| Compared with conventional nitrification/denitrification processes, completelyautotrophic nitrogen removal over nitrite （CANON） has low aeration requirements andlow sludge yield, and does not require carbon; thus, this technology is consideredeconomical and environment friendly. However, because anaerobic ammoniumoxidizing bacteria （AnAOB） growth doubles slowly （11days）, and survives in verycomfortable environment, yet the CANON process entails a long start-up time andtreatment performance would be limited over a long period of time function. Theobjective of this paper was to explore the influence of support surface characteristics,dissolved oxygen （DO）, free ammonia （FA） and inorganic carbon （IC） on the CANONprocess, and the characteristics of extracellular polymerie substane （EPS） in CANONprocess were also studied.In order to assess the effects of the surface hydrophilicity of supports on thebiofilm formation and evaluate the performance of CANON process in a sequencingbatch biofilm reactor （SBBR）, unmodified activity carbon fibers （ACFs） and ACFshydrophilic modified by heat treatment were used as supports. CANON process wasinitiated in a SBBR from conventional activated sludge. An operation temperature of32±2°C, DO level at-1.5mg L-1and FA concentration with3.98–15.93mg L-1weremaintained in the SBBR. Fourier transform infrared （FT-IR） spectra and Boehm’sneutralizing titration exhibited that modified ACFs had more oxygen-containing groupsthan unmodified ACFs. Larger biofilm growth on the modified surfaces examined byscanning electron microscopy and biofilm’s total dry weight, and the biofilm on themodified surfaces were more active, compared with those on the unmodified surfaces.This study demonstrates the hydrophilic-modified ACFs have better biological affinitythan unmodified ACFs. Maximal total nitrogen removal rate of0.088kg Nm3day-1wasachieved for the CANON process on day80, and the molar ratio of nitrate production toammonium consumption approached0.11, indicating the CANON process wassuccessfully started up. Apart from supports, the strategies of DO supplying andcontrolling FA concentration were also keys in starting up the CANON process within ashorter period.AOB and AnAOB are autotrophic microorganisms. IC is their main carbon source.The efects of IC limitation on AOB and AnAOB in the CANON process in a SBBR were examined. The optimal IC concentration in the influent was investigated. The AOBand AnAOB activities were limited by an IC concentration of50mg-C·L-1in theinfluent, as the nitrogen loading rate （NLR） was200mg-N·L-1·d-1. The experiment onrecovering the influent IC showed that the activities of AOB and AnAOB wererecovered by increasing the IC concentration in the influent. From an economic point ofview, the optimal IC concentration in the influent was250mg-C·L-1at200mg-N·L-1·d-1NLR in this CANON system.FA plays an important role in the stable, long-term CANON system operation. Theinfluence of FA on the CANON process in a sequencing batch biofilm reactor wasexplored. Under controlled FA concentrations of5.0mg·L-1to-10.0mg·L-1,nitrite-oxidizing bacteria （NOB） was inhibited and achieved partial nitrification, whichwas important for a successful quick start-up of the CANON process from activatedsludge. However, NOB was acclimated to the condition after the process start-up.Ammonia-oxidizing bacteria （AOB） and AnAOB activities were unaffected when FAconcentration was increased from-10mg·L-1to-17mg·L-1, but NOB was completelyinhibited only briefly. The AOB and AnAOB activities were inhibited and the CANONsystem was deteriorated when FA concentration reached30mg·L-1to32.5mg·L-1at pH8.5, whereas NOB activity was unaffected. Correlation analysis was performed todemonstrate that FA concentration higher than20mg L-1resulted in the deterioration ofthe system.The composition and distribution of EPS that were extracted from biofilm andactivated sludge in CANON system were investigated. The conclusions were asfollows：EPS content, including carbohydrates, proteins, humic and DNA, with differentlayers changed great. The composition of EPS in CANON process was mainlycomposed of TB-EPS, rather than SEPS and LB-EPS, compared with the EPS ofconventional activated sludge. So, compared with conventional activated sludge, thesludge in the CANON process owned more stability. In the same reactor, differentcarrier own different EPS content including carbohydrates, proteins, humic and DNA.The amount of EPS biofilm on carrier SCP was-181.7mg/gVSS, which was-1.51timesof that on carrier ACFs. The difference of EPS of the two biofilms was almostly causedby the significant difference of protein composition. The protein content of biofilm oncarrier SCP was96.5mg/gVSS, which was-1.6times of that on carrier ACFs.The research results of this paper could provide theoretical basis for starting up theCANON process within a shorter period and long term stable operation, as well as lay dawn the foundation for further research on the CANON process.This research was supported by the Natural Science Foundation of China（51108482） and the Research Fund for the Doctoral Program of Higher Education ofChina （2010019120035）. |
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