Removal of sediment and bacteria from water using green chemistry

Arabinoxylan and rhamnogalacturonan mucilage: Outgoing and potential trends of pharmaceutical, environmental, and medicinal merits

Demand for safe, environmentally friendly and minimally processed food additives with intrinsic technological (stabilizing, texturizing, structuring) and functional potential is already on the rise. There are actually several natural excipients eligible for pharmaceutical formulation. Mucilage, as a class constitutes arabinoxylan and rhamnogalacturonan-based biomolecules used in the pharmaceutical, environmental as well as phytoremediation industries owing to its particular structure and properties. These compounds are widely used in pharmaceutical, food and cosmetics, as well as, in agriculture, paper industries. This review emphasizes mucilage valuable applications in the pharmaceutical and industrial fields. In this context, much focus has recently been given to the valorization of mucilage as an ingredient for food or nutraceutical applications. Furthermore, different optimization and extraction techniques are presented to develop better utilization and/or enhanced yield of mucilage. The highlighted mucilage extraction methods warrant assessing up-scale processes to encourage for its industrial applications. The current article capitalizes on cutting-edge characteristics of mucilage and posing for other possible innovative applications in non-food industries. Here, the first holistic overview of mucilage with regards to its physicochemical properties and potential novel usages is presented.

Interfacial Phenomena of Natural Dispersants for Crude Oil Spills

A natural surfactant was studied to simulate the dispersion process of crude oil in water. The interfacial phenomena of this natural dispersant was compared with a commercially available chemical dispersant, COREXIT EC9500A. This functional surfactant was extracted from the mucilage of the Opuntia ficus-indica cactus species. The evaluation to determine the efficacy to disperse crude oil of the cactus-based mucilage extract (nongelling extract, NE) was based on characterizing surface and interfacial tension, dispersion efficiency, mixing effects, salinity effects, stability, and droplets size distributions. We found that surface tension values follow a linear relationship with respect to the natural logarithm of the concentrations of NE. The application of NE in the water phase led to decreasing oil/water interfacial tensions. Surface tension tests were also used to quantify the effect of oil-in-water (O/W) emulsion ratios once either natural or commercialized dispersants were added. A key finding of our work is that the surface tension between typical 6% and 3% v/v O/W emulsions was significantly reduced with the addition of discrete amounts of NE. This result indicated that the dynamic balance between O/W and water-in-oil (W/O) emulsions was thermodynamically more stable toward O/W emulsion states with NE. We also found that O/W emulsions with higher dispersion effectiveness were formed for both 10 and 35 practical salinity units, as the dispersant to oil ratios increased, with a significant correlation to the mixing energy. We observed that the O/W emulsions with natural dispersants had a significantly smaller weighted average diameter compared to those with COREXIT EC9500A. Such a phenomenon can be explained by understanding intermolecular interactions due to the structure and type of dispersant. In conclusion, cactus-based mucilage extracts could be used as environmentally benign dispersants and, therefore, reduce negative social perceptions of the application of dispersants to clean up spilled oil.

Environmental evaluation of flocculation efficiency in the separation of the microalgal biomass of Scenedesmus sp. cultivated in full-scale photobioreactors

In this paper the environmental evaluation of the separation process of the microalgal biomass Scenedesmus sp. from full-scale photobioreactors was carried out at the Research and Development Nucleus for Sustainable Energy (NPDEAS), with different flocculants (iron sulfate - FeCl₃, sodium hydroxide - NaOH, calcium hydroxide - Ca(OH)² and aluminum sulphate Al₂(SO₄)₃, by means of the life cycle assessment (LCA) methodology, using the SimaPro 7.3 software. Furthermore, the flocculation efficiency by means of optical density (OD) was also evaluated. The results indicated that FeCl₃ and Al₂(SO₄)₃ were highly effective for the recovery of microalgal biomass, greater than 95%. Though, when FeCl₃ was used, there was an immediate change in color to the biomass after the orange colored salt was added, typical with the presence of iron, which may compromise the biomass use according to its purpose and Al₂(SO₄)₃ is associated with the occurrence of Alzheimer's disease, restricting the application of biomass recovered through this process for nutritional purposes, for example. Therefore, it was observed that sodium hydroxide is an efficient flocculant, promoting recovery around 93.5% for the ideal concentration of 144 mg per liter. It had the best environmental profile among the compared flocculant agents, since it did not cause visible changes in the biomass or compromise its use and had less impact in relation to acidification, eutrophication, global warming and human toxicity, among others. Thus, the results indicate that it is important to consider both flocculation efficiency aspects and environmental impacts to identify the best flocculants on an industrial scale, to optimize the process, with lower amount of flocculant and obtain the maximum biomass recovery and decrease the impact on the extraction, production, treatment and reuse of these chemical compounds to the environment. However, more studies are needed in order to evaluate energy efficiency of the process coupled with other microalgal biomass recovery technologies. In addition, studies with natural flocculants, other polymers and changes in pH are also needed, as these are produced in a more sustainable way than synthetic organic polymers and have the potential to generate a biomass free of undesirable contaminants.

