(c) Environmental Indicators
The environmental indicators include emissions, effluents and wastes in the form
of water eutrophication/solid waste generation/global warming and resource usage
in the form of land occupation/material depletion/energy demand/water depletion
(Toledo-Cervantes et al. 2017). Processes like chemical absorption method and
cryogenic separation reduce the methane slip, but the electricity demand is high in
cryogenic process.
Pressurised swing adsorption method is environmentally suitable since the energy
consumption is very low. Hybrid technologies encompassing two technologies
combined together enhance more environmentally sustainable features such as
high carbon dioxide and sulphur capturing efficiency and low energy consumption
(Sahota et al. 2018).
Methane loss is up to 8% (high), <2%, <4%, <0.1%, <3%, <5% and < 0.1% for in
situ methane enrichment technique, pressurised water scrubbing method, organic
physical scrubbing method, amine scrubbing method, adsorption method, membrane
technology and cryogenic technology, respectively. But, the methane loss is very
less for hybrid technologies, cryogenic/membrane technology and membrane technology/pressurised water scrubbing method.
About 0.2–0.5 kWh/Nm
3 , 0.1–0.33 kWh/Nm
3 , 0.05–0.18 kWh/Nm
3 , 0.16–0.43
kWh/Nm
3 , 0.18–0.35 kWh/Nm
3 and 0.18–0.25 kWh/Nm
3 energy are utilised for
pressurised water scrubbing method, organic physical scrubbing method, amine
scrubbing method, adsorption method, membrane technology and cryogenic technology, respectively. For industrial lung method, energy utilised is high and for
hybrid technologies, cryogenic/membrane technology and membrane technology/
pressurised water scrubbing method, the energy utilised is very less. The amount of
water used is about 600m
3 /year, 90–180 m
3 /year and 300m
3 /year for pressurised
water scrubbing method, amine scrubbing method and cryogenic technology,
respectively. However, water usage is very minimum for supersonic method,
polymeric membrane technology and hybrid technologies, cryogenic/membrane
technology and membrane technology/pressurised water scrubbing method
(Sahota et al. 2018).
While comparing the biological method (algal-bacterial photobioreactor and
physical/chemical method), 1860 times more land is utilised for the biological
method with less energy consumption (208,837 kW-hy
À1 ), less water consumption,
no solid waste generation, less GHG emissions and minimum environmental
impacts. For physical and chemical upgrading methods, 100 m
2 (3 m
2 (Nm
3 /h)
À1
treated biogas) land is required, 99.8% energy is consumed, high effluent discharge
is manifested, solid waste generation is observed, GHG emissions occurs and more
water consumption is required.
The sustainability of the biological method is favoured by the replenished
nutrient, N and P, and the harmful occurrence of the harmful H 2 S gas (ToledoCervantes et al. 2017). During the process of upgrading, the methane gas is lost, and
it can be minimised using the latest technologies (Petersson and Wellinger 2009).
Methane slip is high for pressure swing adsorption method and low for amine
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
271
The environmental indicators include emissions, effluents and wastes in the form
of water eutrophication/solid waste generation/global warming and resource usage
in the form of land occupation/material depletion/energy demand/water depletion
(Toledo-Cervantes et al. 2017). Processes like chemical absorption method and
cryogenic separation reduce the methane slip, but the electricity demand is high in
cryogenic process.
Pressurised swing adsorption method is environmentally suitable since the energy
consumption is very low. Hybrid technologies encompassing two technologies
combined together enhance more environmentally sustainable features such as
high carbon dioxide and sulphur capturing efficiency and low energy consumption
(Sahota et al. 2018).
Methane loss is up to 8% (high), <2%, <4%, <0.1%, <3%, <5% and < 0.1% for in
situ methane enrichment technique, pressurised water scrubbing method, organic
physical scrubbing method, amine scrubbing method, adsorption method, membrane
technology and cryogenic technology, respectively. But, the methane loss is very
less for hybrid technologies, cryogenic/membrane technology and membrane technology/pressurised water scrubbing method.
About 0.2–0.5 kWh/Nm
3 , 0.1–0.33 kWh/Nm
3 , 0.05–0.18 kWh/Nm
3 , 0.16–0.43
kWh/Nm
3 , 0.18–0.35 kWh/Nm
3 and 0.18–0.25 kWh/Nm
3 energy are utilised for
pressurised water scrubbing method, organic physical scrubbing method, amine
scrubbing method, adsorption method, membrane technology and cryogenic technology, respectively. For industrial lung method, energy utilised is high and for
hybrid technologies, cryogenic/membrane technology and membrane technology/
pressurised water scrubbing method, the energy utilised is very less. The amount of
water used is about 600m
3 /year, 90–180 m
3 /year and 300m
3 /year for pressurised
water scrubbing method, amine scrubbing method and cryogenic technology,
respectively. However, water usage is very minimum for supersonic method,
polymeric membrane technology and hybrid technologies, cryogenic/membrane
technology and membrane technology/pressurised water scrubbing method
(Sahota et al. 2018).
While comparing the biological method (algal-bacterial photobioreactor and
physical/chemical method), 1860 times more land is utilised for the biological
method with less energy consumption (208,837 kW-hy
À1 ), less water consumption,
no solid waste generation, less GHG emissions and minimum environmental
impacts. For physical and chemical upgrading methods, 100 m
2 (3 m
2 (Nm
3 /h)
À1
treated biogas) land is required, 99.8% energy is consumed, high effluent discharge
is manifested, solid waste generation is observed, GHG emissions occurs and more
water consumption is required.
The sustainability of the biological method is favoured by the replenished
nutrient, N and P, and the harmful occurrence of the harmful H 2 S gas (ToledoCervantes et al. 2017). During the process of upgrading, the methane gas is lost, and
it can be minimised using the latest technologies (Petersson and Wellinger 2009).
Methane slip is high for pressure swing adsorption method and low for amine
9 Recent Trends in Biogas Upgrading Technologies for Biomethane Production
271