Deeper Into the Science.

Thermophilic, mesophilic, C:N ratio’s, nitrogen robbing, and convective currents; go from novice to informed in under 30 minutes and if you have more questions (most likely), we are just an email away.

Temperature is a key parameter determining the success of composting operations. Physical characteristics of the biomass, including moisture content and particle size, affect the rate at which co-composting occurs. Other physical considerations include rate of aeration and the tendency of the compost to retain or dissipate the heat that is generated.

TEMPERATURE CURVE

Compost heat is produced as a by-product of the microbial breakdown of the organic compounds. The heat production depends on the size of the bed, its moisture content, aeration, and C/N ratio. Additionally, ambient (indoor or outdoor) temperature affects compost bed temperatures.

A typical temperature curve for an unturned bed is shown below.

A bed may take three to five days to heat up and reach temperatures of 60-70°C. Process managers strive to keep the compost below 69°C because hotter temperatures cause the beneficial microbes to die off. If the bed gets too hot, syringing sprays and turning will help to dissipate the heat.

Decomposition occurs most rapidly during the thermophilic stage of composting (40-69°C), which lasts for about 14 days. This stage also is important for destroying thermosensitive pathogens, fly larvae, and weed seeds. To achieve a significant reduction of pathogens during composting, the compost should be maintained at minimum operating conditions of 40°C for five days, with temperatures exceeding 55°C for at least four hours of this period.

As the bed begins to cool, turning the bed will result in a new temperature peak because of the replenished oxygen supply and the exposure of organic matter not yet thoroughly decomposed. After the thermophilic phase, the compost temperature drops. At this point, decomposition is taken over by mesophilic microbes through a long process of "curing" or maturation. Chemical reactions continue to occur that make the remaining organic matter more stable and suitable for oil palm.

MECHANISMS OF HEAT LOSS

The temperature at any point during composting depends on how much heat is being produced by microorganisms, balanced by how much is being lost through conduction, convection, and radiation. Through conduction, energy is transferred from atom to atom by direct contact; at the edges of a compost bed, conduction causes heat loss to the surrounding air molecules.

Convection refers to transfer of heat by movement of a fluid such as air or water. When compost gets hot, warm air rises within the system, and the resulting convective currents cause a steady but slow movement of heated air upwards through the compost and out the top. Much of the energy transfer is in the form of latent heat -- the energy required to evaporate water. You can sometimes see steamy water vapor rising from a hot compost bed.

The third mechanism for heat loss, radiation, refers to electromagnetic waves like those that you feel when standing in the sunlight or near a warm fire. Similarly, the warmth generated in a compost bed radiates out into the cooler surrounding air.

Moisture content affects temperature change in compost; since water has a higher specific heat than most other materials. Water acts as a kind of thermal flywheel, damping out the changes in temperature as microbial activity ebbs and flows.

PARTICLE SIZE

Microbial activity generally occurs on the surface of the organic particles. On the other hand, when particles are too small and compact, air circulation through the pile is inhibited. This decreases O2 available to microorganisms within the bed and ultimately decreases the rate of microbial activity. The process of maceration at specific intervals helps address this issue ensuring just the right balance of both.

BARformula is currently the only technology that treats ‘whole’ empty fruit bunches, saving the mill the cost of implementing and operating a shredder. Particle size affects the availability of carbon and nitrogen. Whole bunches provide a good bulking agent that helps to ensure aeration through the bed but they provide less available carbon per mass. A combination of Process One and our unique process technology balances these two considerations.

AERATION

Oxygen is essential for the metabolism and respiration of aerobic microorganisms, and for oxidizing the various organic molecules present in the organic compound. At the beginning of microbial oxidative activity, the O2 concentration in the pore spaces is about 15-20% (similar to the normal composition of air), and the CO2 concentration varies form 0.5-5%. As biological activity progresses, the O2 concentration falls and CO2 concentration increases. As microorganisms oxidize the carbon in the oil palm organic compound for energy, oxygen is used up and carbon dioxide is produced. Without sufficient oxygen, the process will become anaerobic and produce undesirable odors, including the rotten-egg smell of hydrogen sulfide gas.

Aerobic conditions require a minimum oxygen level. Although the atmosphere is 21% oxygen, aerobic microbes can survive at concentrations as low as 5%. Oxygen concentrations greater than 10% are considered optimal for maintaining aerobic composting.

If the average oxygen concentration in the pile falls below about 5%, regions of anaerobic conditions develop. BARformula technology ensures that anaerobic activity is kept to a minimum allowing the compost bed to act as a bio-filter to trap and degrade the odorous compounds produced as a by-product of anaerobic decomposition.

MOISTURE

A moisture content of 50-60% is generally considered optimum for composting. Microbially induced decomposition occurs most rapidly in the thin liquid films found on the surfaces of the organic particles. Whereas too little moisture (<30%) inhibits bacterial activity, too much moisture (>65%) results in slow decomposition, odor production in anaerobic pockets, and nutrient leaching.

The effluent is high in nitrogen and the biomass is high in carbon. These organic compounds must be combined in a manner that yields optimal results. For this we use a method of calculation to determine the resulting C:N ratio. You could use the less precise "squeeze test" to gauge moisture content. (Using the squeeze test, the compost should feel damp to the touch, with about as much moisture as a wrung-out sponge).

C/N RATIO

Of the many elements required for microbial decomposition, carbon and nitrogen are the most important. Carbon provides both an energy source and the basic building block making up about 50 percent of the mass of microbial cells. Nitrogen is a crucial component of the proteins, nucleic acids, amino acids, enzymes and co-enzymes necessary for cell growth and function.

The ideal C/N ratio for compost is around 30:1, or 30 parts carbon for each part nitrogen by weight. At lower ratios, nitrogen will be supplied in excess and will be lost as ammonia gas, causing undesirable odors. Higher ratios mean that there is not sufficient nitrogen for optimal growth of the microbial populations, so the compost will remain relatively cool and degradation will proceed at a slow rate. This is the case against the practice of EFB mulching. The higher than ideal C:N ratio ‘robs’ the soil of nitrogen as it decomposes until it reaches a safe C:N ratio of about 35:1. This is an important consideration when mulching young palms.

As composting progresses, the C/N ratio gradually decreases from 50:1 to about 30:1 for the finished product. Each time the organic compounds are consumed by microorganisms, two-thirds of the carbon is given off as carbon dioxide. The remaining third is incorporated along with nitrogen into microbial cells, then later released for further use once those cells die. Some of the carbon bound in the EFB fibres are subject to longterm biological degradation because it is made up of cellulose fibers sheathed in lignin, a highly resistant compound.

The C:N ratio is also conditional to the bioavailability of the organic compound. The fertilisation programme of the oil palm trees from which the organic compound originates play a considerable factor in this.

NUTRIENT BALANCE

Adequate phosphorus, potassium, and trace minerals (calcium, iron, boron, copper, etc.) are essential to microbial metabolism. These nutrients are present in ample concentration in the oil palm organic compound.

PH

A pH between 5.5 and 8.5 is optimal for the microbial blend in Process One. As the bacteria and fungi digest organic matter, they release organic acids. In the early stages of composting, these acids accumulate. The resulting drop in pH encourages the growth of fungi and the breakdown of lignin and cellulose. The organic acids become further broken down during the composting process.