A novel floatable and biodegradable carrier material was made by coating puffed foxtail millet (PFM) with a calcium alginate (CA)-chitosan compound membrane. A diesel oil-degrading marine bacterial strain, Acinetobacter sp. F9, was immobilized on the carrier material. The number of viable F9 cells immobilized on the carrier material reached approximately 5×109CFU/g. This formulation could be stored at −20°C and 4°C for 10weeks without a significant decrease in the number of viable immobilized cells. SEM results showed that the coating membrane was porous and that F9 cells were immobilized on the walls of the pores. The immobilized F9 cells were able to remove more than 90% of the diesel oil by the second day, while free F9 cells did not remove 90% of the diesel oil until the seventh day. GC–MS analysis indicated that the immobilized F9 cells could remove diesel oil more completely than free cells. The immobilization of the F9 cells enhanced their ability to biodegrade diesel oil.

The bacterium Streptomyces sp. is a common genus of the actinomycetes class found in soils and rhizospheres. This bacterium can produce substances with bio-stimulant capacity through the fixation of nitrogen from the air. In this work, the Streptomyces sp. bacterium was immobilized on a ZnMgAl-hydrotalcite clay and embedded in calcium alginate beads to generate a novel bio-composite that functions as a bacterial reservoir and as a controlled release material for bacteria to be used as a bio-fertilizer.The results showed that the novel bacterium-hydrotalcite/alginate bio-composite was very efficient as a bio-fertilizer showing a plant length of 64 mm in only 14 days of growing, which corresponds to an increase of ca. 760% in the lettuce plant growth in comparison with the materials without bacteria. In short, the present results demonstrate that the hydrotalcite and alginate served as an excellent container to keep the bacteria alive, providing nutrients to them and controlling their delivery.

In this work, an aqueous solution containing industrial dyes consisting of methylene blue (MB), and methyl red (MR) was treated with bio-oxidize grape marc entrapped or not in calcium alginate hydrogels. Experiments were carried out in batch, a room temperature using different concentration of adsorbents and dyes. When dyes were evaluated separately, non-immobilized grape marc hydrogel was unable to remove any MR, whereas when the bioadsorbent was immobilized in calcium alginate beads the removal of MR was around 88%. Contrarily, 98% of MB was removed with both, non-entrapped or entrapped grape marc. Regarding binary mixtures, it was observed that the adsorption of MR was not affected by the presence of MB, whereas the adsorption of MB decreased in high extend on non-entrapped grape marc when MR was present.Adsorption conditions were optimized for binary mixtures using a Box-Behnken factorial design, obtaining theoretical equations that allowed to calculate the removal percentage and capacity of calcium alginate-grape marc hydrogel depending on the concentration of dyes (40–100 mg/L), ratio between bioadsorbent and water stream (0.6–1.2) and adsorption time (10–60 min). The equations obtained revealed that grape marc hydrogel is able to remove 100.0–93.3% of MB and 78.72–57.80% of MR in 10 min in the range of dye and bioadsorbent stablished in the experimental design, being the extraction time the less significant variable. Additionally, the kinetic study showed that pseudo-second-order was the model that better explained the bioadsorption process for both dyes in binary mixtures onto grape marc hydrogel.

Calcium alginate beads entrapping a mixture of Fe(0) and nanosized magnetite (NMT) were prepared and evaluated for their capability to reduce nitrate in groundwater. Microscopic and spectroscopic analyses of the beads revealed that clusters of Fe(0)/NMT were entirely embedded in alginate polymer matrix containing a large number of carboxylic and hydroxyl functional groups. The extent of nitrate reduction increased with increasing content of Fe(0) and NMT in the beads, but there was a critical NMT mass limit relative to Fe(0) mass where no further increase in nitrate reduction occurred. The beads showed slower nitrate reduction kinetics than bare Fe(0)/NMT but had comparable capacity in overall nitrate removal. Nitrate reduction increased proportionally with an increase in bead dosage to give a maximum removal of 94.5 % at 37.5 g L⁻¹ in 48 h. Nitrate reduction with 50 g L⁻¹ beads achieved completion of two reduction cycles in 72 h to reduce 2.19 mM nitrate to less than 0.71 mM (10 mg-N L⁻¹) in each cycle. The overall results demonstrated that the beads developed in this study have a potential utility in remediation of nitrate in groundwater.