Combining Ferric Salt and Cactus Mucilage for Arsenic Removal from Water

New methods to remediate arsenic-contaminated water continue to be studied, particularly to fill the need for accessible methods that can significantly impact developing communities. A combination of cactus mucilage and ferric (Fe(III)) salt was investigated as a flocculation-coagulation system to remove arsenic (As) from water. As(V) solutions, ferric nitrate, and mucilage suspensions were mixed and left to stand for various periods of time. Visual and SEM observations confirmed the flocculation action of the mucilage as visible flocs formed and settled to the bottom of the tubes within 3 min. The colloidal suspensions without mucilage were stable for up to 1 week. Sample aliquots were tested for dissolved and total arsenic by ICP-MS and HGAFS. Mucilage treatment improved As removal (over Fe(III)-only treatment); the system removed 75-96% As in 30 min. At neutral pH, removal was dependent on Fe(III) and mucilage concentration and the age of the Fe(III) solution. The process is fast, achieving maximum removal in 30 min, with the majority of As removed in 10-15 min. Standard jar tests with 1000 μg/L As(III) showed that arsenic removal and settling rates were pH-dependent; As removal was between 52% (high pH) and 66% (low pH).

Harvesting microalgae grown on wastewater

The costs and life cycle impacts of microalgae harvesting for biofuel production were investigated. Algae were grown in semi-continuous culture in pilot-scale photobioreactors under natural light with anaerobic digester centrate as the feed source. Algae suspensions were collected and the optimal coagulant dosages for metal salts (alum, ferric chloride), cationic polymer (Zetag 8819), anionic polymer (E-38) and natural coagulants (Moringa Oleifera and Opuntia ficus-indica cactus) were determined using jar tests. The relative dewaterability of the algae cake was estimated by centrifugation. Alum, ferric chloride and cationic polymer could all achieve >91% algae recovery at optimal dosages. Life cycle assessment (LCA) and cost analysis results revealed that cationic polymer had the lowest cost but the highest environmental impacts, while ferric chloride had the highest cost and lowest environmental impacts. Based on the LCA results, belt presses are the recommended algae dewatering technology prior to oil extraction.

Removing heavy metals in water: the interaction of cactus mucilage and arsenate (As (V))

High concentrations of arsenic in groundwater continue to present health threats to millions of consumers worldwide. Particularly, affected communities in the developing world need accessible technologies for arsenic removal from drinking water. We explore the application of cactus mucilage, pectic polysaccharide extracts from Opuntia ficus-indica for arsenic removal. Synthetic arsenate (As (V)) solutions were treated with two extracts, a gelling extract (GE) and a nongelling extract (NE) in batch trials. The arsenic concentration at the air-water interface was measured after equilibration. The GE and NE treated solutions showed on average 14% and 9% increases in arsenic concentration at the air-water interface respectively indicating that the mucilage bonded and transported the arsenic to the air-water interface. FTIR studies showed that the -CO groups (carboxyl and carbonyl groups) and -OH (hydroxyl) functional groups of the mucilage were involved in the interaction with the arsenate. Mucilage activity was greater in weakly basic (pH 9) and weakly acidic (pH 5.5) pH. This interaction can be optimized and harnessed for the removal of arsenic from drinking water. This work breaks the ground for the application of natural pectic materials to the removal of anionic metallic species from water.

Surface engineered magnetic nanoparticles for removal of toxic metal ions and bacterial pathogens

Surface engineered magnetic nanoparticles (Fe(3)O(4)) were synthesized by facile soft-chemical approaches. XRD and TEM analyses reveal the formation of single-phase Fe(3)O(4) inverse spinel nanostructures. The functionalization of Fe(3)O(4) nanoparticles with carboxyl (succinic acid), amine (ethylenediamine) and thiol (2,3-dimercaptosuccinic acid) were evident from FTIR spectra, elemental analysis and zeta-potential measurements. From TEM micrographs, it has been observed that nanoparticles of average sizes about 10 and 6 nm are formed in carboxyl and thiol functionalized Fe(3)O(4), respectively. However, each amine functionalized Fe(3)O(4) is of size ~40 nm comprising numerous nanoparticles of average diameter 6 nm. These nanoparticles show superparamagnetic behavior at room temperature with strong field dependent magnetic responsivity. We have explored the efficiency of these nanoparticles for removal of toxic metal ions (Cr(3+), Co(2+), Ni(2+), Cu(2+), Cd(2+), Pb(2+) and As(3+)) and bacterial pathogens (Escherichia coli) from water. Depending upon the surface functionality (COOH, NH(2) or SH), magnetic nanoadsorbents capture metal ions either by forming chelate complexes or ion exchange process or electrostatic interaction. It has been observed that the capture efficiency of bacteria is strongly dependent on the concentration of nanoadsorbents and their inoculation time. Furthermore, these nanoadsorbents can be used as highly efficient separable and reusable materials for removal of toxic metal ions.