Food Waste Composting With Selected Paper Products

By Sung, Menghau Ritter, William F

Food waste composting with selected paper material was conducted in this study to determine the composting efficiency of various paper materials, (regular paper plates, Earthshell-made plates, and a commercial biogradable paper product) to be used in the food service industry, and to understand the effects of the finished compost as a growing medium. Composting experiments were carried out in three piles each with a total weight of approximately 340 kg and a height of 90 cm. Major ingredients in the compost recipe include food waste, dairy manure, and silage. Finished compost was mixed with a sassafras sandy loam in various ratios to grow corn and tomato plants in a greenhouse potting experiment. Composting experiment results indicated that the recipe we developed was very successful in disintegrating all types of paper products. The addition of 25% by weight of the finished compost in the composite growing medium had the least effect on plant germination and growth. Significantly different growth behaviors were observed between corn and tomato plants. Introduction

Today there is interest in developing biodegradable food service products to be used in fast food restaurants and amusement park food concessions like Bush Gardens or Walt Disney World. Since the products are to be biodegradable, there is the potential to compost the material with food waste. It has been demonstrated that composting is a viable alternative to landfilling for food waste. It has become a popular practice to add various paper products to composting operations. Although there are many common guidelines for this type of composting process, a trial study is still necessary to understand the effects of new biodegradable materials.

Adding various paper products, mainly packaging materials, in composting of food wastes has been performed both in the field and in the laboratory (Brink 1994; Itavaara et al. 1997; Kunzler and Roe 1995; Shin and Jeong 1996; Spencer 1991; Stutzenberger et al. 1970; Yu et al. 1991). Biodegradable packaging materials are mostly derived from starch, and belong to the following main classes (Bastioli 2001): (1) starch-based materials: starch is either used alone or complexed with natural or synthetic biodegradable polymers. (2) polylactic acid (PLA): starch is first fermented to obtain lactic acid, which is then polymerized to polylactic acid. (3) others: polyhydroxyalkanoates, protein and cellulose derivatives. In 2004, the market for bioplastic packaging was estimated to be 85,000 tonne, while world wide packaging demand was 12.2 million tonne (Plastic News 2007).

The European Committee for Standardization has developed a test scheme to verify the compostability of packaging materials (Degli- Innocenti and Bastioli 1997; Pagga et al. 1996). Four important factors are considered to define compostability: (1) physical persistence, (2) chemical persistence, (3) toxicity, (4) and the effect on the quality of compost. A series of testing schemes were developed to test these factors. In their confirmation test (i.e., composting test conducted under a similar environment in which the material ultimately will reside), degree of mineralization (production of CO2) compared to the reference material (cellulose) and disintegratability measured by particle size and thickness of test material were the major two parameters considered. The finished compost also has to satisfy several ecotoxicology tests to prove that there are no negative effects on compost quality.

Standard methods such as ASTM D5338-92 (ASTM 1993) are available to test degradability of biodegradable plastics in the composting process and they can generate highly reproducible data within a short test period (45 days). The percentage of decomposition is determined based on the difference in the amount of CO2 evolution from matured compost absent from any Biodegradable plastic. These methods are desirable if the degradation intermediates of biodegradable plastic do not promote or inhibit the degradation of the matured compost or do so to a limited degree (Ohtaki et al. 1998). However, it is impossible to examine the degradation of biodegradable plastics in a vigorous composting process. Therefore, methods that use fresh waste as a substituent for mahired compost to mix with biodegradable plastics are still necessary and have been performed in several cases (Ohtaki et al. 1998; Tosin et al. 1998).

Composting of waxed corrugated cardboard (WCC) has been practiced (Croteau and Alpert 1994; Raymond et al. 1997). The addition of 25%, and 50% (volume based) of WCC in the feedstock can significantly promote the decomposition as evidenced by the increased respiration rate in these trials compared to the controlled one (Raymond et al. 1997). The paraffin wax on the WCC has been proved to be inherently decomposable and is a readily available carbon source for many microorganisms (Hanstveit 1990; 1991). Some composting experiments focused on the degradation of specific components such as cellulose and lignin contents in the paper. Lignin is often treated as undegradable in compost (Haug 1993). This is mainly due to its complex polymer structure, which is very resistant to degradation (Kirk and Farrell 1987). Paper made of mechanical pulp usually contains up to 20% of lignin (Biermann 1993). The carbohydrate fraction of the paper materials associated with lignin is responsible for their slow degradation (Haug 1993; Kuhad et al. 1997; Stutzenberger et al. 1970). In some studies, thermophilic phase composting was found to be essential for lignin degradation (Tuomela et al. 2000). In addition, effects of finished compost on plant growth have been studied. It was found that compost from a mixture of food waste, waste paper and topsoil was rich in nutrients and could supply tomato plants with nutrients for a long time. However, compost from a mixture of food waste, milk carton and topsoil was found to be toxic to tomato plants (Brink 1994).

