Development of a hybrid system for advanced wastewater treatment using high-rate settling and a flotation system with ballasted media

• The T-P quality standard from WWTPs in Republic of Korea has been tightened from 2 to 0.2 mg/L since 2012.
• WWTPs such as tertiary system can be happened high operation cost because of using a lot of chemical.
• A hydrocyclone can separate solids from liquid, operates at a high hydraulic loading rate, and has low maintenance expenses.
• DAF can be employed to remove particles and nonprecipitated matter within SRT and has low maintenance expenses.

High-rate phosphorus removal was performed to meet the stringent requirement (0.2 mg/L) for wastewater discharged from a wastewater treatment plant. To meet the stringent standard, a hybrid system of a hydrocyclone combined with a dissolved air flotation (DAF) unit was investigated. The optimum conditions for the hydrocyclone and DAF unit were determined by changing the flow rate, split ratio (Rs), and recycling ratio (Rr). Sand and sawdust as ballasted media were injected to increase the weight of the flocs and to increase the sedimentation rate through enhancement of coagulation in the hybrid system. In the optimum volumetric concentration of polyaluminum chloride (PAC) with cationic polymer, the required retention times of sand and sawdust were 2 and 6 min, respectively. The results for the hydrocyclone show that injecting sand with PAC and cationic polymer provided a higher phosphorus and turbidity removal efficiency than injecting sawdust with PAC and cationic polymer. The optimum operating conditions of the hydrocyclone were Rs of 10% and a flow rate of 2.8 m/s. Rr of 10%–15% provided optimum DAF operation. Phosphorus and turbidity were each reduced by 98% in the hybrid system.