Page 268 - Industrial Wastewater Treatment, Recycling and Reuse

242 Industrial Wastewater Treatment, Recycling, and Reuse

Table 6.1 Factors affecting fermentative H 2 production with corresponding
optimum values
Parameter Optimum values
Operating pH range 4.5–6.5

Operating Mesophilic (30–40 C) and thermophilic (55–70 C)
temperature
Retention time 4–14 h
Organic loading rate 3-50 g of COD/L
Biocatalyst Anaerobic consortia
Pretreatment Combined treatment
Reactor Biofilm/suspended
configuration
Mode of operation Batch mode
Substrate Organic-based waste/wastewater with good
biodegradability
Nitrogen 0.01–0.10 g/L
Phosphorus 0.60 g/L

essential for the up-scaling of this technology. Changing the temperature
influences H 2 production as well as metabolite distribution, substrate degra-
dation, and bacterial growth. H 2 production by dark-fermentation was

reported under ambient (15–27 C), mesophilic (30–45 C), moderate ther-

mophilic (50–60 C), and extreme thermophilic (over 60 C) conditions
(Yokoyama et al., 2009). The optimal temperature for pure cultures was
found in the range of 37–45 C, while diverse optimum temperatures were

reported for mixed consortia (Tang et al., 2008). The optimum temperature
for H 2 production usually depends on the nature of the biocatalyst and the
type of wastewater used. Temperature control is especially important for
regaining the spore-forming acidogenic culture during the reactor
operation.
The acidic microenvironment facilitates pyruvate conversion to fatty
acids associated with H 2 production by AB. Neutral operations facilitate
CH 4 formation by MB. However, the basic operation leads to solventogen-
esis. The activity of AB is crucial and is the rate limiting step during the dark-
fermentative H 2 production process (Venkata Mohan, 2008; Venkata
Mohan et al., 2008a, 2010b). AB function well below pH 6, while the opti-
mum pH range for MB is between 6.0 and 7.5. Good H 2 production was
observed by maintaining the system’s pH in and around 6.0 (Van Ginkel
et al., 2001; Venkata Mohan et al., 2008b). However, highly acidic pH
(<4.5) is considered to be detrimental for H 2 production because it