Evahating compost qality by George E. Johnson and Steven L. Crawford

1 nitial results of a compost quality study point to the

benefits of source separation.

Minnesota leads the nation in solid waste composting, with over one-third of the oper- ating systems in the U.S. The operating his- tories and experience gained at these facili- ties are a valuable source of information for communities considering composting their wastes.

Minnesota’s composting facilities repre- sent a variety of capacities, technologies, feed- stocks and political infrastructures. All eight Minnesota operations have some leve1 of household separation of recyclables and haz- ardous materials.

Composting facilities in Minnesota Minnesota’s solid waste composting systems cover a broad spectrum of technology and scale (see Table 1). The largest operation in the state is the East Central facility in Mora, Minnesota. The facility serves fke COUntieS

and processes 250 tons per day (TPD) of municipal solid waste (MSW) using the Daneco technology. The plant has been oper- ating for two years, and has a tipping fee of $87 per ton. (The facility tipping fees cited in this article should not be construed as an accurate portrayal of total processing costs due to varying rates of public subsidy.)

The second largest operation is the Wright County facility located in Buffalo, Minneso- ta, with a design capacity of ahnost 200 TPD of MSW. The operation incorporates two

shifts a day and uses the Buhler technology. This plant has been operating for a year and has a tipping fee of $89 per ton. Both the East Central and Wright County plants separate recyclables from mixed waste streams and compost the residual organics. Nonprocess- able wastes are sent to landfills.

The Prairieland composting facility is located in the City of Truman, Minnesota. It has a 100 TPD capacity and processes the MSW from two counties. The technology used at this facility is the OTVD (Siloda) sys- tem, and the plant began operations about two years ago. The tipping fee is $75 per ton.

George E. Johnson and Steven L. Crawford are environmental scientists with Malcolm Pimie, Inc. in Minneapolis, Minnesota. Johnson is the administrator of the Compost Utilization Program.

In fact, progressive highway officials in states such as Arizona, California, Florida and Kansas will push ahead with rubber asphalt use, while their trade group - AASHTO - does battle with Sen. Chafee and other leg- islative supporters of recycled product use. This will be a tense confrontation - in late October, AASHTO decided to seek a repeal of Section 1038 of Ice Tea.

Thus, rubber asphalt use is heading for a prolonged political match. The amendment

80 million scrap tires would be utilized annu- ally when the 20 percent use rate is reached in 1997. RPA estimates that if rubber-asphalt were used for 15 percent of al1 paving in the U.S., al1 the scrap tires generated in this coun- try would be reclaimed.

In fact, the Ice Tea program could leadto strong competition for scrap tires in states where large whole-tire incinerators operate, such as Connecticut, or in regions where sig- niticant volumes of tires are used in,solid-fuel boilers, such as the Upper Midwest and Pacif- ic Northwest.

Growing opposition The opponents of mandated rubber-asphalt use, led by the Ameritan Association of S,tate Highway Transportation Officials and the National Asphalt Pavement Association, lob- bied heavy and hard to get the requirement repealed.

Rep. Bob Carr (D-MI) introduced an amendment in Section 330 of the $37 billion Transportation Appropriations Bi11 to pro- hibit the use of federal funds to implement, administer or enforce the rubber-asphalt paving program. Rather, some monies would be allocated for further study of the issues. Some 42 states said they agreed with the Carr amendment. The amendment passed the House 312-89 on September 23.

The Senate then received the brunt of the political furor. The political battle was fre- netic, with The Wall Street Journal editors asking, “How do these sorts of strange ideas tind their way into law?” The nation’s lead- ing business periodical labeled the Ice Tea requirement “an entitlement program” for the 15 members of RPA.

On October 6 the Senate followed suit, adopting the Carr amendment by a 90-9 vote. However, this limited amendment is certain- ly not the death knell of the rubber asphalt industry, since it does not remove the provi- sions of Ice Tea’s requirements. Further, it does not protect states from the penalties in the law.

has “emboldened” the opponents of rubber asphalt, says Gordon MacDougall, RPA’s executive director, as it “breathes new life into the political process.” RR

The 41-page joint federal report referred to in this article (A Study of the Use of Recycled Paving Material) is available for $20.50 as Publication No. PB93-219061 from the National Technical Information Service, 5285 Port Roya1 Road, Springfield, VA 22161.

