Monitoring denitrification by pH-Stat titration

Potential of endogenous PHA as electron donor for denitrification

The use of wastewater streams to obtain polyhydroxyalkanoates (PHA) as high added-value products is widely studied. However, nitrogen removal is not well integrated into this process. In this study, the optimal conditions to track the specific endogenous denitrifying activity (SEDA) driven by PHA as carbon source were selected as: sludge concentration of 0.5-2 g VSS/L, COD_PHA/N ratio higher than 5.4 g/g and between 40 and 60 mg NO₃^--N/L. The seeding biomass used to perform the activity tests was collected from two sequencing batch reactors and was able to store up to 69% wt/wt of PHA. SEDA values of 0.26-0.39 g N₂-N/(g VSS_act d) were achieved, which proved the potential of PHA-accumulating mixed microbial cultures to be used in nitrogen removal processes. The results indicated that there is not a preference in the consumption of hydroxybutyrate over hydroxyvalerate and that PHA concentrations lower than 5% wt/wt do not allow the obtainment of the maximum SEDA value. Finally, N₂O gas production was not detected in the SEDA experiments.

Simultaneous removal of sulfide, nitrate and acetate under denitrifying sulfide removal condition: modeling and experimental validation

Simultaneous removal of sulfide (S(2-)), nitrate (NO3(-)) and acetate (Ac(-)) under denitrifying sulfide removal process (DSR) is a novel biological wastewater treatment process. This work developed a mathematical model to describe the kinetic behavior of sulfur-nitrogen-carbon and interactions between autotrophic denitrifiers and heterotrophic denitrifiers. The kinetic parameters of the model were estimated via data fitting considering the effects of initial S(2-) concentration, S(2-)/NO3(-)-N ratio and Ac(-)-C/NO3(-)-N ratio. Simulation supported that the heterotrophic denitratation step (NO3(-) reduction to NO2(-)) was inhibited by S(2-) compared with the denitritation step (NO2(-) reduction to N2). Also, the S(2-) oxidation by autotrophic denitrifiers was shown two times lower in rate with NO2(-) as electron acceptor than that with NO3(-) as electron acceptor. NO3(-) reduction by autotrophic denitrifiers occurs 3-10 times slower when S(0) participates as final electron donor compared to the S(2-)-driven pathway. Model simulation on continuous-flow DSR reactor suggested that the adjustment of hydraulic retention time is an efficient way to make the reactor tolerating high S(2-) loadings. The proposed model properly described the kinetic behaviors of DSR processes over wide parametric ranges and which can offer engineers with basis to optimize bioreactor operation to improve the treatment capacity.

Biological removal of nitrate by an oil reservoir culture capable of autotrophic and heterotrophic activities: kinetic evaluation and modeling of heterotrophic process

Kinetics of heterotrophic denitrification was investigated using an oil reservoir culture with the ability to function under both autotrophic and heterotrophic conditions. In the batch system nitrate at concentrations up to 30 mM did not influence the kinetics but with 50mM slower growth and removal rates were observed. A kinetic model, representing the denitrification as reduction of nitrate to nitrite, and subsequent reduction of nitrite to nitrous oxides and nitrogen gas was developed. The value of various kinetic coefficients, including maximum specific growth rate, saturation constant, yield and activation energy for nitrate and nitrite reductions were determined by fitting the experimental data into the developed model. In continuous bioreactors operated with 10 or 30 mM nitrate, complete removal of nitrate (no residual nitrite) and linear dependency between nitrate loading and removal rates were observed for loading rates up to 0.21 and 0.58 mM h(-1), respectively. The highest removal rates of 0.31 and 0.94 mM h(-1) observed at loading rates of 0.42 mM h(-1) and 1.26 mM h(-1), with corresponding removal percentages of nitrate and total nitrogen being 75.4, 54.4%, and 74.4 and 17.9%, respectively. Developed kinetic model predicted the performance of the continuous bioreactors with accuracy.

Experimental assessment and modelling of the proton production linked to phosphorus release and uptake in EBPR systems

The modelling of the enhanced biological phosphorus removal (EBPR) process is a recent focus of interest. The pH profile is a promising output variable for EBPR modelling as it is very sensitive to the consumption or production of acid and base species (e.g. phosphate or VFA). pH-based EBPR modelling is based on the assumption that phosphorus is released and taken up as H(2)PO(4)(-), but this assumption has not been experimentally confirmed yet with enriched EBPR biomass. Therefore, the objective of this work was to assess the species in which P is released and taken up under different pH conditions. Several batch experiments were performed with an enriched culture of Accumulibacter (around 70+/-10% of total microorganisms). The total observed proton production, inorganic carbon, ammonium, phosphate and VFA were measured to evaluate the titrimetric contribution of anaerobic P-release and aerobic P-uptake over the total observed proton production. The results show that the only phosphorus form involved in P-release and P-uptake is equivalent in terms of proton production to H(2)PO(4)(-) in the pH range of 6.5-8.5. Finally, proton production and pH in several SBR cycles were modelled and resulted in good agreement with the experimental profiles.