|
|
Survival of thermotolerant coliform bacteria and E. coli during vermicomposting
Stegbauerová, Klára ; Hanč, Aleš (advisor) ; Petra, Petra (referee)
The aim of this thesis survival of thermotolerant coliform bacteria (TCB) and Escherichia coli during vermicomposting is to assess the ability of the earthworm Eisenia species (Eisenia andrei and Eisenia fetida) to reduce the number of these pathogens in the process of vermicomposting.
To prove or disprove the hypothesis that vermicomposting process is able to eliminate the number of these pathogenic organisms, an experiment was conducted at the research facility FAPPZ in Červený Újezd, which was followed by eight-week laboratory experiment carried out in the laboratory of SZÚ in Prague.
Vermicomposting is a process whereby it is possible to decompose various kinds of biodegradable material of plant or animal origin. In the experiment only the substrates of vegetable nature - apple pomace and marc were compared with each other. These plant materials were mixed in a ratio of 75 % of preprocessed material and 25 % of the fresh material. 50 g of this mixture was inserted into each individual perforated container. The laboratory experiment included four variants of samples suspension/ earthworms, suspension/ without earthworms with the addition of the inoculum and control variants without inoculum (without suspension/ without earthworms and without suspension/ earthworms).
To inoculated variants it was added the exact amount of pathogenic organisms, Escherichia coli (2,1.107 cfu/ g) and TCB (6,1.108 cfu/ g) and to the respective variants additional 2.5 g of earthworms. These samples were analyzed on two-week intervals in a lab (beginning November 9, 2015, then November 23, 2015, December 7, 2015, December 21, 2015, January 4, 2016). Prior to the microbiological analysis the earthworms were always removed and their weight and vitality were determined. Also the initial substrates were examined to define the total number of microorganisms (CPM) growing at 30°C to assess the impact of their own composting process on the development of microbial communities. For marc it was CPM 9,4.106 cfu/ g and for apple pomace 1,2.107 cfu/ g. The results of individual variations were compared with one another.
According to the results, earthworms influence acceleration of the process of reducing the number of pathogenic Escherichia coli bacteria, when even during the period of the experiment a complete elimination of the pathogen occurred. However, there is no clear evidence to the degree of how much earthworms participate on the elimination and how much of that was caused by the actual process of composting. The largest decline in the number of monitored pathogens was always observed during the second week of the experiment, then the decrease was only moderate.
The results of monitoring the reduction of thermotolerant coliform bacteria suggest that the presence of earthworms in the substrate has no significant impact on the reduction of these pathogens. Initial substrate contained high initial quantity of CPM, so it can be assumed that the reduction in the number of TCB was mainly influenced by the actual composting process. The complete elimination of TCB did not occur. In this case it is necessary to extend the testing period to prove or disprove the hypothesis whether vermicomposting process is capable of eliminating these pathogens.
Details of the experiment are thoroughly described in the methodology of this thesis and the results of the experiment are summarized in the results section.
|
guest ::
