematically analyzed. The results showed that for each carbon source, the first-order kinetic equation was basically followed during the carbon release process. PVA-SA, CC and PS had higher carbon release capacity with accumulative dissolved organic carbon (DOC) of 16.22-20.63 mg·g^-1 and chemical oxygen demand (COD) of 100.86-134.10 mg·g^-1. Correspondingly, they showed excellent denitrification performance with almost no residual NO₃^--N, and the denitrification process well followed the Monod equation. PCL, PBS and OR had lower carbon release capacity with accumulative DOC of 2.06-3.14 mg·g^-1 and COD of 13.29-24.13 mg·g^-1, respectively. Nevertheless, these materials can also improve the denitrification performance, with the residual NO₃^--N in the range of 6.02-6.36 mg·L^-1, and the effluent DOC was in the range of 10-15 mg·L^-1. Synthetic polymers are more suitable for nitrogen removal in groundwater treatment, while agricultural wastes are ideal carbon sources for secondary effluent treatment.

Immobilized-microbial bioaugmentation protects aerobic denitrification from heavy metal shock in an activated-sludge reactor

The inhibition of denitrification by heavy metals is a problem in nitrogen wastewater treatment, but the solutions are rarely studied. In this study, Pseudomonas brassicacearum LZ-4, immobilized in sodium alginate-kaolin, was applied in an activated-sludge reactor to protect denitrifiers from hexavalent chromium (Cr(VI)). Q-PCR result showed that the strain LZ-4 was incorporated into activated sludge under the help of immobilization. In the non-bioaugmentation system, the removal efficiency of nitrate was decreased by 86.07% by 30 mg/L Cr(VI). Whereas, denitrification was protected and 95% of nitrate was removed continuously in immobilized-cell bioaugmentation system. Miseq sequencing data showed that bioaugmentation decreased the impact of Cr(VI) on microbial communities and increased the abundance of denitrifiers. Based on the results of biomass and extracellular polymers, activated sludge was protected from Cr(VI) toxicity. This discovery will provide a feasible technique for nitrogen wastewater treatment in the presence of distressing heavy metals.

Electrospun Nanofibers: from Food to Energy by Engineered Electrodes in Microbial Fuel Cells

Microbial fuel cells (MFCs) are bio-electrochemical devices able to directly transduce chemical energy, entrapped in an organic mass named fuel, into electrical energy through the metabolic activity of specific bacteria. During the last years, the employment of bio-electrochemical devices to study the wastewater derived from the food industry has attracted great interest from the scientific community. In the present work, we demonstrate the capability of exoelectrogenic bacteria used in MFCs to catalyze the oxidation reaction of honey, employed as a fuel. With the main aim to increase the proliferation of microorganisms onto the anode, engineered electrodes are proposed. Polymeric nanofibers, based on polyethylene oxide (PEO-NFs), were directly electrospun onto carbon-based material (carbon paper, CP) to obtain an optimized composite anode. The crucial role played by the CP/PEO-NFs anodes was confirmed by the increased proliferation of microorganisms compared to that reached on bare CP anodes, used as a reference material. A parameter named recovered energy (Erec) was introduced to determine the capability of bacteria to oxidize honey and was compared with the Erec obtained when sodium acetate was used as a fuel. CP/PEO-NFs anodes allowed achieving an Erec three times higher than the one reached with a bare carbon-based anode.

Biodegradation of phenol in saline or hypersaline environments by bacteria: A review

With the continuous demand from industry for chemical raw materials, a large amount of high-salinity wastewater containing phenol is discharged into the aquatic environment, and the leakage of dangerous chemicals into the sea may lead to phenol pollution of the ocean. Phenol is a common chemical posing serious environmental hazard. Biodegradation is an effective, low-cost, environment-friendly method of removing phenol from water, but in hypersaline environments, traditional freshwater organisms are less efficacious. Here, at least 17 genera of bacteria from three phyla are found that can degrade phenol in different saline environments. The sources and taxonomy of halotolerant and halophilic bacteria are reviewed. Moreover, the pathway of phenol removal, kinetics of biodegradation, influencing factors, and recent treatment processes of wastewater are discussed.

