Viability and removal assessment of Escherichia coli and Salmonella spp. by real-time PCR with propidium monoazide in the hygienization of sewage sludge using three anaerobic processes.

Sewage sludge should be stabilized for its beneficial use and pathogens, among other factors, should comply with environmental regulations. Three sludge stabilization process were compared to assess their suitability for producing Class A biosolids: MAD-AT (mesophilic (37 °C) anaerobic digestion (MAD) followed by an alkaline treatment (AT)); TAD (thermophilic (55 °C) anaerobic digester); and TP-TAD (mild thermal (80 °C, 1 h) pretreatment (TP) followed by a TAD). E. coli and Salmonella spp. were determined, differentiating three possible states: total cells (qPCR), viable cells using the propidium monoazide method (PMA-qPCR), and culturable cells (MPN). Culture techniques followed by the confirmative biochemical tests identified the presence of Salmonella spp. in PS and MAD samples, while the molecular methods (qPCR and PMA-qPCR) showed negative results in all samples. The TP + TAD arrangement reduced the concentration of total and viable E. coli cells in a greater extent than the TAD process. However, an increase of culturable E. coli was observed in the corresponding TAD step, indicating that the mild thermal pretreatment induced the viable but non-culturable state in E. coli. In addition, the PMA technique did not discriminate viable from non-viable bacteria in complex matrices. The three processes produced Class A biosolids (fecal coliforms < 1000 MPN/gTS and Salmonella spp, < 3 MPN/gTS) maintaining compliance after a 72 h storage period. It appears that the TP step favors the viable but not culturable state in E. coli cells, a finding that should be considered when adopting mild thermal treatment in sludge stabilization process arrangements.

Methane emissions from anaerobic sludge digesters in Mexico: On-site determination vs. IPCC Tier 1 method.

Wastewater treatment is an important source of methane (CH4) emissions. In most large-size aerobic treatment plants, the excess sludge is digested in anaerobic reactors (AD), with the concomitant CH4 emissions. The guidelines of the Intergovernmental Panel on Climate Change (IPCC) have been adopted worldwide for quantifying the national emission inventories, which include wastewater treatment plants (WWTP) as a key category. The IPCC recommends using default emission factors (Tier 1) for countries with limited available data (such as Mexico and most developing countries). However, these estimates have a high degree of uncertainty, owing to the lack of reliable information about the operation process and local environmental conditions. In order to reduce uncertainty in the estimation of CH4 emission from WWTP in Mexico, a country-specific emission factor was determined for AD associated with activated sludge process. This was accomplished with on-site data obtained from the AD of six activated sludge WWTP. In addition, the measured CH4 emissions were compared to those resulting from the application of the IPCC Tier 1 method, using the recommended default methane correction factor (MCF: 0.8) as well as alternate values (0.32 and 0.26) recently proposed by the authors. Results show that the IPCC Tier 1 method, using the recommended MCF, highly overestimate CH4 emissions compared with the values obtained on-site. In contrast, the alternate MCF achieved better estimations than the IPCC-recommended MCF, much closer to the observed emission values. The CH4 emission factor proposed as country (Mexico) specific value is 0.49 kg CH4/kg BODrem, which would allow the application of IPCC Tier 2 method. By doing so, the uncertainty associated with CH4 emission from aerobic treatment plants with AD would be reduced. This, in turn, would provide important information for implementing appropriate CH4 mitigation strategies for the water sector.

Methane correction factors for estimating emissions from aerobic wastewater treatment facilities based on field data in Mexico and on literature review.

Wastewater treatment (WWT) may be an important source of methane (CH4), a greenhouse gas with significant global warming potential. Sources of CH4 emissions from WWT facilities can be found in the water and in the sludge process lines. Among the methodologies for estimating CH4 emissions inventories from WWT, the more adopted are the guidelines of the Intergovernmental Panel on Climate Change (IPCC), which recommends default emission factors (Tier 1) depending on WWT systems. Recent published results show that well managed treatment facilities may emit CH4, due to dissolved CH4 in the influent wastewater; in addition, biological nutrient removal also will produce this gas in the anaerobic (or anoxic) steps. However, none of these elements is considered in the current IPCC guidelines. The aim of this work is to propose modified (and new) methane correction factors (MCF) regarding the current Tier 1 IPCC guidelines for CH4 emissions from aerobic treatment systems, with and without anaerobic sludge digesters, focusing on intertropical countries. The modifications are supported on in situ assessment of fugitive CH4 emissions in two facilities in Mexico and on relevant literature data. In the case of well-managed centralized aerobic treatment plant, a MCF of 0.06 (instead of the current 0.0) is proposed, considering that the assumption of a CH4-neutral treatment facility, as established in the IPCC methodology, is not supported. Similarly, a MCF of 0.08 is proposed for biological nutrient removal processes, being a new entry in the guidelines. Finally, a one-step straightforward calculation is proposed for centralized aerobic treatment plants with anaerobic digesters that avoids confusion when selecting the appropriate default MCF based on the Tier 1 IPCC guidelines.

