| Abstract: |
General The objective of the present work is to investigate the phosphorus, BOD and COD removal efficiency achieved by a combined suspended/attached growth bioreactor for domestic wastewater treatment. The results obtained from the present study offer the following conclusions.Results also, Pointed out identifications of possible directions that further research may have to investigate. In this final chapter the study conclusions will be presented and followed by some recommendations for further research needed.5.2 ConclusionIn conclusion, The most important findings in this study can be summarized as follows:5.2.1 Regarding phosphorus removal process:1) The best conditions for phosphorus removal process were 100% return sludge with diffused air (dual growth process)at hydraulic retention time equals to 12 hours, where the efficiency of phosphorus removal was 92.2%. While the efficiency of phosphorus removal at zero% return sludge with diffused air (dual growth process) at hydraulic retention time equals to 16 hours was 97.3% but this HRT is high and costive which the low improvement in efficiency of phosphorus removal may not equivalent to the cost of this high HRT.2) The effluent concentration of phosphorus was acceptable (less than the standard limit 0.5-1.0 mg/L) in case of dual growth process for 100% return sludge at hydraulic retention time equals to 10 and 12 hours and at zero% return sludge at hydraulic retention time equals to 12 and 16 hours.3) Hydraulic retention time has great effect on phosphorus removal process, where efficiency of phosphorus removal increased from 66% to 75.7% and then to 86.3%, 91.2% and 97.3% when hydraulic retention times increased from 6 hours to 8 hours and then to 10, 12 and 16 hours respectively in case of dual growth process at zero% return sludge. But the standard specification for effluent phosphorus had been achieved at hydraulic retention time equals to 12 and 16 hours.Also, it has been founded that the efficiency of phosphorus removal increased from 67.4% to 76.0% and then to 87.1% and 92.2% when hydraulic retention times increased from 6 hours to 8 hours and then to 10 and 12 hours respectively in case of dual growth process at 100% return sludge. But the standard specification for effluent phosphorus had been achieved at hydraulic retention time equals to 10 and 12 hours.4) The efficiency of phosphorus removal increased by the increase of hydraulic retention time at a specified range of MLSS, and the same results can be achieved for other ranges of MLSS.5) Diffusing air in the combined bioreactor in sets of dual growth process increased the efficiency of phosphorus removal from 56.7% to 66% at zero% return sludge while in case of 100% return sludge, this diffused air increased the efficiency of phosphorus removal from 84.05% to 92.2%.6) Returning the sludge increased the efficiency of phosphorus removal in case of dual growth process from 87.1% to 92.2% at zero% return sludge and 100% return sludge respectively, While in case of attached growth process from 57% to 84.05% at zero% return sludge and 100% return sludge respectively.7) Returning the sludge had nearly no effect on efficiency of phosphorus removal in case of attached growth process in batch pattern. This may be due to the lack of oxygen which required to growth of the recycled biomass. Also, returning the sludge has effect on phosphorus removal approximately 11% in case of dual growth process.5.2.2 Regarding BOD and COD removal process:1) The best conditions for BOD and COD removal process were 100% return sludge with diffused air (dual growth process) at hydraulic retention time equals to 12 hours, where the efficiency of BOD and COD removal was 85.4% and 84.4% respectively.2) Hydraulic retention time has a great effect on BOD and COD removal process, where efficiency of BOD removal increased from 59% to 64.7% and then to 70%, 74.4% and 83.6% when hydraulic retention times increased from 6 hours to 8 hours and then to 10, 12 and 16 hours respectively in case of dual growth process at zero% return sludge, While at 100% return sludge the efficiency of BOD removal increased from 63.8% to 69.5% and then to 75.3% and 85.4% when hydraulic retention times increased from 6 hours to 8 hours and then to 10 and 12 hours.Also, efficiency of COD removal increased from 53.9% to 61% and then to 67.9%, 73.7% and 82% when hydraulic retention times increased from 6 hours to 8 hours and then to 10, 12 and 16 hours respectively in case of dual growth process at zero% return sludge, While at 100% return sludge the efficiency increased from 61% to 65.6% and then to 72.8% and 84.4% when hydraulic retention times increased from 6 hours to 8 hours and then to 10 hours and 12 hours.3) The efficiency of BOD and COD removal increased by the increase of hydraulic retention time at a specified range of MLSS, and the same results can be achieved for other ranges of MLSS.4) Diffusing air in the combined bioreactor in sets of dual growth process increased the efficiency of BOD and COD removal from 50% to 59% and from 46% to 54% respectively at zero% return sludge, While in case of 100% return sludge, This diffused air increased the efficiency of BOD and COD removal from 74% to 80.5% and from 68% to 80% respectively.5) Returning the sludge increased the efficiency of BOD and COD removal in case of dual growth process from 74.4% to 83.5% and from 73.7% to 79.5% at zero% return sludge and 100% return sludge respectively, While in case of attached growth process from 58.3% to 74% and from 47% to 68% at zero% return sludge and 100% return sludge respectively.6) Returning the sludge had nearly no effect on the efficiency of BOD and COD removal in case of without diffused air in batch pattern. This may be due to the lack of oxygen which required to the growth of the recycled biomass. Also, returning the sludge has effect on BOD and COD removal approximately 9% in case of dual growth process.5.3 Recommendations for further researchFurther technical and economical studies are required to investigate the following subjects:1) Effect of temperature changes on efficiency of phosphorus removal process in the used combined reactor.2) Effect of different pH ranges on efficiency of phosphorus removal process in the used combined reactor.3) The effect of adding chemical precipitants on phosphorus removal at biological treatment by the used reactor.4) The impact of the feed COD/TP ratio on the performance of biological phosphorus removal in the used of combined reactor.5) The effect of different amounts of diffused air supplied to the used combined reactor and study its effect on phosphorus, BOD and COD removal efficiencies.6) The study of microbiology and biochemistry of the enhanced biological phosphorus removal process in the used combined reactor.7) Economical study to evaluate the benefits of increasing hydraulic retention time with returning the sludge and diffused air compared to the additional costs of them
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