**6. Application of biohythane process**

employed successfully by using a diluted waste stream with relatively small reactor volumes in ASBR, SAB, and UASB reactors. However, such a reactor configuration has a poor mass transfer system, which is mainly caused by a lack of mixing; this can lead to gases accumulat-

Mass transfer can be improved by mechanical stirring or liquid recirculation, depending on the reactor type and configuration. Also, applying proper bioreactor shapes and optimizing reactor dimensions such as the height to diameter ratio can help to improve mass transfer

genesis and methanogesis. When optimizing a methanogenic process using VFA rich, soluble

keeping the reactor stable [37]. The acetogenesis is limited mainly by VFA degradation, especially propionate that is the rate-limiting factor in the second stage anaerobic process. The investigation into optimizing the methanogenic reactor is mostly carried out by varying OLRs via increasing the substrate concentration or decreasing the HRTs to obtain satisfactory performance [25, 120]. The main signs of methanogenic reactor instability or overloading are decrease in pH [121]. As a drop of pH actually corresponds to VFA accumulation, pH below 6.3 has an impact on enzyme activity in the microorganisms involved in the second stage anaerobic digestion. Methanogenic archaea can function properly in a pH range between 6.5 and 7.8 [122]. Thus, a buffering solution is needed in order to resist a pH drop from VFA accumulation in the methanogenic process and maintain stability. The main buffer in the anaero-

et al. [25] found that the pH drop below 6.4 caused by the accumulation of 122 mM VFA in the attached growth reactor operated at 55°C and fed with 11.0 gVS/L·d (5.13 d HRT) of the food waste fermentation. The pH could inhibit the bioactivity of methanogenesis. Meanwhile, the

at pH around 7.5, where the reactor was operated at a 7.7 day HRT (7.9 gVS/L·d OLR) and almost VFA degradation was achieved. For the high rate anaerobic reactor, UASB reactor was operated at double OLR comparing to CSTR at thermophilic temperature (55°C) which providing better VFAs degradation than mesophilic temperature (35°C) [125]. This is mainly attributed to the increase of chemical and biological reaction rates for operating temperature of thermophilic condition and the organic acid oxidation reactions become more energetic at

matters as the consequence of hydrolysis and acidogenesis in the first stage, the reactor type

biofilm systems as reviewed by Demirel et al. [27]. Cell mass is retained well in the biofilm/ granular aggregates in biofilm systems, leading to have much higher sludge retention time (SRT) compared to HRT, which provides the advantage that the reactor can run at a higher flow rate and can tolerate higher toxic concentrations [128]. Various types of high rate biofilm systems such as UASB, ABR, and SAB can be operated by continuous feeding with the H<sup>2</sup> reactor effluent, with HRTs of less than 5 days [114, 125, 129, 130]. Among the high rate reactor types, the UASB is the most popular for anaerobic treatment of soluble organic matters

/L·d with a CH4

by H2

is mainly associated with sequential stages of aceto-

), which is usually added to carbohydrate rich substrates

fermentation because the first stage needs to be

reactor effluents are in soluble form of organic

in the second stage are based on high rate


content of 65% was obtained

production and VFA degradation, while


ing in the biofilm or granular sludge that risk losing H<sup>2</sup>

efficiency [91, 98, 117–119].