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Resource Recycling December 1993 m

St. Cloud is served by Minnesota’s only privately owned operation (Recomp). The facility has a current design capacity of 75 TPD (60 TPD of waste and 15 TPD of an adjunct nitrogen source). This plant has the longest operating history of any composting plant in the state or nation - over a decade - and the current tipping fee is $83.37 per ton. The St. Cloud operation also sends fuel- quality residuals to a nearby resource recov- ety facility in Elk River, Minnesota.

Minnesota has four other plants with capacities less than 100 TPD. The Penning- ton County facility located in Thief River Falls is currently processing approximately 50 TPD of MSW. The plant is unique, in that the oper- ation not only removes recyclables from rnixed waste and composts the residual organ- ics, but also produces a densified refuse- derived fuel product, which is being burned at a local medical facility. The tipping fee is $45 per ton. The Pennington plant has oper- ated since 1985.

Minnesota’s three smallest operations are in Lake of the Woods, Fillmore and Swift counties. These facilities were al1 custom- designed. Al1 three operations focus primar- ily on composting source-separated organic materials.

The facility in Lake of the Woods Coun- ty has a processing capacity of 10,TPD. Although the operation prefers to process only source-separated organic wastes, it continues to receive mixed waste. Commingled and source-separated recyclables are received at a separate facility. The Lake of the Woods plant opened in early 1989, and the fee struc- ture is $80 per household per year.

The operations in Fillrnore and Swift coun- ties accept only source-separated organic feed- stccks and commingled recyclables. The Fill- more operation was originally designed to receive mixed wastes, but has since amend- ed its operations to process only cleaner organic materials. Source-separated non- processables received at these facilities are sent to landfills. The tipping fee at the Fill- more County facility, which opened in 1987, is $57.67 per ton. The Swift County facility charges $80 per ton and began its operations three years ago.

Many of these facilities are undergoing some degree of expansion or retrofit, and are applying for additional funding from the Min- nesotat Office of Waste Management. Al1 of the operations have encountered some prob- lems, but continue to operate successfully.

Compost quality and use More than 100,000 tons of refuse-derived composts are being produced annually by Minnesota’s facilities. Because of the diver- sity of the processing scale, technologies, feedstocks and end-use product quality, OWM conceived the Compost Utilization Program. The focus of CUP was to examine the physical-chemical and biological attrib-

ti A training program for facility opera- tors in sampling techniques will con- tribute to improve the consistency and reliability of compost samples over time and place.

(/ Source separation of noncompost- ables by householders will improve the quality of compost.

c/ Minnesota standards should be evalu- ated (and perhaps revised) in terms of federal standards.

utes of composts produced at Minnesota’s facilities to answer fundamental questions about appropriate applications for compost material.

Minnesota’s CUP concentrated on two pri- mary objectives. First, CUP was to provide guided research and demonstrate MSW com- post use in various applications. This work is being canied out at the University of Min- nesota, where the departments of Soil Sci- ence, Horticulture and Forestty are al1 con- ducting end-use studies.

Second, CUP was to characterize the prod-

uct quality of MSW composts produced with- in the state with the intent of minimizing the uncertainty regarding chemical and biologi- cal characteristics of compost. Sampling and statistical analysis were necessary because no database yet exists with extensive analysis of refuse-derived composts produced in the U.S. Many of the analytical data compiled and available do not employ standard quality con- trol methods for consistent material sampling and analysis. This lack of uniformity has made it difficult to compare analytical results from the various compost facilities and tech- nologies.

In early 1993, OWM awarded Stillwater, Inc. (now associated with Malcolm Pimie, Inc.) a $250,000 grant to evaluate the quali- ty of compost produced at Minnesota’s facil- ities. The national Composting Council, Proc- ter & Gamble and Buhler (an MSW com- posting technology vendor) offered additional technical and financia1 assistance to CUP. The objectives of the two-year stndy were to: n characterize the compost produced at Min-

nesota’s composting facilities n assist in developing market outlets for the

compost W investigate real and perceived environ-

mental risks from compost use H determine the benefits and cost of com-

post production H ultimately provide technical assistance

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to composting facilities based on these data. Monthly testing began

in April 1993. The first of seven quarterly reports was submitted to OWM in November 1993 for review. The database includes ap- proximately 40 different vari- ables determined to be the most significant indicators of compost quality. Some of these preliminary data estab- lished the need to modify analytical techniques and to research additional areas. The initial report also includes conclusions and recommen- dations based on the data col- lected to date.

