PAPERMILL SLUDGE COMPOSTING AND COMPOST UTILIZATION Gregory K. Evanylo, W. Lee Daniels, and Ren Sheng Li Department of Crop and Soil Environmental Sciences Virginia Polytechnic Institute & State University Blacksburg, VA 2406 1-0403 INTRODUCTION Economically viable and environmentally acceptable methods to recycle organic wastes are needed by the pulp and paper industry. Previous studies have demonstrated the successful utilization of papermill sludge in land reclamation projects (Bellamy et al., 1990; Pridham and Cline, 1988), as soil amendments for field-grown agricultural and forest crops (Cline and Chong, 1991 ; Henry, 1991 ; Logan and Esmaeilzadeh, 1985), and as potting media, after composting. for production of container-grown greenhouse and nursery crops (Chong and Cline, 1993; Chong et ai., 1987; Cline and Chong. 1991). Papermill sludge is usually composted in the U.S. and Canada by blending with organic wastes such as sawdust and animal manures, placed in windrows, and allowed to compost for three to five weeks with frequent turning of the windrows (Campbell et al., 1991; Chong and Cline, 1991; Chong et al., 1991). Completely cured compost that is acceptable for containerized plant production can be achieved by maintaining the compost in a static phase for an additiopal four to six weeks with occasional turning (Chong and Cline, 1991). The Virginia Fibre Corporation (VFC) requested that we monitor the composting efficiency of its combined primary and secondary dewatered papermill sludge and test the suitability of the finished product as a soil amendment and/or as a potting soil substitute. Papermill sludge normally has a moderate to high carbon:nitrogen (C:N) ratio, which often requires supplemental N to facilitate complete composting; however, the Virginia Fibre dewatered papermill sludge has been enriched with N (as NH,OH) to enhance secondary wastewater treatment biological digestion. and the sludge may not require additional N to complete composting. PURPOSE AND OBJECTIVES The purpose of the research was to determine how much, if any, supplemental N is necessary to facilitate complete cornposting of the VFC papermill sludge. Research wits also conducted to determine the suitability of the papermill sludge compost as a potting mix constituent. Specific objectives were: I. To determine the effect of threerates of NH,NO, as a supplemental N source on the temperature relationships of composting papermill sludge and on chemical properties of the finished compost, and 2. To compare various proportions and size fractions of composted papermill sludge and a commercial soilless potting mix as media for plant growth. COMPOSTING STUDY PROCEDURES The composting study was conducted at the VFC production facility in Amherst, Virginia on a Virginia Department of Environmental Quality-approved clay-surfaced composting pad of low permeability and having a 2% slope. The downslope boundary of the pad was bermed using scraped topsoil to ensure that runoff was funneled to a collection point that drained to a retention pond. ExDerimental desien Three compost windrow treatments, consisting of papermill sludge plus three rates of fertilizer N, were:
Treatment 1 : Dewatered papermill sludge plus no supplemental N Treatment 2: Dewatered papermill sludge plus 30 Ibs NH,NOl per 1000 Ibs sludge (dry weight basis) Treatment 3: Dewatered papermill sludge plus 60 Ibs NH,NO, per 1000 Ibs sludge (dry weight basis) The ammonium nitrate was applied to the sludge when the windrows were formed. The treatments were designed to ensure that a wide range of C:N ratios were achieved at the start of composting. Each treatment was replicated four times and completely randomized within blocks. Windrow PreDaration Sludge windrows 12 to 18 feet wide at the base, 8 to IO feet high, and 30-40 feet long were constructed between 30 May and 1 June, 1995. The windrows were oriented to enable the runoff to drain toward the collection drain. Nitrogen was applied on June 5, and windrows were turned initially on the same day. Windrows were turned throughout the study with a front-end loader. Monitoring Temperatures were measured daily with long-stemmed thermometers to determine when windrows needed turning. The thermometer sensor was inserted about 24 inches below the pile surface at approximately 1/3 of the distance from the ground to the top of the pile in two locations in the windrow. Windrows were turned initially when the lowest temperature reading exceeded 130 F and the average of the two readings exceeded 135 F. Water was added to the piles as they were turned to approximate 50-60% moisture content ;sing the hand squeeze method. Later, windrows were turned and watered after temperature readings peaked as the windrows decomposed and failed to attain the initial high temperatures. Active composting and temperature monitoring was discontinued after 129 days (on 16 October, 1995). The compost was permitted to cure