Quality Control of Organic Fertilizers

Condition control of organic fertilizer production, in practice, is interaction of physical and biological properties in the process of compost making. On the one hand, the control condition is interactional and coordinated. On the other hand, different windrows are mixed together, because of diverse in nature and different degradation velocity.

Moisture control
Moisture is an important requirement for organic composting. In the process of manure composting, the relative moisture content of the original material of composting is 40% to 70%, which ensures the smooth progress of composting. The most suitable moisture content is 60-70%. Too high or too low material moisture content can impact aerobe activity so that moisture regulation should be carried out before fermentation. When material moisture is less than 60%, the temperature is slowly rising and the decomposition degree is inferior. When the moisture content exceeds 70%, the ventilation is hindered and anaerobic fermentation will be formed, which is not conducive to the whole fermentation progress.

Studies have shown that appropriately increase the moisture of the raw material can accelerate compost maturity and stability. Moisture should keep at 50-60% in the very early stage of composting and then should be maintained at 40% to 50%. Moisture should be controlled below 30% after composting. If the moisture is high, it should be drying at the temperature of 80℃.

Temperature control.

It is the result of microbial activity, which determines the interaction of materials. When the initial temperature of the composting is 30 ~ 50℃, thermophilic microorganisms can degrade a large amount of organic matter and decompose cellulose rapidly in a short time, thus promoting the increase of the temperature of the pile. The optimum temperature is 55 ~ 60℃. High temperature is a necessary condition to kill pathogens, insect eggs, weed seeds and other toxic and harmful substances. At 55℃, 65℃ and 70℃ high temperatures for a few hours can kill harmful substances. It usually takes two to three weeks at normal temperatures.

We mentioned that moisture is a factor that affects compost temperature. Excessive moisture will lower the temperature of compost, and adjusting the moisture is beneficial to the temperature raising in the later stage of fermentation. The temperature can also be lowered by adding extra moisture.

Turning over the pile is another way to control the temperature. By turning over the pile, the temperature of the material pile can be effectively controlled, and water evaporation and the air- flow rate can be accelerated. The compost turner machine is an effective method to realize short – time fermentation. It has the characteristics of simple operation, affordable price and excellent performance. The compost turner machine can effectively control the temperature and time of fermentation.

C/N ratio control.

Proper C/N ratio can promote the smooth fermentation. If the C/N ratio is too high, due to the lack of nitrogen and the limitation of the growing environment, the degradation rate of organic matter slows down, making the compost cycle longer. If the C/N ratio is too low, the carbon can be fully utilized, and the excess nitrogen can be lost as ammonia. Not only does it affect the environment, but also reduces the effectiveness of nitrogen fertilizer. Microorganisms form microbial protoplasm during organic fermentation. Protoplasm contains 50% carbon, 5% nitrogen and 0. 25% phosphoric acid. The researchers suggest a suitable C/N ratio is 20-30%.

The C/N ratio of organic compost can be adjusted by adding high C or high N materials. Some materials, such as straw, weeds, branches and leaves, contain fiber, lignin and pectin. Due to its high carbon/nitrogen content, it can be used as a high carbon additive. The manure of livestock and poultry is high in nitrogen and can be used as high nitrogen additive. For example, the utilization rate of ammonia nitrogen in pig manure to microorganisms is 80%, which can effectively promote the growth and reproduction of microorganisms and accelerate the composting.

The new organic fertilizer granulation machine is suitable for this stage. Additives can be added to different requirements when raw materials enter the machine.

Air-flow and oxygen supply.

For the fermentation of manure, it is important to have enough air and oxygen. Its main function is to provide necessary oxygen for the growth of microorganisms. The maximum temperature and time of composting can be controlled by adjusting the temperature of the pile through the fresh air flow. Increased air flow can remove moisture while maintaining optimum temperature conditions. Proper ventilation and oxygen can reduce nitrogen loss and odor generation from compost.

The moisture of organic fertilizers has an effect on air permeability, microbial activity and oxygen consumption. It is the key factor of aerobic composting. We need to control moisture and ventilation according to the characteristics of the material to achieve the coordination of moisture and oxygen. At the same time, both of them can promote the growth and reproduction of microorganisms and optimize the fermentation conditions.

Studies have shown that show that the oxygen consumption increases exponentially below 60℃, grows slowly above 60℃, and is close to zero above 70℃. Ventilation and oxygen should be adjusted according to different temperatures. 

PH control.

The pH value affects the whole fermentation process. In the initial stage of composting, pH will affect the activity of bacteria. For example, pH=6.0 is the critical point for pig manure and sawdust. It inhibits carbon dioxide and heat production at pH <6.0. At pH >6.0, its carbon dioxide and heat increase rapidly. In the high temperature phase, the combination of high pH and high temperature causes ammonia volatilization. Microbes decompose into organic acids through compost, which lowers the pH to around 5.0. Volatile organic acids evaporate as the temperature rises. At the same time, the erosion of ammonia by organic matter increases the pH value. Eventually, it stabilizes at a higher level. The maximum composting rate can be achieved at higher composting temperatures with pH values ranging from 7.5 to 8.5. A high pH can also cause too much ammonia volatilization, so the pH can be reduced by adding alum and phosphoric acid.

In short, it is not easy to control the efficient and thorough fermentation of organic materials. For a single ingredient, this is relatively easy. However, different materials interact and inhibit each other. In order to realize the overall optimization of composting conditions, it is necessary to cooperate with each process. When the control conditions are appropriate, the fermentation can proceed smoothly, thus laying the foundation for the production of high quality organic fertilizer.

Post time: Jun-18-2021