Risk factors and outcomes of severe acute respiratory failure requiring invasive mechanical ventilation in cancer patients: A retrospective cohort study.

OBJECTIVES: To determine the risk factors for severe acute respiratory failure requiring invasive mechanical ventilation (SARF-MV) and its effect upon clinical outcomes in critically ill cancer patients. DESIGN: A retrospective cohort study was carried out. SETTING: A 12-bed oncological intensive care unit (ICU) from January 2014 to December 2015. PATIENTS: A total of 878 consecutive cancer patients were included. Patients with an ICU stay of ≤1 day were excluded. The final sample size was 691 patients. INTERVENTIONS: None. VARIABLES: Clinical variables at ICU admission were extracted from the medical records. The primary outcome was SARF-MV. We also measured ICU and hospital mortality, as well as length of stay. RESULTS: The SARF-MV rate was 15.8%. The multivariate analysis identified brain tumour (OR 14.54; 95%CI 3.86-54.77; p<0.0001), stage IV cancer (OR 3.47; 95%CI 1.26-9.54; p=0.016), sepsis upon admission (OR 2.28; 95%CI 1.14-4.56; p=0.020) and an APACHE II score≥20 points (OR 5.38; 95%CI 1.92-15.05; p=0.001) as being independently associated to SARF-MV. Compared with the patients without SARF-MV, those with SARF-MV had a prolonged length of ICU stay (p<0.0001), a lower ICU survival rate (p<0.0001) and a lower hospital survival rate (p<0.0001). CONCLUSIONS: A number of clinical factors are related to SARF-MV. In this regard, SARF-MV is a powerful factor independently correlated to poor outcomes. Future studies should investigate means for preventing SARF-MV in critically ill cancer patients, which may have an impact upon outcomes.

Control of dissolved CH4 in a municipal UASB reactor effluent by means of a desorption - Biofiltration arrangement.

The direct anaerobic treatment of municipal wastewater represents an adapted technology to the conditions of developing countries. In order to get an increased acceptance of this technology, a proper control of dissolved methane in the anaerobic effluents should be considered, as methane is a potent greenhouse gas. In this study, a pilot-scale system was operated for 168 days to recover dissolved methane from an effluent of an upflow anaerobic sludge blanket reactor and then oxidize it in a compost biofilter. The system operated at a constant air (0.9 m3/h ±0.09) and two air-to anaerobic effluent ratio (1:1 and 1:2). In both conditions (CH4 concentration of 2.7 ± 0.87 and 4.3% ± 1.14, respectively) the desorption column recovered 99% of the dissolved CH4 and approximately 30% ± 8.5 of H2S, whose desorption was limited due to the high pH (>8) of the effluent. The biofilter removed 70% ± 8 of the average CH4 load (60 gCH4/m3h ± 13) and 100% of the H2S load at an empty bed retention time of 23 min. The average temperature inside the biofilter was 42 ± 9 °C due to the CH4 oxidation reaction, indicating that temperature and moisture control is particularly important for CH4 removal in compost biofilters. The system may achieve a 54% reduction of greenhouse gas emissions from dissolved CH4 in this particular case.

Optimization of the thermophilic anaerobic co-digestion of pig manure, agriculture waste and inorganic additive through specific methanogenic activity.

The anaerobic co-digestion of three wastes (manure, rice straw and clay residue, an inorganic additive) at different concentration levels and their interactive effects on methanogenic activity were investigated in this work at thermophilic conditions in order to enhance hydrolytic activity and methane production. A central composite design and the response surface methodology were applied for the optimization of specific methanogenic activity (SMA) by assessing their interaction effects with a reduced number of experiments. The results showed a significant interaction among the wastes on the SMA and confirmed that co-digestion enhances methane production. Rice straw apparently did not supply a significant amount of substrate to make a difference in SMA or methane yield. On the other hand, clay residue had a positive effect as an inorganic additive for stimulating the anaerobic process, based on its mineral content and its adsorbent properties for ammonia. Finally, the optimal conditions for achieving a thermophilic SMA value close to 1.4 g CH4-COD/g VSS · d(-1) were 20.3 gVSS/L of manure, 9.8 gVSS/L of rice straw and 3.3 gTSS/L of clay.

