Windrow for composting pomace – Part Two

The composting regime advocated by Wechmar (2010) and outlined here

involves a series of steps to ensure best results. The windrow (preferred name

for the compost site) is constructed on a 2 – 5% slope in the direction of the

prevailing wind. The length of the windrow is approximately 4 metres long, 2m

wide and at a height of 1,5m high and is built using various layers of organic


The first foundation layer is straw, followed by sawdust to soak up leachates from

the fresh pomace.  Fresh pomace is placed directly onto the straw / sawdust layer

and a lime solution of approximately 2L/m3 is added to adjust the pH from around

4 to 7.   Fresh pomace generally has a low pH (3.5 – 3.8) which needs to be

adjusted to activate the microorganisms and ensure microbiological conversion.

Once the pomace is added to the foundation layers, inoculants are added to

introduce new microbes to the organic feedstock. The microbes work together to

break down cellular tissue and fibre to produce a humus-rich end product.

Microbes include bacteria, actinomycetes, fungi and nitrogen binding bacteria,

which ensure that available nitrogen is firmly bound for slow release into the soil

at a later stage.  There are various inoculants available for composting and

selection thereof is based on the choice of organic material to be composted.

After the addition of inoculants, the following organic feedstock and additives are

added in varying amounts to increase the pH and C:N ratio9, thereby facilitating

effective composting; manure (cow or horse), greens such as herbs, botanicals,

flowers, clay, rockdust, Zeolite and ground seaweed kelp.

Successful composting relies on a non-toxic environment, thus the windrow

includes several chimneys constructed from natural reed, to allow oxygen to enter

at the top and CO2 to be released into the soil. An oxidative environment is thus

created and the build up of methane and other toxic gases such as ammonia

(NH3), hydrogen phosphide (PH3), hydrogen sulphide (SH2) and boron hydride

(BH3) is negated.

The temperature of the windrow in the first two weeks should be between 60 – 70

deg C to kill off weed seeds and pathogens and thereafter, it should remain

between 40 – 50 deg C to continue the breakdown of solubles. Temperatures

exceeding 70 deg C could result in combustion, destroying valuable organisms

and microbes.

Source: Waste Management in the South African Wine Industry – Catherine Dillon, 2011

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