Biomethane production using ultrasound pre-treated maize stalks with subsequent microalgae cultivation

Abstract

This study utilized a renewable energy source, agricultural waste, in anaerobic digestion (AD) at appropriate conditions to obtain biogas and biomethane as an energy carrier. Maize stalks underwent ultrasound (US) pre-treatment for better accessibility for microorganisms, as lignocelluloses have a stable structure, insoluble in water and resist both mechanical and enzymatic attack. The digestate after an anaerobic digestion process was used for cultivation of algae after adsorption with activated carbon for clarification. Photosynthetic microalgae have industrial and economic perspectives, so their low-cost cultivation has a great potential for many applications. The results showed the impact of US pre-treatment of maize stalks as a sole substrate and codigested with algal biomass. The total yields were 1116 cm 3 /L, 1350.5 cm 3 /L and 1293.25 cm 3 /L for the untreated, ultrasonically pre-treated and microwaved maize stalks. The possibility of accumulating algal biomass using anaerobic digestate as a medium was demonstrated. US pretreatment (400 W) showed high efficiency with respect to the extractives obtained per unit of energy input. Addition of 4 g/L of microalgal biomass as a co-substrate led to an increase in the biogas yield compared to native stalks. A small closed circle system, starting from anaerobic digestion of lignocellulosic substrates followed by microalgae cultivation in the digestate and subsequent return of microalgal biomass back in the bioreactor as a co-substrate was realized, encouraging circular economy. The suggested scheme is a simple and low-cost technology, as the substrate used is freely available and renewable, and algae proved to grow in a waste effluent as medium.

Biogas Production Potential of Thermophilic Anaerobic Biodegradation of Organic Waste by a Microbial Consortium Identified with Metagenomics

“…Substrates were only milled in a chopper/knife mill. Previously, for the delignification of lignocellulosic substrates, various physical, chemical, and biological pretreatment techniques were performed [ 25 , 26 ]. This was required due to the lignocellulosic substrates’ complexity, as the typical composition of lignocellulosic materials comprises 10–25% lignin, 40–50% cellulose, and 5–30% hemicellulose [ 27 ].…”

Current and future perspectives of a microalgae based circular bioeconomy to manage industrial wastewater– A Systematic Review

“…Numerous investigations have been done to understand the bioavailability of nutrients for microalgal growth in crop residues (Tango et al, 2018). This has also been explored in previous studies where nitrate, among all the nutrients, is available in trace for microalgae (Hubenov et al, 2020). A few of the major agricultural wastes like Palm Oil Mill Effluent (POME), soybean processing water, and solid crop wastes, are discussed below:…”

Circular Economy in the Food Chain: Production, Processing and Waste Management

“…Few works consider the full circularity concept, with the reintroduction of output streams in the same chain, what CE call as "closed-loops," or the use of these outputs to another productive cycles, what CE call as "open-loops." Reuse of water through wastewater treatment [30], use of bagasse [31] or other biomasses for energy generation [32][33][34][35] as well as replacement of volatile solvents by greener ones [36][37][38], are other CE alternatives proposed in literature for food production in the CE context.…”