'VERMICULTURE REVOLUTION' (NOVA, USA)

Worms Destroy Pathogens in the End Product Making them Pathogen Free

Written by Rajiv K. Sinh, PhD

Many research articles, scientific papers, University thesis papers and books have been published regarding the earthworm's ability to convert many types of organic waste into a badly needed resource, (soil). The earthworms release coelomic fluids that have anti-bacterial properties and destroy virtually all pathogens in the waste biomass. (Pierre et al.,1982). They also devour the harmful protozoa, bacteria and fungus as food. They seem to realize instinctively that anaerobic bacteria and fungi are undesirable and so feed upon them preferentially, thus arresting their proliferation. More recently, Dr. Elaine Ingham has found in her research that worms living in pathogen-rich materials (e.g. sewage and sludge), when dissected, show no evidence of pathogens beyond 5 mm of their gut. This confirms that something inside the worms destroys the pathogens, and excreta (vermicast) becomes pathogen-free (Appelhof, 2003).

In the intestine of earthworms some bacteria & fungus (Pencillium and Aspergillus) have also been found (Singelton et. al, 2003). They produce ‘antibiotics’ that kills the pathogenic organisms in the sewage sludge making it virtually sterile. The removal of pathogens, fecal coliforms, (E. coli), Salmonella spp., enteric viruses and helminth ova appear to be much more rapid when they are processed by E. fetida. Of all E. coli and Salmonella are greatly reduced. (Bajsa et al., 2003). 

In a conventional aerobic composting system, which is a ‘thermophilic’ process, pathogens are killed due to high temperature (beyond 55 °C). Wu & Smith (1999) studied that for efficient composting and pathogen reduction a temperature of 55 °C must be maintained for 15 consecutive days. But this also kills several beneficial microbes. If this high temperature is not achieved, which could be the case in small scale composting, pathogen die off will not be effective. In vermicomposting systems temperatures do not increase beyond 30° C, (86 degrees F) and the harmful microbes (pathogens) are killed selectively by the worms through biological (physiological), microbial and enzymatic actions. 

Vermicompost Is Free of Toxic Chemicals

Several studies have found that earthworms effectively bio-accumulate or biodegrade several organic and inorganic chemicals including ‘heavy metals’, ‘organochlorine pesticide’ and ‘polycyclic aromatic hydrocarbons’ (PAHs) residues in the medium in which it feeds. (Nelson et al., 1982; Ireland, 1983 & Sinha et. al., 2008).

Table 6. Removal of Pathogens (E. coli & E. faecalis) in Conventional Thermophilic Composting Vis-a-Vis Vermicomposting Processes

				E.coli (MPN/g)	E.faecalis (MPN/g)
Composting Process	Composting Period	After 2 Months	3 Months	After 2 Months	3 Months
Thermophilic	21 days	> 110	110	> 110	46
Vermicomposting	21 days	110	7.5	110	4.3
Thermo + Vermi	6 dT & 15 dV	24	21	46	2.3
Thermo + Vermi	9 dT & 12 dV	46	15	46	9.3
Thermo + Vermi	12 dT & 9 dV	110	15	46	4.3
Thermo + Vermi	15 dT & 6 dV	> 110	4.3	24	2.3

Source: Nair et. al., (2006).

Key: dT = days of Thermophilic composting; dV = days of Vermicomposting.

N.B. E.coli & E. faecalis was tested using the Most Probable Number (MPN) per gram of compost (Standards Australia, 1995 a & b respectively).

GHG Emissions in Vermicomposting Systems

Our studies showed that on average, aerobic, anaerobic and vermicomposting bins released 504, 694 and 463 CO2-e m-2 hr-1 as N2O and CH4, with N2O accounting for >80% of total emissions. These emission rates are equivalent to 0.0043-0.0062 kg CO2-e kg-1 waste assuming 4.5 kg food and green wastes were processed in each bin each week. Among the 3 types of bins, vermicomposting bins had the lowest emission of N2O. The GHG emissions generally increased with increasing temperature and/or moisture content. This indicates the importance of proper maintenance of the bins to minimize GHG emissions. 

