To evaluate continuous and sporadic nitrification inhibition at the HRSD Nansemond Wastewater Treatment Plant, which has a history of nitrification upsets, continuous sequencing batch reactors (SBRs) were operated to simulate the full-scale plant. Four reactors were operated in this study. One reactor was fed with raw influent (RWI) from the Nansemond Wastewater Treatment Plant (NP). Another was fed with NP primary clarifier influent (PCI), which includes the raw influent, as well as plant recycle streams and truck delivered septage, grease, and chemical toilet waste. The remaining two SBRs were fed with RWI from the VIP Wastewater Treatment Plant, which achieves reliable nitrification year-round. One of these VIP SBRs would remain a control at all times, while the other would be used to evaluate suspected inhibitors to nitrification. The first phase of this project was to determine whether NP was inhibited when compared to VIP, which would be ascertained through a comparison of nitrification performance. The next step was to determine whether the source of inhibition was an industry within the collection system or plant recycles and delivered wastes, which would be ascertained based on comparison of the NR RWI and NP PCI reactor performance. If nitrification performance was comparable between the two SBRs, then it would indicate that the source of inhibition is somewhere within the collection system, whereas if the NP PCI reactor was inhibited when compared to the NP RWI reactor, it would mean that the inhibition is a result of plant recycles or delivered wastes. The next phase would be to determine the specific source by either working back up the collection system or by testing the plant recycles and delivered wastes. After approximately 27 weeks of SBR sampling and monitoring, there was no statistical difference between nitrification rates in reactors A and B, and no signs of nitrification inhibition in either reactor when compared to the VIP control Simulation modeling of reactors A, B, and D (control) was performed with BioWin 3.1 (EnviroSim, Ltd.) as a means for comparison and to ensure reactors were performing as intended. Results suggest that there was some level of continuous inhibition for both NP RWI and PCI reactors, however no sporadic inhibition events were observed. It also appeared that the VIP RWI control reactor experienced some level of continuous nitrification inhibition, although BioWin modeling results indicated that both NP RWI and NP PCI were more inhibitory than VIP RWI. Conclusions drawn from modeling results conflict with those drawn from nitrification rate comparisons. Since solids retention time (SRT) was maintained at exactly 15 days for all reactors, it was assumed that a direct comparison of corrected maximum nitrification rates could be used to compare nitrification performance between SBRs, however the significantly higher influent COD, TKN, and TSS loading to the NP reactors resulted in higher nitrification rates when compared to the VIP RWI control reactors. This was confirmed with BioWin modeling, which also showed consistently higher nitrification rates for NP when compared to VIP RWI, however BioWin also showed that maximum specific growth rates for ammonia-oxidizing bacteria (?maxAOB) in NP RWI and PCI were consistently lower than the ?maxAOB for VIP RWI. This indicates that NP RWI and NP PCI are slightly inhibitory to nitrification, with ?maxAOB values between 0.65 and 0.75 days??, and the fact that both NP RWI and NP PCI are both inhibitory suggests that the source of inhibition is somewhere within the collection system. In a simultaneous study using the reactors fed with raw influent from the VIP Wastewater Treatment Plant, reactor C was spiked with aqueous Film Forming Foam (AFFF) such as that used in methanol feed facility fire suppression systems, while reactor D was left as a control. AFFF was initially added at a concentration of 20 ppm with no effect on either nitrification or denitrification performance. When increased to 40 ppm, the AFFF reactor experienced a complete loss of denitrification, while nitrification rates were not affected when compared with the control reactor. Reactor C took 31 days to fully acclimate to the AFFF feed and fully regain denitrification, and then exhibited no other performance problem throughout this acclimation period. This result was completely unexpected, appears to be repeatable, and is one of very few cases of selective denitrification (and COD uptake) inhibition, as opposed to more commonly observed nitrification inhibition. / Master of Science

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

