Vol.4, No.10, 529-535 (2013) Agricultural Sciences
Feasibility of a novel vermitechnology using
vermicast as substrate for activated sludge
disposal by two epigeic earthworm species
Kui Huang1*, Fusheng Li2, Xiaoyong Fu3, Xuemin Chen3
1Graduate School of Engineering, Gifu University, Gifu, Japan; *Corresponding Author: q3812102@edu.gifu-u.ac.jp
2River Basin Research Center, Gifu University, Gifu, Japan
3School of Environmental and Municipal Engineering, Lanzhou Jiaotong University, Lanzhou, China
Received 11 July 2013; revised 12 August 2013; accepted 1 September 2013
Copyright © 2013 Kui Huang et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This study was conducted to investi gate the fea-
sibility of vermicomposting by using vermicast
as the substrate for the st abilization of municip al
activated sludge, called hereafter as direct ver-
mistabilization, in which the pre-treatment and
bulking materials required in previous practices
were all omitted. For this purpose, two epigeic
earthworm species, namely Eisenia foetida and
Bimastus parvus, were inoculated into substrate
for composting fresh dewatered activated sludge.
Direct vermistabilization resulted in significant
reductions in pH, TOC, C/N ratio and the content
of heavy metals, as well as increases in EC, total
N, total P and total K in the final vermicast.
Moreover, both Eisenia foetida and Bimastus
parvus sho wed faster growth rate and higher co-
coon production. The results of this study sug-
gest that the direct vermistabilization has the ad-
vantages of being simple, cost-effective and ef-
ficient, and can thus be used as a feasible ver-
micomposting approach to convert fresh dewa-
tered activated sludge into a valuable product
for agricultural use. The r esults also suggest that
Bimastus parvus can be used as a new potential
candidate for vermicomposting of municipal ac-
tivated sludge.
Keywords: Activated Sludge; Biology; Earthworms;
Heavy Metals; Nutrients; Vermicomp osting
Large scale urbanization in recent years has resulted in
the generation of large amount of municipal sewage slu-
dge, which has become one of emerging environmental
issues in the world. Currently, the primary means of sludge
treatment include direct application for agricultures, land-
fill, incineration, and so on. According to the situations of
developing cou ntries, the use of sludge for agricultural pur-
poses is probably the most appropriate method for its di-
sposal. However, it is well known that municipal sludge
is a complex waste that contains not only large amounts
of organic matter and nutrient elements, but also many
heavy metals and harmful organic pollutants and patho-
gens. Direct application of sludge as the fertilizer, with-
out undergoing prestabilization treatment, may pollute
agricultural lands and cultivated crops. It is thus neces-
sary and urgent to seek ecologically sound technologies
that enable sustainable recycling of rich nutrients and
high organic content in municipal sludge, and at the same
time, can ensure a significant reduction in the risk-caus-
ing hazardous substances.
Vermicomposting is a process for stabilization of or-
ganic waste materials through the joint involvement of
earthworms and microorganisms. Microorganisms are re-
sponsible for biochemical degradation of organic matter
contained in the waste materials; while earthworms play
their roles as mechanical blenders and drivers of the pro-
cess through modifying the biological, physical and che-
mical status, gradually reducing the C/N ratio of organic
matter, increasing the surface area attachable by micro-
organisms, and converting the waste materials into ones
more favourable for microbial activity and further de-
composition [1]. During the vermicomposting process,
the important p lant nu trients such as n itrogen, po tassium,
phosphorus and calcium present in the organic waste ma-
terials are converted into more available forms for plant
growth [2]. Moreover, the worms themselves can serve
as a protein source for animals’ feeds [3]. For all these
Copyright © 2013 SciRes. OPEN A CCESS
K. Huang et al. / Agricultural Sciences 4 (2013) 529-535
reasons, vermicomposting has been considered as an eco-
logical and cost effective technology for the treatment and
recycling of different organic waste materials, particular-
ly for developing countries.
