BACK TO COMPOST SITE

CONCLUSIONS SUMMARY

1. A significant increase in microbial activity is supported by the higher temperatures achieved and sustained in the test heap, and was manifest in a more advanced state of degradation after two months.

2. Oxygen limitation may have limited the potential of the product in maintaining or increasing the physical disparity between the test and control heaps after two months. Assumption of a low oxygen

environment is supported by the low pH (caused by fermentation by-products) and probable denitrification in the test heap.

3. pH, if monitored, should be measured on site.

4. Benefit from the product could likely be increased by managing heap turning to balance the needs for high temperatures, mixing and oxygen. Temperature based management calls for turning the heaps when the average temperature exceeds 60 to 65oC (to re-aerate), or falls below 50 to 55oC (to remix).

Forced aeration through piping would reduce the required turning frequency.

5. There is no evidence that re-inoculation increased the rate of degradation.

6. Nitrogen was amended in excess of the amount needed, most likely due to overestimation of heap weight. The need for this practice can be determined by analyzing the carbon:nitrogen ratio and targeting 30 to 40:1 as a starting ratio. Leaf litter is typically nitrogen deficient.

INTRODUCTION

In November of 1991, Sybron Chemicals entered into a trial at the Gloucester County Utilities Authority (GCUA) to test the potential benefit of a compost acceleration product. The GCUA receives leaf litter from portions of Gloucester County every fall and winter. The litter is arranged into windrows and turned approximately once per month until deemed ready for soil conditioning, indicated primarily by a reduction in windrow size and other visual indicators such as particle size and compost color. This process normally requires 12-18 months. The finished product is available to county homeowners, farmers, and various county soil conditioning projects.

The operation is limited to accepting leaf litter from only a minority of the county's municipalities due to space limitations. The trial was entered to explore the potential for using the space more efficiently, thus allowing GCUA to turnover a greater portion of the county's leaf waste. Success would be indicated by a decrease in the time required to prepare the leaf litter for removal from the site. It was agreed that chemical monitoring of the leaf piles would be minimal since the cost to properly monitor parameters such as pH, and the carbon:nitrogen (C:N) ratio, among others, was prohibitive. Although such analytical data provides information that contributes to optimizing any given compost operation, the purpose of the current trial was to simply indicate the potential of the compost accelerator as a means of effecting an increase in site utilization. Options such as temperature dependant turning, monitoring C:N ratios, and forced air injection can be explored separately.

The compost accelerator product is composed of bacterial and fungal strains as well as several enzymes whose function is to increase the availability of organic material to the microorganisms. The strains chosen for the product complement normal compost cycling and seek to reduce the time required to achieve a given state of degradation. The bacterial strains dominate during the initial thermophilic phase when heap temperatures are elevated by microbial activity. The maturation phase is typified by reduced heap temperatures and the increased abundance of fungal strains (Streptomyces sp.)

METHODS

The trial began on November 12th, 1991. One normally sized windrow (approximately 150 yd3) was divided into two equal portions. One heap was left untreated to serve as a control while the other was inoculated with 200 grams of Leaf Compost Accelerator. To inoculate, the product was diluted at a ratio of 100 grams of product to 2 gallons of water, then manually sprayed over the leaves with common lawn and garden type applicators. The leaves had been spread out by a front-end loader to facilitate thorough coverage with the product. A multiple input temperature recorder was installed to monitor and record temperatures in both heaps. Inputs 1-4 were installed in the treated heap while inputs 5-8 were installed in the untreated heap.

Both heaps were turned by a front-end loader on a weekly basis. The front end loader operator would scoop a load of leaves, move to different area, and drop the load from a fully elevated shovel to aerate the heaps as they were turned. The shovel elevation was about 10-12 feet.

On January 23, 1992, the author took a set of photographs and the temperature recorder was removed for interpretation. On March 24, 1992, the test pile was re-inoculated with 100 grams of product and both piles were dosed with ammonium nitrate (NH4NO3) to prevent nitrogen deficiency from limiting the composting process. The ideal carbon:nitrogen (C:N) ratio for leaf litter is considered to be in the 30 to 40:1 range, while un-amended leaves can range as high as 100:1. Nine hundred pounds of NH4NO3

was added to each heap, based on an estimated heap weight of 50 tons. The temperature recorder was re-installed and the turning frequency was reduced to once every two weeks. The trial was completed on May 22, 1992 when samples were sent to Woods End Research Laboratory in Mount Vernon, Maine for analysis and the temperature recorder was removed for evaluation.

RESULTS

The results will be presented in two phases to reflect the break in monitoring that occurred between January 23 and March 24.

