COD and total phosphorus (TP) in the range 62–81% and 72–80% respectively. In a
single reactor, Wang et al. 2010a, b used plant Phragmites australis and Eisenia
fetida to treat domestic wastewater. Nuengjamnong et al. (2011) used earthworm
Pheretima peguana in a two-stage vermifilter, macrophyte filter for effective treatment of swine wastewater, and reported more than 90% COD and Total Nitrogen
(TN) removal efficiency. Xu et al. (2013a, b) explored the potential of earthworm for
nitrification-denitrification and TN removal efficiency by adding Eisenia fetida to
the vertical flow wetland, planted with various plants. Through planting macrophyte
in vermifilter, some structural and functional problems are reported to be solved.
Planting macrophytes in vermifilters or introducing earthworms in built wetlands
have been reported in laboratory and pilot-scale experiments (Tomar and Suthar
2011; Wang et al. 2010a, b). Using plant-mediated system can benefit both the plants
and earthworms as it is a well-known fact that both act in a symbiotic manner. The
overall system performance also increases as does the filter’s lifetime. Macrophytes
also extract organics, nitrogen, and phosphorus from wastewater and make it easier
for earthworms to work (Xu et al. 2013a). Oxygen leakage from underground tissue
produces oxidized layer or 1–4 mm oxidizing protective film on the root surface
primarily from root tips (Brix and Schierup 1990; Bezbaruah and Zhang 2005).
Thus, the aerobic condition maintained in filter media is considered favorable for
earthworm’s survival (Ye et al. 2012). Earthworms create macro pores and loosen
soil so that plant roots penetrate the media and form new tubular pores into deep soil.
For this reason, the rate of infiltration in the top and bottom layers is maintained
uniformly. A variety of processes can lead to clogging such as accumulation of
suspended solids (SS), surplus production of sludge, chemical precipitation and
deposition in substratum pores, growth of plant rhizomes and roots, gas generation,
and clogging layer compaction (Caselles-Osorio et al. 2007; Sun et al. 1999).
Earthworms digest the accumulated organic suspended solids for a blocked filter
and their burrowing operation gradually loosens the substrates to restore the system
smoothly (Xing et al. 2010). Plant root system provides a higher surface area for the
production of various heterotrophs, autotrophs, nitrifiers, and ammonium-oxidizing
bacteria (Vymazal 2005; Konnerup et al. 2009). Organic pollutants are reported to
degrade very rapidly due to the enrichment of the diversified microbial population in
the rhizospheric environment. For denitrification, plant litter and root exudates, i.e.,
citrate, malate, acetate, and oxalate, act as carbon sources (Lin et al. 2002).
The addition of plants in the vermifilter also leads to pollutant removal and improves
the efficiency of the process (Samal et al. 2017a). Samal et al. (2018a) also stated that
the main benefit from the introduction of plants is the elimination of nutrients
(nitrogen and phosphorus from the wastewater). Penetration of plant root in bedding
helps to aerobicize the environment by producing cracks throughout the bedding
(Bezbaruah and Zhang 2005). The formed cracks make it easy for earthworms to
burrow deeper. Because of the root expansion and cracks, the aerobic depth of the
bedding profile increases to three- to fourfold as compared to the plant-free filter
(Samal et al. 2017b). The increase in aeration within the bedding also helps to
increase the organics oxidation and nitrification. The plant roots often release
oxygen that is useful in the removal of pollutants from wastewater. The plant root
42
A. B. Chowdhary et al.
single reactor, Wang et al. 2010a, b used plant Phragmites australis and Eisenia
fetida to treat domestic wastewater. Nuengjamnong et al. (2011) used earthworm
Pheretima peguana in a two-stage vermifilter, macrophyte filter for effective treatment of swine wastewater, and reported more than 90% COD and Total Nitrogen
(TN) removal efficiency. Xu et al. (2013a, b) explored the potential of earthworm for
nitrification-denitrification and TN removal efficiency by adding Eisenia fetida to
the vertical flow wetland, planted with various plants. Through planting macrophyte
in vermifilter, some structural and functional problems are reported to be solved.
Planting macrophytes in vermifilters or introducing earthworms in built wetlands
have been reported in laboratory and pilot-scale experiments (Tomar and Suthar
2011; Wang et al. 2010a, b). Using plant-mediated system can benefit both the plants
and earthworms as it is a well-known fact that both act in a symbiotic manner. The
overall system performance also increases as does the filter’s lifetime. Macrophytes
also extract organics, nitrogen, and phosphorus from wastewater and make it easier
for earthworms to work (Xu et al. 2013a). Oxygen leakage from underground tissue
produces oxidized layer or 1–4 mm oxidizing protective film on the root surface
primarily from root tips (Brix and Schierup 1990; Bezbaruah and Zhang 2005).
Thus, the aerobic condition maintained in filter media is considered favorable for
earthworm’s survival (Ye et al. 2012). Earthworms create macro pores and loosen
soil so that plant roots penetrate the media and form new tubular pores into deep soil.
For this reason, the rate of infiltration in the top and bottom layers is maintained
uniformly. A variety of processes can lead to clogging such as accumulation of
suspended solids (SS), surplus production of sludge, chemical precipitation and
deposition in substratum pores, growth of plant rhizomes and roots, gas generation,
and clogging layer compaction (Caselles-Osorio et al. 2007; Sun et al. 1999).
Earthworms digest the accumulated organic suspended solids for a blocked filter
and their burrowing operation gradually loosens the substrates to restore the system
smoothly (Xing et al. 2010). Plant root system provides a higher surface area for the
production of various heterotrophs, autotrophs, nitrifiers, and ammonium-oxidizing
bacteria (Vymazal 2005; Konnerup et al. 2009). Organic pollutants are reported to
degrade very rapidly due to the enrichment of the diversified microbial population in
the rhizospheric environment. For denitrification, plant litter and root exudates, i.e.,
citrate, malate, acetate, and oxalate, act as carbon sources (Lin et al. 2002).
The addition of plants in the vermifilter also leads to pollutant removal and improves
the efficiency of the process (Samal et al. 2017a). Samal et al. (2018a) also stated that
the main benefit from the introduction of plants is the elimination of nutrients
(nitrogen and phosphorus from the wastewater). Penetration of plant root in bedding
helps to aerobicize the environment by producing cracks throughout the bedding
(Bezbaruah and Zhang 2005). The formed cracks make it easy for earthworms to
burrow deeper. Because of the root expansion and cracks, the aerobic depth of the
bedding profile increases to three- to fourfold as compared to the plant-free filter
(Samal et al. 2017b). The increase in aeration within the bedding also helps to
increase the organics oxidation and nitrification. The plant roots often release
oxygen that is useful in the removal of pollutants from wastewater. The plant root
42
A. B. Chowdhary et al.