F. J. Humenik

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.

SOLID-LIQUID SEPARATION OF SWINE MANURE WITH POLYMER TREATMENT AND SAND FILTRATION

Small particles typical of liquid swine manure often clog sand filter beds and fine filters. We evaluated the effectiveness of polymer flocculants to improve drainage and filtration performance of sand filter beds by increasing the particle size of manure. A pilot separation unit was evaluated at the Swine Unit of the NCSU Lake Wheeler Road Laboratory in Raleigh, North Carolina, in 40 consecutive cycles during a 20-month period. The unit consisted of a homogenization tank that mixed the flushed swine manure, an in-line polymer mixer, and two sand filter beds (29.7 m2) designed to receive 30.5 cm (1 ft) depth of the polymer-treated effluent. Flocculation treatment using polyacrylamide (PAM) polymer improved drainage characteristics of the sand filter by preventing clogging and surface sealing. The combination of flocculation and filtration treatment removed 97% of total suspended solids (TSS) and volatile suspended solids (VSS), 85% of biochemical oxygen demand (BOD5), and 83% of chemical oxygen demand (COD) from the flushed manure. Along with the solids, treatment resulted in capture of 61% total Kjeldahl nitrogen (TKN) and 72% total phosphorus (TP). Most of the nutrients removed in the solids were organic forms. Drying time to produce removable cakes varied significantly with the loading rate of solids applied to the sand filter bed. A load of <2 kg TSS m-2 per drying cycle allowed completion of the drying cycle in about 8 days, which is desirable to reduce potential fly problems. Our results indicate that PAM flocculation enhances performance of dewatering sand filter beds for swine manure applications.

EVALUATION OF A PERMEABLE, 5 CM THICK, POLYETHYLENE FOAM LAGOON COVER

Anaerobic lagoons and liquid manure storage basins are widely used for the treatment and storage of livestock and poultry manure. Although relatively inexpensive to construct, these devices have been widely criticized based upon their odor and ammonia release. A floating, permeable, composite cover manufactured from recycled polyethylene chips topped with a geotextile layer containing zeolite particles was evaluated under both laboratory and field conditions. Under laboratory conditions, the cover was found essentially to eliminate odor release and to reduce ammonia emissions by approximately 80%. When installed on a 0.4 ha swine manure lagoon in eastern North Carolina, the cover survived severe storms and allowed even intense rainfall to pass through without causing cover inundation. Under these field conditions, the cover was found to reduce ammonia emissions approximately 80%. Odor emissions measured twice during one month of the study were consistently low in concentration and near neutral relative to quality, as determined by an analysis by a trained odor panel. Microbiological examination of the cover after four months of use showed an active population of aerobic bacteria and protozoa; analysis showed that nitrifying, sulfide oxidizing, and methanotrophic bacteria were likely trophic components of the microbial populations observed. The surface of the cover became covered with an algal population within two weeks of installation. This and other vegetative growth had no discernable impact on the performance of the cover.

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.

Swine wastewater treatment by media filtration

A media filter was constructed to treat swine wastewater after anaerobic lagoon treatment. The media filter consisted of a tank (1.5-m-diameter x 0.6-m-height) filled with marl gravel. The marl gravel had a carbonate content of 300 g kg-1. Gravel particle size distributions were 85 and 14% in the 4.7- to 12.7-mm and 12.7- to 19-mm size classes, respectively. Pore space of the filtration unit was 57%. Wastewater flow rate was 606 L m-2 d-1, and total Kjeldahl nitrogen (TKN) load was 198 g m-2 d-1. The media filter removed 54% of chemical oxygen demand (COD) content after one cycle, but increased cycling did not produce additional COD reduction. Total suspended solids (TSS) removal after one cycle was 50% of initial levels, and additional cycling reduced TSS levels at a much lower rate of 7% per cycle. Removal efficiencies for total phosphorus (TP) ranged from 37% to 52% (one to four cycles), but long-term phosphorus removal would be limited by the sorption capacity of the gravel. Up to 24% of TKN was converted to nitrate-plus-nitrite-N (NO3+NO2-N). Effluents with high NO3+NO2-N levels can be treated further for denitrification with constructed wetlands or anaerobic lagoon. This is important in cases where land is limited for wastewater application.

Treatment of swine wastewater using a saturated-soil-culture soybean and flooded rice system

Constructed wetlands have potential for treatment of livestock wastewater, but they generally contain wetland plants rather than agronomic crops. We evaluated two agronomic crops, saturated-soil-culture (SSC) soybean and flooded rice, in a constructed wetland system used for swine wastewater treatment. Both crop production and treatment efficiency were evaluated from 1993 to 1996 in two 4-m ×33.5-m constructed wetland cells that were connected in series. The first cell contained SSC soybean — four cultivars planted in a randomized complete block design with four replications. Flooded rice ‘Maybelle’ was planted in the second cell. From the first to fourth year, wastewater application rates were gradually increased to obtain rates of 2.0 to 8.8 and 0.5 to 2.2 kg ha –1 d –1 for total N and P, respectively. The best soybean grain and dry matter yields were 4.0 and 9.1 Mg ha –1 , respectively. These were obtained with soybean ‘Young’ at the lowest wastewater application rate. Increasing total N loading rates and the associated higher NH 4 -N concentrations depressed soybean seed yield and dry matter production. On the other hand, both rice grain and dry matter production were stable over the application range; mean values were 4.0 and 10.9 Mg ha –1 , respectively. Nutrient mass reductions were good; removal values increased linearly with loading rates (y = 0.69N load + 0.45 , R 2 = 0.99 and y = 0.45P load + 0.20, R 2 = 0.95). At the highest loading rate, the system removed 751 and 156 kg ha –1 yr –1 N and P, respectively. It appears that the SSC soybean and flooded rice system could be useful for liquid manure management in confined livestock production. The system produced comparable treatment to systems with natural wetland plants; moreover, the soybean and rice are marketable crops. However, the flooded rice seems to be the more robust component for high wastewater application rates.

Nitrification options for pig wastewater treatment

Abstract Nitrification is a necessary and often limiting process in animal waste treatment for removal of nitrogen as N2 through biological nitrification/denitrification systems. We evaluated three technologies for enhancing nitrification of pig lagoon wastewater prior to denitrification: overland flow, trickling filter, and a bioreactor using nitrifying pellets. The overland flow system consisted of a 4 × 20‐m plot with 2% slope with a subsurface impermeable barrier receiving a total N loading rate of 64–99 kg N ha−1 day−1. Total N removal efficiency ranged from 36 to 42%, and 7% of the total N application was recovered in the effluent as nitrate. The trickling filter consisted of a 1‐m3 tank filled with marl gravel media which supported a nitrifying biofilm. Lagoon wastewater was applied as a fine spray on the surface at hydraulic loading rates of 684 litres m−3 day−1 and total N loading rates of 249 g m−3 day−1. The media filter treatment transformed up to 57% of the inflow total N into nitrate when wastewater was supplemented with lime. The nitrifying pellets technology used acclimated nitrifying cells immobilised in 3–5 mm polymer pellets. Pig wastewater was treated in an aerated fluidised reactor unit with a 15% (w/v) pellet concentration. Nitrification efficiencies of more than 90% were obtained in continuous flow treatment using total N loading rates of 438 g N m−3 day−1 and hydraulic residence time of 12 h. Two conclusions are suggested from this research: (1) that substantial nitrification of pig lagoon wastewater can be attained particularly using aerobic treatments with enriched nitrifying populations, and (2) that large mass removal of N from pig wastewater may be possible by sequencing nitrification and denitrification unit processes.