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28 Bioconversion of Food Waste to Wealth – Circular Bioeconomy Approach

Emergency measures

Application of anti-foam

additives

Avoidance of foam supporting

feeding substrates

Resolving process upsets

Change of pysico-chemical

conditions

Change of mixing and feeding

strategy

Technical measures

Lowering of the filling level

Commercial anti-foam products

Vegetable oil or biodiesel

Buffering additives

Reduction of foam supporting substrates

Feeding of these substrates into the post-digester

Change of feeding intervals

Application of trace elements if necessary

Avoidance of inhibitors, re-inoculation after toxification

Reduction of feeding after overfeeding

Change of the viscosity

Controlled change of temperature

Change of alkalinity

Shortening of pauses between mixing intervals

Shortening of pauses between feeding intervals

Variation of mixer speed and/or direction

Installation of fan nozzles

Installation of an overflow pipe at filling level height

Installation of a mixer at filling level height

Reduction of feeding

Adjustment of stirrers to the top level

Figure 28.2

Strategies applied to reduce the foaming in 327 biogas plants . Source:

Lindorfer and Demmig [26].

agents by microorganisms due to improper digester operations; and (iii) high loading

of organic dry matter [25, 26]. Unexpected decrease in pH and increase in tempera-

ture can also cause foaming due to sudden release of large volume of dissolved CO2

gas [27]. Foaming problems in digesters can be avoided by (Figure 28.2) control-

ling the loading rate of foam generating substrates, changing the physicochemical

conditions, and application of anti-foaming agents.

Agro- and food processing wastes are grouped into seven categories based on

chemical characteristics including energy crops, byproducts of lignocellulosic,

herbaceous, vegetable and fruit crops, livestock effluents, and miscellaneous food

processing byproducts [13]. Energy crops such as millet, barley, sorghum, maize,

and triticale are justified by high methane yields (250–350 l CH4/kg total volatile

solids) due to high hydrolysis constant rates (0.15 d⁻¹) which indicate the good

degradation potential. Food wastes are the most abundant waste in urban area and

are characterized by their methane yield (250–350 l CH4/kg total volatile solids) [13].

This will overcome the disadvantage of mono-digestion of food waste by increased