High-tech composting at Unimelb

High-tech composting at Unimelb

By Jose Alfredo López   5:34   1 comentario:

At the University of Melbourne Student Union (UMSU) various food services generate lots of food waste. A significant amount of this food waste is composted in an aerobic digester to produce compost. Although it is small scale and highly efficient, this aerobic digester is not a system that I would suggest to anyone because of its high cost and energy requirement. However, the machine is ingenious and is worth to know more about it.

Aerobic digester

The aerobic digester is fed daily with 150 kg of food waste. Air and heat (45 °C) are injected into the chamber where food waste is continuously turned with an endless screw. The impressive thing is that while typical composting systems produce compost in two months at least, this aerobic digester produces compost in just one week.

The food waste after one week

According to the IPCC, composting is a carbon neutral process. This means that despite composting emits carbon dioxide; these are not counted in the greenhouse gas inventory because its carbon dioxide emissions come from biological sources. However, the fact that this aerobic digester requires electricity cancels the carbon neutral characteristic of the process. In energy terms, is this process better than sending the food waste to a landfill? That is a research question yet unknown. For UMSU, this system is perfect because they obtain discounts from the manufacturer, saves space, part of the energy used comes from renewables (favours carbon neutrality), do not generate odours and divert waste from landfills.

This machine can has as a target audience groups of food services. Take a look at this new:

http://www.abc.net.au/news/2016-06-03/recycling-food-waste-melbourne-precinct/7474714

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Composting at Unimelb Community Garden

Composting at Unimelb Community Garden

By Jose Alfredo López   5:30   1 comentario:

A long time ago, an Australian friend I met in Peru told me about home composting. By my previous experience with windrow composting, I could not imagine how an odorous and high-volume process could be performed at a home’s garden. In Australia, garden waste is sent to composting facilities, but food waste is encouraged by authorities to be composted at home.

The University of Melbourne Community Garden composts the food waste donated by some students and offices in composting bins. The composting bins are bottomless barrels in which food waste and coffee chaff (sometimes dried leafs) are added daily in similar proportion until the composting bin is full. Then, the composting mix is left resting for about one month.

Food Waste

Compost

Not much technical data has been retrieved from this process, but here are some facts about it:

1 – The process works. However, it does not reach enough temperature to destroy wild herbs seeds and thus, not all vegetable pathogen is killed. However, this situation can be improved by turning the compost, so the upper part goes to the centre of the barrel. The Community Garden uses a tool that facilitates this operation.

2 – Coffee chaff is mixed with food waste in similar proportions (weight) because a proper composting has a carbon: nitrogen relationship between 20:1 – 30:1. Food waste contains a very low C: N relationship which is why it needs to be mixed with a carbon-rich substrate as coffee chalk to get to the proper C: N relationship. 

3 – The process releases unpleasant odours. People who have worked doing composting before, like me, might not sense the odours, but the ones who are not accustomed to the scents of this process may be very sensitive. Odours are released when opening the lid for feeding and especially when turning the compost. The carbon source reduces the odours, so make sure you count with the carbon-rich substrate when composting at home.

4 – You do not obtain mature compost after one month. After one month, the compost is still young and may be added to the soil, so it degrades in it. The problem here is that because of the low aeration, high moisture and low carbon, compost may not be ready yet and the process might have to continue for more weeks. Mature compost requires more than one month, but after one month you may be wanting to use the composting bin for a new batch.

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About me

About me

By Jose Alfredo López   5:18   1 comentario:

I am Jose Alfredo Lopez (28) from Peru. I am currently studying at The University of Melbourne, the Waste Management stream of the Master of Environment. At first, I studied Animal Science at the Agrarian University (Lima) and specialised myself in rabbit production. After releasing my book “Breeding, Commercialisation and Production of Rabbits” I decided to start looking at new things besides rabbits, mainly because of the lack of job opportunities in this field. While studying at the University, I noticed that few of my professors and colleagues knew what to do with manure besides selling it for a low price, giving it for free or even paying for getting rid of it which is ridiculous! So I decided to venture into the waste treatment field to give new alternatives to farmers.

My passion for small-scale organic waste treatment started in early 2014 when my first biodigester lighted up. I had been working with composting before that date, but this treatment was always very boring for me because almost everything is already known about composting, what I always wanted to learn was how to build biodigesters. I was lucky that when I started working at the Agrarian University Waste Treatment Centre, a couple of European guys showed up around and were willing to teach me under the condition that what they taught me should be then spread to others. So I started running a 1 m3 biodigester fed with rabbit manure and the day it lighted up changed the whole figure for me and defined what I want to work with the rest of my life. I never took a proper class on biogas production and everything I learned was through my research and the basics taught by my European friends. I guess I already fulfilled my part of the deal after giving lectures and organising biogas workshops at my home university, but I have realised that when you teach, it is when you also learn the most, and that is why this blog is on the run!

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