Study On Flotation-Aerobic Filter Process For The Reclaimed Water Advanced Treatment

In order to meet water quality standard for urban miscellaneous water consumption (GB/T18920-2002) or discharge 1st standard A class of pollutants for municipal wastewater (GB/T18918-2002), Wastewater Treatment Plant faces a problem that the current secondary treatment process will upgrade to advanced treatment process. Additionally, hazards and the removal of trace organic pollutants in wastewater are also concerned.In this article, the flotation and aerobic filter technology were selected, Instead of traditional sedimentation and filtration technology. Flotation-aerobic filter process had been chosen as the reclaimed water advanced treatment of municipal wastewater treatment plant. The test studied the appropriate operating parameters of the flotation and aerobic filter technology, a comprehensive evaluation of flotation-aerobic filter process in improving the secondary effluent conventional water quality indicators (color, COD, ammonia nitrogen, total phosphorus, turbidity, UV254, total bacteria, etc.) and a typical micro-organisms di(2-ethylhexyl)phthalate(DEHP) removal efficiency.First, the flocculation reaction parameters were optimized. There were level 3 mixing, mixing intensity was 50/30/20(S-1), retention time was 20 minutes. According to flotation on the COD, TP, turbidity indicators of treatment effect, PAC was optimized as a coagulant and the best coagulant dosage was 30mg/L under the test water quality conditions.Bubble size and the release of gas bubbles are two important parameters of flotation process. Gas pressure and reflux ratio of the gas-liquid mixing pump system determine the size of these two key parameters. Appropriate parameters of gas pressure and reflux ratio were proved to be 4.5kgf/cm2 and 40%.Aerobic filter started with a small flow of water first, and then gradually increase the water flow to the design flow. Under the conditions of the low COD, high ammonia secondary effluent quality, a stable nitrification biofilm formed after 20d.Upflow aerobic filter was not only less prone to vapor lock, but also can effectively extended the filtration cycle, at the same time could guarantee the quality of effluent. When the filter head loss increased to 1m, the filter cycle ended. Filter had a strong ability to resume filtering after the filter backwash. The filter would be able to return to pre-treatment filter backwash state in the 4h.It proved that effluent dissolved oxygen for aerobic filter 2mg/L can ensure adequate dissolved oxygen. Aerobic Filter oxygenation method combined aeration with pre-oxygenation. The upper part of aeration device was oxygenation state, and the lower part was designed to pre-oxygenation state. Upflow aerobic filter can make full use of flotation effluent saturated dissolved oxygen as the lower part pre-oxygenation.For low concentrations of secondary effluent, flocculation-flotation Process and flocculation-sedimentation process on the turbidity, COD, UV254, and the total number of bacteria had a high removal rate, and water quality can be further improved. In the low amount of flocculant dosing conditions, flocculation - Flotation Process on the removal rate of each index is higher than flocculation-sedimentation process.Aerobic filter and ordinary fast filter could further improve the water quality in removing COD, turbidity of secondary effluent. However, the removal principle of the two filters was different. Aerobic filter on the ammonia-nitrogen removal rate was high, but there was no removal efficiency for ordinary fast filter.Under the secondary emission standards water quality, the color, COD, ammonia nitrogen, total phosphorus, turbidity were able to achieve 1st standard A class of pollutants for municipal wastewater (GB/T18918-2002) and water quality standard for urban miscellaneous water consumption (GB/T18920-2002) after flotation-aerobic filter advanced treatment process. At the same time the total number of bacteria and UV254 were well removed. The results showed that flotation unit played a key role in the removal of organic matter, turbidity, total phosphorus and UV254, and the follow-up aerobic filter unit played a gatekeeper role in the removal of the ammonia, turbidity and organic matter.Tests found that the concentration of DEHP was very low after secondary wastewater treatment and flotation-aerobic filter process treatment, and the lowest concentration of DEHP dropped to 1.3ug/L, which was lower than the national standard of 8ug/L requirements. By comparison of flotation and sedimentation unit, sedimentation was found more conducive to the removal of DEHP. Because floatation process may easily lead to DEHP adsorbed on the floc particles back into the water, it is not conducive to the removal of DEHP.When the excessive dosing DEHP were added into wastewater, Secondary biological treatment, flocculation-sedimentation, flocculation-flotation, aerobic filter process on the removal of DEHP had shown good removal effect, but the effluent concentration of DEHP after treatment was still far higher than the national standard. Therefore, the traditional secondary biological treatment and flocculation-flotation/ sedimentation-aerobic filter technology are not suitable for the removal of high concentrations of DEHP.