100 Advances in Biofuels and Bioenergy

The anaerobic conversion of VFA to CH<sup>4</sup>

bic digester is bicarbonate (HCO<sup>3</sup>

maximum CH<sup>4</sup>

before feeding them to the first stage of H<sup>2</sup>

higher temperature [126, 127]. Because the H2

used to convert these soluble organic matters to CH<sup>4</sup>

controlled with pH within the favorable range of 5–6 for H2

production rate of 2100 mL CH4

organic matters, the goal is to maximize both CH<sup>4</sup>

Methane is being commonly used, not only in the chemical industry but also in transport as compressed natural gas (CNG), which has been regarded as the clean energy carrier in comparison to gasoline or diesel. By combining the advantages of H2 and CH4 , biohythane is considered one of the important fuels involved in achieving the transition of technical models from a fossil fuel-based society to renewable-based society. CH4 used as a fuel for vehicle has weak points on its narrow range of flammability, slow burning speed, poor combustion efficiency as well as requirement for high ignition temperature of CNG-powered vehicles. Interestingly, H2 perfectly complements the weak points of CH4 such as the hydrogen/carbon ratio which is increased by adding H2 , which reduces greenhouse gas emissions. Adding H<sup>2</sup> , thus, improves the fuel efficiency and can extend the narrow range of flammability of CH<sup>4</sup> . The flame speed of CH<sup>4</sup> can be greatly increased by adding H2 , eventually reducing combustion duration and improving heat efficiency. The quenching distance of CH<sup>4</sup> can be reduced by the addition of H2 , making the engine easy to ignite with less input energy. A two-stage process technique, combining acidogenesis and methanogesis appears to give more efficient waste treatment and energy recovery than a single methanogenic process [13]. As the results reported by Kongjan and Angelidaki [129], mixed gas of CH<sup>4</sup> , CO2 , and H2 with the volumetric content of 44.8, 38.7, and 16.5%, respectively, containing approx. 10% H<sup>2</sup> on energy basis could be achieved. This specification was found to be most suitable for burning directly in the internal combustion engines [131] and could be biohythane. In addition to economical concern, the two-stage thermophilic anaerobic process has been previously evaluated that the payback time is around 2–6 years, depending on the disposal costs of organic wastes/ residues [28].

Various types of organic wastes can be used as substrate for biohythane production such as starch wastewater, palm oil mill effluent (POME), biowaste, sugarcane syrup, olive pulp, desugared molasses, food waste, and organic solid waste [13, 18, 19]. H2 and CH4 yield from two-stage biohythane production of palm oil mill effluent (POME) was 201 mL H<sup>2</sup> /gCOD and 315 mL CH4 /gCOD, respectively [13], which were higher than those of starch wastewater (130mL H<sup>2</sup> /gCOD and 230mL CH4 /gCOD, respectively) [18], sugarcane syrup (88mL H<sup>2</sup> /gCOD and 271 mL CH4 /gCOD, respectively) [111], and biowaste (21 mL H<sup>2</sup> /gCOD and 55 mL CH4 /gCOD, respectively) [112]. H2 and CH4 yield from two-stage biohythane production of olive pulp (190 mL H<sup>2</sup> /gVS and 160 mL CH<sup>4</sup> /gVS, respectively) [110] was lower than that of food waste (205 mL H<sup>2</sup> /gVS and 464 mL CH<sup>4</sup> /gVS, respectively) [21]. Successful biohythane production from POME by two-stage thermophilic H<sup>2</sup> reactor and mesophilic CH4 reactor was achieved with biohythane production rate of 4.4 L/L·d with biogas composition of 51% CH4 , 14% H2 , and 35% CO2 [13]. POME is a suitable substrate for H<sup>2</sup> production in terms of high biogas production volume. Energy analysis of two-stage anaerobic fermentation process has greater net energy recovery than the single stage H2 production and single stage CH4 production process. O-Thong et al. [15] applied two-stage thermophilic fermentation and mesophilic methanogenic process with methanogenic effluent recirculation to H2 reactor for biohythane production from POME. The pH two-stage reactor was control by recirculation of methanogenic effluent with H<sup>2</sup> and CH4 yield of 135 mL H2 /gVS and 414 mL CH4 /gVS, respectively. Flow diagram of successful thermophilic two-stage anaerobic fermentation for biohythane from POME at lab scale 5 L CSTR and 25 L UASB, semi-pilot scale 50 L CSTR and 250 L UASB and industrial scale 5 m<sup>3</sup> CSTR and 25 m<sup>3</sup> UASB are shown in **Figure 3**.

