Biological phosphate removal from municipal wastewater

Phosphate removal from wastewater during treatment is a legal requirement to prevent environmental damage caused by releasing large amounts of nutrients into water courses. The most commonly applied removal methods, due to their ease of use, are based upon precipitation of the phosphate by chemical addition. An alternative method has been developed involving specialised micro-organisms, termed phosphate accumulating organisms (PAO), which take up and store greater than required amounts of phosphate. This process, designated enhanced biological phosphate removal (EBPR), has developed empirically since the observation that cycling the wastewater through anaerobic/aerobic phases selects for these PAO and the phosphate is removed from the liquid. There are still many aspects of the EBPR process that are far from fully understood; these include the identity of the organisms that are responsible for the phosphate uptake and the reasons why plants will occasionally stop removing phosphate. This project addresses these points, firstly by determining the effect of knockout and over-expression of ppk and ppx - genes known to be important in cellular polyphosphate metabolism in Pseudomonas putida, an organism found in sludge, which can accumulate polyphosphate. Previous mutational studies have mostly focused on Escherichia coli and Pseudomonas aeruginosa, which do not proliferate in sewage plants. The effect of the mutations upon growth, polyphosphate production and stress responses were ascertained. It appeared that two separate populations of polyphosphate were present, one being synthesized by polyphosphate kinase, the other by some as yet unidentified pathway. Further investigation of this 'large polyphosphate' established it was not polyphosphate but an unknown contaminating material that co-separated during the extraction procedure. Analysis of this compound suggested it was an exopolysaccharide, similar in character to alginate. The second aspect of the project focussed on the isolation of micro-organisms from a local EBPR plant followed by the selection, identification and characterization of potential PAOs. The development of a fully defined phosphate removing sludge community was attempted, in order to facilitate the study of the process. This was undertaken by operating a two litre bioreactor under EBPR conditions and allowing a self-selected community to develop from the inoculated isolates.EThOS - Electronic Theses Online ServiceGBUnited Kingdo