Year: 2014
Type: dissertation
Abstract: In recent years, it has been reported that numbers of Escherichia coli increase \nsignificantly following centrifugation of sludge during the treatment process. E. \ncoli is used as an indicator of the microbiological quality of sludge-derived \nproducts destined for agricultural recycling and of the efficacy of the sludge \ntreatment processes. The re-growth phenomenon is of concern because of the \npotential for additional treatment requirement / higher disposal costs and loss of \nconsumer confidence associated with a compliance failure. It is hypothesised \nthat a competitive exclusion treatment could be the solution wherein the \ndigestate be exposed to a ‘probiotic’ or defined mixture of micro-organisms, to \neffectively out compete or eliminate any resident E. coli remaining following \ntreatment. The competitive exclusion principle as a treatment method has \nalready seen application in various industrial sectors, the most well-known \nbeing the poultry industry. In experiments it was determined that an \nantimicrobial producing organism would be most likely to succeed. From the \ncandidates screened, Lactobacillus reuteri proved the most promising. L. reuteri \nis a known producer of reuterin in the presence of glycerol and organic acids as \na part of its normal metabolic activity. In sludge derived nutrient broth in the \npresence of glycerol and low pH, L. reuteri addition resulted in a reduction of E. \ncoli to undetectable levels. In sludge cake under the same conditions, L. reuteri \nwas less successful. However the addition of glycerol and L. reuteri to sludge \ncake restricted E. coli growth to a 2 log increase from the initial concentration of \nE. coli recorded following pasteurisation (an average of around 1x102 cfu/gDs), \nin comparison in the positive control a 4 log increase was recorded. From this \nresult the sludge cake could be defined as conventionally treated. It can be \nconcluded that competitive exclusion and L. reuteri show promise as a \ntreatment for reducing E. coli re-growth in sludge cake
Source: CERES (Cranfield University)
Author: Tyson Williams
Language: English
Subfield: Food Science
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W1434667014