The use of earthworms in sludge management is term-
ed as vermistabilization [4]. Recent studies have demon-
strated that vermicomposting is highly useful and com-
petitive for stabilization of activated sludge generated in
sewage treatment plants [5-8]. However, intensiv e litera-
ture review revealed clearly that most previous studies
on vermicomposting were conducted using batch sys-
tems, in which pre-treatment and/or bulking materials
were used for improving the activ ities of earthwo rms and
microorganisms. This makes the process much compli-
cated when activated sludge is dealt with. So far, studies
using continuous vermicomposting systems are very li-
mited; and experimental approaches using vermicast as
the substrate for improving the efficiency of vermicom-
posting, which may allow the omission of pre-treatment
and the use of bulking materials, can be hardly found.
This study was aimed to evaluate the feasibility of
direct vermistabilization by using vermicast as the sub-
strate for composting of municipal activated sludge in
continuous vermicomposting system. For this, Eisenia
foetida, a worm species that has been commonly used in
vermicomposting, was utilized. Meanwhile, for compari-
son and searching for new effective species, Bimastus
parvus that has not yet been reported so far in existing
literature was also investigated. The analytical items in-
cluded the physicochemical properties of the end pro-
ducts of vermicast, and the growth and the fecundity of
the earthworms during direct vermicomposting.
2.1. Earthworms and Municipal Activated
Two species of epigeic earthworms (E. foetida and B.
parvus), originally collected from the piles of cow dung
in a local cattle farm, were randomly picked out for
experimentation from individual stocking bin, respecti-
vely. The stock earthworms were cultured in the labora-
tory for one year by using biosolids (i.e., food waste,
municipal sludge and cow dung) as the feed materials.
The municipal activated sludge used in this experiment
was obtained from the Lanzhou Wastewater Treatment
Plant, Lanzhou, China. The characteristics of the sludge
were: water content = 75%, pH = 7.82, electrical con-
ductivity (EC) = 0.46 S/cm, total organic carbon (TOC)
= 32.32%, total nitrogen (TN) = 36.42 g/kg, total pho-
sphorus (TP) = 7.70 g/kg, total potassium (TK) = 11.22
g/kg, C/N ratio = 9.72, copp er (Cu) = 210 .00 mg/k g, zinc
(Zn) = 1557.67 mg/kg, lead (Pb) = 68.42 mg/kg, and
chromium (Cr) = 125.68 mg/kg .
2.2. Experimental Design
The experiment was conducted in perforated cylindri-
cal plastic containers, each with a capacity of about 10 L
(25 cm in diameter and 20 cm in height). The thickness
of the substrate bedding was maintained at about 10 cm
in all the containers throughout the experiment. The earth-
worms of E. foetida and B. parvus were introduced into
individual containers, respectively, for acclimatization
prior to the addition of sludge. Following one day’s ac-
climatization, 700 g of the fresh dewatered sludge was
directly added onto the substrate bedding. A control was
also operated in parallel for investigation of the perfor-
mance of degradation, for which worms were not intro-
duced. All containers were kept in dark at the room tem-
peratures (22˚C - 28˚C). The moisture content of the feed
in each container was maintained at 70% ± 10%. To pre-
vent moisture loss and avoid direct sunlight, all contai-
ners were covered with shade plastic bags and black bur-
lap. For each experiment, three replicate were operated
and the running time length was 30 days. Vermicompos-
ting samples were collected at different times, i.e., 0, 10,
20 and 30 days, after each experiment was commenced.
2.3. Chemical Analysis
Physicochemical analysis was conducted on the dry
weight basis. All chemicals used were of the analytical
reagent grade. All samples were analyzed in triplicate
and the results were averaged. pH and EC were mea-
sured with 1/10 (w/v) suspensions by using digital pH
and EC meters (Systronic made), respectively. TOC was
measured using the method of [9]. TN was measured us-
ing the Kjeldahl method. TP was measured using the mo-
lybdenum colorimetric method. The total concentrations
of K, Cu, Zn, Pb and Cr were quantified using ICP-AES
(IRIS Intrepid XSP, Thermo Elemental, America)
after digesting the sample in the mixed acidic solution
of HNO3 and HClO4 (HNO3:HClO4 = 4: 1, v/v).
