Abstract
The goal of the project was to improve the utilization of
sludge in a cost-efficient manner. Thermophilic anaerobic
digestion (TAD) is an option to improve the energy
efficiency of sewage sludge due to potentially higher
biogas yield. TAD also offers other advantages over
mesophilic process such as reduction in sludge volume and
better hygienic properties of the treated sludge and thus
better potential for agricultural utilization.
The experimental part of the project focused on the
modification of anaerobic digestion process from
mesophilic to thermophilic. The aim was to investigate
and compare the biogas yield and quality, process
loadability, digestate and reject water properties and
digestor material durability in the two processes. Basic
data on anaerobic digestion was gathered in comparative
pilot scale experiments.
Loading tests were carried out to determine the maximum
loading rate of the digestion processes. In the first set
of loading tests, the TAD process produced more biogas
than the MAD process. The average total biogas production
and unit production in TAD were as high as 1.3 times
those of MAD. The biogas unit production started to
decrease when the retention time was shorter than 17
(TAD) or 15 (MAD) days. In the second set of loading
tests, thickened sludge was let to hydrolyse for ca. two
days and the formation of gas bubbles caused flotation.
This procedure more than tripled the biogas unit
production compared to previous test set, but now both
TAD and MAD processes produced similar amounts of
methane.
Biogas methane content was similar in both reactors
throughout the pilot runs. However, the elevated
temperature caused increased siloxane concentrations in
the gas phase. Also the sulphur concentration in TAD was
higher than in MAD. Overall, the sulphur content of the
biogas was low in both processes.
TAD process hygienized the sludge when the retention time
was > 15 days. According to CST measurements (Capillary
Suction Time), dewatering properties of thermophilic
sludge were inferior and the reject water contained more
NH4+-N and CODCr compared to mesophilic sludge.
Thermophilic sludge was times more odorous and more
volatile organic compounds were released from it. Reactor
material tests indicated that thermophilic process caused
slightly more corrosion in stainless steel. However, no
significant differences between the two processes were
observed.
Original language | English |
---|---|
Title of host publication | The 12th Nordic/NORDIWA Wastewater conference, Conference book |
Place of Publication | Helsinki |
Pages | 299-308 |
Publication status | Published - 2011 |
MoE publication type | A4 Article in a conference publication |
Event | 12th Nordic Wastewater Conference - Helsinki, Finland Duration: 14 Nov 2011 → 16 Nov 2011 Conference number: 12 |
Conference
Conference | 12th Nordic Wastewater Conference |
---|---|
Country/Territory | Finland |
City | Helsinki |
Period | 14/11/11 → 16/11/11 |
Keywords
- Sludge
- digestion
- thermophilic
- biogas
- trace compounds