considered as an unconventional water resource (Eriksson et al. 2002). Treated
wastewater contains organic nutrients that have potential use in agriculture, but
because of the high ionicity, the soil salinity is increased (Huang et al. 2018). The
variety of techniques such as post-precipitation, adsorption, membrane filtration,
electrochemical methods, nanocatalysis technology, and ion exchange have been
applied to remove dissolved minerals and toxic compounds from the treated wastewater (Khan et al. 2012; Husain et al. 2014; Zhang et al. 2017). However, the
application of some of these techniques is restricted by cost and economic factors,
compatibility, efficiency, and existing regulations and standards (Khan et al. 2019a;
Sinha and Chakma 2019). The increase in pollution along with the scarcity of water
gives rise to the lookout for suitable treatment technologies for the removal of
pollutants and reuse of treated effluents in operations requiring low-quality water.
Among different options, physical unit operations are easy and economical, but it
results in less success due to incomplete removal of contaminants (Sheehan and
Greenfield 1980). The chemical treatment options have already been used in the
remediation of wastewater (Huang et al. 2009). However, chemical treatments are
mostly centered on the pH regulation for the removal of colloids. Despite being an
effective solution for targeting pollutants of special concern, chemical treatments
lack attention from the environmentalists as they require high capital investment in
operation and maintenance (Rao et al. 2007). Lom (1977) stated that chemical
treatments generate several by-products that require special attention and highly
skilled manpower. On the other hand, compared to the other techniques mentioned
above, biological remediation methods using earthworms (vermifiltration) seem to
be a cost-effective, eco-friendly, hygienic, chemical-free method in the treatment of
domestic and industrial wastewater. According to Kumar et al. (2015),
vermifiltration process exploits the earthworms as a biofilter in combination with
suitable bedding materials to treat domestic and industrial wastewater. Wastewater
treatment by the vermifiltration system is carried out simultaneously by both germs
and earthworms as earthworms host millions of microorganisms and their body walls
are used to remove BOD, COD, and TDS through ingestion, biodegradation, and
absorption (Singleton et al. 2003). Besides, these favorable conditions for the
aerobic activity of microorganisms are being created by the movement of the
earthworms in the filter bed, improve oxygen penetration (Khan et al. 2019b;
Samal et al. 2019), and also prevent odors and sludge formation (Lourenço and
Nunes 2017). Furthermore, the vermifiltration process required less area for the
establishment and has the same efficiency as the activated sludge process (Samal
et al. 2017).
6.4.2.1 Application of Vermifiltration
According to Sinha et al. (2008), a promising treatment method of vermifilter can
now be used to treat the wastewater generated from domestic chores such as
washing, cooking, toilet, etc. There has been a great result in the treatment efficiencies of BOD, COD, TDS, and TSS of the order greater than 90%, 80–90%, 90–92%,
and 90–95%, respectively, with the application of vermifilters in treating effluents
98
S. I. Singh et al.
wastewater contains organic nutrients that have potential use in agriculture, but
because of the high ionicity, the soil salinity is increased (Huang et al. 2018). The
variety of techniques such as post-precipitation, adsorption, membrane filtration,
electrochemical methods, nanocatalysis technology, and ion exchange have been
applied to remove dissolved minerals and toxic compounds from the treated wastewater (Khan et al. 2012; Husain et al. 2014; Zhang et al. 2017). However, the
application of some of these techniques is restricted by cost and economic factors,
compatibility, efficiency, and existing regulations and standards (Khan et al. 2019a;
Sinha and Chakma 2019). The increase in pollution along with the scarcity of water
gives rise to the lookout for suitable treatment technologies for the removal of
pollutants and reuse of treated effluents in operations requiring low-quality water.
Among different options, physical unit operations are easy and economical, but it
results in less success due to incomplete removal of contaminants (Sheehan and
Greenfield 1980). The chemical treatment options have already been used in the
remediation of wastewater (Huang et al. 2009). However, chemical treatments are
mostly centered on the pH regulation for the removal of colloids. Despite being an
effective solution for targeting pollutants of special concern, chemical treatments
lack attention from the environmentalists as they require high capital investment in
operation and maintenance (Rao et al. 2007). Lom (1977) stated that chemical
treatments generate several by-products that require special attention and highly
skilled manpower. On the other hand, compared to the other techniques mentioned
above, biological remediation methods using earthworms (vermifiltration) seem to
be a cost-effective, eco-friendly, hygienic, chemical-free method in the treatment of
domestic and industrial wastewater. According to Kumar et al. (2015),
vermifiltration process exploits the earthworms as a biofilter in combination with
suitable bedding materials to treat domestic and industrial wastewater. Wastewater
treatment by the vermifiltration system is carried out simultaneously by both germs
and earthworms as earthworms host millions of microorganisms and their body walls
are used to remove BOD, COD, and TDS through ingestion, biodegradation, and
absorption (Singleton et al. 2003). Besides, these favorable conditions for the
aerobic activity of microorganisms are being created by the movement of the
earthworms in the filter bed, improve oxygen penetration (Khan et al. 2019b;
Samal et al. 2019), and also prevent odors and sludge formation (Lourenço and
Nunes 2017). Furthermore, the vermifiltration process required less area for the
establishment and has the same efficiency as the activated sludge process (Samal
et al. 2017).
6.4.2.1 Application of Vermifiltration
According to Sinha et al. (2008), a promising treatment method of vermifilter can
now be used to treat the wastewater generated from domestic chores such as
washing, cooking, toilet, etc. There has been a great result in the treatment efficiencies of BOD, COD, TDS, and TSS of the order greater than 90%, 80–90%, 90–92%,
and 90–95%, respectively, with the application of vermifilters in treating effluents
98
S. I. Singh et al.