[Post-intensive care syndrome one month after hospital discharge of critical patients surviving COVID 19.] / Síndrome post-cuidados intensivos al mes del alta hospitalaria de pacientes críticos supervivientes a COVID 19.

OBJECTIVES: incidence of post-intensive care syndrome at one month after hospital discharge in surviving critically ill COVID 19 patients and to identify associated factors. DESIGN: prospective cohort study. SETTING: two multipurpose critical care units of the Araba University Hospital.Patients admitted to critical care units for severe acute respiratory failure secondary to COVID 19. INTERVENTION: none. VARIABLES OF INTEREST: demographic variables, length of stay, Charlson index, APACHE II, SOFA, days of mechanical ventilation, tracheotomy, delirium, tetraparesis of the critical patient, EuroQol 5D5L, Minimental Test. RESULTS: a deterioration in the EuroQol health index (HI) from 90.9 ± 16.9 to 70.9 ± 24.7 (p < 0.001) was observed. The impairment of the five EuroQol domains is: mobility (46.1%), usual activities (44.7%), discomfort/pain (30.7%), psychological domain (27.3%) and self-care (20.3%). The 61.5% suffer a significant decrease in their health index. Multivariate analysis by logistic regression shows us that delirium (OR= 3.01; 95%CI: 1.01-8.9; p= 0.047) and tracheostomy (OR= 2.37; 95%CI: 1.09-5.14; p= 0.029) show association with drop in EuroQoL 5D5L SI. The area under the ROC curve of the model is 67.3%, with a confidence interval between 58% and 76%. The model is calibrated using the Hosmer-Lemeshow test:(χ2=0.468; p=0.792). Only 1.2% of patients showed a score ≤ 24, clearly pathological, on the Folstein's Minimental Test. CONCLUSIONS: delirium and need for tracheostomy are associated with post-intensive care syndrome assessed by EuroQol 5D5L.

Short-term neuropsychiatric outcomes and quality of life in COVID-19 survivors.

BACKGROUND: The general medical impacts of coronavirus (COVID-19) are increasingly appreciated. However, its impact on neurocognitive, psychiatric health and quality of life (QoL) in survivors after the acute phase is poorly understood. We aimed to evaluate neurocognitive function, psychiatric symptoms and QoL in COVID-19 survivors shortly after hospital discharge. METHODS: This was a cross-sectional analysis of a prospective study of hospitalized COVID-19 survivors followed up for 2 months after discharge. A battery of standardized instruments evaluating neurocognitive function, psychiatric morbidity and QoL (mental and physical components) was administered by telephone. RESULTS: Of the 229 screened patients, 179 were included in the final analysis. Amongst survivors, the prevalence of moderately impaired immediate verbal memory and learning was 38%, delayed verbal memory (11.8%), verbal fluency (34.6%) and working memory (executive function) (6.1%), respectively. Moreover, 58.7% of patients had neurocognitive impairment in at least one function. Rates of positive screening for anxiety, depression and post-traumatic stress disorder were 29.6%, 26.8% and 25.1%, respectively. In addition, 39.1% of the patients had psychiatric morbidity. Low QoL for physical and mental components was detected in 44.1% and 39.1% of patients respectively. Delirium and psychiatric morbidity were associated with neurocognitive impairment, and female gender was related with psychiatric morbidity. CONCLUSION: Hospitalized COVID-19 survivors showed a considerable prevalence of neurocognitive impairment, psychiatric morbidity and poor QoL in the short term. It is uncertain if these impacts persist over the long term.

Features of aerobic granular sludge formation treating fluctuating industrial saline wastewater at pilot scale.

A pilot-scale sequencing batch reactor, with a working volume of 3 m3, was installed in a fish cannery to develop aerobic granular sludge treating the produced effluents. Depending on the nitrogen (N) and organic matter (COD) concentration, the effluents were named in this study as medium-low-strength (Stage I) and high-strength (Stage II) wastewater. The composition of the wastewater was found to be a crucial factor to select granule-forming organisms. With medium-low-strength wastewater as feeding, the first granules were observed after 30 days, but the extremely high COD/N ratios of the wastewater provoked the overgrowth of filamentous bacteria after 4 months of operation (Stage I). When treating high-strength wastewater, stable aggregates with good settleability appeared, but well-shaped granules were not observed since the granulation process was not completed. The system was able to remove both COD (70-95%) and N (30-90%) treating both types of effluents. Biomass growth was the main N removal pathway. The reactor was found to be robust against factory production stops and, thus, a suitable alternative to treat wastewater from industries with discontinuous operation.

