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Protozoan and bacterial populations in biological water-treatment processes

 Mansour Galal

Faculty of Science, Menoufeyia University

ABSTRACT

            Bacterial populations are one of the most important micro-organisms playing a role in the flow of carbon, nitrogen and phosphorous in nature. Bacteria perform an important role in releasing nutrients from dead organic matter and their ability to perform this role appear to be influenced by the presence of protozoa. It was proved that protozoa may play a direct and indirect role in nutrient recycling. The role of the bacterial-feeding protozoa is to increase the bacterial production and to enhance the oxidation of organic compounds in different water treatment processes. Nutrient regeneration, which means the release of soluble organic and inorganic nutrients  from dead organic matter in different habitats is necessary for primary production. Simultaneously, much of the phosphorus and nitrogen incorporated into aquatic primary and secondary production may be regenerated by processes other than the bacterial action. Accordingly, it is possible to conclude that the grazing activities of protozoa on bacteria, their small size, their stimulatory effect on the bacterial production rates, their high growth,  and other metabolic rates showed the valuable role played by these microorganisms in regenerating the nutrients in nature.

It was found that maximal densities of ciliates develop mainly at the top 5cm of sand and towards the second half of the run whereas, below 5cm, densities were much lower and either constant or increased slowly during the course of the run.

          Regarding the bacterial populations, it was found that their numerical densities were low and more or less similar during the first sampling occasions. After that, there was an increase with the duration especially at the top 5 cm sand, while throughout the lower 20 cm the bacterial densities were much less than those of the upper layer.

Key words: Bacteria - Protozoa - water treatment