This dissertation aims to expand our knowledge of glycerol-driven engineered biological nitrogen removal processes by elucidating the link between operational controls and the structure and function of the microbial ecology grown under stoichiometrically-limited and excess glycerol conditions. Specific objectives were to: 1. Develop and experimentally evaluate an improved metric for denitratation performance that can be objectively compared across studies; 2. characterize the process kinetics, nitrogen conversion efficiencies, and microbial ecology of a glycerol-driven, stoichiometrically-limited denitratation process; 3. elucidate the impact of kinetic limitation on microbial community structure and function in a glycerol-driven, stoichiometrically-limited denitratation process; 4. explore the biological mechanisms contributing to nitrite (NO2-) accumulation in a glycerol-driven denitratating microbial community; and, 5. characterize the nitrogen conversion efficiencies and microbial ecology that favor dissimilatory nitrate reduction to ammonium (DNRA) in a glycerol-driven denitrification process at stoichiometric excess. Accordingly, a nitrate (NO3-) conversion ratio (NaCR) was first proposed as an improved metric of denitratation performance metric. Previous metrics used throughout literature were deemed insufficient as they provided an incomplete and subjective representation of denitratation performance by not accounting for residual NO3- remaining in the system following the selective reduction of NO3- to NO2-. The NaCR represented a singular metric that better signifies true denitratation performance and can be compared across studies regardless of carbon source or system configuration. Second, a glycerol-driven denitratation process was optimized according to different operational controls. Steady-state reactor operation and in situ and ex situ batch assays indicated that the influent chemical oxygen demand to NO3- (COD:NO3--N) ratio was determined to influence process kinetics and nitrogen conversion efficiencies leading to significant NO2- accumulation. A singular microbial community structure correlated to system performance was identified. Third, the application of kinetic limitation (by imposing different solids retention times [SRTs]) at a given influent COD:NO3--N ratio was demonstrated as an effective mechanism in the selection for a denitratating microbial ecology capable of significant NO2- accumulation. Steady-state reactor operation was used to characterize process kinetics and nitrogen conversion ratios supporting the determination of the optimal SRT for reactor operation. Analysis of the microbial community structure elucidated the impacts of kinetic limitation on the microbial ecology which were correlated to system performance. Functional denitrification gene transcripts were found to be significantly different under kinetic limitation, indicating that NO2- accumulation was driven more by differences in microbial community structure as opposed to differential expression at different operating SRTs. Fourth, ex situ batch assays were used to elucidate the microbial transcriptional response to the presence of varied sequences of electron acceptors. The microbial community was found to be enriched with NO3--respirers, or microorganisms incapable of NO2- reduction, and progressive onset denitrifiers, which express functional denitrification genes in sequence. The presence or re-introduction of NO3- in a NO2--reducing community was found to elicit an immediate transcriptional change and shift of electron flow to NO3- reductase. Electron competition as the primary contribution to NO2- accumulation was confirmed through the artificial inactivation of NO3- reductase. Lastly, an influent COD:NO3--N ratio was applied in stoichiometric excess to create the conditions necessary to support DNRA over denitrification. System performance at steady-state was found to vary under different kinetic regimes. The induction of DNRA was found to be far more complex than simply providing glycerol in stoichiometric excess. Additionally, glycerol does not appear to be an optimal COD source for DNRA under these conditions. In sum, the optimization of engineered biological nitrogen removal processes through the manipulation of process kinetics and the resulting impacts on nitrogen conversion efficiencies and microbial community structure and function was investigated in detail. From an engineering perspective, this knowledge can help guide the design and operation of biological nitrogen removal processes to systematically maximize the accumulation of targeted nitrogenous products or mitigate unintentional and undesired products.

