Patrick G. Hunt

Impact of pyrolysis temperature and manure source on physicochemical characteristics of biochar

While pyrolysis of livestock manures generates nutrient-rich biochars with potential agronomic uses, studies are needed to clarify biochar properties across manure varieties under similar controlled conditions. This paper reports selected physicochemical results for five manure-based biochars pyrolyzed at 350 and 700°C: swine separated-solids; paved-feedlot manure; dairy manure; poultry litter; and turkey litter. Elemental and FTIR analyses of these alkaline biochars demonstrated variations and similarities in physicochemical characteristics. The FTIR spectra were similar for (1) turkey and poultry and (2) feedlot and dairy, but were distinct for swine biochars. Dairy biochars contained the greatest volatile matter, C, and energy content and lowest ash, N, and S contents. Swine biochars had the greatest P, N, and S contents alongside the lowest pH and EC values. Poultry litter biochars exhibited the greatest EC values. With the greatest ash contents, turkey litter biochars had the greatest biochar mass recoveries, whereas feedlot biochars demonstrated the lowest.

Livestock waste-to-bioenergy generation opportunities

The use of biological and thermochemical conversion (TCC) technologies in livestock waste-to-bioenergy treatments can provide livestock operators with multiple value-added, renewable energy products. These products can meet heating and power needs or serve as transportation fuels. The primary objective of this work is to present established and emerging energy conversion opportunities that can transform the treatment of livestock waste from a liability to a profit center. While biological production of methanol and hydrogen are in early research stages, anaerobic digestion is an established method of generating between 0.1 to 1.3m3m(-3)d(-1) of methane-rich biogas. The TCC processes of pyrolysis, direct liquefaction, and gasification can convert waste into gaseous fuels, combustible oils, and charcoal. Integration of biological and thermal-based conversion technologies in a farm-scale hybrid design by combining an algal CO2-fixation treatment requiring less than 27,000m2 of treatment area with the energy recovery component of wet gasification can drastically reduce CO2 emissions and efficiently recycle nutrients. These designs have the potential to make future large scale confined animal feeding operations sustainable and environmentally benign while generating on-farm renewable energy.

The potential impacts of biomass feedstock production on water resource availability

Biofuels are a major topic of global interest and technology development. Whereas bioenergy crop production is highly dependent on water, bioenergy development requires effective allocation and management of water. The objectives of this investigation were to assess the bioenergy production relative to the impacts on water resource related factors: (1) climate and weather impact on water supplies for biomass production; (2) water use for major bioenergy crop production; and (3) potential alternatives to improve water supplies for bioenergy. Shifts to alternative bioenergy crops with greater water demand may produce unintended consequences for both water resources and energy feedstocks. Sugarcane and corn require 458 and 2036 m(3) water/m(3) ethanol produced, respectively. The water requirements for corn grain production to meet the US-DOE Billion-Ton Vision may increase approximately 6-fold from 8.6 to 50.1 km(3). Furthermore, climate change is impacting water resources throughout the world. In the western US, runoff from snowmelt is occurring earlier altering the timing of water availability. Weather extremes, both drought and flooding, have occurred more frequently over the last 30 years than the previous 100 years. All of these weather events impact bioenergy crop production. These events may be partially mitigated by alternative water management systems that offer potential for more effective water use and conservation. A few potential alternatives include controlled drainage and new next-generation livestock waste treatment systems. Controlled drainage can increase water available to plants and simultaneously improve water quality. New livestock waste treatments systems offer the potential to utilize treated wastewater to produce bioenergy crops. New technologies for cellulosic biomass conversion via thermochemical conversion offer the potential for using more diverse feedstocks with dramatically reduced water requirements. The development of bioenergy feedstocks in the US and throughout the world should carefully consider water resource limitations and their critical connections to ecosystem integrity and sustainability of human food.

