Frequently Asked Questions

About The Aeromaster Composting System


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What makes the Aeromaster Composting System (ACS) superior to other methods?
Combining our Aeromaster compost turners with our Aeromaster Composting System (ACS) methodology, we know how to produce the highest quality compost end product available on the market today. We are able to do this because we understand what the crop needs to grow to its full potential — naturally — so we have developed our process and methods to produce compost that gives the crop what it needs. We did not begin with the thought, “How do we degrade this large organic waste stream?” but rather with, “What do the soil and plant want?” This reverse engineering was how the ACS was developed.

Now a frequent ACS Compost Workshop speaker, Craig Witt, operator of Full Circle Compost of Minden, NV, originally selected Aeromaster compost turners and the ACS because: “When I was first considering composting, I talked to seven composting equipment manufacturers. The first six talked about their equipment — Midwest Bio talked about the soil.” This is what distinguishes our approach to composting from that of the rest of the industry. Focusing on results in the soil instead of waste disposal is a paradigm shift for the composting industry.

ATTRA (The National Sustainable Agriculture Information Service arm of USDA) scientist, Steve Diver, recently said regarding Midwest Bio-Systems’ ACS Composting Workshops, “You get information here you do not receive anywhere else.” MBS teaches the compost-soil-plant connection so that you learn what is happening and why.

Typically, composters utilizing our compost turners and system (relative to their competitors in the USA) receive from $20 to $40 more per ton for their compost, and their customers receive an additional $40 to $80 additional benefit per ton when it is applied to their fields. Several of our lower volume speciality producers are receiving up to $120 per ton in bulk for their finished high quality humified compost product.

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How does this system help me improve profitability?

The Aeromaster Composting System (ACS) is a systems approach for the production of high quality Humus Compost and its use in high production agriculture.

The higher the quality of the Humus Compost produced, the greater the benefit to the soil and the greater the increase in crop quality and yield – far greater than the results that can be achieved with typical compost.

A two (2) to Four (4) year implementation of ACS Humus Technology is the best system we have found for improving agricultural profitability.

What are the benefits of ACS compost to the soil?

As you can imagine, there are many. As a simple reminder, we like to use the acronym “DIP ‘N’ CHEW”

D isease suppression — ACS compost has a healing effect on plants and a cleansing action on soils.

I ncreases plant yield.

P orosity increased in the soil-has more air voids than typical soils.

N utrient retention — magnetic charge from high CEC holds nutrients longer.

C ompaction reduction — it makes soil spongy and enables it to spring back.

H elps reduce dependence on chemicals — promotes healthier plants.

E rosion reduced — disperses the force of raindrops.

W ater retention increased — like a sponge holding water.

Beyond these, high quality compost:

  • Increases soil fertility and soil digestion
  • Increases microbial activity and organic matter content of soil
  • Provides high humus levels
  • Suppresses weed growth
  • Alters soil to have a positive effect against insects and pests
  • Improves buffering capacity (neutralizes pH in the soil)
  • Neutralizes harmful compounds
  • Converts and stores excess nutrients in a plant-friendly manner
  • Reduces leaching
  • Infiltration of water is improved
Do you just sell equipment or do you help me have success with it also?

We view ourselves as a full-service company that does not believe it is successful until you are successful and are achieving your composting goals. We do not merely “sell iron,” but offer numerous consulting packages and custom tailored consulting services to serve your needs. We do more in the area of education in the production of high quality humified compost than anyone in the industry. MBS serves as a technical consultant at well over 100 compost sites.

About Aeromaster Compost Windrow Turners


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Why are Aeromaster Compost Turners Better?

Waste stream management — Aeromaster compost windrow turners make the best use of the main factors of production — time, space, and inputs.

Production cost/ton — Because the Aeromaster compost turner treats every particle, not just large lumps, it requires fewer handling cycles, resulting in lower labor and fuel costs.

PT170 product image

Aeromaster PT-170 Compost Windrow Turner

Fuel Requirements — Because the Aeromaster compost turner works gently and efficiently, fuel requirements are lower.

Cycle Time — Because the Aeromaster compost turner applies water evenly, particles get the moisture they need

Land Usage — The Aeromaster compost turner’s shorter cycle time means your material is ready to sell and leave the premises faster, so you have less space required

Space — Because the Aeromaster compost turner operates along the windrows, not between them, less space is wasted on aisles or drive ways

Capital cost — Because of lower power requirements and less required land, less capital has to be spent

Final appearance — Because the Aeromaster compost turner treats every particle, the product has a more uniform consistency and appearance throughout the cycle

Smoother operation — The Aeromaster compost turner re-shapes the windrow towards the ideal on every pass, reducing the need for additional materials management. The Aeromaster is designed to draw itself easily through the windrow, reducing mechanical strain on all equipment. Because it allows vertical removal from the windrow, obstacles are much easier to avoid and work around.

EPA/Odor — Because the Aeromaster compost turner applies moisture and inoculant to the individual particles, odor and other chemical problems are drastically reduced.

