formed by a variety of microorganisms and its adsorbed organic and inorganic
substances, as given in Fig. 4.1 (Christensen et al. 2015). The sludge not only has
high content of organic matter but also enriches protein, humus, nitrogen, phosphorus, and potassium and other nutrients and trace elements necessary for plant growth
(Zhang et al. 2017). According to a survey (Yang et al. 2015), the average contents
of organic matter, nitrogen, phosphorus, and potassium in sludge were 41.35%,
3.02%, 1.57%, and 0.69%, respectively, which exceeded the Chinese nutrient
standard of compost. But at the same time, the sludge also contains parasitic eggs,
pathogenic microorganisms, toxic and harmful heavy metals, and a large number of
nondegradable substances (Yang et al. 2015; Zhang et al. 2017; Qu et al. 2019).
These characteristics strongly affect the subsequent treatment and disposal of sludge.
With the development of the ecological civilization, the number of municipal
sewage treatment plants in China has reached to 3781 in the end of 2017, and the
treatment capacity of the sewage is over 186.1 million m
3 /d (Statistical Yearbook of
Urban and Rural Construction in China 2017). In general, the quality of the sludge
accounts for 0.05–0.1% of the treated water (80% moisture content). It is estimated
that the production of municipal sludge (including domestic and industrial sludge) in
China is more than 40 million tons a year. Therefore, how to dispose the large
quantity and complex sludge safely and effectively has become an important problem in the environmental protection industry in China.
4.2.2 Methods of Sludge Treatment and Disposal
The principle for sludge treatment and disposal refers to reduction, stabilization, and
innocuity in the procession. Sludge treatment is a part of sewage treatment, including
concentration, anaerobic digestion, dehydration, and other processes, in which
concentration and dehydration are the core of sludge reduction. Sludge disposal is
considered as the final process after sludge dewatering. The disposal methods are
mainly comprised of sanitary landfill, aerobic composting, dry incineration, land use
Fig. 4.1 Structural characteristics of sludge
4 Recycling of Municipal Sludge by Vermicomposting
57
substances, as given in Fig. 4.1 (Christensen et al. 2015). The sludge not only has
high content of organic matter but also enriches protein, humus, nitrogen, phosphorus, and potassium and other nutrients and trace elements necessary for plant growth
(Zhang et al. 2017). According to a survey (Yang et al. 2015), the average contents
of organic matter, nitrogen, phosphorus, and potassium in sludge were 41.35%,
3.02%, 1.57%, and 0.69%, respectively, which exceeded the Chinese nutrient
standard of compost. But at the same time, the sludge also contains parasitic eggs,
pathogenic microorganisms, toxic and harmful heavy metals, and a large number of
nondegradable substances (Yang et al. 2015; Zhang et al. 2017; Qu et al. 2019).
These characteristics strongly affect the subsequent treatment and disposal of sludge.
With the development of the ecological civilization, the number of municipal
sewage treatment plants in China has reached to 3781 in the end of 2017, and the
treatment capacity of the sewage is over 186.1 million m
3 /d (Statistical Yearbook of
Urban and Rural Construction in China 2017). In general, the quality of the sludge
accounts for 0.05–0.1% of the treated water (80% moisture content). It is estimated
that the production of municipal sludge (including domestic and industrial sludge) in
China is more than 40 million tons a year. Therefore, how to dispose the large
quantity and complex sludge safely and effectively has become an important problem in the environmental protection industry in China.
4.2.2 Methods of Sludge Treatment and Disposal
The principle for sludge treatment and disposal refers to reduction, stabilization, and
innocuity in the procession. Sludge treatment is a part of sewage treatment, including
concentration, anaerobic digestion, dehydration, and other processes, in which
concentration and dehydration are the core of sludge reduction. Sludge disposal is
considered as the final process after sludge dewatering. The disposal methods are
mainly comprised of sanitary landfill, aerobic composting, dry incineration, land use
Fig. 4.1 Structural characteristics of sludge
4 Recycling of Municipal Sludge by Vermicomposting
57