The tremendous increase in human population and rapid decline in freshwater resources have necessitated the development of innovative and sustainable wastewater treatment methods. Africa as a developing continent is currently backing on sustainable solutions to tackle impending water resource crisis brought forward by wastewater‐induced environmental pollution and climate change. Microalgae‐based wastewater treatment systems represent an emerging technology that is capable of meeting the new demand for improved wastewater treatment and climate change mitigation strategies in an environmentally friendly manner. This review critically looks at the opportunities of Africa in harnessing and exploiting the potential of microalgae for the treatment of various wastewaters based on their capacity to recycle nutrients and for concurrent production of valuable biomass and several useful metabolites. Wastewaters, if improperly/completely untreated and discharged, simultaneously pollute freshwater sources and present significant health and environmental risks. Nutrients in wastewater can be utilized and recovered in the form of marketable biomass and products when integrated with the cultivation of microalgae. Several valuable bioproducts can be generated from wastewater‐grown microalgal biomass including biofuels, biofertilizers, animal feed, and various bioactive compounds. This biorefinery approach would most certainly improve wastewater treatment process economics, enhancing the technical feasibility of algae‐based wastewater remediation in African countries.
BackgroundAlthough advantages of immobilization of cells through entrapment in calcium alginate gel beads have already been demonstrated, nevertheless, instability of the beads and the mass transfer limitations remain as the major challenges.ObjectiveThe objective of the present study was to increase the stability, porosity (reduce mass transfer limitation), and cell immobilization capacity of calcium alginate gel beads.Materials and MethodsSodium alginate was mixed with various concentrations of the starch or sugar and gelled in 2% calcium chloride solution. During the gelling and curing, the starch or sugar leached out of the beads and created micro-pores.ResultsMicro-porous beads prepared with starch were more stable and had higher immobilization capacity than those prepared with sugar. After 24 hours of incubation (curing) of the micro-porous beads prepared with starch in calcium alginate, the solubilization time in citrate buffer was 93 minutes compared to 41 minutes for the control beads (without starch). The compressive strength of the micro-porous beads was also higher (5.62 Mpa) than that of the control beads (5.54 Mpa). The optimal starch concentration for cell immobilization was 0.4%. With this starch concentration, the immobilized Bacillus subtilis and Saccharomyces cerevisiae cell densities were 5.6 × 109 and 1.2 × 108 cells/beads, respectively. These values were 36.5% and 74% higher than the value obtained for the control beads. This method of immobilization resulted in more uniform cell distribution.ConclusionAddition of starch to the sodium alginate solution before gelation in calcium chloride solution increased the stability of the beads, increased the immobilized cell density, and resulted in a more uniform cell distribution in the beads.
Food colourants are pigments or dyes added to food to maintain, intensify or add colour to foods. Although, the initial natural sources of food colourants were plants and animals, these sources have become inadequate due to increase in demand. This led to the use of synthetic colourants, some of which have harmful effects on human. Filamentous fungi are good sources of colourants since they are capable of synthesizing large quantities of pigments with different colour sheds. Various genera of filamentous fungi such as Monascus, Penicillium, Talaromyces and Fusarium, have been used for colourant production. Some fungal pigments also have antimicrobial, antioxidant and cholesterol lowering effects. However, some fungi co-produce pigments with mycotoxins such as citrinin. It is therefore necessary to select non-citrinin producing fungal strains or employ culture conditions that limit citrinin biosynthesis. Production of fungal pigments is affected by some nutritional and environmental factors such as carbon and nitrogen sources, pH, temperature, light, moisture, agitation speed and dissolved oxygen concentration. This article highlights major species of pigment-producing filamentous fungi, antimicrobial activities of fungal pigments, and control of pigment and mycotoxin coproduction by fungi. The nutritional and culture parameters that affect pigment production by the fungi are discussed in details.
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