In the present work, goethite (α-FeO(OH)) impregnated calcium alginate (Cal-Alg-Goe) beads were used to sorb the arsenic from groundwater without disturbing its physicochemical characteristics. Beads were formed by dropwise addition of homogenized mixer of goethite and 4 % sodium alginate solution in 0.2 M CaCl₂solution. Charge, size, and morphology of sorbents were characterized by using various techniques. The results of batch sorption experiments suggest that Cal-Alg-Goe beads are very effective for removal of arsenic in the pH range 3.0 to 7.5, and sorption was more than 95 % in the concentration range of 10–10,000 ng mL⁻¹. Beads were successfully tested for groundwater samples collected from areas having elevated levels of arsenic. Equilibrium sorption follows Langmuir isotherm model, and the maximum arsenic uptake calculated was 30.44 mg g⁻¹. The sorption kinetics could be explained by pseudo-first-order model, and the time needed for equilibrium was 24 h.

Different lignocellulosic substrates consisting of modified barley husk, peanut shells and sawdust were entrapped in calcium alginate beads and used as adsorbents to remove dye compounds from vinasses. For comparative purposes, a biocomposite formulated with humus was also included in this work. Kinetic studies were carried out by applying pseudo-first-order, pseudo-second-order, Chien–Clayton and intraparticle diffusion models, observing a good agreement between theoretical and experimental results when the data were adjusted to pseudo-second-order kinetic model. The results of this study show that lignocellulosic-based biocomposites could be used as an effective and low-cost adsorbent for the removal of dyes from aqueous solutions. Among the heterogeneous biopolymers evaluated, the biocomposite based on barley husk gave the best capacity for dye removal. Moreover, in all cases, it was found that there exists a direct relationship between the capacity of the biocomposites to remove dyes and the percentage of carbon contained in the lignocellulosic residues.

The feasibility of using cell-free extracts of nitrifying sludge to treat synthetic wastewater containing 4-methylphenol and ammonium was examined. Nitrifying cells were broken by sonication and encapsulated into calcium alginate. Cell-free extracts (CFE) of nitrifying sludge oxidized 4-methylphenol threefold faster than whole-cells, but CFE were not able to oxidize ammonium. The CFE encapsulated into calcium alginate (CFEA) displayed partial nitrification and 4-methylphenol oxidation. Five hours was enough to oxidize 100 % of ammonium and 4-methylphenol, at volumetric rates of 20.80 mg N/L h and 42.86 mg C/L h, respectively. It is inferred that an interaction between the CFE and calcium alginate resulted in the protection of the enzymes.

Methylibium petroleiphilum PM1, which is capable of degrading of methyl tert-butyl ether (MTBE), was immobilized in calcium alginate gel beads. Various applications were explored to increase the mechanical strength of these gel beads. The introduction of 0.3 mol/L calcium chloride into the crosslinking solution, 0.002 mol/L calcium chloride into the growth medium, and 0.2% polyethyleneimine (PEI) as chemical crosslinking agent increased the stability of the Ca-alginate gel beads under the operation conditions of the bioreactor. The degradation rates of MTBE by the immobilized cells in the bioreactor system operated in batch and continuous mode , respectively, were compared. A MTBE biodegradation rate of 5.79 mg/L·h was reached for over 400 h (50 batches), and the immobilized cells in the bioreactor removed >96% MTBE during 50 days of operation. Molecular analysis of the PM1 cells revealed that microbial growth occurred predominantly as microcolonies in the outer area of the beads during the first 20 days of operation. The results of this study show that a continuous-mode, fixed-bed bioreactor reactor coupled with PM1-immobilized cells is a promising technology for remediating MTBE-contaminated groundwater.

