|We call to your attention a pasteurization chart and approximate instructions on carrying out this technological process.|
The compost pasteurization chart
The goal of this stage is leveling the temperatures in the whole mass of compost and entering the temperature of primary conditioning. The duration of the given stage is usually a few hours. The important element of compost temperature leveling is recirculation. The percent of air supply depends on the compost's temperature. At average compost temperature that is lower than the temperature of primary conditioning (48-51°C), the air supply decreases. At a higher average temperature, the air supply increases. You can have an effect on the compost's average temperature by choosing the fan speed. At low compost temperature the speed is lower, and at high temperature, the speed is higher.
2. Primary conditioning.
The goal of the given stage is to decrease the ammonia concentration. The parameters of this conditioning – the temperature and time – are specified by a technologist (the head of the compost house), depending on the test results of phase 1 compost. The test results are given by an agrochemical laboratory on the day when compost is filled into the pasteurization tunnel. The standard temperature is 49-51 degrees Celsius. The duration of primary conditioning with a standard content of ammonia nitrogen of 0.4%, is about 30 hours. In practice, the duration of this stage depends on the content of ammonia nitrogen in phase 1 compost. The primary conditioning is carried out until the concentration of ammonia in the air above compost is decreased to 0.015% (150ppm). The percent of recirculation screen opening during the primary conditioning depends on the compost temperature sensor. With the occurrence of differences in the compost temperature sensors' indications, the percent of recirculation opening increases. In practice, through almost all stages of compost pasteurization, the recirculation is 100% open. The principle of air supply and the fan's work is the same as on the leveling stage.
3. Raising the compost temperature to the temperature of pasteurization.
On this stage, the temperature rises to 58-60°C. Here, it is desirable that the rate of the rise in temperature doesn't exceed 1.5 degrees an hour. This should be done so that the microorganisms that live in conditioning temperature conditions could «prepare themselves» for pasteurization temperatures. The compost temperature usually rises due to the decrease of air supply and the decrease in fan speed until it stops. Steam can also be used to raise the compost temperature. In any case, the air supply is reduced to minimum. The duration of this stage is 6-8 hours. With the rise in the compost temperature and the presence of steam in pasteurization tunnels it is advisable to raise the tunnel's base temperature at least to 60°C, before starting the fan.
4. Compost pasteurization.
The goal of this stage is to destroy pests and diseases in the compost. Pasteurization begins when the tunnel's base temperature reaches 56.6°C. During pasteurization, the maximal compost temperature must exceed 62°C. The total pasteurization time is 10-12 hours. Air supply and fan speed are minimal. During pasteurization, it's important that the air temperature above and beneath the compost didn't go below 56.6°C. The compost temperature during compost pasteurization can be maintained with the help of steam that is supplied into the tunnel's base. An additional factor that defines the pasteurization process duration is the gaseous ammonia concentration. When the concentration of ammonia reaches 0.03% (300ppm) and higher, it is advisable to start cooling the compost after 1-1.5 hours. A long-continued effect of temperature with above mentioned ammonia concentration can kill the microorganisms that are necessary to end phase 2 of composting successfully.
UG – 2 Device for measuring gaseous ammonia concentration
5. Cooling the compost to the temperature of conditioning.
The goal of this stage is to reduce the compost temperature down to 48-50°C. The temperature is reduced due to the increase in air supply and the fan speed. It is recommended to begin the cooling process 2-3 hours before the end of pasteurization (the moment suitable to begin cooling depends on the compost's activity). The cooling speed might be up to 2°C an hour.
The goal is to reduce the ammonia concentration to <0.1%. The conditioning is carried out at a temperature of 48-50°C. The percent of air supply opening depends on the compost temperature fluctuations. The fresh air supply decreases with the decrease in compost temperature. It increases with the increase in the temperature. The recirculation is usually 100% open. The rate at which the fan runs depends on the compost temperature. The duration of conditioning is usually 48-60 hours.
7. Cooling the compost for spawning.
The goal is to reduce the compost temperature down to 24-25°C as fast as possible. The compost temperature depends on the time of the year and the time it takes to unload the compost from the tunnel. In winter, it's best that the compost temperature is slightly higher, so that the compost doesn't cool down as it is transported to a place where it's filled. If the process of emptying the tunnel takes a long time, the compost is cooled down to a lower temperature in order to escape the compost self-heating.