Effect of "Fly Ash" Byproduct From Electrical Co-generation Plant on Bacterial Growth In Various Forms of Dairy Cattle Manure

John Kirk¹, Charles Holmberg², Jerry Higginbotham³

Veterinary Medicine Extension¹ and Population Health and Reproduction², School of Veterinary Medicine, Veterinary Medicine and Research Center; Fresno County Cooperative Extension³, Universi ty of California, Davis

The combustion of wood waste from agriculture for production of steam or electricity creates localized sources of fly ash. Ash composition varies with the source of the waste wood being burned. In one study of pine sawdust ash, the pH was abou t 13 and the ash contained 18 to 26% Ca, 6 to 9% Mg, 0.4 to 11% K and 1.7 to 2.5% P. The temperature at which the waste was burn influenced the composition of the ash. Another study with hardwood ash found that they contained about 6% potash, 2% phosphor ic acid, and 30% lime. The agricultural use of wood waste is increasing (Wood Ash in Agricultural Uses of Municipal, Animal, and Industrial Byproducts, USDA Conservation Research Report Number 44, Jan 1998).

Dairymen are interested in using the fly ash byproduct from electrical co-generation plants in their corrals and bedding. The ash reportedly provides an good base material in the corrals when used at interfaces between concrete surfaces and dirt. The purpose of this study was to determine if the fly ash had any antimicrobial properties which might be of benefit in controlling potentially harmful bacterial populations in materials used for bedding on dairies.

The protocol called for fly ash to be mixed in various proportions with several types of manure. Manure was taken from the pile after separated from the waste water lagoon, from the alley at the feeders and from bedding in the freestalls. Afte r mixing and at later times, samples were taken and cultured for coliform bacteria and the pH of the mixtures was measured.

In most cases, manure mixtures were made up in triplicate. Manure samples were cultured using MacConkey's agar. This agar permits the growth of coliform bacteria of several types. The types were identified into three general types: lactose positive (+ ), lactose negative (-) and small (<2 mm) lactose negative (-). After the manure samples were mixed with sterile water, the pH was measured using a Coli-Parmer pH tester.

In a much less intensive test, fly ash was placed on top of freestall bedding. It was applied to provide a covering over the bedding of thickness of a sheet of paper to about the thickness of a sheet of cardboard (0.0144 gm/cm2 to 0.144 g/cm2). In hal f the tests, water was sprinkled over the test plots to simulate an approximate 0.5 inch rain.

Additionally, fly ash was spread on the ground where four milking cows were being held. About 80 pounds was scattered over approximately 2500 ft2. After three days, there was not visible effect on the teats of the cows.

The various forms of manure from a local dairy has a variety of coliform bacteria types and bacterial numbers (Table 1).

Table 1. Bacteria types and numbers (colonies/gram) in manure from dairy cattle.

The ranges of bacterial numbers are due to sampling in different locations and on different days. Thus the bacterial numbers varies for each type of bacteria that were grown.

There is also variation in the pH of manure from different sources on the dairy (Table 2).

Table 2. pH of manure from various source on the dairy.

The addition of fly ash to manure in the proportions tested reduced the numbers of bacteria which were recovered by culture on MacConkey agar (Tables 3-5). These tables should be compared to Table 1 to estimate the effect of the fly ash on bacterial g rowth.

Table 3. The distribution of bacterial growth (colonies/gram) on MacConkey agar at various proportions of separator manure and fly ash mixtures.

Table 4. The distribution of bacterial growth (colonies/gram) on MacConkey agar at various proportions of free stall bedding and fly ash mixtures.

Table 5. The distribution of bacterial growth (colonies/gram) on MacConkey agar at various proportions of alley manure and fly ash mixtures.

The addition of fly ash to the various forms of manure had the effect of raising the pH of the manure in all cases (Table 6).

Table 6. The pH distribution of various proportions of separator manure and fly ash mixtures.

 Table 7. The pH distribution of various proportions of alley manure and fly ash mixtures.

The pH range for free stall manure was 8.8 – 9.7. When mixed 50:50 with fly ash, the pH for free stall manure ranged from 10.7 – 11.9.

Table 8. The distribution of bacterial growth ( colonies/gram) on MacConkey agar at various proportions of separated manure and fly ash at 22 days after mixing.

Application of fly ash to the surface of bedding materials, with or without water added, had little impact on the bacterial populations or the pH.

The different manure types each had distinct bacterial populations. Separator manure had generally large numbers and more diverse types of coliform bacteria. The bedding manure had higher lactose+ populations and lower lactose-, particularly the <2 mm forms, than the separator manure. Manure from alley was more like the bedding manure in that it had high lactose+ populations and low lactose- populations.

Within two days after mixing fly ash with separator manure, the bacterial populations were significantly reduced. No bacterial growth was found at 50:50 or 75:25 ash:separator manure. Mixtures of down to 5% ash reduced the bacterial populations by gre ater than 90%. Mixing bedding from freestalls with ash at 50:50 proportions completely eliminated all types of bacterial growth at 2 days. Fly ash mixed with alley manure markedly reduced all types of bacterial growth at up to 25:75, ash:manure proportio ns. At 15:85, ash:alley manure, the lactose + bacterial growth was reduced by 60% while the other bacterial types were less affected. However, 5:95, ash:alley manure mixture reduced the lactose + bacterial growth by 20%, but had little effect on the lact ose - bacterial types.

Nearly 3 weeks after initial mixing, the populations of the lactose+ and larger lactose- bacteria were still markedly reduced compare to initial mixing and 2 days after mixing in ash:separator manure at 75:25 to 25:75 proportions. The smaller lactose- (<2mm) bacteria had made some recovery but were still reduced by 90% compared to the initial populations.

The pH of the fly ash was in the range of 12.0 to 13.0. Manure from the separator and bedding had a pH range of from 7.5 to 8.9, while the manure from the alley ranged from 8.8 to 9.7. Mixing fly ash with the various manure form generally increased th e pH as the proportion of fly ash increased.

Fly ash has a high pH compared to manure. Fly ash will reduce coliform bacterial growth when mixed with various forms of manure. The reduction seems to be in proportion to the increased pH of mixture. Under the circumstances of our study where no new manure was added to the mixtures after the initial mixing, the reduction in bacterial growth lasted for 3 weeks. The effect of the fly ash was greatest when the ash was mixed with manure rather than placing it on the surface of the manure.

We did no testing for any heavy metal or other chemical contaminates which might have been in the fly ash.

The fly ash should be tested under farm conditions in freestalls to see if the reduction in bacterial numbers would be seen when fresh manure and urine are added to the bedding. We have a cooperator dairy that would be very interested in testi ng the ash in their freestalls.

Additional test might need to be done to determine what if any affect the fly ash:manure mixture might have on crops where the mixture is spread for disposal.

The project was funded in part by the Mendota Biomass Power, Ltd. from Mendota, CA.