The consequences of changes planned in the European Union legislation relevant to the disposal of sewage sludges are discussed. A specific municipal waste water treatment plant is analyzed in terms of drying and subsequent combustion or pyrolysis of the produced stabilized sludge, and the respective net energy balances are carried out. A simplified economic analysis of the two disposal options is presented, which suggest that combustion of the sludge would be economically infeasible while pyrolysis of the sludge in a modular, self-sufficient container unit can bring a small financial benefit due to the selling of the produced phosphorus-rich biochar.
. [J]. Frontiers of Chemical Science and Engineering, 2018, 12(4): 660-669.
Vojtěch Turek, Bohuslav Kilkovský, Zdeněk Jegla, Petr Stehlík. Proposed EU legislation to force changes in sewage sludge disposal: A case study. Front. Chem. Sci. Eng., 2018, 12(4): 660-669.
????????Obtainable from combustion of the organic matter
15510 MJ·d–1
????????Required to sustain combustion (at 80% combustion efficiency)
12035 MJ·d–1
Net thermal energy gain
3475 MJ·d–1
Tab.4
Fig.4
Fig.5
Fig.6
Value
Notes/reference
Dryer
Thermal energy demand for drying
18641 MJ·d–1
See Table 3
Investment cost
591500 €
From the technology supplier
Operating cost including maintenance and personnel
85080 €·y–1
Scenario 2: Biogas production & combustion of the dried digestate
Incinerator investment cost
6605000 €
Ashwekar et al. [43]
Total investment cost incl. dryer
7196500 €
Incinerator operating cost incl. maintenance and personnel
1317700 €·y–1
Ashwekar et al. [43]
Total operating cost incl. dryer
1402780 €·y–1
Landfilling of ash incl. transport
8700 €·y–1
From a landfill operator
Profits
–
Net balance excl. investment cost
–1411480 €·y–1
Scenario 3: Biogas production & pyrolysis of the dried digestate
PYREG investment cost
820000 €
From the technology supplier
Total investment cost incl. dryer
1411500 €
PYREG operating cost incl. maintenance and personnel
18590 €·y–1
From the technology supplier
Total operating cost incl. dryer
103670 €·y–1
Other associated costs
–
Profit from selling biochar at 500 EUR·t–1
113740 €·y–1
Sundberg [44]
Net balance excl. investment cost
10070 €·y–1
Tab.5
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