Ammonia removal in food waste anaerobic digestion using a side-stream stripping process

Abstract

Three 35-L anaerobic digesters fed on source segregated food waste were coupled to side-stream ammonia stripping columns and operated semi-continuously over 300 days, with results in terms of performance and stability compared to those of a control digester without stripping. Biogas was used as the stripping medium, and the columns were operated under different conditions of temperature (55, 70, 85 ⁰C), pH (unadjusted and pH 10), and RT (2 to 5 days). To reduce digester TAN concentrations to a useful level a high temperature (≥70⁰C) and a pH of 10 were needed; under these conditions 48% of the TAN was removed over a 138-day period without any detrimental effects on digester performance. Other effects of the stripping process were an overall reduction in digestate organic nitrogen-containing fraction compared to the control and a recovery in the acetoclastic pathway when TAN concentration was 1770 ± 20 mg kg -1 . Keywords IntroductionThe source segregation, separate collection and subsequent anaerobic digestion of food waste can help to reduce the organic fraction of municipal solid waste for disposal and, in some cases, help governments to meet the targets of the EU Directive on the landfilling of waste (1999/31/EC). Importantly, it also offers a method of reclaiming potential energy in the waste in the form of a fuel gas, and opens up a route by which nutrients can be recycled back to land. This has advantages even compared to incineration for energy recovery, as the high moisture content of food waste negates much of the energy gain and in thermal processing most nutrients are lost. Digestion may therefore offer a more sustainable route to resource recovery compared to other waste treatment technologies that are less suited to dealing with this high moisture fraction. Anaerobic digestion of food waste is not without difficulties, however, mainly associated with its high protein content. On hydrolysis this releases ammoniacal nitrogen which, although essential for the growth of anaerobic microorganisms, can lead to free ammonia concentrations that are inhibitory to the digestion process. The ammonia inhibits the methanogenic archaea, in particular the acetoclastic methanogens (Kayhanian, 1999, Chen et al., 2008, Liu and Sung, 2002, Prochazka et al., 2012, Angelidaki and Ahring, 1993. The result is operational instability, a decrease in biogas production, and in the worst cases failure of digestion. To some extent these problems have been resolved at mesophilic temperatures through stimulation of the hydrogenotrophic metabolic pathway by the addition of selenium and cobalt, both of which are commonly deficient in food waste (Climenhaga and Banks, 2008). This strategy has allowed stable digestion of food waste at high organic loading rates (OLR) (> 5 kg VS m -3 day -1 ) and total ammoniacal nitrogen (TAN) concentrations > 6 g l -1 (Banks et al., 2012). At temperatures in the thermophilic range the toxic threshold is reduced as the equilibrium moves towards free ammonia, and under these conditions trace e...

Biogas production from undiluted chicken manure and maize silage: A study of ammonia inhibition in high solids anaerobic digestion

“…This indicated that acetoclastic methanogenesis was able to resume when ammonia inhibition stress was relieved in a timely manner. A similar effect was reported by Serna-Maza et al (2014) who found that the acetoclastic pathway in a mesophilic food waste digester could be recovered when TAN concentration was reduced by ammonia stripping, even after operation over a long period.…”

Contribution of precipitates formed in fermentation liquor to the enhanced biogasification of ammonia-rich swine manure by wheat-rice-stone addition

“…(Lauterböck et al, 2012;Lin et al, 2013;Rico et al, 2010;Serna-Maza et al, 2014). Indeed, some of the above-mentioned methods exhibited high efficiency of alleviating ammonia inhibition to anaerobic fermentation.…”

Effects of thermal pretreatment on acidification phase during two-phase batch anaerobic digestion of kitchen waste

“…However, common problems that occur during the conventional AD of KWdproblems related to the high oil content and the presence of macromolecular compounds in the wastedinclude the accumulation of lactic acid at an early stage of the digestion process resulting in a dramatic pH drop [38] and inhibitory levels of ammonia, sulphide and long-chain fatty acids [2,23]; these factors usually diminish and impede digestion stability, thus restricting the application of digestion. In order to relieve inhibition caused by these problems, numerous pretreatment methods, such as chemical and thermal pretreatment [3,4,12,22,28], and new process techniques, such as co-digestion with substrates containing high levels of ammonium nitrogen and alkalinity to compensate for their absence in KW [25,43], have been suggested to improve the properties of organic waste to promote biogas production and the solubilisation of particulate organics.…”