title: The use of Phragmites australis (common reed) in biofuel production
title: Effects of chemical and mechanical pre-treatments, harvesting season and co-digestion with food waste on biogas production.
titleType: Subtitle
Creators: name: Al-Iraqi, Ahmed R.
Publisher: name: Lancaster University
Year: 2024

description: Lignocellulosic materials possess various features that make them
 exceptionally
 
 attractive as organic substrates in anaerobic bioreactors. Among these
 substrates, wetland plants such as common reed (Phragmites australis) are
 highly interesting as a promising feedstock for biogas production due to
 their vast abundance, sustainable nature, and lack of competition with
 arable land and food and feed production. However, the main obstacle lies
 in the recalcitrance of these feedstocks to biological conversion due to
 their high lignin content, impeding their full-scale adoption for biogas
 production. Therefore, additional steps are necessary to overcome this
 challenge and maximize their
 
 biodegradability.
 
 
 In the present work, a series of screening assays were conducted using
 microcosm vessels (125 mL) operating at mesophilic conditions to evaluate
 the potential of utilising alkaline pre-treatment (using NaOH) and
 co-digestion with food waste for augmenting the biogas production from P.
 australis. And determining the parameters that promote P. australis
 degradation efficiency and anaerobic digestion process stability, such as
 P. australis particle size, NaOH concentration, incubation time of
 pre-treatment process, inoculum to
 
 substrate ratio, and substrates mixing ratio. Furthermore, two batch
 experiments were performed using a 1 L bioreactor to investigate the
 effect of P. australis harvesting time, co-digestion with food waste and
 mechanical pre-treatment (P. australis biomass grinding to smaller than
 0.4 mm) compared to chemical pre-treatment on the chemical composition of
 P australis and enhancing methane production.
 
 
 The results revealed inverse correlation between the biogas production
 level and the particle size of P. australis (10, 5, 2, and &lt;1 mm),
 achieving the highest biogas production at particle size &lt;1mm. As
 well as it was found that the pre-treatment of P. australis substrate with
 0.5, 1, 2, and 4% NaOH positively affected biogas production, causing an
 increase by 2.4, 3, 3.6 and 3.9-fold than biogas produced from untreated
 P. australis, respectively. Besides, the P. australis substrate
 pre-treated with NaOH for long periods (72-120 h) showed improved biogas
 production compared to the P. australis substrates treated for shorter
 periods (12-48 h). Regarding the inoculum-to-substrate ratio
 
 (ISR), it was found that the increasing P. australis substrate proportion
 (ISR of 1:2 and 1:4) resulted in higher biogas production than that
 produced from ISR with low P. australis proportion (4:1, 2:1, and 1:1). On
 the other hand, this study revealed that the co-digestion of pre-treated
 P. australis with synthetic food waste at a high substrate ratio (ISR of
 1:4) and high synthetic food
 
 waste proportion at ISR 1:2 (synthetic food waste to P. australis mixing
 ratios of 50:50 and 75:25) resulted in systems acidification and
 inhibition. In contrast, the systems stability and biogas production
 increased at a lower substrate ratio (ISR of 1:1), with the highest biogas
 production achieved at synthetic food waste to P. australis mixing ratio
 of 75:25. Finally, the change in the harvest season showed a remarkable
 influence on P. australis composition, cellulose degradation, and methane
 production. The monodigestion and co-digestion of pre-treated P. australis
 harvested during the summer and autumn seasons showed higher methane
 production than P. australis harvested in the winter. Overall, the
 chemical pre-treatment of P. australis using NaOH improved methane
 production more than mechanical pre-treatment using the grinding method.
 As
 
 well as the co-digestion of P. australis with food waste contributed
 significantly to increasing the efficiency of the mechanical pre-treatment
 process in enhancing the biodegradability of P. australis and increasing
 methane production.