Stability of short-cut nitrification nitrogen removal performance was studied in a step-feeding, intermittently aerated sequencing batch reactor (IASBR) at 30°C to treat digested piggery wastewater. Results showed that the nitrogen removal was greatly influenced by the ratio of chemical oxygen demand (COD) to total nitrogen (TN) in the influent. Nitrite nitrogen kept accumulating up to 800 mg · L⁻1 when the influent COD/TN ratio was 0.8 ± 0.2, and the removal rates of TN, ammonium nitrogen and total organic carbon (TOC) were only 18.3% ± 12.2%, 84.2% ± 10.3% and 60.7% ± 10.7%, respectively. By contrast, as the influent COD/ TN ratio was increased to 2.4 ± 0.5, the accumulated concentration of nitrite nitrogen sharply decreased from 800 mg · L⁻¹ to below 10 mg-L⁻¹, and the removal rates of TN, ammonium nitrogen and TOC were increased to over 90%, 95% and 85%, respectively. Gradually shortened hydraulic retention time ( HRT) reveales that the ammonia load is a restricting factor for nitrogen removal. The ammonia load should be controlled at no more than 0.30 kg · (m³ · d) ⁻¹, or else, the removal rates of TN, ammonium and TOC would be greatly decreased. The nitrite accumulation rate over the whole run was 74.6%-97.8% and the TN removal rate in the stable phase was over 90%. With efficient and stable short-cut nitrification-denitrification in a low COD/TN, moreover, and unnecessary for addition of alkaline, IASBR shows great advantage for treating wastewater with high concentration of ammonia while low COD/TN ratio.
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