A Comparative Study of Improvement of Phycoremediation Using a Consortium of Microalgae in Municipal Wastewater Treatment Pond Systems as an Alternative Solution to Africa’s Sanitation Challenges

The reuse of wastewater has been observed as a viable option to cope with increasing water stress in Africa. The present case studies evaluated the optimization of the process of phycoremediation as an alternative low-cost green treatment technology in two municipality wastewater treatment pond systems that make up the largest number of domestic sewage treatment systems on the African continent. A consortium of specific microalgae (Chlorella vulgaris and Chlorella protothecoides) was used to improve the treatment capacity of domestic wastewater at two operational municipality wastewater pond systems under different environmental conditions in South Africa. Pre- and post-phycoremediation optimization through mass inoculation of a consortium of microalgae, over a period of one year under different environmental conditions, were compared. It was evident that the higher reduction of total phosphates (74.4%) in the effluent, after treatment with a consortium of microalgae at the Motetema pond system, was possibly related to (1) the dominance of the algal taxa C. protothecoides (52%), and to a lesser extent C. vulgaris (36%), (2) more cloudless days, (3) higher air temperature, and (4) a higher domestic wastewater strength. In the case of the Brandwag pond treatment system, the higher reduction of total nitrogen can possibly be related to the dominance of C. vulgaris, different weather conditions, and lower domestic wastewater strength. The nutrient reduction data from the current study clearly presented compelling evidence in terms of the feasibility for use of this technology in developing countries to reduce nutrient loads from domestic wastewater effluent.

A Comparative Analysis of Emissions from a Compression–Ignition Engine Powered by Diesel, Rapeseed Biodiesel, and Biodiesel from Chlorella Protothecoides Biomass Cultured under Different Conditions

The priority faced by energy systems in road transport is to develop and implement clean technologies. These actions are expected to reduce emissions and slow down climate changes. An alternative in this case may be the use of biodiesel produced from microalgae. However, its production and use need to be justified economically and technologically. The main objective of this study was to determine the emissions from an engine powered by biodiesel produced from the bio-oil of Chlorella protothecoides cultured with different methods, i.e., using a pure chemical medium (BD-ABM) and a medium based on the effluents from an anaerobic reactor (BD-AAR). The results obtained were compared to the emissions from engines powered by conventional biodiesel from rapeseed oil (BD-R) and diesel from crude oil (D-CO). The use of effluents as a medium in Chlorella protothecoides culture had no significant effect on the properties of bio-oil nor the composition of FAME. In both cases, octadecatrienoic acid proved to be the major FAME (50% wt/wt), followed by oleic acid (ca. 22%) and octadecadienoic acid (over 15%). The effluents from UASB were found to significantly reduce the biomass growth rate and lipid content of the biomass. The CO2 emissions were comparable for all fuels tested and increased linearly along with an increasing engine load. The use of microalgae biodiesel resulted in a significantly lower CO emission compared to the rapeseed biofuel and contributed to lower NOx emission. Regardless of engine load tested, the HC emission was the highest in the engine powered by diesel. At low engine loads, it was significantly lower when the engine was powered by microalgae biodiesel than by rapeseed biodiesel.

The carbon fixation efficiency in biomass of Cylindrotheca closterium (Ehrenberg) Reimann & J. C. Lewin (Bacillariophyceae) under the conditions of cumulative cultivation

The carbon utilization efficiency is an important characteristic of the cultivated object. Diatom Cylindrotheca closterium (Ehrenberg) Reimann & J. C. Lewin is known to use carbon from aquatic environment quite effectively, as it has many unique carbonic anhydrases and carbon transporters. However, the carbon fixation efficiency for many types of diatoms in culture is still unknown. When calculating the carbon fixation efficiency, researchers use different terminology and methods, and it leads to significant difficulties when comparing the carbon fixation efficiency in the biomass of various types of microalgae. The aims of this study are: 1) to update terms and definitions used in literature on the basis of modern concepts of carbon fixation in microalgae biomass, as well as absorption of inorganic carbon by microalgae culture; 2) to evaluate the carbon fixation efficiency in the biomass of C. closterium diatom under conditions of cumulative cultivation. C. closterium was grown at a temperature of +20 °C on a nutrient medium RS. During the cultivation, the culture was bubbled with air (1.1 L of air per 1 L of culture per minute). The air temperature at the outlet of the suspension was of +19 °C; the maximum productivity of the culture was of 1.254 g·L−1·day−1. According to the results of the CHN analysis, the proportion of carbon in C. closterium dry biomass was of 23 %. Under the conditions of cumulative cultivation in C. closterium, the carbon fixation efficiency in biomass was of 90 %. Compared with other algae species, C. closterium is characterized by a rather high CO2 fixation efficiency. For example, in green microalga Chlorella protothecoides and Ch. vulgaris, the CO2 fixation efficiency was of 20 % and 55.3 %, respectively; in cyanobacteria Spirulina sp. – of 38 %; in red microalgae Porphyridium purpureum – of 69 %. It was observed that to ensure an increase of 1 g of C. closterium dry biomass per day at a temperature of +19 °C, a minimum of 0.46 L of CO2, or 1132 L of air, should be consumed. Possibly, it is high carbon fixation efficiency, as well as low carbon fraction in C. closterium biomass, that explains the high production indices of this species. Under equal conditions of cultivation in terms of light and carbon availability, the productivity of C. closterium can exceed the productivity of other types of microalgae by 5–10 times. So, while Spirulina sp. productivity reaches 0.2 g·L−1·day−1, C. closterium productivity is of 1.254 g·L−1·day−1.