The difficulty with sludge settleability is considered one of the main drawbacks of sequencing batch reactors. The aim of this study therefore is to improve sludge settleability by introducing a novel, two-stage settling sequencing batch reactor (TSSBR) separated by an anoxic stage. The performance of the TSSBR was compared with that of a normal operating sequencing batch reactor (NOSBR), operating with the same cycle time. The results show a significant improvement in sludge settleability and nitrogen compound removal rates for the TSSBR over the NOSBR. The average removal efficiencies of ammonia-nitrogen (NH3-N), nitrate-nitrogen (NO3-N) and nitritr-nitrogen (NO2-N) have been improved from 76.6%, 86.4% and 87.3% respectively for the NOSBR to 89.2%, 95.2% and 96% respectively for the TSSBR. In addition, the average sludge volume index (SVI) for the NOSBR has been reduced from 42.04 ml/g to 31.17 ml/g for the TSSBR. After three months of operation, there was an overgrowth of filamentous bacteria inside the NOSBR reactor, while the morphological characteristics of the sludge inside the TSSBR reactor indicated a better and homogenous growth of filamentous bacteria. TSSBR system proves to be more efficient than NOSBR by improving the sludge settleability and enhancing nitrogen compounds’ removal efficiency, therefore, the TSSBR operating conditions including (mixed liquor suspended solids, hydraulic retention time, fill conditions, fill time, volumetric exchange rate, organic loading rate and hydraulic shock) have been optimised to obtain the optimal performance of the TSSBR system regarding the treatment efficiency and sludge settling performance. The results of optimising the TSSBR operating conditions are as follows: the optimal MLSS range was 3000 mg/l to 4000 mg/l; the optimal HRT was 6 h; unaerated feeding was better than the aerated feeding, and 15 minutes was the optimal feeding time; the optimal VER value was 20%; the optimal OLR ranges were 750 to 1000 mg/l glucose loading rate and 50 to 150 mg/l potassium nitrate loading rate. Finally, the TSSBR system was operated under the obtained optimal operating conditions. The results showed that the treatment efficiency of COD and NO3-N had been improved significantly. Although the removal efficiency of NH3-N and NO2-N did not improve, the removal efficiency of both is more than 90%, which is considered a good treatment efficiency for the TSSBR system. In addition, the settling performance of the TSSBR was significantly improved after operating the system under the optimal operating conditions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:755789 |
| Date | January 2018 |
| Creators | Al-Attabi, A. W. N. |
| Contributors | Harris, C. ; Al Khaddar, R. |
| Publisher | Liverpool John Moores University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://researchonline.ljmu.ac.uk/9402/ |
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