Improvements on activated sludge settling and flocculation using biomass-based fly ash as activator

Biomass-based fly ash and wastewater are undesired products of the pulping industry. Recently, the use of biomass-based fly ash as an adsorbent (i.e., a valued material) for constituents of wastewater effluents was reported. In this work, the settling performance and properties of activated sludge were studied in the presence of fly ash. Upon mixing, fly ash increased the zeta potential of the sludge from -31 mV to -28 mV, which was due to the release of cationic ions from fly ash in the sludge suspension. The sludge settling and its flocculation affinity were improved through the complexation of flocs and released cation ions from fly ash. The relationships between the protein/polysaccharide (PN/PS) ratio and the content of extracellular polymeric substances (EPS) as well as the ratio and the properties of the sludge flocs were determined. A correlation between the total loosely bound-EPS (LB-EPS) content and the effluent suspended solids (ESS) (Pearson's coefficient, r_p = 0.83) was observed. The performance of sludge flocculation and settling were much more closely correlated with LB-EPS than with tightly bound EPS (TB-EPS). Scanning electron microscopy (SEM) analysis of sludge flocs before and after EPS extraction showed that the sludge flocs contained a large number of microorganisms, mainly Bacillus and Cocci. The amount of LB-EPS had an adverse influence on bioflocculation, effluent clarification and sludge settling affinity. The sludge properties had a moderate relationship with the PN/PS ratio of LB-EPS. Also, no correlation could be established between the ratio and the TB-EPS content.

Uranium biosorption by immobilized active yeast cells entrapped in calcium-alginate-PVA- GO-crosslinked gel beads

A novel biosorbent, i. e. Saccharomyces cerevisiae entrapped in graphene oxide (GO), polyvinyl alcohol (PVA) and alginate and cross-linked in CaCl2- boric acid solution, was prepared, characterized and applied for U (VI) biosorption. The performance of U sorption and cations release (Na, K, Ca and Mg ions) was investigated under different contact time, initial uranium concentration and initial pH. Uranium sorption equilibrium basically achieved after 360 min. The kinetic data of U biosorption and Ca release were best described by the pseudo first-order equation. Both Langmuir and Freundlich models could fit the U sorption isotherm data. With increase of initial uranium (3.7 ~ 472.2 μmol/L) and sodium concentration (78.8 ~ 3911.7 μmol/L), the cations release ((Na + K)/2 + (Ca + Mg)) decreased from 116.9 to 30.1 μmol/g when the corresponding U sorption increased from 0.6 to 77.3 μmol/g. Initial solution pH at 3 was favorable for U sorption when pH ranged from 3 to 7. With increase of uranium concentration, ion exchange played a less role in U removal. The maximum U sorption capacity reached 142.1 μmol/g, calculated from the Langmuir model at initial pH 5. The O-containing functional group, such as carboxyl on the gel bead played an important role in U adsorption according to FTIR and XPS analysis. XPS analysis showed the existence of U (VI) and U (IV) on the surface of gel bead. Ion exchange, complexation and uranium reduction involved in uranium adsorption by the immobilized active dry yeast gel beads.

Heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride degradation

The application of the electro-Fenton process for organic compound mineralisation has been widely reported over the past years. However, operational problems related to the use of soluble iron salt as a homogeneous catalyst involve the development of novel catalysts that are able to operate in a wide pH range. For this purpose, polyvinyl alcohol-alginate beads, containing goethite as iron, were synthesised and evaluated as heterogeneous electro-Fenton catalyst for 1-butylpyridinium chloride mineralisation. The influence of catalyst dosage and pH solution on ionic liquid degradation was analysed, achieving almost total oxidation after 60 min under optimal conditions (2 g/L catalyst concentration and pH 3). The results showed good catalyst stability and reusability, although its effectiveness decreases slightly after three successive cycles. Furthermore, a plausible mineralisation pathway was proposed based on the oxidation byproducts determined by chromatographic techniques. Finally, the Microtox® test revealed notable detoxification after treatment which demonstrates high catalyst ability for pyridinium-based ionic liquid degradation by the electro-Fenton process.