Overall, in addition to laboratory standard tests of compostability and degradability, there is still the need to conduct trial studies to understand the performance of the composting process and the quality of finished compost in the presence of biodegradable paper products in food waste composting. Specific objectives of this study were 1) to compare the degradation of three different paper products (regular food service plates, a commercial biodegradable paper product and Earthshell-made plates) in the composting process, 2) to monitor changes in materials during composting such as particle size, temperature, pH, and chemical compositions. 3) to conduct greenhouse pot experiments on the finished composted materials.

Materials and Methods

Food Waste Composting

Food waste was mixed with dairy manure and grass silage for all the composting trials. The materials mixture was similar to that which Perm State University used for their dining hall food composting project (Graves et al. 2000). Mushroom compost and leaf compost was also added as a seed along with a commercial composting seeding agent. Most of the food waste used in this experiment was purchased from a local grocery store and some of it (approximately 1/ 8 by weight) was obtained from the produce disposed by the grocery store. Dairy manure was freshly scraped from the University of Delaware dairy lot and the grass silage was obtained from silage stored on the University of Delaware dairy farm. The mushroom compost was obtained from a mushroom farm in Pennsylvania and the leaf compost was from the city of Newark’s composting site. The compost Bio-Excelerator” was purchased from the Espoma Company. Table 1 lists some of the chemical and physical properties of the compost materials.

TABLE 1.

Chemical and physical parameters for organic materials used for composting.

The recipe used in each pile trial had the following mass ratio:

manure: food waste: grass silage: inoculum:

plates = 101 kg: 55 kg: 64 kg: 16 kg : 60.

To start each pile, 32 kg of grass silage were first spread evenly on the ground, then, 55 kg of manure (premixed with Bio- Excelerator) was layered on the silage. Next, 27 kg of chopped food wastes plus 30 sets of regular paper plates (from the supermarket) that were cut into quarters were added evenly on top of the silage. The inoculum (mushroom compost) of 8 kg and some leaf compost were then added onto the top. The entire compost was then mixed extensively and water was added to adjust moisture content to the 50% to 60% range. This completed half of the pile. The above process was repeated to make the other half. These two half piles were then mixed together to make one pile. The entire pile was stacked to a height of about 90 cm in one corner of the composting chamber. Finally, broiler litter mixed with peanut shells was used to cover each pile to eliminate any odors that may have occurred. Two more identical piles were made following the same steps except that the commercial biodegradable made papers and Earthshell papers were added instead of regular paper plates. Both the number and size of the papers added were made the same as in the pile for regular plates.

All three piles were subjected to composting for two months from 08/02/2002 to 10/03/2002. During the first two weeks, each pile was turned twice a week. After that, it was turned weekly. Thermocouples and a data logger were employed to monitor temperature changes. The thermocouples were inserted at the top, middle, and bottom of each pile to record temperatures at these positions. Samples of compost in each pile were taken every three weeks and were analyzed at the University of Delaware Soil Testing Laboratory. Parameters analyzed included pH, total carbon, total nitrogen, moisture content, soluble salts, potassium, and total phosphorus. Pof Experiments

The cured compost was used to grow corn and tomato plants in 10 cm pots in the greenhouse. Sassafras sandy loam soil from the University of Delaware’s Research and Education Center (Georgetown, DE) was used as a control. The different composts were mixed with the sandy loam soil at mass ratios of soil to compost of 75%/25% (3:1), 50%/50% (1:1), and 25%/75% (1:3). The composite samples of the different growing mixtures were analyzed for carbon, nitrogen, sulfur, pH, soluble salts, and metals (K, Ca, Mg, Mn, Zn, Cu, Fe, B, Al). Each treatment was replicated three times. Four seeds of corn and four eeds of tomatoes were planted in each pot. The normal germination rate for the seeds was in the 85-90 % range. All pots were watered daily. Plant germination measurements were made after two weeks. Plants were grown for a total of six weeks and then were harvested. Plant heights were measured before harvest and the plant biomass was weighted. All samples were dried in an oven for 48 hours at 105[degrees]C and then ground for analysis of nitrogen, sulfur, phosphorus, potassium, magnesium, calcium, sodium, and other metals (B, Zn, Mn, Fe, Cu, Al).

FIGURE 1. Temperature data of ambient air and three compost piles.

