Treatment of industrial effluent with high ammonium concentration using new autotrophic nitrification/denitrification biological techniques

Resumen

Today, one of the most important ecological problems in the world is the proliferation of wastewater. The presence of nitrogen in urban wastewater in form of urine, synthetic nitrogen fertilizers and industrial wastewater are evidently a significant environmental risk that must be eliminated before their discharge into natural wasters. In this work the effect of different operational conditions and the structure of the microbial communities through submerged-bed partial nitritation technology constructed at bench-scale were studied. Different hydraulic retention time (HRT) has been used to get the perfect ammonium-nitrite mixture converting the 50% of ammonium in nitrite. Moreover to find a perfect HRT several bench scale submerged-bed partial nitritation bioreactors were built to determine several physico-chemical parameters, such us Ammonium, nitrite and nitrate concentrations over the time. Molecular biology techniques were used to compare the microbial communities growing in the different bioreactors under these different HRT(7,9, and 12 hours). Scanning electron microscope was used to determinate the most accurate position and growth rates of the biofim in the carrier (Bioflow 9). On the other hands Molecular biology techniques have been used to study the microbial population (16S rRNA genes) and specific bacterial groups involved in the nitrification process, such as ammonium oxidizing (CTO) and nitrite oxidizing (nxrA) using a cultivation-independent approach based on PCR-TGGE fingerprinting. On the other hand, once obtained the results of the optimum HRT, four bench scale submerged-bed partial nitritation bioreactors were constructed to evaluate the influence in the submerged-bed partial nitritation bioreactors under different concentrations of a emerging contaminant (ciprofloxacin) over the nitrogen removal performance and microbial population.To establish an objective correlation between physico-chemicals parameters and microbial communities and reveal the relationships between the structure of nitrifying microbial communities and a set of variables (ammonium, nitrite, time, antibiotic concentration and HRT) related to the operating parameters a Statistical multivariate analysis by CANOCO and 3D surface polynomial fitting redundancy analysis (RDA) was performed. Using these different techniques we observed that the HRT affects the functioning of partial nitritation bench scale bioreactor built with submerged-filter technology and the microbial community structure. The application of HRT of 7h can be reach using a submerged-bed partial nitritation technology increases the biotransformation of ammonium into nitrite and reducing the HRT 3 times in comparison with fluidized bed bioreactors.The HRT in a partial-nitritation bioreactor constructed as a submerged fixed-biofilm bioreactor affect the structure of the microbial community. Thus with HRT of 12 h, the majority of bacteria were Nitrosomonas eutropha, while with a HRT of 9 h Nitrosomonas europea and Nitrosospira sp were dominant. Moreover, other bacterial groups analysed, such us nitrite-oxidizing bacteria, also showed modifications in response to the HRT used in each experiment. On the other hand, the presence of Ciprofloxacin has an impact on the performance of partial nitritation bioreactors. Under the concentration of 100 ng/L of ciprofloxacin, the system acquired a more efficient removal of ammonium than the desired 50% ammonium-50% nitrite. However, concentration up to 350 ng/L of ciprofloxacin, the partial-nitritation bioreactors could no longer reach operation equilibrium with regard to ammonium removal. Moreover, The presence of ciprofloxacin in wastewaters affect the microbial community structure in partial-nitritation systems. In this context, the presence of low concentration of antibiotic produce a period of adaptation with changes in respect to bioreactors without the addition of ciprofloxacin, lead to different steady-states of the partial-nitritation reactors, as well as to different microbial communities inside the bioreactors. In addition, with antibiotic concentration up 350ng/L, microbial community structure experienced a deep change with a significant reduction of the AOB populations. Finally, the presence of high concentration of ciprofloxacin in urban wastewater produces an enrichment of resistant strains.