WORKING VERSION 1.0 – October 1, 2015
Download a PDF Version of the Guide (ADD LINK)
We welcome feedback from small-scale site operators and other interested parties on this guidance document. What challenges are you facing? How have you addressed these? What lessons have you learned? What works? What does not? Please share feedback with Linda Bilsens at firstname.lastname@example.org
Neighborhood Soil Rebuilders’ Capstone Project
Compost Best Management Practices & Monitoring Guide
Compost site operators need to optimize certain conditions in order to produce high-quality mature compost without nuisance odors and pests. The Neighborhood Soil Rebuilders (NSR) Composter Training Program – a partnership between the Institute for Local Self-Reliance and ECO City Farms – has developed this best management and monitoring practices guide for small-scale community composting.
- C:N Ratios
- Storing and Collecting Materials
- Recording and Weighing Materials
- Tracking Data
- Compost Curing
- Community Compost Management
- What to Avoid!
To ensure efficient decomposition, the carbon to nitrogen (C:N) ratio of materials – or feedstocks – entering the compost process at the beginning should be between 25:1 and 40:1, with a target of 30:1.[i] Tables 2 and 3 show C:N ratios for common feedstocks at community compost sites. C:N ratios are provided in dry weight (and do not take into account moisture content). An appropriate C:N ratio is a critical starting point for troubleshooting problems.
One general rule of thumb for reaching the 30:1 C:N ratio is:
Add 3 parts by volume “brown” (high carbon) materials to 1 part “green” (high nitrogen) materials.[ii
For example., 3 wheelbarrows of fall leaves to 1 wheelbarrow of vegetable trimmings (the same size wheelbarrow!
When first starting a project as well as in preparation for adding new feedstocks, operators should calculate the C:N ratio or refer to a C:N calculator to develop an appropriate recipe based on feedstocks. To establish a firm foundation of knowledge, ILSR recommends, The Field Guide to On-Farm Composting – it provides easy-to-read tables and standard formulas to assist in compost recipe making
Klickitat County (WA) has an online Compost Mix Calculator (this online calculator will show moisture levels for individual feedstocks but does not calculate the final moisture level of the recipe nor the bulk density of materials.) There is also a sophisticated Compost Calculator Online Tool from Green Mountain Technologies that can help guide your compost recipes.
Note: Adjusting recipes is inevitable as feedstocks, moisture levels, and pile porosity change. Alter your C:N feedstock recipe in consideration with other key parameters such as moisture, material bulk density, odor, and temperature data.
Temperature is the primary measure of the composting process. It’s a window into the microbial activity in the pile as the heat produced is directly related to the microbial activity.[iii] Because temperature is the best indicator of what’s going on, it is important to track temperature data regularly.
Composting takes place within two main temperatures ranges: mesophilic (50 to 105° F) and thermophilic (over 105° F). We recommend aiming for temperatures in the thermophilic range between 131 and 153° F. Compost processing time and temperatures should be sufficient to kill weed seeds, reduce pathogens, and prevent attraction of unwanted critters. Reaching 131 and 153° F is important to destroy more pathogens, weed seeds, and fly larvae. At 145° F, most weed seeds are destroyed. Tomato seeds typically need 153° F to be destroyed.
New Maryland compost permitting regulations require commercial-scale compost sites to follow the “process for further pathogen reduction” or PFPR. This entails reaching a minimum of 131° F (55° C) for a specified period of time, which varies depending on the compost system in place.
Windrow: The compost must be maintained at a minimum average temperature of 131° F (55° C) or higher for 15 days or longer. During this period, there shall be a minimum of five turnings with a minimum of 3 days between turnings. The 15 or more days do not have to be continuous.
Aerated static pile or in-vessel: Material maintained at a minimum average temperature of 55° C or higher for 3 continuous days, followed by at least 14 days with a minimum of 113° F (45° C)
While community-scale compost sites are exempt from these regulations, we recommend that neighborhood small-scale composters accepting food wastes or manures treat their 2- or 3-bin community-scale system as an aerated static pile, and therefore maintain a minimum average temperature of 131° F or higher for 3 continuous days, followed by at least 14 days with a minimum of 113° F. We further recommend 150° F as the ideal temperature to reach for at least 3 continuous days.
