Some Aspects of the Biology of Sewage Oxidation Pond Sediments

Abstract

Core sampling techniques were used to examine the profiles of organic sediments deposited in the oxidation pond. Deeper sediments were darker in colour and more compacted than those at the top of the core, which were frequently capped by a green zone of pond Algae. Vigorous gas production occurred in the middle core regions. Analysis of Imhoff effluent showed the presence of carbon as the most abundant element, followed by nitrogen, sulphur and phosphorus. Solubilities are contrasted for nitrogen and carbon. Physical analyses have shown the presence of finely divided material throughout the sediment profile and also a decreasing proportion of ignitable material with increasing depth. Sediment components have been resolved into solubility classes secured by the application of a range of inorganic and organic solvents in sequence. This technique was also applied to a laboratory experiment on the microbial decomposition of toilet paper pulp. These results are contrasted and compared with the object of relating the results of sequential analyses to the microbially induced breakdown of organic nutrients. Evidence is presented on the effects of sequential extraction on the amounts of nutrient elements in sediments and suggestions made concerning the interpretation of these results in terms of possible availability to the sediment biomass. Small scale investigations into the nature, distribution and origin of yellow sediment pigments are also reported. An Algal flora, mainly of Chlorococcalean genera, was present at the sediment interface and entangled at differing core depths. Genera such as Chlorella, Scenedesmus, and Ankistrodesmus were present all the year round. By contrast Euglena was an ephemeral. Total Algal counts and determinations of the frequencies of certain Algal genera have been made over a period of twenty consecutive months. There is evidence of seasonal and site variations for which no complete explanation is given. Chlorella was the dominant genus of the Pond flora. Embedded Algal populations decreased with increasing core depth and decreases were most marked at a depth of 4-6 cm below interface. Limited laboratory culture work has shown that Scenedesmus and Chlorella populations grew most rapidly with organic nitrogen materials as the sole or main source of the element. Growth also occurred when a range of amino acids, amines and amides were tested as sole nitrogen sources. Changes in viable and pasteurisation survivor counts followed the addition of nutrient supplements to sediments. Unsupplemented sediments were used in an investigation of some extracellular enzyme secreting properties of untreated, pasteurised and antibiotic treated sediments. Lipolysis and pectinolysis appeared to be the main properties of the bacterial population of untreated sediments. Some enzymatic properties of populations surviving pasteurisation and antibiotic treatment are compared and contrasted with those of the untreated sediments. Experiments on the effects of single nutrient supplementation on related enzymatic activity are also reported. Aspects of bacterial activity related to the circulation of nitrogen, sulphur and iron in the ponds are reported together with unsuccessful attempts to isolate bacteria concerned with methanogenesis and its subsequent metabolism. Evidence is presented on the occurrence, properties and possible identities of bacteria concerned with cellulolysis and chitinolysis in sediments. Results from bacteriological investigations are discussed and related to those arising from work on the chemical composition of Imhoff effluent and sediments, together with those arising from examination of sediment Algal populations.