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[Steve Diver <steved AT ncat.org>]

Vermicomposting of biosolids with cow manure and oat straw

Biology and Fertility of Soils
Issue: Volume 41, Number 3
Date: April 2005
Pages: 190 - 198

http://dx.doi.org/10.1007/s00374-004-0821-8

S. M. Contreras-Ramos, E. M. Escamilla-Silva and L. Dendooven

(1) Laboratory of Soil Ecology, Department Biotechnology and 
Bioengineering,
CINVESTAV-IPN (Centro de Investigación y de Estudios Avanzados),
Mexico City, Mexico D.F., Mexico


Abstract

Biosolids, mainly from textile industries and the rest from
households, were vermicomposted with Eisenia fetida, cow
manure and oat straw for 2 months at three different moisture
contents (60%, 70% and 80% dry weight base) in triplicate to
reduce pathogens and toxic organic compounds, and to find
the best medium for growth of E. fetida.

The vermicompost with the best stability and maturity and a
weight loss of 18% was obtained with 1,800 g biosolid, no straw
and 800 g manure at 70% water content.

This vermicompost had the following properties: pH 7.9; organic C
content of 163 g kg–1; an electrolytic conductivity of 11 mS cm–1;
a humic-to-fulvic acid ratio of 0.5 (HA/FA); total N content of 9 g kg–1;
water soluble C (Cw) less than 0.5%; cation exchange capacity of
41 cmolc kg–1; a respiration rate of 188 mg CO2-C kg–1 compost-C
day–1; a NO3–/CO2 ratio greater than 8; and a NH4+/NO3– ratio
lower than 0.16.

The vermicompost gave a germination index for cress (Lepidium
sativum) of 80% after 2 months while the earthworm production
increased 1.2-fold and volatile solids decreased five times.

In addition, the vermicompost contained less than 3 CFU g–1
Salmonella spp., no fecal coliforms and Shigella spp. and no
eggs of helminths.

Concentration of sodium was 152 mg kg–1 dry compost, while
concentrations of chromium, copper, zinc and lead were below
the limits established by the USEPA.

Keywords: Sewage sludge - Pathogens - Heavy metals -
Stability and maturity



EXCERPTS


Introduction

Vermicomposting has been successfully used for composting
different types of wastes, such as municipal and industrial sludges
(Edwards and Bohlen 1996; Elvira et al. 1998), though optimal
moisture and the best proportions of organic waste are
required for an efficient vermicomposting.

Although moisture requirements and preferences of Eisenia fetida
are well known, the optimal conditions of vermicomposting depend
on the type of substrates (Domínguez and Edwards 1997).

The objective of this study was to use biosolids from a
waste water treatment plant in a vermicomposting process
with E. fetida. The biosolid was vermicomposted with oat
straw and cow manure at different concentrations and at
three different moisture contents to obtain optimum
conditions for growth and biomass production of E. fetida.
The reduction of pathogens, and the stability and maturity
of the final product was determined.


Results and Discussion

Before vermicomposting, all mixtures had large amounts
of Salmonella and fecal coliforms. After 60 days, Salmonella
and fecal coliforms values of mixtures 1, 3 and 7 were
lower than limits reported by USEPA (1995) making these
composts suitable for use though coliforms were higher
than the limit of 1,000 CFU g−1 for an excellent biosolid
(Table 6). Amounts of Salmonella spp., Shigella sp. and
helminths were lower than USEPA limits for “an excellent”
biosolid in all mixtures, but those for fecal coliforms were
higher than USEPA limits in mixture 2. The reduction of
the pathogen numbers might be related to the release of
coelomic fluids by the earthworms during vermicomposting,
which have antibacterial properties and kill pathogens
(Pierre et al. 1982; Sinha et al. 2002). Cardoso and Ramírez
(2002) reported a 90% removal of fecal coliforms and
100% removal of helminths from sewage sludge and water
hyacinth after vermicomposting.


Selected References:

Cardoso L, Ramírez E (2002) Vermicomposting of sewage sludge:
a new technology for Mexico. Water Sci Technol 46:153–158

Pierre V, Phillip R, Margnerite L, Pierrette C (1982) Anti-bacterial
activity of the haemolytic system from the earthworms Elsinia
foetida andrei. Invertebr Pathol 40:21–27

Senesi N (1989) Composted materials as organic fertilizers.
Sci Total Environ 81:521–542

Sinha RK, Heart S, Agarwal S, Asadi R, Carretero E (2002)
Vermiculture and waste management: study of action of earthworms
Elsinia foetida, Eudrilus euginae and Perionyx excavatus on
biodegradation of some community waste in India and Australia.
Environmentalist 22:261–268

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