As recommended in the On-Farm Composting Handbook, record temperatures daily if possible until you acquire a feel for the process. A pattern should emerge after several batches of materials have been composted. Utilize compost thermometers to gauge and record temperatures throughout the composting process, letting the temperature and moisture content guide the process.
When temperatures reach too high, the microorganisms can die or become dormant and the composting process slows. At 153° F, aerate or turn the pile to facilitate heat loss. Temperatures above 153° F can also indicate a moisture level below 40%, so watering may be needed. If microorganisms have died, you may need to reinvigorate the pile by remixing or adding material from another active pile.
Composting is an aerobic process requiring oxygen. Adequate oxygen is essential to a thriving composting system.[iv] The billions of microorganisms associated with composting need adequate oxygen. As O2– and CO2-meters are not commonly used at the community-scale, consistent aeration is critical. Use temperature as your gauge. Tracking temperature will give you an indication if oxygen is adequate or not. If the temperature is above 150° F, most likely oxygen is low and carbon dioxide is high.
Favorable conditions within the pile will increase microbial activity; the proliferation of microbes will increase temperature and the consumption of more oxygen. Material must be turned or aerated to maintain an adequate oxygen level (>5% is critical but 10% is the optimal level).[v]
During the active composting stage (the first 2 to 3 weeks), turn material every 3 to 4 days, and once per week at a minimum.[vi]
Composting generates odors. The key is not generating nuisance odors. Something is wrong if your piles are emitting strong putrid odors. Bad odors could be a sign that the pile has gone anaerobic or has anaerobic pockets. If this is the case, turning and remixing will help inject more oxygen. (Not enough carbon could also create nuisance odors.)
Adequate moisture is essential for the microorganisms to thrive. Above 60% moisture levels, they drown. Below 40%, they die or go dormant.
Operators can most practically gauge proper moisture levels (40 to 65%) on-site by conducting a “hand squeeze test.” The squeeze test entails taking a handful of decomposing material from the compost system and squeezing. If the material sticks together, and the hand is moist and glistening, this is an indicator of ideal moisture content ranging between 50 to 60%. Material that is crumbly, leaving the hand dry indicates inadequate moisture, whereas material that sticks together with excessive dripping down the arm indicates too much moisture.[vii]
Proper material handling at compost sites is paramount.
Certain putrescible materials such as food scraps need to be managed with particular care. Ideally they should be incorporated into the composting process immediately. Food scraps should only be added to the composting system raw or fermented (using a process such as Bokashi). If they must be stored and fermentation is not possible, food scraps should be immediately mixed with enough browns to soak up any liquid and prevent anaerobic conditions (that is, a starved oxygen environment that leads to odors).
Even non-putrescible materials such as leaves and wood chips require proper storage to avoid becoming an eyesore or home for critters.
All storage units (as well as the composting system itself) should be adequately secured. Properly sealed and fastened lids, bungee chords, combination locks, and other devices should be used to securely close units until composting is finished. Composters that closely monitor for and prevent vector disturbances, unsightly and unsanitary messes, and unpleasant smells will have the greatest success.
In terms of collection, in the DC-metro region, there is no shortage of food scraps (which are a “green” or nitrogen heavy material). However, the collection of “brown” materials can require added attention. Food scraps should not be accepted unless the appropriate amount of “browns” are available and ready to use on-site.
Ways and places to get brown materials include hosting seasonal community leaf drop-offs; contacting local landscaping, tree removal, and construction companies; and collecting shavings from carpenters and wood working companies that do not use hazardous chemicals. Grinding, chopping or shredding brown as well as green feedstocks into small (say <2 in) pieces before they enter the composting system can speed up the composting process but is not necessary.[viii] (Large uncomposted pieces can be screened out at end and put back into the active composting piles.)
Small scale community composters are expected to keep a record of the volume or weight of all material composted, as well as the finished compost. These numbers are needed for operators to be able to estimate the volume or weight of feedstocks needed to be ordered or collected, to predict the amount of finished compost that can be created, and to generally inform operators about the capacity and proficiency of their system. These records will also allow operators to estimate their cumulative impact in regard to waste diverted, which is particularly helpful when seeking financial or political support.[ix]
Operators can designate a “weigh station” area on a flat portion of their site and can utilize a wood surface (e.g. piece of plywood, 1×8, etc.) or other flat object beneath the scale. If using a hanging scale, find a place that will safely hold the weight of a container full of your heaviest feedstock and that can be easily and safely reached and a container that can easily be hung.