November 12, 1991 - January 23, 1992

Temperature data from this period covers 63 days and reveals that inoculation caused a rapid increase in temperature to over 60oC and that the treated heap's average temperature was significantly higher than that of the control heap for longer periods of time (see Figures 1 & 2). The regular dip seen in the temperature data over the first 35 days of the trial corresponds to days when the heaps were turned.

Throughout the first phase of the trial, visual observations supported the temperature data. Frost was observed on the control heap but not the test heap on several mornings, and on those mornings where frost was present on both heaps, it melted several hours earlier on the test heap. These observations were made by the front-end loader operator and are supported by Photos 1 and 2, which allow the test and control heaps to be distinguished by the amount of steaming. Photos 1 and 2 were taken after approximately one third of the contents of each heap had been removed from the end of each heap by the front end loader.

Photo 3 shows a close-up of samples collected from the exposed centers of each heap. The sample from the test heap is on the left side of the photo while the sample from the control heap is on the right.

The test heap sample is darker in color, smaller grained, and had a "earthy" odor while the control heap sample is lighter in color, less broken up, and smelled like dry leaves, without the "earthy" quality. The test heap sample is readily distinguishable from the original leaves while the control heap sample bears a much closer resemblance to the original leaves.

March 24, 1992 - May 22, 1992

Samples were submitted to Woods End Research Laboratory to determine chemical differences between the heaps. Table 1 shows the results on a dry matter basis.

TABLE 1

PARAMETER	TREATED	UNTREATED
Density (lbs./ft3)	23	26
Moisture (%)	46.1	46.2
PH	5.5	7.1
Organic Matter (%)	64.4	65.9
Conductivity (mmhos/cm)	4.2	9.1
C:N Ratio	20.7	12
Total Nitrogen (%)	1.68	2.97
Organic-N (%)	1.371	2.158
Ammonium-N (ppm)	3012	8069

DISCUSSION

Temperature data and visual observations during the trial clearly show a higher level of microbial activity in the test heap and indicate that a more advanced state of decomposition was achieved.

The results from these samples are similar for most of the tested parameters, with the exception of pH, nitrogen content, and the carbon:nitrogen ratio. The pH of 5.5 for the test heap sample is unusually low for deciduous leaf litter compost. It might be explained by the difference in activity between the test and control heaps. If this difference was similar to that evidenced by the temperature data in first phase of the trial, then the combination of high temperature and microbial activity could have created a largely

oxygen-less environment in the test heap, resulting in the formation of acidic by-products via fermentation.

A second explanation is that oxygen in the sample may have been consumed during transport to the lab, causing fermentative generation of acidic by-products. Note that the samples were transported in sealed plastic bags to prevent moisture loss.

Lower total and ammonia nitrogen in the test sample indicates a loss of nitrogen due either to denitrification or volatilization. High temperatures in the test heap seem to favor volatilization, but two factors point towards denitrification as the most likely pathway of loss. First, denitrification occurs only in oxygen deficient environments, which may well have existed in the test heap, as explained above.

Second, at low pH ammonia exists almost entirely as the non-volatile ammonium ion (NH4+). At a pH of 5.5, under equilibrium conditions, the ratio of NH4 +:NH3 is approximately 10,000:1. Significant volatilization will not occur below a pH of about 9.0.

The carbon:nitrogen ratios indicate that there was no deficiency of nitrogen in either heap at the end of the trial. In fact, the ratios indicate that too much was added, since the most favorable ratio is considered to be between 30 and 40:1. An excess of nitrogen will not enhance the degradation rate.

There is some question as to whether the samples were representative since it was not expected that the added amount of NH4NO3 would result in the low ratios obtained. However, there were no means of weighing the materials in the trial, and it is believed that the greater source of error was derived from estimating heap weight.

The reason for re-inoculation at the beginning of the second phase of the trial is due to observations during the first phase, which indicate that the majority of the differences seen in Photo 3 occurred during the month following the initial inoculation. It was desirable to see if re-inoculation would cause a subsequent increase in the physical disparity between the two heaps, and possibly become a necessary part of a managed program.

The visual differences evident in Photo 3 were not as marked at the end of the second phase of the trial.

This might be explained in light of the chemical disparities discussed above. If the test heap was indeed largely oxygen-less, fermentation would have predominated. It is important to note that fermentative

metabolism results in no net change in the oxidation state of the metabolic products relative to the substrates, and so can not result in the complete oxidation of organic matter to carbon dioxide (CO2).

In other words, fermentation transfers electrons from one organic compound to another organic compound. It is also true that fermentation proceeds at a slower rate than aerobic oxidation. Even though the temperature data clearly support a higher degree of microbial activity in the test heap, an aerobic environment is necessary for this activity to result in significant increases in the rate of mass reduction. Oxygen limitation in the test heap may have allowed the control pile to "catch up", accounting for the similarities in organic content of both heaps at the end of the trial (see Table 1).

BACK to compost SIDE