Improvement methods such as effluent recirculation to mix with feedstock in H<sup>2</sup> reactor, biomethane gas recirculation to H2 reactor, and the combined effluent recirculation to H<sup>2</sup> reactor with biomethane gas sparging to CH4 reactor were reported to enhance biohythane production (**Figure 4**). The two-stage anaerobic fermentation process with methanogenic sludge recirculation (two-stage recirculation process) could be successfully operated and maintained at pH around 5.5 in H2 reactor without any alkaline addition [21]. The recirculation of part of the methanogenic sludge to a H2 reactor was provided as the buffer for the first stage. Kim et al. [132] also reported the recycling of a methanogenic effluent to a H<sup>2</sup> reactor with H2 production increased from 1.19 to 1.76 m<sup>3</sup> H2 /m3 ·d, and decreased the requirement for alkali addition. H2 yield from the two-stage anaerobic fermentation with the recirculation process was 2.5–2.8 mol/mol hexose [25], which was relatively high comparing to 4 mol/mol hexose from the maximum theoretical H<sup>2</sup> yield. The recirculation of the CH4 effluent to hydrogen reactor could protect the H2 fermentation process from a sharp drop in pH or organic overloading. Operations with the circulation of heat-treated sludge performed considerably better than those with the recirculation of raw sludge with respect to both the H2 production rate and yield [19]. Lee et al. [25] improved two-stage anaerobic fermentation for biohythane production by biomethane gas sparging to second stage and recirculation biomethane effluent for pH adjustment in H2 reactor. The gas yields were 2.3 mol H2 /mol hexose and 287 L CH<sup>4</sup> /kg COD, respectively, while TS of food waste was kept at 10%. The recirculation of methanogenesis effluent provides ammonia-rich buffer, which flavors H<sup>2</sup> -producing bacteria eventually and improves the performance of the H2 reactor. Liu et al. [34] were the first group to develop a two-stage CSTR-CSTR system for mesophilic H<sup>2</sup> and CH4 production using household solid waste as both inoculum and substrate. The yields of H2 and CH4 were 43 and 500 L/kg VS, respectively, while the TS of the H<sup>2</sup> CSTR was maintained at 10%. CH<sup>4</sup> production was over 20% higher than that in single-stage CH4 fermentation. Cavinato et al. [120] established a two-stage CSTR-CSTR reactor under thermophilic condition for biohythane production from municipal solid waste. The H2 and CH4 gas yields were 52 L H2 /kg VS and 410 L CH<sup>4</sup> /kg VS, respectively. Willquist et al. [113] proposed a biohythane process from wheat straw including pretreatment, H2 production using *Caldicellulosiruptor saccharolyticus*, CH4 production using a methanogenic consortium, and gas upgrading using an amine solution. The first reactor was extreme thermophilic CSTR and the second reactor was mesophilic UASB applying for biohythane production. A biohythane gas with the composition of 46–57% H<sup>2</sup> , 43–54% CH4 , and 0.4% CO2 could be produced at high production rates (2.8–6.1 L/L·d), with 93% chemical oxygen demand (COD) reduction, and a net energy yield of 7.4–7.7 kJ/g dry straw. The CO<sup>2</sup>

has to be removed before the biogas can be used as hythane by an amine solution, consisting of a mixture of 40% N-methyldiethanolamine (MDEA), 10% piperazine (PZ) and 50% water,

**Figure 3.** Flow diagram of scaling-up of the two-stage anaerobic fermentation for biohythane production from POME;

Biohythane Production from Organic Wastes by Two-Stage Anaerobic Fermentation Technology

http://dx.doi.org/10.5772/intechopen.74392

103

in various

CSTR and

by weight. This is a solvent commonly used in industry for the removal of CO2

a lab scale 5 L CSTR and 25 L UASB (A), semi-pilot scale 50 L CSTR and 250 L UASB (B), industrial scale 5 m<sup>3</sup>

mixtures of gases, including biogas.

25 m3

UASB (C).

