Destruction of Pathogens

Biosolid waste in general and vermicast are tested by external NATA accredited laboratories to ensure product compliance with regulatory pathogen reduction requirements. Biosolids contain a range of bacterial, viral and parasitic organisms that have been positively linked with infection and severe illness in humans. The destruction of pathogens occurs naturally, but the die off rate varies (Table 4). Of most concern is Helminth.

Mean Pathogen Level of Casts Through the Vermitech Process

Pathogen (measure)

Fresh Biosolids

Work in Progress

Point of Despatch Final

NSW EPA

Grade A

Faecal Coliform (cfu/g)

>310,000

270

180

<1,000

E coli (cfu/g)

>110,000

18

4

<100

Salmonella

Not detectable, masked by Faecal and Ecoli

Not detected

Not detected

Not detected

Enteric Viruses (pfu/g)

Not tested

<1

<1

<1

Helminth Ova (ova/g)----- ----------------------------Ascari ------------------------ Taenia

Sludge not tested

Trial seeded to 23/gm

N/d

<1

N/d

<1

 

<1

Stabilisation Grade

..

A

A

..
Our combination of the strictest Quality Assurance regimen and maintenance of a healthy active Biomass ensure a Process Management routine second to none. In fact no regrowth has been detected in any resampled material over 30 months of operations at our established sites. Regrowth is highly unlikely for two reasons. Firstly a high degree of stabilisation occurs. Secondly the end product is microbially active containing over 70 million beneficial soil microbes / gram on harvest and over 10 million at point of use after 12 months.

Survival Times of Pathogens in Soil and on Plant Surfaces (US EPA, 1992a)

Pathogen

Soil

Plants

Absolute

Maximum

Common

Maximum

Absolute

Maximum*

Common Maximum

Bacteria

1 year

2 months

6 months

1 month

Viruses

1 year

3 months

2 months

1 month

Protozoan cysts b

10 days

2 days

5 days

2 days

Helminth ova

7 years

2 years

5 months

1 month

(US EPA, 1992a)

a. Greater survival time is possible under unusual conditions such as consistently low temperatures or highly sheltered conditions

b. Little if any data are available on the survival times of Giardia cysts and Cryptosporidium cysts

HELMINTHS

The helminths of concern are nematodes (roundworm) and cestodes (tapeworm). The most common pathogenic helminths likely to be found in biosolids are Ascaris lumbricoides (human roundworm), Ascaris suum (pig roundworm), Trichuris trichiura (human whipworm), Taenia saginata (beef tapeworm), Taenia solum (pork tapeworm) and Toxacara canis (dog roundworm) (US EPA, 1992b).

For helminths, single eggs are infective and hence exposure should be minimised. (US EPA, 1992b) Because Helminth may not be present in biosolids, a trial was commissioned by Vermitech to determine Helminth Ova destruction by the action of earthworms (Luke, 1999 ). A suspension of parasitic Helminth Ova containing 70,000 ova in a 1:3 ratio of Ascaris lumbricoides to Trichuris trichiura was poured over a 3L earthworm/biosolids culture system, left for 28 days and then sampled up until 85 days. The initial concentration of ova in the culture was approximately 23 ova/gram.

The sampling area was randomly selected from a 16 square grid on the surface of the culture and a total of forty eight 4 gram samples were removed from depths of 0, 2, 4 and 6 cm in either a straight or diagonal line across the grid. The sample was then repeatedly centrifuged and decanted before the surface film was sampled using a wire loop (Stewart, 1985, cited in Luke). The sample was then examined microscopically for parasitic helminth ova. The technique used to sample the worm culture has a sensitivity of 1 ovum/gram.

The results of the trial were no detection of Helminth Ova in any of the samples. Luke suggests that the principal element of the culture was worms and therefore worm activity must have contributed significantly to the destruction of the Helminth Ova.

Reduction of Impact of Plant Pathogens

One of the most significant benefits of BioVerm may be in its ability to suppress the impact of plant pathogens. Grower trials have identified the reduction in the impact of sclerotinia, downy mildew, club root and various nematode infections. Very little has been done on a reported scientific basis.

Club root is a serious threat to brassica growers with no effective treatment. Research conducted by Dr Peter Stevens at the DPI in Queensland found that BioVerm increased the viable root mass by 250%, decreased the number and weight of club root by 49% with the club to viable root ratio decreasing 83%. The result was a net yield increase of over 30%. This confirms the value of BioVerm to broccoli grower. The Gatten trials measured a 26 - 42% yield increase in uninfected soil.