Dragoljub Bilanovic

Flocculation of microalgae with cationic polymers: effects of medium salinity

Chemical flocculation is considered to be a reliable and economical means for the harvesting of microalgae. Organic cationic polymers can induce efficient flocculation of freswater microalgae at low dosages (between 1 and 10 mg litre−1). However, the high salinity of the marine environment was found to inhibit flocculation with polyelectrolytes. This phenomenon was studied with three different cationic polymers. Inhibition of flocculation was diminished at reached salinity levels, and effective flocculation was attained at salinity levels lower than 5 g litre−1. The reduced effectiveness of cationic polymers to induce microalgae flocculation in sea and brackish water is primarily attributed to the effect of medium ionic strength on the configuration and dimension of the polymer, as indicated by changes in the intrinsic viscosity. At high ionic strength, the polymer shrinks to its smallest dimensions, and fails to bridge between algal cells.

Flocculation of microalgae in brackish and sea waters

Flocculation is an essential step in the concentration and harvesting of microalgae from aquatic media. Salinity of brackish water and sea water requires high flocculant dosages and renders flocculation less effective than in freshwater algal media. Experiments with the marine microalgae Isochrysis galbana and Chlorella stigmatophora showed that effective alum or ferric chloride flocculation was obtained only with dosages which are 5 to 10 times higher than the dosages required for the flocculation of freshwater microalgae. The flocculant dosages required for removing over 90% of the algae from suspensions were found to increase linearly with salinity as expressed in ionic strength. High salinity was found to inhibit flocculation with polyelectrolytes which are quite effective in freshwater algae flocculation. This inhibition was diminished at reduced salinity levels and effective flocculation was attained at salinity levels of 5 g/liter and below, which is typical of desert brackish water. Two methods were found to induce flocculation in sea water: (a) combining polyelectrolytes with inorganic flocculants such as ferric chloride or alum, and (b) ozone oxidation pretreatment followed by flocculation with inorganic flocculants.

Xanthan fermentation of citrus waste

Abstract Four different fractions of citrus waste were compared as substrates for xanthan fermentation: whole citrus waste, pectic, hemicellulosic and cellulosic extracts. The whole waste was found to be a good substitute for glucose media for xanthan production. Xanthomonas campestris utilized both simple and complex carbon compounds originating from citrus wastes. Substrate utilization in the medium based on pectin extract was similar to that in the medium based on a whole citrus waste and the pectic extract yielded the same amount of xanthan as the whole waste. This indicated that watersoluble substances in citrus waste such as pectins, organic acids and simple carbohydrates were readily converted into xanthan and that they were the main contributor to xanthan production from the whole waste. The biodegradabilities of the hemicellulose and cellulose extracts were found to be much lower than that of the pectic extract.

The effect of various citrus waste fractions on xanthan fermentation

Abstract Four different media of citrus waste origin were compared as substrates for xanthan fermentation: whole citrus waste, pectic, hemicellulosic and cellulosic extracts. It was found that Xanthomonas campestris utilized in parallel both simple and complex carbon compounds originating from citrus wastes. The substrate utilization rate in the medium based on pectic extract was similar to that in the medium based on whole citrus waste. In addition, pectic extract of citrus waste yielded the same amount of xanthan as whole citrus waste. This indicates that water soluble substances in citrus waste such as pectins, organic acids and simple carbohydrates are readily converted into xanthan and that their contribution to xanthan production is higher than that of the other constituents of citrus waste. The biodegradability of the hemicellulose and cellulose extracts of citrus waste was found to be much lower than that of the pectic extract. Substrate utilization and its conversion to xanthan in the hemicellulosic extract was 36% lower, and in the cellulosic extract 60% lower, than those in the whole citrus waste.

Co-cultivation of microalgae and nitrifiers for higher biomass production and better carbon capture

The aim of this work was to study co-cultivation of nitrifiers with microalgae as a non-intrusive technique for selective removal of oxygen generated by microalgae. Biomass concentration was, at least, 23% higher in mixed-cultures where nitrifiers kept the dissolved oxygen concentration below 9.0μLL(-1) than in control Chlorella vulgaris axenic-cultures where the concentration of dissolved oxygen was higher than 10.0μLL(-1). This approach to eliminating oxygen inhibition of microalgal growth could become the basis for the development of advanced microalgae reactors for removal of CO2 from the atmosphere, and concentrated CO2 streams. CO2 sequestration would become a chemically and geologically safer and environmentally more sound technology provided it uses microalgal, or other biomass, instead of CO2, for carbon storage.

Preparation of biodegradable xanthan-glycerol hydrogel, foam, film, aerogel and xerogel at room temperature.

Polymers, hence hydrogels, pollute waters and soils accelerating environmental degradation. Environmentally benign hydrogels were made in water from biodegradable xanthan (X) and glycerol (G) at 22.5±2.5°C. Molar ratio [G]/[X]<3.0 was used to maximize crosslinking by mono-glycerol instead by poly-glycerol. XG-hydrogels were transformed into: XG-foams, XG-films, and XG-aerogel. Anionic character of XG-materials changes with changing [G]/[X] ratio. XG-films made from XG-hydrogels absorb up to 40 times more water than XG-films made from XG-foams. The films made from XG-foams and HCl do not dissolve in water during 48h. Making XG-materials is a no-waste process which decreases pollution, eliminates waste disposal costs, and minimizes energy expenses. XG-materials are suitable for both industrial and environmental applications including slow release and concentration of cations. XG-materials, made of xanthan, microbial polysaccharide, could also be used in applications targeting populations that do not consume meat or meat based products.

Carbon Footprint – An Environmental Sustainability Indicator of Large Scale CO2 Sequestration

To slow down the degeneration of the planetary life support system atmospheric CO2 concentration must be reduced. There are no insignificant CO2 emissions since all CO2 ends-up in a single atmosphere of finite size. To minimize anthropogenic CO2 emissions and to bring its atmospheric concentration to 320 ppm, the world economies should replace fossil fuels with alternative energy sources and construct large facilities for reduction of atmospheric CO2.

TiO2 P-25 anatase rapid precipitation from water by use of struvite formation.

UV(360nm) irradiation of TiO(2) P-25 nanoparticle in water suspension is used for photocatalytic mineralization of pollutants or inactivation of microorganisms. Removal of TiO(2) particles from large volumes of water following photocatalytic process is problematic due to their nano-size. So far no chemical methods are available for TiO(2) rapid precipitation while filtration or centrifugation is not feasible because of high cost and limited performance. In the present study TiO(2) was rapidly precipitated from water suspension by formation of the mineral struvite. Addition of Mg, P, and NH(4)(+) at stochiometric rates of 1:1:1 at pH>8.3 resulted in TiO(2) entrapment into struvite formed flocs and rapid precipitation. Struvite sludge formed and precipitated was observed under HSEM revealing TiO(2) entrapment into struvite mineral.