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Wastewater treatment methods have always gravitated towards the use of biological methods for the treatment of domestic grey water. This has been proven to offer a series of advantages such as the reduction of pollution attributed to the use of synthetic chemicals; therefore, this decreases the requirement of further costly post primary treatment methods. Although such biological methods have been used for decades, their efficiency and sustainability has always been challenged by inhibitory toxicants which renders the systems redundant when these toxins are prevalent in high concentrations, culminating in the deactivation of biomass which facilitates the treatment. In most instances, this biomass is anaerobic sludge. Hence, the proposal to utilize biofilms which are ubiquitous and selfsustaining in nature. The use of engineered biofilms in wastewater treatment and their behaviour has been studied extensively, with current research studies focusing on reducing plant footprint, energy intensity and minimal usage of supplementary synthetic chemicals. An example of such processes include traditional nitrification and denitrification systems, which are currently developed as simultaneous nitrification and aerobic denitrification systems, i.e. in a single stage system, from the historical two stage systems. However, there is limited literature on biofilm robustness against a potpourri of toxicants commonly found in wastewater; particularly for total nitrogen removal systems such as simultaneous nitrification and denitrification (SND). This study was undertaken (aim) to assess the ability of biosurfactant producing biofilms in the removal of total nitrogen in the presence of toxicants, i.e. heavy metals and phenol, as biosurfactants have been proven to facilitate better mass transfer for pollutant mitigation. Unlike in conventional studies, the assessment of biosurfactant producers in total nitrogen removal was assessed in both planktonic and biofilm state. Since biofilms are known to have increased tolerance to toxic environmental conditions, they were developed thus engineered using microorganisms isolated from various sources, mainly waste material including wastewater as suggested in literature reviewed, to harness microorganisms’ possessing specified traits that can be developed when organisms are growing under strenuous environments whereby they are tolerant to toxic compounds. The assessment of these engineered biofilms involved the development from individual microorganisms to form biofilms in 1L batch reactors where the isolated microorganisms were grown in basal media containing immobilisation surfaces. The assessment of the total nitrogen efficiency was conducted using Erlenmeyer flasks (500mL) in a shaker incubator, with the biofilm TN removal efficiency being assessed in batch systems to ascertain simultaneous nitrification and denitrification rates even in the presence of heavy metals (Cu2+, Zn2+) and C6H5OH. Ambient temperature and dissolved oxygen conditions were kept constant throughout the duration of biofilm development with microorganisms (initially n = 20) being isolated for the initiation of biosurfactant studies which included screening. Results indicated that the engineered biofilms, constituted by biosurfactant producing organisms (n = 9), were consisiting of bacteria (97.19%), Protozoa (2.81%) and Archaea (0.1%) as identified using metagenomics methods. Some of the biosurfactant produced had the following functional group characteristics as determined by FTIR: -CH3-CH2, deformed NH, -CH3 amide bond, C-O, C=O, O-C-O of carboxylic acids, and C-O-C of polysaccharides. Other selected microorganisms (n = 5) tolerated maximum concentrations of the selected toxicants (Cu2+, Zn2+ and C6H5OH) of 2400 mg/L, 1800 mg/L and 850 mg/L, respectively. Enzyme analysis of the total nitrogen removal experiments indicated a higher nitrogen removal rate to be the Alcanigene sp. at 180 mg/L/h.

Efluentes com grandes concentrações de fenol e nitrogênio amoniacal apresentam grande potencial poluidor ao meio ambiente. Exemplo deste tipo de despejo é o da unidade de coqueria da indústria siderúrgica que apresenta em termos quantitativos os fenóis como os principais constituintes orgânicos. Constituintes inorgânicos também estão presentes neste tipo de despejo e são principalmente cianeto, tiocianato, sulfato e nitrogênio amoniacal, sendo que a concentração deste último pode atingir níveis de centenas de miligramas por litro. No Estado de São Paulo, para atendimento às legislações em vigor - Decreto Estadual 8468/76 e Resolução CONAMA 357/05 - em termos de nitrogênio amoniacal e fenóis, as fontes poluidoras devem atender aos limites de emissão de 20 mg N/L para nitrogênio amoniacal total e 0,5 mg C6H5OH/L para índice de fenóis, e além disso, devem atender a classificação do corpo d\'água. Após resultados bem sucedidos de pesquisas realizadas anteriormente no Departamento de Engenharia Hidráulica e Sanitária da EPUSP objetivando remoção de compostos fenólicos e nitrogênio amoniacal, presentes em uma água residuária sintética de coqueria, através de nitrificação/desnitrificação do afluente em sistemas de lodo ativado, idealizou-se a presente pesquisa objetivando promover a nitrificação/desnitrificação de um despejo similar contendo altas concentrações de fenol (1000 mg/L) e nitrogênio amoniacal (500 a 1000 mgN/L) em sistema piloto de lodo ativado de lodo único, com duas concepções distintas: parcial (\"P\") a nitrito (ou \"nitritação/desnitritação\") em um primeiro caso, somente com fonte interna de carbono para a desnitrificação, e total (\"T\") num segundo caso, com fontes interna e externa de carbono. Além disso, também foi objetivo comparar os resultados obtidos do sistema piloto \"P\" com um sistema em bateladas seqüenciais operado paralelamente para remoção de nitrogênio via nitrito. A pesquisa permitiu concluir que o sistema contínuo, em virtude de seu regime operacional, não foi eficiente para remoção de nitrogênio via nitrito por não favorecer a manutenção de amônia livre na fase aeróbia em concentrações inibitórias aos microrganismos oxidadores de nitrito, já que segundo os resultados satisfatórios do sistema em bateladas seqüenciais, a existência de amônia livre e o pH se mostraram os principais parâmetros que regem o acúmulo de nitrito no reator. Apesar disso, o sistema apresentou resultados satisfatórios quanto à desnitrificação com fenol como fonte de carbono sendo que, durante toda a operação do sistema, o efluente final apresentou concentrações de fenol desprezíveis. Resumindo, o sistema contínuo só se mostrou adequado para remoção de nitrogênio via nitrato, ao passo que o sistema em batelada favoreceu a remoção via nitrito. Quanto ao sistema \"T\", que visava nitrificação/desnitrificação completa com fontes interna e externa de carbono, os resultados permitiram concluir que, apesar do etanol ser utilizado com eficiência pelas bactérias heterotróficas para promover a desnitrificação, seu uso como fonte externa de carbono não foi adequado em sistema de lodo único. Isto porque os microrganismos deixaram de utilizar o fenol na desnitrificação passando a utilizar somente o etanol, provocando acúmulo de fenol e desequilíbrio do sistema. Sendo assim, concluiu-se que o uso de etanol como fonte externa de carbono para a desnitrificação só seria recomendável em reator anóxico em separado, ou seja, em sistema de dois lodos e não de lodo único, como o da presente pesquisa. / Wastewaters containing high phenol and ammonium concentrations present a great pollutant potential to the environment. An example of this kind of effluent is the discharge of coke-plants, which presents, quantitatively, the phenols as the main organic compound. Inorganic compounds are also present in these wastewaters and are mainly cyanide, thiocyanate, sulphate and ammonium, the last one being able to achieve hundreds of milligrammes per litre. In Sao Paulo State, there are two legislations to be accomplished, State Decree 8468/76 and CONAMA Resolution 357/05 that stand that the polluters must accomplish the discharge limits of 20 mg N/L to total ammonium nitrogen and 0,5 mg C6H5OH/L to phenols, as well as accomplish the waterbody classification. The present research was planned after well succeded results of former researches in EPUSP\'s Hydraulic and Sanitation Engineering Department aiming to remove phenolic compounds and ammonium from a synthetic coke-plant wastewater, by nitrification/denitrification of the influent in activated sludge plants. The main purpose of this work was to remove nitrogen of a similar wastewater containing high phenol (1000 mg/L) and ammonium (500 a 1000 mgN/L) concentrations in two activated sludge pilot plants (single sludge): a partial one (\"P\") to remove nitrite (or \"nitritation/denitritation\") in the first case, only with internal carbon source for the denitrification, and a total one (\"T\") in a second case, with internal and external carbon sources. It was also aim of this work to compare the results obtained by the Partial (\"P\") pilot system with a parallel batch sequence reactor operated to remove nitrogen via nitrite. The research concluded that the continuos system, due to its operational characteristic, was not efficient to remove nitrogen via nitrite that does not favor the maintenance of free ammonia in the oxic phase in inhibitory concentrations to the nitrite oxidizers, as according to the wellsucceeded batch system, the existance of free ammonia and the pH have been the main parameters to raise the nitrite accumulation in the reactor. Nevertheless, the system presented satisfactory results to the denitrification with phenol as carbon source and, during the whole experimental work, the final effluent just showed despicable phenol concentrations. Summing up, continuos system was just adequate to remove nitrogen via nitrate, while the batch system favored its removal via nitrite. Due to the Total (\"T\") system which aims to complete nitrification/denitrification with internal and external carbon sources, the results showed that, despite ethanol having been successfully used by the heterotrophic bacteria to denitrification, its use as external carbon source was not adequate in single sludge system, because the microorganisms do not use phenol in denitrification, just using ethanol, causing phenol accumulation and unbalance of the system. Therefore, it was concluded that the use of ethanol as external carbon source to denitrification would be recommended only in anoxic separated reactor, i.e., in a double sludge system and not in a single sludge one, as this research.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 169-180).