2.4. Statistical Analysis
Statistical analysis was conducted using the Statistica
Package (Version 8.0). ANOVA was performed to ana-
lyze the significance of the differences among the che-
mical properties at the significance level of 0.05. For in-
dependent samples, t-test was performed between E. fo-
etida and B. parvus for their biological differences.
3.1. Changes in Nutrients Properties during
Vermicomposting Process
After 30 days of vermistabilization, the end products
became much darker, more granular and homogeneous in
Copyright © 2013 SciRes. OPEN A CCESS
K. Huang et al. / Agricultural Sciences 4 (2013) 529-535 531
appearance, and odour free. Table 1 shows variations of
pH and EC during vermicomposting. Statistically signi-
ficant decreases of pH with the vermicomposting time
were observed for treatment with both worms (p < 0.001)
as compared to the control; and a significant difference
in the decreasing extent of pH between two worm species
were also confirmed existent (p < 0.001). For instance,
after 30 days of composting, pH with E. foetida was
nearly neutral (7.03 ± 0.06), while that with B. parvus
was slightly acidic (6.20 ± 0.20). This result supports
previous ones obtained by others on vermicomposting of
sludge [5,6]. The shift of pH during vermicomposting is
probably due to mineralization of nitrogen and phos-
phorus into nitrites/nitrates and orthophosphates, respec-
tively, and due to bioconversion of organic materials into
intermediate species of organic acids [2]. The different
decreasing extent of pH between E. foetida and B. parvus
observed in the present study may indicate the species-
specific differences of worms in their mineralization ef-
ficiency, for which further elaborative studies are requir-
ed. In regard of the changes of EC during vermicom-
posting, the data shown in Ta b l e 1 revealed that EC in-
creased gradually with time. Compared to the control bed -
dings where earthw orms were not introd uced, the experi-
mental beddings introduced with earthworms displayed a
significant increasing trend (p < 0.001), with the value of
EC being increased by approximately 4 folds. This in-
crease was probably due to the loss of organic matter and
the release of different mineral salts in available forms
such as phosphate, ammonium and potassium [10]. More-
over, comparison of the EC values at all treatment times
between the tested two earthworm species demonstrated
less apparent difference (p > 0.05).
Changes of TOC and TN during vermicomposting are
illustrated in Table 2. TOC reduced by about 30% for the
treatment with two earthworms as against the control
treatment (p < 0.001). Significant differences between
the tested two earthworms species were not confirmed (p
> 0.05). The reduction in TOC during vermicomposting
observed in the present result is consistent with previous
reports that earthworms can accelerate decomposition
and mineralization of organic matter contained in sludge
[5,11,12]. The loss of carbon, in the form of CO2, was
probably the result of earthworms’ roles in enhancing the
activity of decomposers, e.g. bacteria, fungi, nematode
and protozoa, populated in the vermicomposting system,
as reported by [7]. The conversion of so me organic frac-
tions of the waste into the earthworm biomass was also a
likely reason leading to the observed carbon reductions
[5-7]. In contrary to the decreasing trend of TOC, the
content of TN increased by approximately 30% through
vermicomposting (p < 0.001); and no significant diffe-
rences were found between the tested two earthworm
species (p > 0.05). The results of the present study are
supported by the previous ones documented [13,14]. It
was postulated that earthworms can enhance nitrogen le-
vels by adding their excreta, mucus, body fluid and en-
zymes, etc. into the substrate; moreover, the decaying tis-
sues of dead worms also add a significant amount of ni-
trogen into the vermicomposting system [14].