You want to go further. If you want the highest quality compost for your own use and/or for resale, Aeromaster turners offer superior design.


Drum speeds — Aeromaster compost turners have variable drum speeds within a low rpm range. Equipment does not make compost — microbes do! So high quality composting is simply based on creating the optimal environment for beneficial microbes to flourish and undesirable microbes to diminish. High drum speeds retard rather than enhance the quality composting process as well as limiting humus formation. Materials need not be propelled against shields (limiting aggregation) or thrown many feet behind the drum. Safety is also an issue here as projectiles can be propelled from the windrow with high speeds.

Hourly cost of operation — clearly affected by drum speeds is hourly cost of operation and downtime. Aeromaster turners have proven to cost less than 1/2 the industry standard.

Volumes —extremely large compost turners can be used to create a high heat environment for pathogen elimination and size reduction. But excessively large windrows reduce oxygen access for the microbes and quality is negatively impacted.

Tine shape and material movement pattern —an ideal turning environment will lift, blend, and aerate compost feedstocks. A key evidence of composting excellence will be O2 and CO2 exchange. What are windrow CO2 levels prior to turning compared to directly behind the turner? Best turning and movement patterns will provide new contact points in the feedstocks for microbial and chemical interaction. Tines should therefore handle the materials gently, moving perimeter materials to the center of the row and center materials to the perimeter. Tines should not cut, shred, or pulverize materials, especially after the first week in the row.

Watering —to create an optimal microbial environment, a turner must be able to apply water evenly throughout the row, rather than only to the perimeter.

Is Midwest Bio-Systems the only turner builder which embraces this composting philosophy? No. The key questions then among turner manufacturers sharing this philosophy are ones of value, durability, and service. Contact us today for this value, durability, and service information.

What are the features of your windrow turners?

Our compost turners feature the following:

  • One man operation — No separate water truck is necessary for watering the windrows.
  • Reduced compost production cycle time — Typically eight weeks from windrow formation to a finished product when using an Aeromaster turner combined with the ACS system.
  • The variable speed drum maximizes humus formation. Machines with excessive drum speeds pulverize feedstocks and retard, rather than enhance, the composting process. Our drums work in the 150-300 rpm ranges — the optimal environment for a quality end product. Microbes make compost, not equipment.
  • Our watering system applies water to the compost as it is tossed over the drum, distributing the water evenly throughout the material rather than just on the outside of the windrow which results in “dust here and mud there.” This equal distribution of moisture is essential for an optimum microbial environment.
  • This same watering system enables proper distribution of inoculant (the addition of special beneficial microbes) when water is applied to the windrow. Inoculants can be ineffective when applied with many watering systems on the market.
  • Aeration or the exchange of carbon dioxide in the windrow with air having its full oxygen content. Grover Landscaping of Modesto, Calif., measured carbon dioxide levels at 18% in front of their previous machine and 15% after turning. They switched to Aeromaster compost turners and found carbon dioxide levels at 18% before turning and 1% after.
  • The drum can be moved vertically removing the drum from the windrow at any time. This enables the operator to view an interior profile of the windrow to assess progress or, if the material is too wet, simply pull out and move on.
  • Durability — It is not uncommon for us to receive testimonials that a customer has used the equipment for 2-3 years without a single hour of down time, which is most unusual in this industry.
  • The finished product — Most importantly, we will challenge any of our competitors to utilize their equipment and their composting methodology or system, then submit their finished product to an independent lab comparison of the vital characteristics of their compost compared to same characteristics of compost produced with Aeromaster equipment and the ACS methodology.
How durable is the Aeromaster?

We recently received a call from a composter who said he needed to make a repair on his PT-120. He’d had his turner for seven years and this was its first breakdown.

Aeromaster turners have been built to last. In fact, they have been described as “overbuilt.” This is important because decomposing feedstocks do not wait for the operator’s convenience. When they need aeration, they need it today.

Grover Landscaping in Modesto, California has described their SP-155 (since replaced by the larger SP-170 self propelled turner) as “virtually indestructible.” They are especially pleased that they never need worry about becoming stuck in wet ground. They say their Aeromaster has “exceeded all our expectations.”

Per hour operating and maintenance costs for the self-propelled turner have been demonstrated to be less than one-half the industry standard. A combination of building durability into the equipment along with a different composting paradigm make this possible.

General Questions About The Composting Process


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Does CO2 from composting contribute to global warming?

Yes, CO2 is released, but since it is part of a natural process, it isn’t considered man-made; therefore, it isn’t figured into greenhouse gas emission calculations. Actually, composting, when done properly, as with our Advanced Composting System, reduces greenhouse gases a great deal, (especially methane and nitrous oxide, which are considered far more dangerous than CO2) when compared to simply dumping an equivalent amount of organic waste into a landfill.

What is the microbial inoculation process & guidelines?
Composting is a microbial driven process that:

  • First, breaks down organic matter, then
  • Builds that material into humus.

Having the right microbes on the job at the right time is what makes high quality, high value compost.

