| Ozone-BAC process has been widely used in water works as advanced treatmenttechnology both at home and abroad, a new process called mid-positioning biologicalaeration carbon filter was developed in term of the existing problems of postpositionalBAC filter which was used in the hot and humid southern China. Pilot test wasimplemented on different scale to this new mid-positioning BAC process. Comparativestudy was conducted in different operation modes of the carbon filter, with up-flowand down-flow modes, to analyze the treatment efficiency and operation stability. Thena deeper research about filter thickness optimizing and filter rate optimizing was made.The results showed that:(1)When using the single packing filter, turbidity was distributed throughout thewhole carbon layer. Under a filter rate of12m/h and an aeration gas-water ratio as0:1~0.5:1,the mean removal efficiency of42.6%and57.8%were obtained for CODMnand UV254respectively by the up-flow BAC process，while the mean removalefficiency of40.1%and58.7%were obtained for CODMnand UV254respectively bythe down-flow BAC process. The removal efficiency were at the same level and thehead loss fluctuated largely that it lead to a short backwash cycle of only24hours forboth operation modes, while the up-flow filter still has a lower head loss than thedown-flow filter has.(2)When using the composite packing filter, the cushion layer thickness of0.7mwas filled with diameter3-5lightweight ceramic, the average growth rate of head losswere1.67cm/d and2.31cm/d respectively by up-flow and down-flow filter, with theunit height head loss of5.7cm/m and7.4cm/m respectively,while the head loss oflightweight ceramic layer were12.2cm and12.3cm respectively. It showed thatceramic layer was in favour of maintaining the up-flow filter’s stability of head loss.Ceramic layer played an important role in filtering the turbidity, and created a lowturbidity condition for adsorption in carbon layer, and it would help to improve theremoval efficiency of organics. (3)Plankton and benthos emerged in both filter effluent, and plankton was in themajority. In general, the amount of microorganism in up-flow carbon filter was leastthan that in down-flow carbon filter.(4)Adopting the filter filled the thickness of3m cylindrical carbon whosediameter was3mm and another filter filled the thickness of2m cylindrical carbonwhose diameter was2mm, the comparative results showed that the average head losswere35.5cm and54.3cm respectively, and the mean removal efficiency of66.4%and27.1%for turbidity and CODMnrespectively by the former, while the mean removalefficiency of55.9%and27.7%for turbidity and CODMnrespectively by the latter.Water quality treatment effect were at the same level, while the former filter gainedless head loss and had a better operational stability.(5)The cushion layer thickness of0.7m was filled with diameter3-5mm andanother thickness of1.2m with diameter6-8lightweight ceramic. The average headloss were35.5cm and29.5cm respectively, and they increased11.5cm and8.7cmrespectively for each average backwash cycle. The whole removal of CODMnwere40.6%and47.1%respectively, while the ceramic layer filtrated50.3%and59.7%ofthe turbidity respectively. It showed that thicken the ceramic layer would prominentlycontribute to head loss controlling and water quality removal efficiency. When using athickness of1.2meter ceramic layer, the filter rate could reach to16m/h, and the headloss was34.0~49.0cm and the CODMnremoval efficiency was41.7%. Copmared withthe12m/h filter rate, the CODMnremoval efficiency decreased by5.4%,while thehydraulic load increased by33.3%. |
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