Immobilization of powdery calcium silicate hydrate via PVA covalent cross-linking process for phosphorus removal

Calcium silicate hydrate (CSH) is a popular material used for phosphorus removal in recent years. In this work, a novel immobilized material, polyvinyl alcohol-CSH (PVA-CSH), was prepared using a 1:10 weight ratio of CSH powder to 8% PVA solution and then used for phosphorus removal. Samples were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The adsorption mechanism and practical application properties of phosphorus wastewater were studied by sequential batch and continuous flow experiment. The results showed PVA-CSH possessed a porous network structure and an average pore diameter of 24.94 ± 0.11 nm. Furthermore, the CSH functional groups were unaffected by PVA immobilization. Compared with CSH, PVA-CSH did not easily lose CSH after being immobilized by PVA, and the duration of efficient phosphorus removal stage was approximately 20 h longer than that of CSH. In addition, the effluent turbidity of PVA-CSH was 0.11 ± 0.03 NTU during the continuous operation period, which was significantly lower than CSH. In summary, this research study demonstrated the significant potential of PVA-CSH for practical phosphorus removal.

Microalgae cultivation for phenolic compounds removal

Microalgae are promising sustainable and renewable sources of oils that can be used for biodiesel production. In addition, they contain important compounds, such as proteins and pigments, which have large applications in the food and pharmaceutical industries. Combining the production of these valuable products with wastewater treatment renders the cultivation of microalgae very attractive and economically feasible. This review paper presents and discusses the current applications of microalgae cultivation for wastewater treatment, particularly for the removal of phenolic compounds. The effects of cultivation conditions on the rate of contaminants removal and biomass productivity, as well as the chemical composition of microalgae cells are also discussed.

Immobilization of Sphingomonas sp. GY2B in polyvinyl alcohol-alginate-kaolin beads for efficient degradation of phenol against unfavorable environmental factors

In this study, batch experiments were carried out to evaluate the biodegradation of phenol by Sphingomonas sp. GY2B, which were immobilized in polyvinyl alcohol (PVA)-sodium alginate-kaolin beads under different conditions. The optimal degradation performance was achieved by GY2B immobilized in beads containing 1.0% (w/v) of kaolin, 10% (w/v) of PVA, 0.3% (w/v) of sodium alginate, 10% (v/v) of biomass dosage, and exposed to an initial phenol concentration of 100 mg/L. The experimental results indicated that PVA-sodium alginate-kaolin beads can accelerate the degradation rate of phenol by reducing the degradation time and also improve degradation rate. The biodegradation rate of phenol by immobilized cells (16.79 ± 0.81 mg/(L·h)) was significantly higher than that of free cells (11.49 ± 1.29 mg/(L·h)) under the above optimal conditions. GY2B immobilized on beads was more competent than free GY2B in degradation under conditions with high phenol concentrations (up to 300 mg/L) and in strong acidic (pH = 1) and alkaline (pH = 12) environments. Higher phenol concentrations inhibit the biomass and reduce the biodegradation rate, while the lower biodegradation rate at low initial phenol concentrations is attributed to mass transfer limitations. The Haldane inhibitory model was in agreement with the experimental data well, revealing that phenol showed a considerable inhibitory effect on the biodegradation by Sphingomonas sp. GY2B, especially at concentrations higher than 90 mg/L. Intra-particle diffusion model analysis suggests that adsorption of phenol by immobilized beads was controlled by both rapid surface adsorption as well as pore diffusion mechanism. It's worth noting that the presence of 1 mg/L Cr(VI) enhanced the biodegradation of phenol by free cells, while Cr(VI) showed no obvious impact on the removal of phenol by immobilized cells. In addition, immobilized cells were reused 16 times and removed 99.5% phenol, and when stored at 4 °C for 90 days, more than 99% phenol was removed. These results showed that immobilized cells can significantly improve the microbial degradation performance, and protect microorganisms against unfavorable environment. It is implied that PVA -sodium alginate-kaolin beads have great potential to be applied in a practical and economical phenolic wastewater treatment system.

