Effects Of Influent Salinity Fluctuation On Removal Of Pollutants From Sewage Treatment Plant

The raw water of coastal municipal wastewater treatment plant in southern China is directly taken from the tidal river. At high tide, more and more seawater returning into the tidal river, causes the inflow salinity of the wastewater treatment plant to increase gradually, while at low tide, the proportion of seawater mixed with sewage in the tidal river is reduced, which makes the inflow salinity decrease gradually. Along with the ocean tides, the inflow salinity of the wastewater treatment plant periodically fluctuates in a short period of time, and it will affect the treatment effect of wastewater treatment plant. At present, the researches on the effect of the inflow salinity on the wastewater treatment plant are mainly focus ed on a constant salinity, and there is almost no researches on a periodically fluctuant inflow salinity. The paper investigates the effect of the inflow salinity on the wastewater treatment plant through the laboratory test, based on the investigation on some wastewater treatment plant in Shenzhen of which the inflow salinity is periodically fluctuant, and studies the corresponding control measures.In addition, when the temperature is relatively high in the rainy and dry seasons, the removal effect of pollutant is better, and the effluent COD, NH₄⁺-N and TN can reach emission standards of level A. But the effluent NH₄⁺-N and TN can not reach emission standards of level A, because of the low temperature and wide range of salinity fluctuation, though the effect on removal of COD is still good. According to the results of the survey, the inflow salinity fluctuati on and temperature have a great influence on wastewater treatment plant. It is difficult to determine the real influence of salinity fluctuation on the treatment effe ct, because other factors such as inflow quality and quantity in raw water variate greatly. Therefore, this article systematically studies the effect of inflow salinity fluctuation and temperature on treatment effect. The results show that at the high temperature of 25±2 ? and the low temperature of 15±2 ?, when the inflow salinity ranges from 0‰?2‰ to 0‰?10‰, there is no significant effect on COD removal, but the NH₄⁺-N and TN removal are worse with the increase of salinity range. And under the same salinity fluctuation range, the NH₄⁺-N and TN removal effect is poorer at the temperature of 15±2 ?. When inflow salinity range is above 0‰?4‰, the effluent can not reach the emission standards of level A.Therefore this article researches building regulation-pool, adjusting the nitrifying liquid reflux ratio and seasonly water allocation, because the effluent can not reach the emission standards of level A at a low temperature and broad range of salinity fluctuation. The results show that when the inflow salinit y range is 0‰?6‰, building a regulation-pool with a volume of 30% of the basic inflow quantity, adjusting the nitrifying liquid reflux ratio of 300% can both make the salinity range in 0‰?4‰ and the effluent reach the emission standards of level A. And running the wastewater treatment plant on the condition that the inflow quantity is respectively 130% of the basic inflow quantity, 100% of the basic inflow quantity and 50% of the basic inflow quantity when it is sequentially in rainy season at a high temperature, in dry season at a high temperature, and in the dry season at a low temperature. It can guarantee the whole inflow quantity.