earthworms, anecic earthworms, and endogeic earthworms (Domínguez 2004).
Among them, epigeic earthworms like eating organic matter, showing a strong
environmental adaptability and fecundity. Thus, they are considered to be suitable
for sludge treatment. The main species used in vermicomposting of municipal sludge
include Eudrilus eugeniae, Eisenia fetida, Bimastus parvus, Lumbricus rubellus,
Eisenia andrei, and Dendrobaena veneta, as presented in Table 4.2. At present,
Eisenia fetida is a common species used in vermicomposting of sludge. In general,
the adult of E. fetida has the following features: is 60–160 mm long and 3–5 mm
wide, has 80–110 segments, and is 0.5–1.2 g. However, it shows a longer length and
higher growth and reproduction rate in the vermicomposting system, due to its rich
nutrients of sludge. In our study, the maximum weight of earthworm in sludge can
reach up to 2.3 g with a length of 155 mm. Given that earthworms are a valuable
source of traditional Chinese medicine and aquaculture, vermiculture in sludge is
also important income during vermicomposting.
4.4.2 Temperature
The environmental temperature can directly affect the metabolism, growth, reproduction, and activity of earthworm and microorganism, thus affecting their ability in
degradation of organic matter. As shown in Table 4.2, the temperature set in
vermicomposting showed a stronger inconsistency, and most studies selected room
temperature (15–30
C) as vermicomposting temperature, displaying a wide range of
temperature for treating sludge (Fu et al. 2016; Huang et al. 2018; DomínguezCrespo et al. 2012; Cesar et al. 2012; Molina et al. 2013; Lv et al. 2014; Zhang et al.
2015; Babić et al. 2015; Xie et al. 2016; Cui et al. 2018; Ozdemir et al. 2019). Only a
few publications clearly reported that 20
C was the optimal temperature condition
for treating activated sludge (Hait and Tare 2012). Although the increase in temperature can accelerate the degradation and transformation rate of organic matter by
promoting microbial activity, earthworms are prone to heatstroke and even to death
if the temperature exceeds 30
C. Hence, vermicomposting process is a biological
and chemical decomposition of organic wastes under mesophilic condition to produce a stable bioorganic fertilizer.
4.4.3 Organic Matter Content Carbon/Nitrogen Ratio (C/N)
To provide proper nutrition for earthworms and microorganisms during
vermicomposting, carbon and nitrogen in the substrates should be presented at the
correct ratio (Ndegwa and Thompson 2000). The high ammonia nitrogen content
can cause protein poisoning of earthworms, and even death. But lack of nitrogen
may lead to a lower growth rate of earthworms in vermicomposting. In addition,
vermicomposting substrate with low carbon/nitrogen ratio is better for older
4 Recycling of Municipal Sludge by Vermicomposting
61
Among them, epigeic earthworms like eating organic matter, showing a strong
environmental adaptability and fecundity. Thus, they are considered to be suitable
for sludge treatment. The main species used in vermicomposting of municipal sludge
include Eudrilus eugeniae, Eisenia fetida, Bimastus parvus, Lumbricus rubellus,
Eisenia andrei, and Dendrobaena veneta, as presented in Table 4.2. At present,
Eisenia fetida is a common species used in vermicomposting of sludge. In general,
the adult of E. fetida has the following features: is 60–160 mm long and 3–5 mm
wide, has 80–110 segments, and is 0.5–1.2 g. However, it shows a longer length and
higher growth and reproduction rate in the vermicomposting system, due to its rich
nutrients of sludge. In our study, the maximum weight of earthworm in sludge can
reach up to 2.3 g with a length of 155 mm. Given that earthworms are a valuable
source of traditional Chinese medicine and aquaculture, vermiculture in sludge is
also important income during vermicomposting.
4.4.2 Temperature
The environmental temperature can directly affect the metabolism, growth, reproduction, and activity of earthworm and microorganism, thus affecting their ability in
degradation of organic matter. As shown in Table 4.2, the temperature set in
vermicomposting showed a stronger inconsistency, and most studies selected room
temperature (15–30
C) as vermicomposting temperature, displaying a wide range of
temperature for treating sludge (Fu et al. 2016; Huang et al. 2018; DomínguezCrespo et al. 2012; Cesar et al. 2012; Molina et al. 2013; Lv et al. 2014; Zhang et al.
2015; Babić et al. 2015; Xie et al. 2016; Cui et al. 2018; Ozdemir et al. 2019). Only a
few publications clearly reported that 20
C was the optimal temperature condition
for treating activated sludge (Hait and Tare 2012). Although the increase in temperature can accelerate the degradation and transformation rate of organic matter by
promoting microbial activity, earthworms are prone to heatstroke and even to death
if the temperature exceeds 30
C. Hence, vermicomposting process is a biological
and chemical decomposition of organic wastes under mesophilic condition to produce a stable bioorganic fertilizer.
4.4.3 Organic Matter Content Carbon/Nitrogen Ratio (C/N)
To provide proper nutrition for earthworms and microorganisms during
vermicomposting, carbon and nitrogen in the substrates should be presented at the
correct ratio (Ndegwa and Thompson 2000). The high ammonia nitrogen content
can cause protein poisoning of earthworms, and even death. But lack of nitrogen
may lead to a lower growth rate of earthworms in vermicomposting. In addition,
vermicomposting substrate with low carbon/nitrogen ratio is better for older
4 Recycling of Municipal Sludge by Vermicomposting
61