Treatment Of Oil Wastewater With Biological Aerated Filter

BAF has many advantages,such as small volume,little covering earth and hydraulic retention time(HRT), high treatment efficiency and effluent water quality,low investment and running cost etc.BAF has been used widely for many years in the world and been used to treat several wastewater in our country.In this paper, BAF with expaded clay media was studied on the treatment of oil wastewater.The biofilm colonization of BAF was observed with simulativing sewage and the effection of the BAF treating oil wastewater was studied on HRT, hydraulic loading, organic loading, initial oil concentration. The main results are summarized as folows:1. BAF has good performance in treating wastewater,when the HRT is 4h, the ratio of gas to liquidis about 3: 1 ,the biofilm colonization would mature in 20 days, and the removal rate of COD,NH4-N is probably 75%,65%,respectively.The stable nitrificated biofilm colonization grew more slowly than the heterotrophic aerobic biofilm, which was performed as the stable removal rate of NH4-N was reached later 7～10 days than the COD's.2. The removal of pollutants showed different characteristics along with the high height in Biological Aerated Filter:for along the filter the removal of organic matter CODcr mainly occurred in the filter of the first part (that is 60 cm from input), and which is different from the removal CODcr, the optimum media height for the removal of the NH4-N was mainly 20 cm～80cm from the end of the output.3. The oil processing tests show that: HRT, organic load, the initial concentration of oil played very important fact on the oil removal when the CODcr varied from 0～300mg/L and the gas-water ratio was 4:1 .When the HRT was longer, the oil concentration of output was lower., the average oil removal rate was 90.19% when the HRT was 8 h ,and oil content in output was about1.48 mg / L . As long as the HRT was more than 3 h, the oil removal rate can be maintained above 75%. With the increase of hydraulic loading, the average removal rate of oil declined in gradually and negatively correlated. Therefore in the actual process, appropriate hydraulic loading ensured a better efficiency.The BAF had a high removal rate on oil and CODcr When the organic load was 0～2.79 kgCODcr / (m~3·d) and the HRT was 4 h.The CODcr and oil concentrations of effluent were lower than 77.40mg / L and 5 mg / L, respectively.The average removal rate of oil was more than 80%.When the initial concentration of oil was 0～10mg/L, Biological Aerated Filter had a best result.The effluent CODcr were lower than 50 mg/L, oil were lower than 1 mg/L, and the removal rate of oil was more than 90 %.when oil concentration exceeded 30 mg/L, the efficiency of the reactor dropped significantly. The system would turn out of useless a sign when oil concentration was beyond 50 mg/L.4. The influent load will affect the performance of BAF directly. The results of the experiment show that the BAF has better capability to CODcr impact than to oil impact when the stable situation was chosed as: the CODcr was between 0～300 mg/L, the oil content ranked 0～20mg/L, the ratio of gas to liquid about 3:1, the HRT was 4 h with the temperature varing from 12 degree to 19 degree.5. Backwashing pilot study showed that: the filter running cycle was 6～7 days. Gas -washed was along with water-washed.The backwashing way was showed as:a separate gas washing 4 min (backwashing intensity 0.46 m~3 gas/ (m3media·min))→water and gas joint washing 5 min→separate washing washed 6 min (backwashing intensity 0.18 m~3 water / (m~3 media·min)), the whole backwashing lasted 15 min. the optimum condition of BAF would return rapidly after backwashing .It would been close to normal levels after 2 h, three hours could be restored to the best level of treatment.