Browsing by Author "Ncube, Philani"

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    Consequences of pH change on wastewater depth filtration using a multimedia filter
    (Elsevier, 2017-10-21) Ncube, Philani; Pidou, Marc; Stephenson, Tom; Jefferson, Bruce; Jarvis, Peter
    Different media materials in a multimedia filter have the potential to trap particles of different characteristics dependent on the media-suspension particle interactions. However, the removal of particles from wastewater secondary effluent using granular media filtration is relatively poorly understood because of the complexity of the wastewater matrix. Often the wastewater treatment process is liable to undergo pH changes due to removal or addition of chemicals in the treatment chain or from biological instability which in turn may alter the wastewater characteristics. Wastewater contains a mixture of organic and inorganic components, dissolved or particulate which may influence the aggregation and deposition of suspension solids during depth filtration. Changes in wastewater pH has the potential to change the wastewater matrix and media surface properties hence affecting aggregation and deposition in wastewater filtration. This study investigated how pH change affects wastewater filtration by monitoring zeta potential, aggregation and deposition of solids. The wastewater and filter media were also characterised over a range of pH from 1 to 13. Aggregation and deposition of wastewater solids was found to be most efficient near neutral pH. This was not concurrent with the conditions of lowest net charge in the system.
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    Dissolved methane recovery from anaerobic effluents using hollow fibre membrane contactors
    (Elsevier, 2015-12) Cookney, Joanna; McLeod, Andrew J.; Mathioudakis, Vasileios; Ncube, Philani; Soares, Ana; Jefferson, Bruce; McAdam, Ewan J.
    Hollow fibre membrane contactor (HFMC) systems have been studied for the desorption of dissolved methane from both analogue and real anaerobic effluents to ascertain process boundary conditions for separation. When using analogue effluents to establish baseline conditions, up to 98.9% methane removal was demonstrated. Elevated organic concentrations have been previously shown to promote micropore wetting. Consequently, for anaerobic effluent from an upflow anaerobic sludge blanket reactor, which was characterised by a high organic concentration, a nonporous HFMC was selected. Interestingly, mass transfer data from real effluent exceeded that produced with the analogue effluent and was ostensibly due to methane supersaturation of the anaerobic effluent which increased the concentration gradient yielding enhanced mass transfer. However, at high liquid velocities a palpable decline in removal efficiency was noted for the nonporous HFMC which was ascribed to the low permeability of the nonporous polymer provoking membrane controlled mass transfer. For anaerobic effluent from an anaerobic membrane bioreactor (MBR), a microporous HFMC was used as the permeate comprised only a low organic solute concentration. Mass transfer data compared similarly to that of an analogue which suggests that the low organic concentration in anaerobic MBR permeate does not promote pore wetting in microporous HFMC. Importantly, scale-up modelling of the mass transfer data evidenced that whilst dissolved methane is in dilute form, the revenue generated from the recovered methane is sufficient to offset operational and investment costs of a single stage recovery process, however, the economic return is diminished if discharge is to a closed conduit as this requires a multi-stage array to achieve the required dissolved methane consent of 0.14 mg l−1.
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    The effect of high hydraulic loading rate on the removal efficiency of a quadruple media filter for tertiary wastewater treatment
    (IWA Publishing, 2016-10-24) Ncube, Philani; Pidou, Marc; Stephenson, Tom; Jefferson, Bruce; Jarvis, Peter
    It is well known that filtration removal efficiency falls with an increase in flow rate; however, there is limited supporting experimental data on how removal efficiency changes for filters with multiple layers of media and for wastewater filtration, a practice that is becoming more common. Furthermore, information is not available on the characteristics of particles that are removed at different flow rates. Here, a quadruple media filter was operated at hydraulic loading rates (HLRs) between 5 and 60 mh−1 with subsequent measurement of total suspended solids, turbidity and particle size distribution (PSD). Samples were collected from the filter influent, effluent and also from between media layers. Pressure changes across the filter layers were also measured. The solids removal efficiency of the filter varied inversely with the increase in filtration rate. However, the multiple media layers reduced the negative impact of increased HLR in comparison to a single media filter. High filtration rates were shown to transport solids, such that particle retention and headloss development was distributed across the entire depth of the multi-media filter. There was also a progressive decrease in the suspension particle size leaving each of the filter layers. The particle hydrodynamic force simulation was consistent with the changes in measured PSD through the filter layers.
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    The impact of filter bed depth and solids loading using a multimedia filter
    (Taylor and Francis, 2018-02-23) Ncube, Philani; Pidou, Marc; Jarvis, Peter
    Design and operation of tertiary wastewater filters are not always well understood because of the inherent complexities of the wastewater matrix. Here, comparison of single, dual, triple and quadruple media (anthracite, flint, alumina and magnetite) filters were made to understand how the depth, media type and solids concentration influenced performance. The filter was improved by making the media deeper; however, the top 0.1 m of the filter retained the most solids. Additional layers of filter materials from single, dual, triple to quadruple improved the filter performance for the same depth of filter bed.
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    Tertiary treatment of wastewater using multimedia filtration for solids removal
    (2015-11) Ncube, Philani; Jarvis, Peter; Pidou, Marc
    The tightening of wastewater discharge standards for environmental protection and the increasing requirements for wastewater reuse have pushed for further tertiary treatment of wastewater to remove pollutants including suspended solids. This thesis explores the process science behind the removal of suspended solids from wastewater secondary effluent with the aim of improving the process for high quality effluent and efficient operation. Treatment plants receive diurnal flows and wastewater quality which challenges the production of a consistent compliant quality which meets reuse or discharge standards to receiving water bodies. A pilot-scale quadruple media filter was operated at the Cranfield Sewage Works to investigate the removal of suspended solids from secondary treated wastewater effluent under controlled and variable hydraulic loading rate, solids concentration and different wastewater characteristics. To measure the solids removal and operational performance of the filter, total suspended solids, turbidity, particle size analysis, zeta potential, headloss and temperature were measured under different operational conditions such as wastewater hydraulic loading rate, pH, solids concentration and filter depth. The media materials were examined to determine how they could be used to improve process performance and yield improved predictions in the application of filter models. A new method was developed for measuring the sphericity of media grains which improves the application of filter theory models to irregular shaped media grains. The method measured accurately the sphericity of glass spheres as 1.01 ± 0.02; the determined sphericity values correlated well with the measured headloss through filter media beds. The organic matter in the wastewater masked the media surface charge characteristics through coating on the media surface. Aggregation and deposition of wastewater solids was found to be most efficient near neutral pH. Adjustment of operational conditions were also explored. The solids removal efficiency of the filter varied inversely with an increase in hydraulic loading rate. However, multiple media layers reduced the negative impact of increased hydraulic loading rate and moderated headloss development. Particle retention was predominantly in the first 0.1 m depth of the filter, with further increases in filter depth producing marginal performance improvements whilst the headloss developed more quickly, reducing filter run times and wastewater throughput. While the specific deposit increased with rising influent concentration, the solids removal efficiency reduced. Thus, for an increase in the influent solids concentration of 10 mgL-1, the specific deposit increased by a factor of 1.2 while the removal efficiency decreased by an average factor of 0.9. Thus, the effluent deteriorates with increase in influent concentration while the filter holds more solids.