Pediatric tracheostomy tube change. / Cambio de cánula de traqueostomía en pediatría.

INTRODUCTION: Changing the tracheostomy tube in children is a key procedure, however, some of its aspects re main unclear. OBJECTIVE: To characterize the tracheostomy tube change in children from a long-stay health institution. PATIENTS AND METHOD: Retrospective observational analytical study based on the 2-year clinical record of hospitalized children who underwent tracheostomy. The variables evaluated were the reason for tracheostomy tube change, size and brand of the tube, operator and participants (assistants/spectators) of the procedure, complications, and education. RESULTS: We analyzed 630 tracheostomy tube changes. The most frequent operators were relatives (33.7%). The main reason for the change was routine (83.3%). 10.7% of the changes presented some complications, where the most frequent was peristomal bleeding (47.37%) and the first failed attempt (34.21%). There was no association between the presence of balloon and complications (p = 0.24), nor with the use of Mechanical Ventilation (p = 0.8) or the operator (p = 0.74). CONCLUSION: The routine change of the tracheostomy tube in children with prolonged artificial airway use is a safe procedure, which can be performed by both health professionals and properly trained family members.

Biomass aggregation influences NaN3 short-term effects on anammox bacteria activity.

The main bottleneck to maintain the long-term stability of the partial nitritation-anammox processes, especially those operated at low temperatures and nitrogen concentrations, is the undesirable development of nitrite oxidizing bacteria (NOB). When this occurs, the punctual addition of compounds with the capacity to specifically inhibit NOB without affecting the process efficiency might be of interest. Sodium azide (NaN3) is an already known NOB inhibitor which at low concentrations does not significantly affect the ammonia oxidizing bacteria (AOB) activity. However, studies about its influence on anammox bacteria are unavailable. For this reason, the objective of the present study was to evaluate the effect of NaN3 on the anammox activity. Three different types of anammox biomass were used: granular biomass comprising AOB and anammox bacteria (G1), anammox enriched granules (G2) and previous anammox granules disaggregated (F1). No inhibitory effect of NaN3 was measured on G1 sludge. However, the anammox activity decreased in the case of G2 and F1. Granular biomass activity was less affected (IC50 90 mg/L, G2) than flocculent one (IC50 5 mg/L, F1). Summing up, not only does the granular structure protect the anammox bacteria from the NaN3 inhibitory effect, but also the AOB act as a barrier decreasing the inhibition.

Short- and long-term orange dye effects on ammonium oxidizing and anammox bacteria activities.

The effects of orange azo dye over ammonia oxidizing bacteria (AOB) and anammox bacteria activities were tested. Performed batch tests indicated that concentrations lower than 650 mgorange/L stimulated AOB activity, while anammox bacteria activity was inhibited at concentrations higher than 25 mgorange/L. Long-term performance of a continuous stirred tank reactor (CSTR) for the partial nitritation and a sequencing batch reactor (SBR) for the anammox process was tested in the presence of 50 mgorange/L. In the case of the partial nitritation process, both the biomass concentration and the specific AOB activity increased after 50 days of orange azo dye addition. Regarding the anammox process, specific activity decreased down to 58% after 12 days of operation with continuous feeding of 50 mgorange/L. However, the anammox activity was completely recovered only 54 days after stopping the dye addition in the feeding. Once the biomass was saturated the azo dye adsorption onto the biomass was insignificant in the CSTR for the partial nitritation process fed with 50 mgorange/L. However, in the SBR the absorption was determined as 6.4 mgorange/g volatile suspended solids. No biological decolorization was observed in both processes.

Filamentous bacteria existence in aerobic granular reactors.

Filamentous bacteria are associated to biomass settling problems in wastewater treatment plants. In systems based on aerobic granular biomass they have been proposed to contribute to the initial biomass aggregation process. However, their development on mature aerobic granular systems has not been sufficiently studied. In the present research work, filamentous bacteria were studied for the first time after long-term operation (up to 300 days) of aerobic granular systems. Chloroflexi and Sphaerotilus natans have been observed in a reactor fed with synthetic wastewater. These filamentous bacteria could only come from the inoculated sludge. Thiothrix and Chloroflexi bacteria were observed in aerobic granular biomass treating wastewater from a fish canning industry. Meganema perideroedes was detected in a reactor treating wastewater from a plant processing marine products. As a conclusion, the source of filamentous bacteria in these mature aerobic granular systems fed with industrial effluents was the incoming wastewater.

