Operation of lab-scale reactors aimed at obtaining pure cultures of Candidatus Accumulibacter phosphatis

Abstract

Phosphate is an inorganic chemical essential for the life and growth of all organisms and it also plays an essential role in molecules such as DNA and RNA [1, 2]. Phosphate is often utilized to obtain phosphorus, which is used in agriculture as a fertilizer or in industries as a detergent [3]. However, the incremental use of phosphorus generates large amounts of phosphate wastes, which are released into water bodies, such as lakes and rivers. This high concentration of nutrients, also known as eutrophication, leads to the growth of cyanobacteria. Cyanobacteria or blue-green algae blooms can produce cyanotoxins, which can poison animals and humans. These blooms can also increase turbidity and endorse oxygen reduction on water leading to death of aquatic organisms such as fishes. The degradation of cyanobacteria also increases odors in water. The eutrophication effect facilitates amphibian diseases and parasite infections, caused by the raise, growth and reproduction of herbivorous snails, which host parasites [4].

Therefore, the removal of phosphate from water that contains high concentration levels of this nutrient is essential. The most common phosphate removal methods used in wastewater treatment plants are chemical precipitation and biological removal. Chemical precipitation consists in the addition of flocculants such as aluminum chloride, ferric chloride, calcium hydroxide or others to water. This method is effective for phosphate removal, but there are some disadvantages. Appropriate storage and handling space is required due to the large volumes of chemicals used. The chemical volume also results in a higher operational cost. Effluent could have quality and quantity variation that affects the chemical dose required [3].

The use of chemicals can increase the quantities of chemical sludge making it difficult to remove. The biological removal method most used is enhanced biological phosphorus removal (EBPR). This method consists on polyphosphate accumulating organisms (PAOs) that release phosphate anaerobically and then uptake phosphate aerobically. This accumulation occurred inside the microbial cells [5, 6].

EBPR has been studied for a long time; the physiology of microorganisms performing EBPR is still poorly understood because it has not been possible to isolate microorganisms that performed the EBPR process. Several studies have shown that the primary polyphosphate accumulating organism responsible for EBPR is Candidatus ?Accumulibacter phosphatis? (CAP). This work will focus on various attempts to isolate CAP.