Quality Compost from Source Separated Organic Material and Biosolids in East Prince County Prince Edward Island

Transcription

1 Quality Compost from Source Separated Organic Material and Biosolids in East Prince County Prince Edward Island A Paper presented by D.E. Jardine Director of Pollution Prevention, Department of Fisheries, Aquaculture and Environment and H.D. Chowen of the Island Waste Management Corporation at the International Composting Symposium Halifax/Dartmouth, Nova Scotia September 19-23, 1999

2 QUALITY COMPOST FROM SOURCE SEPARATED ORGANIC MATERIAL AND BIOSOLIDS IN EAST PRINCE COUNTY, PRINCE EDWARD ISLAND. D.E. Jardine, Prince Edward Island Department of Technology & Environment, Charlottetown, P.E.I., C1A 7N8; H. D. Chowen, Island Waste Management Corporation, P.O. Box 271, Slemon Park, P.E.I., C0B 2A0. 2. ABSTRACT Source separated organic material from 13,000 households and 1,000 businesses is mixed with biosolids from a primary sewage treatment plant to produce a top quality compost product. The organic material is shredded and then composted using an open windrow process without forced aeration. The active composting detention time averages 40 days inside a covered compost building. The compost is then cured outdoors on an asphalt pad with a curing detention time of up to 6 months. For the past four years this system has processed an average of 9,000 tonnes of raw materials a year into 5,000 tonnes of finished product. The finished compost is screened prior to marketing using a mechanical power screen unit. The composting process is monitored regularly for temperature, oxygen, ph and moisture content. Representative samples of the compost have been tested for heavy metals and nutrients since the site was commissioned in December The average concentration for all heavy metals analysed, except for copper, meets the requirements of Category A compost in the Canadian Guidelines of Compost Quality, CCME 106E, March Keywords: Biosolids, compost, municipal solid waste, quality, source separation.

3 3. INTRODUCTION Residents and businesses in East Prince County, Prince Edward Island began participating in a mandatory source separation, solid waste diversion program in December In 1999 over 13,000 households and over 1,000 businesses are participating in the program. This represents nearly 30 per cent of the province s population. Waste materials are sorted into three categories: Recyclables Compostables Remaining Waste The compostable materials separated at source include: - food waste, including meat, fish and bones - boxboard containers and packaging - milk cartons - all non-recyclable paper products including paper towels, paper tubes, paper plates, construction paper, poster paper, food wrapping materials, waxy cardboard and wax paper leaves and yard wastes biosolids and potato processing wastes - all other biodegradable, organic materials. These compostable materials are delivered to a central composting facility located at Wellington Center, Prince Edward Island. The facility has experienced good success in composting all these materials with the exception of the milk cartons. The milk cartons do not fully decompose in the time span of six months. The organic material is shredded if necessary, and then placed in an open windrow, which is located inside a totally enclosed, galvanized steel building, except on the south end.

4 Biosolids from a primary sewage treatment plant are disposed of through the composting process. Biosolids are added to the windrows and mixed with other materials using a compost turner. The material is protected from the weather for 40 days and then cured outdoors on an asphalt pad with a total curing detention time of up to 6 months. The facility utilizes the windrow process without forced aeration. The cured compost is screened using a trommel screener (1.25 cm screen size) to remove contaminates and over sized particles once the material is at least 4 months old. During the first 3 years of operation, a straddle type turner or front end loader was used to turn windrows. The straddle turner was replaced by an elevated face turner. The compost is tested on a monthly basis for the parameters listed in the Canadian Council of Ministers of the Environment (CCME) 106E, March 1996,Guidelines for Compost Quality. The objective of this paper is to describe the composting process in detail including the results of laboratory testing that determined compost quality. 4. MATERIALS AND METHODS The facility processed quantities of source separated materials into compost as outlined in Table 1.

5 TABLE 1 COMPOST SOURCE MATERIALS (AMOUNTS IN TONNES) MATERIAL PROCESSED Residential Compost Commercial Compost Yard Waste Sewage Sludge TOTAL The composting process was monitored to maintain a temperature range of between 45 to 65 degrees Celsius in the windrows and a temperature of at least 55 degrees Celsius was maintained for at least 15 consecutive days. A typical temperature profile for the composting operation is given in figure 1. Figure 1 - Compost Temperature Profile Temp. in Degrees C Days Since Formation 45 55