Influence of dissolved oxygen concentration on the start-up of the anammox-based process: ELAN®.

The anammox-based process ELAN® was started-up in two different sequencing batch reactor (SBR) pilot plant reactors treating municipal anaerobic digester supernatant. The main difference in the operation of both reactors was the dissolved oxygen (DO) concentration in the bulk liquid. SBR-1 was started at a DO value of 0.4 mg O2/L whereas SBR-2 was started at DO values of 3.0 mg O2/L. Despite both reactors working at a nitrogen removal rate of around 0.6 g N/(L d), in SBR-1, granules represented only a small fraction of the total biomass and reached a diameter of 1.1 mm after 7 months of operation, while in SBR-2 the biomass was mainly composed of granules with an average diameter of 3.2 mm after the same operational period. Oxygen microelectrode profiling revealed that granules from SBR-2 where only fully penetrated by oxygen with DO concentrations of 8 mg O2/L while granules from SBR-1 were already oxygen penetrated at DO concentrations of 1 mg O2/L. In this way granules from SBR-2 performed better due to the thick layer of ammonia oxidizing bacteria, which accounted for up to 20% of all the microbial populations, which protected the anammox bacteria from non-suitable liquid media conditions.

Molecular classifiers for acute kidney transplant rejection in peripheral blood by whole genome gene expression profiling.

There are no minimally invasive diagnostic metrics for acute kidney transplant rejection (AR), especially in the setting of the common confounding diagnosis, acute dysfunction with no rejection (ADNR). Thus, though kidney transplant biopsies remain the gold standard, they are invasive, have substantial risks, sampling error issues and significant costs and are not suitable for serial monitoring. Global gene expression profiles of 148 peripheral blood samples from transplant patients with excellent function and normal histology (TX; n = 46), AR (n = 63) and ADNR (n = 39), from two independent cohorts were analyzed with DNA microarrays. We applied a new normalization tool, frozen robust multi-array analysis, particularly suitable for clinical diagnostics, multiple prediction tools to discover, refine and validate robust molecular classifiers and we tested a novel one-by-one analysis strategy to model the real clinical application of this test. Multiple three-way classifier tools identified 200 highest value probesets with sensitivity, specificity, positive predictive value, negative predictive value and area under the curve for the validation cohort ranging from 82% to 100%, 76% to 95%, 76% to 95%, 79% to 100%, 84% to 100% and 0.817 to 0.968, respectively. We conclude that peripheral blood gene expression profiling can be used as a minimally invasive tool to accurately reveal TX, AR and ADNR in the setting of acute kidney transplant dysfunction.

Influence of the shear stress and salinity on Anammox biofilms formation: modelling results.

Anammox biomass has a long duplication time and low yield, thus the process must be operated in reactors with good sludge retention, such as biofilm systems. Therefore, it would be important to research the ability of Anammox biomass to form biofilms under different conditions. The effects of shear stress and salinity (NaCl and CaCl2) on Anammox biofilm formation were studied. Anammox bacteria showed good attachment capacity, with an initial adhesion phase lasting for 5-7 days at the different flow rates tested (Reynolds numbers 54, 63, 188 and 400). A four-parameter model was developed and the experimental data fitted well into the model. The presence of 5 g/L of each of the two salts favoured the formation of Anammox biofilm. The effects of CaCl2 were stronger than those caused by NaCl. 15 g/L of NaCl was detrimental for the biofilm, probably due to an inhibitory effect.

Implications of full-scale implementation of an anammox-based process as post-treatment of a municipal anaerobic sludge digester operated with co-digestion.

