title: Microbial safety of air-dried and rewetted biosolids.
abstract: To assess microbial safety of treated sewage sludge (biosolids), we examined the inactivation of microbial indicators for potential bacterial, viral and protozoan pathogens. The levels of indicators were determined throughout the air-drying and storage phases of anaerobically digested sewage sludge. Samples were collected from two wastewater treatment plants (WWTPS) in Victoria, Australia. Established methods were applied for analysis of bacteria and coliphages, based on membrane filtration and layered plates, respectively. In the pan drying phase, the prevalence of Escherichia coli was reduced by >5 log10 compared with sludge entering the pan. Thus, after pan drying of 8-11 months at WWTP A and 15 months at WWTP B, the numbers of E. coli were reduced to below 10(2) cfu/g dry solids (DS). This level is acceptable for unrestricted use in agriculture in Australia (P1 treatment grade), the UK (enhanced treatment status) and the USA (Class A pathogen reduction). Coliphage numbers also decreased substantially during the air-drying phase, indicating that enteric viruses are also likely to be destroyed during this phase. Clostridium perfringens appeared to be an overly conservative indicator. Survival, but not regrowth, of E. coli or Salmonella was observed in rewetted biosolids (15-20% moisture content), after being seeded with these species, indicating a degree of safety of stored biosolids upon rewetting by rain.
authors.affiliation: Biotechnology and Environmental Biology, School of Applied Sciences, RMIT University, Bundoora West Campus, Plenty Road, Bundoora Vic 3083, Australia. duncan.rouch@rmit.edu.au
authors.forename: Duncan A
authors.initials: DA
authors.lastname: Rouch
authors.forename: Tania
authors.initials: T
authors.lastname: Mondal
authors.forename: Sneha
authors.initials: S
authors.lastname: Pai
authors.forename: Florian
authors.initials: F
authors.lastname: Glauche
authors.forename: Vennessa A
authors.initials: VA
authors.lastname: Fleming
authors.forename: Nerida
authors.initials: N
authors.lastname: Thurbon
authors.forename: Judy
authors.initials: J
authors.lastname: Blackbeard
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Smith
authors.forename: Margaret
authors.initials: M
authors.lastname: Deighton
mesh_terms: D000388:Air; D001673:Biodegradation, Environmental; D003016:Clostridium perfringens / Q000302:isolation & purification; D015169:Colony Count, Microbial; D004755:Enterobacteriaceae / Q000302:isolation & purification; D016983:Enterococcus / Q000302:isolation & purification; D004784:Environmental Monitoring / Q000379:methods; D005374:Filtration / Q000295:instrumentation; D012475:Salmonella / Q000302:isolation & purification; D012722:Sewage / Q000382:microbiology*; D014739:Victoria; D018508:Water Purification
chemical_list: D012722:Sewage