The C/N ratio of organic materials reflects the extent
of mineralization and stabilization during the process of
composting or vermicomposting. As shown in Figure 1,
the C/N ratio decreased by 47.3% in the earthworm treat-
ment systems, which is much higher than in the control
(p < 0.001); and the differences between the tested two
earthworm species were insignificant (p > 0.05). The
final C/N ratios of the vermicast, i.e., the vermicast after
treatment for 30 days, by E. foetida and B. parvus des-
cended to 5.16 and 5.08, respectively. The decrease in
C/N is probably a combined effect of the loss of carbon
as carbon dioxide due to microb ial respiration and of the
simultaneous addition of nitrogen by earthrms in the form
of mucus and nitrogenous excretory materials during ver-
micomposting, as suggested by [8]. Compared to pre-
vious studies, in which some bulking materials, such as
cow dung, straw and compost, were added into sludge
before vermicomposting [5,6,13,14], although the C/N
ratio in the material (activated sludge) of the present stu-
dy was lower, apparent decreases of its value in the treat-
ment systems with earthworms were still observed. This
may thus suggest that a greater extent of organic matter
stabilization of municipal activated sludge was achieved
through vermicomposting even if no bulking materials
and pre-treatment were employed.
The changes in TP and TK during vermicomposting of
activated sludge are shown in Table 3. The content of TP
was significantly higher in the treatment systems with E.
foetida (12.53%) and B. parvus (9.10%) than in the con-
trol (p < 0.001), with the increasing extent being less de-
pendent on the earthworm species (p > 0.05). The ob-
served result of increases in P during vermicomposting is
consistent with the findings of others [5,8] and was pro-
bably due to mineralization of organic phosphorous. Ac-
cording to Lee (1992) [15], the passage of organic matter
through the gut of earthworms could convert phosphorus
into forms much more available to plants. In another
study, Le Bayon and Binet (2006) [16] conuded that the
impact of earthworms on the biogeochemical transforma-
tion of phosphorus in soils depends on the close relation-
ship between the properties of the organic phosphorous
sources and the specific burrowing behaviour and food
preferences of worms. For the total potassium, a gradual
increase of TK with time was also observed (Table 3).
Statistically, the increases in the content of TK in the
treatment systems with earthworms (by up to 9.8%) was
significant than in the control (p < 0.001). Nevertheless,
the difference of TK between two worm species was
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K. Huang et al. / Agricultural Sciences 4 (2013) 529-535
Copyright © 2013 SciRes.
Table 1. Changes of pH and EC during vermicomposting of activated sludge.
pH EC (S/cm)
Vermicomposting Vermicomposting
Days Control E. foetida B. parvus Control E. foetida B. parvus
0 7.83 ± 0.06 7.83 ± 0.06 7.83 ± 0.06 0.46 ± 0.04 0.46 ± 0.04 0.46 ± 0.04
10 7.57 ± 0.04 7.43 ± 0.06 7.25 ± 0.05 0.52 ± 0.03 0.78 ± 0.02 0.70 ± 0.02
20 7.50 ± 0.03 7.13 ± 0.05 6.71 ± 0.15 0.58 ± 0.02 1.79 ± 0.06 1.68 ± 0.04
30 7.42 ± 0.05 7.03 ± 0.06 6.20 ± 0.20 0.63 ± 0.03 2.23 ± 0.08 2.19 ± 0.03
Table 2. Changes of TOC and TN during vermicomposting of activated sludge.
TOC (%) TN (g/kg)
Vermicomposting Vermicomposting
Days Control E. foetida B. parvus Control E. foetida B. parvus
0 32.32 ± 2.32 32.32 ± 2.32 32.32 ± 2.32 36.55 ± 1.30 36.55 ± 1.30 36.55 ± 1.30
10 31.27 ± 1.52 29.16 ± 2.31 29.24 ± 0.11 36.87 ± 1.09 38.50 ± 0.25 37.99 ± 0.69
20 29.67 ± 0.91 25.33 ± 0.83 26.26 ± 0.35 36.54 ± 0.64 43.87 ± 0.90 42.99 ± 0.7
30 28.33 ± 0.36 23.59 ± 2.22 22.89 ± 0.26 35.37 ± 0.71 50.25 ± 2.10 49.48 ± 0.12
Table 3. Changes of TP and TK during vermicomposting of activated sludge.