Fluorescein Diacetate Hydrolysis Using the Whole Biofilm as a Sensitive Tool to Evaluate the Physiological State of Immobilized Bacterial Cells

Due to the increasing interest and the use of immobilized biocatalysts in bioremediation studies, there is a need for the development of an assay for quick and reliable measurements of their overall enzymatic activity. Fluorescein diacetate (FDA) hydrolysis is a widely used assay for measuring total enzymatic activity (TEA) in various environmental samples or in monoculture researches. However, standard FDA assays for TEA measurements in immobilized samples include performing an assay on cells detached from the carrier. This causes an error, because it is not possible to release all cells from the carrier without affecting their metabolic activity. In this study, we developed and optimized a procedure for TEA quantification in the whole biofilm formed on the carrier without disturbing it. The optimized method involves pre-incubation of immobilized carrier in phosphate buffer (pH 7.6) on the orbital shaker for 15 min, slow injection of FDA directly into the middle of the immobilized carrier, and incubation on the orbital shaker (130 rpm, 30 °C) for 1 h. Biofilm dry mass was obtained by comparing the dried weight of the immobilized carrier with that of the unimmobilized carrier. The improved protocol provides a simple, quick, and more reliable quantification of TEA during the development of immobilized biocatalysts compared to the original method.

Study on the diffusion coefficients for ammonia nitrogen and nitrite and nitrate in PVA gels

In order to quantify the proliferation of polyvinyl alcohol (PVA) gels in a matrix and optimize the performance of mass transfer, activated carbon (AC) and CaCO₃ were selected as adding materials in this experiment. For the performance of mass transfer, the optimal conditions were analyzed using response surface method (RSM) considering the inter-correlated effects of the amount of AC and CaCO₃. For RSM, 13 trials resulted in a partial cubic polynomial equation, which best predicted the amount of residual debris after homogenization. The results of the study show that the effective diffusion coefficient test device can analysis the diffusion rate nitrogen, nitrite and nitrate within the PVA gels quantitatively; adding appropriate amounts of AC and CaCO₃ in the biological active filter can improve the performance of mass transfer effectively; the maximum effective diffusion coefficient of nitrogen and nitrite and nitrate in the packing were 1.3637 × 10^-9 and 1.0850 × 10^-9 and 1.0199 × 10^-9 m²/s, respectively, at optimal addition amount.

Intensified nitrogen removal in immobilized nitrifier enhanced constructed wetlands with external carbon addition

Nitrogen removal performance response of twelve constructed wetlands (CWs) to immobilized nitrifier pellets and different influent COD/N ratios (chemical oxygen demand: total nitrogen in influent) were investigated via 7-month experiments. Nitrifier was immobilized on a carrier pellet containing 10% polyvinyl alcohol (PVA), 2.0% sodium alginate (SA) and 2.0% calcium chloride (CaCl2). A batch experiment demonstrated that 73% COD and 85% ammonia nitrogen (NH4-N) were degraded using the pellets with immobilized nitrifier cells. In addition, different carbon source supplement strategies were applied to remove the nitrate (NO3-N) transformed from NH4-N. An increase in COD/N ratio led to increasing reduction in NO3-N. Efficient nitrification and denitrification promoted total nitrogen (TN) removal in immobilized nitrifier biofortified constructed wetlands (INB-CWs). The results suggested that immobilized nitrifier pellets combined with high influent COD/N ratios could effectively improve the nitrogen removal performance in CWs.

Treatability of cheese whey for single-cell protein production in nonsterile systems: Part I. Optimal condition for lactic acid fermentation using a microaerobic sequencing batch reactor (microaerobic SBR) with immobilized Lactobacillus plantarum TISTR 2265 and microbial communities

Cheese whey contains a high organic content and causes serious problems if it is released into the environment when untreated. This study aimed to investigate the optimum condition of lactic acid production using the microaerobic sequencing batch reactor (microaerobic SBR) in a nonsterile system. The high production of lactic acid was achieved by immobilized Lactobacillus plantarum TISTR 2265 to generate an acidic pH condition below 4.5 and then to support single-cell protein (SCP) production in the second aerobic sequencing batch reactor (aerobic SBR). A hydraulic retention time (HRT) of 4 days and a whey concentration of 80% feeding gave a high lactic acid yield of 12.58 g/L, chemical oxygen demand (COD) removal of 62.38%, and lactose utilization of 61.54%. The microbial communities in the nonsterile system were dominated by members of lactic acid bacteria, and it was shown that the inoculum remained in the system up to 330 days.

