Advanced Treatment Of Municipal Wastewater Using Flotation - BAF Technology

In recent years, with the rapid economic development, water consumption increased every year in Qiqihar, so did the wastewater discharge resulted in decrease in the amount of available water resource in downstreams of Nen River, deteriorated with more and more untreated wastewater was discharged in to Nen River. Therefore the construction of the water reuse project in Qiqihar city (central city) wastewater treatment plant is of great importance.Qiqihar wastewater treatment plant using adsorption biodegradation (AB) process as the mian process, Since AB process does not have the function of nitrogen and phosphorus removal, the process needs to be upgraded so that the quality of the effluent can meet calss B standard in Municipal Sewage treatment plant Pollutant discharge Standard (GB18918-2002). On the basis of this, a flotation - Biological Aerated filter (BAF) process has to be constructed in order to satisfy the requirement of treated water reuse. Water quality of treated water has to meet the standard for cooling system in Code for design of wastewater reclamation and reuse (GB50335-2002).The investigation of raw water quality, process parameters, operating conditions in the southern suburbs of Qiqihar wastewater treatment plant was carried out, on the basis of which a pilot test in the field using flotation-BAF process to treat the effluent from the secondary settling tank was conducted.The upgraded process was established on the basis of careful consideration, that is to preserve the A section, change the B section into A / O form. The chemical agents for phosphorus removal was Polymeric aluminum-iron (PAFC), which was added in the flotation tank and the optimum dosage was 40mg / L.Effects of organic loading rate, hydraulic loading and the load of total phosphorus removal efficiency on the performance of the flotation tank was investigated. The results showed that the removal of COD and SS in the flotation system increased initially and then decreased with the increased of the organic loading rate. The removal of SS, COD, TP increased with the increase of the surface hydraulic loading The maximum removal efficiency of SS, COD and TP of 40.83%, 38.65% and 56.8% was achieved. the surface loading was 15 m³/m²·h, The removal of SS and COD increased with the increase of influent total phorphrous concentration, while the maximum TP removal efficiency was achieved when the TP concentration in the influent was 8 mg/L.Through comparison of C / N-type BAF and A / O-type BAF, an A / O-type BAF with the duration of anaerobic to aerobic equals to 1:4 was selected. After 2 weeks continuous operation of BAF, a, COD removal rate of 50%, ammonia nitrogen removal rate of 70% was achieved, which indicated that the biofilm was completed formed. An optimal air to water ratio of 5:1, the reflux ratio of 100%, the maximum BOD loading rate of 101.2kgBOD / (m³·d) and ammonia loading rate of 10.2kgNH₃-N / (m³·d) to 50.1 kgNH₃-N / (m³·d) were determined.Finally a flotation - BAF coupling pilot g process was applied to optimize the parameters so that the effluent quality could meet the discharge standard.