Recent trends in Ni(II) sorption from aqueous solutions using natural materials

The use of materials of natural origin for the adsorption of heavy metal ions from aqueous solutions has gained attention in recent years among the scientific community. This is explained by the fact that nickel compounds, due to severe health consequences, are considered to be among the most dangerous to the environment. This article reviews the results of studies on the use of biosorbents for purification of aqueous solutions from nickel ions, and then attempts to classify them according to their origin. The characteristics of materials and their sorption capacity have been compared, and the removal mechanisms identified of which chemisorption and ion exchange are considered to be the most common. From the analyses, a major trend is the use of biomass; however, biosorbents from other groups also continue to attract the interest of researchers. Conducting laboratory studies can help select materials with high efficiency. The highest sorption capacity values for the materials in each group were: for waste products 56 mg Ni·g−1 (olive stone), for peat 61 mg Ni·g−1, for miscellaneous 225 mg Ni·g−1 (microbial flocculant GA1), for biomass 286 mg Ni·g−1 (Plantanus orientalis bark) and for composites/modified materials calcinated eggshells 769 mg Ni·g−1 (calcinated eggshells). However, for some materials the sorption phenomenon may be accompanied by precipitation in the presence of hydroxides, which significantly affects the sorption capacity achieved. There is a need to transfer these experiments to an industrial scale so as to verify their applicability. In such industrial scale applications, attention should be paid not only to the effectiveness of the material, but also to its availability, price, and ease of use, as well as the effect of the biosorbent in terms of changing the quality parameters of the aquatic environment.

Biosafety and Removal Potential of Pollutants in Wastewater by the Microbial Flocculant from Marine Bacterium Obtained from Umlalazi Catchment, RSA

Bioflocculants have been reported to be successfully used in the removal of pollutants and dye decolourization from wastewater as they (pollutants) have negative impact on both humans and aquatic life if not properly treated. Thus, the potential removal rate of a microbial flocculant produced by the marine bacterial strain of Bacillus safensis KX94275.1 from uMlalazi estuary, Mthunzini area, KZN for pollutants from wastewater samples and dyes from different dye solution was investigated. B. safensis produced a non-toxic microbial flocculant showed margin of safety in both breast cancer cells and normal cells with 87% and 96% cell survival after treatment with maximum dosage of bioflocculant solution of 100 µg/µL, respectively. Functional groups such as amino, carboxylic and hydroxyl group were revealed with FT-IR spectrum to be possessed by the microbial flocculant produced. Above 65% of microbial flocculant was attained when the flocculant was subjection to 700 oC using the thermogravimetric analyser. A produced bioflocculant was aqua-solvable and have no inhibitory effect in bacteria tested. This heat-stable and cation-dependent (Ba2+) bioflocculant removed more than 85% dye from different dye solutions, such as basic fuchsine (93%), congo red (87%), crystal violet (90%) and methylene blue (93%), using 0.4 mg/mL optimum dosage concentration at neutral pH. This wide pH (3-12) tolerant bioflocculant showed improvement on both domestic and coal mine wastewaters for the removal of biochemical oxygen demand with 66% and 99%, chemical oxygen demand with 48% and 93%, phosphate with 61% and 59%, total nitrogen with 69% and 68% and sulphide with 71% and 83% removal rate, respectively, and flocculation rate of 91% (domestic) and 95% (coal mine) wastewater. Thus, the application of the bioflocculant on wastewater treatment indicated the tremendous prospective in replacing risky traditional flocculating agents frequently utilized for purification of wastewater.

Recent advances and perspectives in efforts to reduce the production and application cost of microbial flocculants

Microbial flocculants are macromolecular substances produced by microorganisms. Due to its non-toxic, harmless, and biodegradable advantages, microbial flocculants have been widely used in various industrial fields, such as wastewater treatment, microalgae harvest, activated sludge dewatering, heavy metal ion adsorption, and nanoparticle synthesis, especially in the post-treatment process of fermentation with high safety requirement. However, compared with the traditional inorganic flocculants and organic polymeric flocculants, the high production cost is the main bottleneck that restricts the large-scale production and application of microbial flocculants. To reduce the production cost of microbial flocculant, a series of efforts have been carried out and some exciting research progresses have been achieved. This paper summarized the research advances in the last decade, including the screening of high-yield strains and the construction of genetically engineered strains, search of cheap alternative medium, the extraction and preservation methods, microbial flocculants production as an incidental product of other biological processes, combined use of traditional flocculant and microbial flocculant, and the production of microbial flocculant promoted by inducer. Moreover, this paper prospects the future research directions to further reduce the production cost of microbial flocculants, thereby promoting the industrial production and large-scale application of microbial flocculants.

