Veterinary Medicine Teaching and Research Center
School of Veterinary Medicine
University of California, Davis
Tulare, Ca 93274

¹Veterinary Medicine Teaching and Research Center, ²Veterinary Medicine Extension, ³Population Health and Reproduction, and ⁴University of California Cooperative Extension, Fresno/Madera Count ies

March 3, 1999

Ash1.doc

In California, cogeneration plants burn various combustible materials to produce steam for the production of electricity. Much of the waste materials comes from agricultural waste in the form of wood, trees and rice hulls. Some plants burn coal while other located near lumber mills burn sawdust. At these facilities, the materials are burned at very high temperatures (1800 F) leaving only a powdery, gray ash which is commonly called fly ash. The oxide and carbon content and the pH of the fly ash varie s from plant to plant depending on which materials are burned (Photo 1). Currently many dairymen are experimenting with fly ash in cattle bedding materials hoping to control the growth of mastitis causing bacteria. In the past, other materials such as li me have been used for this purpose.

Since the Spring, 1998, studies have been conducted at the Veterinary Medicine Teaching and Research Center (VMTRC) in Tulare and on nearby dairies to determine the potential uses of fly ash in bedding on dairies. The primary focus of these studies ha s been on the use of fly ash mixed with various types of manure bedding. The aim was to determine if fly ash could significantly reduce the bacterial populations in the manure bedding. If such an effect could be documented, the use of fly ash might prove to be an aid in controlling environmental mastitis.

Our first studies were carried out under laboratory conditions at the VMTRC. Various types of manure such as separated manure from lagoons, free stall bedding manure and manure from alleys were mixed in varying proportions with fly ash in shoebox size , plastic containers. The fly ash in these experiments had a pH ranging from 12.2 to 13.0 and a calcium carbonate equivalence of about 57. The pH of the mixtures and the coliform bacterial populations were determine at mixing and then monitored for 3 wee ks after mixing without significantly changing the original mixture. No additional fly ash or manure was added to the containers after the initial mixing. As the proportion of fly ash increased in the mixtures the pH increased and the coliform count decr eased (Table 1). Significant reduction in coliform growth was noted when the mixture contained 15-25% fly ash and this reduction remained for up to 3 weeks. This level of fly ash in the mixture was associated with a pH greater than 10 which was the likel y reason for inhibition of bacterial growth (Table 2).

In a small scale germination study, tomato and radish seeds were planted in small containers with up to 20% of the same fly ash mixed into potting soil (Photo 2). The containers were placed outside in direct sunlight and watered daily. The radishes be gan germinating within 2 days and by 4 days, 70-80% of the seeds had sprouted in all the containers. Three containers with 20% fly ash had 100% germination of the radishes. The tomatoes germinated later and with a lower germination rate. In all cases, th e number of sprouted tomatoes in the fly ash mixtures exceeded that of potting soil alone.

In these field studies, faculty of the Milk Technology Laboratory, VMTRC, mixed a similar fly ash with either corral dried manure or manure separator solids and almond hulls. A 25% fly ash: 75% manure mixture was formed to be used as bedding material for free stalls. The bedding was thoroughly mixed prior to loading into free stalls. Another control stalls were bedded with only manure and almond hulls. This study was initially done with 50 test and 50 control stalls during warm weather and then repea ted with 100 test and 100 control stalls in cool weather (Photo 3). These mixtures were loaded into the free stalls on a seven-day cycle. Stalls were mechanically leveled daily. The stalls were hand-raked twice daily to remove moist bedding and manure pa ts. In randomly selected stalls, bedding samples for analysis were collected in a standardized manner on each loading day after loading, in the middle of the cycle and just before re-loading at the end of the week. Samples were cultured for bacterial num bers and the pH and moisture content were determined.

In these experiments, the bedding with fly ash lowered the bacterial numbers in the bedding during each loading cycle compared to the control bedding with manure and hulls. However, the difference was not great and by the end of each seven-day loading period the bacterial levels were similar. The bacterial growth was inhibited for about 2/3's of the loading cycle in the fly ash mixture compared to less than 1/3 of the cycle for the manure and hull mixture (Figure 1). It should be noted that excellent freestall bedding maintenance was practiced during this field trial.

The last experiment involved exposing cows to fly ash and observing for signs of teat or feet irritation. Cows were confined under dry corral conditions to an area covered with 6 to 8 inches of fly ash and composted manure (Photo 4). Mixtures of 25% a nd 50% fly ash were studied. Teats were washed and observed every 3 days. No signs of irritation were noted during a 50-day exposure period. In a shorter study at the VMTRC, four cows were held for 3 days in a small corral on which 2-4 inches of 100% fly ash had been spread. Each cow was observed at twice daily milking. No irritation was noted on the feet or teats after 3 days of exposure.

It is well to keep in mind that the fly ash from the different cogeneration plants varies significantly in its composition and thus its ability to alter bacterial growth. This depends mostly on the plant's fuel source. The materials burned in the plan ts include trees, rich hulls, sawdust, coal and other fuels. Predictably, most plants burn only a single fuel. The fuel source determines the pH and calcium carbonate equivalence of the ash. The pH of the fly ash is an important indicator of the bacteria l killing power so it is important to know the pH before using the fly ash. Fortunately, the pH can be easily measured using pH paper or a pH meter once a watery solution is prepared. The solution should contain about 10 grams of fly ash dissolved in 90 ml of water. The real killing power of the ash and its long term buffering power is due to the oxides in the ash, primarily calcium oxide. The calcium carbonate equivalence test of the ash can be performed in a laboratory to determine the buffering abili ty. Most soil test laboratories can determine the calcium carbonate equivalence for a cost of about $25.

Most fly ash is a very dry powder and moves readily with the wind or when handled. Care should be used when working with the ash to prevent injuries. A nose and mouth mask will reduce possibilities of inhalation. Protective goggles and gloves will red uce the hazard of irritation to the eyes and skin.

When fly ash is to be used in bedding, it is important to completely mix the ash into the bedding material. An old feed mixer wagon can serve as a good mixer. At this time, a 3 parts manure and 1 part fly ash mixture is suggested for fly ash similar t o the study ash. Wet weather will affect the texture of the ash resulting in clumps and make mixing more difficult. The fly ash intended for use in bedding should be kept under cover to prevent hardening when wet.

Fly ash from different plants may have a very different pH and calcium carbonate equivalence, therefore it is important to determine the characteristics of the fly ash before it is used as bedding. Based on our laboratory and field research up to this point, we feel that adding fly ash to manure bedding is of some benefit in reducing the bacterial load of the bedding. It remains to the determined if this is an economic benefit or produces a reduction in cow diseases such as environmental mastitis . There appears to be no harmful effect on animal health from adding fly ash to bedding. Adding fly ash to bedding certainly does not replace the need for good management practice focused on providing optimal comfort and sanitation in the cow bedding are as.

We gratefully acknowledge the financial support from the Milking Technology Laboratory at the VMTRC, William Sischo's Laboratory, Pacific Ultrapower Chinese Station, Mendota Biomass Power Ltd., Woodland Biomass Power Ltd., Delano Energy Company, a nd Cain Trucking Inc.