Composting and its beneﬁts on agriculture have been known since the 10th century. Greeks and Romans knew about compost, a fact contained in 12th-century Arab writings, medieval Church texts, and in Renaissance literature. Even the Aztecs were known for such a practice. Since then, as science evolved, compost has evolved with it.
Temperature plays a key role in compost process management.
In general, compost is high-quality, nutrient-rich, inactive manure that detracts insects and pests. It is a natural soil curb that enhances organic-matter content and functions as a water reserve, preventing runoff and soil erosion, a characteristic that is typical in the Mediterranean due to its mostly hilly terrain. Producing high-quality compost requires uninterrupted attention and intervention, and certain expertise in the ﬁeld. The overall process is delicate and easily corrupted. Process corruption can lead to toxicity in the produced material which can be disastrous for agriculture.
The Aztecs built a system of human latrines throughout their city. The feces from these were collected and used as compost, along with guano.
Physical characteristics of the compost ingredients, including moisture content and particle size, affect the rate at which composting occurs. Other physical considerations include the size and shape of the system, which affect the type and rate of aeration and the tendency of the compost to retain or dissipate the heat that is generated.
With an increased understanding of how this process works, we can control it more accurately and make it more efficient.
Temperature plays a key role in the composting process
The rate at which composting occurs depends on physical as well as chemical factors. The temperature of a compost pile is primarily a product of the metabolic heat being generated in the pile from microbial activity. Pile temperatures can also be affected by the physical characteristics of the materials being composted (more versus less insulating), as well as chemical reactions (at high temperatures) and external environmental variables. Pile temperatures are an imperfect but useful indication of microbial activity.
Newly formed piles commonly reach or exceed 55℃ within several days to several weeks of pile construction. Piles constructed during extremely cold weather or with frozen feedstocks will take longer. If you are trying to ensure weed seed and pathogen destruction you will need to obtain 55℃+ degree temperatures for several days and obtain these temperatures again following multiple turnings.
“Temperature is a key parameter determining the success of composting operations.”
The composting procedure is divided into two main phases, the decomposition and maturation phases. The decomposition phase is characterized by intense microbial activity, which introduces the rapid decomposition of the material. This phase is dissected in two subphases depending on the material’s temperature. In the 1st subphase (mesophilic), decomposition has just started, and the temperature rises, reaching up to 60◦C. In the second phase (thermophilic), decomposition is in full extension and the temperature rises up to 65–70◦C. During these two subphases, the material’s moisture must be kept between 50% and 60%. Moisture decrease below 50% slows down or even stops the degradation process since, in order for the nutrients to be consumed by micro-organisms, they must be in the solution. Moisture increase above 60% renders the process anaerobic and results in contamination of the procedure. The overall duration of the 1st phase varies, from 15 to 30 days.
In the maturation phase, decomposition has ﬁnished, and the material starts to mature and settle. The temperature steadily drops, and the material volume starts to decrease. The overall duration of the 2nd phase varies, from 30 to 60 days.
Figure 1: Temperature evolution during the composting process.
It is obvious from the above description that the successful completion of composting heavily depends on the material’s moisture and temperature. Hence, in any manned or unmanned system that supervises composting, these two parameters should be permanently monitored as composting progress to assure, via interventions, maintenance of the material within the required maturation curves.
Compost has to be monitored throughout the whole process. Temperatures above 65 °C, will burn valuable carbons and turn them into ‘invaluable ashes’.
Composting in the IoT Era
Composting is a rather delicate procedure that requires constant supervision by experts to produce high-quality compost in a timely manner, thus requiring the employment of specialized personnel.
Automated composting machinery has emerged to minimize human intervention as much as possible but overall fails to deliver high-quality outcomes in supervising the compost process. To tackle human absence and provide continuous supervision and effective manipulation of the compost material, computation systems are required that can perform real-time analysis of sensor data concerning the compost material and its surrounding environment and export relevant conclusions concerning the necessary actions to be taken to facilitate an optimal composting procedure.
Cloud computing, along with the proliferation of the Internet of Things (IoT) systems, frameworks, and architectures, has recently played a signiﬁcant role in the development of intuitive and unsupervised systems and services.
The IoT monitoring system provides real-time and continuous temperature monitoring to optimize the transformation process of biowaste into compost. Wireless temperature probes which are dug into piles at different depths, allow you to monitor your compost piles continuously and effortlessly without being tethered by cables.
The temperature history gives a complete view of the composting process from fermentation to curing and maturation. The generated reports are a guarantee for sanitary authorities and customers that compost has been produced in compliance with the regulations in effect. It reduces the risks of work accidents by avoiding contact with dangerous fumes (e.g. ammoniac, nitrogen). Temperature monitoring is done remotely and continuously and is available online at any time.
KOU10 is a cost-effective compost temperature probe. It operates on LoRaWAN technology and lasts up to 7 years on one set of batteries.
Advanced aerated compost systems
Unlike static piles, turned aerated pile systems are turned 2 to 3 times per week to break up organic material, re-establish porosity, and re-wet the compost. Turned aerated pile systems require below-grade aeration systems to allow for regular turning without the hassle of re-positioning above-grade piping. GMT specializes in below-grade reversing aeration system design. Odors are managed using bio-filters and bio-covers that meet the most stringent air quality regulations. The compact footprint makes it possible to put a facility inside a building and also minimize the stormwater collection requirements for outdoor installations.
While these sorts of solutions are proven to work best, they are still very expensive and most compost management groups cannot afford such a big investment in their facilities.
Comparing different types of compost temperature-checking solutions brings up an obvious advantage to the automated readings provided by IoT smart sensors. A simple calculation shows that labor costs over a 5-year period, result in extremely high expenditures.
While temperature readings seem simple, it still takes a lot of time for a worker to go around the compost area and stuff the temperature probes into compost piles. Because the temperature changes during the day, I presumed it takes about half a person to do that constantly (having the other half for other activities).
IoT sensors provide automatic readings, but there are other costs that have to be taken into account. The probes themselves are more expensive, there has to be some kind of software or middleware installed in the base computer to provide the readings. Then there is also battery life.
Figure 2: Comparing different types of compost temperature-checking solutions
If we compare WiFi or cellular to LoRaWAN, there is also a noticeable edge on the side of high performance, low power, and affordable connectivity. LoRaWAN networks provide long-range, low-energy use readings which result in almost maintenance-free operation over a 7-year battery lifetime. They also have a significantly longer range (up to 50km) which means there can be only one gateway installed over a large compost management area.
“IoT solutions differ, most notably in the type of network they use. LoRaWAN has an advantage here over Wifi or cellular.”