Because of our obsession with source separation, organic waste diversion may soon find itself juxtaposed between a plateau and a wall.
Currently, residential wastes make up about 35 per cent of the Canadian municipal solid waste stream, and broadly 35 per cent of that consists of what could be defined as source separated organics (SSO). To date almost all of our SSO diversion efforts have been placed on that lowest hanging piece of fruit—the single-family household. It makes up 65 per cent of Canada’s housing stock (although only 35 per cent in densely populated cities like Toronto). The SSO these households generate make up eight per cent of the Canadian waste stream. If we assume a generous capture rate of 60 per cent, we would be lucky to divert five per cent of the total Canadian waste stream if all of these households had access to such a program. We are largely missing multi-residential SSO, which makes up four per cent and the commercial and institutional parts of IC&I SSO, which make up another 16 per cent of the Canadian waste stream.
We generally try to apply the single-family source separation solution to the multi-residential sector. It goes something like this: jam round peg into square hole. Study why it doesn’t work. Repeat. Never mind the largely ignored commercial and institutional organic wastes. To get ourselves off the Einsteinian treadmill of doing things the same way but expecting different results, we need to take a look at the whole concept of source separation. It is built around composting and being able to produce the best possible quality compost.
Composting, although it has taken us a long way, is the “wall” part of the aforementioned juxtaposition. The overused maxim of “what you put in is what you get out” remains true but only because the composting pre-processing technology to fully clean up (to compost standards) the more heavily contaminated single-family source separated streams does not exist. Moreover, composting does not stand a chance in dealing with the organic wastes in the more contaminated multi-residential and ICI waste streams, not to mention the organics that end up in the garbage bag. The real kicker is that in this age of climate, composting blasts off 50 per cent of its (biogenic) carbon into the air like an inefficient fireplace leaving post-application sequestration as arguably its only real carbon benefit.
Moving past the source separation “plateau” will require processes and technologies that can handle more contaminated streams and biologically capture the energy of organics. In this regard, composting as a process will remain but it is going to be subsumed as a primary organic waste processing technology by anaerobic digestion and other technologies. For multi-
residential and a great swath of ICI organics, composting will only be used to polish digestate, if that.
So what does the future look like? Getting rid of the algorithm and its self-perpetuating source separation do-loop could be a start. Taking a fresh (and truthful) look at other technologies should be task one. Given our waste generating profligacy and our inefficiency in diverting it (not to mention our quirky moralizing about energy from waste somehow not counting as diversion) we could try something completely different.
On a recent trip to the Netherlands I had the opportunity to see mixed processing in action. Anaerobic digestion is used to capture the energy from garbage.
Attero is a major Dutch waste management company that manages more than four million tonnes of waste annually at a number of facilities. About one-half of this waste is received at the Wijster facility in northeastern part of the Netherlands. The company handles the usual source separated streams sending out recycled printed paper and packaging, creating biogas through anaerobic digestion and energy from its energy-from-waste facility.
Notwithstanding the various programs the Dutch have for waste diversion and their reduced waste generation profligacy, they do have garbage, with 35 per cent organics. About 850,000 tonnes of this arrives at the Wijster facility. Approximately 15 per cent of the inbound waste is recovered, including beverage cartons, plastics, and organics, with the balance proceeding to the on-site energy-from-waste facility. The above noted materials are separated using shaker screens, into coarse, medium, and fine waste, which are directed to further separation including ballistic, air, and optical sorting.
The organic waste is further processed to remove metal, stones, and glass prior to being directed to the anaerobic digester to strip out the energy. It is not possible to sort out all contaminants in this stream. This organics stream is directed to a dedicated plug flow “dry” digester. They obtain a biogas yield of about 90 m3/ tonne. The digestate is too contaminated to process further and is directed to the energy-from-waste facility. A second digester is devoted to source separated organics and its digestate is used to produce high quality compost.
At the Heerenveen facility in northern Netherlands, a municipally-owned waste management collective called Omrin (which is a Frisian word for recycling) receives about 220,000 tonnes of municipal solid waste annually at what is essentially a mechanical biological treatment (MBT) plant. About 35 per cent of this garbage consists of organic waste.
Using a series of trommels, conveyors,magnets, eddy currents, and opticalsorters, they manage to strip off thepaper, plastic, metal, and organics. The organics go through a washing plant to remove sand and inert materials. From all of this they are able to recover 55- 60 per cent refuse-derived fuel, which is further processed, and 40-45 per cent enters the wet organics stream. This contaminated organics stream is directed to three wet digesters (21- 28 day residence time) that includes a patented way to flush light and heavy fractions and with a biogas yield of approximately 150 m3/tonne.
They use the same digesters for this and source separated organic waste streams. The digestate from this process is directed to energy from waste. The gas from the organics has been converted into electricity. Theyare currently building a gas hub to turnit exclusively into natural gas and put it to the grid. Finally, 60 of the company’s 180 vehicles use this gas and all new vehicles purchased run on it.
There are limited examples of mixed waste processing in Canada (e.g. City of Edmonton and Otter Lake) but its true potential has not been explored. With climate being a key driver and jurisdictions such as Ontario setting a goal for zero greenhouse gas emissions from waste, finding ways to deal with difficult to source separate organics streams and the organics in the garbage stream is imperative.