July 14, 2008 | General

Measuring Material Volumes At Composting Sites

BioCycle July 2008, Vol. 49, No. 7, p. 42
Volumes reported to Ohio EPA by composting facilities are generally within 20 percent of actual amounts when accurate records are maintained on loader buckets of material received and sold. Part II
H. M. Keener, M.H. Wicks and James A. Skora
Web Extra, pdf file featuring complete report with additional figures

COMPOSTING facilities in Ohio are required by the Ohio Environmental Protection Agency (Ohio EPA) to complete an annual report on the amount of materials received and processed annually either on a weight or volume basis. Ohio EPA also requires annual reporting on the quantity of compost sold or given away. Scales, visual estimate, or the capacity of the vehicle hauling the material typically is used to measure the incoming volume. Outgoing material is either reported in cubic yards or by the ton.
To better understand how volumes are determined and reported – as well as to develop a consistent methodology for use by facilities – a study was undertaken by Ohio EPA, the Ohio State University, the Ohio Composting Association and GT Environmental, Inc. Part I of this article (June 2008) described the materials and methods used to measure moisture, wet bulk density, dry bulk density, volumes based on the dimensions and geometrical shape of a pile, and volumes based on weight of material with a front end bucket loader. Research was conducted at eight composting sites in Ohio. The majority are Class IV facilities (under Ohio EPA rules) that may only accept source separated yard trimmings and specified bulking agents. Part II describes the test procedures at each site and reports on the accuracy of the measurement tools outlined in Part I. The full report on this study contains findings at each site; this article presents a summary of the findings. The complete report can be found in the July Web Extra, on-line at A training manual, “Compost Measurement Methodology & Product Sampling,” is available at the Ohio Compost Association’s website (
Operators at the eight composting sites were asked a series of questions pertaining to their operations to gain background on how facilities are managed. For collecting data at each site, the tools identified under methods described in Part I were used. For the bulk densities of material, the 5-gallon bucket was filled with compost and the top leveled to maintain consistency. A person would stand on the scale with either the bucket empty or full and determine a weight. This process was completed three times for each material at the site. Samples were taken from each pile, categorized by age and physical characteristics, and bagged for analysis of moisture content. Where bucket loaders were available, operators were asked to move and pile 1 to 10 buckets of a material for volumetric measurements. A measuring wheel was used to determine the circumference of the pile; a 26-foot tape was used to measure the major axis, minor axis, and the height of the pile. Pictures were taken of incoming material, aged material, equipment used and facility setup. Unless indicated, the facilities are Class IV sites.
Site 1, Medina County: The Medina County facility is located in North Central Ohio and has both a Class I (permitted to receive any solid waste) and Class IV composting facility. For the Class IV facility, material at the site was arranged as follows: 2-year old leaf waste; 1-year old leaf waste; incoming yard waste; 1-month old first ground material; 5-6 month old first ground material; 10-12-month old first ground material; and final product ground and screened (10 to 12 months old). Figure 1 shows the 3-cubic yard loader that was used to measure material for volumetric measurement. Unground yard waste was scaled with the loader and pile size measured afterwards.
Site 2, Columbus: The Kurtz Bros. facility is located near Columbus in Central Ohio. It is a large composting facility that sells product to both the individual consumer and landscape businesses. Incoming waste is measured by the cubic yard using vehicle volumes; outgoing product is sold both by weight and cubic yard. Piles are measured once per month and turned three to four times per year; salable products are watered when necessary to keep down the dust. Yard waste is composted approximately 10 to 12 months before it is sold. Product is loaded into trucks with a 1-cubic yard bucket and a 6-cubic yard bucket. A portion of the unground yard waste and a sample of the first ground yard waste were moved by a 1-cubic yard bucket, scaled, and then piled in order to take volumetric measurements (Figure 2).
Site 3, Cincinnati: The Rumpke Facility is located at a landfill near Cincinnati in Southwest Ohio. Yard waste is brought to the site and processed by a tub grinder. The freshly ground material is generally shipped out and sold to other composting facilities. Product is reported to Ohio EPA in tons. Piles are not measured and are not watered on a definite schedule. Material left on-site is put in piles and turned 3 to 4 times per year using a wheel loader with a 6-cubic yard bucket. Material ranges in age from incoming to five years old. A roll off truck (Figure 3) was used to measure volume of compost.
