Establishing the mechanisms underpinning solids breakthrough in UASB configured anaerobic membrane bioreactors to mitigate fouling

Abstract

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 for limiting 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 similarly low levels of membrane fouling can be achieved within flocculent AnMBR by managing solids retention time to constrain sludge bed height and excess

Pathways of wastewater treatment for resource recovery and energy minimization towards carbon neutrality and circular economy: technological opinions

“…Their results indicated that DWW contains an energy generation potential of 7.6 kJ/L (Heidrich et al, 2011). Anaerobic technologies, including the up-flow anaerobic sludge blanket (UASB) and anaerobic MBR (AnMBR) based on the anaerobic digestion (AD) (Smith et al, 2014;Wang et al, 2020), and microbial electrochemical technologies (METs) including microbial fuel cells (MFCs), MECs and microbial recycling cells (MRCs) (Vadillo et al, 2013), are the main advancement in energy production from wastewater.…”

“…Among the anaerobic technologies, AnMBR is more efficient than conventional AD systems in biogas production and is currently in potential for practical application (Wang et al, 2020). The combined process of AnMBR and anammox has shown high effectiveness in energy production, where anammox could preserve OC from the denitrification (Dai et al, 2015).…”

Advances in anaerobic membrane bioreactor technology for municipal wastewater treatment: A 2020 updated review

“…Most common AnMBR-UASB configurations include the membrane module in an external tank [49,98,117,144,145] or at the top of the UASB reactor [77,146,147]. The former is the most reported system.…”

Application of Recycled Filling to Improve the Purification Performance of Confectionery Wastewater in a Vertical Anaerobic Labyrinth Flow Bioreactor

“…The operational problems reported by operators in regards to typical UASB reactors using granulated sludge became the basis for the search for new technological solutions. The stated shortcomings of UASB systems involve the high cost of obtaining the anaerobic sludge inoculum [34]; the long adaptation period of the microbial biomass [35]; the absolute need to remove fats and suspensions before the wastewater is introduced into the anaerobic chamber [36]; the lack of separation of the phases, requiring different technological conditions for the fermentation process [37]; a sometimes too-small gas exchange surface [38]; the destruction of the granulated sludge and its removal outside the reactor [39]; the clogging of the space between the anaerobic sludge granules [40]; and the inability to effectively remove phosphorus compounds, which are an element limiting the eutrophication of natural water reservoirs [41]. Hybrid reactors can be a competitive and often technologically justified alternative.…”