Study On Treatment Of Urea Wastewater By Anaerobic Ammonia Oxidation Process

Urea wastewater is a kind of typically industrial wastewater with with high nitrogen content and complex composition,which has great harm to the environment.Treatment of urea wastewater with Anaerobic ammonium oxidation?Anammox?process,is more economical and efficient than the traditional urea treatment process,because of no additional carbon source is needed for the complete autotrophic nitrogen removal process.But at present,the application of Anammox process in the treatment of urea wastewater is rarely reported.In this paper,the anammox sludge was taken as the research object.By analyzeing the nitrogen conversion and reaction rate of anammox at different urea concentrations,established a kinetic model of Anammox urea inhibition.The continuous domestication and stepwise domestication methods were used respectively,comparing and discussing the changes of nitrogen removal performance and microbial community structure of Anammox reactor under different culture conditions.The main contents and conclusions are as follows:?1?Low concentration urea?10-100 mg/L urea-N?had no significant effect on the Anammox reaction,and the degradation rate of NH₄⁺-N wans remained at 2.43±0.1mg N/?g VSS·h?.Medium and high concentration of urea?150-2000 mg/L Urea-N?has a certain inhibitory effect on the Anammox reaction,and with the increase of Urea-N concentration,the inhibition is more significant.When Urea-N is 2000 mg/L,the NH₄⁺-N removal rate dropped from 85.49%to 54.16%.Based on the change of nitrogen at different urea concentrations,an Anammox urea inhibition kinetic model was established.The model calculated that the nitrogen concentrations is basically consistent with the measured value,and the correlation coefficient R²>0.988,indicating that the model has good accuracy.?2?Anammox sludge without domestication?denoted as AMX?,the degradation rate of NH₄⁺-N was 1.788 mg N/?g VSS·h?,the reaction rate of Anammox gradually decreases with the increase of Urea-N/NH₄⁺-N ratio in the matrix,indicating that the AMX cannot hydrolyze urea.With the culture time increasess,the Anammox activity in A?30 mg/L NH₄⁺-N and 30 mg/L Urea-N?and B?60 mg/L Urea-N?reactors using continuous domestication mode was first decreased and then increased.After 24 days of culture,the degradation rate of NH₄⁺-N were 2.644 and 2.970 mg N/?g VSS·h?respectively,which were higher than those of AMX.The Anammox sludge in the A and B reactors has a certain urea degradation capacity after domestication,and the urea degradation rates are0.045 and 0.210 mg N/?g VSS·h?,respectively.The results of 16S high-throughput sequencing showed that the relative abundance of Anammox Bacteria?An AOB?in AMX reactor was 24.61%,mainly Candidatus Brocadia and Candidatus Kuenenia.Adding urea will decrease the abundance of An AOB in 8 days?A1=19.54%,B1=22.57%?,and then quickly rise back.The An AOB abundance of B reactor was 4.73%higher than AMX.at the 24 days?3?The R1?low concentration and low HRT?and R2?high concentration and high HRT?reactors were operated by stepwise domestication mode with constant total nitrogen loading rate?NRR?.The Anammox activity was inhibited by urea at the beginning of operation.After 30 days of domestication,the reaction activity of Anammox was recovered.The degradation rate of NH₄⁺-N were 1.503 and 1.398 mg N/?g VSS·h?respectively,but they were still lower than those of AMX?1.788 mgn/?g VSS·h??.At 30days,the R1 and R2 reactors can completely hydrolyze 15 and 18 mg/L Urea-N,and the urea degradation rate is 0.0983 and 0.1123 mg N/?g VSS·h?,respectively.The species difference between R1/R2 and AMX was obvious.The types of An AOB in R1 and R2sludge are the same as AMX,but the relative abundance?R1:15.29%,R2:13.86%?is significantly reduced compared to AMX?24.61%?.And Calorithrix and Saprospiraceae?AMX:1.67%and 0.35%?,two kinds of bacteria which that can directly use organic matter,the abundance has increased?R1:4.25%and 2.62%,R2:3.45%and 3.70%?after domestication,guess that these two types of bacteria are related to the hydrolysis of urea.