Site 4, Medina: The Greenleaf site is located in Marietta in Southeast Ohio. A tipping fee is charged for incoming material. A contractor grinds the material once per year in January. There are three piles of material at the site – incoming, one-year-old composting yard waste (Figure 4) and 2 to 5 year old final product. There were no scales or loaders available upon arrival at the site. Bulk densities and samples of material were taken. Composting data is reported to the Ohio EPA in cubic yards. Visual estimate of material is made when material arrives at the site. Outgoing material is sold by the cubic yard. Compost is loaded with either a 1-cubic yard bucket or a 3-cubic yard wheel loader bucket.
Site 5, Lima: The City of Lima Compost Facility in Western Ohio is located right outside of Lima. Yard waste is ground and processed by a contractor. No scales are available at the site. Composting data is reported to Ohio EPA in cubic yards. Visual estimates are made when the yard waste arrives at the site. The facility does not water or turn their piles. Figure 5 shows freshly brought in material that has not been ground. Samples were taken of the final product; no known age could be determined for the final product being sold.
Site 6, Ashtabula County: The Conneaut Composting facility in Northeast Ohio is located in Ashtabula County. Material is in three distinct piles – fresh yard waste, 1 to 2 year old leaf waste and 2 to 5 year old final product (Figure 6). Incoming composting data is reported to Ohio EPA in tons. Samples and bulk densities were taken of the final product and the leaf waste. Piles are not measured and are not turned during the year. Outgoing material is sold by the yard.
Site 7, Huron County: The Barnes Compost Yard Waste Recovery facility is located in Huron County in North Central Ohio. It is a relatively large Class II composting facility (can receive yard trimmings, animal waste, food scraps and specified bulking agents). Product is sold to both the individual consumer and other businesses. Scales measure incoming waste; outgoing product is sold by the cubic yard. Piles are turned every three to six weeks (Figure 7). Watering of piles is not generally done. Yard waste is composted approximately 10 to 12 months before product is sold. A 1-cubic yard bucket is used to load outgoing trucks.
Site 8, Stark County: The Earth’N Wood composting facility (Figure 8) is located in Stark County in Eastern Ohio. Scales weigh incoming waste; outgoing product is sold by the cubic yard. A “comtiller” is used to turn piles weekly for the first 3 weeks. Yard wastes are composted approximately 10 to 12 months before material is sold. Product is loaded into trucks with a 1 cubic yard bucket.
Moisture Content: The wet moisture content for compost materials at different stages of composting for the eight sites visited varied from a maximum of 70 percent in composting material to a minimum of 6.9 percent in the screenings. Generally material moisture was 20 to 55 percent. For some unfinished compost, it would be concluded that it was overly dry, i.e. below the range of 45 to 65 percent. This could have been due to summer conditions.
Bulk Density: The 5-gallon bulk densities (BD) ranged from 8 lb/ft3 (4-inch freshly ground) to 48.8 lb/ft3 (5-year old ground) for compost materials at various sites. The dry bulk densities varied from a maximum of 5.4 lb/ft3 to 32.4 lb/ft3. Results for bulk density did not show any correlation between BD (wet or dry) and moisture for the materials tested. Although no relationship was determined between BD and moisture contents as a part of these studies, wet bulk density should increase with moisture contents due to filling of pore space with water for a given material (water density is 62.4 lb/ft3).
Results for bulk density using a loader (BDL) and 5-gallon bucket (BDb) at three test sites gave a linear relationship of BDL = 1.25 BDb – 1.62 with an R2 of 0.7814 (Figure 9). On a percentage basis, bulk density based on loader weights and operator stated loader volumes was an average of 25 percent higher then the small bucket provided. This higher bulk density is likely due in part to the front loader bucket containing more material than the designed loader bucket volume.
Comparison of wet bulk densities obtained by the loader bucket for the ground and unground material at the different sites is presented in Figure 10 and Table 1. Results showed bulk densities of ground material were from 7.5 percent to 291 percent more than unground yard waste. Because 5-gallon pail densities on the unground material were not practical to measure, no comparison was possible based on BDb.