In this study, microalgae Scenedesmus quadricauda was entrapped in calcium alginate/polyvinyl alcohol composite hydrogel beads by phase-inversion techniques. The composite biosorbents were used for removal of Cu(II) and Cd(II) ions from single component and binary systems using cell-free composite beads as a control system. The effects of the experimental conditions (such as pH, initial metal ions concentrations, temperatures, contact time, and biosorbent concentrations) on Cu(II) and Cd(II) removal efficiencies were studied. The maximum metal ions on the bare and algal biomass immobilized in alginate beads were observed between pH 5.0 and 6.0. The biosorption of metal ions by the bare and composite beads increased as the initial concentration of the metal ions increased in the medium. The biosorption of Cu(II) and Cd(II) on the composite beads appears to be slightly temperature dependent. The maximum biosorptions of metal ions onto microalgae entrapped in composite beads were 0.970 ± 0.028 and 0.682 ± 0.017 mmol/g for Cu(II) and Cd(II) ions, respectively. The equilibrium experimental data for two metallic species fitted well by the Langmuir model. The values of ΔG° at all temperatures are negative, indicating the spontaneous nature of the biosorption process. When the metal ions competed (in the case of the biosorption from their mixture), the amounts of biosorption onto microalgae cells entrapped in beads were 0.857 ± 0.033 mmol/g for Cu(II) and 0.593 ± 0.024 mmol/g for Cd(II). Under noncompetitive and competitive conditions, the affinity order of ions for biosorbents was Cu(II) > Cd(II).

The present investigation was carried out to evaluate the detoxification potential of Pseudomonas fluorescens SM1 strain immobilized in calcium alginate beads for some major toxicants of Indian water bodies. The toxicants selected in this study were benzene hexachloride, mancozeb, 2,4-dichloro-phenoxyacetic acid (pesticides); phenol, catechol, cresol (phenolics); and Cd++, Cr(VI), Cu++ and Ni++ (heavy metals), which were taken as mixtures up to a concentration of roughly twice that usually found in highly polluted sites. Allium cepa phytotoxicity test, Ames fluctuation test and plasmid nicking assay were employed to estimate the phytotoxicity and genotoxicity of the model water containing the test toxicants under different combinations before and after exposure to our bioremediation-cum-detoxification system. The IC50 of the model water containing all the test toxicants, treated with the immobilized SM1 cells, was recorded to be 0.7× compared to 0.06× for the same but untreated water sample, enhancing the IC50 value by 12-fold. The IC25 of the test heavy metal mixture only could enhance from 0.07 to 1.30× (18-fold). The IC25 of the test pesticide mixture alone was increased from 0.07 to 1.71× (24-fold). The IC25 values for the mixture of test phenolics were 0.07× and 2.18× under the pre- and post-treatment conditions, respectively, exhibiting a 31-fold increase. A mutational induction (Mi) corresponding to the 0.5 value in the Ames fluctuation test was used to evaluate the mutagenicity of the test model water containing all the toxicants before and after exposure to the immobilized SM1 cell system. The Mi (0.5) value with the TA98 tester strain was estimated to be 0.08× for the untreated and 0.6× for the treated model water, whereas the same index was calculated to be 0.48× and 1.8×, respectively, for the TA100 strain. A remarkable improvement in the quality of the test water as a result of exposure to this bioremediating system was observed in terms of the absence of the linear form of the plasmid contrary to the visible linearization with the untreated model water. In view of the above findings, it is quite clear that the test of P. fluorescens SM1 strain immobilized in the calcium alginate beads could be used as an efficient system of bioremediation and for water decontamination strategies owing to its remarkable detoxification potential.