6 The windrows typically were turned 5 times during this 15 day period to achieve a pathogen kill. Oxygen levels were measured with a Teledyne oxygen analyzer and are usually around 10%. Moisture levels were measured to maintain a moisture level at 50 per cent and water was added to the windrows as required to maintain this moisture level. The ph of the windrows was measured and adjusted if necessary, by the addition of lime or wood ash. The ph was maintained at around seven. Representative compost samples were collected on a regular basis since the facility commenced operation in Nutrient samples were collected bimonthly from the windrows inside the building and on the outdoor curing pad. Six samples were collected from representative locations along each windrow at a depth of 0.6 meters. One kilogram samples were collected from each windrow in polyethylene sample bags and submitted to the PEI Department of Agriculture and Forestry, Soil and Feed Laboratory in Charlottetown for analysis. The parameters tested included: dry matter, C:N ratio, ph, zinc, copper, potassium, phosphorous, nitrogen, magnesium, carbon and calcium. In June of 1999, soluble salts, sodium and chloride were added to this list. Samples of screened compost (1kg/ sample) were collected from 10 compost windrows at least annually for heavy metal analysis. The samples were shipped on the day of collection via courier to the Phillip Analytical Services Laboratory in Halifax, NS. Samples of screened compost were collected annually in an autoclaved sample bag for pathogen analysis and delivered to the PEI Department of Technology and Environment microbiology laboratory in Charlottetown. Samples were delivered to the laboratory within 2 hours of collection. Source material samples were collected to determine the chemical composition of the raw materials used to produce the compost. The sewage sludge was sampled in 1995 and

7 1996 to determine the concentration of priority pollutants in this material. The City of Summerside primary sewage treatment plant de-waters the sludge with a vacuum filter, and adds lime prior to shipment to the Wellington Center Waste Management Facility. The sludge is delivered to the facility twice a week and is evenly distributed into the windrows inside the compost building. Samples of commercial compost, yard waste, shredded cardboard and waste feed were also collected. 5. RESULTS AND DISCUSSION Table 2 provides an analysis of compost samples from the Wellington Center compost facility. This table includes samples collected during the first four years (1995 to 1998) of operation of the facility. This table provides information on the compost quality prior to the production of the end product.

8 TABLE 2 COMPOST ANALYSIS IN PROCESS (expressed as dry weight basis, mg/kg) ANALYSIS CCME A # OF % MAX. MIN. AVG. COMPOST SAMPLES PASSING GUIDELINE CCME boron cadmium calcium % carbon % chromium copper iron lead manganese magnesium % nickel nitrogen % phosphorous % potassium % zinc Salt K Value dry matter % C:N ratio < ph The results for the finished compost are given in table 3. Again these are results for samples collected during the first four years (1995 to 1998) of operation.

9 TABLE 3 - COMPOST ANALYSIS FINAL PRODUCT (expressed as dry weight basis, mg/kg) ANALYSIS CCME A # OF % MAX. MIN. AVG. COMPOST SAMPLES PASSING GUIDELINE CCME aluminum antimony arsenic barium beryllium bismuth boron cadmium chromium cobalt copper iron lead lithium manganese mercury molybdenum nickel rubidium selenium silver sodium strontium tellurium tin thallium uranium vanadium zinc Fecal < coliform Salmonella < Foreign matter %

10 Based on the average values, all parameters, except copper, meet the CCME guidelines for Class A compost. Parameters with exceedances for individual samples include: copper, C:N ratio and fecal coliform. One fecal coliform sample out of 33 exceeded the CCME limit. The cause of the high copper concentrations is not clear. Analysis of the primary sewage sludge, which is composted at the facility indicates one potential source. Table 4 gives the results of the limited testing of the sewage sludge received at the facility.

11 TABLE 4 PRIMARY SEWAGE SLUDGE ANALYSIS SUMMERSIDE TREATMENT PLANT Analysis Performed (in ppm unless indicated otherwise) Aluminum Antimony 1.10 Arsenic 2.00 Barium Beryllium 0.30 Bismuth 3.50 Boron Cadmium 0.66 calcium calcium % carbon % Chromium Cobalt 3.50 Copper Iron Lead Manganese Magnesium Mercury 5.25 Molybdenum 4.40 Nickel Nitrogen % Phosphorous % Potassium Selenium 1.00 Silver Sodium Strontium Tin Vanadium Zinc dry matter % C:N ratio ph -wet 5.73

