Globally refuse disposal is still one of the great growth industries of our time. The majority of what we buy and use, is destined for the dustcart, and in an ever shorter time and breaking all previous records for quantity as civilization becomes more affluent.
We purchase great quantities of goods which come with a relatively short lifespan and abundant quantities of packaging material. In times gone by many of us composted our putrescible waste in our gardens ad vegetable plots.
Gardens are getting smaller, we grow fewer food crops, and there is little room left for the compost heap and the garden bonfire is often banned due to clean-air regulations.
Dustbins are getting larger and refuse collection authorities are becoming more efficient and helpful in collecting ever larger quantities of household refuse and civic amenity wastes.
To reduce the sheer bulk of waste destined for our landfill sites, to extend their operating lives and to minimize the environmental and safety hazards of the materials delivered unto them, there is increasing public and legislative pressure to recycle and reuse a greater proportion of the discarded possessions we call “municipal solid waste” (“MSW”).
There is also a growing demand for energy and for that energy to be “green” and not from a fossil fuel based source which contributes to the greenhouse gas effect and climate change. There are lots of ways that waste, with its locked-in energy, can be used as a fuel source, but one of the very best, if not the best is a process called Anaerobic Digestion.
The scope for anaerobic digestion of MSW “putrescibles” becomes apparent when one examines the composition of household refuse and the limitations of existing recycling schemes. The big advantage possessed by anaerobic digestion is that using it to produce “biogas” can not only provide a fuel for ordinary diesel generators, but also can be converted into biofuel which can be used in the automotive industry. This can potentially provide us with green fuel in the place of fossil fuels which are saved.
Anaerobic Digestion is still a technology which needs a lot of improving and developing though. There are quite a few problems in using it reliably for the fermentation of wastes, despite the fact that Anaerobic Digestion has been used for sludge digestion at sewage works for at least 50 years.
The problems become apparent when one examines the cost and complexity of the anaerobic digestion equipment and the need to find appropriate outlets for the “refined digestate” liquid it produces.
The incentives derive from consideration of the alternatives:
- The other alternatives, including refuse-sorting and incineration, refuse-derived fuels and refuse-reclaimed materials do not seem likely to offer an obvious straight forward quick-fix solution.
- Landfilling is generally considered to be cheap and effective, if it’s available, if it’s acceptable in the locality, and it will always be required as the ultimate resting place for a small proportion of our refuse.
- But landfill sites do fill up and the problem always remains of finding appropriate new sites..
To summarise this we would say that:
- Household waste is inherently putrescible (compostible), and provides a natural material for decomposition by methane bacteria.
- It will ferment naturally, in a landfill, which even when lined and capped is at comparatively little cost.
- But, landfills do bring with them considerable environmental and safety hazards. They require extensive gas abstraction and leachate control systems to protect neighbouring crops, neighbouring properties and underground water supplies. Even then possibly 30% to 50% of the methane produced leaks out and can’t be collected..
- Household waste will also ferment rapidly in anaerobic digestion plants to provide a convenient source of biogas as fuel and a stabilised “digestate” for landfilling, or refining into useful soil conditioners and soil substitutes for agriculture, forestry or land reclamation. .
- It will capture almost 100% of the methane produced, and this methane can also be processed into a automotive biofuel. It is carbon negative (helps reduce carbon emissions) and “green”.
Anaerobic Digestion technology may not be as reliable as other processes and the cost is high at present, but further investment in research into the processes will almost certainly be able to improve reliability very rapidly.>
Shouldn’t you consider Anaerobic Digestion for your waste processing solution?.
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