Abstract
This study demonstrates the application of hollow-fiber membrane contactors (HFMCs) for the recovery of biogas from the ultrafiltration permeate of an anaerobic membrane bioreactor (AnMBR) and synthetic effluents of pure and mixed CH4 and CO2. The developed membrane degassing setup was coupled with a pilot-scale AnMBR fed with synthetic domestic effluent working at 25 °C. The membrane degassing unit was able to recover 93% of the total dissolved CH4 and 83% of the dissolved CO2 in the first two hours of permeate recirculation. The initial recovery rates were very high (0.21 mg CH4 L−1 min−1 and 8.43 mg CO2 L−1 min−1) and the membrane was able to achieve a degassing efficiency of 95.7% for CH4 and 76.2% for CO2, at a gas to liquid ratio of 1. A higher mass transfer coefficient of CH4 was found in all experimental and theoretical evaluations compared to CO2. This could also be confirmed from the higher transmembrane mass transport resistance to CO2 rather than CH4 found in this work. A strong dependency of the selective gas transport on the gas and liquid side hydrodynamics was observed. An increase in the liquid flow rate and gas flow rate favored CH4 transport and CO2 transport, respectively, over each component. The results confirmed the effectiveness of the collective AnMBR and membrane degassing setup for biogas recovery. Still, additional work is required to improve the membrane contactor’s performance for biogas recovery during long-term operation.
Highlights
Wastewater, which is currently becoming a significant source for water reuse, is a potential renewable energy and nutrient resource in the form of biogas and fertilizers [1,2]
The results revealed that the resistance to the mass transfer of CH4 from the real anaerobic membrane bioreactor (AnMBR) permeate was very low compared to the resistance recorded for CO2
The results revealed that the resistance to the mass transfer of CH4 from the real AnMBR permeate was very low compared to the resFisitagnucreere1c1or.dEedxpFfoiegrruCirmeO12e1..nTEhtxaipslerhmiimgaehnsrtsaelstmirsatasnnsstcrfeaentrosfcethroceeotferfifaficnciseepnnotrottfoobffioCbgaOiso2fgocroaAuslndfMobBreRAjupesnrtMmifieeBadteRs apt leiqrumideRaetyensolad,t liquid Reynold, brReyseiistlsta=hnicg1eh.3asto0tl–hu5eb.il1liiqR=t9yue1,ili0d=ln0i1qstm.hi3udLe0e–iem)d5f,.fi1wnlfl9u−h,1eo,liinTcwqthu=(idad2rs5eafctl°thorCeewe.,aesrQaertdelli,ie=Qtrslf1=din0e1d0g00ia–n–s44gs0is0n0o0gmfpmtLhomitLseiwnnm−t1oiaarilnkncds−ougm1agsgpaReansertyededndogtltodah,CesRHmeRg4a=e.iIny0t.n07o, gldas,flRowegra=te,0Q.g07, gas flow rate, sQhogul=d b1e0n0omtedLthmatinth−e 1lo,wTr=esi2st5an◦cCe .and high transport of CH4 is favorable and desirable
Summary
Wastewater, which is currently becoming a significant source for water reuse, is a potential renewable energy and nutrient resource in the form of biogas and fertilizers [1,2]. Anaerobic membrane bioreactor (AnMBR) technology has emerged as a potential alternative for low-strength wastewater treatment [8,9,10] by coupling anaerobic bioreactors and membrane separation This technology requires low energy input, reduces the footprint, and provides an easy scale-up and selective separation between resources and nutrients [11,12]. A macroporous PP membrane was used by Jiménez-Robles et al, 2021 [37], for the recovery of CH4, from synthetic effluent (CH4 dissolved in water), by combining vacuum and sweep gas desorption. We coupled a membrane contactor degassing system with an anaerobic membrane bioreactor bench-scale unit and synthetic effluent preparation unit to study and compare the recovery of biogas from real AnMBR permeate and synthetically prepared mixtures. Simultaneous recovery allowed us to investigate the selective transport of CH4 and CO2 and to study and compare their mass transfer coefficients and transmembrane mass transport resistance to each gas component
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