BioCycle June 2008, Vol. 49, No. 6, p. 38
Study develops consistent methodology for accurately measuring volumes of unprocessed and processed materials at yard trimmings composting facilities. Part I
H.M. Keener, M.H. Wicks and J.A. Skora

OHIO has a total of four classes of compost facilities (I-IV) regulated by the Ohio Environmental Protection Agency (Ohio EPA), distinguished by the types of materials received and size of the facility. Class I facilities may receive any solid waste and require a permit prior to construction and a license. Class II can only receive yard trimmings, animal waste, food scraps and specified bulking agents. Other separated organics can also be processed with Ohio EPA approval. Class III facilities may receive only yard trimmings and/or animal waste along with specified bulking agents. Class IV facilities may accept only source separated yard trimmings and specified bulking agents.
Ohio EPA requires all composting facilities to complete an annual report on the amount of materials received and processed annually either on a weight or volume basis. They must also report compost sold or given away. As such, there are over 400 compost facilities either permitted or registered in Ohio.
Compost has been reported to the Ohio EPA over the past several years using the “Solid Waste Composting Facility Daily Log of Operations” data sheet. Scales, visual estimate, or the capacity of the vehicle hauling the material was used to measure the incoming material. The type of equipment available at the site is completed at the beginning of each year. Incoming material is recorded by date, load number, amount of waste, type of waste and Ohio county or state of origin. Outgoing material is either reported in cubic yards or by the ton. After each day, data is recorded upon inspection of the facility making sure it is meeting regulatory requirements issued by the Ohio EPA. If unauthorized material is brought into the site, the incident is recorded and actions by the operator are reported.
In order to better understand how volumes of materials are determined and reported for composting sites in Ohio, a study was undertaken to develop a consistent methodology to determine the volumes of materials accepted and produced at the composting facility. The measurement methodology includes the cubic yard estimation for piles of leaves, grass, woody materials and mixtures. Evaluation of procedures for measurement of volumes at Ohio Class IV compost facilities was done at eight sites in Ohio.
STUDY OBJECTIVES
Participants in the study included the Ohio EPA, the Ohio State University, the Ohio Composting Association and GT Environmental, Inc. (see sidebar). The objectives were as follows:
1. Evaluate methodology using lineal pile dimensions of diameter(s), circumference, length and geometrical shape to calculate the volume of piles at facilities with no scales.
2. Evaluate volume of piles (at sites with scales) based on the weight of pile and bulk densities of the various compost materials, i.e. incoming and outgoing, using a five-gallon bucket (GB) and compare with results from Objective 1.
3. Evaluate wet bulk densities based on the weight of compost delivered with a front-end loader bucket at the compost facilities with scales and compare results with densities obtained in Objective 2.
4. Evaluate volumes of the piles based on the standards of the front-end loader bucket used in composting operations.
5. Determine the moisture contents of the samples of the various materials at the different stages of composting and evaluate whether any correlation exists between bulk density, compost type and moisture.
The results provide insight on how the weights and volumes reported to Ohio EPA are determined and enable comparison between the standards of the compost facility operator and the measurement techniques applied. In addition, the findings assist regulators in specifying procedures to calibrate equipment used in the measurement of volumes at the composting sites.
MATERIALS AND METHODS
Data recorded during the study for the different sites was 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. Equipment used in the study for lineal measurements included two measuring tapes (a 200 ft measuring tape, and a 26 ft/8 m measuring tape), a Stanley ground wheel, a clinometer and a rod surveyor. The 200 ft and 26 ft tapes were used to measure major and minor axis of the compost pile base. The height of the pile was approximated by aligning the eye with the peak of the pile, at a distance of approximately 30 feet from the pile, using the rod surveyor.
For larger piles, the clinometer, which has a degree scale (left side) and percent scale (right side) was used. It was calibrated for a horizontal distance of 66 feet from the pile. The circumference of the pile was measured with a ground wheel. For weighing the compost a bathroom scale weighing up to 400 lbs ± 0.2 lbs was used, or the truck scales at the compost site (accuracy ±20 lb).
Compost wet bulk densities were determined using weight of compost in a five-gallon bucket. A representative sample of the compost was put in the bucket with a shovel, leveled to ensure uniformity in the data collection and weighed using the bathroom scale. The scale was placed on a leveled wooden board to eliminate the unevenness of the ground at the locations. In addition, at sites with truck scales, compost weight of a pile constructed using a front-end bucket loader was also used. The compost pile was formed by dumping from 1 to 10 buckets, ranging from 1 to 6 cubic yards, heaped with compost material into a cone shaped pile following weighing of the filled bucket loader. At one site the weight recorded was for a roll off truck (container capacity 30 cubic yards) used to measure volume.
For moisture measurements, samples were collected in Ziploc bags from each location of the pile where bulk densities were measured, transported back to the composting laboratory and dried. For moisture determination, a 100 to 300 g sample of compost was dried in a forced air oven for 48 hours at 70°C. Weighing was done with a laboratory balance accurate to ± 0.1 g.
MEASURING MOISTURE CONTENT
Moisture content and bulk density are chemical and physical properties of compost materials that play an important role in achieving the optimum efficiency of the composting process. The wet basis moisture content, MCw, is the ratio of the total weight of the free available and bound water in the wet mass of the compost sample. It is calculated using the following equation:
MCW = 100 * (W2 – W3) – (W4 – W5)
W2 – W1
In the equation above, W1 is weight of the sample empty cup,W2 is weight of the cup filled with compost,W3 is weight of the dried sample after 48 hours at 70°C in an oven, W4 is reference cup weight before drying and W5 is reference cup weight after drying. This equation implies that the reference cup is similar to the sample cup. If cups for the sample are pre-dried, then W4-W5 is zero. An alternative to oven drying would be use of a microwave, where the sample is dried in small time steps of one to two minutes until weight of the sample doesn’t change. For weighing purposes, a laboratory scale accurate to ±0.1 g or better is used.