Midwest Bio-Systems offers compost production inoculants formulated to optimize the composting process at each inoculation point: the SYNCHRONIZATION, BREAKDOWN, BUILD-UP, and STABILIZATION phases of the composting process.

Learn More About The Process

View The Guidelines

Why Use Windrow Covers? Do they help the process?

Increased Control:

In the ACS compost production process, windrows are covered to prevent heavy rains from damaging the compost while maintaining moisture in hot weather. The covers block ultraviolet rays from the sun, protecting the microbial population while helping maintain temperature levels in cooler weather.

Cover your windrows to better control the composting process:

Rain falling on uncovered windrows is absorbed into the row opening the potential that windrow materials could leach into the ground. Rain falling on windrows covered with a special gas-permeable, water shedding fabric is not allowed to be absorbed into the row. Rain water runs off the cover and onto the ground between the rows. The clean rain water is then absorbed by the ground.

Covering your windrows:

Lay the windrow cover out over the windrow length-wise. Throw weights attached to rope across the width of the windrow every few feet. The weights/ropes combination keeps the cover in place through wind, rain and other weather conditions. If the climate is wet, excess moisture is kept out of the windrow; if the climate is dry, moisture is retained within the row. While shedding rain, gaseous exchange is still permitted. Nutrient retention is higher, the compost cycle will finish sooner, and ultraviolet ray damage is minimized.Covered compost retains temperature levels better than uncovered. In freezing conditions, covered compost does not freeze as deeply during winter and warms faster in spring.Leaching is significantly reduced when compost is covered.


Fabric covers, because they help control the process, offer a spectrum of benefits to raise quality, consistency, and predictability in the finished compost product. Those benefits include:

  • Moisture management — If the climate is wet, excess moisture is kept out of the windrow; if the climate is dry, moisture is retained within the row.
  • While shedding rain, gaseous exchange is still permitted.
  • Nutrient retention is higher in covered compost than uncovered.
  • The compost cycle will finish sooner.
  • Ultra-violet ray damage is minimized.
  • Covered compost retains temperature levels better than uncovered. In freezing conditions, covered compost does not freeze as deeply during winter and warms faster in spring.
  • Leaching is significantly reduced when compost is covered.

General Questions About Composting Equipment


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What is the importance of drum speed to the process?

All Aeromaster turners offer variable drum speeds in the 150-300 rpm range. Some composting paradigms call for 650 rpm or faster drum speeds. We believe a variable drum speed in the lower range offers a spectrum of benefits:

  • Decomposition of varying feedstocks may benefit from specific rpm.
  • Differing time frames (number of days along) during the composting cycle may suggest differing speeds.
  • Equipment does not make compost, microbes do. The optimum drum speed and tine shape can provide the ideal environment for beneficial microbes to flourish.
  • Drum speed and tine shape should lift, blend, and aerate compost feedstocks rather than cut, shred, and pulverize.
  • High drum speeds retard, rather than accelerate, the composting process.
  • Aggregation for crumb structure and humus development are limited when high drum speeds or a pulverizing approach are used.
  • A perfect turn should move center materials to the perimeter and perimeter materials to the center of the windrow. Aeromaster turners do this rather than bouncing them off a hood or curtain.
  • A perfect turn should get oxygen into the windrow and most carbon dioxide out. Respiration tests in front of and behind an Aeromaster turner will demonstrate the quality of this exchange.
  • Lower drum speeds reduce maintenance costs as stress is reduced throughout the turner.
  • Safety is enhanced as the risk of projectiles flying from the pile is largely eliminated.

As always, if a company or operator wishes to compare the quality of our equipment or the ACS process, we simply ask them to submit finished compost samples for the broadest array of tests to examine the quality of the finished product for its soil and plant benefits. We are happy to evaluate similar feedstocks under their current system/equipment paradigm with the Aeromaster Composting System approach to see which best succeeded.

What are the advantages of a retractable drum?

Firstly, at any point in the composting process the operator can stop, raise the drum, and walk into the middle of a row to examine the windrow Aeromaster PT-170 Compost Windrow Turner from Midwest Bio-Systems profile. Such an examination reveals the extent of mixing and blending of feedstocks, windrow stratification, the presence of molds, and the extent of feedstock decomposition.

Also, if after beginning turning, the operator discovers the row is too wet, he can cease immediately and drive on rather than needing to complete the row or use a loader and shovels to dig himself out.

Finally, the drum can be locked in place for transportation from one site to another.

What are the tractor requirements for an Aeromaster pull-type turner?

Horsepower: Generally, 80-100 for model PT-120 and 90-120 for model PT-130. However, lower or higher horsepower may be suitable depending on your feedstocks, additional demands on the tractor (i.e. loader attachment) and site conditions. For assistance in determining tractor horsepower requirements for your Aeromaster turner, contact your local Midwest Bio-Systems representative.

540 PTO

Two remote hydraulic outlets

Creeper gear or hydrostatic drive

The tractor needs to travel slowly at a range of 20-50 feet per minute (.2 mph at rated PTO speed), depending on the stage of the composting cycle.