TP (g/kg) TK (g/kg)
Vermicomposting Vermicomposting
Days Control E. foetida B. parvus Control E. foetida B. parvus
0 7.70 ± 0.13 7.70 ± 0.13 7.70 ± 0.13 11.22 ± 0.13 11.22 ± 0.13 11.22 ± 0.13
10 7.76 ± 0.05 7.98 ± 0.17 7.87 ± 0.14 11.56 ± 0.20 12.65 ± 0.14 12.42 ± 0.34
20 8.05 ± 0.07 8.51 ± 0.25 8.31 ± 0.23 11.62 ± 0.40 12.78 ± 0.51 13.36 ± 0.38
30 8.14 ± 0.13 9.16 ± 0.52 8.88 ± 0.37 12.02 ± 0.39 13.48 ± 0.82 14.80 ± 0.59
Vermiomposting tim e (days)
C/N ratio
Control without earthworm
Vermicomposting by
E. foedita
Vermicomposting by
B. parvus
Figure 1. Change of C/N ratio during vermicomposting.
found statistically insignificant (p > 0.05). The increase
of TK during vermicomposting was also reported in
existing literatures [5,6]. The en hanced release o f K from
the sludge due to the production of acids by microor-
ganisms and the increased number of micro flora in the
gut of earthworms is a likely reason behind the observed
increases of K in the vermicast [10]. However, cautions
should be addressed here since some researchers observ-
ed decreases in the content of K, as a result of probable
leaching of soluble potassium by the excess water con-
tent [17].
3.2. Changes in Heavy Metals during
Vermicomposting Process
Heavy metals in the sewage sludge may come from a
variety of sources like batteries, consumer electronics,
ceramics, light bulbs, plastics, house dust and paint etc.
If higher concentrations of heavy metals remain in the
vermicast, they may cause detrimental effects upon the
growth of plants. So, it is essential to trace the behaviour
of heavy metals during vermicomposting. As shown in
Figure 2, for all four targeted heavy metals (Cu, Zn, Pb
and Cr), dramatic decreases in their content occurred
even if the decreasing extent was somewhat different: Cu
decreased by 20.5%, Zn by 15.0%, Pb by 13.0% and Cr
K. Huang et al. / Agricultural Sciences 4 (2013) 529-535 533
by 9.8% in the treatment systems with earthworms as
against the control (for Cu, p < 0.001; for Zn, p < 0.001;
for Pb, p < 0.001; for Cr, p < 0.05). The differences in
the content of these four metals in the end products of
vermicomposting with both tested worm species were
found less significant (p > 0.05). The decreases in the
content of heavy metals were probably due to accumu-
lation of these metals into the bodies of earthworms. In
general, as decomposers for organic matters, many soil
faunas like earthworms, enchytraeids and mites can in-
gest and digest organic compounds for their own meta-
bolism. During the metabolic process, the decomposers
inevitably accumulate a certain quantity of contaminants
into their bodies and skins through direct or indirect ad-
sorption and absorption [18,19]. Previous studies have
revealed that, during vermicomposting, earthworms re-
duced a considerable amount of heavy metals from the
substrate through bioaccumulation [11,14]. Earthworms
ingest a large quantity of organic materials in order to
achieve necessary nutrition and, during the process they
can liberate metals into free forms as a result of enzy-
matic reaction in their gut [12]. The free forms of metals
are then sorbed onto different organs such as chlorago-
genous cells, gizzard and connective tissues [20]. On the
other hand, the results also suggested that different heavy
metals exhibited different reductions during vermicom-
posting. The extent of reductions of heavy metals due to
bioaccumulation of earthworms was found to be directly
related to the availability and the initial levels of heavy
metals in the substrate [12].
3.3. Biology of Earthworms in
Vermicomposting of Activated Sludge
Vermicomposting is considered in terms of the bio-
mass and the cocoon production of earthworms as well.
