Sarah K. Liehr

Development of a constructed subsurface-flow wetland simulation model

Abstract This paper presents a mechanistic, compartmental simulation model of subsurface-flow constructed wetlands. The model consists of six submodels, including the nitrogen and carbon cycles, both autotrophic and heterotrophic bacteria growth and metabolism, and water and oxygen balances. Data from an existing constructed wetland in Maryland were used to calibrate the model. Model results reproduced seasonal trends well. Interactions between the carbon, nitrogen, and oxygen cycles were evident in model output. In general, effluent biochemical oxygen demand, organic nitrogen, ammonium and nitrate concentrations were predicted well. Because little is known about rootzone aeration by wetland plants, oxygen predictions were fair. The model is generally insensitive to changes in individual parameters. This is due to the complexity of the ecosystem and the model, as well as the numerous feedback mechanisms. The model is most sensitive to changes in parameters that affect microbial growth and substrate use directly. This dynamic, compartmental, simulation model is an effective tool for evaluating the performance of subsurface-flow constructed wetlands. The model provided insights into treatment problems at an existing constructed wetland. With further evaluation and refinement, the model will be a useful design tool for subsurface-flow constructed wetlands.

Mechanisms of dinitrogen gas formation in anaerobic lagoons

Abstract Anaerobic lagoons have been widely used to treat agricultural waste and waste from small municipalities for many years. Oxidation of ammonia is generally assumed to not occur in such lagoons because of their anaerobic environment. Nitrification, the most likely process that would lead to ammonia oxidation, has not been considered a significant process in anaerobic lagoons because of the negligible concentrations of dissolved oxygen measured in these systems. Therefore observed nitrogen losses are usually assumed to be due to ammonia volatilization. However, in field studies of primary swine waste lagoons in the south-eastern US Coastal Plain, rates of dinitrogen (N 2 ) gas production have been observed to be much greater than rates of NH 3 volatilization. This paper discusses possible mechanisms that could explain observations of N 2 gas generation in anaerobic waste lagoons. Chemical and microbial reactions have been documented that combine ammonia with nitrite, or nitrous acid, to form N 2 under anaerobic conditions. Nitrification and denitrification reactions have also been observed under microaerobic conditions. Each of these reactions requires low levels of oxygen for the initial nitrification of ammonia to nitrite. Diffusion rates of oxygen through the lagoon surface appear to be adequate to allow enough nitrite formation to explain observed N 2 fluxes.

Ammonia Recovery from Swine Belt Separated Liquid

An evaluation of the feasibility of ammonia stripping for ammonia recovery from waste liquid resulting from an in-house belt separation system is presented. The liquid stream produced is a low-volume stream with a high concentration of ammonia and relatively low suspended solids. These characteristics make this waste stream favorable for recovery of the ammonia using physical/chemical processes. Immediate separation of liquids and solids greatly reduces ammonia volatilization, and the majority (77%) of excreted nitrogen remains in the liquid stream. This liquid also has high alkalinity, which means that a large amount of base is needed to raise the pH to a high enough level to achieve ammonia stripping. The need to raise pH can be reduced by raising the temperature. A countercurrent stripping tower process was tested at laboratory scale. The laboratory reactor used in this research was a PVC column of 0.15 m (6 in) diameter and 1.2 m (4 ft) height, packed with plastic media. Operating conditions of pH 8.0 – 10.5, temperatures of 45 – 60 oC, and gas:liquid flow ratio of 80 were evaluated. The trade-off between increasing pH and temperature are discussed in relation to the cost of the process. Results indicate that increasing the temperature to 50 – 60oC will significantly reduce the amount of pH adjustment needed for efficient stripping.

Engineering and Economic Approaches to Technology Evaluations: A Call for a New Approach

Environmental regulations related to manure management in large confined animal feeding operations have increased costs and focused producer interest in treatment or processing options that will help reduce the need for additional land used for nutrient uptake. Engineering and economic analyses have been used to evaluate various treatment options at the farm level but have not yet addressed the impact of emissions at larger spatial scales or the optimization of resource utilization from societys perspective. The purpose of this paper is to describe the short comings of past and present approaches to the development and evaluation of manure management systems, to suggest a new way of looking at environmental issues in food animal production, and to invite a discussion of new metrics of the problem and the solution. Some alternative ways of looking at confined animal feeding operations include 1) the ecological footprint of the industry or each individual animal species; 2) the equivalent solar energy, embodied energy or emergy, required to produce our food animal; 3), and the life-cycle assessment of our food animal production systems. Whatever tools are used or developed, the important insight is that we find ways to produce food and manage waste so that we make the most of what we have as a society, that we protect our natural resources for ecological stability and that we do not disrupt the income of producers of our food animals.

