|Ibekwe, Abasiofiok - Mark|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/2003
Publication Date: 9/20/2003
Citation: Ibekwe, A.M., Grieve, C.M., Lyon, S.R. 2003. Characterization of microbial communities and composition in constructed dairy wetland wastewater effluent. Applied and Environmental Microbiology. 69(9):5060-5069. Interpretive Summary: One of the main reasons for the establishment of constructed wetlands is to use the final effluent for irrigation and or for disposal into other bodies of water. Data from our study showed that there is a diverse community of bacteria that are involved in the treatment process in the wetlands, ultimately influencing the final effluent water quality On-site reuse of the wetlands treated washwater through spray irrigation on disposal lands was optimized by the reduction of organic loads and solids in washwater, allowing more water of higher quality to be used for the irrigation of pasture in this farm. Improved washwater quality also reduced the buildup of solids in irrigation lines, and decreased the need for pump and line service by the farmer. The removal of the main pollutants from the dairy washwater will have beneficial impact on the surface and groundwater in the Chino Basin. In turn, this process will benefit the quality of water leading into the Santa Ana River and the Orange County groundwater basin. The wetland project will serve as an innovative model for waste management for the dairy industry and other confined animal facilities. Providing a cost-effective, low-maintenance process that can be independently built and managed, wetland treatment systems will have a significant long-term impact on the quality of the ground and surface water supply.
Technical Abstract: Constructed wetlands have been recognized as a removal treatment option for high concentrations of contaminants in agricultural waste before land application. The goal of this study was to characterize microbial composition in two constructed wetlands designed to remove contaminants from dairy washwater. Water samples were collected weekly for 11 months from two wetlands to determine the efficiency of the treatment system in removal of chemical contaminants and total and fecal coliforms. The reduction by the treatment was greatest for biological oxygen demand (BOD), suspended solids, chemical oxygen demand (COD), nitrate, and coliforms. There was only moderate removal of total nitrogen and phosphorus. Changes in the total bacterial community and ammonia-oxidizing bacterial composition were examined using denaturing gradient gel electrophoresis (DGGE) and sequencing of PCR-amplified fragments of the gene encoding the *-subunit of the ammonia monooxygenase gene (amoA) recovered from soil samples and DGGE bands. DGGE analysis of wetlands and manure samples revealed that the total bacterial community composition was dominated by bacteria from phylogenetic clusters relating to Bacillus, Clostridium, Mycoplasm, Eubacteriium, and Proteobacteria originally retrieved from gastrointestinal tract of mammals. The population of ammonia-oxidizing bacteria showed a higher percentage of Nitrosospira-like sequences from the wetland samples, compared to a higher percentage of Nitrosomonas-like sequences from manure, feces, raw washwater and facultative pond. These results show that the wetland system is a natural process dependent upon the development of healthy microbial communities for optimal wastewater treatment.