b. Acidogenesis

The hydrolysis soluble products of biodegradable material are easily diffused in to the cell membranes of acidogenic microorganisms. Acidogenic reactions are associated with obligate and facultative microbes, viz., *Micrococcus*, *Peptococcus*, *Streptococcus*, *Desulfomonas*, and *Escherichia coli*. The acidogenic microorganisms further convert the hydrolytic products into CO2, H2, and various organic acids which are known as volatile fatty acids (VFA) like acetates, propionate and butyrate along with this small amount of ethanol and lactate [24, 25]. The rate of reaction of VFA production is more in lower pH conditions, that is, pH 5 and ethanol production occurs in pH 4 [26]. The final acidic product can be used as a liquid and dry fertilizer [27]. VFA also creates the precursors for the final stage of methanogenesis. Chemical reactions that occur in acidogenesis are:

Compositing process is also mediated by different microorganisms in aerobic environment so it is also known as aerobic decomposition. The most common

Compositing process occurs in two phases which include: 1. degradation and 2.

1.Degradation: In this phase simpler organic matter are degraded by aerobic microorganisms. This phase is for several weeks to few months and occurs with high speed. This step needs temperature with full aeration for cooling the support also termed as thermophillic phase. Various phytotoxins also release as decomposition proceeds [35]. After degradation of simpler organic matter then decomposition of complex organic matter starts. At the end of this phase, most of the microorganisms die due to nonavailability of sufficient food. In addition to this, thermophillic condition changed to mesophillic and temperature drops from 50-55C to 25 C. According to several authors [33, 34, 36], this stage

2.Maturation: During the mesophillic phase or maturation phase, actinomyces appear and start degrading compost material of first phase into finer particles.

3. Solid-state fermentation (SSF) process is another bioprocess for solid waste disposal in absence of free water [37]. Microbial growth is very important for

Lots of invertebrates like earthworms, ticks, and centipedes further disintegrate by chemical and biological transformations (**Figure 4**). These transformations are termed as humification which is endorsed by the oxidative polymerization of phenolic compounds acquired by degradation of organic

� þ SO4

<sup>2</sup>� <sup>þ</sup> Heat

microorganisms are: bacteria, fungi, algae, and protozoans [34]. Compositing process can be explained by this equation:

*Role of Decomposers in Agricultural Waste Management DOI: http://dx.doi.org/10.5772/intechopen.93816*

Organic matter þ O2 ! Compost þ CO2 þ H2O þ NO3

occurred for longer period of time.

matter in the first phase.

*Hierarchy of bio-decomposers in compositing process.*

maturation.

**Figure 4.**

**531**

C6H12O6 \$ 2 CH3CH2OH þ 2 CO2 C6H12O6 þ 2 H2 \$ 2 CH3CH2COOH þ 2 H2O C6H12O6 ! 3 CH3COOH

c. Acetogenesis

The acidogenesis products like acetates and other organic acids further convert into hydrogen gas by dehydrogenation reactions. The hydrogen produced in this stage is the main substrate for methanogenic microorganisms. The reactions involved in this stage are [28, 29]:

> CH3CH2COO � þ3 H2O \$ CH3COO � þH þ HCO3 � þ3 H2 C6H12O6 þ 2 H2O \$ 2 CH3COOH þ 2 CO2 þ 4 H2 CH3CH2OH þ 2 H2O \$ CH3COO � þ3 H2 þ Hþ

The hydrogen produced in this step causes an inhibitory effect toward acetogenic microorganisms and the produced hydrogen is available for the consumption of methanogens. So, microorganisms of acetogenisis and methanogenisis work symbiotically in association.

d. Methanogenesis

In the final stage of anaerobic digestion, all the intermediates convert into H2, CH4, CO2, and CH3COOH [30]. The microbial species mainly include *Methanobrevibacter ruminantium*, *M. bryantic* and *M. thermoautotrophicum*, *Methanogenium cariaci and M. marinsnigri*, etc. [31]. Methane-producing bacteria can be divided into two groups, namely, acetophilic and hydrogenophilic.

The reaction equations in the methanogenic stage are as follows [32]:

CH3COOH ! CH4 þ CO2 CO2 þ 4 H2 ! CH4 þ 2 H2O 2 CH3CH2OH þ CO2 ! CH4 þ 2 CH3COOH

3.**Compositing:** Compositing is defined as the process of decomposition of complex waste organic matter into the simpler molecular chains. These smaller molecular compounds further decompose and form soil humus [33].

*Role of Decomposers in Agricultural Waste Management DOI: http://dx.doi.org/10.5772/intechopen.93816*

Compositing process is also mediated by different microorganisms in aerobic environment so it is also known as aerobic decomposition. The most common microorganisms are: bacteria, fungi, algae, and protozoans [34].

Compositing process can be explained by this equation:

Organic matter þ O2 ! Compost þ CO2 þ H2O þ NO3 � þ SO4 <sup>2</sup>� <sup>þ</sup> Heat

Compositing process occurs in two phases which include: 1. degradation and 2. maturation.


**Figure 4.** *Hierarchy of bio-decomposers in compositing process.*

**Figure 5.** *Solid fermented product.*

SSF which are very much affected by various environmental factors like moisture content, temperature, Ph, etc. [38]. Moisture is very crucial factor in hindrance of microbial enzymatic activity. The main bio-products of SSF are antibiotics, are organic acids, aromas, biopesticides, bio-fuel, biosurfactants, and bioplastics (**Figure 5**).

3.Macrofauna, including lumbricids, enchytraeids, millipedes, gastropods, and

1.**Primary decomposers:** These microbes have the potential to decompose the compounds present in organic matter. These microbes have the requisite enzymes like pectinase, ligase, cellulose, etc. to break the complex agricultural residues complex components like cellulose, hemicelluloses, lignin, etc.

2.**Secondary decomposers**: These decomposers play a significant role in the fragmentation and comminution of decomposing agricultural waste. These microbes do not require enzymes for decomposition. These decomposers constituted earthworms, collembola, mites, enchytraeids, etc. and the rate of

decomposition gets slower without secondary decomposers [39, 40].

Major decomposers of soil are bacteria, fungi, nematodes, micro-arthropods,

These decomposers further classified on the bases of role in decomposition

arthropods.

**Figure 7.**

**Figure 6.**

*Taxonomical biodeversity of waste decomposers.*

*Role of Decomposers in Agricultural Waste Management DOI: http://dx.doi.org/10.5772/intechopen.93816*

and earthworms [41, 42].

**533**

process primary and secondary (**Figure 4**).

*Classification of bio-decomposers on the basis of size.*
