Abstract
Acetate, ethanol, and hydrolysed rice were used as external carbon sources in an ammonium removal process employing immobilised bacteria. The influence of the carbon source on the occurrence of free cells and total nitrogen removal efficiency was examined at C/N ratios of 1.5 (low), 2.5 (medium), and 3.5 (high). At the low C/N ratio, no free cells were found in the reactors and the use of acetate as the carbon source resulted in the highest total nitrogen removal efficiency, followed by ethanol and hydrolysed rice. The occurrence of free cells in reactors fed with acetate and ethanol led to a negligible increase in the total nitrogen removal efficiency with increasing C/N ratio. The results suggest that acetate is the most appropriate carbon source for nitrogen removal and that the number of free cells should be minimized to achieve the highest efficiency during long-term operation.
Highlights
At the low C/N ratio, no free cells were found in the reactors and the use of acetate as the carbon source resulted in the highest total nitrogen removal efficiency, followed by ethanol and hydrolysed rice
The results suggest that acetate is the most appropriate carbon source for nitrogen removal and that the number of free cells should be minimized to achieve the highest efficiency during long-term operation
The non-aeration chamber directly communicated with the aeration chamber through the perforated divider, and the water containing high concentrations of NO3-N and dissolved oxygen (DO) was immediately introduced to the non-aeration chamber
Summary
Simulated wastewater influent solution containing 40 mg/L of NH4-N was prepared by mixing 0.19 g/L of (NH4)2SO4, 0.48 g/L of NaHCO3, 0.05 g/L of KCl, 0.11 g/L of CaCl2·2H2O, 0.1 g/L of MgSO4·7H2O, and 0.02 g/L of Na2HPO4·12H2O. The carbon concentration of acetate and ethanol feed solutions was fixed at 7.1 g/L. Hydrolysed rice was prepared by adding 35 g of rice and 18 mL of 6 M HCl to 1L of tap water. The resulting carbon concentration of the hydrolysed rice solution was 6.5-7.0 g/L of total organic carbon (TOC) and ~0.1 g/L of volatile organic carbon (VOC). A 34.5 mL portion of 10% concentrated sludge was mixed with 10.5 mL of a solution containing PEG pre-polymer and promoter, and 5 mL of potassium persulfate (K2S2O8) was added to initiate polymerization. The polymerized gel was cut into 3 mm cubes referred to as PEG pellets
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