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16 Bioreactors for the Production of Industrial Chemicals and Bioenergy Recovery from Waste

the process (enhance the capital/working cost) and should be controlled as much

as possible. The fouling is unavoidable incident and could be inhibited if mecha-

nism and dependable factors are known. Membrane fouling is dependent on quality

(Figure 16.4) associated with functional state (operational flux, temperature, HRT,

SRT, pH, hydrodynamics such as shear rate on the membrane surface), membrane

characteristics (hydrophilic/hydrophobic, porosity, material and composition, mem-

brane pore size, surface charge, surface roughness, etc.), and bacterial/mixed liquor

characteristics (skim milk powder [SMP]/exopolysaccharide [EPS], hydrophobicity,

ionic strength, charge, populations density, species, growth phase, and biological

responses, etc.) [19, 20].

16.3.1.2

Biohydrogen Generation Rate and Yield

The unfinished substrate exchange, the subsequent low yields, and production rates

are major barriers which prevent scaling-up of the process. During the biohydrogen

production process, inhibitory byproducts such as short-chain VFAs (acetic, butyric,

propionic, and lactic acid, etc.), alcohols (butanol, ethanol, propanol, etc.), and

biohydrogen-consuming microorganisms (e.g. homo acetogens, methanogens,

nitrate-reducing bacteria, and sulfate-reducing bacteria) will reduce the production

rates and yields [21–23]. In comparison to traditional CSTRs, AnMBRs have diverse

designs, varied geometry of bioreactor, working parameters, recirculation of sludge,

and sparging of gases. Gas bubbling not only helps integration and control of fouling

but also can eliminate produced biohydrogen from liquid phase by increasing the

rate of liquid to gaseous mass transfer, which is pleasing in fermentative hydrogen

production, since hydrogenase activity can be receptive to rising hydrogen con-

centration in the aqueous stage. The partial pressure of hydrogen diminishes the

creation of alcohols and organic acids when the hydrogen production is maximized.

Therefore, it is challenging to advance hydrogen production in one-stage AnMBR.

16.4

Factors Affecting Biohydrogen Production

in AnMBRs

Rates of biohydrogen generation and yields are the function of a number of parame-

ters such as the nutrient availability, HRT, SRT, pH, temperature, and concentration

of substrates.

16.4.1

Nutrients Availability

The availability of nutrients such as nitrogen, phosphate, and other inorganic trace

minerals are crucial apprehension for bioreactors including AnMBRs. In order to

achieve best possible microbial growth and biohydrogen generation, element substi-

tution is required predominantly for carbohydrate-rich wastewater including other

waste streams. Organic nitrogen source, mineral salt medium, and iron concentra-

tion are the key variables as they can either restrain or improve the hydrogen gen-

eration in AnMBR [21]. Biohydrogen generation from microbes can be influenced