Simultaneous flue gas bioremediation and reduction of microalgal biomass production costs.

A flue gas originating from a municipal waste incinerator was used as a source of CO(2) for the cultivation of the microalga Chlorella vulgaris, in order to decrease the biomass production costs and to bioremediate CO(2) simultaneously. The utilization of the flue gas containing 10-13% (v/v) CO(2) and 8-10% (v/v) O(2) for the photobioreactor agitation and CO(2) supply was proven to be convenient. The growth rate of algal cultures on the flue gas was even higher when compared with the control culture supplied by a mixture of pure CO(2) and air (11% (v/v) CO(2)). Correspondingly, the CO(2) fixation rate was also higher when using the flue gas (4.4 g CO(2) l(-1) 24 h(-1)) than using the control gas (3.0 g CO(2) l(-1) 24 h(-1)). The toxicological analysis of the biomass produced using untreated flue gas showed only a slight excess of mercury while all the other compounds (other heavy metals, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and dibenzofurans, and polychlorinated biphenyls) were below the limits required by the European Union foodstuff legislation. Fortunately, extending the flue gas treatment prior to the cultivation unit by a simple granulated activated carbon column led to an efficient absorption of gaseous mercury and to the algal biomass composition compliant with all the foodstuff legislation requirements.

Influence of processing parameters on disintegration of Chlorella cells in various types of homogenizers.

The following bead mills used for disruption of the microalga Chlorella cells were tested: (1) Dyno-Mill ECM-Pilot, grinding chamber volume 1.5 L; KDL-Pilot A, chamber volume 1.4 L; KD 20 S, chamber volume 18.3 L; KD 25 S, chamber volume 26 L of Willy A. Bachofen, Basel, Switzerland, (2) LabStar LS 1, chamber volume 0.6 L of Netzsch, Selb, Germany, (3) MS 18, chamber volume 1.1 L of FrymaKoruma, Neuenburg, Germany. Amount of disrupted cells decreased with increasing Chlorella suspension feed rate and increased up to about 85% of the beads volume in the grinding chamber of the homogenizers. It also increased with agitator speed and number of passes of the algae suspension through the chamber. The optimum beads diameter was 0.3-0.5 mm in the homogenizers Dyno-Mill and LabStar LS 1 and 0.5-0.7 mm in the homogenizer MS 18. While the degree of the cell disruption decreased with increasing cell density in Dyno-Mill and LabStar, the cell disruption in the MS 18 increased. Depending on processing parameters, more than 90% of algae cells were disrupted by passing through the bead mills and bacteria count in algae suspension was reduced to about two orders.

Effect of temperature and pH on absorption of carbon dioxide by a free level of mixed solutions of some buffers.

The rate of absorption of carbon dioxide by solutions of NaHCO3, KH2PO4, hydrogencarbonate, phosphate and borate buffers at 20, 30 and 40 degrees C was determined manometrically. The absorption rate increases for all buffers tested with increasing pH. The CO2 absorption rate by KH2PO4 and by the phosphate buffer at low pH is lower than that of water. For other buffers tested it is equal to or higher than that of water, especially at higher temperatures.

Buffering capacity of the chief components of nutritive media for algae.

The buffering capacity of solutions of KH2PO4 and NaHCO3 increases with their concentration, the behaviour being describable by mathematical expressions. Solutions of KH2PO4 prepared from tap water exhibit a buffering capacity higher by an order of magnitude than those prepared from distilled water. However, there is no difference between the buffering capacities of solutions of NaHCO3 prepared from tap and distilled water. Urea and NH4NO3 have almost no effect on the buffering capacities of solutions.

Effect of dilution rate, pH and temperature on the growth of Chlorella kessleri in a continuous autotrophic culture.

In a culture of Chlorella kessleri illuminated with a sodium vapour lamp at 33 degrees C and pH 6.5 the maximum rate of biomass production was 4.5 g L-1 d-1. Of the total volume of 3.6 L or the suspension 2.5 L were placed between two glass concentric cylinders surrounding the tube. Examples of the course of specific growth rate mu in the transient state following jump changes in the dilution rate, pH and temperature are presented. After a jump change of pH or temperature of the suspension maximal and minimal values, respectively, of mu are observed.

Removal of biogenic elements, polychlorinated diphenyls and heavy metals during the biological final treatment of waste-waters.

Algae were cultivated in the effluents from a treatment plant processing communal sewage and waste-water from a large-scale hoggery. The content of nitrogen. phosphorus and also COD and BOD were estimated in the effluent before and after cultivation of algae. It was found that the removal of nitrogen and phosphorus by Chlamydomonas geitleri from the effluent was optimal at highest at the high effluent concentrations while the purification efficiency in relation to PCD content depends on algae used.

Optimization of costs per unit of microbial biomass produced in a batch culture.

The time course of costs per unit mass of produced biomass is calculated under the assumption that the production costs during the cultivation of microorganisms are proportional to the cultivation period. The costs are shown to attain a minimum during the cultivation. The cultivation period corresponding to this minimum is calculated in the case when the time dependence of microbial concentration in a culture can be expressed explicitly.

Effect of the nonilluminated part of suspension on biomass production in an algal reactor.

The production of algal biomass in the illuminated and nonilluminated part of the suspension in an algal reactor was analyzed with regard to the biological inertia of the algae. The calculations indicate a considerable effect of nonilluminated part of the reactor on algal biomass production. The intensity of suspension stirring affects biomass production only slightly.

Semicontinuous cultivation of autotrophic algae.

Mathematical expressions were derived for the dilution rate and concentration of algae determining the maximum biomass production in a semicontinuous algal culture.

Fatty acids in green algae cultivated on a pilot-plant scale.

Fatty acids from Chlorella vulgaris, Scenedesmus obliquus var. acutus and from a mixed culture of the two strains, Melnik, were converted to methyl esters, separated by gas chromatography, and identified by means of standards. The spectrum of fatty acids included both saturated and unsaturated acids (with odd and even numbers of carbon atoms) from C12 to C22. Fatty acids C16:0, C18:0 and C20:3 were the major components in all cultures. Pure strains differed from the mixed culture in the production of C18:1, C12:0 and C19:2 acids; the first of these was present in higher amounts in pure cultures only, the latter two being found in the mixed culture. The level of lipids was lower as compared to the literature data and their extractability was affected by the manner of preparation of algae and extraction conditions.

Calculation of biomass production in algal suspension layer illuminated from two sides.

Equations were derived for biomass production in optically dense algal suspension under the limit conditions of low- and very high-intensity stirring. A formula was obtained for the concentration of algae which gives maximum production at a given intake of radiation energy.