In this study the composition of the denitrifying bacterial community among constructed wetlands in agricultural areas was investigated. Thirty-two constructed wetlands located in Southern Sweden were surveyed, and biofilm samples from each were analyzed by applying denaturing gradient gel electrophoresis, to investigate the community composition of the three denitrifying bacterial enzyme genes nirK, nirS and nosZ. The DNA sequences of the enzyme genes were compared to known DNA sequences in GeneBank using BLAST. The results of the denitrifying bacterial enzyme genes indicated that these habitats may harbour a heterogeneous denitrifying bacterial community. Individual analysis of the enzyme genes revealed that nirS was more heterogeneous than both nirK and nosZ. Most sequences from the present study clustered with known sequences from species belonging to the group of α-Proteobacteria, and to a lesser extent with β- Proteobacteria and γ-Proteobacteria, and only nirS clustered with a member of gram-positive bacteria. / <p>Included in doctoral thesis: Milenkovski, Susann. Structure and Function of Microbial Communities in Constructed Wetlands - Influence of environmental parameters and pesticides on denitrifying bacteria. Lund University 2009.</p>

Sulphide containing streams must be treated before releases to environment due to the toxicity, corrosivity and unpleasant odour of sulphide. Anaerobic chemolithotrophic desulphurization under denitrifying conditions is the preferred process when compared with others like physicochemical processes, photoautotrophic and aerobic chemolithotrophic desulphurizations as the catalysts, high pressure, high temperature, light energy and oxygen are not needed. Another main advantage of this process is that the denitrification can be achieved with desulphurization simultaneously. In this work, the anaerobic chemolithotrophic desulphurization under denitrifying conditions (autotrophic denitrification) and heterotrophic denitrification processes were studied. Desulphurization under denitrifying conditions was studied in continuous stirred tank bioreactors (CSTB), while batch, continuous stirred tank and biofilm reactors were used to investigate the heterotrophic denitrification. The kinetics of desulphurization, autotrophic and heterotrophic denitrifications obtained in different systems and under various conditions were compared.<p> Using three different feed sulphide concentrations in the range 10-20 mM, a linear relationship between sulphide loading rates and sulphide removal rates was observed in continuous stirred tank reactors, regardless of initial sulphide concentration. The highest sulphide removal rate of 1.79 mM h-1 was obtained in CSTB fed with 15 mM sulphide. In these systems cell washout occurred at lower dilution rates as sulphide concentration in the feed was increased from 10 to 20 mM. The ratio of sulphide to nitrate loading rates influenced the composition of the sulphur oxidation end products where higher ratios favored the formation of elemental sulphur and lower ratios promoted the formation of sulphate.<p> In the batch system initial concentration of nitrate (5 to 50 mM) did not have a notable effect on denitrification process. Nitrate was converted to nitrite first and the produced nitrite was then converted to other gaseous end products such as nitrogen. Increases of temperature in the range of 15 to 35ºC increased the bacterial growth rate significantly with the value of apparent activation energy for specific growth rate being 60.6 kJ mol-1. Using the experimental data generated in two continuous bioreactors operated with feeds containing 10 and 30 mM nitrate biokinetic coefficients for heterotrophic denitrification were determined. The values of µm, Ks, ms, YMX/S, kd for initial nitrate concentrations of 10 and 30 mM were 0.087 and 0.082 h-1, 2.01 and 5.27 mM (NO3-), 1.441 and 1.096 mM (NO3-) (g biomass) -1 h-1, 0.011 and 0.013 g (biomass) (mM NO3-)-1, and 0.016 and 0.014 h-1 respectively. In the biofilm system the linear relationship between nitrate loading rate and nitrate removal rate was observed again for the whole range of tested nitrate loading rate range (up to 183 mM h-1), regardless of the approach used to increase the loading rate (increases in feed flow rate or feed nitrate concentration). The highest nitrate removal rate was 183 mM h-1 which was around 194 times higher than that achieved in the continuous stirred tank bioreactor with free cells.<p> A comparison of the autotrophic and heterotrophic denitrification processes studied in the CSTB system indicated that in case of autotrophic denitrification wash-out occurred suddenly and at a much lower loading rate of 0.75 to 0.96 mM (NO3-) h-1 for initial sulphide concentrations 10 to 20 mM, while in case of heterotrophic denitrification increase of nitrate loading rate did not have such a drastic effect and removal rate of nitrate decreased slowly with the increases of nitrate loading rate. A comparison of the kinetic data obtained in the biofilm reactor in the present work and those generated for autotrophic denitrification in an earlier work conducted at University of Saskatchewan (Tang, 2008) showed that the dependency of nitrate removal rate on its loading rate were linear in either case and somewhat similar. However, the maximum nitrate removal rate obtained in the heterotrophic system (183 mM h-1) was much higher than that obtained in the autotrophic system with sulphide.