CUP compost testing One-of the primary research objectives was to character-

n Table 2 - Minnesota compost metals contaminant concentrations, May 1993 (1)

Cadmium Copper Chromium Mercurv Nickel &J

CWA 503 standards (2) 39 1,500 1,200 17 420 300 Minnesota standards 10 500 1,000 5 100 500

Zinc

2,800 1,000

East Central (five-county)(3) 12.1 677.0 210.4 1.2 66.5 393.7 1,820 Fillmore County (3,4) 1.4 73.2 26.8 3.4 6.9 60.7 260 Lake of the Woods County (3) 4.1 227.6 50.5 3.2 21.5 267.2 729 Pennington County (3) 6.4 638.2 58.1 3.4 41.1 348.8 1,046 Prairieland (5) ll.9 951.2 105.7 6.8 71.7 379.0 1,918 St. Cloud (5) 13.7 385.4 72.9 6.9 64.7 298.8 831.3 Swift County (3,4) 2.1 252.4 37.2 4.0 45.8 181.9 1,056 Wright County (5) 9.9 346.7 78.9 6.9 60.2 361.8 1,507.2

(1) Comparative metals levels, in parts per million. Shaded areas highlight concentrations that exceed Minnesota limits for unrestricted use.

(2) Standards in the federal Clean Water Act for high-quality sludge/sludge composts. Richard, et al. (3) Single composite (20 to 25 grab) sample taken in May 1993. (4) Source-separated organics feedstock. (5) Average of 15 composite samples taken in May 1993.

ize final product quality. Following the char- acterization, markets could be developed, and risks to the environment could be examined. Compost quality traditionally involves the separate and distinct issues of environmental safety and beneficial use.

Issues of safety are usually wit,hin the purview of state and federal environmental

regulations for compost land application. Issues of land application normally deal with compost stabilization and contamination by metals, certain organic compounds (e.g., poly- chlorinated biphenyls), and to a lesser extent, soluble salts and inerts (e.g., glass shards). Issues of beneficial use are the market-driven requirements of nutrient value, compost matu-

rity, texture, pH, cation exchange capacity (CEC), etc.

Composts produced at Minnesota’s com- posting facilities were sampled by adminis- trators of CUP and the individual facility oper- ators. Because of some previously noted dis- parities in sampling results, CUP placed con- siderable emphasis on developing a stan-

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m Resource Recycling December 1993

dardized sampling method- ology. The method involves compositing 20 to 25 grab samples from various three- dimensional locations with- in the cure pile.

n Table 3 - Minnesota compost beneficial use parameters June 1993

A cross section of tbe data from the first samplings in May and June at each of Minnesota’s composting fa- cilities is shown in Tables 2 and 3.

Table 2 presents safety issues regulated by the state of Minnesota Pollution Con- trol Agency and includes Minnesota’s uppermost lim- its allowable for a Class 1 compost (unrestricted use). Shaded areas in Table 2 high- light concentrations that exceed Minnesota limits for unrestricted use. MPCA also limits the concentration of polychlorinated biphenyls (PCBs) to cl.0 ppm in a Class 1 compost. Table 3 presents issues of beneficial use. The analytical results for the PCBs in com- Stabilization is shown as a function of micro- posts have not been included in Table 2 because the results were inconclusive; how-

bial respiration. Unstable composts can result

ever, in severa1 cases, PCB levels exceeded in odor release from the facility and, after land

the state standard. These data will be sum- application, seed and plant inhibition. Although

marized in a later report. no test for stabilization is universally accept- ed, respirometry is rapidly gaining acceptance

Compost auality assessment Resp (1) pI& C:N(2) TKN (4) S salts (3) plsl K.fa East Central (five-county) 0.48 20.3 7.3 15.8 1.26 3,576 4,28 1 Fillmore County (SS) 1.30 17.1 7.9 8.2 1.61 1,727 5,233 Lake of the Woods County 0.68 13.7 8.3 8.0 1.05 3,413 3,731 Pennington County 0.21 13.1 7.7 19.5 0.84 2,842 5,424 Prairieland (6) 0.62 24.8 8.1 16.2 0.98 2,733 5,741 St. Cloud (6) 0.21 27.0 8.2 16.8 1.09 2,496 5,936 Swift County (SS) 1.32 17.1 8.2 10.4 1.63 3,962 9,139 Wright County (6) 0.69 18.6 8.4 22.0 1.33 2,93 1 7,587

SS = Source separated. (1) Respiration coeffícient. A measurement of compost stabilization as a function of the respiratory activity of the resi-

dent microbial population. The measnrement is in mgOYgm Volatile SoIids/hour. A coefficient of 2 mg02/gmVS/honr normally characterizes a raw feedstock. A coeffcient of 0.5 mg02/gm/VS/hour is an indicator of a stablized materi- al. Iannotti, et al.

