N-removal with low carbon and phosphorus levels

Low carbon and phosphorus concentrations were controlled to investigate their influences on nitrogen removal in activated sludge reactors. Results demonstrated that when the initial COD/ NH₄⁺-N (C/N) ratio was adjusted to 4/1, NH₄⁺-N removal efficiency achieved the maximum value of 93.0%. With the rising of C/N ratio, total nitrogen (TN) removal efficiencies increased gradually while NH₄⁺-N removal efficiencies had slight downward trend. When the C/N ratio was 10/1, TN removal efficiency in the system reached the maximum value of 64.2% comparing to those at C/N ratios of 8/1, 6/1 and 4/1. However, TN removal efficiencies decreased with the reduction of total phosphorus concentration in the influent at constant C/N ratio. When the C/P ratio varied from 100/1 to 100/0.6, TN removal efficiencies declined a little. When the C/P ratio decreased to 100/0.4, TN removal efficiencies reduced dramatically. In general, low carbon level had little impact on NH₄⁺-N removal efficiency, just adverse to total nitrogen removal efficiency which was low at C/N ratio of 4/1. Low phosphorus concentration had a significant negative effect on NH₄⁺-N and total nitrogen removal efficiency. Low phosphorus concentration had significant negative effect on NH₄⁺-N and total nitrogen removal efficiency which even resulted in sludge bulking.