Bioresource Technology 102 (2011)612-620 Contents lists available at ScienceDirect BIORESOURCE TECHNǒOGY Bioresource Technology ELSEVIER journal homepage:www.elsevier.com/locate/biortech Anaerobic digestion of source-segregated domestic food waste:Performance assessment by mass and energy balance Charles J.Banks2,Michael Chesshireb,Sonia Heaven,Rebecca Arnoldb School of Civil Engineering and the Environment,University of Southampton.Southampton S017 1BJ.UK BiogenGreenfinch,The Business Park,Coder Road,Ludlow SY8 1XE,UK ARTICLE INFO ABSTRACT Article history: An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over Received 14 July 2010 a period of 426 days.During this time information was gathered on the waste input material.the biogas Received in revised form 1 August 2010 production,and the digestate characteristics.A mass balance accounted for over 90%of the material Accepted 2 August 2010 Available online 6 August 2010 entering the plant leaving as gaseous or digestate products.A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh.Bio- gas production in the digester was stable at 642 m3tonne-1VS added with a methane content of around Keywords: 62%.The nitrogen in the food waste input was on average 8.9 kg tonne-1.This led to a high ammonia con- Anaerobic digestion Food waste centration in the digester which may have been responsible for the accumulation of volatile fatty acids Energy that was also observed. Biogas 2010 Elsevier Ltd.All rights reserved. Mass balance 1.Introduction and industry in methods of processing source segregated house- hold food waste by the anaerobic digestion route. Many examples exist on the use of anaerobic digestion (AD)to There are,however.reasons why food waste has not been pop- treat the mechanically separated biodegradable fraction of munici- ular in the past as a single substrate,since digestion of this energy- pal waste.Both 'wet'and 'dry'anaerobic technologies have been rich material can lead to operational problems.The protein content used as part of mechanical-biological treatment (MBT)(Mata of food waste typically gives a high nitrogen content on hydrolysis, Alvarez,2003).There are also examples of the processing of mixed which leads to elevated concentrations of ammonia or ammonium source segregated biodegradable wastes such as kitchen and gar- ion in the digester.The distribution of the two species and their den wastes(Archer et al.,2005):but there are few reports of AD relative toxicity is pH dependent,with the more toxic form domi- plants operating entirely on source segregated household food nating at higher pH(Mata-Alvarez,2003).There is still uncertainty waste.Interest in this approach is growing within Europe due to concerning the concentration at which ammonia becomes inhibi- rising energy costs associated with the processing of wet waste. tory to methanogenesis,and this is reflected in the various limit the requirement to meet the diversion targets of the EU Landfill values given in recent literature.According to Mata-Alvarez directive(99/31/EC),and the need to comply with regulations for (2003),inhibition occurs at total ammonia concentrations of the disposal of animal by-products (EC 1774/2002).When AD is 1200 mgl-1 and above.Hartmann and Ahring (2005)showed used to process source segregated waste it not only produces bio- ammonia inhibition begins at free ammonia concentrations above gas,but also presents an opportunity to recover additional value 650 mg I'NH3-N,whereas Angelidaki et al.(2005)in a study of 18 from the waste material,in the form of a quality assured nutri- full-scale biogas plants in Denmark co-digesting manure and or- ent-rich fertiliser product that can applied to agricultural land used ganic waste only found decreases in efficiency when total ammo- in food production.If the waste is not source segregated and the nia was above 4000 mg NH3-NI-1.El Hadj et al.(2009)found organic fraction is recovered through a MBT plant,regulations in that methane generation in batch tests with a high-protein syn- many European countries do not permit the digestate product to thetic biowaste under mesophilic conditions fell by 50%at ammo- be used on land in this way (Stretton-Maycock and Merrington, nium ion concentrations of 3860 mg NH-N 1-1.Although 2009).Consequently,there is strong interest from government ammonia has been shown to create operational difficulties in anaerobic digesters,it is also recognised that populations can accli- mate,making it difficult to predict the exact concentration at Corresponding author.Tel.:+44(0)2380 594650:fax:+44 (0)2380 677519 which process instability or failure may occur (Fricke et al.. E-mail address:cjb@soton.ac.uk (C.J.Banks). 