Table 2. GHG emission rates in aerobic, anaerobic and vermicomposting bins (min - max values in bracket)

Greenhouse Gases	Aerobic bins	Anaerobic bins	Vermicomposting bins
Number of samples	40	45	42
GHG Emissions (mg m-2 hr-1) CO2 CH4 N2O Total Emissions (mg CO2-e m-2 hr-1) Excluding CO2 Including CO2	882 (23 – 5764) 2.17 (0.00 – 38.05) 1.48 (0.01 – 16.25) 504 (4 – 5038) 1386 (28 – 7554)	2950 (91 – 10069) 9.54 (0.00 – 52.90) 1.59 (0.00 – 16.37) 694 (0.76 – 5073) 3644 (259 – 14351	1675 (146 – 5669) 4.76 (0.00 – 40.89) 1.17 (0.00 – 24.78) 463 (4 – 8475) 2138 (189 – 14144)

Source: Sinha and Chan (2009); Chan et al. (2010).

Our study found that on average the anaerobic composting systems emitted the highest amount of CO2 (2950 mg /m2/hour) and CH4 (9.54 mg/m2/hour), while both aerobic and vermicomposting systems emitted the least amount of CO2 (882 mg/m2/hour) and CH4 (2.17 mg/m2/hour). Vermicomposting systems had the ‘lowest emission’ of N2O (Sinha & Chan, 2009; Chan et al, 2010). Anaerobic bins and vermicomposting bins emitted significantly higher amounts of CO2 and CH4 than the aerobic bins. This indicates that anaerobic and vermicomposting systems were more efficient in decomposing the carbon in waste into CO2 and more favourable for methane (CH4) production (if they have to be captured and used as bio-fuel) than the aerobic bins. 

On the other hand, aerobic and anaerobic systems emitted significantly higher amounts of powerful GHG N2O than the vermicomposting system. Presumably, the N2O emitted from the composting bins were mainly from the denitrifying process in anaerobic zones in the compost, but might also be created in the nitrifying process in aerobic zones (Beck-Friis et al. 2000) and the activities of the denitrifying bacteria within the earthworm gut (Hobson et al. 2005). The lower emission of N2O from vermicomposting bins indicated that the emission of N2O from worm gut was probably offset by the reduction of anaerobic denitrification, due to the burrowing action of the earthworms. 

In terms of CO2-e (equivalent), CO2 emissions contributed approximately 64% on average of the total GHG emissions in the aerobic system, and about 80% of the total GHG emissions in the anaerobic and vermicomposting systems. When CO2 emission was excluded from the accounting as is common practice, the three waste treatment methods emitted 463-694 mg CO2-e / m2 / hour- on average, largely attributable to N2O emissions. However, the findings from our study show that properly maintained vermicomposting systems have a greater potential of reducing N2O emissions whilst producing more ‘nutritive compost’ as compared to other methods. Among the 3 systems, vermicomposting has greater potential to provide better composting conditions and compost products with more neutral pH and lower carbon/nitrogen ratio. (Sinha & Chan, 2009).

In theory also, vermicomposting of waste by worms should provide some potentially significant advantages over conventional aerobic or anaerobic composting with respect to GHG emissions. First, the vermicomposting system do not require manual or mechanical turning (which need fuel and emit GHG), as the worms keep aerating the system while moving through it. Worms significantly increase the proportion of ‘aerobic to anaerobic decomposition’ in the compost pile by burrowing and aerating actions leaving very few anaerobic areas in the pile, and thus resulting in a significant decrease in GHG and also volatile sulfur compounds which are readily emitted from the conventional (microbial) composting process.(Mitchell et al., 1980). Second, as the vermicompost promote growth and yield several times more than that of other compost, even the chemical fertilizers, it implies that as much compost or chemical fertilizer could be displaced per unit of vermicompost use, reducing the GHG emissions proportionally. Then, analysis of vermicompost samples has shown generally higher levels of available nitrogen (N) as compared to the conventional compost samples made from similar feedstock. This implies that the vermicomposting by worms is more efficient at retaining nitrogen (N) rather than releasing it as N2O. 

(Written by Rajiv K. Sinh, PhD)