Biological treatment and thickening with a hollow fibre membrane bioreactor

Abstract

Aerobic operation of an immersed hollow fibre membrane bioreactor, treating municipal wastewater supplemented with molasses solution, has been studied across mixed liquor suspended solids (MLSS) concentrations between 8 and 32 g L(-1), the higher concentrations being normally associated with thickening operations. Only a marginal loss in membrane permeability was noted between 8 and 18 g L(-1) when operation was conducted without clogging. The sustainable operational flux attainable above 18 g L(-1) was highly dependent upon both the MLSS concentration and the state of the membrane. A temperature-corrected flux of 28 L m(-2) h(-1) (LMH) was sustained for 18 h at an MLSS of 8 g L(-1) using membranes close to initial their virgin-state permeability. This value decreased to around 14 LMH at 20 g L(-1) and 5 LMH at 32 g L(-1) MLSS for an aged membrane whose permeability had been recovered following clogging. Below the threshold flux operation without significant clogging was possible, such that the membrane permeability could be recovered with a chemically enhanced backflush (CEB). Above this flux clogging took place at a rate of around 7-14 g solids per m(2) membrane per m(3) permeate volume passed irrespective of the MLSS concentration. The permeability of the unclogged membrane was depressed and could not be recovered using a standard CEB, indicative of irrecoverable pore clogging. The outcomes corroborated previously reported observations concerning the deleterious long-term impacts of clogging, and confirmed the critical importance of operation at a sustainable flux value.

Clogging vs. fouling in immersed membrane bioreactors

“…It has been assumed by practitioners that problems associated with clogging are only effectively ameliorated through both: a) fine screening of the feed to remove the inlet gross solids (Frechen et al 2008;Impero, 2015), incurring additional costs associated with screenings management, and b) appropriately limiting the MLSS (mixed liquor suspended solids) concentration in the membrane tank (Zsirai et al, 2014).…”

“…However, there has been very limited research on clogging/sludging, to substantiate these rules of thumb. Despite its practical significance, only a few isolated studies (Buzatu at al, 2011, Zsirai et al, 2014 have sought to quantify sludging gravimetrically. Specifically, the key MLSS characteristics to which sludging may be attributed have not been identified, such that the efficacy of any remedial measures taken to address it cannot be established.…”

Membrane technology costs and me

“…immersed MBRs with membrane air scouring of polymeric membranes. Decreased membrane aeration always increases the risk of membrane fouling and/or channel clogging (Zsirai et al, 2014): the intervention required to mitigate clogging in particular is more punitive economically and practically than the energy cost savings offered by aeration reduction.…”

Sludge Treatment by Supercritical Water Oxidation and the Optimization of Operational Conditions

“…New technologies have started using membrane processes (e.g., flat-sheet membranes, hollow fiber membranes) for sludge thickening, and some combine thickening with digestion such as the simultaneous thickening and digestion (SMTD) process (Wang et al, 2008;Zsirai et al, 2014). Membranes are very effective and they allow a better control on the particle size and concentration allowing a much thicker sludge.…”