Denitrification Kinetics of Nitrate by a Heterotrophic Culture in Batch and Fixed-Biofilm Reactors

Partial denitrification in rope-type biofilm reactors: Performance, kinetics, and microflora using internal vs. external carbon sources

Stable nitrite accumulation through partial denitrification (PDN) represents an efficient pathway to support the anammox process, but limited studies explored the internal wastewater carbon sources and biofilm processes. This study assessed the viability of the PDN process, biofilm community evolution, and functional enzyme formation in rope-type biofilm media reactors using primary effluent (PE) and anaerobically pretreated wastewater carbon sources for the first time. Comparison was made with external carbon (acetate) under varied pH and biofilm thicknesses, maintaining a favourable sCOD: NO3-N ratio of 3. The wastewater's internal carbon resulted in thinner biofilms; nevertheless, modest nitrite accumulation (0.24 g/m2/d) occurred only at elevated pH. The highest nitrite accumulation (0.79 g/m2/d) was exhibited in the biofilm thickness-controlled acetate-fed reactor, featuring porous biofilms dominated by denitrifier Thauera (10.24 %) and imbalance between Nar, Nap, and Nir reductases. Using internal wastewater carbon sources offers a sustainable avenue for adopting the PDN process in full-scale application.

High rates of nitrogen removal in aerated VFCWs treating sewage through C-N-S cycle

The efficiency of deep aerated vertical flow constructed wetlands (DA-VFCWs) being operated in Hyderabad, India, was evaluated herein using physicochemical analysis and 16S rRNA amplicon sequencing. The results showed 2-4-fold higher removal rate coefficients for Biochemical oxygen demand (1.32---3.53 m/d) and nitrogen (0.88--1.36 m/d) in DA-VFCWs than those of passive VFCWs. Elevated sulfate concentration in the DA-VFCWs effluent (84-113 mg/L) indicated possibility of sulfur-driven autotrophic denitrification (SDAD) as a major pathway operating in these wetlands besides the classical nitrogen removal pathways. The presence of nitrifiers (3.09-10.02 %), heterotrophic and aerobic denitrifiers (0.79-0.83 %), anammox bacteria (1.31-2.22 %) and SDAD bacteria (0.08-0.73 %) in the biofilm samples collected from the DA-VFCWs exemplify an interplay of Carbon-Nitrogen-Sulfur cycles in these systems. If proven, the presence of an operational SDAD pathway in DA-VFCWs can help reduce surface area requirement in VFCWs substantially besides alleviating biological clogging of the wetland substrate.

Modeling biological denitrification in the presence of metal ions and elevated chloride content: Insights into abiotic and biotic mechanisms regulating metal bioprecipitation

Biological denitrification is a critical process in which microorganisms convert nitrate to nitrogen gas. Metal ions, such as those found in industrial wastewater, can be toxic to microorganisms and impede denitrification. It is critical to identify the mechanisms that allow microorganisms to tolerate metal ions and understand how these mechanisms can be utilized to improve denitrification efficiency by modeling the process. This study presents a mathematical model of biological denitrification in the presence of metal ions. The model includes key biotic and abiotic mechanisms and is based on pilot scale results. The model predicts the bioprecipitation of metal ions due to pH shift and alkalinity production during the metabolic activity of microorganisms. The model parameters are estimated to fit the experimental results and the mechanisms regulating metal detoxification via biological metal precipitation are presented. The model provides a valuable tool for understanding the behavior of denitrification systems in the presence of metal ions and can be used to optimize these systems for more efficient and effective treatment of industrial wastewater.

Experimental study and modeling of denitrification in an MBBR reactor

A denitrification mathematical model was used to describe the nitrates and organic carbons use by the denitrify biomass in the Moving Bed Biofilm Reactor (MBBR). The model integrates the diffusive mass transfer mechanism as well as double substrates Monod kinetics. Preliminary experiments were realized in order to assess the operating conditions for growth of attached biomass, the determination of the optimal (COD/NO3-N) ratio, moreover the results of the previous study of the residence time distribution in this MBBR established the optimal hydrodynamic operating conditions with a dead volume of 22%. In this reactor, seeded with a mixed liquor from a purification station, kaldnesk1 were used as carriers. A total of 6 kinetic and stoichiometric constants under anoxic conditions were determined by batch-test pulsed respirometry; some parametric have been determined experimentally, such as YHD, YNO, μ ˆ HD ${\widehat{\mu }}_{\text{HD}}$ and KS, and with their values 0.4 mgCOD (mgCOD)−1, 0.6 mg COD (mgCOD)−1,0.864 d−1 and 12.48 mg COD L −1, respectively. The other constants were determined using the model fitting (using MATLAB), such as KNO3 and bHD with its values, 0.25 mg NO3-N. L−1 and 0.061 d−1, respectively. The model was used to simulated different operating condition and the results included the concentration profiles of NO3-N, COD and XBH, which showed good agreement with the experimental ones, mainly by using the effective volume determined experimentally in the hydrodynamic study (RTD test) and which can reach 62% of the total volume under some operating. Additionally, these findings demonstrate that moving bed reactor characterization may be accomplished using in situ pulsed respirometry (MBBR).