| Phenol is a kind of organic pollutant which is toxic, and people always try to find a way to degrade phenol effectively. It was reported that GS-15 could degrade phenol with Fe(Ⅲ) oxide serving as electron acceptor under anaerobic condition. However, it did not tell if the degradation rate of phenol could be accelerated by adding Fe(Ⅲ) oxide and if microbes could use Fe3+ as electron acceptor in mixed culture. Furthermore, there were few studies about phenol decomposition depending on co-metabolism, and glucose was the most commonly used as co-substrate by these researches but obtaining limited enhancement.In this study, some kinds of Fe(Ⅲ) compounds (ferric citrate, ferroferric oxide, ferric oxide and ferric hydroxide) were added into anaerobic actived sludge to explore their effects on decomposition of phenol, and glucose and citrate were used as co-substrates respectively to compare their effects on decomposition of phenol. The conclusions were as follow:1. In batch experiments,100 mg/L phenol was completely removed in the groups with adding ferric citrate within 4 days while the removal ratio of the control groups with no ferric citrate was just 39.69%. When increasing the concentration of phenol to 380 mg/L, the removal ratio of groups with ferric citrate was still 93.93%compared to 26.94% in the no ferric citrate groups. On the other hand, adding ferroferric oxide or ferric oxide displayed significantly improvement of removing phenol compared with control groups. Even, the groups with ferric hydroxide showed a decrease of phenol removal. In agreement with the significant increase of the removal with ferric citrate, when amending sodium citrate and ferric hydroxide simultaneously, the phenol degradation was obviously accelerated.2. Dissimilatory iron reducing bacterium could use Fe3+ as electron acceptor to degrade phenol in the anaerobic condition. At the first three days, Fe2+ released from the Fe(Ⅲ) rapidly increased to 158 mg/L and then decreased gradually to 30 mg/L. The trend of Fe2+ changes was similar to the production of CH4 and CO2 from these anaerobic systems, which also increased rapidly at the first three days and then decreased and kept stability. Phenol degradation pathway in this anaerobic condition was also investigated, and the results suggested that phenylphosphoric acid might be an essential intermediate product.3. When the initial concentration of phenol was 150 mg/L, phenol removal rate of groups supplemented with glucose, sodium citrate, ferric citrate and sodium citrate+ferric hydroxide were 12.39%,35.77%,48.24% and 74.32%, respectively. When increasing the phenol concentration to 270 mg/L, the phenol removal ratio on 5 days were 34.35%,60.14%,84.59% and 97.05% accordingly. It indicated that coexistence of ferric iron and citrate could accelerate phenol degradation, and the solid ferric iron performed better than the soluble one.4. High-throughput 16SDNA gene pyrosequencing was used to analyze microbial community in phylum, class, order, family, genus and species level respectively. The results showed that Fe(Ⅲ) compounds could enhance the abundance of phenol degradative bacterium. Taking phylum level as example, a number of bacterium belonging to Proteobacteria and Firmicutes was reported to be capable of degrading phenol, and the abundance of Proteobacteria and Firmicutes in microcosms with ferric citrate, ferroferric oxide, ferric oxide, ferric hydroxide and unamended controls were 46.56%,45.22%,36.92%,29.15% and 34.74%, respectively. Furthermore, the results also showed that Fe(Ⅲ) compounds could enhance bacterial diversity. For example, ACE index of micro flora with ferric citrate, ferroferric oxide, ferric oxide, ferric hydroxide and unamended controls were 6791,6051, 6134,6050 and 4958, respectively. Acetic acid-utilizing methanogens as the sole archaea was found which belong to Methanomicrobia class, Methanosaetaceae family and Methanosaeta genus. |
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