12) Total carbon and total Kjeldahl nitrogen. 13) Soluble salts. Conductance in a compost sluny. 14) Total Kjeldahl nitrogen. 15) Units in parts per million for phosphorum (P) and potassium (K). 16) Composite of 15 samples taken in May 1993. Because of a gap in the database, parameters for respiration and phos-

phoms were taken from data compiled in June 1993, rather than May. ty data were covered in the same manner.

Similar gaps in the St. Cloud and Wright Coun-

Source: Minnesota Office of Waste Management, Compost Utilization Program, 1993.

as an accurate and easily determined measure of compost maturity. The other parameters described in Table 3 are explained in the foot- notes. These parameters can serve to quanti- fy the nutrient value and soil utility of the com- post after land applicaiton.

Fourteen indicators of compost quality are

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included in Tables 2 and 3, from approxi- mately 40 variables witbin the database. The the data presented here, however, are repre- sentative of tbe fust-quarter report submitted to OWM for review. The report includes detailed descriptions of individual facility process flows, sampling and analytical methodologies, sampling and analysis data, plus conclusions and recommendations. The conclusions and recommendations will be used to determine the costs and benefits of compost production, and to provide techni- cal assistance to composting facilities in Min- nesota and elsewhere.

Testing conclusions Minnesota’s mixed MSW composting facil- ities show substantial differences in many aspects of product quality.

Generally, the four larger facilities had higher contaminant concentrations tban did the four smaller facilities. Differences exist between the sampling methods used by each operation.

The contaminant concentrations of met- als and PCBs in compost appear to be an accu- rate measure of the effectiveness of tbe MSW pre-treatment and source separation.

Analytical data from individual facilities

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tend to vary over time and within the pile due to seasonal variations and the intrinsic het- erogeneity of the incoming feedstock.

Recommendations Compost quality is improved signiticantly by household and commercial separation of non- compostable items fmm the feedstock. Devel- opment of separation programs should be encouraged.

To ensure analogous data, facility opera- tors need detailed training in the sampling of product. An operator training program should be designed and implemented.

Chemical analysis for selenium should be included in the testing regimen to conform with recently promulgated federal Clean Water Act 503 requirements for land appli- cation of sewage sludge biosolids.

Minnesota regulatory agencies should remove restrictions on the use of sludge biosolids in Class 1 composts. Clean sludge biosolids can serve as a valuable source of nitrogen and other nutrients to the process, without signilicantly increasing contarninant metals levels.

Minnesota regulatory agencies should re- evaluate compost contaminant limits based on the federal CWA 503 standards.

The State of Minnesota rules use the volatile solids reduction test for demonstrat- ing compost stabilization. The test requires tbat the composting process reduce the avail- able feedstock volatile solids by at least 60 percent. The test methodology does not include a standard method of determining the levels of volatile solids in the feedstock. A methodology or benchmark needs to be agreed upon and incorporated into the Min- nesota rules. RR

Acknowledgement

The authors would like to thank Elena C. West- brook for her editorial comments.

Referentes

Iannotti, D.A. et al., “A Quantitative Respiromet- ric Method for Monitoring Compost Stability,” Compost Science and Utilization, 1(3):52-65.

Johnson, G.E. et al., “Successful Composting on 100 Tons Per Day,” World Wastes, 36(8):62- 67.

Johnson, G.E. et al., “Facilities Evolve to Meet Challenge of Compost,” World Wastes, 36(6): 34-44.

Nordhagen, R.D. et al., “Small-scale Mixed Solid Waste Materials Recovery and Composting: An Operator’s Perspective,” World Wastes, (submitted for publication).

Richard, T. et al., “MSW Composts: Impacts of Separation on Trace Metal Separation,” in Hoitink and Keener (eds.), Science and Engi- neering of Composting: Design, Environmen- tal, Microbiological and Utilization Aspects, 401-421, Renaissance Publications, Worthing- ton, OH.

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m Resource Recycling December 1993