Enhancing anaerobic digestion of okra waste with the addition of iron nanocomposite (Ppy/Fe₃O₄)

Abstract

The high reactivity, adsorptive capacity and environmental stability of polypyrrole-magnetic nanocomposite (nano-PPy/Fe₃O₄) additive are the sterling properties that make it useful for water/wastewater treatment. PPy/Fe₃O₄ is akin to other previously studied iron-based additives used for improving biodeterioration of lignocellulosic substrates with their electron donation capability during anaerobic digestion process. This study examined the enhancement of anaerobic digestion of okra waste with nano-PPy/Fe₃O₄ additive. Portions of okra waste were treated with different dosages of PPy/Fe₃O₄ additives (0, 20, 75, 750, and 1000 mg/l) and digested anaerobically using the biomethane potential bioreactors at mesophilic condition and hydraulic retention time of 32 days. The morphological deformation and elemental analysis of the undigested substrate, the control and digestates of substrate supplemented with nano-PPy/Fe₃O₄ additive evaluated with Scanning Electron Microscopy (SEM-EDS) revealed structural decomposition in the digested samples and increased Fe ions (0.1-3.9 wt%) in the digestates. The bioreactor with 20 mg/l cumulative volumes of the PPy/Fe₃O₄ additives recorded the highest increase of 2.74% rise in biomethane yield. Artificial neural network (ANN) and kinetic models (first-order kinetic and modified Gompertz model) were validated with the experimental data at 95% confidence level, but ANN model showed better goodness of fit and better correlated with the experimental data.

Keywords:

• PPy/Fe3O4
• Iron-based
• additives
• anaerobic digestion
• okra
• nanocomposite

Acknowledgments

This research was conducted with the assistance of NRF-TWAS- SFH160606168084. We thank Dr. Uyiosa Aigbe of Physics Department, University of South Africa (UNISA) for the Polypyrrole-magnetic nanocomposite and for the okra waste, we appreciate Organic Farmers, Centurion, South Africa. Dr. Samson Masebinu for giving us inoculum from his anaerobic digester.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Research Foundation (ZA) and The World Academy of Sciences.