Quicklime Stabilization of Belt-separated Swine Manure Solids

Quicklime may be used to raise the pH of manure solids thus initiating a stabilizing effect of killing pathogens, reducing vector attraction, and controlling odors. A range of 5% to 15% quicklime doses were tested on separated manure solids. The largest dose (15%) rendered higher stabilization temperatures, a higher initial pH increase during mixing, and lower residual moisture in the stabilized product for the highest doses. Solids treated with doses of 10 and 15% quicklime can produce a stabilized product which meets the same requirements as Class A biosolid defined in Part 503 of the CFR 40. Manure treated with 10% quicklime lost approximately 80% of the original ammonia content over a period of 7 days through volatilization, an additional 10% was liberated over the next 21 days.

Dinitrogen Gas Collection Method for Lagoon Waste Treatment Systems

A method for collecting dinitrogen gas emissions from lagoon waste treatment systems was developed. The method was critically tested in a laboratory for sources of air contamination to ensure reliable gas measurements. The method was also tested in a laboratory to determine the significance of non-nitrogen bubbles stripping dissolved dinitrogen and influencing gas measurements. The results of these experiments revealed on average 0.57 % of N2 was contributed from air contamination and on average 3.5 % N2 contributed from nitrogen stripping in a 0.53 m water column. These results were used to estimate a dinitrogen volumetric mass transfer coefficient involved in the stripping process. This paper also includes the implementation of a simple design for applying the method for field use. The dinitrogen volumetric mass transfer coefficient was adjusted for field conditions and used to estimate the amount of dinitrogen stripped. The results reveal a positive linear relationship between the measured methane flux and the estimated rate of dissolved nitrogen stripped.

The Differences Between Production System, Production Capacity, and Ownership Structure and the Occurrence of Violations and Deficiencies on Permitted Swine Farms in Three North Carolina Counties

This study focused on understanding the factors that may influence the occurrence of regulatory violations on 108 permitted swine farms in three North Carolina counties, between 1997 and 2000. The goal of this study was to evaluate the relationship between swine production systems, production capacity, farm ownership, and cropping system with the occurrence of permit violations during regular and non-scheduled inspections of swine facilities. The majority of violations or permit deficiencies were related to the management of anaerobic lagoons. Lagoon liquid levels were observed to be within the lagoons 25-year, 24-hour storm storage level during 17.2% of all visits. Lagoon levels were only found within the lagoon 1-foot deep engineering freeboard on 6.1% of all visits during a period of heavy rainfall from three tropical storms during the summer and fall of 1999. Significant differences were found between the occurrence of permit deficiencies related to wastewater discharges and management of land application fields and the type of swine production system. Generally, as the production steady state live weight capacity increased, so did the occurrence of wastewater discharges, lagoon management and manure utilization violations. Farms with less than a halfmillion pounds steady state live weight were found to have significantly fewer manure discharges than those farms of greater capacity. The ownership of the swine farms was a significant factor in the occurrence of all groups of violations studied. Following three tropical storms, contract and independent growers reduced lagoon liquid levels, whereas on many corporately owned farms lagoon levels rose or remained at unsafe conditions from the preceding year. The disparity between corporate facilities and contract and independent farms suggests that factors, other than extreme weather, are influencing the occurrence of high lagoon levels and other permit violations.

Role of Internal Nutrient Storage in Duckweed for Secondary Swine Wastewater Treatment

This study aims to investigate a relationship of duckweed growth with nitrogen and phosphorus concentrations in swine wastewater and nitrogen and phosphorus content in duckweed biomass. Batch tests of Spirodela punctata cultured in SAM were conducted in a temperaturecontrolled growth chamber with 16-hour photoperiod. Results showed that there was an irregular lag period that growth continued after the nutrient concentration in the medium was exhausted. Prediction of growth using medium concentration as an independent variable therefore cannot describe this behavior. Luxury consumption, which suggests internal nutrient storage, was identified as key to connect growth with the nutrient uptake process. During 30-day growing period, nitrogen and phosphorus content varied from 59.7 to 19.7 mg/g and from 14.8 to 6.8 mg/g, respectively. Patterns of nutrient uptake in relation to internal nutrient storage were discussed.