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Title: Pollutant transformation processes in sewers under aerobic dry weather flow conditions
Author: Almeida, Maria do Ceu de Sousa Teixeira de
ISNI:       0000 0000 6851 1609
Awarding Body: Imperial College London (University of London)
Current Institution: Imperial College London
Date of Award: 1999
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Urban wastewater characteristics are altered during transportation through sewers as a result of biochemical processes. Quantification of these changes is relevant to predict inflow loads to wastewater treatment plants, to calculate pollutant emissions from urban drainage systems (CSOs) and to ascertain any in-sewer treatment effect. Improved knowledge of in-sewer processes potentially leads to changes in the design, analysis and management of urban wastewater systems. The aim of this thesis is to contribute to the understanding, description and assessment of mechanisms involved in the transport of pollutants in sewers, by combining experimental investigations with model development. The focus is restricted to dry weather flow processes occurring either in foul or in combined sewers, under aerobic conditions and free surface flows. The basic approach of the resulting model sought to provide a detailed description of the transport processes, together with the transformation processes modelled by a method similar to that of the lAWQ Activated sludge models nr.1 and nr.2. The intention was to separate the effect of advection-dispersion on the concentration of key pollutants from those due to biochemical transformation processes. The model thus contains modules for hydrodynamics, advection-dispersion and water quality. Processes such as reaeration, heterotrophic growth (suspended and attached), heterotrophic decay, hydrolysis and ammonification are included. COD fractionation describes the oxygen demanding components, and ammonia is included because of its environmental importance and active role in the transformation processes. Data requirements for both model calibration and verification were established by means of sensitivity analysis. Extensive experimental work was carried out at a case study site to supply data for model calibration and verification and to support the selection of the relevant processes occurring in sewers. Aspects studied include: quantification of COD, BOD, ammonia, nitrate and solids removals; determination of oxygen uptake rates (respirograms) in wastewater; evaluation of diurnal variation of flow and quality determinands; determination of the Manning coefficient; measurements of reaeration at drops; and estimation of the dispersion coefficient. The respirograms were essential to calculate model parameters and COD fractions. Model fit was found to be good for the COD fractions and ammonia but poorer for dissolved oxygen. The latter was found to be the key variable and very sensitive to small variations in parameter values. The relative importance of dispersion and transformation processes on pollutant concentrations was evaluated. Further applications and developments of the model are discussed.
Supervisor: Butler, David Sponsor: Portuguese Program PRAXIS XXI Blosas Individuais
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available