Synergistic Effects of Magnetic Nanomaterials on Post-Digestate for Biogas Production

Abstract

Digestate is characterized by high water content, and in the water and wastewater treatment settings, necessitates both large storage capacities and a high cost of disposal. By seeding digestate with four magnetic nanoparticles (MNPs), this study aimed to recover biogas and boost its methane potential anaerobically. This was carried out via biochemical methane potential (BMP) tests with five 1 L bioreactors, with a working volume of 80% and 20% head space. These were operated under anaerobic conditions at a temperature 40 °C for a 30 d incubation period. The SEM/EDX results revealed that the morphological surface area of the digestate with the MNPs increased as compared to its raw state. Comparatively, the degree of degradation of the bioreactors with MNPs resulted in over 75% decontamination (COD, color, and turbidity) as compared to the control system result of 60% without MNPs. The highest biogas production (400 mL/day) and methane yield (100% CH4) was attained with 2 g of Fe2O4-TiO2 MNPs as compared to the control biogas production (350 mL/day) and methane yield (65% CH4). Economically, the highest energy balance achieved was estimated as 320.49 ZAR/kWh, or 22.89 USD/kWh in annual energy savings for this same system. These findings demonstrate that digestate seeded with MNPs has great potential to improve decontamination efficiency, biogas production and circular economy in wastewater management.

Biophotocatalytic Reduction of CO2 in Anaerobic Biogas Produced from Wastewater Treatment Using an Integrated System

“…The characterised distribution (Table 1) of the wastewater was outsourced from a local eThekwini municipal wastewater treatment plant in the KwaZulu-Natal province, South Africa. A magnetite-titanium photocatalyst (Fe-TiO 2 ) synthesised via the co-precipitation technique reported in our previous works [21,37] was used. Additional characterisation with the Brunauer-Emmett-Teller theory (Micromeritics, TriStar II Plus, Norcross, GA, USA) recorded a BET surface area of 62.73 m 2 /g, pore volume of 0.017 cm 3 /g and particle size of 1.337 nm.…”

“…Considering the electricity requirement of the UV lamp (Figure 8), the bioenergy (Figure 7) produced was at least able to compensate this energy required (Figure 10). Herein, by applying an electricity unit cost of R3.22 ($0.23) per kWh [21], from the bioenergy produced (Figure 7) and utilised (Figure 8), the net average energy of 0.216 kWh was priced R0.72 ($0.5). As illustrated in Figure 10, the component net energy of 3.065 kWh (AD); 4.26 kWh (AN); −3.44 kWh (AOP) and −3.02 kWh (Ms) corresponded to the price of R9.87 ($0.7); R13.73 ($0.98); −R11.07 (-$0.79) and −R9.73 (−$0.7).…”

“…Moreover, variations in the AD process feedstock and environmental conditions can result in high complex sludge that is difficult to treat economically and environmentally [9,12,19]. On this basis, our previous work [17,20,21] and other researched studies [9,12,18,19,[22][23][24] show that using a photocatalyst (Fe-TiO 2 ) with magnetic properties has tremendous potential in wastewater settings. With this, and the need to meet future water demands, creating a cost-effective, user-friendly and reliable technology with a significant impact on energy production and recuperation in water settings is urgently needed [3,5,15,16].…”

Recent Advances and Perspectives of Nanotechnology in Anaerobic Digestion: A New Paradigm towards Sludge Biodegradability

“…The digestate remained off for disposal containing certain remediating NPs such as Zn and Cu that could be remediated, i.e., Zn to ZnS, and can be reutilized as agricultural fertilizers. In addition to this, production of NPs using natural resources prevent the risk associated with effluent disposal [75].…”

Exploring CO2 Bio-Mitigation via a Biophotocatalytic/Biomagnetic System for Wastewater Treatment and Biogas Production

“…Anaerobic digestion (AD) is a technique that transforms organic matter in biomass resources into biogas with methane (CH 4 ) as a source of sustainable energy [5,10,11]. Of essence, AD creates economic opportunities by producing bioenergy (60-70% methane) and stabilized digestate under suitable conditions to ease pollution [12].…”