3.2.1 Manure source

Managing the amount of manure produced from the hundreds, sometimes thousands, of animals on the farm which house dairy cows, beef cattle, hogs, chickens, and other traditional farm animals, is a significant undertaking (Centner, 2004). In the US, 33.7 million head of cattle were slaughtered in 2006. Kansas and Nebraska were the first and second largest producers of commercial cattle, respectively, with each producing over seven million cattle. Texas was the third largest producer of commercial cattle with 6.48 million head (NASS, 2007).

The potential manure production from cattle in feedlots is over 365 million wet tonnes per year for the US; 70.4 million wet tonnes per year for Texas. Most of these cattle are kept in highly concentrated feedlot operations during the weeks before they are slaughtered. Potentially harvestable manure biomass from all of the concentrated animal feeding operations (CAFOs) in the US easily exceeds 100 million dry tonnes per year and 6-12 million dry tonnes in the Texas Panhandle alone. Sometimes it is cheaper to store them and spread it over the land. Feedlots in the Texas and Oklahoma panhandle regions can range between 5000 and 75,000 head (Harman,

2004) . The Texas Panhandle is regarded as the “Cattle Feeding Capital of the World”, producing 42% of the fed beef cattle in the United States within a 200-mile radius of Amarillo. Manure produced from the 7.2 million head fed each year amounts to more than 5 million tonnes/year
on an as-collected basis. Hence, it has been used extensively for irrigated and dry land crop production, and in some cases on CRP lands being converted to rangelands. Declining water tables in the Ogallala Aquifer and increasing fuel costs have reduced irrigation water use per acre. As these trends continue, they will likely reduce demand for manure as fertilizer in a per-acre basis. Cattle feedlots will encounter longer hauling distances to achieve P — or N-based nutrient balances on irrigated crops or dry land situations. The amount of manure to be applied is usually determined by the amount of nitrogen contained in the solids. One hectare of grass requires about 250 kg of N. Sometimes this can lead to an overloading of phosphorus on the land. Only recently have farms begun to switch to P-based land application and composting (Osei et al, 2000).

Apart from cattle feedlots, the number of dairy operations with more than 500 head of cows increased from 29% of all dairies in 1997 to 39% of all dairies in 2001. Even though the overall number of dairy operations in the US has declined to 91,240 in 2002, 86,360 in 2003, and 81,440 in 2004, the expansion in milk output is well established and should continue with only modest deceleration (USDA, 2005). This is because the number of larger, more efficient dairies, with over 500 head of cows, has increased while smaller dairies have begun to disappear (Keplinger et al, 2004; NASS, 2002). Among dairy cattle, feeder steers or heifers, each animal (having a live weight between 544 to 907 kg/head or 1200 and 2000 lb/head) produces between 27 to 57 kg (approximately 5 to 6% of its body weight) of wet manure per day containing 85-90% moisture and 10-15% solids (including volatile matter, nutrients, ash and combustibles; Fig. 3.3) (DPI&F,

2003)

. About 110,000 dairy cattle in over 250 dairies in Erath County produce 1.8 million tonnes of manure biomass (excreted plus bedding) per year. The dairy cows in this region make up about 25% of the total number of dairy cows in Texas (TX PEER, 1998). Dairy manure termed as dairy biomass (DB) is used over 7% of the landscape in the Bosque River Watershed.

Figure 3.3. (a) Manure production and environmental effects, (b) soil surfaced feedlot manure or high ash

feedlot biomass or HAFB (Carlin, 2009), (c) paved surfaced feedlot manure or low ash (LA) feedlot biomass or LAFB; (Carlin, 2009).

Currently most dairies, as well as other CAFO’s, utilize large lagoon areas to store wet animal biomass. Water along with nutrients seeps into the soil (Fig. 3.3). This has been the case, for example, in the Bosque River Region and Erath County, just north of Waco, Texas. Water runoff from these lagoons has been held responsible for the increased concentration of phosphorus and other contaminates in the Bosque River, which drains into Lake Waco, the primary source of potable water for Waco’s 108,500 people. Thus the growth of cattle, dairy and swine industries will likely exacerbate the nutrient balance situation (Annamalai et al., 2012). Further, when the manure gets very dry, the cattle’s feet grind the dry manure, creating a dust problem. Particulate matter (PM) or dust from feedlot ranges from 8.5 to 12 microns. The total suspended particles (TSP) in feedlot dust normally range from 150 ^g/m3 to 400 ^g/m3 but there are also reports having average values exceeding 400 ^g/m3 (Sweeten etal., 1979). The PM 10 regulation requires concentration of particles less than 10 ^m should be less than 150 ^g/m3. Moreover, when wet and composting manure streams decompose or anaerobically digest in relatively uncontrolled settings, such as poorly maintained manure storage lagoons, methane (CH4) and malodorous odors can form, reducing the quality of life near the farm (Mukhtar, 1999). A video demonstration on biogas from a digester is available at the web site Climatetechwiki (2010). Methane is also a very strong (about 24 times more harmful than CO2) greenhouse gas.

The total energy usage ranged from as low as 464 kWh per year per head (kWh/y/hd) for a pasture dairy inNortheast Texas, to as high as 1637 kWh/y/hd for a hybrid facility in Central Texas. Where possible, the electricity usage at the dairies was allocated to four main energy sinks: the milking parlor, the animal housing areas, feeding, and manure management. Generally, milking and housing components dominated the electricity usage for hybrid dairies, with the milking parlor being the primary consumer of energy for the open-lot facilities (Sweeten et al., 2012).

The total amount of agricultural manure in the 15 EU countries was estimated to be 1124 x 106 tonnes in 1993 which includes 887 x 106 tonnes from cattle (Eurostat, Waste Statistics). The total energy consumption of the 27 EU member countries in 2009 was 1,113.6 million tonnes of oil equivalent, the biomass consumption made up 7.5% with 83.68 Mtoe. 43.9 Mtoe was input to power plants. Figure 3.4 summarizes the contribution every biomass category can make to the total EU biomass potential. Note that animal waste based biomass makes up only less than 5% while forest (41%) and waste (38%) sectors can contribute the greatest share of the potential (AEBIOM, 2011).

Similar to feedlot and dairy cattle, broiler chickens are raised in confinement buildings i. e. chicken houses on a bed of material that can be straw, sawdust, or rice hulls, upon which the

I Dry manure C:, Wet manure i: Stla’.’.

‘■$І Verge grass [ ■ Prunings a: Animal waste К Organic waste industry і:; Paper cardboard waste I Common sludges I Dedicated cropping [. .1 Additional harvestable roundwood

■ Primary forestry residues

■ Black liquor

broiler chicken manure is deposited on the bedding, along with spilled feed and feathers over the life of the birds. Hence the waste material is termed poultry litter or broiler litter or litter biomass (LB). At the end of one or more growing cycles, the broiler litter is harvested by scraping out the chicken houses typically using a small wheel loader and must be stored, disposed of, or utilized.

Though the focus of the present chapter is on thermal energy (non-biological) conversion, a brief overview is presented on biological conversion, typically a slow process but producing medium quality gas (with HHV of almost 50% of natural gas).