2007).It has been reported on a number of occasions that digestion 0960-8524/$-see front matter2010 Elsevier Ltd.All rights reserved. doi:10.1016j.biortech.2010.08.005Anaerobic digestion of source-segregated domestic food waste: Performance assessment by mass and energy balance Charles J. Banks a, *, Michael Chesshire b , Sonia Heaven a , Rebecca Arnold b a School of Civil Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK b BiogenGreenfinch, The Business Park, Coder Road, Ludlow SY8 1XE, UK article info Article history: Received 14 July 2010 Received in revised form 1 August 2010 Accepted 2 August 2010 Available online 6 August 2010 Keywords: Anaerobic digestion Food waste Energy Biogas Mass balance abstract An anaerobic digester receiving food waste collected mainly from domestic kitchens was monitored over a period of 426 days. During this time information was gathered on the waste input material, the biogas production, and the digestate characteristics. A mass balance accounted for over 90% of the material entering the plant leaving as gaseous or digestate products. A comprehensive energy balance for the same period showed that for each tonne of input material the potential recoverable energy was 405 kWh. Bio￾gas production in the digester was stable at 642 m3 tonne1 VS added with a methane content of around 62%. The nitrogen in the food waste input was on average 8.9 kg tonne1 . This led to a high ammonia con￾centration in the digester which may have been responsible for the accumulation of volatile fatty acids that was also observed. 2010 Elsevier Ltd. All rights reserved. 1. Introduction Many examples exist on the use of anaerobic digestion (AD) to treat the mechanically separated biodegradable fraction of munici￾pal waste. Both ‘wet’ and ‘dry’ anaerobic technologies have been used as part of mechanical–biological treatment (MBT) (Mata￾Alvarez, 2003). There are also examples of the processing of mixed source segregated biodegradable wastes such as kitchen and gar￾den wastes (Archer et al., 2005); but there are few reports of AD plants operating entirely on source segregated household food waste. Interest in this approach is growing within Europe due to rising energy costs associated with the processing of wet waste, the requirement to meet the diversion targets of the EU Landfill directive (99/31/EC), and the need to comply with regulations for the disposal of animal by-products (EC 1774/2002). When AD is used to process source segregated waste it not only produces bio￾gas, but also presents an opportunity to recover additional value from the waste material, in the form of a quality assured nutri￾ent-rich fertiliser product that can applied to agricultural land used in food production. If the waste is not source segregated and the organic fraction is recovered through a MBT plant, regulations in many European countries do not permit the digestate product to be used on land in this way (Stretton-Maycock and Merrington, 2009). Consequently, there is strong interest from government and industry in methods of processing source segregated house￾hold food waste by the anaerobic digestion route. There are, however, reasons why food waste has not been pop￾ular in the past as a single substrate, since digestion of this energy￾rich material can lead to operational problems. The protein content of food waste typically gives a high nitrogen content on hydrolysis, which leads to elevated concentrations of ammonia or ammonium ion in the digester. The distribution of the two species and their relative toxicity is pH dependent, with the more toxic form domi￾nating at higher pH (Mata-Alvarez, 2003). There is still uncertainty concerning the concentration at which ammonia becomes inhibi￾tory to methanogenesis, and this is reflected in the various limit values given in recent literature. According to Mata-Alvarez (2003), inhibition occurs at total ammonia concentrations of 1200 mg l1 and above. Hartmann and Ahring (2005) showed ammonia inhibition begins at free ammonia concentrations above 650 mg l1 NH3-N, whereas Angelidaki et al. (2005) in a study of 18 full-scale biogas plants in Denmark co-digesting manure and or￾ganic waste only found decreases in efficiency when total ammo￾nia was above 4000 mg NH3-N l1 . El Hadj et al. (2009) found that methane generation in batch tests with a high-protein syn￾thetic biowaste under mesophilic conditions fell by 50% at ammo￾nium ion concentrations of 3860 mg NHþ 4 -N l1 . Although ammonia has been shown to create operational difficulties in anaerobic digesters, it is also recognised that populations can accli￾mate, making it difficult to predict the exact concentration at which process instability or failure may occur (Fricke et al., 2007). It has been reported on a number of occasions that digestion 0960-8524/$ - see front matter 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.08.005 * Corresponding author. Tel.: +44 (0)2380 594650; fax: +44 (0)2380 677519. E-mail address: cjb@soton.ac.uk (C.J. Banks). Bioresource Technology 102 (2011) 612–620 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech