Performance Of Biological Nitrogen And Phosphorus Removal For Saline Wastewater

The utilization of seawater is an effective approach to solve the problem of fresh water resources shortage in china. A plenty of saline wastewater produced in the process is probable discharged into municipal pipeline network. This process enhances the salinity of municipal wastewater, which can result in the deterioration of original biological nitrogen and phosphorus removal system in the wastewater treatment plant. Therefore, studying the performance of biological nitrogen and phosphorus removal for saline wastewater has important signification to increase the efficiency of seaside municipal wastewater treatment.Utilizing the SBR and MUCT process based on the domestic wastewater mixed with sea salt. The conventional activated sludge is from sewage treatment plants in Beijing Gaobeidian. Salt-tolerant activated sludge is from the MUCT process and it has been domesticated in 10g/L salinity for two years.Firstly, the experiment studied the effect of salinity on advanced nitrogen removal of the pulsed SBR. The results show that two and three sections on advanced nitrogen removal can be achieved in the range of 0~10g/L salinity. When the salinity was 0g/L, two and three sections were saving carbon of 8.14% and 9.69% than one. When the salinity was 5g/L, two and three sections were saving carbon of 9.46% and 10.81% than one. When the salinity was 10g/L, two and three sections were saving carbon of 6.31% and 3.4% than one. Therefore, three sections was becoming to 0~5g/L salinity. Two sections was becoming to 5~10g/L salinityEffects of salinity on salt-tolerant activated sludge nitrogen removal were studied, the results show that the tolerance of nitrifiers to salinity enhanced. When the salinity was changed into 0,5,15,20g/L from 10g/L, ammonia removal efficiency could also kept above 99%. Nitrite accumulation ratio increased whatever the salinity reduced or increased, indicating that nitrite oxidation bacteria (NOB) had stronger tolerance to salt change than ammonia oxidation bacteria (AOB). Increase or decrease in salinity could inhibit the nitrifiers. After a long-time domestication under 10g/L salinity, filamentous bulking was observed in the salt-tolerant sludge. SVI reduced with the increasing salinity, due to decreased quantity of filamentous bacteria. Increased salt also make the flocs diminish and dense. However, decreasing salinity led to the bulking and the loss of sludge.Next, the experiment investigated the effects of shock salinity on conventional activated sludge in the system of phosphorus removal. The results show that, the salt-tolerant limit was 20g/L. In the anaerobic stage, specific phosphorus released rate will gradually increase with the increased of salinity change. However, the corresponding glycogen degradation and PHA synthesis will gradually reduce. During the aerobic stage, specific phosphorus uptake rate will gradually reduce with the increased of salinity change, the corresponding PHA degradation and glycogen synthesis will gradually reduce.Meanwhile, the experiment also studied the effects of shock salinity on salt-tolerant activated sludge in the system of phosphorus removal. The results show that, the salt-tolerant limit was 35g/L. In the anaerobic stage, specific phosphorus released rate will gradually reduce with the increased of salinity change, the corresponding glycogen degradation and PHA synthesis will gradually reduce. During the aerobic stage, salinity increased (higher than 10g/L) had more inhibitory effects than salinity reduced (less than 10g/L). Specific phosphorus uptake rate, Phosphorus and COD removal rate will gradually reduce with the increased of salinity change, the corresponding glycogen synthesis and PHA degradation will gradually reduce. Lower PHA degradation will lead to low glycogen synthesis.The experiment also investigated the influence of wastewater initial pH and influent C/P on enhanced biological phosphorus removal system. The results show that, the phosphorus removal rate on the salt-tolerant activated sludge in enhanced biological phosphorus removal system were 94% and 84% when the initial pH value were 7.5 and 6.5. Due to the reduced of glycogen degradation, the PHA synthesis of SBR2 was lower than SBR1. PHA degradation of SBR1 was slightly lower than SBR2, and the glycogen synthesis of SBR1 was slightly higher than SBR2, however, phosphorus uptake of SBR1 was more than SBR2, suggesting the number of PAO in SBR1 was higher than SBR2. Therefore, SBR1 had higher phosphorus uptake and PHA utilization than SBR2. In addition, the influent C/P of SBR3 was about 20, and the phosphorus removal rate was 64% which was decreased by 30% than SBR1 (C/P=50). The influence of influent C/P for enhanced biological phosphorus removal system was significantly, increase the C/P can improve the phosphorus removal system. Phosphorus release and COD removal rate will gradually increase with the increased of influent C/P.Finally, the experiment studied the effects of shock salinity on PAO which was enriching by the synthetic feed water. The results show that, PAO accounted for 80.23% of total bacteria. The salt-tolerant limit was 15g/L. In the anaerobic stage, phosphorus released, PHA synthesis and glycogen degradation will gradually reduce with the increased salinity. Meanwhile, VFA degradation and specific phosphorus released rate will gradually decrease with the increased salinity. During the aerobic stage, phosphorus removal and specific phosphorus uptake rate will gradually decrease with the increased salinity. Meanwhile, phosphorus uptake, ammonia degradation, PHA degradation and glycogen synthesis will gradually reduce with the increased salinity.