Browsing by Author "Wang, Kanming"
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Item Open Access Anaerobic membrane bioreactors in upflow anaerobic sludge blanket configuration for energy neutral sewage treatment.(2018-03) Wang, Kanming; McAdam, Ewan; Soares, AnaAnaerobic membrane bioreactors (AnMBRs) are emerging as a promising technology to offer the prospect to achieve energy neutral sewage treatment. The key challenges limiting full-scale application of AnMBR for municipal wastewater treatment are high operational cost of energy demand for fouling control and high capital cost of membrane investments. This thesis explores a novel pseudo dead-end gas sparging regime for membrane fouling control, enabling a high sustainable flux (15 L m ¯² h¯¹) with low energy demand (0.14 kWh m⁻³ ) in upflow anaerobic sludge blanket (UASB) configured AnMBR, sufficient to achieve energy neutral sewage treatment. However, this strategy is only possible within low solids environment, emphasising the importance of solids management in the UASB reactor. Solids accumulated in the sludge blanket enhances UASB treatment efficiency during the steady-state operation, indicating to control the sludge blanket at a threshold between the sludge blanket development and steady-state period. The granular inoculum has good stability which exerts a positive influence on reactor stability and sustained permeability, whilst the flocculent inoculum enables to deliver similar sustained membrane operation provided the sludge blanket is controlled. Low temperatures (average temperature of 10 °C) cause the instability of UASB reactor especially for the one with flocculent inoculum biomass. It is therefore proposed to keep relatively high upflow velocity (Vup) of 0.8-0.9 m h⁻¹ in the UASB reactor for granular AnMBR to promote the stratification of particular and granular material, whilst reducing Vup to 0.4 m h⁻¹ for flocculent AnMBR to minimise solids washout and sustain membrane operation at low temperatures. The potential for permeability recovery following peak flow (diurnal peaks and storm water flows) has been investigated and evidenced, suggesting that membrane surface area for AnMBR can be specified based on average flow, providing a considerable (67 %) capital cost reduction compared with the design based on peak flows (three times of average flow). Importantly, this thesis promotes UASB configured AnMBR as a highly reliable and more economically viable technology, facilitating to achieve the energy neutral sewage treatment at ambient temperature.Item Open Access Comparable membrane permeability can be achieved in granular and flocculent anaerobic membrane bioreactor for sewage treatment through better sludge blanket control(Elsevier, 2019-02-05) Wang, Kanming; Soares, Ana; Jefferson, Bruce; McAdam, EwanMBR, to establish the impact of biomass selection on sustaining membrane permeability for sewage treatment. When operated as an UASB (10 °C), similarly poor organics removal was observed for both inocula, which was overcome by membrane integration, producing solids-free permeate and consistently low CODt (34–39 mg L−1) and BOD5 (10–13 mg L−1), sufficient to meet discharge standards. At an average sewage temperature of 22 °C, membrane permeabilities in granular (G-AnMBR) and flocculent (F-AnMBR) systems were comparable. However, at lower temperature (10 °C), significant fouling was observed in F-AnMBR at a flux of 7.5 L m−2 h−1. The permeability decline was ascribed to a decreased particle settling velocity which induced washout of smaller particles into the membrane tank, subsequently increasing the colloidal concentration due to the floc erosion induced by gas sparging. This was confirmed by halving UASB upflow velocity in the F-AnMBR, which reduced pCOD and colloidal load by 31–36% onto the membrane, permitting comparable permeability to G-AnMBR. The UASB configured AnMBR promoted low solids loading onto the membrane, enabling pseudo dead-end gas sparging to be used which reduced specific energy demand. Analysis of the dead-end filtration cycle attributed the primary resistance (85–88%) to the development of a concentrated but less compact cake. Importantly, this study evidences comparable permeabilities in G-AnMBR and F-AnMBR through controlling solids retention, and specifying filtration cycle length to minimise solids deposition, such that low energy membrane operation can be achieved (<0.122 kW h m−3).Item Open Access Establishing the mechanisms underpinning solids breakthrough in UASB configured anaerobic membrane bioreactors to mitigate fouling(Elsevier, 2020-03-26) Wang, Kanming; Soares, Ana; Jefferson, Bruce; Wang, Hongyu; Zhang, L. J.; Jiang, Shengfeng; McAdam, Ewan J.In this study, the mechanisms for solids breakthrough in upflow anaerobic sludge blanket (UASB) configured anaerobic membrane bioreactors (AnMBRs) have been described to establish design parameters to limit membrane fouling. As the sludge blanket develops, two periods can be identified: (i) an initial progressive enhancement in solids separation provided through sludge blanket clarification, via depth filtration, which sustains downstream membrane permeability; and (ii) sludge blanket destabilisation, which imposed solids breakthrough resulting in a loss in membrane permeability. The onset of sludge blanket destabilisation was identified earlier in the flocculent AnMBR, which was ascribed to an increased gas production, caused by hydrolysis within the sludge blanket at extended solids residence time. Whilst hydrolysis also induced higher gas productivity within the granular AnMBR, solids breakthrough was not evidently observed during this period, and was instead only observed as the sludge blanket approached the UASB overflow. However, solids breakthrough was observed earlier for both reactors when treating wastewater with lower temperatures. This was explained through characterisation of the settling velocity of discrete particles from the sludge blanket of both MBRs; solids washout was evidenced to be induced by the increase in fluid viscosity with a reduction in temperature, which lowered terminal particle settling velocity. Nevertheless, particle settling velocity was comparable for particles from both sludge blankets. We therefore propose that the enhanced stability imparted by the granular AnMBR is due to the higher inertial force of the dense granular sludge. From this study, we suggest that similarly low levels of membrane fouling can be achieved within flocculent AnMBR by managing solids retention time to constrain sludge bed height and excess hydrolysis, together with adopting an upflow velocity based on particle buoyancy at the lowest expected operating temperature.