The Use of Floating Islands to Enhance Dairy Wastewater Treatment in Southeast Louisiana

Vinicius Moreira, Southeast Research Station, Louisiana State University, Baton Rouge, LA, 70803, vmoreira@lsu.edu; Brian D. LeBlanc, Agriculture Center School of Plant, Environment and Soil Sciences and Louisiana Sea Grant, Louisiana State University, Baton Rouge, LA, 70803, blebl28@lsu.edu; and Eric C. Achberger, School of Biological Sciences, , Louisiana State University, Baton Rouge, LA, 70803. eachber@lsu.edu

Animal wastes have been listed as contributors to water pollution. In Louisiana, most dairy farms rely on grazing as the main source of feed to their cows. Consequently, most manure is in the form of wastewater collected in milking parlor and adjacencies, highly diluted with washwater. For that reason, anaerobic lagoons are the primary management practice in Louisiana dairies. Lagoons are designed to treat liquid waste by reducing solids and oxygen demand, but may release methane, ammonia, odors, and pathogens in the process. Treatment intensification may be a more efficient and economical long-term solution for small grazing dairies. The LSU AgCenter Dairy Waste and Nutrient Management Team has been evaluating technologies and practices to improve wastewater treatment using the Southeast Research Station Dairy Wastewater Treatment Evaluation System (DWTES) for the past 11 years. The system consists of a replicated set of anaerobic lagoon, aerobic lagoon and constructed wetlands. The objective of this study is to evaluate the impact of artificial floating islands on DWTES effluent quality. Biohaven® Floating Islands (Martin Ecosystems, Baton Rouge, LA) were deployed in an anaerobic lagoon (186 m2 floating islands) and an aerobic lagoon (93 m2 floating islands). Wastewater was sampled from every stage, on average every 3 months for 26 months. Samples were analyzed for temperature, pH, chlorophyll-A, chemical oxygen demand (COD), total solids, total dissolved solids, total suspended solids (TSS), ammonia-N, nitrate-N, nitrite-N, total Kjeldahl nitrogen (TKN), total phosphorus, anions, dissolved oxygen concentrations, total coliforms and E. coli. Total solids (1081 mg/L), TSS (338 mg/L), COD (900 mg/L), TKN (72 mg/L), ammonia-N (45 mg/L) and sulfate (13 mg/L) concentrations in raw wastewater decreased by 50% or more in the system’s effluent (wetlands). Escherichia coli counts were reduced from 6.6 log MPN/100 mL in raw wastewater to 2.87 ± 0.2 log MPN/100 mL in wetland effluents. In combination, those results demonstrate DWTES efficiency in reducing potential pollutants in dairy wastewater. Floating islands improved treatment effluent for TSS (76 vs. 55 ± 11.6 mg/L), COD (207 vs. 148 ± 42 mg/L), and TKN (24.5 vs. 19.1 ± 3.1 mg/L). Phosphate (7.09 vs. 7.83 ± 1.09 mg/L), ammonia-N as a proportion of TKN (54.4 vs. 84.6 ± 23.6 mg/L), nitrate-N (2.96 vs. 3.84 ± 0.84 mg/L) and chlorophyll-A (29.9 vs. 37.0 ± 9.72 mg/L) increased slightly in the effluent of the replicate containing floating islands. The results appear to suggest that increased anaerobic activity may enhance solid degradation, but in the process may release nutrients that can enhance biological activity downstream. More studies are necessary to better establish the role of floating islands in wastewater treatment systems. Preliminary results from the current study indicate that floating islands may improve dairy parlor wastewater treatment in a multi-stage treatment system.