Gudigopuram B. Reddy

Soil bacterial communities in constructed wetlands treated with swine wastewater using PCR-DGGE technique

Marsh-pond-marsh (MPM) constructed wetlands were designed for the treatment of swine wastewater. The goal of this study was to characterize bacterial communities in these wetlands and determine the nutrient removal from influent to effluent. Surface soil samples were collected and analyzed by culture-dependent and culture-independent techniques. The results showed that the bacterial colony forming units (CFU) and the average concentrations of total nitrogen, NH(4)(+), total phosphorous (TP) and PO(4)(3-) from the influent to the effluent decreased. The NH(4)(+) and the PO(4)(3-) concentrations showed the most dramatic changes, with decreases of 39.97% and 16.92%, respectively. Data of culture-independent samples produced by using PCR-denaturing gradient gel electrophoresis (DGGE) technique showed that the Shannon diversity index and richness decreased significantly (P<0.05) from influent to effluent. Bacterium species distributions strongly correlated with the concentrations of TP, NH(4)(+) and the PO(4)(3-). Sequencing of partial 16S rRNA genes fragments revealed that the total bacterial community composition was dominated by Pseudomonas sp., Arthrobacter sp., Bacillus sp. and other soil bacteria. Anammox (anaerobic ammonium oxidation) stains were detected. Phylogenetic analysis demonstrated that some of the partial 16S rRNA gene sequences had close relationships with unculturable denitrification bacteria. The activities of these bacteria might contribute to the nutrient removal in the wetlands.

Sorption and desorption of ammonium by zeolite: Batch and column studies

The major objective of this research was to investigate the efficiency of zeolite in the removal of NH4-N from swine wastewater and desorption of the sorbed NH4-N from the zeolite saturated with N. Sorption experiments were conducted on the sorbents, zeolites I, II and III. Zeolites II and III which are natural and unmodified, showed better sorption (4400–4500 mg kg−1 with 500 mg L−1 feed concentration) compared to Zeolite I (3053 ± 127 mg kg−1 with 500 mg L−1 feed concentration), which is a surfactant modified zeolite. Freundlich and Langmuir isotherms were plotted from the sorption experimental data. Column studies indicated that, columns with flow rates of 2 and 3 mL min−1, reached the breakthrough point within about 100 h. The possibility of regeneration of the column material was investigated by flushing the column with 0.1 N HCl. The results from this experiment showed that even after desorption with DI water for more than 250 h, considerable amount of N was still available in the column that was available for desorption by 0.1 N HCl. This confirms that zeolite could be a good substrate for slow N release in soil. The application of Zeolite II for the NH4-N removal from swine wastewater supports this observation.

Nutrient removal and bacterial communities in swine wastewater lagoon and constructed wetlands

Surface constructed wetlands, including marsh-pond-marsh (MPM) and continuous marsh (CtM) were used to treat swine wastewater in this study. The objectives of this research were to evaluate the surface constructed wetland effects on swine wastewater treatment, and to investigate bacterial distribution shifts along treatment flows. Water quality parameters and bacterial community diversity were analyzed in each section of the entire wastewater treatment system, which was from the anaerobic lagoons (La1 and La2), through the wetlands, to the storage lagoon (La3) receiving wetland effluent. The results of water quality parameters demonstrated that the concentration of TKN, NH+ 4, o-PO3− 4, and COD decreased significantly (P < 0.05) from La1 to La3. If ammonia volatilization is integrated for N removal in MPM wetland cell, then there was no difference between MPM and CtM cells. The total bacterial community in each section of the system was examined by using PCR-DGGE (polymerase chain reaction-denaturing gradient gel electrophoresis) technique. Our finding disclosed that the bacterial communities in different sections of the wastewater treatment system showed high diversities. The bacterial community compositions shifted gradually with the wastewater treatment procedure. Principal component analysis (PCA) and redundancy analysis (RDA) confirmed that the bacterium species distribution was strongly related to the COD, o-PO3− 4, and TKN concentrations, whereas moderately related to the NH+ 4 concentration. Flavobacterium sp. and Methylomonas sp. were detected according to partial 16S rRNA gene sequences.

Comparison of aerated marsh-pond-marsh and continuous marsh constructed wetlands for treating swine wastewater.

