Due to the nutrient characteristics of the high concentration of available ammonium in digested piggery wastewater (DPW), microalgae can be used to treat DPW before its final discharge. Four green microalgae (Hydrodictyaceae reticulatum Lag, Scenedesmus obliquus, Oedogonium sp. and Chlorella pyrenoidosa) and three blue-green algae (Anabaena flos-aquae, Oscillatoria amoena Gom and Spirulina platensis) were used to remove the nutrients (N, P, C), especially ammonium nitrogen (NH4+-N), from diluted DPW with 300 mg/L algae density in batch tests. The microalgae with the best NH4+-N nutrient removal was then selected for further optimization of the variables to improve NH4+-N removal efficiency using a central composite design (CCD) experiment. Taking into account the nutrient removal efficiency, Oedogonium sp. showed the best performance (reduction of 95.9% NH4+-N, 92.9% total phosphorus (TP) and 62.5% chemical oxygen demand (COD)) based on the results of the batch tests. The CCD results suggested that the optimal values of variables were initial Oedogonium sp. density of 399.2 mg/L and DPW diluted by 16.3, while the predicted value of NH4+-N removal efficiency obtained was 97.0%.

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