1.1 Introduction
Increase in global population, urbanization and industrialization has resulted in
environmental pollution and degradation including diminished water quality
(Verma et al. 2012). Disposal of untreated sewage and industrial effluents into the
surface water bodies leads to water pollution (Goel 2006). Wastewater carrying
organics like biochemical oxygen demand (BOD), chemical oxygen demand (COD)
and nutrients like nitrogen and phosphorus results in the problems like depletion of
dissolved oxygen (DO) and eutrophication (Metcalf et al. 1991; Zheng et al. 2013).
In addition, exposure to the water contaminated by the release of pathogens from
sewage into the surface water leads to water-borne diseases (Reddy and Smith 1987).
Thus, deterioration of river ecology along with the loss of freshwater sources creates
an unhealthy environment for humans (Wang et al. 2012). Furthermore, the per
capita available water is becoming less with an increase in the population pertaining
to the limitation of freshwater sources (Pimentel et al. 2004). Therefore, it becomes
necessary to reuse wastewater generated from households and other places after
giving a certain level of treatment. Owing to the water scarcity and water pollution
due to anthropogenic activities, there is an urgent need to treat and reuse the treated
effluent in industrial, agricultural and non-potable purposes.
For wastewater treatment, anaerobic and aerobic processes are being used worldwide (Speece 1983). In the anaerobic process, microbes convert organic matters into
methane and carbon dioxide, whereas in the aerobic process, aerobic microbes
convert organic matters into biomass and carbon dioxide (Metcalf et al. 1991).
The anaerobic process is effective for high COD wastewater, requires less energy,
and produces less sludge in comparison to aerobic process. However, it has been
documented that the aerobic process is comparatively better than the anaerobic
process in terms of acclimatizing the variation in pH, temperature and organic
loading rates (OLR) (Degremont 1991). Further, the aerobic process requires less
time to restart and can work between a range of temperature from 25 to 35
C as
compared to the optimum temperature for the anaerobic process is 30
C (Singh et al.
2019b). However, both conventional wastewater treatment techniques required high
capital cost, recurring expenditures, skilled manpower, more time to restart after
complete shutdown and mechanized and energy-intensive operations (Noumsi et al.
2005). In addition, the sludge generated from conventional processes requires further
treatment before getting disposed into the environment. Other than the biological
treatment process, physical and chemical processes are also being used in some part
of the world (Adin and Asano 1998). However, physical and chemical processes are
not efficient organic and nutrient removal from wastewater (Ra et al. 2000). Thus, in
the present scenario, an economical and sustainable process is required to treat
wastewater with less capital and operation and maintenance cost and ease of
operation process.
Integration of earthworms in wastewater filtration process has evolved as an
eco-friendly and economical alternative to conventional wastewater process, collectively known as vermifiltration (Tomar and Suthar 2011). Wastewater passing
4
Bhavini et al.
Increase in global population, urbanization and industrialization has resulted in
environmental pollution and degradation including diminished water quality
(Verma et al. 2012). Disposal of untreated sewage and industrial effluents into the
surface water bodies leads to water pollution (Goel 2006). Wastewater carrying
organics like biochemical oxygen demand (BOD), chemical oxygen demand (COD)
and nutrients like nitrogen and phosphorus results in the problems like depletion of
dissolved oxygen (DO) and eutrophication (Metcalf et al. 1991; Zheng et al. 2013).
In addition, exposure to the water contaminated by the release of pathogens from
sewage into the surface water leads to water-borne diseases (Reddy and Smith 1987).
Thus, deterioration of river ecology along with the loss of freshwater sources creates
an unhealthy environment for humans (Wang et al. 2012). Furthermore, the per
capita available water is becoming less with an increase in the population pertaining
to the limitation of freshwater sources (Pimentel et al. 2004). Therefore, it becomes
necessary to reuse wastewater generated from households and other places after
giving a certain level of treatment. Owing to the water scarcity and water pollution
due to anthropogenic activities, there is an urgent need to treat and reuse the treated
effluent in industrial, agricultural and non-potable purposes.
For wastewater treatment, anaerobic and aerobic processes are being used worldwide (Speece 1983). In the anaerobic process, microbes convert organic matters into
methane and carbon dioxide, whereas in the aerobic process, aerobic microbes
convert organic matters into biomass and carbon dioxide (Metcalf et al. 1991).
The anaerobic process is effective for high COD wastewater, requires less energy,
and produces less sludge in comparison to aerobic process. However, it has been
documented that the aerobic process is comparatively better than the anaerobic
process in terms of acclimatizing the variation in pH, temperature and organic
loading rates (OLR) (Degremont 1991). Further, the aerobic process requires less
time to restart and can work between a range of temperature from 25 to 35
C as
compared to the optimum temperature for the anaerobic process is 30
C (Singh et al.
2019b). However, both conventional wastewater treatment techniques required high
capital cost, recurring expenditures, skilled manpower, more time to restart after
complete shutdown and mechanized and energy-intensive operations (Noumsi et al.
2005). In addition, the sludge generated from conventional processes requires further
treatment before getting disposed into the environment. Other than the biological
treatment process, physical and chemical processes are also being used in some part
of the world (Adin and Asano 1998). However, physical and chemical processes are
not efficient organic and nutrient removal from wastewater (Ra et al. 2000). Thus, in
the present scenario, an economical and sustainable process is required to treat
wastewater with less capital and operation and maintenance cost and ease of
operation process.
Integration of earthworms in wastewater filtration process has evolved as an
eco-friendly and economical alternative to conventional wastewater process, collectively known as vermifiltration (Tomar and Suthar 2011). Wastewater passing
4
Bhavini et al.