High Rate BAF with Filter Media of Large-Size Lightweight Ceramisite for Micro-Polluted Raw Water Pretreatment

Abstract

On account of micro-polluted raw water, high rate up-flow biological aerated filter (HUBAF) is used to remove the ammonia nitrogen and micro organic pollutants in raw water. Using ceramisite as filtration media, at a diameter of 6mm to 10 mm, a surface density of above 1g/cm3 and a filtration rate of 16 m/h to 20 m/h, ceramisite layer is in a state of micro expansion, which is beneficial to keep a high nitrification efficiency. On account of raw water where NH3-N is below 4mg/L, NH3-N concentration t can be stabilized at less than 0.5 mg/L in HUBAF effluent. Since lack time of biochemical action, the CODMn removal rate by HUBAF is low. As the effluent of BAF carried abundant amounts of microbes and dissolved oxygen, it increased the CODMn removal rate by 11% in final effluent compared to the individual conventional process of “flocculation-sedimentation-filtration-disinfection”. The turbidity removal efficiency is only the 1/3 of ordinary BAF, which reduces the head loss and energy consumption, and multiple filters to share a centralized aeration system is possible. In addition, HUBAF system is aerated by the single-pore aeration filter heads under the filtration board, equipped with both up-flow and down-flow backwash systems and no need for extra grit chamber, HUBAF is convenient for maintaining and administration.