Sulphide containing streams must be treated before releases to environment due to the toxicity, corrosivity and unpleasant odour of sulphide. Anaerobic chemolithotrophic desulphurization under denitrifying conditions is the preferred process when compared with others like physicochemical processes, photoautotrophic and aerobic chemolithotrophic desulphurizations as the catalysts, high pressure, high temperature, light energy and oxygen are not needed. Another main advantage of this process is that the denitrification can be achieved with desulphurization simultaneously. In this work, the anaerobic chemolithotrophic desulphurization under denitrifying conditions (autotrophic denitrification) and heterotrophic denitrification processes were studied. Desulphurization under denitrifying conditions was studied in continuous stirred tank bioreactors (CSTB), while batch, continuous stirred tank and biofilm reactors were used to investigate the heterotrophic denitrification. The kinetics of desulphurization, autotrophic and heterotrophic denitrifications obtained in different systems and under various conditions were compared.<p> Using three different feed sulphide concentrations in the range 10-20 mM, a linear relationship between sulphide loading rates and sulphide removal rates was observed in continuous stirred tank reactors, regardless of initial sulphide concentration. The highest sulphide removal rate of 1.79 mM h-1 was obtained in CSTB fed with 15 mM sulphide. In these systems cell washout occurred at lower dilution rates as sulphide concentration in the feed was increased from 10 to 20 mM. The ratio of sulphide to nitrate loading rates influenced the composition of the sulphur oxidation end products where higher ratios favored the formation of elemental sulphur and lower ratios promoted the formation of sulphate.<p> In the batch system initial concentration of nitrate (5 to 50 mM) did not have a notable effect on denitrification process. Nitrate was converted to nitrite first and the produced nitrite was then converted to other gaseous end products such as nitrogen. Increases of temperature in the range of 15 to 35ºC increased the bacterial growth rate significantly with the value of apparent activation energy for specific growth rate being 60.6 kJ mol-1. Using the experimental data generated in two continuous bioreactors operated with feeds containing 10 and 30 mM nitrate biokinetic coefficients for heterotrophic denitrification were determined. The values of µm, Ks, ms, YMX/S, kd for initial nitrate concentrations of 10 and 30 mM were 0.087 and 0.082 h-1, 2.01 and 5.27 mM (NO3-), 1.441 and 1.096 mM (NO3-) (g biomass) -1 h-1, 0.011 and 0.013 g (biomass) (mM NO3-)-1, and 0.016 and 0.014 h-1 respectively. In the biofilm system the linear relationship between nitrate loading rate and nitrate removal rate was observed again for the whole range of tested nitrate loading rate range (up to 183 mM h-1), regardless of the approach used to increase the loading rate (increases in feed flow rate or feed nitrate concentration). The highest nitrate removal rate was 183 mM h-1 which was around 194 times higher than that achieved in the continuous stirred tank bioreactor with free cells.<p> A comparison of the autotrophic and heterotrophic denitrification processes studied in the CSTB system indicated that in case of autotrophic denitrification wash-out occurred suddenly and at a much lower loading rate of 0.75 to 0.96 mM (NO3-) h-1 for initial sulphide concentrations 10 to 20 mM, while in case of heterotrophic denitrification increase of nitrate loading rate did not have such a drastic effect and removal rate of nitrate decreased slowly with the increases of nitrate loading rate. A comparison of the kinetic data obtained in the biofilm reactor in the present work and those generated for autotrophic denitrification in an earlier work conducted at University of Saskatchewan (Tang, 2008) showed that the dependency of nitrate removal rate on its loading rate were linear in either case and somewhat similar. However, the maximum nitrate removal rate obtained in the heterotrophic system (183 mM h-1) was much higher than that obtained in the autotrophic system with sulphide.