Jesús Colprim

Autotrophic nitrite removal in the cathode of microbial fuel cells.

Nitrification to nitrite (nitritation process) followed by reduction to dinitrogen gas decreases the energy demand and the carbon requirements of the overall process of nitrogen removal. This work studies autotrophic nitrite removal in the cathode of microbial fuel cells (MFCs). Special attention was paid to determining whether nitrite is used as the electron acceptor by exoelectrogenic bacteria (biologic reaction) or by graphite electrodes (abiotic reaction). The results demonstrated that, after a nitrate pulse at the cathode, nitrite was initially accumulated; subsequently, nitrite was removed. Nitrite and nitrate can be used interchangeably as an electron acceptor by exoelectrogenic bacteria for nitrogen reduction from wastewater while producing bioelectricity. However, if oxygen is present in the cathode chamber, nitrite is oxidised via biological or electrochemical processes. The identification of a dominant bacterial member similar to Oligotropha carboxidovorans confirms that autotrophic denitrification is the main metabolism mechanism in the cathode of an MFC.

Autotrophic Denitrification in Microbial Fuel Cells Treating Low Ionic Strength Waters

The presence of elevated concentrations of nitrates in drinking water has become a serious concern worldwide. The use of autotrophic denitrification in microbial fuel cells (MFCs) for waters with low ionic strengths (i.e., 1000 μS·cm(-1)) has not been considered previously. This study evaluated the feasibility of MFC technology for water denitification and also identified and quantified potential energy losses that result from their usage. The low conductivity (<1600 μS·cm(-1)) of water limited the nitrogen removal efficiency and power production of MFCs and led to the incomplete reduction of nitrate and the nitrous oxide (N(2)O) production (between 4 and 20% of nitrogen removed). Cathodic overpotential was identified as the main energy loss factors (83-90% of total losses). That high overpotential was influenced by denitrification intermediates (NO(2)(-) and N(2)O) and the potential used by microorganisms for growth, activation, and maintenance.

Microbial fuel cell application in landfill leachate treatment

The feasibility of using microbial fuel cells (MFCs) in landfill leachate treatment and electricity production was assessed under high levels of nitrogen concentration (6033 mg NL(-1)) and conductivity (73,588 μS cm(-1)). An air-cathode MFC was used over a period of 155 days to treat urban landfill leachate. Up to 8.5 kg COD m(-3)d(-1) of biodegradable organic matter was removed at the same time as electricity (344 m Wm(-3)) was produced. Nitrogen compounds suffered transformations in the MFC. Ammonium was oxidized to nitrite using oxygen diffused from the membrane. However, at high free ammonia concentrations (around 900 mg N-NH(3)L(-1)), the activity of nitrifier microorganisms was inhibited. Ammonium reduction was also resulted from ammonium transfer through the membrane or from ammonia loss. High salinity content benefited the MFC performance increasing power production and decreasing the internal resistance.

Effect of pH on nutrient dynamics and electricity production using microbial fuel cells

The aim of this work was to study the effect of pH on electricity production and contaminant dynamics using microbial fuel cells (MFCs). To investigate these effects, an air-cathode MFC was used to treat urban wastewater by adjusting the pH between 6 and 10. The short-term tests showed that the highest power production (0.66 W.m(-3)) was at pH 9.5. The MFC operation in continuous control mode for 30 days and at the optimal pH improved the performance of the cell relative to power generation to 1.8 W.m(-3). Organic matter removal (77% of influent COD) and physical ammonium loss were directly influenced by pH and followed the same behavior as the power generation. At a pH higher than the optimal one, anodic bacteria were affected, and power generation ceased. However, biological nitrogen processes and phosphorus dynamics were independent of the exoelectrogenic bacteria.

Heterotrophic denitrification on granular anammox SBR treating urban landfill leachate

The anammox process was applied to treat urban landfill leachate coming from a previous partial nitritation process. In presence of organic matter, the anammox process could coexist with heterotrophic denitrification. The goal of this study was to asses the stability of the anammox process with simultaneous heterotrophic denitrification treating urban landfill leachate. The results achieved demonstrated that the anammox process was not inactivated by heterotrophic denitrification. Moreover, part of the nitrate produced by anammox bacteria and part of the influent nitrite were removed by heterotrophic denitrifiers with associated biodegradable organic matter consumption. In this sense, the contribution on nitrogen removal of each process was calculated using a nitrogen mass balance methodology. An 85.1+/-5.6% of the nitrogen consumption was achieved via anammox process while the average heterotrophic denitrifiers contribution was 14.9+/-5.6%. Heterotrophic denitrification was limited by the available easily biodegradable organic matter.

