Mellow Compost Lab

Finished Compost Statistics

Find out about annual and long term trends, Input/output ratios, densities and  other aspects of our finished compost  

In this article, we share some key data and insights for our finished compost (FC); We present these on an annual basis, external & home context. We explain the difference in frequency between input waste and output compost.  We also explain when most of the decomposition takes place.  

Statistical Highlights

  • The finished compost (FC)  annual average output: ~ 1030L
  • FC annual average output (home waste): ~780L
  • FC density: 0.668Kg/L
  • Organic input waste decays by  of its volume to give  of finished compost
  • ~60% of the input waste decays in the Active phase

Annual Distribution

The finished compost is collected a few times a year. Typically 4 to 6 bin cycles mature over a year. At MCL, we wait until the compost has matured and a cycle finished  before completely emptying the bin. There is no partial removal from the bin (e.g. as and when needed). The full clearance of a compost bin helps in having controlled experiments where output is reviewed against input and examines the phases it goes through.

So whilst the input waste comes to the bins in continuous regular (near weekly) loads, the finished compost is collected a few times a year. The chart above shows the  number of bin cycles completed on an annual basis. 

The  chart below  shows the total FC obtained on an annual basis (from 2012). The first compost bin was ready in 2013; there is a cycle lag (~ 7.5 months) for the conversion from waste to compost. In the first two years, we had three compost bins (A,B,C) and worked on expanding garden space and vegetable (planting) areas.  

External waste impact

The large variation in volume output from 2017 is the waste addition from external sources. Friends, family and neighbours learnt about our compost project and started to bring additional material (mainly grass and hedge clippings). The Covid pandemic however has somehow reduced the contribution from these sources.

The long term FC annual average is ~1030L. The annual average for home compost is  ~780L (and ~390L for other sources from 2017). This is a split of ⅔ and ⅓  between the two sources. 

Input/Output ratios

The finished compost obtained typically is reduced by ⅔ of its original (waste) volume. Most of this decomposition occurs in the Active phase of the cycle. The pie chart below shows the long term decomposition breakdown of ~35,000L of waste across 56  bin cycles over 12 years. 61% of the waste decays in the Active phase and only 6% during the cooling & maturing phase, leaving roughly ⅓ of compost material (33%) at the end of the cycle.