Plastic Mulch Color Effects on Reflected Light and Tomato Plant Growth

Abstract Effects of plastic mulch color on upwardly reflected light and on the growth of tomato plants were investigated. Plants grown in sunlight over black polyethylene mulch had fewer axillary shoots (branches) and were taller than plants grown over white polyethylene mulch. The black surface reflected less total light and less blue light, but a higher ratio of far-red (FR) relative to red (R) light. In a controlled environment, tomato plants that were exposed to brief periods of FR at the end of the daily photosynthetic period were taller than those that received brief periods of R. The effect of FR on plant height could be reversed by R and implies phytochrome involvement. Differences in the light spectrum reflected from the plastic, and the similar differential responses to mulch color and light treatments, suggest that tomato plants grown in plastic mulch culture may respond to relatively small changes in light environment induced by the surface color of the mulch.

Improved nitrogen treatment by constructed wetlands receiving partially nitrified liquid swine manure

Denitrification is more desirable than ammonia volatilization for nitrogen removal from constructed wetlands treating animal manure but is limited by the availability of nitrate/nitrite. The research objective was to determine if partial nitrification of swine wastewater prior to wetland application affects the nitrogen removal and ammonia volatilization from constructed wetlands. From September 2000 through November 2001, partially nitrified and unaltered swine wastewater from an anaerobic waste lagoon were applied to two parallel sets of constructed wetlands (3.6 � /67 m) in North Carolina, USA. Constructed wetlands were more efficient at removing total nitrogen from partially nitrified (64 and 78%) than from unaltered wastewater (32 and 68%). Both wetlands were effective in removing nitrate/nitrite from partially nitrified wastewater. However, the Schoenoplectus -dominated wetland was more effective than the Typha-Echinochloa dominated wetland in removing total (85 vs. 61%) and ammoniacal nitrogen (91 vs. 52%) from both types of wastewater. Only one of eight tests showed significant evidence of ammonia volatilization (2.1 mg nitrogen m � 2 h � 1 ) when the wastewater was partially nitrified. A correlation (r 2 � /33%) between ammonia-nitrogen volatilization and ammoniacal nitrogen concentration suggested that partial nitrification reduced ammonia volatilization because it lowered ammoniacal nitrogen of the wastewater. # 2003 Elsevier Science B.V. All rights reserved.

Thermochemical conversion of livestock wastes: Carbonization of swine solids

Slow pyrolysis or carbonization promotes the conversion of animal manures such as swine manure into charcoal. In this paper, the carbonizing kinetics of swine solids taken from different treatment stages were investigated with a thermogravimetric analyzer. Compared to their biologically stabilized counterpart (lagoon sludge) with an activation energy of 160 kJ mol(-1), the activation energies for fresh swine solid samples such as homogenized flushed manure and dewatered solids were much lower between 92 and 95 kJ mol(-1). Compared to the kinetics of first order decomposition of cellulose, the pyrolytic decomposition of the swine manures were more complex with the reaction orders varying at 3.7 and 5.0. The two different mathematical methods employed in this paper yielded the similar values of activation energy (E) and pre-exponential factor (A), confirming the validity of these methods. The results of this study provide useful information for development of farm-scale swine solid carbonization process.

EXTRACTION OF SOLUBLE PHOSPHORUS FROM SWINE WASTEWATER

Manure phosphorus (P) in excess of the assimilative capacity of land available on farms is an environmental concern often associated with confined livestock production. A wastewater treatment process was developed for removal of phosphorus from livestock wastewater. It includes nitrification of wastewater to remove ammonia and carbonate buffers, and increasing the pH of the nitrified wastewater by adding an alkaline earth metal-containing compound to precipitate phosphorus. Since ammonia nitrogen has been mostly converted to nitrate, increased pH does not result in significant gaseous nitrogen loss. The amount of phosphorus removed, and consequently the N:P ratio of the effluent, can be adjusted in this process to match specific crop needs or remediate sprayfields. In addition to the phosphorus removal aspect, the high pH used in the process destroys pathogens in liquid swine manure. The final product is calcium phosphate, which has the potential to be reused as fertilizer or processed to produce phosphate concentrates.

