With the rapid development of animal husbandry, animal husbandry is becoming more and more localized and intensive. As the scale of breeding expands, the amount of livestock and poultry manure produced also increases. The application of livestock and poultry manure directly affects the environmental safety and sustainable development of animal husbandry. Livestock and poultry manure is the most direct and effective way to use it in agriculture. The commercial organic fertilizer made from organic waste can not only realize the recycling of nutrients and improve soil fertility, but also reduce the use of chemical fertilizers and promote the sustainable development of agriculture. In the process of organic fertilizer production, livestock and poultry manure composting and organic waste fermentation are the core technologies. The purpose is to create good environmental conditions for the normal reproduction of microorganisms, promote the metabolic process of microorganisms, accelerate the decomposition and transformation of organic waste, kill pathogens and parasite eggs, and finally make high-quality commercial granular organic fertilizer. In the process of organic waste fermentation, there are 5 factors that affect the final quality of organic compost, and these 5 factors will directly affect the final quality of granular organic fertilizer. Environmental factors include moisture, temperature, carbon-nitrogen ratio, ventilation and oxygen supply, pH value, etc. In the whole fermentation process, by artificially controlling the fermentation and organic composting conditions, a suitable aerobic environment is created to promote rapid fermentation of raw materials and produce standardized commercial organic fertilizers.
Organic fertilizer quality control
In practical applications, the control of organic fertilizer production conditions is the result of the interaction between physical properties and biological properties in the composting process. On the one hand, the control conditions interact and inhibit each other. On the other hand, different piles are mixed together. Due to their diverse properties and different degradation rates, it is difficult to control organic fertilizers. Many studies and experiments have shown that the environmental factors that affect the production process of organic fertilizers are mainly moisture, temperature, C/N, ventilation and oxygen supply, pH, etc. By artificially controlling fermentation, a suitable environment is created for microbial activities, fermentation is promoted, and high-quality organic fertilizers are produced.
1. Moisture control
Moisture is an important requirement for organic composting. In the process of manure composting, the relative moisture content of the compost raw materials is 40% to 70% to ensure the smooth progress of composting. The most suitable moisture content is 60% to 70%. Too high or too low moisture content of the material will affect the activity of aerobic microorganisms, so moisture adjustment should be performed before fermentation. When the moisture content of the material is less than 60%, the temperature rises slowly, the temperature is low, and the decomposition degree is poor. When the moisture content is higher than 70%, it affects ventilation, forms anaerobic fermentation, and the temperature rises slowly, and the decomposition effect is poor.
Studies have shown that adding water to the compost pile can accelerate the maturity and stability of the compost during the most active stage of composting. The amount of water added should be maintained at 50% ~ 60%. The amount of water added thereafter should be maintained at 40% ~ 50%, but no water leakage. The moisture content in the finished product should be controlled below 30%. If the moisture content is high, it needs to be dried at 80°C.
2. Temperature control
Temperature is the result of microbial activity, which determines the interaction between materials. The initial temperature of composting is 30~ 50°C. The activity of mesophilic microorganisms generates heat, which promotes the increase of compost temperature. The optimum temperature is 55~ 60°C. Thermophilic microorganisms can degrade organic matter in large quantities in a short period of time and quickly decompose cellulose. High temperature is necessary to kill harmful waste, including pathogens, parasite eggs, weed seeds, etc. Under normal circumstances, it takes 2 to 3 weeks at 55°C to kill harmful waste, 1 week at 65°C, and several hours at 70°C.
Moisture content is a factor that affects compost temperature. Excessive moisture will reduce the compost temperature. Adjusting the moisture content is conducive to the temperature increase in the later stage of composting. The compost temperature can be reduced by increasing the moisture content to avoid excessive temperature during the composting process.
Composting is another factor in temperature control. Composting can control the temperature of the material and enhance evaporation, forcing air to pass through the compost pile. Using a self-propelled composting turner is an effective way to reduce the temperature of the reactor. It is characterized by simple operation, low price and high performance. Adjusting the frequency of composting can control the temperature and the time of the highest temperature.
3. Control of C/N ratio
Only with an appropriate C/N ratio can composting proceed smoothly. If the C/N ratio is too high, due to insufficient nitrogen and limited growth environment, the degradation rate of organic waste slows down, resulting in a longer composting time for manure. If the C/N ratio is too low, carbon cannot be fully utilized, and excess nitrogen is lost in the form of ammonia, which not only affects the environment, but also reduces the utilization rate of nitrogen fertilizer. During the composting process of organic matter, microorganisms form microbial protoplasm, which contains 50% carbon, 5% ammonia and 0.25% phosphate by dry weight. Therefore, researchers recommend that the appropriate C/N ratio for composting is 20~30%.
The C/N ratio of organic compost can be adjusted by adding high-carbon or high-nitrogen substances. Some substances, such as straw, weeds, dead wood, leaves, etc., contain fiber, lignin and pectin, etc., and can be used as high-carbon additives due to their high C/N. Due to the high argon content in livestock and poultry manure, it can be used as a high-nitrogen additive. For example, the ammonium nitrogen contained in pig manure can be used by 80% of microorganisms, which can effectively promote the growth and reproduction of microorganisms and accelerate the composting. The new organic fertilizer granulator is suitable for this stage. After the raw materials enter the machine, additives can be added according to different needs.
4. Ventilation and oxygen supply
Having enough air and oxygen is an important factor in composting, and its main function is to provide the necessary oxygen for microbial growth. The reaction temperature is adjusted by controlling the ventilation volume, thereby controlling the maximum temperature and occurrence time of the composting. While maintaining the optimal temperature conditions, increasing the ventilation volume can remove moisture. Proper ventilation and oxygen supply can reduce hydrogen loss, odor generation, and reduce the moisture content of the compost product, making it easier to store. The moisture content of organic fertilizer affects the ventilation porosity and microbial activity, affects the oxygen consumption, and is the decisive factor in aerobic composting. It is necessary to control the moisture content and ventilation volume according to the properties of the material to achieve water-oxygen coordination, take both aspects into consideration, promote the growth and reproduction of microorganisms, and optimize the control conditions.
Studies have shown that oxygen consumption increases exponentially below 60°C, oxygen consumption is low above 60°C, and oxygen consumption is close to zero above 70°C. The ventilation volume and oxygen supply should be controlled according to different temperatures.
5. pH control
The pH value affects the entire composting process. In the early stage of composting, pH affects the activity of bacteria. For example, pH=6.0 is the dividing point between pig manure and sawdust. When pH<6.0, the generation of carbon dioxide and heat is inhibited. When pH>6.0, the generation of carbon dioxide and heat increases rapidly. Entering the high temperature stage, the combined effect of high pH and high temperature leads to the volatilization of ammonia. As the composting progresses, microorganisms degrade into organic acids, resulting in a decrease in pH to around 5. Subsequently, volatile organic acids volatilize due to the increase in temperature.
At the same time, ammonia is degraded by organic matter, causing the pH to rise and finally stabilize at a higher level. In the high temperature stage of composting, the composting rate is highest when the pH is 7.5~8.5. Too high pH will also cause excessive volatilization of ammonia. The pH can be reduced by adding alum, phosphoric acid and other methods. In short, the quality control of organic fertilizer is not easy. It is relatively easy to control a single condition, but there are interactions and mutual inhibitions between materials. To achieve the overall optimization of composting conditions, it is necessary to cooperate with each process and control conditions appropriately. Only then can the composting proceed smoothly and high-quality organic fertilizer can be produced to provide the best fertilizer for plants.
