Mixed-source community fermentation for ethanol production from municipal solid waste

Abstract

Ethanol from lignocellulosic waste is a sustainable alternative to fossil transport fuels. While most research has been directed towards agricultural and industrial wastes as feedstocks, little attention has been paid to the organic fraction of municipal solid waste (OMSW). The production of bioethanol from OMSW would contribute to the integral solutions of climate change mitigation and transportation energy security, along with the reduction of the increasing amount of municipal solid waste generated, especially in developing countries. Additionally, studies on ethanol (EtOH) production have largely focused on genetically engineering single microorganisms to fully convert lignocellulosic substrates into EtOH. However, mixed culture fermentation (MCF) represents a suitable approach to handle the complexity and variability of organic wastes and to avoid expensive and vulnerable closedcontrol operational conditions. In this work, a mixed-source bacterial community, mainly comprised of Clostridium, Pseudomonas, Leuconostoc, Ruminococcus, Petrimonas and Leptolinea genera members, has been reproducibly enriched from sheep rumen and anaerobic granular sludge after testing a range of environmental inocula sources. This community generates 59.8mM ± 2.8mM of EtOH in batch microcosms incubated at room temperature under initial aerobic conditions and without further conditioning of the acid pre-treated OMSW used as substrate. The EtOH yield obtained (0.070L/Kg) is about 1/6 of the current corn grain-based EtOH industrial production yield (0.42 L/Kg). EtOH production from such a complex substrate as OMSW in addition to the minimal inputs required by this community, makes it a good candidate for implementation in biorefinery projects in both developed and developing countries. Despite the reproducibility of these results, where batch cultures were started from the original inocula sources, a drastic loss of EtOH production occurred across successive culture transfers to fresh media conducted at 14 and 3 days after inoculation, where EtOH production decreased by 80% and 50% of the originally inoculated batches, respectively. Nevertheless, during five successive 3-day transfers a functional and structurally stable community was achieved, producing 30.5mM ± 1.3mM of EtOH and consistently enriching Clostridium and Pseudomonas as the most relatively abundant community members. Transfer timing could have played a critical role to maintain organisms with the desired activity before they passed into non-viability, thus having a competitive disadvantage against other more viable bacteria at the time of transfer. While experimental optimisation and control of EtOH production by these communities remains a challenge, these are promising results encouraging further studies of these communities for their implementation in biorefinery projects. The present study contributes to the scientific literature by presenting the first report of Mixed-source Community Fermentation for Ethanol production from the Organic fraction of Municipal Solid Waste