Study On Removal Of Ammonia Nitrogen In Coking Wastewater By Micro Oxygen Granular Sludge+Diatomite

Along with the rapid growth of the steel industry, coke as the basic raw materials is increasingly demanded. However, the water consumption is2.5times in weight as the coke production. Therefore, the coking wastewater dischargement is tremendous. The concentration of ammonia nitrogen in the coking wastewater is very high and it is harmful to water body, human, industry and so on. However, the treatment on coking wastewater especially ammonia nitrogen in the coking wastewater is not satisfying at present which leading to the ammonia nitrogen concentration in effluent cannot meet discharge standards. Hence, the removal of ammonia nitrogen in coking wastewater has become one of the urgent problems at present. This experiment uses two-stage micro oxygen EGSB reactor to treat coking wastewater. It is proved that removal of ammonia nitrogen with this method is not well enough and a more suitable process is needed to remove the ammonia nitrogen in coking wastewater. Then the subsequent experiments adopt two-stage micro oxygen granular sludge+diatomite and micro oxygen granular sludge+aerobic sludge methods separately.The main contents and results of this research are as follows:1. In the two-stage micro oxygen EGSB reactors, with1120~2200mg/L of influent COD concentration, at12h of hydraulic retention time,2.7m/h of rising velocity and feeding water temperature of28～35℃, the ammonia nitrogen removal effect is low.The ammonia nitrogen concentration of the effluent after two-stage reactors is40to157mg/L and can't meet discharge requirements. The highest total removal rate is only46%and sometimes it even has negative removal rate. The ammonia nitrogen removal effect in this system is low and the ammonia concentration in the effluent can't meet the discharge standards. A more suitable process is needed.2. After the two-stage micro oxygen granular sludge+diatomite process, with1100-2060mg/L of influent COD concentration,12h of hydraulic retention time,3.2m/h to2.9m/h of rising velocity, feeding water temperature of2529℃, the ammonia nitrogen concentration of the effluent is2～12mg/L which meet the first level of discharging standard in the "integrated wastewater discharge standard"(GB8978-1996).When the system may make sure that the ammonia nitrogen concentration in effluent could meet the standard and operated steadily for half month, the adding of diatomite is ceased and it still meet meet the standard. After the system run stably for a period of time, a long time (1month) stopping won't impact the restart and the treating effect obviously. In addition, the ammonia nitrogen concentration of influent, the diatomite dosage and the sludge concentration in the reactor all will affect the process on ammonia nitrogen removal effect.3. In the micro oxygen granular sludge+aerobic sludge system, with1600～2060mg/L of influent COD concentration, at12h of hydraulic retention time,3.2m/h of rising velocity and the feeding water temperature of23～29℃, the ammonia nitrogen concentration of the effluent is0.2～10mg/L which meets the discharge standard. After the system run stably for a period of time, a long time (1month) stopping won't impact the restart and and the treating effect obviously. In addition, aeration time and pH value in the aerobic system will affect the process on ammonia nitrogen removal effect.4. From the point of technology, the two processes of two-stage micro oxygen granular sludge+diatomite and micro oxygen granular sludge+aerobic sludge both have efficient and stable removal effect on ammonia nitrogen; From the point of economy, the micro oxygen granular sludge+aerobic sludge process costs far higher in operation than two-stage micro oxygen granular sludge+diatomite process. Therefore, two-stage micro oxygen granular sludge+diatomite process has provided a new efficient and economic method for removing ammonia nitrogen in coking wastewater.