Regulating Compost Moisture during Hot Composting

Hot composting is most effective at decomposing organic waste when moisture levels are approximately 50%.  A compost with excessive moisture will cause

  • Low temperatures that are below 40°C (104°F);
  • smells foul; and/or
  • brown liquid to be visible or easily freed when squeezing compost.

Excessive moisture while composting does not provide a viable environment for aerobic decomposers to thrive. Too much moisture reduces the oxygen supply to aerobic decomposers; as a result, these decomposers become less active, and compost temperatures remain low and stagnant.  Alternatively, excess moisture creates an inviting environment for the undesired anaerobic decomposers. Anaerobic decomposers are very slow at breaking down organic materials, and they create volatile acids that have a putrid smell. 

This article provides some tips on how to avoid excess moisture while using an Actium Batch Compost Drum for hot composting.

Prepping the composter

When starting a new compost batch in the Actium Compost Drum, first fill the vessel 1/4 full with dry shredded paper or dry sawdust/wood shavings.  Adding these dry and high carbon materials before other organic wastes provide a good start-up environment for aerobic decomposers, and helps the temperature to rise quickly for effective hot composting.

Consider the moisture content of organic inputs

Organic materials such as garden waste, food waste, and deadstock can all be composted; however each of these materials contains water.  For instance, vegetable peelings contain 70% of water, chicken deadstock contains approximated 67% water, and salad or juice pulp contain 90% water.  During the decomposition process, the cells of the “wet” organic materials break and release water into the greater compost pool.  With time and warm temperatures, much of the water will leave the compost through evaporation, and the wet organic materials will continue to decompose – reducing in weight and volume.  These reductions allow us to add organic waste continually over two to four months. The recommended loading rate for the Compost Drum is 50 lb (23 kg) per day.  The Compost Drum has a holding weight capacity of 2000 lb / 907 kg.  The weight capacity of the drum is not the same as the total weight of waste that can be added to the Drum.  The overall weight of waste added during a batch is much more than 2000 lb (close to double the capacity) due to the decomposing process. 

Have dry carbon and bulking agents available

It is a good habit to add dry carbon and/or bulking agents when adding “wet” organic materials to the Compost Drum. The dry carbon absorbs excess moisture, and the bulking agents improve oxygen supply. Dry carbon materials include shredded paper, shredded corrugated cardboard, wood shavings, and coconut husks.  When mixing a bulking agent with the compost, it alleviates compost compaction and allows for aeration. Examples of bulking agents include wood chips, grass clippings, autumn leaves, and chopped corn stalks.  Some bulking agents that contain little moisture can be used to aerate and absorb excess moisture, such as, peanut shells, sawdust, and straw.  As an example, if 10 lbs of food waste were added to the Compost Drum, it would be favourable to include 5 lbs of shredded paper and 2 lbs of wood chips. 

Remove excess  moisture from the composter

The Actium Batch Composter Drum is constructed to maintain high temperatures for hot composting.  The vessel of the Composter Drum has three vents (two along the sides and one on the input door) to allow for gases and water vapour to be released.  If the moisture content is too high due to insufficient additions of dry carbon materials, there will not be enough energy/heat for water to be evaporated and released through the vents as water vapour.   If the compost in the vessel becomes saturated with moisture (such as visible liquid in the vessel or liquid is easily freed when squeezing compost), then there are a couple operations that can be conduction to remove excess liquid from the vessel.

Operation 1

On a warm, dry, and sunny day,  open the input door of the drum. Turn the drum counter clock-wise until the input door is facing upwards or towards the sky.  This action allows for excess moisture to easily evaporate and escape from the vessel. Near the end of daylight hours, return to the composter and turn the vessel clock-wise to its standard position and close the input door.  Continue this operation until the moisture levels are at a point where adding dry carbon materials can correct the moisture content. 

Operation 2

Slide the input door very slightly (i.e. 1-2”) to make the door ajar.  Turn the vessel slowly clockwise. Stop turning the vessel when liquid is exiting from the input door.  Be cautious in preventing compost from pushing the ajar input door to the point that it will open.  Leave the vessel to drain for 6 to 48 hours – depending on the amount of excess moisture.  If interested in saving the liquid (a.k.a. compost tea or liquid fertilizer), collect the liquid using a large container that fits under the drum. When drainage is complete, turn the Composting Drum vessel counter clock-wise to the standard position, add dry carbon and bulking agent materials, then fully close the compost drum and turn the compost. 

The take-home message on compost moisture

Excess moisture hinders decomposition and can reduce the quality of the finished compost. Additionally, excess moisture causes unnecessary weight to the Compost Drum.  In extreme cases, when there is too much liquid in the Compost Drum, the weight can surpass capacity; this can lead to problems with the crank and chain.  Maintaining ideal moisture in the compost (approximately 50%) dedicates the volume and weight capacity of the Compost Drum to transforming up to 4500 lb of organic materials into nutrient-rich compost.