| Cellar rainwater has been playing an important role in relieving water resources shortage in Northwest China, especially in the vast rural area, which is perennially droughty. Because the rainwater is polluted in the process of producting and collecting, some water quality indexs cannot reach the standard. Based on the local actual situation, BAF was used to treat and improve slightly polluted cellar rainwater. The experiment studied on the BAF for slightly polluted cellar rainwater treatment and got the best operating parameters. On this basis, ozone pre-oxidation was used to strengthen treatment effect of BAF.Under the natural biofilm formation method, the start-up cycle of BAF, filled with bio-ceramic, was 23 days. The removal rate of CODMn and NH3-N were respectively about 30% and 70%. Fulvous biofilm could be found attached on the surface of bio-ceramic. Many kinds of microorganism and metazoan were found by sediments microscope inspection. The good water quality meant the biofilm matured.By Studying on the different treatment effect of BAF, the best operating parameters were got: the volumetric ratio of A/O was 2:3, the gas-water ratio was 3:1, the hydraulic was 0.90m3/(m2·h), the reflux ratio was 200%. The removal rate of CODMn, NH3-N, UV254, TN and turbid were respectively 57%, 85%, 35%, 38% and 87%, with stable water quality. Among them, the effluent NH3-N and turbid accorded with the related regulations.The period of backwashing cycle was determined for 8 days, after considering the change of effluent quality during the operation period. To recovery the interception capacity and keep the high biofilm activity, the backwashing procedure of BAF was determined as follows: firstly, air washing 5 min with flow rate of 18L/(s·m2), then water washing 5 min with flow rate of 12L/(s·m2). The turbid, NH3-N and CODMn concentration in effluent increased after backwashing but recovered in 4 hours. Then the removal effect became stable and the recovery ability of backwashing was great.Different time of pre-ozonation was analyzed to study the effects of dissolved oxygen and SUVA on the cellar rainwater. The best contact pre-ozonation time was 3 min. The removal rate of CODMn, NH3-N and UV254 decreased 9%, 3% and 7% with 3-min pre-ozonation. Pre-ozonation changed the molecular weight distribution and improved biodegradability of the slightly polluted cellar rainwater, decreasing the percentage of macromolecular organics(>50 K) and increasing the percentage of small molecular organics(<3 K). The three-dimensional fluorescence spectrum showed that: the humic-like was removed largely after pre-ozonation, making it more suitable for the treatment by BAF.Compared with the effluent of BAF without pre-ozonation, the removal rate of CODMn, NH3-N and UV254 of BAF with pre-ozonation increased 7%, 6% and 5% respectively. The removal rate of tryptophan-like increased 38%. The concentration of effluent CODMn of BAF with pre-ozonation was 2.97 mg/L, which can reach the Standards for Drinking Water Quality(GB5749-2006). |
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