Immobilization of Ochrobactrum tritici As5 on PTFE thin films for arsenite biofiltration

Ochrobactrum tritici SCII24T bacteria is an environmental strain with high capacity to resist to arsenic (As) toxicity, which makes it able to grow in the presence of As(III). The inactivation of the two functional arsenite efflux pumps, ArsB and ACR3_1, resulted in the mutant O. tritici As5 exhibiting a high accumulation of arsenite. This work describes a method for the immobilization of the mutant cells O. tritici As5, on a commercial polymeric net after sputtered modified by the deposition of poly(tetrafluoroethylene) (PTFE) thin films, and demonstrates the capacity of immobilized cells to accumulate arsenic from solutions. Six different set of deposition parameters for PTFE thin films were developed and tested in vitro regarding their ability to immobilize the bacterial cells. The surface that exhibited a mild zeta potential value, hydrophobic characteristics, the lowest surface free energy but with a high polar component and the appropriate ratio of chemical reactive groups allowed cells to proliferate and to grow as a biofilm. These immobilized cells maintained their ability to accumulate the surrounding arsenite, making it a great arsenic biofilter to be used in bioremediation processes.

A pilot-scale study on PVA gel beads based integrated fixed film activated sludge (IFAS) plant for municipal wastewater treatment

In the present study, a pilot-scale reactor incorporating polyvinyl alcohol gel beads as biomass carrier and operating in biological activated sludge mode (a combination of moving bed biofilm reactor (MBBR) and activated sludge) was investigated for the treatment of actual municipal wastewater. The results, during a monitoring period of 4 months, showed effective removal of chemical oxygen demand (COD), biological oxygen demand (BOD) and NH3-N at optimum conditions with 91%, ∼92% and ∼90% removal efficiencies, respectively. Sludge volume index (SVI) values of activated sludge varied in the range of 25-72 mL/g, indicating appreciable settling characteristics. Furthermore, soluble COD and BOD in the effluent of the pilot plant were reduced to levels well below discharge limits of the Punjab Pollution Control Board, India. A culture dependent method was used to enrich and isolate abundant heterotrophic bacteria in activated sludge. In addition to this, 16S rRNA genes analysis was performed to identify diverse dominant bacterial species in suspended and attached biomass. Results revealed that Escherichia coli, Pseudomonas sp. and Nitrosomonas communis played a significant role in biomass carrier, while Acinetobactor sp. were dominant in activated sludge of the pilot plant. Identification of ciliated protozoa populations rendered six species of ciliates in the plant, among which Vorticella was the most dominant.

Immobilization of Acidithiobacillus ferrooxidans on cotton gauze for biological oxidation of ferrous ions in a batch bioreactor

The ability of Acidithiobacillus ferrooxidans to oxidize ferrous iron has been extensively studied in bioleaching to recover metal resources. Although immobilization of A. ferrooxidans is of great importance to achieve high bioleaching performance in practical application, the reported approaches of immobilization of A. ferrooxidans are still limited. This paper is attempting to develop a novel method to immobilize A. ferrooxidans by a less-costly effective carrier from zeolite, activated carbon, and cotton gauze. The results showed that cotton gauze was the most suitable carrier to immobilize A. ferrooxidans cells in comparison with zeolite and activated carbon. Acidithiobacillus ferrooxidans immobilized on the cotton gauze by gravity dehydration could achieve an average ferrous iron oxidation rate of 0.73 g/(L·h). Furthermore, the ferrous iron oxidation ratio attained in the bioreactor under batch operation was maintained above 97.83%. All results indicated that cotton gauze could be an efficient carrier for immobilizing A. ferrooxidans cells for the biooxidation of ferrous ions.

