Food waste disposal is a big problem in all countries, especially affluent ones. There are numerous places which generate large amounts of food waste including hotels, restaurants, malls, residential societies, canteens, airline caterers, markets etc. A proper food waste management strategy needs to be devised for them to make sure that either they are disposed off in a safe manner or utilized efficiently. Let us learn the basics of biogas production from food waste:
Biogas Production from Food Waste
The feedstock for the food waste biogas plant includes leftover food, vegetable refuse, stale cooked and uncooked food, meat, teabags, napkins, extracted tea powder, milk products etc.
Raw food waste is shredded to reduce to its particle size to less than 12 mm. The primary aim of shredding is to produce a uniform feed and reduce plant “down-time” due to pipe blockages by large food particles. It also improves mechanical action and digestibility and enables easy removal of any plastic bags or cling-film from food waste.
Fresh food waste and re-circulated digestate (or digested food waste) are mixed in a mixing tank. The homogenized waste stream is pumped into the feeding tank, from which the anaerobic digestion system is continuously fed. Feeding tank also acts as a pre-digester and subjected to heat at 55-600C to eliminate pathogens and to facilitate the growth of thermophilic microbes for faster degradation of waste.
From the predigestor tank, the slurry enters the main digester where it undergoes anaerobic degradation by a consortium of Archaebacteria belonging to Methanococcus group. The anaerobic digester is a CSTR reactor having average retention time of 15 – 20 days. The digester is operated in the mesophilic temperature range (33 – 38°C), with heating carried out within the digester.
As per conservative estimates, each ton of food waste produces 150 – 200 m3 of biogas, depending on reactor design, process conditions, waste composition etc. Biogas contain significant amount of hydrogen sulfide (H2S) gas which needs to be stripped off due to its corrosive nature.
Biogas is eventually utilized in a combined heat and power (CHP) unit for its conversion into thermal and electrical energy. The exhaust gases from the CHP unit are used for meeting process heat requirements. The digested substrate leaving the reactor is rich in nutrients like nitrogen, potassium and phosphorus which are beneficial for plants as well as soil.
Salman is a prolific environmental writer, and has authored more than 500 articles in reputed journals, magazines and websites. He is proactively engaged in creating mass awareness on renewable energy, waste management, sustainability and conservation all over the world.
Salman can be reached on salman@cleantechloops.com
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Thank you for this good introduction to the anaerobic digestion, with the advantages and feedstocks of the biogas production. In Germany the technology is also quite famous and at the moment there is the attempt to connect the anaerobic digestions plants with the natural gas grid. For that the produced biogas will be treated in a way, that only the energy intensiv methan will remain. There are some problems with the market integration of this technology, but I think its a great national project. Best wishes, Ron
Food waste is a multi-faced issue which is getting more attention. Petsonally, I have a pasdionate interest in this field. My MSc thesis covers mainly household food waste. I have conducted an environmental and techno-economic assessment for food waste treatment options in Oxford city. My research covers IV-composting, home composting, AD, gasification, and incineration. AD is the most attractive option due to the generous incentives from the UK government. Home composting van play a key role in the future but more work should be done in terms of the social factors. Thanks for thia interesting article. my comment was typed via my phone. My apologies for any spelling problems.
Implementing biogas production from food waste can have numerous benefits, including reducing greenhouse gas emissions, providing an alternative energy source, and promoting a circular economy. It’s an excellent example of how innovative approaches can transform waste management into a valuable resource.
Thank you for shedding light on this fascinating aspect of food waste management.