Increased swine production in North Carolina has resulted in greater waste generation and is demanding some emerging new innovative technologies to effectively treat swine wastewater. One of the cost-effective and passive methods to treat swine wastewater is using constructed wetlands. The objective of this study was to evaluate the N removal under two N loads in 3 different wetland systems: aerated marsh-pond-marsh (M-P-M), aerated marsh-covered pond-marsh (M-FB-M), and continuous marsh (CM) with two days drain and five days flood cycle. Swine wastewater from an anaerobic lagoon was applied to the constructed wetland cells (11 m wide x 40 m length) at two N loading rates of 7 and 12 kg N ha−1 day−1from June to July and August to September 2005, respectively. Weekly inflow and outflow samples were collected for N, P, TS, and COD analysis. Total N reductions (%) at low and high N loading rates were 85.8 and 51.8; 86.3 and 63.3; and 86.2 and 61.8 for M-P-M, M-FB-M, and CM, respectively. Aeration had no significant (P > 0.05) impact on N removal. However, significant (P < 0.05) differences were observed for wetland systems between low and high N loading rates. No difference (P > 0.05) in N reduction was found among wetland systems. Vegetation uptake of N was negligible, ranging from 1.2 to 1.8 %. No significant (P > 0.05) differences in TS and COD removal were observed between the wetland systems.

Oxygen transfer in marsh-pond-marsh constructed wetlands treating swine wastewater

Oxygen transfer efficiencies of various components of the marsh-pond-marsh (M-P-M) and marsh-floating bed-marsh (M-FB-M) wetlands treating swine wastewater were determined by performing oxygen mass balance around the wetlands. Biological oxygen demand (BOD) and total nitrogen (TN) loading and escaping rates from each wetland were used to calculate carbonaceous and nitrogenous oxygen demands. Ammonia emissions were measured using a wind tunnel. Oxygen transfer efficiencies of the aerated ponds were estimated by conducting the ASCE standard oxygen transfer test in a tank using the same aeration device. Covering pond water surface with the floating bed slightly decreased oxygen transfer efficiency. The diffused membrane aeration (26.7 kg O2 ha-1 d-1) of M-P-M was surprisingly not as effective as plant aeration in the marsh (38.9 to 42.0 kg O2 ha-1 d-1). This unusually low oxygen transfer efficiency of the diffused aeration was attributed to its low submergence depth of 0.8 m compared to typical depth of 4.5 m. The wetlands consisting entirely of marsh removed similar amounts of C and N without investing additional equipment and energy costs of aerating ponds in the middle of wetlands.

Sorption and desorption of phosphorus by shale: batch and column studies

Constructed wetland systems have gained attention as attractive solutions for wastewater treatment. Wetlands are not efficient to treat wastewater with high concentrations of phosphorus (P). In order to remove high soluble P loads by wetland, sorbent beds can be added prior to the discharge of wastewater into wetlands. Sorption by sorbent materials is identified as a method for trapping excess P in wastewaters. In the present investigation, shale has been identified as a sorbent material for removal of phosphate (PO(4)-P) due to the cost effectiveness, stability and possibility of regeneration. The study focuses on the removal of PO(4)-P from wastewater using shale and the feasibility of using the P-sorbed material as slow-release fertilizer. Phosphorus sorption experiments were conducted by using shale (2 mm and 2-4.7 mm). Results indicate that Shale I (particle size = 2 mm) showed the highest sorption of PO(4)-P (500 +/- 44 mg kg(-1)). Breakthrough point was reached within 10 h in columns with flow rates of 2 and 3 ml min(-1). Lower flow rate of 1 ml min(-1) showed an average residence time of about 2 h while columns with a higher flow rate of 3 ml min(-1) showed a residence time of about 40 minutes. Variation in flow rate did not influence the desorption process. Since very low concentrations of PO(4)-P are released, Shale saturated with PO(4)-P may be used as a slow nutrient release source of P or as a soil amendment. The sorbent can also be regenerated by removing the sorbed PO(4)-P by using 0.1 N HCl.

