Jorge Gómez

Nitrogen removal from wastewaters at low C/N ratios with ammonium and acetate as electron donors

A denitrifying upflow anaerobic sludge blanket (UASB) reactor was operated at different nitrate loading rates at a C/N ratio of 1.2, with acetate as an electron donor. This resulted in an increase in the accumulation of nitrite. After this, the UASB reactor was supplemented with 100 mg NH4+-Nl(-1) d(-1), while acetate was gradually limited in the medium. This prevented nitrite accumulation at a C/N ratio of 0.6 due to an enhanced nitrite reduction rate achieved in the reactor. An increasing amount of ammonium was consumed when the C/N ratio was lowered in the medium. This suggested that ammonium was used as an alternative electron donor during denitrification, which is supported by nitrogen balances. Nitrite was shown to be toxic for the nitrogen removal process at 200-400 mg NO2--N(l(-1) when the C/N ratio was decreased to 0.4 leading to formation of ammonium. The present study showed that addition of ammonium as an alternative electron donor for denitrification achieved a nitrogen removal process with negligible accumulation of undesirable intermediates.

Amperometric biosensor based on a high resolution photopolymer deposited onto a screen-printed electrode for phenolic compounds monitoring in tea infusions

An amperometric biosensor based on laccase, from Trametes versicolor (LTV), was developed and optimized for monitoring the phenolic compounds content in tea infusions. The fungal enzyme was immobilized by entrapment within polyvinyl alcohol photopolymer PVA-AWP (azide-unit pendant water-soluble photopolymer) onto disposable graphite screen-printed electrodes (SPE). Sensitivity optimization in terms of pH, temperature and applied potential was carried out. The linear range, detection limit, operational and storage stabilities were also determined. The laccase biosensor (LTV-SPE) was calibrated for o-, m- and p-diphenol as well as caffeic acid. The highest response was found at 0.1M acetate buffer pH 4.7, though it must be added the good reproducibility and operational stability were also obtained. The useful lifetime of the biosensor is estimated to be greater than 6 months. LTV-SPE was used for the determination of the equivalent phenol content (EPC) in tea infusions by the direct addition into the electrochemical cell: the results were compared with those from the Folin-Ciocalteu spectrophotometric method. The amperometric detection exhibits some interesting advantages such as high simplicity, minimal sample preparation and shorter response time. A stable and sensitive amperometric response was obtained toward standard diphenolic compounds and herbal infusions. These biosensors are useful for easy and fast monitoring of EPC that can be related to the antioxidant capacity of natural extracts.

Effect of nitrogen loading rate and carbon source on denitrification and sludge settleability in upflow anaerobic sludge blanket (UASB) Reactors

The combined effect of carbon source and nitrogen loading rate (NLR) on denitrification and sludge granular settleability in upflow anaerobic sludge blanket (UASB) bench-scale reactors was studied. Acetate, lactate and glucose were used as carbon sources for denitrification. Three NLR were evaluated: 500, 1000 and 2000 mg NO3−-N/ld. It was found that NO3−-N consumption efficiency was 99% for all the cases. Denitrification efficiencies were high (85-96%) for all substrates and NLR tested, but specific denitrifying rates were a better representation of the denitrifying process. The results showed that specific denitrifying rate was dependent on type of carbon source and NLR. It was also found that sludge settleability and reactor stability was influenced by the carbon source. The use of acetate did not influence the sludge settleability while, sludge flotation was always observed when lactate was used as carbon source. Foaming was present when glucose was used, causing reactor unstability. An increase in the exopolymeric protein and carbohydrate content was observed when lactate and glucose were fed, in comparison with acetate as carbon source. Results obtained in this work suggest that the exopolymeric composition here referred to as protein/carbohydrate ratio (P/C) could be a better stability indicator than the sludge volumetric index (SVI).

Effect of initial sulfide concentration on sulfide and phenol oxidation under denitrifying conditions.

The objective of this work was to evaluate the effect of the initial sulfide concentration on the kinetics and metabolism of phenol and sulfide in batch bioassays using nitrate as electron acceptor. Complete oxidation of sulfide (20 mg L(-1) of S(2-)) and phenol (19.6 mg L(-1)) was linked to nitrate reduction when nitrate was supplemented at stoichiometric concentrations. At 32 mg L(-1) of sulfide, oxidation of sulfide and phenol by the organo-lithoautotrophic microbial culture was sequential; first sulfide was rapidly oxidized to elemental sulfur and afterwards to sulfate; phenol oxidation started once sulfate production reached a maximum. When the initial sulfide concentration was increased from 20 to 26 and finally to 32 mg L(-1), sulfide oxidation was inhibited. In contrast phenol consumption by the denitrifying culture was not affected. These results indicated that sulfide affected strongly the sulfide oxidation rate and nitrate reduction.

The Effect of Antibiotics on Nitrification Processes Batch Assays

The effect of different antibiotics at several concentrations of ampicillin (0–250 mg/L),benzylpenicillin (0–250 mg/L), novobiocine (0–150 mg/L), oxytetracycline (0–250 mg/L), and chloramphenicol (0–50 mg/L) on a stabilized nitrifying sludge was evaluated under aerated and lithoautotrophic conditions. No effect resulting from the presence of antibiotics on the biomass and nitrate production was noticed. The specific growth rate and volumetric nitrification rate average values for the controls were 8.28 × 10−3/h−1 and 2.74 × 10−3 g/L·h, respectively. Similar rate values were found when different kinds of antibiotic and concentrations were tested. These results may be explained by the nature of the floc or the instability of the antibiotics.

p-Cresol biotransformation by a nitrifying consortium.