Record keeping is critical for running a composting system efficiently, especially when a group is involved, and for communicating the benefits of the system to the surrounding community. Record keeping also promotes accountability, provides a baseline, evidence-based data, and helps troubleshooting by identifying specific problems and areas requiring the operator’s attention.
Operators should consistently monitor and record the data points outlined in some sort of log book (here is an example of a community composting monitoring log). These include, at a minimum: date of composting, name of composter, C:N ratio (by volume) of feedstock mix, volume or weight of feedstocks compost, temperature, moisture content (poor, fair, or good), volume or weight of finished compost and any specific problems. Here is an example of an community composting environmental impact log to track the overall waste reduction and compost production levels of the project.
In addition to composting-related data, community outreach data are also important for proving the social impact potential of your project. Here is an example of a composting community impact log that provides a space for collecting information.
Compost must be cured before it is completely finished, mature, and ready to be used. Designate an area for the compost to cure. While this curing process can add additional months (a 4- to 8-week curing period is usually recommended), it is necessary to allow the compost to gradually complete degradation to produce a more chemically stable finished product. Adding unfinished compost, or incompletely decomposed material, to a garden will result in compost bacteria competing with plants for nitrogen in the soil, which can stunt growth.[x] Immature compost will continue to consume oxygen, reducing the availability of oxygen to plant roots. It can also contain high levels of organic acids, a high C:N ratio, and other characteristics that may be damaging for certain horticultural applications.[xi]
Curing continues the aerobic decomposition process and occurs at low, mesophilic temperatures. Adequate aeration is necessary so be sure to limit the size and moisture content of the curing pile. Avoid an anaerobic curing pile. [xii]
Completely finished compost is a dark brown, earthy-smelling material similar to rich organic soil that is homogenous, without recognizable feedstock ingredients, and will no longer heat up after turning.[xiii] It is ambient temperature.
Clear and visible signage facilitates awareness, education, and proper site maintenance for all composters and site visitors alike. Consider signs that depict: (1) incoming organic materials (distinguishing between “browns” and “greens”); (2) composting system (bin or other system itself); (3) curing compost; (4) finished compost; (5) weigh station; (6) the Composting Monitoring Toolkit; (7) NSR Capstone Site Resource Binder (on binder cover); (8) list of acceptable and non-acceptable materials.
Site managers can find signage templates and potential options here. (Coming soon!)
Numbering the composting operation components (e.g. drop-off location, each bin compartment, etc.) to show clear, sequential, steps in the process can also benefit users. Types of signage include: wooden hand-painted (preferably treated wood for outdoor longevity), well-laminated paper, durable plastic, aluminum (e.g. 0.040 thickness), and Coroplast® material (e.g. a corrugated yard sign). Signs can either be mounted on posts in the ground or fastened directly to the object, so long as they are solidly in place.
Identify the composting system manager who will be responsible for training other operators and site participants. Composting sites should only be active if at least one operating manager is in place. That person can take a leadership role in establishing a composting team (such as a cooperative management team) or other ways to engage participants. Identifying and training “compost captains” and recruiting qualified helpers of all ages to assist the operating team can be beneficial. Requiring weekly compost shifts for managers and monthly shifts for other participants can ensure a collaborative effort and enhance experience and education. Expanding the group of knowledgeable composters involved in the project will enhance the program’s success.