The feasibility of treating the supernatant of a municipal sludge digester supplemented with co-substrates by means of an anammox-based process (ELAN(®)) was tested in Guillarei (NW of Spain). Ammonia concentration measured in the supernatant of the sludge digester varied in the range 800-1,500 g N/m(3) due to the fact that the sludge produced in the plant was co-digested with wastes coming from surrounding food industries. Treating this supernatant in the ELAN(®) reactor, nitrogen removal rates up to 1.1 kg N/(m(3) d) were reached in experiments run in a pilot plant reactor operated in batch mode. No nitrite oxidation was registered after several months of operation despite the average dissolved oxygen (DO) concentrations being 1.5 g O2/m(3) and the temperature reaching values as low as 18 °C. By keeping the DO set point at 1-2 g O2/m(3) and tuning the hydraulic retention time, the stability of the process was guaranteed and the presence of co-substrates in the anaerobic digester did not affect negatively the operation of the autotrophic nitrogen removal process. Due to the success of the pilot plant experiment, an upscale of the process to full scale is proposed. Mass balances applied to Guillarei wastewater treatment plant revealed that in the main stream line the average denitrification rate calculated with the data of year 2011 was 226 kg N/d. Since the nitrogen removal efficiency is limited by the amount of readily biodegradable organic matter available to carry out denitrification in the water line, the implementation of an anammox-based process to treat the supernatant seems the best option to improve the effluent quality in terms of nitrogen content. The nitrogen removal rate in the sludge line would be 30 times higher than the one in the water line. The implementation of the process would improve the energetic balance and the nitrogen removal performance of the plant.

Enhanced ammonia removal at room temperature by pH controlled partial nitrification and subsequent anaerobic ammonium oxidation.

The Anammox-based processes are suitable for the treatment of wastewaters characterized by a low carbon to nitrogen (C/N) ratio. The application of the Anammox process requires the availability of an effluent with a NO2- -N/NH4+ -N ratio composition around 1 g g-1, which involves the necessity of a previous step where the partial nitrification is performed. In this step, the inhibition of the nitrite-oxidizing bacteria (NOB) is crucial. In the present work, a combined partial nitrification-ANaerobic AMmonia OXidation (Anammox) two-units system operated at room temperature (20 degreeC) has been tested for the nitrogen removal of pre-treated pig slurry. To achieve the successful partial nitrification and inhibit the NOB activity, different ammonium/inorganic carbon (NH4+/IC) ratios were assayed from 1.19 to 0.82g NH4+-Ng-1 HCO3-C. This procedure provoked a decrease of the pH value to 6.0 to regulate the inhibitory effect over ammonia-oxidizing bacteria caused by free ammonia. Simultaneously, the NOB experienced the inhibitory effect of free nitrous acid which avoided the presence of nitrate in the effluent. The NH4+/IC ratio which allowed the obtaining of the desired effluent composition (50% of both ammonium and nitrite) was 0.82 +/- 0.02 g NH4+-N g-1 HCO3- -C. The Anammox reactor was fed with the effluent of the partial nitrification unit containing a NO2 -N/NH4+ -N ratio of 1 g g-1' where a nitrogen loading rate of 0.1 g N L-1 d-1 was efficiently removed.

Dissemination of hepatocellular carcinoma in subcutaeous tissue after fine needle aspiration cytology (FNAC).

The hepatocellular carcinoma (HCC) is the fifth most frequent tumor in the world, and the third cause of death related to cancer. Histological samples obtained from diseased liver likely to have HCC are currently prescribed in selected patients in whose imaging studies and tumor markers are not sufficient for the diagnosis. In recent years, a risk of tumoral seeding along needle tract of FNAC to obtain histological samples has been reported. We present a case of tumor implantation of HCC cells in the needle tract, a year and four months after a percutaneous fine needle aspiration cytology (FNAC).

Effects of the cycle distribution on the performance of SBRs with aerobic granular biomass.

The aerobic granular systems are mainly sequencing batch reactors where the biomass is submitted to feast-famine regimes to promote its aggregation in the form of granules. In these systems, different cycle distributions can be applied for the simultaneous removal of organic matter, nitrogen and phosphorus. In this work two strategies were followed in order to evaluate the effects of the cycle distribution. In the first experiment, the length of the operational cycle was decreased in order to maximize the treatment capacity and consequently the famine/feast ratio was also decreased. In the second experiment, an initial anoxic phase was implemented to improve nitrogen removal efficiency. The results obtained showed that to reduce the famine/feast ratio from 10 to 5 was possible by increasing the treated organic and nitrogen loading rates in the system to 33%, without affecting the removal efficiencies of organic matter (97%) and nitrogen (64%) and producing a slight detriment of the granules characteristics. On the other hand, the implementation of an anoxic phase of 30 min previous to the aerobic one with a pulse-fed mode increased the nitrogen removal of pig manure from 20 to 60%, while the cycle configuration comprising a continuous feeding simultaneous with an anoxic phase of 60 min did not enhance the nitrogen removal and even worsen the ammonia oxidation.

Impact of outdoor air pollution on severity and mortality in COVID-19 pneumonia.

