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Nitrogen control in source segregated domestic food waste anaerobic digestion using stripping technologies

Nitrogen control in source segregated domestic food waste anaerobic digestion using stripping technologies
Nitrogen control in source segregated domestic food waste anaerobic digestion using stripping technologies
Anaerobic digestion of source segregated domestic food waste (SS-DFW) offers a sustainable management route for reclaiming potential energy in the form of a fuel gas, and nutrients which can be recycled back to land. However, the biochemical characteristics of SS-DFW can lead to free ammonia nitrogen (FAN) concentrations that are inhibitory to the digestion process causing unstable operation and in some cases complete process failure, particularly in thermophilic systems.
With the purpose of reducing the total ammoniacal nitrogen (TAN) in the digester, side-stream and in situ biogas stripping technologies were tested.
Mesophilic and thermophilic temperatures were evaluated under moderate and complete biogas mixing rates (0.4 l min-1 – 2.6 l min-1) in a batch system. Laboratory investigations showed that TAN reductions in an in situ bubbling reactor with moderate and complete gas mixing rates were non-existent at mesophilic temperatures and minimal at thermophilic temperatures. For this reason, it is unlikely that in situ biogas stripping would be adequate to prevent TAN concentrations greater than 2500 mg N l-1 in a food waste digester and thus will not mitigate ammonia inhibition in a thermophilic system.
Semi-continuous trials carried out on SS-DFW in laboratory-scale digesters, fed daily at an organic loading rate (OLR) of 2 kg VS m-3 day-1 and coupled to stripping columns at low bleed rates (2 – 3.5 % digester volume per day treated in the stripping process) were effective in reducing ammonia concentrations to below thermophilic toxic levels (TAN concentration of 2500 – 3500 mg N l-1). The experiments also confirmed that removal of a proportion of the digester contents and their exposure to thermophilic conditions with pH adjustment to 10 had no adverse effects on performance in terms of biogas production (0.83 ± 0.03 l g-1 VS without stripping, 0.84 ± 0.05 l g-1 VS with stripping) or VS destruction (81.8 % without stripping, 88.5 % with stripping). The process required high pH and temperature (?70 ?C) to achieve a TAN concentration below the toxic threshold for thermophilic digestion, and it is unlikely that stripping at 55 ?C and pH 10 would achieve the target reduction.
The research showed the way forward for the application of side-stream stripping to prevent the build-up of ammonia under thermophilic conditions, if the digester is started up with a non-inhibitory FAN concentration in the inoculum.
anaerobic digestion, source segregated domestic food waste, ammonia removal, in situ stripping, side-stream stripping
Serna-Maza, Alba
81ce5c84-2b04-49b3-86fd-3a5a6834efc2
Serna-Maza, Alba
81ce5c84-2b04-49b3-86fd-3a5a6834efc2
Banks, Charles
5c6c8c4b-5b25-4e37-9058-50fa8d2e926f

Serna-Maza, Alba (2014) Nitrogen control in source segregated domestic food waste anaerobic digestion using stripping technologies. University of Southampton, Engineering and the Environment, Doctoral Thesis, 193pp.

Record type: Thesis (Doctoral)

Abstract

Anaerobic digestion of source segregated domestic food waste (SS-DFW) offers a sustainable management route for reclaiming potential energy in the form of a fuel gas, and nutrients which can be recycled back to land. However, the biochemical characteristics of SS-DFW can lead to free ammonia nitrogen (FAN) concentrations that are inhibitory to the digestion process causing unstable operation and in some cases complete process failure, particularly in thermophilic systems.
With the purpose of reducing the total ammoniacal nitrogen (TAN) in the digester, side-stream and in situ biogas stripping technologies were tested.
Mesophilic and thermophilic temperatures were evaluated under moderate and complete biogas mixing rates (0.4 l min-1 – 2.6 l min-1) in a batch system. Laboratory investigations showed that TAN reductions in an in situ bubbling reactor with moderate and complete gas mixing rates were non-existent at mesophilic temperatures and minimal at thermophilic temperatures. For this reason, it is unlikely that in situ biogas stripping would be adequate to prevent TAN concentrations greater than 2500 mg N l-1 in a food waste digester and thus will not mitigate ammonia inhibition in a thermophilic system.
Semi-continuous trials carried out on SS-DFW in laboratory-scale digesters, fed daily at an organic loading rate (OLR) of 2 kg VS m-3 day-1 and coupled to stripping columns at low bleed rates (2 – 3.5 % digester volume per day treated in the stripping process) were effective in reducing ammonia concentrations to below thermophilic toxic levels (TAN concentration of 2500 – 3500 mg N l-1). The experiments also confirmed that removal of a proportion of the digester contents and their exposure to thermophilic conditions with pH adjustment to 10 had no adverse effects on performance in terms of biogas production (0.83 ± 0.03 l g-1 VS without stripping, 0.84 ± 0.05 l g-1 VS with stripping) or VS destruction (81.8 % without stripping, 88.5 % with stripping). The process required high pH and temperature (?70 ?C) to achieve a TAN concentration below the toxic threshold for thermophilic digestion, and it is unlikely that stripping at 55 ?C and pH 10 would achieve the target reduction.
The research showed the way forward for the application of side-stream stripping to prevent the build-up of ammonia under thermophilic conditions, if the digester is started up with a non-inhibitory FAN concentration in the inoculum.

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More information

Published date: November 2014
Keywords: anaerobic digestion, source segregated domestic food waste, ammonia removal, in situ stripping, side-stream stripping
Organisations: University of Southampton, Water & Environmental Engineering Group

Identifiers

Local EPrints ID: 372768
URI: http://eprints.soton.ac.uk/id/eprint/372768
PURE UUID: e683e1ef-57e5-4366-b74b-c3fe59049943

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Date deposited: 19 Jan 2015 11:52
Last modified: 17 Jul 2017 21:38

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