without turning an additional 35 days prior to screening for laboratory testing and for use in the greenhouse potting study. Analysis Compost was sampled from each treatment for analysis of total C, total Kjeldahl N (TKN), NOl-N, and NH,-N at composting initiation (2 June, 1995) and for NOl-N and NH,-N 14 days after composting initiation (2 1 June, 1995). Finished compost was analyzed for: ph; electrical conductivity (EC); total C; TKN; NO,-N; NH,-N; total P; Mehlich I-extractable P, K, Ca, Mg, Mn, B, Mo, Fe, and Zn; water-holding capacity; and stability based on reheating potential (Brinton, et al., 1995). GREENHOUSE STUDY A greenhouse container study employing various proportions of the non-n amended (treatment 1) finished compost and a commercial potting medium (Promix ) was conducted to determine the capability of the compost to support plant growth. We measured plant seed germination and growth response to various combinations of sludge compost and Promix to assess the quality of the compost. Plastic pots having a volume of 128 in3 (approx. % gallon) were used to grow four plant species (radish, snapbean, marigold, and hot green pepper) for yield and growth data in the following soilless media treatments: 1. Commercial potting mix (Promix ) 2. Composted papermill sludge a. 2 mm (0.08 in)< particle size diameter < 7 mm (0.28 in) b. particle size diameter < 2 mm c. particle size diameter < 7 mm 3. 50:50 mix of Promix and composted papermill sludge 2a a. 0 Ibs N/acre b. 60 Ibs N/acre 125
The growth medium treatment no.3b was the only treatment to receive supplemental N. All treatments were replicated three times and randomized within blocks for a total of 72 pots (4 plant species x 6 growth media treatments x 3 replicatiens). To equalize the effects of P and K from the growth media, all pots also received P and K at a rate of 60 Ibs P,O, and K,O per acre. Undrained pots (lined with plastic bags) were filled with growth media and watered to attain 90% field capacity on 20 November, 1995. Eight snapbean and ten of the radish, pepper, and marigold seeds were planted the next day, and the pots were covered with plastic film to preserve moisture until the seedlings emerged. The film was removed after emergence, and seedlings were counted and thinned to two per pot, except for the radish (4/pot). Germination was assessed for radish and pepper by measuring the percentage of seeds that germinated and emerged from the growth media treatments within 2 weeks of sowing. Water loss was replaced by daily addition of water to assure a constant pot weight (60% field capacity). The plants were harvested at maturity on the following dates: 4 January, 1996 (radish), 15 January (snapbean), 5 February (marigold), and 8-23 February (pepper). The following determinations of yield and growth were made after harvest: radish fresh roots and snapbean fresh bean pod and marigold flower pepper fresh fruit and oven-dried above ground biomass weights oven-dried above ground biomass weights number and pedicel length; oven-dried above ground biomass weight oven-dried above ground biomass weights RESULTS and DISCUSSION COMPOSTING STUDY Field monitoring Temperature patterns resulted in 16 windrow turnings (Fig. l-3), and water was added twice. Frequent rainfall during June supplied needed moisture, but composting efficiency may have been reduced by inadequate water additions during July and August. Temperatures rose immediately upon windrow formation and maintained those representative of thermophilic microbial activity for the 129 days of the study. The composting rate, as reflected by windrow temperature, was slower with no supplemental N than with the N additions during the initial three weeks as assessed by the standard errors of the means (not shown on figures). Temperature did not vary among the three treatments between late June and mid- September, but windrow temperatures were significantly higher with the highest NH,NO, rate than with the other N treatments during the last month of composting. The compost probably had not completely stabilized at the time that the experiment was halted as indicated by the windrow temperatures, which exceeded ambient temperatures (>I 10 F in all treatments). Furthermore, the final treatment temperatures were significantly higher with the higher N rate treatments (using standard errors of the means). The VFC stopped temperature monitoring and windrow turning before ambient temperatures were reached. ComDost analysis The concentration of mineral N in the fresh sludge was low (121 ppm mo,+nh,]-n), but the concentration of total N was I.22%. The total C concentration of 50.6% resulted in an initial C:N ratio of 4 1.5, which was higher than the normally recommended starting C:N ratio of 30: 1 for composting. Thus, supplemental N may have been required to facilitate optimum composting. Estimated C:N ratios for treatments 2 and 3. based on starting C and N concentrations ofthe sludge and known additions of fertilizer N. were 22.7 and 15.7, respectively. The effects of N treatments were evident 14 days after composting initiation as NH,- and NO,-N concentrations increased with the NH,NO, application rates (Fig. 4). Ammonium concentrations were more than twice as high as nitrate concentrations. N treatment did not effect the chemical properties of the finished compost, whose chemical analyses gave the following values: ph (mean=6.73), TKN (mean=1.75%), NH,-N (mean=l 1 ppm), total C (mean=37.2%), C:N ratio 126
