Feeding schemes and C/N ratio of a laboratory-scale step-fed sequencing batch reactor for liquid swine manure treatment

ABSTRACT

This study was undertaken to investigate the effect of two split feeding schemes (600 mL/200 mL and 400 mL/400 mL, designated as FS1 and FS2, respectively) on the performance of a step-fed sequencing batch reactor (SBR) in treating liquid swine manure for nutrient removal. The SBR was run on an 8-h cycle with a repeated pattern of anaerobic/anoxic/aerobic phases in each cycle and the two feedings always occurred at the beginning of each anaerobic phase. A low-level aeration was used (1.0 L/m³.sec) for the anoxic/aerobic phase to facilitate nitrification and phosphorus uptake while reducing the energy consumption. The results showed that FS1 reduced NH₄⁺-N by 98.7% and FS2 by 98.3%. FS1 had 12.3 mg/L NO₃-N left in the effluent, while FS2 had 4.51 mg/L. For soluble phosphorus removal, FS1 achieved 95.2%, while FS2 reached only 68.5%. Both feeding schemes achieved ≥ 95% removal of COD. A good power regression was observed between total nitrogen (sum of all three nitrogen species) and the carbon to nitrogen (C/N) ratio, with the correlation coefficients of 0.9729 and 0.9542 for FS1 and FS2, respectively, based on which it was concluded that higher C/N ratios were required to achieve higher nitrogen removal efficiencies.

KEYWORDS:

• carbon to nitrogen ratio
• nutrients removal
• sequencing batch reactor
• step-fed strategy
• swine wastewater

Funding

The authors would like to thank the Idaho Agricultural Experiment Station for providing financial support for this project.