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This paper reviews the effect of the wastewater and sludge treatment on …


Biology Articles » Miscellaneous » Processes for Managing Pathogens » Tables

Tables
- Processes for Managing Pathogens

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Table 1. Removal of bacteria by physical treatment processes.{dagger}

Process
Removal
%
Coarse screens (0.1–0.2 mm) 0–5
Fine screens (0.01–0.1 mm) 10–20
Grit chambers 10–25
Simple sedimentation 25–75
Chemically aided sedimentation
40–80

{dagger} Data from Metcalf and Eddy, Inc. (1991).


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Table 2. Removal or destruction of bacteria and viruses by different treatment processes.

Removal
Process
Fecal
coliform
Salmonellae
Enteric
viruses
%
Primary sedimentation 50–90   50–90    0–30
Trickling filter 90–95   90–95   90–95
Activated sludge 90–99   90–99   90–99
Oxidation ditch 90–99   90–99   90–99
Waste stabilization pond{dagger}  4–7 log 99.99–100 99.99–100
Lagoon
 2–6 log
  99–100
  99–100

{dagger} Three cells, 25-d minimum total retention. Data from Feacham et al. (1980).


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Table 3. Summary of pathogen reduction during sludge treatment.{dagger}

Log reduction
Treatment
Coliform
bacteria
Enteric
viruses
Parasites
Mesophilic anaerobic digestion 0.5 to 4 0.5 to 2 0
Aerobic digestion 0.5 to 4 0.5 to 2 0
Composting  2 to >4  2 to >4  2 to >4
Air-drying 0.5 to 4 0.5 to >4 0.5 to >4
Lime stabilization
 2 to >4
>4
0

{dagger} Data from Ward et al. (1984), Ponugoti et al. (1997), and United Kingdom Water Industry Research (2002).


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Table 4. Effect of sludge treatment processes on numbers of Escherichia coli.

Log reduction in E. coli
Log number of E. coli in treated sludge
(100 g–1 dry wt.)
Treatment
n
25th percentile
Mean
95th percentile
25th percentile
Mean
95th percentile
Lagooning  36 1.47 2.65 6.00 5.08 5.93 8.32
MAD{dagger}, liquid 208 1.04 1.39 2.36 7.10 7.41 8.27
MAD, cake  93 1.76 2.29 3.64 6.27 6.65 7.46
Vermiculture  14 4.2 5.12 6.54 3.20 4.50 5.07
Composting  31 5.75 6.71 9.10 1.05 2.43 4.70
Lime addition  32 5.70 7.10 9.05 0 1.45 3.00
Thermal drying
 70
6.52
7.14
8.90
0.33
1.67
3.56

{dagger} Mesophilic anaerobic digestion. Data from United Kingdom Water Industry Research (1999).


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Table 5. End product microbiological standards for Class A and B sludges (USEPA, 1993).

Standard
Class A
Class B
Fecal coliforms, g–1 dry solids {dagger}
Salmonellae, 4 g–1 dry solids
Enteroviruses, pfu 4 g–1 dry solids {ddagger}
Parasite ova , 4 g–1 dry solids
{ddagger}

{dagger} Geometric mean of seven samples.

{ddagger} For processes unable to satisfy specific operational requirements.


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Table 6. Proposed UK standards for treated and enhanced treated sludge.

Sludge category
Reduction in numbers of E. coli
across sludge treatment process
Number of E. coli
in final product
Number of salmonellae
in final product
Treated 2 log10 105 g–1 dry solids{dagger} no standard
Enhanced treated
6 log10
103 g–1 dry solids{ddagger}
absent from 2 g dry solids§

{dagger} To be achieved on 90th percentile basis for first 2 yr following introduction of the regulations with a maximum allowable concentration of 107 g–1 dry solids; thereafter maximum allowable concentration of 105 g–1 dry solids.

{ddagger} It is expected that well-controlled sludge treatment is likely to consistently produce a sludge containing less than 102 g–1 dry solids. Should routine sampling indicate that the product quality was poorer than this, then the operation of the plant must be checked, even though the batch quality was within the final product standard.

§ In five random samples, each containing 2 g dry solids, with less frequent samples if consistently absent over 6 mo.

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