Results and Discussion

Composting Experiments

The temperature data for each pile is shown in Figure 1. The data in Figure 1 is an average of four temperature readings in various positions of a pile where thermocouples were installed. During the turnings on August 9 and August 13, it was observed that there was an abundant amount of white mold in the compost and the piles were steaming. The mold gradually disappeared and on August 19, it was gone. It was evident that temperatures in all three piles were in the desirable thermophilic range. Within the first two weeks, they were well above 55[degrees]C, which is the critical temperature for killing human pathogens along with 3 days duration.(McFarland 2000). The temperature data indicated that the recipe used was successful in food waste composting. The composting process eventually reached the curing stage when the temperature dropped to the 38[degrees]C range.

The degradation of papers in all three piles was very efficient. In the first pile opening (two weeks after starting), it was not easy to detect paper products. All quarter-cut plates, commercial biodegradable made papers, and Earthshell papers were degraded to very tiny pieces. From visual observation, it was impossible to compare the degradation efficiency of three different plates. It is known that microorganism activity usually slows down above 60[degrees]C, and they could die or become dormant above 71 [degrees]C. During the first two weeks, the temperatures were between 60[degrees]C and 71 [degrees]C. Therefore, we believed that the initial fast degradation was mainly due to heat disintegration. Once the paper products broke down to pieces, they were in much better contact with the microorganisms. This helped in the further degradation of cellulous molecules. In some composting practices, temperature is regularly controlled below 60[degrees]C by turning or venting the pile when they are too warm. The purpose of doing that is to maintain a high microorganism activity. In our experiments, we did not try to maintain a constant temperature. Therefore, it is uncertain whether the temperature control would affect initial disintegration.

Data collected from Perm State’s audit indicated that the food waste generated from Penn State University dining halls was approximately 1.01 kg per patron (Graves et al. 2000). In each of our piles, there were 55 kg of food waste. This corresponded to the food waste of 54 people. The total number of plates we added in each were 60 sets. This essentially assumed that each person would consume one plate. However, from the initial fast disintegration, it was implied that the total number of plates in each could be increased. We believed that there was an optimal capacity for these heat disintegration effects. Also, changing the capacity can probably affect the final compost quality. However, it was not the objective of this investigation to determine this optimal capacity. But given this capacity can significantly enhance the design of food waste composting if paper products degradation was considered.

TABLE 2.

Data of compost analysis

The results of the compost analyses are presented in Table 2. It was evident that the pH of all three composts increased nearly 2 to 3 units within the first 10 days, and stabilized with only a minor decrease afterwards. The rise of pH can be attributed to the generation of ammonia from nitrogenous compounds. Under the initial pH (6 to 7.5), ammonia would react with hydrogen ions to form ammonium ions (NH+) and thus raise the pH. If we assume that ammonia is the only “- 3″ inorganic component of nitrogenous compounds, ammonia mass can thus be estimated from the difference between the total nitrogen and the Kjeldahl nitrogen. To do this, compost samples on August 19 were analyzed for Kjeldahl nitrogen. After carrying out the calculation, it was found that there was 29%, 15%, and 11% of ammonia in the regular, Earthshell, and commercial biodegradable samples, respectively. When the pH value went up to 8.5, ammonia gas would start to escape. The gradual decrease in pH after 2 weeks was probably due to the generation of organic acids. It can also be seen from Table 2 that the C/N ratio decreased due to the loss of CO2 from the starting materials. The percent of carbon loss exceeded the nitrogen loss. Consequently, the C/N ratios decreased.

Final compost quality can be characterized in four different grades: potting grade, potting media amendment grade, top dressing grade, and soil amendment grade (Rynk 1992). The most influential guideline to assign different grades is the soluble salt concentration. They have to be less than 2.5, 6, 5, and 20 mmhos/ cm, respectively, for the four grades, respectively. If compost has a higher salt concentration than required for a specific grade, it needs to be diluted with other materials before it could be used for certain plants. From data in Table 2, total soluble salts in our finished compost (data on 10/04) ranged from 12 to 16 mmhos/cm. Therefore, it could be recommended for use as a soil amendment for improvement of agricultural soils and restoration of disturbed soils.

Potting Experiment

The results of chemical analysis of the media used in the pot experiments are presented in Table 3. The EPA 503 Rule and the No Observed Adverse Effect Level (NOAEL) limits for Cu and Zn are 1500 and 2800 mg/kg, respectively. Therefore, compost media in our germination and growth tests had no toxic risk with respect to these two phytotoxic heavy metals. The C/N ratios of the compost media ranged from 7 to 9, which is somewhat lower than humus or stable soil that ranges from 9 to 12. Note that except for aluminum, elements in the compost media were higher than in the sassafras sandy loam soil. The control soil had relatively low concentrations of potassium and magnesium, therefore the addition of compost to the planting media increased the concentrations of those elements to comparable ranges of average soils. However, as can be seen later, growth in the control soil was usually better than in the compost mixture media. Consequently, effects of potassium and magnesium were not very critical (at this stage of growth). All compost mixtures were high in soluble salts, resulting from the use of dairy manure. According to previous compost quality guidelines, these media were suitable for potting media amendment or top dressing, but still not appropriate for potting grade media (total soluble salts < 2 mmhos/ cm).

