Paul Rosenow Partner, Roseholm-Wolfe Dairy
Michael J. Tiry, PE Tiry Engineering
The Compost Process and Dairy Manure
Dairy manure has been separated and composted at the Rosenholm farm (now Rosenholm-Wolfe Dairy) for over seven years. The farm, located in Buffalo Co. WI, has successfully produced compost for the commercial market using organic solids separated from manure which had been flushed from a 250 head free stall barn. The free stalls are bedded with dry sawdust. Liquid manure is pumped to an overhead static screen separator. The liquid effluent from the separator drains to a series of two ponds where additional settling of suspended solids occurs and the remaining water is again recycled as flush water. The solids which come off of the separator are then used as the feed stock for the compost process.
The recipe for high quality compost is such that separated solids from dairy manure make excellent feedstock for the process. This raw composting material has the C:N ratio of 30:1 and the moisture of 60% - essentially ideal for the production of high quality product in a relatively short time. In addition to keeping the C:N ratio and the moisture content at optimum levels, it is essential to maintain a steady oxygen supply in the composting material and to keep the temperature at the appropriate levels.
Internal windrow temperatures in the range of 110 - 140 degrees Fahrenheit and oxygen levels of 5% will result in thorough composting of the raw materials. The moisture content, temperature, and oxygen levels are monitored daily to determine if mixing of the windrow is needed to maintain or enhance the aerobic process. The manipulation and control of the compost process is done by mechanically mixing of the windrows and by the addition of moisture and nitrogen as may be needed. The windrows are turned using a machine specially designed for this purpose. The compost is placed in windrows which are formed to fit the turning machine.
Seasonal considerations need to be addressed if operating in the upper Midwest region of the US. During the months of December through March, cold ambient air temperatures will slow down the internal heating process most times to the point of having to discontinue mixing activities as not to “freeze” the windrows. If the windrows become “frozen”, the start up date for effective composting will be delayed. Also, the newly separated compost feedstock may become so cold while collecting that it may not be able to “self-start” the heating process until warmer weather arrives.
What Product Standards Can One Expect?
Once the active composting phase is completed, it should be sampled and sent to a laboratory for quality considerations. The finished compost product based on a standard soils laboratory analysis of N, P, K, & S will typically have total quantities of the following; N content of 14 lb., P of 6 lb., K of 14 lb., and S of 0.75 lb. on a per ton basis at 70% dry matter. At a rate of 25 tons per acre on production agriculture crop land, first year available nutrients would be; 87.5 lb. of N, 75 lb. of P, 262.5 lb. of K, and 10 lb. of S.
Other parameters which serve to define the quality of compost are: ammonium (NH4), nitrite (NO2), nitrate (NO3), the pH value, sulfides, heavy metals content, and germination index. Germination index is a measure of how universal a growing medium the compost is. The germination index of compost from this facility (tested at the Agri-Energy Resources Laboratory) was 100. A high quality finished compost will have ammonium at less than 2 mg/kg, nitrite that is not detected, nitrate that is less than 100 mg/kg in cold weather months and less than 300 mg/kg in warmer months, a pH of less than 8, the test for sulfides to be negative, and germination index greater than 90.
In the commercial market, the soil amendment properties of the compost is often scrutinized. These properties would include organic matter content, water holding capacity, bulk density, particle size, and moisture content. The organic matter content should be in the range of 45-65%, with the water holding capacity greater than 100%, the bulk density of 800 - 1100 lb. per cubic yard (dairy manure compost is typically 800 lbs/cu.yd.), the particle size less than 1 inch, and the moisture content from 30 - 50% (some compost from municipal sources have clay added to increase the cation exchange and water holding capacity). Dairy manure typically has no heavy metals.
These factors stated above become the basis of the quality of the product that will be marketed to the Green Industry (floriculture and environmental horticulture) and to the organic food production sector. The higher the quality of compost produced, the greater the market opportunities will be. For example, if the compost produced met all the criteria of the highest quality compost, it would be suitable for potting mixes in plant nurseries (the highest value market). An example of a typical use of low quality and low value compost might be to mulch newly constructed highway landscape greenery.
Is the Compost Market Unique?
It is the opinion of this author that this market, like many markets, is consumer driven. If you can connect with people who are looking for your product, and then deliver a product that meets or exceeds their expectations consistently and in a timely manner, one could expect to be successful. The compost market as a whole is a very diverse market. On one end of the spectrum customers are looking for, and expect, guaranteed analysis. These customers will examine your product to find a suitable medium in which to grow high value plants. On the other end of the spectrum, you will have customers who are looking for something to increase organic matter (as a soil amendment) with some nutrient value for lawn or garden use. In such a diverse market, opportunities abound, but there is a need for education on how to tap those opportunities.
Consumption of compost in the commercial market is growing due to people looking for a more organic or natural substitutes for traditional “chemical” norms. It is a market that has it’s problems, such as an absence of a national standards for testing and rating of compost. Such standardization will eventually come. The COMPOSTING COUNCIL based in Alexandria, VA is a national organization that is trying to address issues that hinder the growth of the industry on the national scene by working with federal and state governments to accomplish standards for compost qualities and other issues such as including compost in usual and standard bidding forms for governmental projects. Rosenholm-Wolfe, Dairy L.L.P. is a member and supporter of this organization.
What About Composting for Odor Control?
