Archive for the ‘Composting’ Category
One of the difficulties in home composting has been the breakdown of woody or cellulosic materials without resorting to burning it. Industrially, there is considerable effort being expended to research processes which will generate useful materials from cellulose, most notably biofuels to replace fossil fuel and intermediates for further processing. Photosynthesis is estimated to produce about 150 billion tons of dry plant material of which half is cellulose (Person et al., 1989). Of that amount, it is known that wheat straw amounts to 150 million tonnes per year in Europe (FAO, 2004).
A key group of enzymes, the cellulases can enzymatically hydrolyse cellulose to generate cellubiose which is then converted to glucose. There are some highly useful reviews covering this subject, the enzymes themselves (Gilbert and Hazlewood, 1993; Bhat, 2000), their production by moulds and fungi using fermentation (Mandels and Weber, 1969) and the strides made to engineer new cellulose enzymes and identify the gaps of which there are many in developing the process further (Bayer et al., 2007; Wilson, 2009).
Cellulase appears to be regarded as a complex made up of hydrolases, β-glucosidases and glucanases which all work synergistically to breakdown wood effectively. This enzyme complex is produced by a range of fungi and bacteria. Cellulose is the major component of cell walls and forms rigid microfibrils which in turn are made up of many dozen linear chains all oriented in parallel. The chains are made up of 1→4 β-linked D-glucose units. The microfibrils are themselves buried in a hemicellulose and lignin matrix. The enzyme complex must work on this mix. Hemicellulose itself is composed of xyloglucans (Type I in primary cell walls) or glucuronoarabinoxlans (Type II in primary cell walls) which in turn are hydrolysed by xyloglucanases and arabinases respectively. In terms of enzyme structure, the cellulases have a common basic structure with a catalytic domain linked to a cellulose binding domain by a glycosylated Pro-Thr-Ser-rich peptide (Gilkes et al., 1991).
When composting the home-user is reliant on exploiting these cellulase producing moulds to breakdown as much of the cellulose as is feasible. Providing a semi-moist, nitrogen balanced environment is crucial hence the disposal of non-wood food waste to provide other nutrients for these fungi to live on.
Bayer, E.A., Lamed, R., Himmel, M.E. (2007) The potential of cellulases and cellulosomes for cellulosic waste management. Curr. Opin. Biotechnol., 18 pp. 237-245
Bhat, M.K. (2000) Cellulases and related enzymes in biotechnology. Biotechnol. Adv. 18(5) pp. 355-383
FAO. (2004) Statistical yearbook production. Food and Agriculture Organization of the United Nations, Rome.
Gilbert, H.J.; Hazlewood, G.P. (1993) Bacterial cellulases and xylanases. J. Gen. Microbiol., 139 pp. 187-194
Gilkes, N. R., Henrissat, B., Kilburn, D.G., Miller, R.C., Jr., Warren, R. A. (1991) Domains in microbial beta-1, 4-glycanases: sequence conservation, function, and enzyme families. Microbiol Rev. 55 pp. 303–315
Mandels, M., Weber, J. (1969) The Production Of Cellulases. In: Cellulases and Their Applications. ACS Adv. In Chemistry. Vol. 95 Chapt. 23 pp. 391-414
Persson, I., F. Tjerneld and B. Hahn-Hägerdahl, (1991) Fungal cellulolytic enzyme production part of: Persson, I. Production and utilization of cellulolytic enzymes in aqueous two-phase systems. Thesis University of Lund, Sweden.
Wilson, D.B. (2009) Cellulases and biofuels. Curr. Opin. Biotechnol. 20(3) pp. 295-299
Home composting which I ‘posted’ on briefly earlier, is a form of solid-state fermentation (SSF) whereby the substrate is moist enough to support the growth of micro-organisms without the visible appearance of water between the particles. The technology is generally much more controlled than in home composting which is very much unstructured at the whim of the gardener. The process of SSF has been widely applied for both the small-scale study (Hölker et al., 2004) and large-scale manufacture of food materials such as koji in Japan, for drugs, antibiotics like penicillin (Barrios-Gonzales et al., 1988) and other intermediates for further manufacturing. One of the most useful has been the production of enzymes (Singh et al., 2008). There are some very comprehensive reviews covering its application (Couto and Sanromán, 2006; Pandey et al., 2008).