0 v) T 0 m 0 0 cv T T 7 07 0 7 I27
4 0 x d\o\ 'X a 0 X a' 0 X Q) I l l oa x I l l 0 0 c9 cv 7 T 128
/94 x CQ Q Q) cn 0 0 9 m 0 N 0 T T Q Q) 0 cn 0 I29
I- z 0 u) 0 I30
Table 1. Effect of N rate on electrical conductivity and Mehlich I-extractable Cu concentration in finished compost. N Electrical Mehlich I rate conductivity cu (Ibs N/ 1000 ds/m PPm Ibs sludge) 0 1.67a 0.088 b 30 I.60a 0.145 b 60 1.19 b 0.210a Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test. (31.3), total P (mean=0.3 IYo), or Mehlich I-extractable P (mean=214 ppm), K (mean=247 ppm), Ca (mean4136 pprn), Mg (mean=449 pprn). Mn (mean=93 ppm), Zn (mean=26 ppm). or B (mean=4.8 ppm). The C concentration typically declined greatly, while N concentration increased slightly. Final N concentrations were not significantly different among treatments despite the differences in the initial concentrations of mineral N. Increased ammonia volatilization from the high N treatments may explain the equalization of compost N concentrations. The composted sludge is a fertile potting medium compared to the Promix (especially with respect to N and P), whose C:N ratio and the concentrations of TKN and total P were 64, 0.57%, and 0.12%, respectively. Total C concentrations were similar (37.2% for composted sludge VS. 36.5% for Promix ). Electrical conductivity was reduced and extractable Cu concentration was increased with the highest N rate (Table I), but the values were within recommended standards for high quality growth media. Reheating potential for the finished compost from the three N treatments were all between 18 and 36 F above ambient temperature. This values indicate that the material, while not completely cured, should support plant growth without phytotoxicity. Therefore, the three N treatments appeared to produce similarly stabilized compost despite the differences indicated by temperature responses. Water potential curves for the Promix, various particle size papermill sludges, and the Promix -papermill sludge mix demonstrated that Promix retained significantly more plant-available water than any papermill sludge or the Promix -sludge mix (Figure 5). The composted sludge retains and provides considerably less moisture for plant growth than does the commercial potting medium. GREENHOUSE STUDY Germination data (Table 2) demonstrated that the sludge compost was statistically equal to the Promix in terms of providing a medium for initiation of plant growth. The intermediate-sized compost provided adequate seedmedia contact for germination. The addition of N to the Promix -compost treatment did not influence yields, biomass production, or other measured plant parameters for any of the plant species investigated; therefore, the remaining discussion will address only the effects of growth media on plant parameters. Potting media treatments significantly affected vegetative and fruit yields and plant biomass in all species. The highest radish fresh root yields (Table 3) and snapbean fruit yields (Table 4) were produced in the Promix. The Promix -compost mix and the finest particle size compost also gave the high radish root yields, and increased snapbean leaf biomass above the larger particle size compost. Growth and yield differences may have been due to differential plant-available water related to water-holding capacity and particle size. 131
F L Q) U 132
Table 2. Radish and pepper germination data for seeds planted in various growth media. Sojlless Germination percentage media Radish Pepper I. Promix 95a 1 OOa 2. Sludge compost a.2mm<x<7mm 95a 95a b.<2mm 65 b c.<7mm 70 b 3. Promix-compost 2a 54 90a b Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test. Table 3. Effects of growth media on radish root yield and top growth biomass. Soilless media treatment 1. Promix ( 100%) 2. Sludge compost (100%) a.2mm<x<7mm b.<2mm c. < 7 mm 3. Promix-compost a (5O:SO) Radish root yield g/pot 58.5a 28.2 b 42.0ab 27.6 b 43.9ab Radish leaf biomass @Pot 3.02a 1.95 b 2.29 b 2.06 b 2.20 b Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test. Table 4. Effects of growth media on snapbean fruit yield and top growth biomass. Soilless Snapbean Snapbean media hit leaf treatment yield biomass 1. Promix 2. Sludge compost a.2mm<x<7mm b.<2mm c. < 7 mm 3. Promix-compost a dp0t 69.0a 34.6 b 40.2 b 45.6 b 64.1 a dp0t 13.5a 6.74 b 6.14 c 8.91 bc 12.lab Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test.
