| Coking wastewater is typical industrial wastewater from the processes of making coke, purifying coal gas and recovering the coke products. Which contains many different kinds of nitrogenous compounds and high dense nitrogen. The new national standard of total nitrogen emissions requirements is 20 mg/L, and as a result, many coking wastewater plants are faced with substantial challenges, such as technical innovation. Ascertain the primary sources of total nitrogen in coking wastewater and its removal behaviors during biological treatment process can provide guidance and basis for the process optimization and engineering operation of coking wastewater nitrogen removal.In the first place, in order to ascertain the primary sources of total nitrogen in coking wastewater, different cases of A(anaerobic)/O1(aerobic)/O2(aerobic), A(anaerobic)/O1(aerobic)/H(hydrolytic)/O2(aerobic), O1(aerobic)/H(hydrolytic)/O2(aerobic) coking wastewater treatment processes were taken as examples. The concentration variation of total nitrogen, ammonia nitrogen, thiocyanate, cyanide, nitrate and nitrite in different biological treatment stages were analyzed. The form of nitrogenous compounds, the proportions of total nitrogen and their transformation during biological treatment process was also studied from engineering data. The results show that the total nitrogen in raw water of three coking wastewater plants is 250 mg/L ~ 620 mg/L, and it was composed primarily of ammonia nitrogen, thiocyanate, cyanide, in which, ammonia nitrogen and thiocyanate accounted for more than 80% of total nitrogen. Transformation of nitrogen compounds in coking wastewater during three types of biological treatment processes similar consisted of two steps: primary aerobic treatment stage and secondary aerobic treatment stage. In primary aerobic treatment stage, thiocyanate and cyanide were oxidized to ammonia nitrogen. Then in secondary aerobic treatment stage, ammonia was further oxidized to nitrite and nitrate.And then in order to explore the removal relationship between primary nitrogenous compounds i( thiocyanate, cyanide, ammonia) and other pollutants like( COD, phenol, sulfide) during biological treatment processes, taking the O1/H/O2 fluidized bed applied in coking wastewater treatment process as typical cases in Tianjin tiantie coking chemical plant, the study focused on the removal efficiency for the primary nitrogenous compounds including( thiocyanate, cyanide, ammonia) and other pollutants like( COD, phenol, sulfide) in each reactor. The relationship between the biodegradation of these pollutants with process indexes( SV30, HRT) was investigated through simulative aerobic reactor; and the biodegradation sequence of these primary pollutants was also discovered. The results show that for the O1/H/O2 processes, the removal rates of COD, phenol, sulfide, thiocyanate, cyanide in the O1 reactor were above 90%, and in this porcess, the thiocyanate, and cyanide were converted to ammonia. In the O2 reactor, the influencing factors of nitrification involved the concentration of ammonia nitrogen, the concentration of nitrite, temperature, pH, when initial ammonia concentration was 380 mg/L~ 400 mg/L, under the operating condition of 23~ 27 ℃, pH = 7.8 ~ 8.3, the completel nitrification could be achieved in 23 days of experiment. In addition, in the simulative aerobic degradation experiment of nitrogenous compounds, given the concentration of COD, and thiocyanate was 4465 mg/L and 1238 mg/L, respectively, when controlling temperature, pH, dissolved oxygen and SV30 at 17~19 ℃, 7~ 7.5, 1~5 mg/L and 30% respectively, the removal rate of COD, thiocyanate could be achieved by 90%, 99% through a 50.5 h continuous aeration. Moreover the microorganism preferentially degraded phenol, cyanide, sulphide; then along with the reduction of inhibiting effect brought by the toxic compounds, the thiocyanate started to be degraded. Finally, when the thiocyanate were removed completely, the COD also reduced to the minimum concentration. |
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