Journal

Composting our Coffee Grounds

MarketLane_Faraday040816_LinseyRendell-19We have been recycling the organic waste produced at our cafes for many years. Each week, about 1,000L of organic waste is recycled across our shops. This recycled waste is mostly coffee grounds, but we also recycle food waste and dead flowers. Most of our locations have been recycling organic waste since they opened, the main exception being our Faraday Street store, which did not recycle organic waste between 2014 and 2016, and our Queen Victoria Market stall, which did not recycle between 2014 and 2015.

Recently, we visited the facility that processes our organic recycling, called Natural Recovery Systems, built 17 years ago. We have a waste contract with KS Environmental, which carries out the local collections and they, in turn, have a contract with Veolia, which operates the Natural Recovery Systems plant in Dandenong South. This plant utilises a type of composting called “in-vessel” composting, as opposed to the more common “wind-row” composting (which is common in farming and in domestic use). 

Natural Recovery Systems has a contract with the “green bin” operators in local councils around Melbourne that collect garden cuttings like leaves and branches. They mulch this waste on site and blend it with sawdust and the food waste that comes in from KS Environmental and other contractors. 

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In-vessel composting is a very active method of composting. There are two main goals to this process: firstly, to break down the organic matter into a fine humus, and secondly to pasteurise the resulting product, to prevent the spread of seeds and weeds in the resulting compost. To break down the food waste, Natural Recovery Systems uses positive airflow through the mixture of food waste, sawdust and plant mulch. This positive airflow generates a lot of aerobic activity in the food waste, enabling microorganisms to oxidise carbon to produce carbon dioxide.

The right mix of green waste mulch (from council green waste bins), food waste, and sawdust is achieved when the moisture content is high enough for the microbial activity, but low enough to allow airflow through the mixture. The mixture is kept in a sealed, concrete-lined 35m3 vessel – about 10 tonnes worth – and fed with oxygen for 7-10 days while the mixture breaks down. To have the compost properly pasteurised, it must be held at 55C or above for 72 hours. At this temperature, all seeds and potential contaminants are eliminated. The resulting compost is 1/3 of the original volume and has lost about 20% of its weight in moisture. 

The final product, a nutrient rich humus, is then sold to broadacre farms across Victoria as an organic compost that enriches the soil for food production. The compost is in high demand because of the guarantee of pasteurisation, and the high nutrient content.

We see waste reduction as a very important factor in reducing our impact on the environment and society. Nationally, organic waste from businesses (food scraps and the like) make up around 15% of all waste sent to landfill, so there is a huge opportunity for us all to improve. We are proud to say that we now recycle waste across all five of our Market Lane locations.

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