10

1 Anaerobic Co-digestion as a Smart Approach for Enhanced Biogas Production

Alternative feed stock

(For co-digestion)

Carbohydrate

based

Protein

based

Lipids

based

Heterogenous

waste

(Crop residue);

Waste collection

%TS – (10–20)

%TC – (20–30)

%N – (1.0–2.5)

COD g/l – (80–99)

%VS – (60–90 of TS)

%Moisture – (50–70)

Processing

Transport

Storage

Substrate mixing ratio

(Ranch)

(FOG)

(MSW)

(WWTP)

(Dairy)

(Poultry)

(Farm)

(Restaurant);

(Retail waste);

Logistics

Feed stock

Weekly tests

Preferred range

OLR

Composition

HRT

(14–35 days)

Temperature*

Sampling

port

Direct testing

Pre treatment

(centrifuged)

Microbial load

VFA*

NH3*

COD

Additives

(Regulators)

VS

TS

pH*

Spent slurry (solids and liquids)

Methane % evaluation*

Biogas

Off-site use

On-site use

Evaluation

(N, P, heavy metals)

Methane,

CO, CO2, H2S, H2

Methanogenesis

Acetogenesis

Acidogenesis

Hydrolysis

Figure 1.2

Real-time monitoring of anaerobic digesters. * Daily tests. FOG – fat, oil, and

grease; P – phosphorus.

remedial action to circumvent the problem and prevent digester failures (Figure 1.2).

Direct monitoring of microbial growth is not always a feasible option, as it requires

an equipped anaerobic laboratory for studies, further the problems are compounded

by slower growth rate of methanogens as it takes days to evaluate the exact microbial

content of the digester. Molecular techniques such as fluorescence in situ hybridiza-

tion (FISH), 16S rRNA, real-time polymerase chain reaction (RT-PCR), and denatur-

ing gradient gel electrophoresis (DGGE) aid in assessment of microbial load feasible

mostly for laboratory studies and applicable to large-scale biogas digesters.

1.2.5.1

The pH Fluctuations

There are other ways of monitoring bioreactor performance; these parameters are

simple and can efficiently diagnose the current status of the working reactors. pH

is one such factor that can be readily checked at regular intervals; neutral pH is