The relationship between exposure to air pollution and the severity of coronavirus disease 2019 (COVID-19) pneumonia and other outcomes is poorly understood. Beyond age and comorbidity, risk factors for adverse outcomes including death have been poorly studied. The main objective of our study was to examine the relationship between exposure to outdoor air pollution and the risk of death in patients with COVID-19 pneumonia using individual-level data. The secondary objective was to investigate the impact of air pollutants on gas exchange and systemic inflammation in this disease. This cohort study included 1548 patients hospitalised for COVID-19 pneumonia between February and May 2020 in one of four hospitals. Local agencies supplied daily data on environmental air pollutants (PM10, PM2.5, O3, NO2, NO and NOX) and meteorological conditions (temperature and humidity) in the year before hospital admission (from January 2019 to December 2019). Daily exposure to pollution and meteorological conditions by individual postcode of residence was estimated using geospatial Bayesian generalised additive models. The influence of air pollution on pneumonia severity was studied using generalised additive models which included: age, sex, Charlson comorbidity index, hospital, average income, air temperature and humidity, and exposure to each pollutant. Additionally, generalised additive models were generated for exploring the effect of air pollution on C-reactive protein (CRP) level and SpO2/FiO2 at admission. According to our results, both risk of COVID-19 death and CRP level increased significantly with median exposure to PM10, NO2, NO and NOX, while higher exposure to NO2, NO and NOX was associated with lower SpO2/FiO2 ratios. In conclusion, after controlling for socioeconomic, demographic and health-related variables, we found evidence of a significant positive relationship between air pollution and mortality in patients hospitalised for COVID-19 pneumonia. Additionally, inflammation (CRP) and gas exchange (SpO2/FiO2) in these patients were significantly related to exposure to air pollution.

Post-intensive care syndrome one month after discharge in surviving critically ill COVID-19 patients.

OBJECTIVES: Incidence of post-intensive care syndrome at one month after hospital discharge in surviving critically ill COVID 19 patients and to identify associated factors. DESIGN: Prospective cohort study. SETTING: Two multipurpose critical care units of the Araba University Hospital. Patients admitted to critical care units for severe acute respiratory failure secondary to COVID 19. INTERVENTION: None. VARIABLES OF INTEREST: Demographic variables, length of stay, Charlson index, APACHE II, SOFA, days of mechanical ventilation, tracheotomy, delirium, tetraparesis of the critical patient, EuroQol 5D5L, Minimental Test. RESULTS: A deterioration in the EuroQol health index (HI) from 90.9±16.9 to 70.9±24.7 (p<0.001) was observed. The impairment of the five EuroQol domains is: mobility (46.1%), usual activities (44.7%), discomfort/pain (30.7%), psychological domain (27.3%) and self-care (20.3%). The 61.5% suffer a significant decrease in their health index. Multivariate analysis by logistic regression shows us that delirium (OR=3.01; 95%CI: 1.01-8.9; p=0.047) and tracheostomy (OR=2.37; 95%CI: 1.09-5.14; p=0.029) show association with drop in EuroQoL 5D5L SI. The area under the ROC curve of the model is 67.3%, with a confidence interval between 58% and 76%. The model is calibrated using the Hosmer-Lemeshow test (χ2=0.468; p=0.792). Only 1.2% of patients showed a score ≤ 24, clearly pathological, on the Folstein's Minimental Test. CONCLUSIONS: Delirium and need for tracheostomy are associated with post-intensive care syndrome assessed by EuroQol 5D5L.

The epidemiologic burden of hepatitis C virus infection in Latin America .

Chronic infection with hepatitis C virus (HCV) is a major and growing public health concern worldwide, including in Latin America. With more efficacious therapies becoming available, decision-makers will require accurate estimates of disease prevalence to assess the potential impact of new treatments. However, few estimates of the epidemiologic burden, either overall or by country, are available for Latin America; and the potential impact of currently-available treatments on the epidemiologic burden of HCV in Latin America has not been assessed. To address this, we systematically reviewed twenty-five articles presenting population-based estimates of HCV prevalence from general population or blood donor samples, and supplemen- ted those with publically-available data, to estimate the total number of persons infected with HCV in Latin America at 7.8 million (2010). Of these, over 4.6 million would be expected to have genotype 1 chronic HCV, based on published data on the risk of progression to chronic disease and the HCV genotype distribution of Latin America. Finally, we calculated that between 1.6 and 2.3 million persons with genotype 1 chronic HCV would potentially benefit from current treatments, based on published estimates of genotype-specific treatment responsiveness. In conclusion, these estimates demonstrate the substantial present epidemiologic burden of HCV, and quantify the impending societal and clinical burden from untreated HCV in Latin America.