Constructed wetlands for treatment of swine wastewater from an anaerobic lagoon

Animal waste management is a national concern that demands effective and affordable methods of treatment. We investigated constructed wetlands from 1993 through 1997 at a swine production facility in North Carolina for their effectiveness in treatment of swine wastewater from an anaerobic lagoon. We used four wetland cells (3.6 U 33.5 m) with two cells connected in series. The cells were constructed by removing topsoil, sealing cell bottoms with 0.30 m of compacted clay, and covering with 0.25 m of loamy sand topsoil. One set of cells was planted with bulrushes (Scirpus americanus, Scirpus cyperinus, and Scirpus validus) and rush (Juncus effusus). The other set of cells was planted with bur–reed (Sparganium americanum)and cattails (Typha angustifolia and Typha latifolia). Wastewater flow and concentrations were measured at the inlet of the first and second cells and at the exit of the second cell for both the bulrush and cattail wetlands. Nitrogen was effectively removed at mean monthly loading rates of 3 to 40 kg N ha –1 day –1 ; removals were generally >75% when loadings were <25 kg ha –1 day –1 . In contrast, P was not consistently removed. Neither plant growth nor plant litter/soil accumulation was a major factor in N removal after the loading rates exceeded 10 kg N ha –1 day –1 . However, the soil–plant–litter matrix was important because it provided carbon and reaction sites for denitrification, the likely major treatment component. Soil Eh (oxidative/reductive potential) values were in the reduced range (<300 mV), and nitrate was generally absent from the wetlands. Furthermore, the wetlands had the capacity to remove more nitrate–N according to denitrification enzyme activity determinations. Our results show that constructed wetlands can be very effective in the removal of N from anaerobic lagoon–treated swine wastewater. However, wetlands will need to be augmented with some form of enhanced P removal to be effective in both P and N treatments at high loading rates.

IMPACT OF SWINEWASTE APPLICATION ON GROUND AND STREAM WATER QUALITY IN AN EASTERN COASTAL PLAIN WATERSHED

Nonpoint source pollution from agriculture has been a major concern, particularly where intensive agricultural operations exist near environmentally sensitive waters. To address these concerns, a water quality project was initiated in Duplin County, North Carolina, in the 2044-ha Herrings Marsh Run watershed. A swine farm within this monitored watershed expanded its operation from 3,300 to more than 14,000 animals. Groundwater nitrate-N increased significantly in three of the seven wells located adjacent to the spray field and in the adjoining riparian zone. Stream nitrate-N concentrations have increased after the expansion of the swine operation in the colder months, but concentrations have remained approximately the same during the warmer months. Stream ammonia-N mean concentrations after expansion have increased as well as the frequency and magnitude of ammonia-N concentration spikes. Ortho-phosphate concentrations in the stream water have been relatively consistent over the study period. The riparian zone is reducing the impact of spray field groundwater nitrate concentrations and ammonia loadings in an adjacent stream.

AMMONIA VOLATILIZATION FROM CONSTRUCTED WETLANDS THAT TREAT SWINE WASTEWATER

Increasingly, large–scale animal production occurs in confinement where large per–unit–area quantities of waste are generated. With the increased scale of production, new environment–friendly technologies are needed to deal with the waste. Constructed wetlands are considered an alternative treatment, but it is not known if volatilization of free ammonia (NH3) governs nitrogen removal in these systems. The objective of this research was to quantify the NH3 volatilization from constructed wetlands that treat swine wastewater. In May and July of 2000, a specially designed enclosure was used to measure NH3 volatilization from constructed wetlands receiving swine wastewater. Laboratory and field calibration tests indicated that the enclosure was effective at measuring NH3 volatilization. Wetland tests indicated that NH3 volatilization was occurring. From average hourly rates, it was estimated that 7% to 16% of the nitrogen load to the wetlands was removed through NH3 volatilization. Although NH3 losses should not be ignored, results indicated that NH3 volatilization was not responsible for removing the majority of nitrogen from the swine wastewater.