K. C. Stone

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.

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.

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.

COPPER AND ZINC ACCUMULATION, PROFILE DISTRIBUTION, AND CROP REMOVAL IN COASTAL PLAIN SOILS RECEIVING LONG-TERM, INTENSIVE APPLICATIONS OF SWINE MANURE

Trace metals like copper (Cu) and zinc (Zn) are added to animal feed as dietary supplements, and trace metals not assimilated by the animals gut are excreted in manure. The accumulation and movement of Cu and Zn in soils has not been as well documented when compared to nitrogen (N) and phosphorus (P). In cases where plant-available Cu and Zn concentrations accumulate to phytotoxic levels, yield may decline for sensitive crops. We investigated the accumulation of Cu and Zn in the topsoil (0 to 15 cm) and the soil profile (0 to 183 cm deep) and estimated uptake by Coastal Bermuda grass (Cynodon dactylon L.) in a Coastal Plain spray field after 4 and 10 years of swine manure effluent application. Effluent was initially applied to a 1 ha portion of this field, which was later enlarged to 5 ha. Top and subsoil samples were collected at nearby control sites that received no swine manure. All soil samples were extracted using Mehlich 3 (M3) and double acid reagent for plant-available and total Cu and Zn concentrations. Comparison of trace metal concentrations in the topsoil after 4 and 10 years of effluent application with control soils showed that total Cu, and M3 and total Zn had accumulated. Mehlich 3 and total Cu and Zn accumulation rates both declined after an increase in spray field area and decrease in effluent application rates. In a 1 ha region of the field, total Cu and Zn concentration both increased between 45 and 90 cm deep after 4 years of effluent applications. Across the 5 ha field, higher subsoil total Cu concentrations relative to controls suggest that Cu leaching occurred; however, leaching of Zn into the total pool was not significant. Estimated times through Coastal Bermuda grass uptake to reduce topsoil M3 Zn concentrations to background levels ranged between 21 to 152 years. Results from this study show that after 10 years of swine manure effluent application, mean topsoil M3 Cu and Zn concentrations were far below concentrations considered phytotoxic to sensitive crops.

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.

Flow-proportional, time-composited, and grab sample estimation of nitrogen export from an eastern coastal plain watershed

The balance between resources expended and information obtained is an integral aspect of water quality investigations. As part of a Water Quality Demonstration Project in the eastern Coastal Plain, we monitored stream water quality at the watershed outlet. Four methods of assessing stream water quality were compared. These methods were time-composite sampling with continuous flow measurements (TC), flow-proportional sampling with independent measurement of flow (FP), grab sampling with instantaneous flow measurements (IG), and grab sampling for quality assurance/quality control checks using daily USGS flow measurements (UG). Flow measurements using the TC and IG methods were highly correlated (r 2 = 0.97). Because of more intensive measurements during high flow, the FP method sampled greater flow rates during the sampling period. For all four methods, nitrate-N, ammonia-N and total Kjeldahl nitrogen (TKN) concentrations were not correlated to stream flow. Because of the significantly greater flow sampled, the FP method predicted significantly greater mass loading rates for both nitrate-N, ammonia-N, and TKN. Grab sampling (IG and UG) and the TC methods were not significantly different for the entire study period; however, a few monthly differences were significant. These results suggest that an appropriate sampling method should adequately weight sampling of both storm and base flows.

