Abstract:
Anaerobic digestion (AD) mitigates high energy demand by converting lignocellulosic waste
into biogas and digestate. This process supports the economy, reduces energy crises, and
enhances environmental sustainability. Agricultural residues serve as promising energy resource
in carrying out AD process. Recalcitrant lignocellulosic structure of Arachis hypogea shells and
high carbon to nitrogen (C/N) ratio of peanut shells (PS) usually impedes efficiency of AD
process. Therefore, this study was conducted with two aims i.e. application of alkaline
pretreatment on PS before initiating AD and use of vegetable waste (VW) as a co-substrate to
balance the C/N for effective AD performance. Exposure of PS was given to varying NaOH
concentrations of 2%, 4%, 6% and 8%, which was followed by batch-mode AD including mono-
and co-digestion under mesophilic temperature range for 45d. The characterization of untreated
and pretreated PS was done using FT-IR (Fourier Transform Infrared) spectroscopy. FT-IR
results confirmed the change in structural peaks after pretreatment. Additional ultimate analysis
depicted the enrichment of essential nutrients in VW, making it suitable for using as co-substrate
with PS. Results showed that 4% NaOH provided maximum cellulose recovery (96.04%) and
75% lignin removal. Further investigation revealed an improvement in biogas production during
co-digestion setup rather than mono-digestion. Anaerobic co-digestion (ACD) of NaOH
pretreated PS with VW has recorded cumulative biogas production in following order: 4% > 2%
> 6% > 8% which produced 65% , 58.75%, 42.2% and 37.5% respectively more cumulative
biogas as compared with control group. Overall, low NaOH dosage i.e. 2% to 4% was found
more effective than high dosage 6% to 8% in delignification. This study concluded that alkaline
pretreatment has effectively improved cellulose recovery and lignin degradation, while ACD
resulted in greater biogas production than mono-digestion.
