Compost Trials

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Composting is the microbial degradation of organic material, used in many agricultural processes to manage wastes, such as animal manure and plant matter to create soil amendments or use as a growing medium such as the cultivated Agaricus bisporus mushroom. Effective composting requires aerobic bacteria to metabolise and assimilate the substrate. Aeration is achieved by mixing, turning or pumping air into the compost, to allowing aerobic respiration throughout the substrate. Regular turning is required to prevent anaerobic fermentation, which decreases the efficiency and creates bad odours.

compost-1

Straw with additions of organic and inorganic nitrogen such as chicken manure, urea and gypsum are composed of sugars, cellulose, urea, protein and lignin. These are used by the micro-organisms within the composting process to produce the nitrogen rich compost. Lignin contained within the straw is retained through the process and used by the mycelium (mushroom spawn) for nitrogen fixation. Ammonia is produced and can be fixed again by some micro-organisms. Composting is an exothermic process, with the micro-organisms releasing heat during the conversion of sugars and cellulose with oxygen to compost. This temperature can be used as an indicator of the bacterial activity within the compost medium. The greater the heat generated, the better the conversion rate of the organic matter to compost. Aerobic respiration is maximised in bunkers where compressed air is forced throughout the compost. These compost temperatures reach excess of 80oC. Composting is considered complete when the straw softens from the action of bacteria and is capable of holding moisture. This compost will contain some remaining carbohydrates, microorganisms and nitrogen rich lignin-humus complex.

In mushroom farms that prepare their own compost, weathered bales of wheat straw are selected, hydrated up to 75%. The straw bales, with a dry mass of around 300 kg and low nitrogen composition (0.5%), compromise of the wheat straw stem mechanically broken down and tightly compacted. The straw stems have a resistant waxy, outer layer. This layer needs to be broken down before hydration can take place as in this form is resistant to water absorption and decomposition. If insufficient moisture is present, the micro-organisms cannot function appropriately conversely excess moisture restricts oxygen and anaerobic fermentation is favoured. The straw is left to compost over a period of days, with additives facilitating the composting process and enters an aerobic bunker. This compost is cured, ammonia is removed, pasteurised then is used as substrate for the mycelium to grow upon.

The FBF: Compost Activator is a liquid that stimulates existing micro-organisms within the compost, creating a beneficial environment for more efficient composting. The activator does not attempt to introduce any new micro-organisms into the system, neither is it an enzyme that could denature in the high temperatures of composting. It is a catalyst, enhancing the micro-organisms. It also enables the bacteria to work aerobically in what are essentially, anaerobic conditions. This means that no turning or aeration is required in the process of composting, minimising time and risk in the composting process.

This product has been modified for the composting application, from the original FBF: Bio-Activator X256 product, which is used in industry to reduce odours from anaerobic ponds, improve sludge reduction and increase microbiological metabolism in wastewater. This has been successfully used in applications such as Wastewater Treatment Works, animal farms, sugar mills and tanneries. See www.franberfran.com

Experimental Procedure:
Trials where established to determine the effect of FBF: Compost Activator on hydrated wheat bales. Four bales of wheat straw, of equal mass were hydrated for three days. The bales were placed in an upright position, with binding rope still attached.
Each bale was treated as described in table 1.

 

Bale no. Conditioning Bale ID.
1 No Additives Control
2 FBF: Compost Activator FBF
3 FBF: Compost Activator + Urea
FBF + Urea
4 Urea Urea

Table 1

The bales remained tightly compacted throughout the duration of the experiment. Temperatures where measured twice daily, with a temperature probe that was inserted into the bale at left, centre and right hand side points and an average taken. At the end of the 5 day duration, bales were opened and examined. Temperature measurement started the day after preparation.
This experiment was repeated with new bales and the following changes:

dot  The volume of FBF: Compost Activator liquid was doubled
dot  The bales were left for 7 days (+ 2 days).

Results:
The results presented in figure 1 and 2.

Compost-trials-fig-1 Compost-trials-fig-2

The temperatures achieved (figure 1 and 2), clearly show the beneficial effect of FBF: Compost activator on the composting process resulting in the greater temperature maximum and increased exponential phase of both FBF: Compost Activator bales. In both sets of results, the higher temperatures are usually indicators of an increased rate, and extent, of conversion of the wheat straw to compost.

The addition of urea decreases rate of increase in temperature, as it gives the necessary source of nitrogen required in the correct formulation of compost. Impacting the composting process by creating a greater oxygen demand from the increased number of micro-organisms required to assimilate more nitrogen into the compost. With insufficient oxygen supply to the system the process rapidly favours the slower anaerobic fermentation of the compost, resulting in lower temperature rates and maximums and greenhouse gasses.

Figure 2 shows the temperature in the FBF bale decreasing over the last 72 hours. This was attributed to the completion of the composting process, with no available nitrogen source for conversion the composting process ceases and temperature recedes.
The use of temperatures as an indicator of composting may be misleading, so analysis of the compost material formed within the bale is essential to confirm the results. At the end of the trial period the bales where opened up to visually and physically asses extent of the compost. Effective composting is visually determined by the change in colouration of the wheat straw from a golden to rich dark colour.

Observations of the bales are represented in table 2

Bale Bale ID Anaerobic? Colour Comments
1 Control No Brown Large zones of firefang,from 0 to 15cm deep in the upper half and throughout the lower section of the bale.
2 FBF No Brown Similar to that of the control, except the presence of firefang was limited to the outer 5cm of the sides of the bale.
3 FBF+Urea No Dark Brown The compost retained moisture well and had a very strong smell of ammonia.
4 Urea Yes Golden Little composting had taken place.

table 2

The presence of actinomycetes (Firefang), a white fungus, indicates a temperature of 48oC. The profile of actinomycetes in both FBF: Compost Activator bales indicate a better temperature profile throughout the bale. The Temperature range was not limited to the centre of the bale as in that of the control.

The structural differences in the compost (Bale 3 and 4), resulted by FBF: Compost Activator indicates more efficient oxygen utilisation. Despite the increased oxygen demand, the microorganisms still function aerobically. The control indicates oxygen does penetrate throughout the bale and is sufficient for a small micro-organism oxygen demand, once that demand is increased by the addition of excess nitrogen; it is inadequate and anaerobic fermentation is favoured as represented by the Urea bale.

The centres of each bale where placed together and compared visually, as shown in the adjacent picture. The control and FBF were similar with the latter slightly darker. The third (FBF + Urea) was very dark rich indicating a good composting process. Bale 4 (urea) showed colouration that indicates negligible composting, with the straw of a light colouration.

 

compost-1

Conclusion:
The use of FBF: Compost Activator increases the composting temperatures, the rate of increase in temperature in limited oxygen environments. FBF: Compost activator facilitates an aerobic process eliminating the requirement for expensive, labour intensive turning or aeration whilst decreasing the time taken for complete composting.
Compost-trials
Simon Pitts

 

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