As summarized in Tabl e 4, earthworms showed a signi-
ficant increase in the individual weight (p < 0.05) at the
E. foetida and B. parvus reached the mean individual
weight of 808.9 ± 45.4 mg and 723.3 ± 35.6 mg after 30
days, respectively. Comparatively, the individual growth
rate (mg/day) of B. parvus was slightly higher that of E.
foetida; however, the difference between these two
worms was statistically insignificant (p > 0.05). In a
previous study, Suthar (2010b) [12] reported the growth
rate of about 1.13 - 5.51 mg/day and 1.44 - 2.50 mg/day
for E. foetida in vermicomposting of cow dung-amended
sewage sludge and primary sludge, respectively. Similar
to his result, a higher cocoon production (Ta bl e 4) with
the tested two earthworm species in the present study
was also observed; with the total cocoon production after
30 days of vermicomposting with E. foetida being ap-
parently lower than that with B. parvus. The food avai-
lability and the stocking density in the vermicompos-
ting system are important factors related to the growth
rate and the cocoon production of earthworms [6,12].
Our results thus suggest that activated sludge without
any pre-treatment and bulking materials remains palata-
ble for earthworms in continuous vermicomposting sys-
tems. In the systems, the activity of populated micro-
organisms may play an important role in earthworms’
diet, which makes organic matter much more palatable.
In batch systems, however, as reported in previous stu-
dies [12-14], pre-treatment and bulking materials are es-
sential to vermicomposting. This difference may be as-
cribed to the fact that these two different vermicompos-
ting systems are associated with different operation me-
thods, which may lead to differences in the patterns of
earthworms’ ingestion and organic matter decomposi-
tion. In regard of the mortality of E. foetida and B. parv us,
an observable difference was existent as could be seen in
Table 4; however, statistical analysis indicated that this
difference was not significant (p > 0.05). The lower mor-
tality of both earthworms indicates that the continuous
vermicomposting systems investig ated in the presen t stu-
dy can produce a favourable environment condition for
earthworms. In addition, it is also inferable that direct
vermicomposting using vermicast as the substrate is a
suitable technology for disposal of municipal activated
Direct vermistabilization of municipal activated sludge
in the continuous system resulted in the drop of pH to
6.20 - 7.03, the increase of EC, total N, total P and total
K by about 3.5 f olds, 35.4% - 37.5%, 15 .4% - 20.0% and
20.1% - 31.9%, and the decrease of TOC, C/N ratio and
content of heavy metals for Cu, Zn, Pb and Cr by 27.0%
- 29.2%, 47.2% - 47.8%, and 35.2% - 37.7%, 29.3% -
38.8%, 21.2% - 27.4% and 17.0% - 23.0%, respectively,
with the earthworm species of B. parvus and E. foetida,
as compared to the results of the parallel control expe-
riment. Moreover, the growth rate and the reproduction
rate of E. foetida and B. parvus were able to reach 4.8 -
5.8 mg/day and 2.3 - 3.7 cocoon/day, respectively. The
results obtained from this study indicate that direct ver-
mistabilization can enhance the nutritive value and re-
duce the phytotoxicity of end products, thus suggesting
that direct vermistabilization by using vermicast as the
substrate bedding could be a feasible technology for the
management of municipal activated sludge.
This work was financially supported by the Natural Science Founda
Copyright © 2013 SciRes. OPEN A CCESS
K. Huang et al. / Agricultural Sciences 4 (2013) 529-535
Copyright © 2013 SciRes.
Ver m icompost i ng time (days)
0 102030
Vermicomposting time (days)
0 102030
Vermicomposting time (days)
0 102030
Vermicomposting time (days)
Control wit hout ea rthworm Vermicomposting by
E. foetida
Vermicomposting by
B. parvus
Figure 2. Changes of heavy metals contents during vermicomposting.
Table 4. Individual growth, cocoon production and mortality of E. foetida and B. parvus.
Mean individual biomass (mg)
Treatment Start End
Mean growth rate of
individual (mg/day) Total cocoon production
after 30 days Mortality after 30
days (%)
E. foetida 586.8 ± 24.9 808.9 ± 45.4 6.50 ± 2.7 144.3 ± 16.2 4.0 ± 6.9
B. parvus 561.9 ± 15.7 723.3 ± 35.6 4.87 ± 0.8 95.7 ± 6.5 2.7 ± 4.6
tion of China (NSFC, 51168029) and the Program of Gansu Provincial
Science and Technology Department (1104FKCA157).
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