Table 5. Effects of soilless media on marigold flower number, pedicel length, and biomass. Soilless Marigold Marigold Marigold media flower pedicel leaf rreatment number length biomass no./pot cmlflower dp0t 1. Promix 24.8a 3.04a 7.63a 7. Sludge compost a.2mm<x<7mm 18.3 b 2.72 b 3.98 b b.<2mm 15.5 b 2.76ab 3.78 b c. < 7 mm 15.8 b 2.58 b 3.87 b 3. Promix-compost a 17.5 b 2.65 b 4.30 b Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test. Table 6. Effects of soilless media on pepper fruit number and yield, and biomass production. Soilless Pepper Pepper Pepper media fn it h i t leaf. treatment biomass number yield 1. Promix 2. Sludge compost a.2mm<x<7mm b. < 2 mm c. < 7 mm 3. Promix-compost a no.ipot gipot g/pot 10.0 16.0 b 1 1.7a 7.75 24.6 b 4.16 b 11.0 59.4a 12.7a 9.00 39. lab 12.4a 13.4 69.9a 16.0a Means within the same column followed by the same letter are not significantly different at the 0.05 level of probability by the Duncan s Multiple Range Test. Marigold flower number, pedicellength,and topgrowth biomass were highest withthe 100% Promix treatment, and plant parameters were reduced in all treatments that included composted sludge (Table 5). Lower water availability may have reduced composted sludge treatment yields. Pepper responded differently to the media treatments than the other plant species (Table 6). There was no effect of media on the number of pepper hit produced; however, the hit yields were greater in the compost-containing treatments than in the commercial potting mix. Pepper may use water more efficiently than radish, snapbean and marigold. In addition, the duration of pepper growth is longer than the other species, and the plant s greater nutrient requirements may have been better satisfied by the fertile compost than by the unamended commercial potting mix. CONCLUSIONS The papermill sludge produced a stable, mature compost although the heating cycle had not plateaued at ambient temperature. The time required to attain complete composting was longer than expected because the material was not optimally homogenized (via mixing) and watered. Under optimum conditions, the papermill sludge should completely compost in 8-12 weeks. The major differences between the commercial potting mix and the composted papermill sludge appeared to be related to the ability of the media to provide plant-available water and the high nutrient (especially N) concentration
of the compost. The commercial potting media held more water than the sludge at all water potentials, thus the commercial potting mix was a more effic~ent supplier of plant-available water. The stability tests, the C:N ratio, and the nutrient-content indicated that the compost was a high quality, fertile growth medium. The pepper probably performed better with some compost than in the commercial potting medium alone because the compost was able to maintain long term nutrient (especially N) availability for crop growth. Therefore, the papermill sludge is an adequate potting medium, but composting should be allowed to proceed until ambient air temperature is attained before the material is used as a high quality soilless media substitute. As produced, the material is best as an organic fertilizer, soil amendment, or supplemental nutrient source for potting media. The compost. will benefit from addition of a waterholding material such as peat moss, but its own water-holding characteristics can be improved by greater homogenization of the sludge during composting, co-composting with other materials that can increase the plantavailable water-holding capacity, and screening the final product. The finer material may be used as a potting medium and the coarser material as a soil amendmentlorganic fertilizer. LITERATURE CITED Bellamy. K.L., N. delint, N.F. Pridham, and R.A. Cline. 1990. Agricultural utilization of paper mill sludge in the Niagara area. Proc. 13th Intl. Symp. Wastewater Treatment and 2nd Workshop on Drinking Water, Montreal. P. 65-8 1. Brinton. W.F.. Jr.. Eric Evans, Mary Drofher, and Richard B. Brinton. 1995. Standardized test for evaluation of compost self-heating. Biocycle 36 ( I 1):64-69. Campbell, A.G., R.R. Engebretson, and R.R. Tripepi. 1991. Composting a combined RMP/CMP pulp and paper sludge. Tappi Journal. 74: 183-191. Chong, C., and R.A. Cline. 1991. Composts from paper mill wastes. Landscape Trades 13(9):8-1 1. Chong, C., and R.A. Cline. 1993. Response of four ornamental shrubs to container substrate amended with two sources of raw paper mill sludge. HortScience 28:807-809. Chong, C., and R.A. Cline. 1994. Response of container-grown nursery crops to raw and composted paper mill sludges. Compost Science & Utilization, Vol. 2. No. 3, 90-96. Chong, C., R.A. Cline, and D.L. Rinker. 1987. Spent mushroom compost and paper mill sludge as soil amendments for containerized nursery crops. Comb. Proc. Intl. Plant Prop. SOC. 37:347-353. Chong, C., R. A. Cline, and D.L. Rinker. 1991. Organic wastes as growing media. Comb. Proc. Intl. Plant Prop. SOC. 411315-319. Cline, R.A., and C. Chong. 1991. Putting paper mill waste to use in agriculture. Highlights Res. Ontario 14( l):16-19. Henry, C.L. 1991. Nitrogen dynamics of pulp and paper mill sludge amendment to forest soils. Water Sci. Technol. 24:411-425. Logan, T.J., and H. Esmaeilzadeh. 1985. Paper mill sludge evaluated for use in cropland. Ohio Rpt. 70(2)22-25. Pridham, N.F., and R.A. Cline. 1988. Sludge disposal: Completing the ecological cycle. Pulp and 89(2): 173-175. Paper Canada I35