Process modeling and optimization of biological removal of carbon, nitrogen and phosphorus from hospital wastewater in a continuous feeding & intermittent discharge (CFID) bioreactor

Abstract

We evaluated the feasibility and treatment performance of a continuous feeding and intermittent discharge (CFID) bioreactor treating real hospital wastewater with the emphasis on simultaneous carbon, nitrogen and phosphorus (CNP) removal. The experiments were based on a central composite design (CCD) and analyzed by response surface methodology (RSM). To analyze the process, three significant variables, aeration time (2–4 h), mixing time without aeration (30–90 min) and MLSS concentration (2,000–6,000mg/l), were studied. Results show that an increase in aeration time increased the nitrogen and phosphorous removal efficiency. However, when the aeration time was more than 3 h, the efficiency of phosphorous removal was decreased due to insufficient acidification. A similar scenario was observed when mixing time was increased for phosphorus and nitrogen removal efficiency. MLSS had a positive effect on all the responses. Under optimal conditions, the concentrations of quality parameter in the influent in average were recorded as 586 mg COD/l, 296mg BOD5/l, 97mgTN/l and 16.47mg TP/l, which yields the following removal efficiencies, 95.6%, 98.3%, 88.0% and 92.0%, respectively.