The dynamics of algal growth, substrate consumption, oxygen production/consumption in batch bench-scale completely~mixed aquatic ecosystems.
Ngcakani, Zolile Thando
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Ecosystems composed of algae, bacteria, and other biota occur widely in lakes, rivers, impoundments, estuaries and waste stabilisation ponds. They enhance under favourable conditions, the self-purification capacity of the water bodies in which they occur, by degrading and assimilating organic and nutrient inputs. Algae and bacteria perform critical functions, which may be beneficial or harmful to water quality, in several areas of water resources management and water pollution control. A proper understanding of the complex and interrelated physic~1t chemical, biological and environmental factors affecting the algal photosynthetic oxygenation of the water bodi.esand the bacterial degradation of organic inputs is necessary for the development of a picture of the biological reactor environment .r j as a predictable functional ecosystem. A study of the dynamic8 of algal growth, substrate consumption, oxygen production!con- sumption was made in model, batch, completely mixed reactors. Two types of batch reactors designed to operate as completely mixed closed systems were used during the.study. An environment cha~acterised by constant light intensity, similar , mixing conditions and reasonably constant temperatures was chosen for the study. The growth reactors were artificially "". UJ.y'minate~. Ni•neexperiments were performed using two types of synthetic sewage as 'growth mediums. All the experiments maintained aerobic conditions except experiment six. Operation of the biomass growth reactors _as monitored by analysing samples for dissolved oxygen, chemical oxygen demand, chlorophyll, xi bacterial numbers and carbon dioxide. Measurements of hydrogen concentration, temperature and microscopic examinations tor identification ot algae species in the samples were carried out. The behaviour of the studied completely mixed biomass growth reactors showed that the relationships between aerobic bacterial growth, substrate consumption, algal growth, oxygen production/consuaption may be characterised as coupled and inter-dependent in nature. The reaction sequencos of aerobic bacterial growth)8ubstrate-consumption-oxygen consumption on the one hand and algal growth - oxygen production/consumption I on the other hand were linked and the intensity ot each response was influenced by that of the preceding component of the syste•• Symbiotic relationships were established but were affected by changing bacterial and algal active phases brought about by tood and nutrient availability. 8S well as by prey-predator interactions. •