2.4.2 Limitations
Vermifiltration process till now has been more successful in the lab-scale operation.
Some limitations were observed during field-scale implementation which are listed
as below:
• Most of the vermifiltration process are carried out in subsurface vertical/horizontal reactors as earthworms are cannot survive in submerged condition. In most of
the reactors, the design is done in such a way that the influent enters in one point,
and effluent is taken out from the other end in the horizontal reactors, and in the
vertical reactors influent is from the top, and effluent is coming out from the
bottom of the reactors.
• Earthworms do not like sunlight, and they breathe through their skin, so the
movement of the earthworms are almost nil during the day time. Therefore, care
should be taken while positioning the reactor by shunting it from sunlight either
by covering it with gunny bags or keeping in shade.
• As most of the earthworms being employed are surface eaters, they concentrate
mostly in the upper part of the reactors, and less activities are seen in middle and
bottom layer of filter. This may lead to reduction in the efficiency of the filter.
• High moisture content in the filter might lead to anaerobic condition and may lead
to the dead of the earthworms. So care has to be taken while deciding on the
hydraulic loading rate of the filter.
• Wastewater with high NaCl cannot be treated in vermifilter as it is toxic for the
earthworms (Hughes et al. 2007, 2008). The earthworms may die reducing the
total biomass available to treat the wastewater, further affecting the efficiency of
the system.
• Earthworms have the ability to accumulate heavy metals in their body. However,
the amount of heavy metal uptake by the earthworm is limited (Sinha et al. 2008).
Owing to which efficiency of treating heavy metals containing wastewater is less.
• The reproduction rate of earthworms is very high, and after certain time, there
may be shortage of food and space as well, which may affect the efficiency of the
treatment process.
• Cleaning of the vermifilter is required after the running period of the reactor is
over which is really a cumbersome process. Proper care should be taken while
handling the earthworms as they are sensitive and any injury may lead to their
death.
• Vermifilters may get choked when wastewater with high organic loads are used.
Another important limitation is the depth of the vermifilter as earthworms cannot
survive in deeper depths.
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Vermifiltration process till now has been more successful in the lab-scale operation.
Some limitations were observed during field-scale implementation which are listed
as below:
• Most of the vermifiltration process are carried out in subsurface vertical/horizontal reactors as earthworms are cannot survive in submerged condition. In most of
the reactors, the design is done in such a way that the influent enters in one point,
and effluent is taken out from the other end in the horizontal reactors, and in the
vertical reactors influent is from the top, and effluent is coming out from the
bottom of the reactors.
• Earthworms do not like sunlight, and they breathe through their skin, so the
movement of the earthworms are almost nil during the day time. Therefore, care
should be taken while positioning the reactor by shunting it from sunlight either
by covering it with gunny bags or keeping in shade.
• As most of the earthworms being employed are surface eaters, they concentrate
mostly in the upper part of the reactors, and less activities are seen in middle and
bottom layer of filter. This may lead to reduction in the efficiency of the filter.
• High moisture content in the filter might lead to anaerobic condition and may lead
to the dead of the earthworms. So care has to be taken while deciding on the
hydraulic loading rate of the filter.
• Wastewater with high NaCl cannot be treated in vermifilter as it is toxic for the
earthworms (Hughes et al. 2007, 2008). The earthworms may die reducing the
total biomass available to treat the wastewater, further affecting the efficiency of
the system.
• Earthworms have the ability to accumulate heavy metals in their body. However,
the amount of heavy metal uptake by the earthworm is limited (Sinha et al. 2008).
Owing to which efficiency of treating heavy metals containing wastewater is less.
• The reproduction rate of earthworms is very high, and after certain time, there
may be shortage of food and space as well, which may affect the efficiency of the
treatment process.
• Cleaning of the vermifilter is required after the running period of the reactor is
over which is really a cumbersome process. Proper care should be taken while
handling the earthworms as they are sensitive and any injury may lead to their
death.
• Vermifilters may get choked when wastewater with high organic loads are used.
Another important limitation is the depth of the vermifilter as earthworms cannot
survive in deeper depths.
2 Vermifiltration for Rural Wastewater Treatment
31