Rapid Biogas Production by Compact Multi-Layer Membrane Bioreactor: Efficiency of Synthetic Polymeric Membranes

Supansa Youngsukkasem,Hamidreza Barghi,Sudip Rakshit,Mohammad Taherzadeh

doi:10.3390/en6126211

Supansa Youngsukkasem, Hamidreza Barghi + Show 2 more

Open Access

https://doi.org/10.3390/en6126211

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Abstract

Entrapment of methane-producing microorganisms between semi-permeable synthetic membranes in a multi-layer membrane bioreactor (MMBR) was studied and compared to the digestion capacity of a free-cell digester, using a hydraulic retention time of one day and organic loading rates (OLR) of 3.08, 6.16, and 8.16 g COD/L·day. The reactor was designed to retain bacterial cells with uprising plug flow through a narrow tunnel between membrane layers, in order to acquire maximal mass transfer in a compact bioreactor. Membranes of hydrophobic polyamide 46 (PA) and hydroxyethylated polyamide 46 (HPA) as well as a commercial membrane of polyvinylidene fluoride (PVDF) were examined. While the bacteria in the free-cell digester were washed out, the membrane bioreactor succeeded in retaining them. Cross-flow of the liquid through the membrane surface and diffusion of the substrate through the membranes, using no extra driving force, allowed the bacteria to receive nutrients and to produce biogas. However, the choice of membrane type was crucial. Synthesized hydrophobic PA membrane was not effective for this purpose, producing 50–121 mL biogas/day, while developed HPA membrane and the reference PVDF were able to transfer the nutrients and metabolites while retaining the cells, producing 1102–1633 and 1016–1960 mL biogas/day, respectively.

Highlights

Biogas or biomethane is a renewable energy source with several applications, e.g., car fuel, heating, cooking, or electricity production
The results revealed that the Membrane bioreactors (MBRs) had better performance than the continuously stirred tank reactor (CSTR) and produced more hydrogen gas [9]
Biogas is one of the oldest biological products in the world, and holds a great potential to substitute at least part of the global oil consumption

Summary

Introduction

Biogas or biomethane is a renewable energy source with several applications, e.g., car fuel, heating, cooking, or electricity production. The anaerobic digestion process subsequent methane production comprises hydrolysis, acidogenesis, acetogenesis, and methanogenesis. The doubling time of the hydrolysis and acidogenesis bacteria is 1.0–1.5 days, while acetogens and methanogens need 1–4 and 5–15 days for doubling, respectively [2]. This implies that methane-producing microorganisms require a long retention time, and there is a risk of bacteria washing out from the digester. A low dilution rate of the methane-producing microorganisms in the digester, or early withdrawal of the digesting bacteria, reduces the population size of these bacteria significantly; and the digestion process and biogas production would not further continue. Retaining the microorganisms inside the digester by entrapment might be an appropriate solution to overcome these problems

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