analyzed, and then optimal conditions for completion of the digestion should be
investigated. Many researchers have reported such kinds of inhibitions due to
substrate. The substrates which were generally found to hinder the process include
pesticides, limonene, furans, metals, and antibiotics (Lallai et al. 2002; Wilkins et al.
2007; Alvarez et al. 2014; Yangin-Gomec and Ozturk 2013). Zabed et al. (2020)
have reviewed the production of biogas from microalgae and opined that commercial
production of microalgae-based biogas is still in its immature stage and a state-ofthe-art technology for producing microalgal biogas is the need of the hour. Excess
amounts of proteins and lipids can also cause substrate-induced inhibition. For
example, excess amounts of proteins may generate ammonium and hydrogen sulfide
which will inhibit microbial growth and change the pH. To overcome these kinds of
obstacles, co-digestion is preferred and can lower the toxicity of the substrate or its
metabolites. Protein at higher concentrations may result in the formation of ammonia
which is toxic for microbial growth (Angelidaki and Ahring 1994). Sousa et al.
reported that long chain fatty acids can inhibit the growth of methanogens. Lansing
et al. (2008) reported that eutrophication of aquatic ecosystems inhibits the growth of
plant and predators which are phototrophic in nature depend on the inorganic carbon
levels depleted along with an increase in pH. Certain heavy metals such as nickel,
zinc, copper, lead, chromium, cadmium, and mercury also have harmful effect on the
environment (Demirel et al. 2013).
Mizuki et al. (1990) reported that limonene (65–88 g/L) can effectively inhibit the
anaerobic digestion process. Furans such as hydroxymethylfurfural are produced
during the dehydration of carbohydrates present in lignin (Barakat et al. 2012). They
are inhibitory to microorganisms present within the digestion process. Monlau et al.
(2013) and Barakat et al. (2012) reported that 5-HMF is more inhibitory than other
furan compounds and the concentration of the compound should be above 6 g per
liter. Pharmaceutical and industrial wastewater consists of antibiotics and pesticides
which can be inhibitory to the process (Ji et al. 2013). A raise in the C/N ratio of the
feedstock can minimize the production of ammonia by the metabolism of excess
protein present in the feedstock (Zeshan et al. 2012). As the ecosystem involved is
very complex, anaerobic treatment process needs to be explored further, and the
process should be optimized. Only when this is achieved, the process of anaerobic
digestion will become sustainable. As long as this is not realized, the process will
continue to be a matter of research (Fagbohungbe et al. 2017).
8.9 Conclusions
The use of biogas health and sanitation benefits, ecological and societal benefits.
Compressing and bottling biogas would be of really help in commercializing the
biogas sector. The use of biogas has been on decline due to urban migration. Many
changes are needed such as research and development for optimizing the process
parameters and design of bioreactors which are efficient and economical. The
present state of giving subsidies to fossil fuels by the Governments should stop so
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R. Kumar et al.
investigated. Many researchers have reported such kinds of inhibitions due to
substrate. The substrates which were generally found to hinder the process include
pesticides, limonene, furans, metals, and antibiotics (Lallai et al. 2002; Wilkins et al.
2007; Alvarez et al. 2014; Yangin-Gomec and Ozturk 2013). Zabed et al. (2020)
have reviewed the production of biogas from microalgae and opined that commercial
production of microalgae-based biogas is still in its immature stage and a state-ofthe-art technology for producing microalgal biogas is the need of the hour. Excess
amounts of proteins and lipids can also cause substrate-induced inhibition. For
example, excess amounts of proteins may generate ammonium and hydrogen sulfide
which will inhibit microbial growth and change the pH. To overcome these kinds of
obstacles, co-digestion is preferred and can lower the toxicity of the substrate or its
metabolites. Protein at higher concentrations may result in the formation of ammonia
which is toxic for microbial growth (Angelidaki and Ahring 1994). Sousa et al.
reported that long chain fatty acids can inhibit the growth of methanogens. Lansing
et al. (2008) reported that eutrophication of aquatic ecosystems inhibits the growth of
plant and predators which are phototrophic in nature depend on the inorganic carbon
levels depleted along with an increase in pH. Certain heavy metals such as nickel,
zinc, copper, lead, chromium, cadmium, and mercury also have harmful effect on the
environment (Demirel et al. 2013).
Mizuki et al. (1990) reported that limonene (65–88 g/L) can effectively inhibit the
anaerobic digestion process. Furans such as hydroxymethylfurfural are produced
during the dehydration of carbohydrates present in lignin (Barakat et al. 2012). They
are inhibitory to microorganisms present within the digestion process. Monlau et al.
(2013) and Barakat et al. (2012) reported that 5-HMF is more inhibitory than other
furan compounds and the concentration of the compound should be above 6 g per
liter. Pharmaceutical and industrial wastewater consists of antibiotics and pesticides
which can be inhibitory to the process (Ji et al. 2013). A raise in the C/N ratio of the
feedstock can minimize the production of ammonia by the metabolism of excess
protein present in the feedstock (Zeshan et al. 2012). As the ecosystem involved is
very complex, anaerobic treatment process needs to be explored further, and the
process should be optimized. Only when this is achieved, the process of anaerobic
digestion will become sustainable. As long as this is not realized, the process will
continue to be a matter of research (Fagbohungbe et al. 2017).
8.9 Conclusions
The use of biogas health and sanitation benefits, ecological and societal benefits.
Compressing and bottling biogas would be of really help in commercializing the
biogas sector. The use of biogas has been on decline due to urban migration. Many
changes are needed such as research and development for optimizing the process
parameters and design of bioreactors which are efficient and economical. The
present state of giving subsidies to fossil fuels by the Governments should stop so
246
R. Kumar et al.