174
I. A. Sanusi et al.
2.4 Biogas Production
Anaerobic digestion is one of the most important techniques used to convert organic
waste biomass into renewable energy in the form of biogas (Abdelsalam et al. 2016).
The anaerobic digestion process is relatively slow and is carried out by a mixed
consortium of microorganisms. Anaerobic digestion depends on various process
parameters such as pH, temperature, hydraulic retention time and carbon/nitrogen
(C/N) ratio, among others (Abdelsalam et al. 2016). This process consists of a series
of microbial processes that convert organic matter to biogas, which could take place
under psychrophilic (<20 °C), mesophilic (25–40 °C) or thermophilic (50–65 °C)
conditions (Abdelsalam et al. 2017a). Biogas production from organic matter mainly
depends on the contents of the substrates that can be degraded to CH 4 and CO 2 .
Substrate composition, biodegradability and nutrients are key factors for biogas yield.
The use of catalytic, stimulatory and biochemical nanoparticles additives in anaerobic digestion processes could improve biogas production significantly and have
previously recorded promising results (Table 4). These positive outcomes have been
related to effective electron transfer (oxidation–reduction potential), cofactor of key
enzymes and improved hydrolysis of organic matter. For example, the influence of
zero valent iron (ZVI) and Fe 2 O 3 nanoparticles on biogas production using activated
waste sludge was reported by Wang et al. (2016). These authors indicted that ZVI NPs
(10 mg/g TSS) and Fe 2 O 3 NPs (100 mg/g TSS) enhanced the biogas production by
2.20-fold and 2.17-fold, respectively (Wang et al. 2016). Their results demonstrate
that nanoparticles inclusion has a positive effect on the activity of methanogenic
archaea. Similarly, Su et al. (2013) assessed the effects of 0.1 wt% ZVI NPs on biogas
production and methane production using activated waste sludge, and these resulted
in 30% and 13.2% increase in concentration, respectively. Furthermore, Abdelsalam
et al. (2017a) reported that the addition of Co NPs (1 mg/L) notably increased biogas
and methane volume by 1.64 and 1.86 times, respectively. The same authors also
observed substantial improvements in the biogas and methane volume by 1.74 and
2.01 times, respectively, when 2 mg/L Ni NPs were included in the anaerobic digestion of livestock slurry. On the other hand, the study by Abdelsalam et al. (2016)
varied Co, Ni, Fe and Fe 3 O 4 nanoparticle concentrations (1, 2, 20 and 20 mg/L)
to assess their impacts on biogas and methane production from anaerobic digestion
of livestock slurry. The aforementioned study revealed that these NPs enhanced the
biogas and methane production.
(Abdelsalam et al. 2016). Similarly, a study by Gonzalez-Estrella et al. (2013)
revealed that Fe 3 O 4 and ZVI nanoparticles enhanced biogas production by 66%
and 45%, respectively. This improved process productivity of nano-base anaerobic digestion can be ascribed to the proliferation of methanogens resulting from
the promotion of direct interspecies electron transfer by nanoparticles (Park et al.
2018). The inclusion of nanometric materials also enhances the formation of essential biogas pathway intermediates such as acetate, butyrate, formate and hydrogen,
while reducing others like ethanol (Sekoai et al. 2019). In addition to the abovementioned impacts of NPs in anaerobic digestion, other catalytic effects include
I. A. Sanusi et al.
2.4 Biogas Production
Anaerobic digestion is one of the most important techniques used to convert organic
waste biomass into renewable energy in the form of biogas (Abdelsalam et al. 2016).
The anaerobic digestion process is relatively slow and is carried out by a mixed
consortium of microorganisms. Anaerobic digestion depends on various process
parameters such as pH, temperature, hydraulic retention time and carbon/nitrogen
(C/N) ratio, among others (Abdelsalam et al. 2016). This process consists of a series
of microbial processes that convert organic matter to biogas, which could take place
under psychrophilic (<20 °C), mesophilic (25–40 °C) or thermophilic (50–65 °C)
conditions (Abdelsalam et al. 2017a). Biogas production from organic matter mainly
depends on the contents of the substrates that can be degraded to CH 4 and CO 2 .
Substrate composition, biodegradability and nutrients are key factors for biogas yield.
The use of catalytic, stimulatory and biochemical nanoparticles additives in anaerobic digestion processes could improve biogas production significantly and have
previously recorded promising results (Table 4). These positive outcomes have been
related to effective electron transfer (oxidation–reduction potential), cofactor of key
enzymes and improved hydrolysis of organic matter. For example, the influence of
zero valent iron (ZVI) and Fe 2 O 3 nanoparticles on biogas production using activated
waste sludge was reported by Wang et al. (2016). These authors indicted that ZVI NPs
(10 mg/g TSS) and Fe 2 O 3 NPs (100 mg/g TSS) enhanced the biogas production by
2.20-fold and 2.17-fold, respectively (Wang et al. 2016). Their results demonstrate
that nanoparticles inclusion has a positive effect on the activity of methanogenic
archaea. Similarly, Su et al. (2013) assessed the effects of 0.1 wt% ZVI NPs on biogas
production and methane production using activated waste sludge, and these resulted
in 30% and 13.2% increase in concentration, respectively. Furthermore, Abdelsalam
et al. (2017a) reported that the addition of Co NPs (1 mg/L) notably increased biogas
and methane volume by 1.64 and 1.86 times, respectively. The same authors also
observed substantial improvements in the biogas and methane volume by 1.74 and
2.01 times, respectively, when 2 mg/L Ni NPs were included in the anaerobic digestion of livestock slurry. On the other hand, the study by Abdelsalam et al. (2016)
varied Co, Ni, Fe and Fe 3 O 4 nanoparticle concentrations (1, 2, 20 and 20 mg/L)
to assess their impacts on biogas and methane production from anaerobic digestion
of livestock slurry. The aforementioned study revealed that these NPs enhanced the
biogas and methane production.
(Abdelsalam et al. 2016). Similarly, a study by Gonzalez-Estrella et al. (2013)
revealed that Fe 3 O 4 and ZVI nanoparticles enhanced biogas production by 66%
and 45%, respectively. This improved process productivity of nano-base anaerobic digestion can be ascribed to the proliferation of methanogens resulting from
the promotion of direct interspecies electron transfer by nanoparticles (Park et al.
2018). The inclusion of nanometric materials also enhances the formation of essential biogas pathway intermediates such as acetate, butyrate, formate and hydrogen,
while reducing others like ethanol (Sekoai et al. 2019). In addition to the abovementioned impacts of NPs in anaerobic digestion, other catalytic effects include