Constructed wetland design and performance for swine lagoon wastewater treatment

Although constructed wetlands have been identified as a potentially important component of animal wastewater treatment systems, their design requirements have been based mainly on municipal systems. The objective of this investigation was to examine various design approaches for constructed wetlands in relation to the performance of our constructed wetlands for swine wastewater treatment. The free water surface wetlands in Duplin County, North Carolina, investigated in this study were constructed in 1992 based on the Natural Resources Conservation Service (NRCS) presumptive design method. We used four wetland cells (3.6 m U 33.5 m) with two cells connected in series; the two series of cells were planted and predominated, respectively, by either bulrushes or cattails and were studied from 1993 to 1999. The wetlands were effective in treating nitrogen with mean total nitrogen and ammonia–N concentration reductions of approximately 85%; however, they were not effective in the treatment of phosphorus. Regression analyses of outflow concentration vs. inflow concentration and hydraulic loading rate for total N and ammonia–N were reasonably correlated (r 2 > 0.66 and r 2 > 0.65, respectively). Our calculated first–order plug–flow kinetics model rate constants (K20) for total–N and ammonia–N (8.4 and 8.9, respectively) were slightly lower than those reported in the limited literature and currently recommended for use in constructed wetland design. Nonetheless, use of our calculated rate constants would result in about the same size constructed wetland for treating swine lagoon wastewater.

DISSOLVED PHOSPHORUS TRANSPORT DURING STORM AND BASE FLOW CONDITIONS FROM AN AGRICULTURALLY INTENSIVE SOUTHEASTERN COASTAL PLAIN WATERSHED

The high density of animal production in southeastern Coastal Plain watersheds has caused some soils to contain excess amounts of plant–available soil phosphorus (P). Runoff, erosion, and leaching can transport P to surface water systems and out of these watersheds. High P concentrations in downstream aquatic ecosystems can increase the risk of eutrophication. Our objectives were to determine stream dissolved phosphorus (DP) mass loads transported under storm and base flow conditions and to examine relationships between precipitation, stream flow, and DP concentrations and export loads from an agriculturally intensive Coastal Plain watershed. This watershed was separated into four subwatersheds, and stream flows at their outlets were separated into base and storm flow conditions. Over the 2–year study period, stream base flow accounted for the majority of total stream flow at all outlets (58% to 73%). Average stream total DP mass loads at the watershed outlet in 1994 and 1995 were 234 and 477 mg DP ha–1 d–1, and higher DP mass loads (57% to 71% of the cumulative total) were exported during base flow conditions. In 1995, a series of intense storm events over two months caused a large DP pulse (approximately 63% of the stream’s yearly annual DP mass load) to exit the watershed. Regression analysis showed a linear relationship (P < 0.001) between log10 instantaneous stream flow and log10 DP export. Our results showed that more DP was exported during stream base flow conditions. However, intensive summer storms can greatly accelerate stream DP export from this agriculturally intensive Coastal Plain watershed.

PROCESS MODEL FOR AMMONIA VOLATILIZATION FROM ANAEROBIC SWINE LAGOONS INCORPORATING VARYING WIND SPEEDS AND GAS BUBBLING

Ammonia volatilization from treatment lagoons varies widely with the total ammonia concentration, pH, temperature, suspended solids, atmospheric ammonia concentration above the water surface, and wind speed. Ammonia emissions were estimated with a process-based mechanistic model integrating ammonia chemistry of the lagoon and interfacial transport characteristics between air and water. This improved model incorporated the effect of internal bubble production and continuously variable wind speed on ammonia volatilization measured at 10 m above the liquid surface (U10). Model simulations were compared to ammonia emission rates measured simultaneously at three contrasting lagoon scenarios: non-treated lagoon (13,633 kg ha-1 year-1), partially pre-treated manure using solid-liquid separation (3,699 kg ha-1 year-1), and treated manure using combined solid-liquid separation with nitrogen and phosphorus removal from the liquid (1,311 kg ha-1 year-1). The simulations only using average U10 with bubble enhancement or U10 distributions without bubble enhancement produced fluxes 42% and 44% below observed fluxes, respectively. However, the simulated fluxes using the U10 distributions along with bubble enhancement for the non-treated lagoon during warm seasons closely matched the observed fluxes (y = 1.04x, with R2 = 0.76). Ammonia emissions would be significantly underpredicted if bubbling-enhanced mass transport was not taken into account during warm seasons, as demonstrated by the improved process model and evidenced by the observed fluxes.