The oxidizing ability of a nitrifying consortium exposed to p-cresol (25 mg CL(-1)) was evaluated in batch cultures. Biotransformation of the phenolic compound was investigated by identifying the different intermediates formed. p-Cresol inhibited the ammonia-oxidizing process with a decrease of 83% in the specific rate of ammonium consumption. After 48 h, ammonium consumption efficiency was 96+/-9% while nitrate yield reached 0.95+/-0.06 g NO(3)(-)-Ng(-1)NH(4)(+)-N consumed. High value for nitrate production yield showed that the nitrifying metabolic pathway was only affected at the specific rate level being nitrate the main end product. The consortium was able to totally oxidize p-cresol at a specific rate of 0.17+/-0.06 mg p-cresol-Cmg(-1) microbial protein h(-1). p-Cresol was first transformed to p-hydroxybenzaldehyde and p-hydroxybenzoate, which were later completely mineralized. In the presence of allylthiourea, a specific inhibitor of ammonia monooxygenase (AMO), p-cresol was oxidized to the same intermediates and in a similar pattern as obtained without the AMO inhibitor. AMO seemed not to be involved in the p-cresol oxidation process. When p-hydroxybenzaldehyde was added (25 mg CL(-1)), the nitrifying process was inhibited in the same way as observed with p-cresol, indicating that p-hydroxybenzaldehyde could be the main compound responsible for nitrification inhibition. p-Hydroxybenzaldehyde was accumulated during 15 h before complete consumption at a specific rate value eight times lower than the p-cresol consumption rate. Results showed that p-hydroxybenzaldehyde oxidation was the limiting step in p-cresol mineralization by the nitrifying consortium.

Accumulation of intermediates in a denitrifying process at different copper and high nitrate concentrations

NO2- accumulation occurred in an upflow anaerobic sludge blanket reactor at 500, 1000 and 1500 mg NO3- -N/l, but not after copper in the medium was increased to 28 μg Cu2/l. N2O release was not avoided even with 56 μg Cu2/l, at 1500 and 2500 mg NO3- -N/l and reached 251 mg N2O-N/l•d.

Simultaneous removal of 2-chlorophenol, phenol, p-cresol and p-hydroxybenzaldehyde under nitrifying conditions: Kinetic study

The kinetic behavior of a stable nitrifying consortium exposed to 2-chlorophenol (2-CP), phenol, p-cresol and p-hydroxybenzaldehyde (p-OHB) was evaluated in batch assays. Phenolic compounds were evaluated either individually or in mixture. In individual assays, 2-CP inhibited stronger the nitrification, diminishing the ammonium consumption efficiency (16%) and the nitrate production rate (at 91%). Nonetheless, the consumption efficiencies for all phenolics were of 100%. On the other hand, in mixture, the inhibitory effect of 2-CP diminished significantly, since ammonium consumption efficiency and nitrate production rate were improved. Consumption efficiencies for most of the phenolic compounds were high. Furthermore, the kinetic of 2-CP oxidation was 2.4-fold-faster than the individual assays. Finally, the experimental results showed the potential of nitrifying consortium for removing 2-CP, phenol, p-cresol and p-OHB. This is the first work showing the simultaneous removal of these pollutants and also this information might be useful for treating wastewaters of chemical complexity.

The effect of antibiotics on nitrification processes

The effect of different antibiotics at several concentrations of ampicillin (0–250 mg/L),benzylpenicillin (0–250 mg/L), novobiocine (0–150 mg/L), oxytetracycline (0–250 mg/L), and chloramphenicol (0–50 mg/L) on a stabilized nitrifying sludge was evaluated under aerated and lithoautotrophic conditions. No effect resulting from the presence of antibiotics on the biomass and nitrate production was noticed. The specific growth rate and volumetric nitrification rate average values for the controls were 8.28 × 10−3/h−1 and 2.74 × 10−3 g/L·h, respectively. Similar rate values were found when different kinds of antibiotic and concentrations were tested. These results may be explained by the nature of the floc or the instability of the antibiotics.

Contribution of quinone-reducing microorganisms to the anaerobic biodegradation of organic compounds under different redox conditions

The capacity of two anaerobic consortia to oxidize different organic compounds, including acetate, propionate, lactate, phenol and p-cresol, in the presence of nitrate, sulfate and the humic model compound, anthraquinone-2,6-disulfonate (AQDS) as terminal electron acceptors, was evaluated. Denitrification showed the highest respiratory rates in both consortia studied and occurred exclusively during the first hours of incubation for most organic substrates degraded. Reduction of AQDS and sulfate generally started after complete denitrification, or even occurred at the same time during the biodegradation of p-cresol, in anaerobic sludge incubations; whereas methanogenesis did not significantly occur during the reduction of nitrate, sulfate, and AQDS. AQDS reduction was the preferred respiratory pathway over sulfate reduction and methanogenesis during the anaerobic oxidation of most organic substrates by the anaerobic sludge studied. In contrast, sulfate reduction out-competed AQDS reduction during incubations performed with anaerobic wetland sediment, which did not achieve any methanogenic activity. Propionate was a poor electron donor to achieve AQDS reduction; however, denitrifying and sulfate-reducing activities carried out by both consortia promoted the reduction of AQDS via acetate accumulated from propionate oxidation. Our results suggest that microbial reduction of humic substances (HS) may play an important role during the anaerobic oxidation of organic pollutants in anaerobic environments despite the presence of alternative electron acceptors, such as sulfate and nitrate. Methane inhibition, imposed by the inclusion of AQDS as terminal electron acceptor, suggests that microbial reduction of HS may also have important implications on the global climate preservation, considering the green-house effects of methane.