TABLE 3.

Analysis of potting compost

Corn and tomato germination results after two weeks are presented in Figure 2. It was observed that the controls using pure sassafras soil had 100% germination in the corn pots. For corn at the soil to compost ratio of 3/1 the germination was dose to the control. For the tomato plants, the germination was about 93% (3.7 out of 4) for the control and when the soil to compost ratio was 3/1 a significant decrease in germination was observed. This phenomenon indicates that tomatoes are more sensitive to the compost addition than corn. As the soil to compost ratio increased to 1/3, germination decreased significantly. For pots with regular-plate compost there was nearly no germination for tomatoes at this ratio (1/3), which could be attributed to its high conductivity value (8.15 mmhos/cm) compared to the other two media (6.01 and 6.43 mmhos/cm for Earthshell and commercial paper, respectively). However, one should take into account the significant deviations that appeared in the data. One cannot conclude that the regular plates at the 1/3 ratio will completely stop gennination of tomatoes. It should be noted that plant heights and weights (see next section) need be considered when evaluating plant vigor. In addition, it was observed that corn plants usually had a germination of greater than 50% (i.e. 2 out of 4) when the ratio of soil to compost was at 1/1. For tomato plants, only the regular and Earthshell compost (at 1 /1 ratio) had over 50% germination but not for the commercial paper. As a general trend, the germination decreased as the compost portion in the pot increased. This was probably due to the high soluble salt concentrations. FIGURE 2. Germination number of corn and tomato seeds in pots with four seeds in each pot initially. For simplicity, only positive standard deviation is shown.

FIGURE 3. Height and weight measurements of corn plants. Only plants that germinated were measured.

Height and weight data in various pots for corn and tomatoes are presented in Figures 3 and 4, respectively. Data for corn plants (Figure 3) indicate that the control treatment had the greatest value in both height and weight. This together with previous germination results suggest that pure sassafras soil is the most effective media for growing corn compared to the other compost media. However, it was also observed that at the soil to compost ratio of 3/1, both the height and weight of corn was close to the control except for the Earthshell addition. This is probably because it had a higher salt concentration (4.17 mmhos/cm) than the regular paper (3.27 mmhos/cm) and the commercial paper (3.33 mmhos/cm) media. For the regular and commercial paper media, the height and weight of corn decreased linearly as the compost portion in the media increased. This was not observed for the Earthshell media, where the soil/compost ratio of 1/3 had a greater height and weight than the ratio of 1/1. It should be noted that variations in these 1/ 3 data were large, indicating that some corn plants in these pots were as tall and heavy as those in the 3/1 ratio, while others were short and light. The large variation could result from a smaller number of samples accounted for in these pots due to its low germination rate (see Figure 2).

Significantly different growth behavior was observed for the tomatoes. First of all, the controls did not have the best growth in terms of height and biomass weight as shown in Figure 4. In fact, the best growth was found for the soil to compost ratio of 3/1 for the commercial paper. Generally, both the commercial paper and the Earthshell media grew better than the control, but the regular paper media did not. Compared to corn, the tomato plants have a very linear relationship between height and biomass weight within six weeks. In other words, tomato plants with greater heights usually have greater biomass weight.

FIGURE 4. Height and weight measurements of tomato plants. Only plants that germinated were measured.

Conclusions

From this study, it was found that the regular food service plates, commercial biodegradable paper, and Earthshell plates were effectively composted. The temperature data indicated that a desirable thermophilic condition was reached. Most paper plates in the three piles were decomposed to a state beyond recognition, implying a success in disintegratability. The fast degradation rate implied that future recipes can consider more than one set of plates per 1.01 kg of food waste. From the final compost analysis, heavy metal concentrations were well below phytotoxic levels. However, due to the high salt concentration, the finished compost is recommended for use as a soil amendment. From the pot experiment, it was learned that the addition of 25% compost can be considered as the ratio not to affect germination and plant growth significantly. The results showed that the finished compost can be recommended as soil amendment grade. It is recommended that a higher salt-tolerant plant should be introduced as a comparison. Finally, effects of compost addition on plant growth are plant specific. Plant height and biomass weight of corn decreased significantly as the compost addition increased, while those of the tomatoes increased to various degrees upon the compost addition. This suggests that it is important to select an appropriate type of plant when using compost as a planting media.

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Menghau Sung1 and William F. Ritter2

1. Department of Environmental Engineering and Science, Chia Nan University of Pharmacy and Science, Tainan, Taiwan

2. Department of Bioresources Engineering, University of Delaware, Newark, Delaware

Copyright J.G. Press Inc. Winter 2008

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