Flocculation Efficiency and Mechanism of Carbamazepine by Microbial Flocculant Extracted from Klebsiella pneumoniae J1

The microbial flocculant (MFX) extracted from Klebsiella pneumoniae J1 was used to remove carbamazepine in prepared wastewater and domestic sewage. The influence factors and flocculation mechanism were studied. The optimal carbamazepine removal conditions for MFX were pH of 7-8, 7 mL of flocculant, 0.1 mL of coagulant, and 35°C, and the removal rate reached 81.75%. MFX was efficient in the removal of carbamazepine in both domestic sewage (75.03%) and secondary sedimentation tank effluent (69.76%). The pseudo-first-order kinetic equation fitted the adsorption process better than the pseudo-second-order kinetic equation, which suggested that the adsorption was not pure chemical adsorption. The analysis of floc size suggested that the repulsive force between carbamazepine and MFX was weakened under alkalescent conditions, which can help the growth and coherence of flocs and increase the carbamazepine removal efficiency. Enough dosage of MFX can generate larger flocs, but excessive dosage of MFX will decrease the carbamazepine removal rate because of increase in electrostatic repulsion. The analysis of 3D-EEM and FTIR suggested that hydroxyl, amino, and carboxyl in MFX played an important role in the removal of carbamazepine. As an eco-friendly and highly efficient microbial flocculant, MFX has potential for practical applications in carbamazepine removal.

Research on the coagulant aid effects of modified diatomite on coal microbial flocculation

Diatomite was modified by chitosan to prepare modified diatomite, and the modified diatomite in an optimized ratio was utilized in coal bio-flocculation. The interaction behavior and flocculation mechanism of modified diatomite on coal slurry water were investigated by single factor experiments, infrared spectroscopy, Brunauer-Emmett-Teller (BET) measurements, and zeta potential measurements. The single factor experiments showed that when the amount of microbial flocculant added was 1.5 ml, the temperature of coal slurry water was 39 °C, the pH was 5, and the amount of modified diatomite was 0.2 g, after 30 min of sedimentation, the flocculation transmittance of the coal slurry water reached 84.3%. The infrared spectra showed that the -NH2 and -OH of the chitosan molecule had a polar interaction with the Si-OH bond in diatomite. The BET measurements showed that the specific surface area of diatomite was not a decisive factor affecting the flocculation effect. Zeta potential measurements indicated that the amino protonation of chitosan increased the isoelectric point (IEP) of modified diatomite. These results showed that modified diatomite has a good effect on coal bio-flocculation.

Implications for industrial application of bioflocculant demand alternatives to conventional media: waste as a substitute

The biodegradability and safety of the bioflocculants make them a potential alternative to non-biodegradable chemical flocculants for wastewater treatment. However, low yield and production cost has been reported to be the limiting factor for large scale bioflocculant production. Although the utilization of cheap nutrient sources is generally appealing for large scale bioproduct production, exploration to meet the demand for them is still low. Although much progress has been achieved at laboratory scale, Industrial production and application of bioflocculant is yet to be viable due to cost of the production medium and low yield. Thus, the prospects of bioflocculant application as an alternative to chemical flocculants is linked to evaluation and utilization of cheap alternative and renewable nutrient sources. This review evaluates the latest literature on the utilization of waste/wastewater as an alternative substitute for conventional expensive nutrient sources. It focuses on the mechanisms and metabolic pathways involved in microbial flocculant synthesis, culture conditions and nutrient requirements for bioflocculant production, pre-treatment, and also optimization of waste substrate for bioflocculant synthesis and bioflocculant production from waste and their efficiencies. Utilization of wastes as a microbial nutrient source drastically reduces the cost of bioflocculant production and increases the appeal of bioflocculant as a cost-effective alternative to chemical flocculants.