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Composting is a common method for organic waste disposal. In composting, micro-organisms convert waste into useful products like fertilizer.

There are 2 kinds of composting: aerobic (with air) and anaerobic (without air). Although both break down organic matter, aerobic composting depends on micro-organisms that get oxygen from the air, whereas anaerobic composting depends on micro-organisms that get oxygen directly from the waste matter.

Aerobic Composting

The advantages of composting is that it naturally kills pathogens like E. coli, converts ammonia nitrogen to organic nitrogen and reduces the waste volume. The disadvantages of composting are the loss of some nutrients including nitrogen, the land area required for the composting, and odor. In addition, temperature, moisture content and aeration must be carefully monitored during decomposition to eliminate pathogens and completely convert the organic waste into compost.

While “compost piles” have been used by backyard gardeners for generations, some modern farms now use large-scale composting techniques in order to get rid of animal waste. One method for turning solid organic waste into compost is to use an ‘in-vessel’ composting technique. Basically a “scaled up” version of a hand-rotated yard composter, these large metal cylinders are slowly rotated as waste enters into one end and compost is extracted from the other. Using this method, the composter turns manure, litter, sour feed stuffs and even animal carcasses into compost in 4 days with minimal labor.

In aerobic composting, the more oxygen that is available, the more carbon dioxide (CO2) produced, the less methane (CH4), and the more complete the decomposition. As biological activity progresses, the oxygen concentration falls and CO2 concentration increases. While CO2 concentrations can vary, a sensor capable of measuring up to 30% CO2 like our K-33 ICB 30% CO2 Sensor should be used.

Anerobic Composting

As an alternative to aerobic composting, anaerobic composting is commonly used to treat human effluent and other livestock waste. Anaerobic digestion involves the degradation of organic waste under anaerobic conditions by microbial organisms to produce methane and inorganic solids. It has the advantage of being a highly efficient process, and can produce biogas for power generation or heating. In addition, the bio-solids remaining after the digester process can be sold as a high quality fertilizer.

In anaerobic composting, organic matter and water combine to generate CH4 and CO2. The difference is that it should primarily generate CH4, some CO2 and trace amounts of hydrogen sulfide (H2S), nitrogen and oxygen. Because CO2 levels in biogas can approach 40%, typically a 50-100% CO2 sensor should be used. For example, our 50% CO2 + 100% CH4 Sensor would work for this purpose.

Regardless of whether aerobic or anaerobic composting is used, CO2 level monitoring is critical for measuring the efficiency of the process.

Controlled CO2 gas inflow and improved air mixture can help maintain optimum CO2 levels in small indoor greenhouses or grow rooms. These were the lessons learned after working with a client who was attempting to control the CO2 levels in a group of 3 10x20” greenhouses.

The client wanted to maintain different consistent CO2 levels in each greenhouse to test the effects on the plants inside. To control the CO2, he used our iSense 1% CO2 Level Controller, a more industrial version of our Day Night CO2 Monitor & Controller for Greenhouses.

In one test greenhouse, the CO2 controller was set to turn on a CO2 Tank Regulator with Solenoid Valve at 700ppm and turn it off at 1,400ppm. While the controller correctly turned the regulator on at 700ppm, the CO2 levels were overshooting 1,400ppm before switching off the solenoid on the regulator. As a result, the clients was seeing wild swings of CO2 levels instead of the consistent level required for his experimentation.

After looking at his CO2 levels vs. time graphs, we noticed a pattern of a quick rise in the level of CO2, followed by slow drops. This lead to the conclusion that the greenhouse was being quickly flooded with CO2 before the CO2 sensor in the controller had a chance to react to the change in CO2 levels.

In other words, the problem was being caused by inefficient air mixture in an enclosed area.

In a perfect world the CO2 flow rate could be set to exactly match the CO2 loss. However, in the real world, minimum and maximum level switches are required to turn the regulator on and off to keep the CO2 levels within a specified range.

We suggested three changes to the client’s setup to help solve his problem.

1. Increase air circulation with fans, especially ones placed near the CO2 gas inlet into the greenhouse.
2. Make a CO2 delivery tube like industrial greenhouses with propane CO2 systems use. Drill small holes in a long piece of flexible tubing that runs the length of the greenhouse, then hang the tubing above the plants. Since carbon dioxide is heavier than normal air, it will naturally mix as it falls.
3. This decreases the amount of CO2 released between the time the room reaches the optimum CO2 level and the controller senses it. In addition, a good regulator with flow control not only limits the amount of CO2 that is released, but it maintains a consistent level of flow as the CO2 is used and the tank pressure changes.

Using our suggestions, the client will be able to maintain a more consistent CO2 level in the test greenhouses in order to complete their experiments.

Most of us who live in the city think of soil as “dirt.” However, soil is actually a living environment of underground plants, animals, and microorganisms that, like humans, need food, water and oxygen to survive.

Soil gas testing is the process of measuring oxygen, carbon dioxide, methane, radon, and other gases in soil. For example, large-scale composters monitor the gases inside long, narrow piles of plant material and manure called wind-rows. The right combination of moisture, temperature, oxygen and CO2 is required to feed the aerobic microbes that turn the materials into compost. Alternatively, biologists measure CO2 or methane gassing from fields or wetlands for long term environmental studies.

To measure compost or soil gas testing, here are 3 inexpensive solutions. Each of them rely on the fact that soil is porous, and over time the gas inside the tube will match the atmosphere in the soil.

Gas Vapor Probe

A Gas Vapor Probe provides the most scientific method for measuring soil gases. While you can purchase $2,500-$4,500 professional kits with an electric bore-hole drill that will reach virtually any depth, this $350 hand-held probe from AMS provides an inexpensive solution for shallow soil or compost pile testing. Either of these probes will work with our CO2+CH4 Sampling Data Logger or our CO2 Sampling Data Logger for soil gas testing. the built-in sampling pump will evacuate the tubing after a few seconds, and you can get an accurate measurement of the soil gas levels at the probe tip.

Permanent Sampling Holes

For clients who need to monitor several soil gas stations over time, an inexpensive solution is to build your own monitoring station with PVC pipe. This station can be built for about $40 in parts. After the sampling hole is dug to the desired depth, a capped PVC pipe with a Locking Vapor Extraction Plug mounted to the top provides a low-cost, permanent station. With the vapor plug, you will not contaminate the gas inside the pipe with outdoor air. When you are ready to take a sample, attach the tubing, open the air lock, and take a reading with any of our hand-held sampling meters.

Shallow Sampling Container

For long-term data logging in shallow soil, you can use a 1% CO2 Data Logger mounted under a leak-proof container. Dig a hole to the desired depth, mount the data logger inside the container using double-sided Velcro, and bury the container in the hole securely. The 1% CO2 Data Logger with 6,000mAh Li-Ion batteries and the optional hydrophobic filter kit can record CO2, temperature and %RH levels for up to 6 months on a single charge.