MEASURING BULK DENSITY
The bulk density of compost is a measure of the mass of the material in a given volume. It influences the compost properties like porosity, strength and resistance to compression. Both dry and wet bulk densities are assessed for compost. The wet bulk density is the ratio of wet or as received compost mass to total volume occupied, while dry bulk density is the mass of the dry compost material to total volume occupied. For this study, volume was determined from pile measurements or information provided by the operator of the equipment.
The equation for calculation of bulk density using a small bucket and a scale is:
BDS = 62.4 * Wcompost – Wbucket
Wwater – Wbucket
Where BDS = bulk density, lb/ft3, Wcompost represents the weight of the small bucket (for this study ?5 gallon) full of compost material, Wbucket is weight of the empty bucket, and Wwater is the weight of the small bucket filled with water.
The equation for the bulk density using a loader bucket is:
BDL = Wcompost – Wloader
Vloader
Wcompost represents the weight of the front end loader bucket (1 to 6 cubic yd) filled with compost, Wloader is weight of the empty loader, and Vloader is the volume of the front end loader bucket. For this study volume was determined from pile measurements or information provided by the operator of the equipment.
Converting wet bulk density to dry bulk density is done using the following equations,
bdS = (1-MCw) BDS
bdL = (1-MCw) BDL
Where bd = dry bulk density, lb/ft3 and MCw is the wet moisture content (decimal) of the compost.
VOLUME OF CONE-SHAPED PILE
For a pile considered as a cone (Figure 1) with a spherical base the volume is given by:
V1 = r2 h/3 = C2 h / (12 )
where
r = radius of the base of the pile, ft
C = circumference of circle base, ft and
h = the height of the pile, ft.
For a pile considered as a cone with an elliptical base (Figure 2):
V2 = a b h/12
where
a = the major axis of the ellipse, ft and
b = the minor axis of the ellipse, ft.
EQUATIONS FOR BUCKET LOADER VOLUMES
Volumes of the bucket loader were determined using: 1. Weight of compost in bucket loader and small bucket bulk density; 2. Volumes of cone, i.e. pile, formed at the site by bucket loader; and 3. Volume of front-end loader bucket as reported by the operator. The equations for the first two are below. For the Operator Volume (#3), VL3, was based on the company standards for the front-end loaders used at the various sites in compost operations as reported by operator. The bucket size varied from 1 to 6 cubic yards.
1. Volume of the bucket loader based on bulk density is
VL1 = n(Wfull – Wempty)i
i=1 n * BDS
where
VL1= volume of the loader bucket using a 5 gallon pail bulk density, ft3
n = number of loads weighed
Wfull = weight of bucket loader with compost for each of the n trials to form the pile, lb
Wempty = empty weight of the bucket loader, lb and
BDS = wet bulk density using the small bucket method, lb/ft3
2. Volume of bucket loader based on pile volume measurements is
VL2 = Vp
n
where
VL2 = volume of front end bucket loader based on pile dimensions, ft3
Vp = volume of the pile (either V1 or V2), ft3
BULK DENSITY OF GROUND VS. UNGROUND MATERIAL
Bulk density differences between ground BDLG and ungrounded material BDLU were evaluated using
%BDdiff = 100(BDLg – BDLu)
BDLu
Loader volume differences were calculated using VL3, VL1 and VL2. The equations used were
%VL3-1 = 100 (VL3 – VL1)
VL3
%VL3-2= 100 (VL3 – VL2)
VL3
Part II of this article, to appear in the next issue, will provide the findings of the research carried out at eight composting facilities across the state of Ohio. The authors evaluate the accuracy of the measurement tools outlined in Part I above.
Harold Keener is Professor and Associate Chair of the Department of Food, Agriculture and Biological Engineering at The Ohio State University. Mary Wicks is Coordinator of the Ohio Compost and Manure Management Program at The Ohio State University. James A. Skora is Manager of the Northeast Ohio office of GT Environmental, Inc.
MANUAL AND TRAINING SESSIONS
THE Ohio Environmental Protection Agency’s requirement that yard trimmings composting facilities report volumes of materials received and processed on an annual basis has been a topic of discussion among members of the Ohio Compost Association (OCA) and the regulatory agency itself for a couple of years. The accuracy of data provided, and the ease with which it could be obtained, were among the issues discussed. “At a meeting of various composting stakeholders, including Ohio EPA, facility operators and our consulting firm, we got the idea to educate the regulated community about how to meet this measurement requirement,” says Michael Greenberg, Owner and Principal Consultant of GT Environmental, based in Westerville, Ohio. “We formed a committee with representatives from OCA, the Ohio State University (OSU), Ohio EPA and one of our staff members, and applied for a grant from the Ohio Environmental Education Fund to assess measurement tools available and test their accuracy at selected Class IV composting facilities in Ohio.” The grant also includes funds to develop a manual and conduct training sessions for facility operators.
Five regional training sessions were held in early 2008 to review the data and research, and instruct operators on methods to measure their compost feedstocks and piles. “We won’t see the results of this outreach and training until next year, when facilities need to file their reports with 2008 data,” notes Greenberg.