Occurrence and levels of indicators and selected pathogens in different sludges and biosolids

Abstract

Aims: Determine the occurrence and levels of pathogens and indicators in raw and treated sludges and compare their persistence after two different treatments. Methods and Results: Helminth ova, Cryptosporidium spp., Salmonella spp., enteroviruses, and bacterial and viral indicators were determined in raw sludges and biosolids produced after mesophilic and thermophilic treatments. Except Salmonella, all of the parameters were quantified. Helminth ova were found at very low concentrations even in raw sludges. Viable Cryptosporidium oocysts were still present in most samples of treated sludges. Faecal coliforms, spores of sulphite‐reducing clostridia (SSRC), and somatic coliphages were the only indicators with values above their detection limits in most of the samples. Conclusions: Pathogens were still detected in some treated sludge samples. SSRC were the most resistant micro‐organisms to treatments and hence may be an indicator for the reduction of protozoan oocysts. Somatic coliphages constitute an alternative as viral indicators due to their detection in sludges before and after treatment. Significance and Impact of the Study: Because of the persistence of some pathogens after sludge treatments, additional indicators are needed. SSRC and somatic coliphages are good candidates. Easy and inexpensive methods for the determination of these indicators are feasible both in industrialized and developing countries.

Coliphages as Model Organisms in the Characterization and Management of Water Resources

“…The ratios of culturable viruses to somatic coliphages (mainly with reference to enteroviruses detected by cell culture) are 10:10 4 or 10:10 5 in the scenarios for which data on both are available. The claim is true for raw sewage, secondary and tertiary effluents [72][73][74][75][76][77], surface waters [73,[78][79][80], and sludge [81,82]. The same ratio is true for infectious rotaviruses detected by cell culture followed by qRT-PCR [83].…”

“…Cole et al and Rahman et al determined the numerical ratios between F-DNA phages and F-RNA phages in surface waters and observed that in summer F-specific RNA phages were in the minority, whereas they accounted for more than 90% during the other seasons [108,109]. The abatement of F-specific RNA phages in sludge mesophilic (30-35˝C) anaerobic digestion is faster (approximately two log 10 units versus one log 10 unit) than that of somatic coliphages or Bacteroides phages [81,101]. This acceleration in the inactivation kinetics of F-specific bacteriophages with increasing temperatures is also observed in experiments with laboratory-grown bacteriophages.…”

“…Concentrations above 10 7 PFU for somatic coliphages and well over 10 6 PFU for F-specific bacteriophages per gram of dry weight of primary and raw sludge have been reported [81,101].…”

Bacteriophage predation regulates microbial abundance and diversity in a full-scale bioreactor treating industrial wastewater

“…However, little is known about phage activity in bioreactors, a subject considered, thus far, in only a handful of publications (Ewert and Paynter, 1980;Hantula et al, 1991;Khan et al, 2002a, b;Otawa et al, 2007;Kunin et al, 2008;Wu and Liu, 2009). Many studies have focused on the detection of viral particles as indicators of survival and release of pathogenic viruses into the environment (Lucena et al, 2004;Gino et al, 2007;Guzman et al, 2007) However, there is little or no information available regarding the impact of viral activity on microbial ecology or process performance. The dense biomass in engineered bioreactors, maintained under homogenized, relatively stable conditions, makes these systems ideal hunting grounds for bacteriophage.…”

Assessing the usefulness of clostridia spores for evaluating sewage sludge hygienization

“…Treatment processes convert sewage sludge into biosolids, a stabilized product suitable for beneficial use. However, due to the high levels of pathogens naturally present in sludge (Guzmán et al, 2007;Lepeuple et al, 2004), only some treatments (or more specifically, only some treatment conditions) guarantee the safe levels required for use of biosolids as fertilizer, the preferred management option. In this context, the use of indicator microorganisms is an excellent tool to evaluate the microbiological risk associated with these practices, since they can indicate the hygienization capacity of treatment processes.…”