Effect of earthworms on the performance and microbial communities
of excess sludge treatment process in vermiﬁlter
Jing Liu, Zhibo Lu
, Jian Yang, Meiyan Xing, Fen Yu, Meiting Guo
State Key Laboratory of Pollution Control and Resources Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China
The vermiﬁlter (VF) had higher sludge reduction ability than a bioﬁlter (BF).
Elemental analysis showed that earthworms enhanced the stabilization of excess sludge.
Dehydrogenase activity in VF bioﬁlms was much higher than that in the BF.
Speciﬁc microbes in earthworm cast enhanced the degradation of organic matter.
Received 20 January 2012
Received in revised form 24 April 2012
Accepted 24 April 2012
Available online 3 May 2012
Previous studies have shown that the stabilization of excess sludge by vermiﬁltration can be improved
signiﬁcantly through the use of earthworms. To investigate the effect of earthworms on enhancing sludge
stabilization during the vermiﬁltration process, a vermiﬁlter (VF) with earthworms and a conventional
bioﬁlter (BF) without earthworms were compared. The sludge reduction capability of the VF was $85%
higher than that of the BF. Speciﬁcally, elemental analysis indicated that earthworms enhanced the sta-
bilization of organic matter. Furthermore, earthworm predation strongly regulated microbial biomass
while improving microbial activity. Denaturing gradient gel electrophoresis (DGGE) analysis showed that
the most abundant microbes in the VF bioﬁlms and earthworm casts were Flavobacterium, Myroides,
Sphingobacterium, and Myxococcales, all of which are known to be highly effective at degrading organic
matter. These results indicate that earthworms can improve the stabilization of excess sludge during
vermiﬁltration, and reveal the processes by which this is achieved.
Ó 2012 Elsevier Ltd. All rights reserved.
Excess sludge is an unavoidable byproduct of the aerobic
biological wastewater treatment process. The costs associated with
handling this residual product are rising, and thus the search is
ongoing for alternative cost-saving techniques to reduce and stabi-
lize excess sludge. This is particularly true for small wastewater
treatment plants in developing countries. Accordingly, there is a
strong impetus to develop low-cost and ecologically sound tech-
niques to improve sludge reduction and stabilization.
Vermiﬁltration is a relatively new technology that uses earth-
worms, and their interactions with microorganisms, to process
organically polluted water and excess sludge. Vermiﬁltration was
ﬁrst developed as an extension of vermicomposting for solid waste
in order to treat anaerobically stabilized efﬂuents from the dried
vine fruit industry (Athanasopoulos, 1993). Since then, several stud-
ies have been conducted to evaluate the use of vermiﬁlters in waste-
water treatment (Sinha et al., 2008; Xing et al., 2011a), sludge
reduction and stabilization (Zhao et al., 2010), and on-site sludge
sanitization (Gajurel et al., 2007). It has been suggested that the en-
hanced performance of the vermiﬁltration process for wastewater
or excess sludge treatment is due to better aerobic conditions from
the burrowing action of earthworms, the greater adsorption effect
of the earthworm casts, and higher levels of microbial activity stim-
ulated earthworm feeding (Sinha et al., 2008; Zhao et al., 2010).
Like vermicomposting, vermiﬁltration is a bio-oxidative process
in which earthworms interact intensively with microorganisms
0960-8524/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
Abbreviations: VF, vermiﬁlter; BF, conventional bioﬁlter; PCR-DGGE, polymerase
chain reaction-denaturing gradient gel electrophoresis; DHA, dehydrogenase
activity; SS, suspended solids; VSS, volatile suspended solids; SVI, sludge volume
index; OLR, organic loading rate; IES, inﬂow excess sludge; BFS, BF-treated sludge;
VFS, VF-treated sludge; VEC, earthworm casts produced by the earthworms in the
VF; BF-1, BF bioﬁlm at a depth of 5 cm; BF-2, BF bioﬁlm at a depth of 25 cm; BF-3, BF
bioﬁlm at a depth of 45 cm; VF-1, VF bioﬁlm at a depth of 5 cm; VF-2, VF bioﬁlm at a
depth of 25 cm; VF-3, VF bioﬁlm at a depth of 45 cm; RDP, Ribosomal Database
Corresponding author. Tel./fax: +86 21 65984275.
E-mail address: email@example.com (Z. Lu).
Bioresource Technology 117 (2012) 214–221
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