Effect of temperature on AOB activity of a partial nitritation SBR treating landfill leachate with extremely high nitrogen concentration

This study investigates the effects of temperature on ammonia oxidizing bacteria activity in a partial nitritation (PN) sequencing batch reactor. Stable PN was achieved in a 250 L SBR with a minimum operating volume of 111L treating mature landfill leachate containing an ammonium concentration of around 6000 mg N-NH(4)(+)L(-1) at both 25 and 35 °C. A suitable influent to feed an anammox reactor was achieved in both cases. A kinetic model was applied to study the influence of free ammonia (FA), the free nitrous acid (FNA) inhibition, and the inorganic carbon (IC) limitation. NH(4)(+) and NO(2)(-) concentrations were similar at 25 and 35 °C experiments (about 2500 mg N-NH(4)(+)L(-1) and 3500 mg N-NO(2)(-)L(-1)), FA and FNA concentrations differed due to the strong temperature dependence. FNA was the main source of inhibition at 25 °C, while at 35 °C combined FA and FNA inhibition occurred. DGGE results demonstrated that PN-SBR sludge was enriched on the same AOB phylotypes in both experiments.

Long-term operation of a partial nitritation pilot plant treating leachate with extremely high ammonium concentration prior to an anammox process

The goal of this work was to demonstrate the feasibility of treating leachate with high ammonium concentrations using the SBR technology, as a preparative step for the treatment in an anammox reactor. The cycle was based on a step-feed strategy, alternating anoxic and aerobic conditions. Results of the study verified the viability of this process, treating an influent with concentration up to 5000 mg N-NH(4)(+) L(-1). An effluent with about 1500-2000 mg N-NH(4)(+) L(-1) and 2000-3000 mg N-NO(2)(-) L(-1) was achieved, presenting a nitrite to ammonium molar ratio close to the 1.32 required by the anammox. Furthermore, taking advantage of the biodegradable organic matter, the operational strategy allowed denitrifying about 200 mg N-NO(2)(-) L(-1). The extreme operational conditions during the long-term resulted on the selection of a sole AOB phylotype, identified by molecular techniques as Nitrosomonas sp. IWT514.

Minimization of sludge production by a side-stream reactor under anoxic conditions in a pilot plant

This study evaluates the application of an anoxic side-stream reactor in the sludge return line of a conventional activated sludge system for the reduction of biomass production. The oxidation-reduction potential was maintained at -150 mV while the applied sludge loading rate was modified by changing the percentage of return sludge treated in this reactor. The observed yield from the conventional system (0.513 kg VSS kg(-1) COD) was continuously reduced when the portion of return sludge treated was increased. A maximum reduction of 18.3% of the observed yield was obtained treating the whole sludge return line. The sludge age maintained through the experiment. The organic matter removal was not deteriorated, even improved, by the proposed plant modification. Thus, simply applying an anoxic side-stream reactor would decrease the final volume of waste sludge while maintaining the sludge retention time and would, in fact, decrease the economic costs in terms of sludge handling.

Impact of influent characteristics on a partial nitritation SBR treating high nitrogen loaded wastewater

The Anammox process allows a sustainable treatment of wastewater with high nitrogen content. Partial oxidation of ammonium to nitrite is a previous and crucial step. Given the variability on wastewater composition, the operation of sequencing batch reactors (SBR) for partial nitritation (PN) is very challenging. This work assessed the combined influence of influent characteristics and process loading rate. Simulation results showed that wastewater composition - Total nitrogen as ammonia (TNH) and total inorganic carbon (TIC) - as well as nitrogen loading rate (NLR) govern the outcomes of the reactor. A suitable effluent can be produced when treating wastewater with different ammonia levels, as long as the TIC:TNH influent molar ratio is around 1:1 and extreme NLR are avoided. The influent pH has a key impact on nitrite conversion by governing the CO(2)-bicarbonate-carbonate equilibrium. Finally, results showed that oxidation of biodegradable organic matter produces CO(2), which acidifies the media and limits process conversion.

A Model for the Simulation of the SHARON Process: pH as a Key Factor

The SHARON process allows partial nitrification of wastewaters with high ammonium content and, when coupled with the Anammox process, represents a more sustainable alternative for N-removal than a conventional nitrification-denitrification. In this work, a mathematical model describing a continuously aerated SHARON reactor is presented. Special attention was given to the pH, because it affects substrates availability and inhibition phenomena, implementing an algorithm for its calculation. Since ammonium-oxidizing and nitrite-oxidizing organisms are inhibited by their own substrates, ammonia and nitrous acid respectively, Haldane kinetics was used in both nitrification steps. A preliminary evaluation of the model using historical experimental data generated in a lab-scale SHARON reactor, fed with synthetic substrate, is also presented, corroborating that the quality of the obtained effluent is highly dependent on pH.