Modelling of nitrification in biofilms under inhibitory conditions using aniline | |
| Author | Gheewala, Shabbir Hussaini |
| Call Number | AIT Diss. no. EV-01-1 |
| Subject(s) | Sewage--Purification--Nitrogen removal Biofilms Nitrification inhibitors |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development |
| Publisher | Asian Institute of Technology |
| Abstract | Performance of nitrifying biofilms under inhibitory conditions was investigated and modelled in this research. Aniline was used as the model inhibitor. A completely mixed, downflow, packed bed biofilm reactor was operated in the continuous-flow mode for nitrification. Its performance vis-a-vis nitrification under inhibitory conditions due to aniline was evaluated. Three sets of experiments were conducted using nitrifying biofilm (i) unacclimated (ii) partly acclimated and (iii) fully acclimated to aniline. The overall objective of the experimentation in each case was to evaluate the performance of nitrifying biofilm under inhibitory conditions through nitrification kinetic experiments. To obtain meaningful results, a proper methodology of experimentation was developed by repeated trials and improvisation of the experimental procedure. Initially after setup of the reactor, it was run with bare media (without biofilm) to ascertain the flow pattern of the reactor. The recirculation rate was maintained at about 9 times the influent flow rate to achieve complete-mix conditions. Tracer experiments were carried out to confirm the complete-mix regime and to determine the residence time of the system. In case of unacclimated biofilm, the media with nitrifying biofilm was obtained from a wastewater treatment plant. Partly acclimated biofilm was produced from unacclimated biofilm obtained from the same wastewater treatment plant by feeding the reactor with aniline for a few days. Seed for acclimated nitrifying biofilm was obtained from an SBR acclimated to 200 mg/L of aniline. The biofilm was grown on the polypropylene media of the packed-bed submerged reactor using the seed. In each of the three cases, the reactor was fed with NH4Cl, NaHC03 and nutrients for the first few days to establish nitrification activity. Nitrification kinetic experiments under noninhibitory conditions were carried out to determine the maximum achievable nitrification rate in the biofilm and also the effective biofilm kinetic thickness. Maximum nitrification rates of 3.5 - 4.0 gN/m2.d were obtained under non-inhibitory conditions. Aniline kinetic experiments were then carried out using excess of NH4Cl, NaHC03 and DO and varying concentrations of aniline in the different runs. Each experimental run with one particular concentration of aniline was carried out for at least 6 HR Ts as it was observed that this was the minimum time required to wash out all the N03N from the previous run. The run was not carried beyond 9 HRTs as it was observed that the nitrification rate started to decrease gradually after stabilising at 6 - 7 HRTs, probably due to long-term toxicity effect of aniline. Also, for higher concentrations of aniline, each run was separated by feeding NH4N, NaHC03 and nutrients only during subsequent days. This was done to ensure that the inhibition effect of aniline from the previous run did not affect the subsequent one and the nitrification activity of the biofilm was maximum at the beginning of each inhibition run. This also prevented the excessive growth of aniline degraders which was observed when experiments with aniline were carried out continuously for 3 - 4 days. A general biofilm model was developed for simulating nitrification in biofilms under inhibitory conditions. For the model, mass transfer and substrate uptake interactions were considered in a planar biofilm with uniform properties (density, diffusivity, biomass concentration, etc.). Nitrification inhibition was modelled using uncompetitive inhibition kinetics. Fitting the experimental results to the model yielded inhibition coefficient, Kb for aniline. In the case of unacclimated biofilm, Ki of 3 .2 mg/L was observed while for acclimated biofilm, the Ki was 3.0 mg/L. For partly acclimated biofilm however, a very low Ki or about 0.2 mg/L was observed. This low value could be attributed to oxygen limitation in the inner portions of the biofilm where the nitrifiers were expected to be, due to the acclimation procedure adopted. The biofilm model and experimental procedure developed in this study can be used for evaluating nitrification inhibition coefficients for any compound toxic to nitrification in biofilms. |
| Year | 2001 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development (SERD) |
| Department | Department of Energy and Climate Change (Former title: Department of Energy, Environment, and Climate Change (DEECC)) |
| Academic Program/FoS | Environmental Engineering and Management (EV) |
| Chairperson(s) | Annachhatre, Ajit P. |
| Examination Committee(s) | Chongrak Polprasert;Jindal, Vinod K.;Wilderer, Ing. Peter |
| Scholarship Donor(s) | Asian Institute of Technology |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2001 |