Biomedical subjects

S A Parsons

Publications and source records attributed to S A Parsons.

21 records · Page 2Linked to original sources

PubMed2001

The impact of residual coagulant on downstream treatment processes.

A series of jar tests were undertaken to optimise for suspended solids (SS) and phosphorus removal from raw wastewater. The residual metal concentration in the settled wastewater from the jar test experiments and the residual concentration from the optimum doses plus two higher doses were selected for investigation. The identified levels of residual metal were fed into a four lane activated sludge pilot plant to investigate the impact of metal concentration on (i) activated sludge performance and (ii) sludge production and characteristics. Optimum pre-precipitation studies showed residual ion concentrations of 1.68 and 3.46 mg l-1 for Fe(III) and Al(III) respectively. At these levels %P removal increased by approximately 25 and 60% respectively. NH3 removal decreased by approximately 20 and 34% in the activated sludge treatment process. Chemically dosed biomass had a significantly lower oxygen uptake rate than the control which was accompanied by a reduction in VSS; 10% for Fe(III) and 17% for Al(III). Changes in sludge characteristics were also observed. Chemical sludge had a greater settleability but a lower dewaterability than biological sludge. Sludge floc morphology was characterised which showed chemical flocs to be consistently smaller and visually denser than biological sludge flocs. The work presented in this paper considers the impact of residual iron and aluminium coagulants on downstream treatment processes.

Aluminum↗

PubMed2001

Small scale water recycling systems--risk assessment and modelling.

This paper aims to use quantitative risk analysis, risk modelling and simulation modelling tools to assess the performance of a proprietary single house grey water recycling system. A preliminary Hazard and Operability study (HAZOP) identified the main hazards, both health related and economic, associated with installing the recycling system in a domestic environment. The health related consequences of system failure were associated with the presence of increased concentrations of micro-organisms at the point of use, due to failure of the disinfection system and/or the pump. The risk model was used to assess the increase in the probability of infection for a particular genus of micro-organism, Salmonella spp, during disinfection failure. The increase in the number of cases of infection above a base rate rose from 0.001% during normal operation, to 4% for a recycling system with no disinfection. The simulation model was used to examine the possible effects of pump failure. The model indicated that the anaerobic COD release rate in the system storage tank increases over time and dissolved oxygen decreases during this failure mode. These conditions are likely to result in odour problems.

Conservation of Natural Resources↗

PubMed2001

Development of an odorant emission model for sewage treatment works.

In the field of odour assessment, much attention has been paid to the measurement of odour concentration. Whilst the concentration of an odour at a receptor is a useful indicator of annoyance, the concentration at the source tells only half the story. The emission rate - the product of odour concentration and air flow rate - is required to appreciate the significance of odour sources. Knowledge of emission rates allows odour sources to be ranked in terms of significance and facilitates appropriate selection and design of odour control units. The emission rate is also a key input for atmospheric dispersion models. Given the increasing importance of odour to sewage treatment works operators, there is a clear need for predictive methods for odour emission rates. Theory suggests that the emission of odorants from sewage to air is controlled by mass transfer resistances in both the gas and liquid phase. These are in turn controlled by odorant and emission source characteristics. The required odorant characteristics are largely known, and mass transfer from many different types of emission sources have been studied. Sewage treatment processes can be described by one or more of six characteristic emission sources, these being quiescent surfaces, channels, weirs and drop structures, diffused aeration, surface aeration and flow over media. This paper describes the development of odorant mass transfer models for these characteristic emission types. The models have been applied in the form of spreadsheet models to the prediction of H2S emissions and the results compared with commercial VOC emission models.

Air Movements↗