12 Table 5 provides results of analysis for other source materials used to manufacture the final compost product. TABLE 5 OTHER SOURCE MATERIALS ANALYSIS Parameter Yard waste Commercial Compost Commercial Compost Shredded Cardboard Waste Feed mg/kg (unless otherwise stated) Boron Carbon % Calcium % Copper Dry Matter % Iron Potassium % magnesium % Manganese Nitrogen % Phosphorous % Zinc C:N Ratio ph The only source materials, which may contain enough copper to cause the elevated copper concentrations in the final compost product are the sewage sludge and the waste feed. The sludge showed concentrations of over 100 mg/kg in one of four samples. This should not cause the high copper levels as the sewage sludge composes only 12.6 % of the total weight of materials processed. The waste feed from a local feed mill composes less than 1 % of the feedstock for the compost process and would not be a major contributing factor to the elevated copper levels. The applicability of some of the CCME Compost Guidelines for applications on Prince Edward Island soils is a matter for discussion. Prince Edward Island soils are known to be deficient in a number of heavy metals, when compared to representative soil analysis on a broader base.

13 Examples of the deficient metal concentrations are provided in Table 6. The average copper concentration in the 2000 soil samples analyzed from Prince Edward Island potato fields in 1999 is given at 2.17 ppm in Table 6. This is compared to a representative soil sample of 50 ppm (Brady) and a CCME Agricultural soil guideline of 63 ppm. The Class A compost guideline for copper is given at 100 mg/kg (Table 2). Application of compost containing more than 100 mg/kg copper to Prince Edward Island soils is not a concern due to the deficient concentration of copper present in Prince Edward Island soils. The Agriculture Canada Research Station in Charlottetown has conducted studies of plant uptake of copper. These studies have shown that copper levels in plants grown on fields, where this compost has been applied, fall well within acceptable levels and continued application is not considered to be detrimental to forage crops (J. A. MacLeod et al). The recommended application rate for the Wellington Center compost is a maximum of 50 mm thickness during the first year of application with subsequent years having a maximum thickness of 25 mm. This compost is then mixed with the native soil to a depth of 300 to 400 mm. This paper provides evidence that the CCME Compost Guidelines should allow provision for composts which exceed certain parameters to be considered class A in regions of Canada which have soils which are deficient in the parameters which are in exceedance. It is not always appropriate to have a national guideline, which is not flexible for this type of situation.

14 TABLE 6 DEFICIENT METAL CONCENTRATIONS IN PEI SOILS PEI POTATO FIELD SOILS 1999 REPRESENTATIVE SOIL SAMPLE (after Brady) 1997 CCME AGRIC. SOIL GUIDELINE METAL (ppm) Boron Iron Copper Manganese Zinc A few samples of the Wellington Center compost had mercury levels above the CCME Category A compost guideline. None of the sample concentrations exceeded the recommended Canadian soil guideline of 6.6 ppm for agricultural soils. The average concentration of mercury was within the acceptable CCME Category A compost guideline. The Wellington Center Waste Management facility uses a number of criteria to determine if their compost can be sold to the general public. These criteria are: 1. The C:N ratio must be less than 25:1 2. The compost must be at least 6 months old. 3. The compost piles cannot be reheated over 25 degrees Celsius. 4. Compost must be at least 4 months old prior to being screened. 5. Except for copper, the compost cannot exceed the CCME Category A Compost Guidelines. 6. ACKNOWLEDGEMENTS The authors wish to acknowledge the assistance of Brian Douglas and Cindy MacLeod of the PEI Department of Agriculture and Forestry, Soil and Feed Laboratory, Charlottetown, Mr. Jim Montgomery of the PEI Department of Technology and Environment, and Dr. John MacLeod of

15 Agriculture Canada Research Station, Charlottetown in supplying data and information for this paper. 6. REFERENCES Brady, N.C., 1974, The Nature and Properties of Soils, MacMillan Publishing Co., Inc., New York. Composting Subcommittee, Solid Waste Management Task Group, Canadian Council of Ministers of the Environment, Guidelines for Compost Quality, CCME 106E, March MacLeod, J. A., Sanderson, J.B., Douglas, B., Henry, R., 1999, The Effects of Application of Municipal Compost With and Without Disposable Diapers on the Composition of Potato, Agriculture Canada Research Station, Charlottetown, PEI. MacLeod, J. A., Sanderson, J.B., Douglas, B., Henry, R., 1998, Use of municipal compost in potato rotation. Report to 1998 Annual Meeting Compost Council of Canada. Subcommittee on Environmental Quality Criteria for Contaminated Sites, Canadian Council of Ministers of the Environment, Recommended Canadian Soil Quality Criteria, CCME, March ADMIN191