Select feedstocks: While all organic materials are compostable, certain items should not be accepted at urban community-based sites. Fats, oils, greases, dairy products, meats, bones, seafood, pet wastes, and chemically treated grasses and yard trimmings hinder the composting process, attract pests, create odors, and/or contaminate the composting system.[xiv]
Exposed food scraps: Even acceptable food material can promote pest and odor issues if left exposed. Composters should make sure that all food is well covered with finished compost or a carbonaceous feedstock such as wood chips.[xv]
Odors: Odor control is critical to advancing community-based composting. Maintaining aerobic (adequate oxygen transport) conditions in the composting system (e.g. by using the correct C:N ratio, mixing wet feedstocks with porous bulking amendments, consistently turning or aerating the composting system) is key to controlling odor.[xvi]
Pests: Controlling odors will help control pests. Following all of the above guidelines and preventing the system from going anaerobic should be the goal. The key is to create favorable, aerobic conditions for the microorganisms within the composting system, not for outside critters. Operators should always ensure their site and tools are left clean with no visible food and that all vector deterrents on their composting system are securely in place (e.g. bins locked, hardware cloth fastened, holes repaired, etc.)[xvii]
Contact and storm water: Maintain sites with good drainage in order to avoid pools of standing water, which can attract mosquitoes and other unwanted pests. Composters can also implement proactive watershed protection measures by installing a buffer (e.g. a vegetated filter strip or compost or wood chip berm) between the composting system and any surface or groundwater resources to intercept potential “contact” water (this is water that has contacted raw feedstocks or actively composting materials).[xviii]
Unsanitary practices: Composting systems are resource recovery sites, not waste disposal facilities and should be treated as such. Always maintain a clean, safe, and friendly environment. Composters, as sustainability stewards, should respect themselves and all site visitors by wearing protective gloves while composting and washing their hands to avoid the spread of bacteria when finished.
[i] Rynk, R., van de Kamp, M., Willson, G. B., Singley, M. E., Richard, T. L., Kolega, J. J., Gouin, F. R., Laliberty, Jr., L., Kay, D., Murphy, D. W., Hoitink, H. A.J., & Brinton, W. F. (1992). On-Farm Composting Handbook, pp. 8-9. Ithaca, NY: Plant and Life Sciences Publishing (PALS) and Chapter 2, Composting Fundamentals | Earth-Kind® Landscaping. (2009). Texas A&M Agrilife Extension. Retrieved March, 2015, from http://aggie-horticulture.tamu.edu/earthkind/landscape/dont-bag-it/chapter-2-composting-fundamentals/
[ii] Composting Made Easy. Cornell University Cooperative Extension Rockland County. Retrieved March, 2015, from http://rocklandcce.org/resources/composting-made-easy
[iii] Robert Rynk, editor, On-Farm Composting Handbook, by Natural Resource, Agriculture, and Engineering Services (NRAES) Cooperative Extension (June 1992), pp. 56-57.
[iv] Rynk, R., van de Kamp, M., Willson, G. B., Singley, M. E., Richard, T. L., Kolega, J. J., Gouin, F. R., Laliberty, Jr., L., Kay, D., Murphy, D. W., Hoitink, H. A.J., & Brinton, W. F. (1992). On-Farm Composting Handbook, pg. 6-9. Ithaca, NY: Plant and Life Sciences Publishing (PALS).
[v] Rynk, R., van de Kamp, M., Willson, G. B., Singley, M. E., Richard, T. L., Kolega, J. J., Gouin, F. R., Laliberty, Jr., L., Kay, D., Murphy, D. W., Hoitink, H. A.J., & Brinton, W. F. (1992). On-Farm Composting Handbook, pg. 8. Ithaca, NY: Plant and Life Sciences Publishing (PALS).
[vi] Compost Fundamentals: Why Compost. Washington State University Whatcom County Extension. Retrieved March, 2015, from http://whatcom.wsu.edu/ag/compost/fundamentals/needs_aeration.htm and Cooperband, L. (2002). The Art and Science of Composting: A resource for farmers and compost producers, pg. 9. University of Wisconsin-Madison Center for Integrated Agricultural Systems. Retrieved March, 2015, from http://www.cias.wisc.edu/wp-content/uploads/2008/07/artofcompost.pdf
[viii] Wilson, C., Feucht, J., & Newman, S. (2014). Composting Yard Waste. Colorado State University Extension. Retrieved March, 2015, from http://www.ext.colostate.edu/pubs/garden/07212.html
[x] Cornell MC Resource Manual, pg 16.
[xi] On-Farm Composting Handbook, Ibid., pp. 13.
[xii] On-Farm Composting Handbook, Ibid., pp. 13.
[xiv] Singer, J. DPR Community Compost Cooperative Network Agreement. DC Department of Parks and Recreation and Van Rossum, J. (2013). Do-It-Yourself Compost Bins: Can Composter. University of Wisconsin-Extension. Retrieved March, 2015, from http://www4.uwm.edu/shwec/composter/resources/G4020-02%20Can.pdf
[xv] Trautmann, N., Op. Cit.