Behavioural determinants of salt consumption among hypertensive individuals.

BACKGROUND: High salt consumption among populations remains a challenge for health professionals dealing with prevention and control of hypertension. The present study aimed to identify the psychosocial predictors of salt consumption among hypertensive individuals, based on an extended version of the Theory of Planned Behaviour (TPB). Three salt consumption behaviours were studied: Behaviour 1- using <4 g of salt per day during cooking; Behaviour 2- avoiding adding salt/table salt use to the prepared foods; and Behaviour 3- avoiding the consumption of foods with high salt content. METHODS: At baseline (n = 108), TPB and additional variables (self-efficacy, habit, past behaviour, hedonic determinant, self-perceived diet quality) were measured. At 2-month follow-up (n = 95), the three behaviours were assessed. Behaviour and intention were sequentially regressed on the study variables, using polytomous logistic regression and hierarchical linear regression with rank transformation, respectively. RESULTS: Behaviour 1 was predicted by intention [odds ratio (OR) = 6.23; 95% confidence interval (CI) = 1.81-21.52], whereas self-efficacy and habit predicted intention. Behaviour 2 exhibited high score mean and low variation and was predicted by self-perceived diet quality (OR = 2.56; 95% CI = 1.03-6.36). Behaviour 3 was predicted by the hedonic determinant (OR = 1.42; 95% CI = 1.01-1.98). CONCLUSIONS: The results indicate that salt-related behaviours are explained by a variety of determinants. Among these determinants, special consideration should be given to motivational and hedonic aspects.

Autotrophic denitrification with sulphide in a sequencing batch reactor.

In this study a sequencing batch reactor was used to simultaneously remove both sulphide and nitrate via an autotrophic denitrification process. The sulphide loading rates were gradually increased from 200 mg S(2-) L(-1) d(-1)-450 mg S(2-) L(-1)d(-1)while the nitrogen loading rates were kept at 450 mg NO(3)(-)-N L(-1)d(-1). The obtained results demonstrated that it was possible to carry out autotrophic denitrification in a Sequencing Batch Reactor with removal efficiencies of sulphide and nitrogen of 100% and 67%, respectively. The efficiency of the process was influenced by the pH value in the reactor. The operation at pH values higher than 9.0 decreased the efficiency of sulphide oxidation into sulphate to 11.3%. The main bacteria populations present in the sludge belonged to Thiobacillus genus.

Short- and long-term effects of ammonium and nitrite on the Anammox process.

Autotrophic anaerobic ammonium oxidation (Anammox) is a biological process in which Planctomycete-type bacteria combine ammonium and nitrite to generate nitrogen gas. Both substrates can exert inhibitory effects on the process, causing the decrease of the specific activity of the biomass and the loss of the stable operation of reactors. The aim of the present work is to evaluate these effects in short- and long-term experiments. The short-term effects were carried out with two different types of Anammox biomass, biofilm on inorganic carriers and flocculent sludge. The effects of ammonium on both kinds of biomass were similar. A decrease of the Specific Anammox Activity (SAA) of 50% was observed at concentrations about 38 mg NH(3)-N·L(-1), while 100 mg NH(3)-N·L(-1) caused an inhibition of 80%. With regards to nitrite, the SAA was not affected at concentrations up to 6.6 µg HNO(2)-N·L(-1) but it suffered a decrease over 50% in the presence of 11 µg HNO(2)-N·L(-1) in the case of the biofilm. The flocculent biomass was much less resistant and its SAA sharply decreased up to 30% of its initial value in the presence of 4.4 µg HNO(2)-N·L(-1). The study of the long-term effects was carried out in lab-scale Sequencing Batch Reactors (SBR) inoculated with the biofilm biomass. Concentrations up to 20 mg NH(3)-N·L(-1) showed no effects on either reactor efficiency or biomass activity. However, when free ammonia concentrations reached values between 35 and 40 mg NH(3)-N·L(-1), the operation turned unstable and the efficiency was totally lost. Nitrous acid concentrations around 1.5 µg HNO(2)-N·L(-1) caused a loss of the efficiency of the treatment and a destabilization of the system. However, a total restoration of the SAA was observed after the stoichiometric feeding was applied to the SBR.