Reactive toughening of polyvinyl alcohol hydrogel and its wastewater treatment performance by immobilization of microorganisms

Toughened PVA hydrogel beads were prepared by co-crosslinking with glycerol, resulting in the formation of a uniform and dense network gel structure, and the tensile property and hydraulic impact resistance were efficiently improved.

Nitrate removal under different ecological remediation measures in Taihu Lake: a 15N mass-balance approach

Ecological remediation is an important measure for the protection of lake water quality in removing nutrients, such as nitrate (NO3 (-)). In this study, four bioremediation processes (bare sediment, immobilized nitrogen cycling bacteria (INCB) added, Elodea nuttallii added, E. nuttallii-INCB assemblage) were operated at a lab to elucidate the effect of macrophyte appearance and INCB addition on NO3 (-) removal and achieve the optimal processes for biomediation. (15) N-NO3 solution was added to microcosms to identify the key nitrogen transformation processes responsible for NO3 (-) removal. Results showed that nitrate removal was significantly enhanced after the addition of INCB and E. nuttallii. In the treatments with INCB added, E. nuttallii added, and INCB and E. nuttallii-INCB assemblage, nitrate removal ratio achieved 94.74, 98.76, and 99.15 %, respectively. In contrast, only 23.47 % added nitrate was removed in the control. Plant uptake and denitrification played an important role in nitrogen removal. The water quality was substantially improved by the addition of INCB and macrophyte that can accelerate denitrification and promote nitrogen assimilation of plants. The results indicated that plant uptake and microbial denitrification were key processes for nitrate removal.

Potential use of low-cost lignocellulosic waste for the removal of direct violet 51 from aqueous solution: equilibrium and breakthrough studies

An efficient biosorbent, sugarcane bagasse was used in native, HCl-treated, and Na-alginate immobilized form for the removal of Direct Violet 51 dye from aqueous solutions. Batch study was performed to optimize important process parameters, such as pH, contact time, biosorbent dose, initial dye concentration, and temperature. Removal of Direct Violet 51 was found to be favorable at pH 2 with the biosorbent dose of 0.05 g. Biosorption process was found to be exothermic in nature. Maximum dye biosorption (39.6 mg/g) was achieved by using HCl-treated biomass. The pseudo-second-order kinetic and Langmuir adsorption isotherm models showed best fitness to the experimental data. Thermodynamic study was also performed to determine the feasibility of biosorption process. Continuous mode study was performed to optimize the important process parameters, such as bed height, flow rate, and initial dye concentration for maximum removal of Direct Violet 51 dye. The higher bed height, low flow rate, and high initial dye concentration were found to be the better conditions for maximum dye biosorption (17.28 mg/g). The linearized form of the Thomas model equation fitted well to the experimental data. The bed depth service time model was used to express the effect of bed height on breakthrough curves. Characterization of biosorbent was performed by scanning electron microscopy and Fourier transform infrared (FT-IR) analysis. The FT-IR spectral analyses showed the involvement of hydroxyl, carbonyl, and carboxyl groups in biosorption process. These results indicated that sugarcane bagasse biomass could be used as a novel biosorbent for the removal of Direct Violet 51 dye from real textile and related industries.

Production of glucose oxidase and catalase by Aspergillus niger free and immobilized in alginate-polyvinyl alcohol beads

The production of glucose oxidase (GOX) and catalase (CAT) by submerged fermentation of the free and immobilized xerophytic fungus Aspergillus niger under equal conditions was compared. To immobilize fungal spores, entrapment in PVA/alginate beads treated with NaNO3/CaCl2 was performed. The yield of immobilization in the beads with a diameter less than 1mm was equal to 100%. Fungus growth and substrate consumption were evaluated in both fermentation systems, demonstrating the lag-period presence in the case of the first cycle of immobilized fungus use. The enzyme production by immobilized fungus reuse was carried out. In these cases, greater enzymatic GOX activity was detected, while CAT activity decreased. SEM micrographs for the beads with immobilized fungus applied in the first and second fermentation cycles were obtained, presenting fungus spreading inside the sphere, spore presence and branching hyphae. Immobilization of A. niger on PVA/alginate beads is effective for GOX and CAT production at least on 2-3 repeated fermentative cycles. Thus, immobilization enables repeated use of microbial cells.