70
solvent scrubbing, pressure swing adsorption and membrane-based upgrading,
while other emerging technologies (for instance, cryogenic methods) for biogas
upgrading are still under developing stage [111]. Also, some chemical methods for
converting CO 2 into valuable products are successfully applied: amine chemical
scrubbing, methanation reaction and methanol and syngas synthesis are used as
biogas upgrading via CO 2 removal and CO 2 utilization technologies [111, 114, 115].
Besides the conventional technologies, the biological biogas upgrading method
has been researched and developed as an alternative to the currently available technologies. According to Bassani, this newly developed method involves hydrogenotrophic methanogens to react CO 2 from biogas and H 2 from external source, thus
producing additional CH 4 through biochemical pathways. Table 4 summarizes the
main features of each of the conventional biogas upgrading methods widely applied
commercially. The emerging technologies which proved good results in removing
contaminants like CO 2 , H 2 S and siloxanes but still need more in-depth research
before being implemented on the market are briefly presented in Table 5.
The techniques presented in Tableq 4 and Table 5 are suitable for removing various unwanted components from biogas, but a single method cannot ensure the complex purification to biomethane; in general, it is recommended that two or more
processes be combined to achieve the effective removal of biogas’ unwanted components. The choice between one conventional/emerging biogas upgrading technology and another is specific to each case and depends on the biogas’ quality
requirements for the given application, but all the mentioned upgrading technologies have different advantages and disadvantages [1].
Carbon dioxide removal from biogas can be achieved by water or organic solvent
scrubbing and also by separation by various means (with membranes, pressure,
cryogenic, adsorption, etc.). Water scrubbing is most commonly used for removing
CO 2 but also for H 2 S, although some organic absorbents (i.e. polyethylene glycolbased solvents) can retain CO 2 more efficiently [117]. Nevertheless, in order to
avoid solvent deterioration due to H 2 S contaminant in the biogas stream, a complete
H 2 S removal using activated carbon should be applied prior to organic scrubbing. In
case the recovery of H 2 S from the solvent is not achieved, the capacity of the solvent
for CO 2 absorption will be greatly diminished [128].
Hydrogen sulphide removal from gas streams can be done through many technologies, but selecting the best one has to take into account several factors such as
the composition of the gas and its final use, H 2 S concentration and the absolute
quantity of H 2 S to be removed, variability and volume of the gas to be treated, etc.
[129]. Among the traditional methods for removing H 2 S from biogas, the followings
dominate the market: adsorption on activated carbon, molecular sieves, iron and
zinc oxides, alkaline solids, water or solvent scrubbing and membrane purification.
In the past year, increased attention has been paid to the biotechnological methods (air/oxygen dosing to biogas reactor, biofilters) that have proved the same or
even higher efficiency in H 2 S removal than the physical-chemical methods [121,
129]. The biological methods are innovative alternatives still under development.
Yet, many large-scale biogas facilities are equipped with H 2 S removal units which
operate on the principle of biological H 2 S oxidation by aerobic bacteria [110].
C. Mateescu and A.-D. Dima
solvent scrubbing, pressure swing adsorption and membrane-based upgrading,
while other emerging technologies (for instance, cryogenic methods) for biogas
upgrading are still under developing stage [111]. Also, some chemical methods for
converting CO 2 into valuable products are successfully applied: amine chemical
scrubbing, methanation reaction and methanol and syngas synthesis are used as
biogas upgrading via CO 2 removal and CO 2 utilization technologies [111, 114, 115].
Besides the conventional technologies, the biological biogas upgrading method
has been researched and developed as an alternative to the currently available technologies. According to Bassani, this newly developed method involves hydrogenotrophic methanogens to react CO 2 from biogas and H 2 from external source, thus
producing additional CH 4 through biochemical pathways. Table 4 summarizes the
main features of each of the conventional biogas upgrading methods widely applied
commercially. The emerging technologies which proved good results in removing
contaminants like CO 2 , H 2 S and siloxanes but still need more in-depth research
before being implemented on the market are briefly presented in Table 5.
The techniques presented in Tableq 4 and Table 5 are suitable for removing various unwanted components from biogas, but a single method cannot ensure the complex purification to biomethane; in general, it is recommended that two or more
processes be combined to achieve the effective removal of biogas’ unwanted components. The choice between one conventional/emerging biogas upgrading technology and another is specific to each case and depends on the biogas’ quality
requirements for the given application, but all the mentioned upgrading technologies have different advantages and disadvantages [1].
Carbon dioxide removal from biogas can be achieved by water or organic solvent
scrubbing and also by separation by various means (with membranes, pressure,
cryogenic, adsorption, etc.). Water scrubbing is most commonly used for removing
CO 2 but also for H 2 S, although some organic absorbents (i.e. polyethylene glycolbased solvents) can retain CO 2 more efficiently [117]. Nevertheless, in order to
avoid solvent deterioration due to H 2 S contaminant in the biogas stream, a complete
H 2 S removal using activated carbon should be applied prior to organic scrubbing. In
case the recovery of H 2 S from the solvent is not achieved, the capacity of the solvent
for CO 2 absorption will be greatly diminished [128].
Hydrogen sulphide removal from gas streams can be done through many technologies, but selecting the best one has to take into account several factors such as
the composition of the gas and its final use, H 2 S concentration and the absolute
quantity of H 2 S to be removed, variability and volume of the gas to be treated, etc.
[129]. Among the traditional methods for removing H 2 S from biogas, the followings
dominate the market: adsorption on activated carbon, molecular sieves, iron and
zinc oxides, alkaline solids, water or solvent scrubbing and membrane purification.
In the past year, increased attention has been paid to the biotechnological methods (air/oxygen dosing to biogas reactor, biofilters) that have proved the same or
even higher efficiency in H 2 S removal than the physical-chemical methods [121,
129]. The biological methods are innovative alternatives still under development.
Yet, many large-scale biogas facilities are equipped with H 2 S removal units which
operate on the principle of biological H 2 S oxidation by aerobic bacteria [110].
C. Mateescu and A.-D. Dima