Does composting have potential for reducing odors from stored manure on dairy farms? Though composting is not a cure-all for odor problems, it does have some benefits worth looking at.
Removing solids from the liquid portion of the manure reduces the anaerobic activity in the storage lagoon and therefor reduces odor. Because composting is and aerobic process, the odors associated with the composted solids portion of the manure are minimal relative to the odors associated with anaerobic storage of manure. By separating solids from the liquid manure, agitation of the manure is not usually necessary for emptying of the storage pond or structure thereby minimizing the odor at the farmstead at the time of field application. By reducing the total solids content, aeration of a third stage pond can be done at less cost. This would have the benefit of not only reducing odors in the recycled flush water but also to kill anaerobic pathogens. Data taken at the ponds are not conclusive but it appears that about 50% of the COD is removed from the liquid portion at the separator and another 33% is removed in the two pond system. If aeration were done to prep the flushwater in a smaller 3rd or 4th stage pond, A relative small amount of power would be used.
The Original System (and what was learned from it).
In 1990 a 250 cow dairy operation was built from ground zero in an existing alfalfa field. A flush system for cleaning manure from the barn and milking parlor was chosen because of its ease of operation and cleanliness. We installed an inclined screen separator and a two-pond storage system for the purpose of maintaining a usable supply of recycled water for use in flushing the freestall-housing barn. We separate all waste flushed and we have not had to agitate any of our ponds before application of wastewater to cropland. Also, it was in 1991 that we started experimenting with composting of our solids collected off the separator. Our purpose at that time was to reduce volume before spreading onto cropland. By word of mouth, consumers heard that we had “compost.” In the early stages (circa 1990) the compost was given to friends and neighbors. It evolved into an interesting supplemental business of the dairy farm.
In that period of time since 1991 we have made advances in our composting processing and marketing based on the lessons learned. The original design captured some of the dairy’s roof water and directed it to the reception pit at the separator and then to the first stage pond. It was calculated that we captured about 240,000 gallons of clean precipitation. By separating solids from the manure, this additional water was not needed, and could be diverted out of the system there by reducing the amount of material handled.
The ponds were designed for 250 cows producing 20,000 pounds per cow per year. Since 1991 we had increased our cow numbers to 290 and milk production to 25,000 pounds per cow per year and had added more animals to the system with a calf facility added in 1995. This resulted in higher total solids per gallon of wastewater available in the system which resulted in an increase in odor when flushing.
The Revised System
In 1997 the business was expanded to a 600 cow dairy operation. In this business expansion, we focused on becoming more efficient in the waste management area since it is a large issue on any dairy. The first decision made was that we could build on the strength of our composting business to handle some of the increased waste load. The second decision made was to stay committed to the “flush” design including separation of the liquids and solids involving moving and handling waste. Thirdly it was decided to keep clean water clean wherever possible. The components of this commitment were than put together.
The components include:
A new separation area that also doubles as a staging area for making homogeneous piles of separated manure solids. Roof water is diverted out of this area. What leaches out of the piles as the solids come off of the separator drains back to the reception pit and to the first stage pond. This area was constructed of watertight concrete. A staging area for the first stage of the composting process was added just off from the separator area. Here the compost heats to over 110o F and begins to compost. Runoff from this area is caught and drained to a vegetative filter strip lined with 2' of silty soil (>50% P#200). A third holding pond in a configuration that does not require any pumping of waste water between ponds was added for the purpose of increasing the recycle water quality and reducing offensive odors. A compost-stacking pad was added which served to produce a higher quality product and to make it easier to serve the compost customers. This pad is a 82,000 square foot area surfaced with asphaltic concrete. It includes a loading ramp for bulk loading of compost. The asphalt surface is also convenient for self-bagging. A system of waterways, diversions, grade stabilization structures, catch basins and pipes were used to keep clean water clean and to control erosion on and around the building site.
The compost stacking pad site was designed to keep clean water clean and capture any leachate from the compost windrows by the use of a grassed settling basin, an aggregate filter, and vegetative filter strip which should utilize any nutrients that travel across it.
The Economics of Composting - Will it cash flow?
The answer to that is “it depends,” because of the situation being different at any given location where compost is being produced. Many questions need to be asked.
Is there a need to improve cropland soils at this location? If you have highly mineralized soils - yes. High organic matter soils - no. Is it a tool to control odors from storage ponds by separating the solids from the liquids? Yes, but it must also be realized that compost operations have odors, short in duration, and aerobic in nature even at a properly managed compost site. These odors are usually less offensive than anaerobic agitated lagoons. Is the market place near enough to attract customers to your location? Is there a firm commitment by the management to make quality compost? Or will it be another waste "problem"? Is it a substitute based solely on commercial fertilizer substitutions? Probably not, if used on lower value crop production.
Complex questions that need asking before starting to compost!
The Composting Council's 1996 Year-End Report; November, 1996; The Composting Council; Alexandria, VA Holly Johnson, UW-Stevens Point, WI, Cooperative Extension; Future Directions in Composting Seminar - April, 1996 Controlled Microbial Composting (information literature); Atrusa Compost Consulting, 1996 On-Farm Composting Handbook; Northeast Regional Agricultural Engineering Service - Cooperative Extension; NRAES-54, 1992 AgriEnergy Resources Laboratory; Princeton, IL; Rosenholm Farms compost sample report- May 1997