The benefits are generally a high productivity rate with minimal technological sophistication which keeps further processing costs much lower than a liquid fermentation system. The other benefits also mean being to use certain physiological states for micro-organisms not available elsewhere. Water is also limited and a high product concentration is possible. Enzyme production looks a viable proposition, especially in the production of pectinases from fruit and cellulases for either breaking down lignin or generating bioethanol. Developing the theme further, I’m looking at ways to use food waste as a substrate source and this process offers some potential. Anybody interested in developing the ideas further ?
Barrios-Gonzales, J., Tomasini, A., Viniegra-Gonzalez, G. and Lopez, L. (1988). (Eds.) Penicillin production by solid-state fermentation in bioconversion of Agro-industrial Raw Materials. Raimbault M. Orsrtom, Montpellier Fr. Pp. 39-51.
Couto S, R., Sanroman MA. (2006) Application of solid-state fermentation to food industry a review: J Food Eng. 76 pp. 291–302.
Hölker, U., Höfer, M., & Lenz, J. (2004). Biotechnology advantages of laboratory-scale solid-state fermentation with fungi. Appl. Microb. Biotechnol., 64, pp. 175–186.
Pandey, A., Soccol, C.R., Larroche, C. (Eds.) (2008) Current Developments in Solid-State Fermentation. Springer
Singh, S.K., Sczakas, G., Soccol, C.R., Pandey, A. (2008) Production of enzymes by solid-state fermentation. In: Current Developments in Solid-State Fermentation. Part 2 Springer pp. 183-204
The effective handling of food wastes at home can prove tricky especially if one is hoping to be responsible by returning nutrients to the soil and improving upon vegetable and fruit production. Landfilling is becoming less attractive globally and is slowly being banned in many countries. In 1999, the EU Landfill Directive (Council of European Union, 1999), requested member states would promote recovery and recycling at both the municipal and domestic level as well as reduce their landfill. Much of the organic waste generated is now passed to municipal treatment facilities.
Composting is another form of solid-state fermentation which relies on microorganisms digesting residual waste, raising the temperature to a point where pathogenic organisms are killed in the process. It also produces a reusable organic substrate, a soil conditioner in some instances for returning to the land and in my household is a valuable resource for further growing of food. There are many scientific articles worth exploring on the ‘art’ or the industry of composting (Haug, 1993; Hoitink and Keener, 1993). The approach of LCA –Life Cycle Assessment has been applied to municipal composting (Guereca et al., 2006) in Spain and I refer to the technique in a preceding post. At the smaller scale, the technique has only recently been applied (Colón et al., 2010) with any success. One recent report suggests that 20% of organic houselhold waste (OHW) might be composted at home, based on a study of composting in West London (Smith and Jasim, 2009). Generally, meat and fish is to be avoided to minimise rat infestation but fats, oils and greases might be composted at home if flies are not considered an issue. Fruit wastes can degrade too rapidly to produce an acidic leachate or waste which might need tempering with other materials to reduce taints and smell (Chanakya et al., 2007). The heat attracts slow-worm which I have been lucky enough to keep without sticking my fork into when I turn the heap monthly.
The study by Colón et al., (2010) looked at the composting of just raw fruit and vegetables in an experimental system. They produced a high organic material with a good nitrogen content. They monitored greenhouse gas emissions such as methane, nitrous oxide, ammonia, and volatile organic compounds (VOCs) with the latter measuring 0.32 kg VOC/Mg raw fruits and veg. Methane (CH4)and nitrous oxide (N2O) are notorius for their global warming potential (GWP). These have been cacluated to be 25 and 298 over a 100 year time frame respectively according to Solomon et al., 2007. This aspect of home composting was investigated further by Andersen et al., (2010).
One criterion for Colón et al., (2010)- the eradication of pathogens and other phytotoxic compounds was achieved. Composting itself might contribute to ozone layer and abiotic depletion based on these measures. The authors also used a garden chipper which had an electricity demand and might contribute to acidification using a life cycle assessment. I’d welcome any further thoughts on the process, especially with regards to the use of a macerator for creating a suitable organic waste which might then be used for further processing by composting and the quality of this material.
