Short-term Saline Shock And Rapid Recovery On Anammox Performance

Anaerobic ammonia oxidation(anammox)is an environment-friendly biological nitrogen removal process,which has been developed as a promising technology in industrial wastewater treatment.However,when anammox process is applied to treat high saline nitrogen-containing wastewater,the anaerobic ammonia oxidizing bacteria(AnAOB)will be susceptible to be inhibited by osmotic stress caused by short-term exposure of the high salinity.This shock is referred to as a salinity shock,of which the saline exposure time is generally less than the doubling time of AnAOB.It is difficult for AnAOB to adjust its metabolic system in such a short period.It will enter a inhibitory state,thus affecting the system performance.In particularly,the short-term saline shock and rapid recovery on anammox performance still lacks comprehensive research.Based on response surface methodology,salinity concentration,saline exposure time and NaCl/Na2SO4 ratio were selected as three independent variables and the inhibitory level of saline shock on anammox activity was chosen as the response for dependent variable for short-term high salinity shock experiments.The salinity concentration and saline exposure time were the main factors causing the significantly inhibition of anammox activity compared to NaCl/Na2SO4 ratio(p<0.01).The approximate linear regression relationship between saline exposure time and salinity concentration was resolved under IC25,IC50 and complete inhibitory.The addition of glycine betaine(GB)at the range of 0.1-5 mM was effective approach for anammox to resist relative lower saline shock intensities(e.g.,IC25 and IC50),with the activity keeping up to 94.7%.However,glycine betaine was not effective under the relative higher saline shock intensities(e.g.,completed inhibited condition),with the activity only up to 58.8%.Uner relative lower saline shock intensities,the addition of 2-3 mM GB has a good effect on resisting saline inhibition.Transmission electron microscopy observed that the distribution density of anammox cell was loosen under the completed inhibited condition.Microbial community analysis revealed that Brocadiaceae accounted for about 7.6%-13.2%under completed inhibited condition.Interestingly,16S rRNA analysis showed that the abundance of activated Brocadiaceae increased initially during saline shocking period compared to the original sludge and continued to decrease after the shock.During saline shocking period,the abundance increased from 51.7%to 70.1%and 52.3%under IC100-G1(a saline exposure time of 54 h and salinity of 7.41%)and IC100-G2(a saline exposure time of 132 h and salinity of 6.11%),respectively.Then the abundance decreased to 5.9%and 1.5%with time.This tendency was consistent with the results of qPCR targeted hzsA gene.The hzsA gene in original sludge was 3.35×106 copies/gVSS.During saline shocking period,the hzsA gene were 4.75×106 copies/gVSS and 3.76×106 copies/gVSS,under IC100-Gl and IC100-G2,respectively.Finally,it decreased to 1.89×105 copies/gVSS and 7.50×105 copies/gVSS,respectively.Finally,a recovery strategy based on quorum sensing was studied.Compared to the anammox activity of original sludge,anammox activity was tested to be recovered to 78.9%or 93.5%by adding 8 μM C6-HSL or 30%origin anammox sludge,respectively.The results of this study can promote the development and operation of salt-tolerant anammox process.