Pile Volumes: Evaluation of pile volumes using equations provided in Part I are given in the Appendix (available in full report, at – Web Extra). A plot of volumes (Figure 11) based on the pile circumference versus volume based on pile major and minor axis showed they were linearly related. Using the circumference gave a pile volume about 16 percent higher (R2 = 0.9264) than major/minor axis. This result was based on 29 of 31 data points (2 omitted as outliers).
Loader Bucket Volumes: Differences in measured bucket loader volumes (VL1) based on loader weights and small bucket density and operator’s volumes (VL3) were as follows: +37% to -15% at the Stark County site (E); +16% to +40% at the Medina site (NC1); +20% to +81% at the Barnes site (NC2); and -46% to +81% at the Kurtz Bros. site (C). The unground grass/leaf material at NC2 and ground yard waste at C had 81 percent over estimation on volume. The general trend of predicting higher loader volumes based on weight than the design volume of the bucket could be due to overfilling of the loader bucket and/or underestimation of bulk density with a small bucket.
Differences in measured bucket loader volumes (VL1) based on major/minor axis technique with the operator’s bucket volume (VL3) for each site were as follows: -30% to +62% at E site; -45% to +5% at NC1 site; -13% to -4% at NC2 site, and -11% to +50% at the C site. Results suggest that the NC1 and NC2 sites were slightly biased toward less volume than stated for loader bucket, whereas the C site was biased toward more volume than the bucket loader. Since no precise measurement of each loader bucket was made, this biasing could be due to inaccurate bucket volume, as well as operator skill or use of formula for a cone.
The general formula for a cone with an elliptical base assumes the volume is one-third the base multiplied by the height. However, in construction of the pile, the shape is such that using a one-third base times height may underestimate the volume. However, based on data collected, use of one-third (i.e. 0.333) is recommended unless more controlled experiments would be done. A plot of the results for differences in volume (ellipse) at the six Ohio sites (n=34) showed a somewhat even balance of errors around 0 difference, with 20 volumes below and 14 volumes above the operator loader volume. On a percentage basis, 62 percent of the results were within 20 percent of the stated volume. Plotting the data from using the equation for a cone based on circumference showed 70 percent of measured volumes were within 20 percent of the stated loader volume, including all underpredicted volumes.
The results show that the compost volumes reported to Ohio EPA by the composting facilities are generally within 20 percent of actual amounts when accurate records are maintained on loader buckets of material received and sold. Based on results of this study, the circumference and major/minor axis estimated volumes were relatively similar, with the circumference method giving a 16 percent higher value. The circumference approach would require only a single person to take the measurements while the major/minor axis needs two people to get the measurement data to determine the volume. Both methods are economical and simple to use and can be taught easily to facility operators for estimating loader volumes.
The method of estimating the loader volume, based on the bulk density by the small bucket and weights of the compost products for the loader bucket, showed percentage differences as high as 81 percent. For this method most volumes were calculated higher than stated loader volumes, which may be due to overfilling the bucket or underestimating bulk density using the small bucket. According to this study, the correlation between bulk density and composting materials based on age or moisture content could not be found.
To maintain accuracy and consistency in the data, sampling procedures need to be developed and followed at each composting site. For example, procedures need to be clearly followed for height measurement of a pile. Picture analysis might enable determining the volume of the pile, but would not be as easily implemented as the methods used in this study.
Harold Keener is Professor and Assoc. Chair, Department of Food, Agricultural, and Biological Engineering at the Ohio State University. Mary Wicks is Coordinator, Ohio Compost and Manure Management Program, Ohio Agricultural Research and Development Center/The Ohio State University in Wooster. James Skora is Manager-Northeast Ohio Office, GT Environmental, Inc., in Akron, Ohio. The authors acknowledge the contributions of the summer students who ably assisted in the collection of data and Mike Klingman, Senior Design Engineer, FABE Department. Research support was provided by the Ohio Compost Association, GT Environmental, Ohio Environmental Education Fund and State and Federal funding appropriated to the Ohio Agricultural Research and Development Center, The Ohio State University.

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