Comparative Study of Effluent Quality from Constructed Wetlands and Oxidation Ponds Treating Piggery Wastewater in Anambra State

Intensive pig farming in Anambra State, South East Nigeria, generates high-strength wastewater that is frequently discharged into streams without adequate treatment, degrading water quality in rural farming communities. This study compares the treatment performance of pilot-scale subsurface flow constructed wetlands planted with Phragmites australis and facultative oxidation ponds for treating piggery wastewater from a commercial pig farm in Awka South Local Government Area. Parallel pilot units were operated at the same hydraulic loading rate over 16 weeks. Influent and effluent samples were collected weekly and analysed for biochemical oxygen demand, chemical oxygen demand, total nitrogen, total phosphorus, total suspended solids, faecal coliforms, and pH. The wetland system consistently outperformed the oxidation pond for biochemical oxygen demand removal (93.7% vs. 81.2%) and total suspended solids removal (96.1% vs. 74.8%). However, the oxidation pond achieved slightly higher faecal coliform removal (99.1% vs. 97.6%), attributed to solar ultraviolet disinfection in the open pond surface. Total nitrogen removal was comparable between both systems at 68 to 73%. Capital cost estimation indicated that the oxidation pond required lower initial investment, while the constructed wetland had lower operational costs. The study provides comparative design guidance for selecting piggery wastewater treatment systems in peri-urban South East Nigeria. Keywords: constructed wetland, oxidation pond, piggery wastewater, nitrogen removal, Anambra State