Biohythane Production from Organic Wastes by Two-Stage Anaerobic Fermentation Technology http://dx.doi.org/10.5772/intechopen.74392 103

process has greater net energy recovery than the single stage H2

by recirculation of methanogenic effluent with H<sup>2</sup>

scale 50 L CSTR and 250 L UASB and industrial scale 5 m<sup>3</sup>

production process. O-Thong et al. [15] applied two-stage thermophilic fermen-

/gVS, respectively. Flow diagram of successful thermophilic two-stage anaerobic

and CH4

reactor, and the combined effluent recirculation to H<sup>2</sup>

reactor without any alkaline addition [21]. The recirculation of part of

fermentation process from a sharp drop in pH or organic overloading.

tation and mesophilic methanogenic process with methanogenic effluent recirculation to

fermentation for biohythane from POME at lab scale 5 L CSTR and 25 L UASB, semi-pilot

tion (**Figure 4**). The two-stage anaerobic fermentation process with methanogenic sludge recirculation (two-stage recirculation process) could be successfully operated and maintained

the methanogenic sludge to a H2 reactor was provided as the buffer for the first stage. Kim

2.5–2.8 mol/mol hexose [25], which was relatively high comparing to 4 mol/mol hexose from

yield. The recirculation of the CH4

Operations with the circulation of heat-treated sludge performed considerably better than

yield [19]. Lee et al. [25] improved two-stage anaerobic fermentation for biohythane production by biomethane gas sparging to second stage and recirculation biomethane effluent for pH

respectively, while TS of food waste was kept at 10%. The recirculation of methanogenesis

two-stage CSTR-CSTR reactor under thermophilic condition for biohythane production from

respectively. Willquist et al. [113] proposed a biohythane process from wheat straw including

a methanogenic consortium, and gas upgrading using an amine solution. The first reactor was extreme thermophilic CSTR and the second reactor was mesophilic UASB applying for

oxygen demand (COD) reduction, and a net energy yield of 7.4–7.7 kJ/g dry straw. The CO<sup>2</sup>

production using *Caldicellulosiruptor saccharolyticus*, CH4

and CH4

CSTR was maintained at 10%. CH<sup>4</sup>

could be produced at high production rates (2.8–6.1 L/L·d), with 93% chemical

gas yields were 52 L H2

yield from the two-stage anaerobic fermentation with the recirculation process was

Improvement methods such as effluent recirculation to mix with feedstock in H<sup>2</sup>

et al. [132] also reported the recycling of a methanogenic effluent to a H<sup>2</sup>

those with the recirculation of raw sludge with respect to both the H2

reactor. The gas yields were 2.3 mol H2

and CH4

biohythane production. A biohythane gas with the composition of 46–57% H<sup>2</sup>

effluent provides ammonia-rich buffer, which flavors H<sup>2</sup>

waste as both inoculum and substrate. The yields of H2

two-stage CSTR-CSTR system for mesophilic H<sup>2</sup>

 H2 /m3

reactor for biohythane production from POME. The pH two-stage reactor was control

stage CH4

102 Advances in Biofuels and Bioenergy

mL CH4

in **Figure 3**.

tion. H2

methane gas recirculation to H2

at pH around 5.5 in H2

with biomethane gas sparging to CH4

duction increased from 1.19 to 1.76 m<sup>3</sup>

improves the performance of the H2

respectively, while the TS of the H<sup>2</sup>

municipal solid waste. The H2

20% higher than that in single-stage CH4

the maximum theoretical H<sup>2</sup>

could protect the H2

adjustment in H2

pretreatment, H2

and 0.4% CO2

H2

production and single

/gVS and 414

reactor, bio-

reactor

pro-

UASB are shown

reactor with H2

effluent to hydrogen reactor

production rate and

/kg COD,

/kg VS,

,

yield of 135 mL H2

CSTR and 25 m<sup>3</sup>

reactor were reported to enhance biohythane produc-

·d, and decreased the requirement for alkali addi-

/mol hexose and 287 L CH<sup>4</sup>

reactor. Liu et al. [34] were the first group to develop a

fermentation. Cavinato et al. [120] established a

and CH4


production using household solid

/kg VS and 410 L CH<sup>4</sup>

were 43 and 500 L/kg VS,

production was over

production using

, 43–54% CH4

**Figure 3.** Flow diagram of scaling-up of the two-stage anaerobic fermentation for biohythane production from POME; a lab scale 5 L CSTR and 25 L UASB (A), semi-pilot scale 50 L CSTR and 250 L UASB (B), industrial scale 5 m<sup>3</sup> CSTR and 25 m3 UASB (C).

