Prisotnost bakterije Escherichia coli in drugih skupin mikroorganizmov v različnih fazah predelave komposta : magistrsko delo

Fajs, Petra (author), Godič Torkar, Karmen (mentor), Griessler Bulc, Tjaša (co-mentor)

Uvod: Pretirana uporaba kemičnih gnojil v zadnjih nekaj desetletij vodi v onesnaženost vode, zraka in prsti. Kmetijstvo se zato usmerja v trajnostni način kmetijske pridelave z uporabo komposta, pridelanega iz biološko razgradljivih odpadkov, ki obnovi rodovitnost prsti. Med kompostiranjem se v kompostu zmanjšuje število patogenih mikroorganizmov, ki bi lahko predstavljali tveganje za zdravje ljudi. Namen: Želeli smo ugotoviti število različnih vrst mikroorganizmov v kompostu iz biološko razgradljivih odpadkov v različnih fazah njegove predelave s poudarkom na prisotnosti in številu bakterij E. coli in Salmonella. Metode dela: 24 tednov smo spremljali celoten proces kompostiranja ene šarže kompostnega kupa v kompostarni podjetja Simbio in pri tem odvzeli skupno 80 vzorcev komposta za mikrobiološke preiskave in 160 vzorcev za fizikalno-kemijske analize. Z mikrobiološkimi preiskavami smo ugotavljali koncentracijo posameznih skupin mikroorganizmov z metodo štetja kolonij na gojiščih. Spremljali smo tudi fizikalno-kemijske parametre vzorcev komposta (temperatura, pH, vsebnost suhe snovi in vsebnost nitritov in nitratov). Rezultati: Začetna mezofilna faza je bila kratka, zajeli smo jo v 1. tednu kompostiranja, kjer smo prisotnost E. coli dokazali v 2 od 10 vzorcev komposta. Bakterije Salmonella v mezofilni fazi nismo zaznali. Termofilna faza kompostiranja je trajala do 18. tedna kompostiranja. V tej fazi se je povprečno število vseh preiskovanih vrst mikroorganizmov znižalo, pri čemer je njihovo število naraslo ob vlaženju kompostnega kupa z izcedno vodo v 5. tednu kompostiranja. Najvišje povprečno število vrste E. coli je bilo v 11. tednu kompostiranja (4,9 log CFU/g) v termofilni fazi. Bakterije Salmonella tudi v termofilni fazi nismo zaznali. Faza ohlajanja in zorenja je trajala od 18. do 24. tedna kompostiranja. V tej fazi smo bakterijo E. coli ugotovili v 8 od 10 vzorcev komposta v 24. tednu kompostiranja; njeno povprečno število v tem tednu je bilo 4,5 log CFU/g. Tudi bakterijo Salmonella smo zaznali v 24. tednu kompostiranja v 3 od 10 vzorcev komposta. Razprava in sklep: Hipotezo, da bosta z Uredbo (2013) predpisani mejni vrednosti število Escherchia coli in prisotnost Salmonella v vzorcih presežena (ne bosta skladni), lahko delno potrdimo. Primerjali smo rezultate 18. in 24. tedna kompostiranja, saj smo v 18. tednu predvideli zaključek kompostnega procesa. Vrednosti števila E. coli in prisotnost Salmonella v kompostu v 18. tednu kompostiranja ustrezata normativom, kar pomeni, da se kompost lahko uvrsti v 1. in 2. kakovostni razred. V 24. tednu kompostiranja je število bakterij E. coli in prisotnost vrst Salmonella presegalo normative iz Uredbe (2013), zato ta šarža komposta ne more biti uvrščena v 1. ali 2. kakovostni razred. Kompost glede na 24. teden kompostiranja, ni primeren za uporabo v kmetijstvu in se ravna v skladu s predpisom, ki ureja odpadke.

• Language: Slovenian
• Keywords: kompostiranje, biološko-razgradljivi odpadki, Escherichia coli, patogeni mikroorganizmi
• Work type: Master's thesis/paper
• Organization: ZF - Faculty of Health Sciences
• Year: 2019
• PID: 20.500.12556/RUL-109988
• COBISS.SI-ID: 5678443
• Publication date in RUL: 11.09.2019

Secondary language

• Language: English
• Title: The presence of bacteria Escherichia coli and other groups of microorganisms in different stages of compost : masterʹs thesis

Abstract

Introduction: In the recent few decades the overuse of chemical fertilizers has led to pollution of water, air, and soil. Agriculture has found a new way to renew the fertility of the soil with a sustainable way of farming with the use of compost made from biodegradable waste. Through the composting process the number of pathogen microorganism that could become a health risk for people decrease. Purpose: We want to find out the number of different species of microorganisms in compost from biodegradable waste in different stages of composting with special reference to bacteria E. coli and Salmonella. Methods: Through compost plant of the company Simbio, we were monitoring a batch of composting pile composting for 24 weeks and took overall 80 samples of compost for microbiological examination and 160 samples for physical-chemical analysis. With microbiological examinations of compost, we were counting colonies on bacteria growth medium for different species of microorganisms. We were also monitoring physical-chemical parameters of compost (temperature, pH value, dry matter content, and the content of nitrites and nitrates). Results: Initiative mesophilic phase was short. We were able to capture it in the first week of composting where E. coli was found in 2 out of 10 samples of compost. Salmonella was not detected in the mesophilic phase. The thermophilic phase of composting lasts until the 18th week of composting. In this phase, the average number of all tested microorganisms decreased but rose again due to watering composting pile with compost leachate water in the fifth week of composting. The highest average number of species E. coli was in the 11th week of composting (4.9 log CFU/g). Bacteria Salmonella was also not detected in the thermophilic phase. The phase of cooling and maturation lasts from the 18th until the 24th week of composting. In this phase, we detected bacteria E. coli in 8 of 10 samples of compost in the 24th week of composting with the average number 4.5 log CFU/g. Salmonella was additionally detected in the 24th week of composting in 3 of 10 samples of compost. Discussion and conclusion: The hypothesis that limiting values of E. coli and the presence of Salmonella in the samples of compost will not be consistent with the Regulation (2013) can be partially confirmed. We were comparing the results from the 18th and 24th week of composting because we predicted the conclusion of composting process at the end of the 18th week of composting. The number of E. coli and the presence of Salmonella in compost at the 18th week of composting were consistent with the norms, which means that this compost can be classified as the first and the second quality class. At the 24th week of composting, a number of bacteria E. coli and the presence of species Salmonella exceeded the norms from the Regulation (2013). Compost batch from 24th week of composting cannot be classified as the first or the second quality class. Regarding the 24th week of composting, compost is not suitable for the use in agriculture and is handled in accordance with adequate waste regulation.

• Keywords: composting, biodegradable waste, Escherichia coli, pathogen microorganisms