Swine Lagoon Wastewater Treatment in Marsh-Pond/Floating Wetland-Marsh Constructed Wetland

Constructed wetlands have been used effectively to reduce the mass loads of organic and nutrient components from swine anaerobic lagoons. Continuous marsh wetlands with gentle slope and intermittent flows seem to be the best for promoting oxidation and minimizing ammonia volatilization. However, the pond section of the marsh-pond-marsh section could potentially be effectively aerated by mechanical means or plant root transport from selected wetland plants. The objective of this research was to determine if covering the pond section with floating wetland vegetation could enhance nitrogen cycling, reduce ammonia volatilization, and lower estrogenic levels. Marsh-pond-marsh wetlands were retrofitted with a floating fabric cover containing slots for wetland plant establishment. Both mechanically aerated and naturally aerated conditions were evaluated for estrogenic component removals, ammonia volatilization, and total nutrient removals. Both the covered and uncovered wetlands reduced the estrogenic levels in the swine wastewater. The floating marsh substantially reduced the ammonia volatilization, but it did not promote significantly greater nitrogen treatment than reported for continuous marsh wetlands.

Carbon sequestration in a surface flow constructed wetland after 12 years of swine wastewater treatment.

Constructed wetlands used for the treatment of swine wastewater may potentially sequester significant amounts of carbon. In past studies, we evaluated the treatment efficiency of wastewater in a marsh-pond-marsh design wetland system. The functionality of this system was highly dependent on soil carbon content and organic matter turnover rate. To better understand system performance and carbon dynamics, we measured plant dry matter, decomposition rates and soil carbon fractions. Plant litter decomposition rate was 0.0052 g day(-1) (±0.00119 g day(-1)) with an estimated half-life of 133 days. The detritus layer accumulated over the soil surface had much more humin than other C fractions. In marsh areas, soil C extracted with NaOH had four to six times higher amounts of humic acid, fulvic acid and humin than soil C extracted by cold and hot water, HCl/HF, and Na pyruvate. In the pond area, humic acid, fulvic acid and humin content were two to four times lower than in the marsh area. More soil C and N was found in the marsh area than in the pond area. These wetlands proved to be large sinks for stable C forms.

Sorption and Desorption of Nitrogen and Phosphorus by Zeolite and Shale

Wastewaters from animal houses contain excess of nutrients namely nitrogen (N) and phosphorus (P) apart from suspended solids and organics. Therefore, cost-effective technologies to remove N and P need to be developed. Sorption methods using the appropriate solid sorbent can be promising since this would serve as a nutrient trap which could be recycled as a nutrient source or soil mulch. Several sorbents have been investigated so far. Due to the cost effectiveness, stability and possibility of regeneration of shale and zeolites as filter media, these materials have been chosen as sorbents in the present investigation. The study focuses on the removal of N and P from wastewater using zeolite and shale and the feasibility of using the nutrient-sorbed material as slow-release fertilizers. Sorption experiments were conducted by using shale (2 mm and 2–4.7 mm) and zeolite (1 mm and 2–4 mm). Varied concentrations of N and P solutions ranging from 0 to 1000 mg L–1 were prepared from NH4Cl and KH2PO4 respectively. Results indicate that Shale 1(particle size = 2 mm) showed the highest sorption of P (170 ± 10 mg kg–1). But, the percent sorption of P was found to have a decreasing trend with increasing concentration of P in solution. Shale 2 (particle size = 2-4.7 mm) of larger particle size showed comparatively lower sorption. Both Shale 1 and 2 showed significant (R2 = 0.9566 and R2 = 0.9333) sorption of P over the P concentration in solution. Zeolites showed approximately 90% sorption of NH4, over a wider range of feed concentrations ranging from 50 to 1000 mg L–1 . The percent desorption was about 30 % of initial phosphate concentration ranging from 200 to 1000 mg L–1 when shale 1 was used as the sorbent. Shale 2 showed a percent desorption of more than 30% after 24 h desorption in deionized water. Zeolites 3 and 4 show very low desorption of less than 10%. Even though the percent sorption of NH4 in 24 h was high, the release of NH4 was slow and hence, zeolite would serve as a substrate with a property of slow ammonia release.

Ammonia and Greenhouse Gas Emissions from Constructed Wetlands Treating Swine Wastewater

Ammonia and greenhouse gas emissions from marsh-pond-marsh constructed wetlands treating swine wastewater were measured with closed-chamber technique using a photoacoustic multigas analyzer. Theory behind the technique was discussed and the technique was demonstrated with actual field data. Nitrous oxide emission was negligible for all three constructed wetlands. Methane readings were not reliable due to the interference caused by the moisture and other short hydrocarbons in the PVC chamber headspace. Ammonia volatilization rates of different sections varied from 0.64 to 1.6 kg-N/ha/d, which compared well with the values obtained from previous wind tunnel studies. Carbon dioxide emission rates varied from 10.9 to 56.9 g/m2/d.