Kevin Heflin

A Low Maintenance Approach to Large Carcass Composting

In recent years, costs of animal mortality pick-up have increased substantially due to reduction in demand for rendered products. Carcass disposal by burial has been the most common method while incineration of poultry and swine carcasses is also practiced in several states. These methods raise concerns over groundwater contamination at burial sites, and odor, air pollution, and unsuitability of disposing large carcasses by incineration. As the cost of dealing with mortalities and environmental concerns increase, the animal feeding operation’s (AFO) use and/or acceptance of on-farm mortality composting could very easily make it a preferred method of handling livestock losses. This paper presents results of a large- carcass (horse and cow mortalities) composting study using an in-bin, static pile composting system. Bins were created using large hay bales and spent horse bedding was used as a co-composting material. In one case, the carcass compost piles were turned at 3 and 6-month intervals after the start of composting. In the other case, the compost piles were built by placing the carcass above wooden pallets and turning the pile only once in a 6-month period. This was a low maintenance composting system because no pre processing of mortalities (cleaving, grinding etc.) was performed, no extra moisture other than that from the natural precipitation was added to the compost pile, and piles were turned no more than twice during the nine-month trial period. Within a few days after composting began, all piles achieved temperatures above 55 OC and remained at or above this temperature for several days or weeks. Turning piles without the wooden pallets after 3 months of composting resulted in a much greater temperature increase for the larger carcass (cow carcass weighing 909 Kg) than that for the smaller (horse carcass weighing 500 Kg) carcass. After six months of composting with and without the wooden pallets, similar carcass conditions in terms of faint odors and a high degree of large bone biodegradation were observed. After 9 months of composting, the C:N ratios of all compost piles were nearly one half of the horse bedding used as a co-composting material. Pathogenic evaluation of 9-month old carcass compost piles indicated low counts of salmonella and fecal coliform bacteria. The final product was ready to be land applied without the need to screen out large bones as they shattered and disintegrated easily. Based upon these results and observations, it was concluded that an in-bin, low maintenance carcass and horse bedding composting operation for the disposal of cow and horse mortalities can be carried out successfully in temperate climates during seasons of normal precipitation.

Combustion-Fuel Properties of Manure or Compost from Paved vs. Un-paved Cattle Feedlots

Research was conducted to determine the effects of feedlot surfacing materials (soil vs. coal-ash paved) and partial composting on feedlot biomass (FB) characteristics for use in thermochemical energy conversion involving reburn or co-firing with coal or lignite. FB was harvested from 12 fly ash-paved pens and 6 soil-surfaced pens and was windrow-composted. Higher heating value (HHV) before composting was more than twice as high for manure from paved (LA-FB) vs. soil-surfaced (HA-FB) pens, and ash content dry matter basis was 66% lower for FB from paved (20.2%) vs. un-paved pens (58.7%). Partial composting (51-55 days) reduced HHV by 2-20% to 5,704 BTU/lb (at 19.6% moisture) and 2,230 BTU/lb (at 17.0% moisture) for low-ash (LA-FB-PC)/paved pens and high-ash (HA-FB-PC)/un-paved pens, respectively.

Time-Varying PM10 Emissions from Open-Lot Dairies and Cattle Feedyards

Typical PM emission-factor studies for dairies and feedyards have involved measuring ground-level concentration as close to the plume centerline as weather predictions permit, followed by dispersion modeling using a single-valued emission factor to match the 24-hour average concentration. Using AERMOD as our dispersion-modeling platform, we confirm that the 24-hour average emission factor cannot reproduce the hourly average concentrations throughout the day and vastly underpredicts the magnitude of the evening dust peak. Moreover, matching a single concentration measurement near the plume centerline is not as rigorous a dispersion-modeling test as attempting to match an entire transverse cross-section of the plume along the downwind boundary.

Determination of Feedyard Evaporation Using Weighing Lysimeters

Six shallow, weighing lysimeters were installed near Etter, TX, to measure quasi-instantaneous evaporation rates from simulated feedyard surfaces. The data revealed a pronounced and consistent hygroscopic period during which the manure appears to have absorbed water from the atmosphere. Daily measurements during late autumn 2003 showed lysimeter evaporation to be 30% of reference evapotranspiration (ETo) of well-watered grass. Warm-season data from an upgraded load-cell system capable of continuous monitoring showed lysimeter evaporation to be poorly correlated with ETo, with a mean of approximately 20% and a range of 15-30%. The lower ratio in the most recent data may be attributed to (a) smaller manure particle size and greater sorptive affinity as compared to the first experiment, (b) increased evaporative demand in the warm-season experiment, which may not have been satisfied due to a flux-limiting hydraulic conductivity in the manure matrix and (c) other unknown factors that require further investigation. The hygroscopic behavior of the manure surface during the nighttime hours dramatically decreases the net daily evaporation, is loosely associated with a decrease in the vapor pressure deficit and reduces the expected water needs for feedyard dust control. Future investigations will quantify the sensitivity of the evaporation rate to surface roughness, manure particle size, target moisture content and advanced manure/soil layering procedures.

CO-FIRING COAL: FEEDLOT AND LITTER BIOMASS (CFB AND CLB) FUELS IN PULVERIZED FUEL AND FIXED BED BURNERS

Intensive animal feeding operations create large amounts of animal waste that must be safely disposed of in order to avoid environmental degradation. Cattle feedlots and chicken houses are two examples. In feedlots, cattle are confined to small pens and fed a high calorie grain-diet diet in preparation for slaughter. In chicken houses, thousands of chickens are kept in close proximity. In both of these operations, millions of tons of manure are produced every year. The manure could be used as a fuel by mixing it with coal in a 90:10 blend and firing it in an existing coal suspension fired combustion systems. This technique is known as co-firing, and the high temperatures produced by the coal will allow the biomass to be completely combusted. Reburn is a process where a small percentage of fuel called reburn fuel is injected above the NO{sub x} producing, conventional coal fired burners in order to reduce NO{sub x}. The manure could also be used as reburn fuel for reducing NO{sub x} in coal fired plants. An alternate approach of using animal waste is to adopt the gasification process using a fixed bed gasifier and then use the gases for firing in gas turbine combustors. In this report, the cattle manure is referred to as feedlot biomass (FB) and chicken manure as litter biomass (LB). The report generates data on FB and LB fuel characteristics. Co-firing, reburn, and gasification tests of coal, FB, LB, coal: FB blends, and coal: LB blends and modeling on cofiring, reburn systems and economics of use of FB and LB have also been conducted. The biomass fuels are higher in ash, lower in heat content, higher in moisture, and higher in nitrogen and sulfur (which can cause air pollution) compared to coal. Small-scale cofiring experiments revealed that the biomass blends can be successfully fired, and NO{sub x} emissions will be similar to or lower than pollutant emissions when firing coal. Further experiments showed that biomass is twice or more effective than coal when used in a reburning process. Computer simulations for coal: LB blends were performed by modifying an existing computer code to include the drying and phosphorus (P) oxidation models. The gasification studies revealed that there is bed agglomeration in the case of chicken litter biomass due to its higher alkaline oxide content in the ash. Finally, the results of the economic analysis show that considerable fuel cost savings can be achieved with the use of biomass. In the case of higher ash and moisture biomass, the fuel cost savings is reduced.