dry anaerobic digestion of municipal solid waste and digestate ...

- Feeding and digested residue withdrawal will be performed once a day. Based on results
of pilot experiments, the chosen retention time will be 24 days. The feedstock will be
stored in feed storage tank for few days (less than a week) before feeding, because
necessary pretreatment processing (shredding and mixing with waste paper) could be
performed in the preceding week for smooth and un-interrupted running of the plant in the
coming week.
- Recirculation rate of 2.5 Ldig/Lreactor vol./d will be maintained during continuous operation
of the reactor as used in pilot experiments (please refer to Table 3.3 and Figure 3.5).
- The pH, ammonia, VFA and alkalinity of the liquid extract of digestate and biogas
composition, should be regularly measured to prevent reactor upset and/or to cure it by
methods like decreasing the organic loads or treating with alkali.
4.5.4 Generation of methane and energy
-Methane yield of 96 m 3 CH4/d (or 200 m 3 biogas/d) will be generated by the plant.
-About 33% of the produced biogas from the proposed decentralized system will be used to
provide energy for running of the plant itself, whereas remaining 67% will be surplus
energy (Appendix B) that can be provided to the community.
-Conversion of biogas to electricity is an environmental friendly and clean process. The
system will be provided with immediate conversion facility (Gas engine) of biogas into
electricity. Moreover, biogas storage tank (100 m 3 ) will also be installed for temporary
storage of biogas.
-The amount of power produced from this system will be 14 kW (Appendix B).
4.5.5 Digestate management
Table 4.8 Technical Data of Sand Drying Bed for Digestate Dewatering
Detail Value/Specification
Dimensions of sand drying beds (m)
-Width
-Length
Thickness of bed layers (cm)
-Sand
-Coarse sand
-Fine gravel
-Medium gravel
-Coarse gravel
Type of sand drying bed Conventional and open
Number of sand drying bed
Under-drainage system
3
-Pipe material
PVC
-Pipe type
Perforated
-Pipe diameter
15 cm
-Pipe spacing
2 m
-Pipe slope
2%
Layer of digestate over bed 20 cm
88
6
16
20
7.5
7.5
7.5
15