Disinfection of sludge with high pathogenic content using silver and other compounds

Abstract

A physicochemical sludge with high microbial content (10²–10⁴ FPU/g TS bacteriophages, 10⁶–10⁷ MPN/g TS faecal coliforms, 10⁴ MPN/g TS Salmonella spp., 10⁴ MPN/g TS Shigella spp., 10³ MPN/g TS Pseudomonas aeruginosa,10² MPN/g TS Vibrio cholerae, 10²–10³ cysts/g TS Giardia sp., 10²–10⁴ oocyts/g TS Cryptosporidium sp., 168–215 viable helminth ova/g TS) was disinfected using silver, silver-copper, and silver-copper plus a synergistic agent (SA). Twenty milligrams Ag/g TS inactivated 4.8 log of faecal coliforms in 1 h; however, 40 mg Ag/g TS are needed to reduce helminth ova viability from 84 to 38.4% in the same period of time. Combinations of Ag-Cu (60:600 mg Ag-Cu/g TS) and Ag-SA (60:24 mg Ag-SA/g TS) inactivated 7.8 log of faecal coliforms and around 90% of helminth ova in 60 min. To produce USEPA class A biosolids, 10:100:8 and 5:50:13.3 mg Ag-Cu-SA/gTS are needed. Bacterial regrowth was not observed for all conditions producing <1,000 MPN/gTS faecal coliforms, suggesting a residual disinfection effect. Recommended doses to produce class A biosolids inactivated 2–4 log of bacteriophages, 4 log of Salmonella spp., 4 log of Shigella spp., 3 log of Pseudomonas aeruginosa, 2 log of Vibrio cholerae, 87–99.9% of Giardia sp., and 75–99.9% of Cryptosporidium sp.