has to be removed before the biogas can be used as hythane by an amine solution, consisting of a mixture of 40% N-methyldiethanolamine (MDEA), 10% piperazine (PZ) and 50% water, by weight. This is a solvent commonly used in industry for the removal of CO2 in various mixtures of gases, including biogas.

The H2

H2 /CH4

/CH4

organic wastes to H2

50–55% of CH4

organic wastes is fermented to H2

based hythane by removing CO2

cantly reducing the fermentation time.

**Acknowledgements**

**Author details**

Sompong O-Thong<sup>1</sup>

Phatthalung, Thailand

**References**

University, Songkhla, Thailand

and *Thermoanaerobacterium* sp., are efficient H<sup>2</sup>

, and 30–40% of CO2

Biohythane Project (Grant number CRP5407010010).

\*Address all correspondence to: sompong@tsu.ac.th

\*, Chonticha Mamimin<sup>1</sup>

ratio of range 0.1–0.25 is suggested for biohythane. A flexible and controllable

Biohythane Production from Organic Wastes by Two-Stage Anaerobic Fermentation Technology

. *Clostridium* sp., *Enterobacter* sp., *Caldicellulosiruptor* sp., *Thermotoga* sp.,

, VFA, lactic acid and alcohols. Effluents from first

) called biohythane. Biohythane could be upgraded to bio-

. The two-stage anaerobic fermentation could increase COD

producers in the first stage. *Methanosarcina*

in the second stage by

http://dx.doi.org/10.5772/intechopen.74392

production rates as well as

production. The

,

105

 ratio afforded by two-stage fermentation is of great importance in making biohythane. Biohythane can be achieved by two-stage anaerobic fermentation; in the first stage,

methanogens under a neutral pH range of 7–8 and HRT of 10–15 days. The pH of 5–6 and an HRT of 2–3 days are optimized for first stage that flavor acidogenic bacteria to convert

combination of biohydrogen and biomethane production from organic wastes via two-stage anaerobic fermentation could yield a gas with a composition like hythane (10–15% of H<sup>2</sup>

high yield and purity of the products. In addition, the two-stage process has advantages of improving negative impacts of inhibitive compounds in feedstock, increased reactor stability with better control of the acid production, higher organic loading rates operation, and signifi-

This work was financially supported by Thailand Research Fund (Grant number RTA6080010) and Agricultural Research Development Agency (Public Organization) (ARDA) under

1 Department of Biology, Biotechnology Program, Faculty of Science, Thaksin University,

2 Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla

[1] Hallenbeck PC, Ghosh D. Advances in fermentative biohydrogen production: The way forward? Trends in Biotechnology. 2009;**27**:287-297. DOI: 10.1016/j.tibtech.2009.02.004

and Poonsuk Prasertsan<sup>2</sup>

, CO2

sp. and *Methanoculleus* sp. played an important role in the second stage CH4

stage containing VFA, lactic acid, and alcohols are converted to CH<sup>4</sup>

degradation efficiency, increase net energy balance, increase CH<sup>4</sup>

**Figure 4.** Schematic flow diagrams of gas yield improving for two-stage anaerobic fermentation for biohythane production by liquid methane effluent recirculation method (A), biomethane gas recirculation method (B), the combine liquid methane effluent recirculation and biomethane mixing method (C), liquid methane effluent heated recirculation method (D), and mixed solid and liquid methane effluent recirculation (E).
