Proportion of Sewage Sludge to Soil Influences the Survival ofSalmonellaDublin andEscherichia coli

Abstract

The survival of enteric pathogens in sewage sludge can lead to their transferral into the soil environment and subsequent contamination of crops and water courses. This, in turn, can increase the potential spread of gastrointestinal disease. This work aims to determine the persistence of several microorganisms, co‐introduced with sewage sludge, when exposed to varying proportions of sewage sludge to soil. Three microcosm‐based studies are established, inoculated with Salmonella Dublin or an environmentally persistent strain of Escherichia coli (quantified periodically over a period of 42 days), or indigenous sewage sludge E. coli (quantified over a period of 56 days). Treatments consist of a mixture containing: 0, 15, 25, 50, 75, and 100% soil or sludge, depending upon the experiment. Each introduced microorganism decline significantly over time, with greater quantities of soil generally instigating greater die‐off particularly in the cases of environmentally persistent E. coli and S. Dublin. However, this relationship is not proportionally related as sludge/soil mixtures show greater declines than pure soil treatments. In contrast, indigenous sewage sludge E. coli has a more consistent decline across all treatments. This indicates that indigenous strains are more resilient and can be indicative of natural behavior. Moreover, the effects of soil‐borne factors on pathogen attenuation are context dependent and non‐linear, possibly arising from the relative spatial distribution of introduced sludge and attendant microbes in soil.

Sanitary and environmental aspects of sewage sludge management

“…Also, Salmonella is one of the most-studied bacteria in WWTP sludge (Jr Krzyzanowski et al, 2016). These bacteria can survive once released into the environment in part through sludge spreading on agricultural plots (Jr Krzyzanowski et al, 2016;Bloem et al, 2017;Ellis et al, 2018). Thus, the consumption of food from these lands could be a way of contamination.…”

Risk Assessment of E. coli Survival Up to the Grazing Exclusion Period After Dairy Slurry, Cattle Dung, and Biosolids Application to Grassland

“…The heterogeneous nature of the above five categorized materials and their diverse treatment conditions like moisture level, seasonality, application dose, and condition were also considered to cover the wide range of data set. Data were obtained from tables or log-linear regression equations where available (Himathongkham et al, 1999;Oliver et al, 2006;Lang and Smith, 2007;Martinez et al, 2013;Hodgson et al, 2016;Roberts et al, 2016); otherwise, data were extracted from digitized figures to derive log-linear regression equation by plotting Log 10 CFU g −1 dw vs. Time (days) (Avery et al, 2004(Avery et al, , 2005Oliver et al, 2010;Schwarz et al, 2014;Biswas et al, 2018;Ellis et al, 2018). The die-off pattern of pathogens can be described by the first-order kinetics Equation 1, which upon integration gives the linear Equation 2 (Mubiru et al, 2000;Martinez et al, 2013).…”

“…The risk model input parameters i.e., initial E. coli concentration (C 0 ) and decay rate (k) were used from the Table 1 as presented in Table 2. In scenario 1, the values of C 0 (i.e., concentration of E. coli at day 0) and k were taken as the average for soil to sludge mixture matrix of un-amended soil (Lang and Smith, 2007), 100% soil (E. coli spiked) (Oliver et al, 2006;Ellis et al, 2018), 75% soil to 25% sludge (Ellis et al, 2018), 50% soil to 50% sludge (Ellis et al, 2018), 25% soil to 75% sludge (Ellis et al, 2018), and 100% sludge (Avery et al, 2005;Ellis et al, 2018). In scenario 2, C 0 was considered as the average of biosolids associated E. coli from five different studies and the k value was considered individually from the respective study and also, as an average value of those studies (Table 1, 2).…”

“…In scenario 2, the E. coli survival trend in biosolids amended soil was assessed based on the empirical data (Tables 1, 2) from five reference studies as shown in Figure 1B. The E. coli concentration (log 10 CFU g −1 dw) after 20 days was ≤0.57 from an initial value of 6.48 for the average biosolids and three study references (Avery et al, 2005;Roberts et al, 2016;Ellis et al, 2018), except for Schwarz et al (2014) (C 20 = 1.14) and Lang and Smith (2007)(C 20 = 1.72). The C 40 value ranged from 0.006 to 0.46 log 10 CFU g −1 dw for all five reference studies.…”

“…The guideline relates to postapplication of biosolids to grassland and restricts the livestock grazing period stating that "cattle should not be turned out onto pasture that has been fertilized with biosolids until 3-6 weeks after the date of application" (Fehily Timoney Company, 1999). There is growing concern on the survival of enteric Escherichia coli (E. coli) in biosolids and associated risk of transferring this fecal indicator organism (FIO) pollutant into the soil environment and subsequently, contamination of crops and nearby water sources, leading to the potential of spread of gastrointestinal disease (Greene et al, 2008;Ellis et al, 2018). The Sewage Sludge Directive 86/287/EC does not specify limits for E. coli counts as a fecal contamination indicator in biosolids, but specifies general land use, harvesting, and grazing limits to provide protection against the risk of infection (Sobrados-Bernardos and Smith, 2012).…”