Andersen, J.K., Boldrin, A., Christensen, T.H., Scheutz, C. (2010) Greenhouse gas emissions from home composting of organic household waste. Waste Manag., 30(12) pp. 2475-2482
Chanakya, H.N., Ramachandra, T.V., Guruprasad, M., Devi, V. (2007) Micro-Treatment options for components of organic fraction of MSW in residential areas. Environ. Monit. Assoc. 135 pp. 129-139
Colón, J., Martinez-Blanco, J., Gabarrell, X., Artola, A., Sanchez, A., Rieradevali, J. Font, X. (2010) Environmental assessment of home composting. Res. Cons. Recycl. 54(11) pp. 893-904
Güereca, L.P., Gasso, S., Baldasano, J.M., Jimenez-Guerrero, P. (2006) Life cycle assessment of two biowaste management systems for Barcelona, Spain. Res., Cons., Recycling 49 pp. 32-48
Haug, R. (1993) The Practical handbook Of Compost Engineering. Lewis Publishers, Boca Raton.
Hoitink, H.A.J., Keener, H.M. (1993) Science And Engineering Of Composting: Design, Environmental, Microbiological And Utilization Aspects. Renaissance Publ., Worthington.
Smith, S.R., Jasim, S. (2009) Small-scale home composting of biodegradeable household waste: overview of key results from a 3-year research programme in West London. Waste Manag. Res., 27 pp. 941-950
Solomon, S., Qin, D., Manning, M., Alley, R.B. et al., (2007) technical Summary In: Solomon, S., Qin, D., Manning, M., Chen, Z., Marquis, M., Averyt, K.B., Tignor, M., Miller, H.L. (eds.) Climate Change 2007: The Physical Science Basis. Contribution of working group I to the fourth assessment resport of the intergogernmental panel on climate change. Cambridge Univ. Press, Cambridge. UK and New York. NY. USA.
Recent investigations into food waste management following my studies in environmental management have led me to look more closely at the life cycle assessment (LCA) approach. It is a systematic method or tool applied to assess the environmental impact of products, processes or any activity throughout its lifecycle. It has been applied to the management of household food waste, from the extraction of raw materials to prepare the food product through production and the end use and disposal of the waste. An inventory analysis describes all relevant inputs, outputs and the transformation with a review of impact on environment and interpretation of results versus objectives a set out by the Inter. Organisation for Standardization (2006). Generally, LCA is not enough on its own to identify the best options but it promotes networking amongst interested parties such as stakeholders, consumers and service providers, and provision of data which is not always forthcoming (Roy et al., 2009).
A study centred on Sydney, Australia (2005) by Lundie and Peters assessed an ‘in-sink’ food waste processor (FWP) with landfilling, and composting at home or in a communal and municipal waste (codisposal) system. The environmental assessment found that composting when managed properly was the least impactful on the environment. When fully aerated (aerobic), composting does not contribute methane gas into the atmosphere until the system is allowed to operate in an oxygen poor environment (anaerobically). Municipal or codisposal composting improves upon the environmental process further by integrating waste disposal although scale-up leads to intensive transportation to a central site, can produce leachates which are eutrophic and generate larger volumes of methane.
The approach is also suitable for application when options for waste disposal are removed such as land fill as in South Korea (Lee et al., 2007) or severely curtailed as is happening in the United Kingdom. I’d be interested to hear from others on the extent of LCA application in waste management.
International Organisation for Standardisation (2006) ISO 14040. Environmental management Life Cycle Assessment – principles and framework. Geneva.
Lee, S-H., Choi, K-I., Osako, M., Dong, J-I. (2007) Evaluation of environmental burdens caused by changes of food waste management systems in Seoul, Korea. Sci Total Environ. 387 (1-3) pp. 42-53
Lundie, S.; Peters, G.M. (2005) Life cycle assessment of food waste management options. J. Cleaner Production 13(3) pp. 275-286
Roy, P., Nei, D.,Orikasa, T., Xu, Q., Okadome, H., Nakamura, N., Shiina, T. (2009) A review of life cycle assessment (LCA) on some food products. J. Food Eng., 90(1) pp. 1-10