The Pilot Plant Research Of WISCO Coking Wastewater Using A/O Process Combined With High Effective Bacteria

Coking wastewater contains abundant refractory organic toxicants, such as heterocyclic compounds,PAHs and so on, which was unable to disposed effectively by conventional biological methods, thereby making the quality of effluent substandard. Dosing pertinent and efficient bacterium as a kind of common biological reinforcement can solve the aforementioned problem viably, which has been widely applied to various coking wastewater treatment plant. According to the quality and characteristics of WISCO coking wastewater , our research group used high effective bacteria which had been isolated in lab to purify coking wastewater within Anoxic/Oxic pilot plant on the site of WISCO coking factory. This paper focus on the study of biological strengthening in this pilot plant.Research results show that: organic pollutants and ammonia nitrogen can be removed availably by A/O process which combined with efficient bacterial technology. On the condition of stable running, total removal percentage of COD reach 95% while the influent's COD concentration was within the range of 1000 1700mg/L, the effluent's COD concentration was controlled under 150mg/L, in most cases, which was lower than 100mg/L. The removal percentage of ammonia nitrogen exceeded 97% during its influent concentration fluctuated between 100mg/L and 300mg/L, the concertration in effluent was less than 10mg/L. The effuent concertration of COD and ammonia nitrogen can reach the discharge standard (GB8978-1996).During the stable running of systerm, the result of denitrification was excellent in anoxic tank. Without additional carbon source, denitrifying rate reached within 50%⁷4% as well as the removal rate of COD undulated between 20% and 42%, the more denitrifying rate increased, the more COD removed. The reflux ratio of anoxic tank at 3 was suitable, dissolved oxygen concentration was mounting if the reflux ratio outnumber 3, which means denitrification suffer adverse impacts. Denitrifying rate was positive correlated with NO₃^--N/C while the ratio of NO₃^--N/C below 0.147, on the contrary, denirtrifying rate descended if NO₃^--N/C surpassed 0.2, in other words, carbon sources was insufficient. The suitable value of pH in anoxic tank was within the range of 7.2⁷.8.Nitrification of aerobic tank was robust while COD/NH3-N below 4, ammonia nitrogen removal efficiency outstriped 95%, meanwhile the removal rate of NH3-N attained 90% when influent concertration of COD reached 1100mg/L and COD/NH3-N beyond 5.7, which means nitrification can bear high load organic pollutants. The optimal condition of nitrification was at HRT>36h, NH3-N<260mg/L, pH=6.8⁷.8. Dissolved oxygen deficiency make phenomenon of the nitrite accumulation emerged, when the aeration volume under 25m3/h, the nitrite accumulated rate reached to 50%, but nitrite accumulation vanished finally due to the aeration volume recovered at 60 m3/h. During the stable running of aerobic tank, ammonia nitrogen was oxidized to nitrate, and nitrite accumulation was not durable.