Microbiological Aspects of Composting

Composting is a biological process mediated by microbes belonging to the kingdom Protest, which includes bacteria, algae, fungi, protozoa, and virus particles (Table 12.2). Microbes can be classified into metabolic types based on the carbon and energy sources utilized by the cell. Autotrophs use carbon dioxide as a

Table 12.2 Microbial populations during aerobic composting (in: Poincelot 1977)

No./Wet gram compost

Mesophilic

Number

initial temp.

Thermophilic

Mesophilic

of species

Microbe

< 40°C

40-70°C

70°C to cooler

identified

Bacteria

Mesophlic

108

106

1011

6

Thermophlic

104

109

107

1

Actino-myces

Thermophlic

104

108

105

14

Fungi

Mesophilic

106

103

105

18

Thermophlic

103

107

106

16

source of cell carbon, whereas heterotrophs use the carbon of organic molecules. Phototrophs obtain energy from light. Litotrophs use the energy of inorganic chemical reactions, while organotrophs use the energy of organic chemical reactions. Most bacteria and all fungi are organoheterotrophs that use organic compounds both as a source of energy and for cell carbon (Haug 1993).

Lemunier et al. (2005) resulted that biowaste compost may support long-term survival of Salmonella serovar Enteridits when sanitation has been unsatisfactory during the thermophilic phase or in the case of colonization during storage of mature compost. Mature biowaste compost did not allow L. monocytogenes survival and also for Escherichia coli only a short survival time was observed. However, this study showed that management of the maturation phase is critical for limiting hazards associated with L. monocytogenes. The authors of the study about the potential survival of the seeded pathogens in biowaste composts conclude that the undesirable long-term survival of E. coli and L. monocytogenes could be prevented by proper management of the maturing phase. No risk of survival during compost storage should occur with L. monocytogenes. The survival time of Salmonella serrovar Enteridits was very short in composts sampled during the ther-mophilic phase but was longer when organisms were inoculated into mature bio-waste compost. Although waste composition affected pathogen growth in sterile composts, no clear relationship between compost physicochemical parameters and pathogen survival was found. Amendments of organic waste can increase nutrient levels and promote soil health, for example, by activation of natural plant pathogen predators (Zhang et al. 1998) and improve soil physical properties such as increasing porosity and pore connectivity, and thereby, improve living conditions for the soil fauna (Giusquani et al. 1995). It has been documented that Collembola and earthworms excrete N in NH4+ (Sjursen and Holmstrup 2004) and hence play an important role in N mineralization. Temperature is also an important selective factor for the development of Actinobacteria populations in composts, and they constitute a substantial part of the community in the different compost stages (Streger et al. 2007). Microbial biomass C correlates strongly with microbial activity but is even strongly correlated with the pH (Gattinger et al. 2004).

The cited papers in the field of biochemistry and microbiology can contribute to find better composing technology to reach higher decomposition rate using optimal temperature, time, and grinding the materials that help to reduce the survival of pathogens and ammonia loss.

Organic Gardeners Composting

Organic Gardeners Composting

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