Influence of hydraulic retention time on UASB post-treatment with UF membranes.

A pilot UASB reactor coupled with an external ultrafiltration (UF) membrane was operated under three different hydraulic retention times (HRT) for domestic wastewater treatment. The aim was to assess the HRT influence on system performance and fouling. The highest concentrations of COD, total solids, extracellular polymeric substances (EPS) and soluble microbial products (SMP) in UASB effluent and permeate were found when the UASB reactor was operated under the lowest HRT studied (4 hours); although the fulfillment of Mexican Standard for wastewater reclamation was not compromised. This fact could be attributed to the higher shear stress forces inside the UASB reactor when it was operated at low HRT, which promoted the release of biopolymeric substances in its effluent. Besides, the fouling propensity in the UASB effluent was worsened with HRT reduction, by increasing the fouling rate and the specific cake resistance. Based on these results, it is recommended to avoid operating the UASB reactor at low HRTs (less than 4 hours) in order to control SMP and EPS fouling potential. The results presented also suggest that HRT reduction has a detrimental effect on performance and fouling.

Effect of thermal alkaline pretreatment on the anaerobic digestion of wasted activated sludge.

The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.

Biofouling and pollutant removal during long-term operation of an anaerobic membrane bioreactor treating municipal wastewater.

Two different sludge retention times (SRTs) were tested in order to assess the impact on membrane fouling and effluent quality in an anaerobic membrane bioreactor (AnMBR). Two up-flow anaerobic sludge bed (UASB) reactors (1 l volume) coupled to external tubular ultrafiltration membranes (filtration area = 81 cm(2)) were operated at a hydraulic retention time of 3 h and two different SRTs (100 and 60 days). The transmembrane pressure (TMP), flux (J) and relevant parameters to assess water quality were measured. Effluents from UASB reactors were filtered for 500 h without intermediate cleaning. The permeate met Mexican standards for wastewater reclamation in both tested conditions. Abrupt and periodical changes in the TMP and J were noticed during the experimental period. A fouling layer collapse and compression hypothesis was set forth in order to explain these changes. An autopsy performed on biofouled membranes indicated that deposited mass was mainly composed of volatile solids (85%) and the rest related to mineral matter, with the presence of inorganic salts containing Ca, Mg, Fe, P and Si. Biomass in the fouling layer was estimated at 0.27% based on the DNA/biomass ratio for the bacterial biofilm. No clear difference in membrane fouling was detected under the two SRTs applied to the systems. However, when operated over 500 h, repetitive sudden TMP and flux changes occurred later in system A (SRT of 100 days) than in system B (SRT of 60 days) suggesting a stronger fouling layer structure in the former.

Short communication. Frequency of dispensing paediatric medicines with high sugar content by pharmacists in Barcelona.

AIM: To determine which high sugar cough syrups sell most frequently in pharmacies in Barcelona. METHODS: 300 pharmacies in 10 districts of Barcelona (Spain) were visited and data collected on the type of syrup-based medicines dispensed most often over a 3-month period in 2008. RESULTS: Data was collected in 142 out of 300 pharmacies. The percentage of the medicines sold by group of antibiotics (sweetener) were: Augmentine (aspartame) 5.72%; Clamoxyl (sucrose) 3.28%; Ceclor (sucrose) 3.66%. In the anti-inflammatory group: Junifen 2.0% (saccharine sódic); 3.59%, Junifen 4.0% (sodic sucrose); 4.35%, Apiretal Codeine (sucrose); 0.31%, Dalsy (sucrose) 39.35%; Febrectal (sodic saccharine): 0.89%. CONCLUSIONS: It is very important to advise parents, pharmacists, paediatricians, and paediatric dentists about low-sweetener paediatric medicine alternatives to control the high content sucrose medicines. The aim should be to reduce the intake of over the counter medication.

Two-phase (acidogenic-methanogenic) anaerobic thermophilic/mesophilic digestion system for producing Class A biosolids from municipal sludge.

Two different arrangements of two-phase anaerobic sludge systems were operated treating a mixture of primary and secondary sludge. Two steady state periods were evaluated: the first acidogenic thermophilic phase was operated at hydraulic retention times of 3 and 2 days and the second methanogenic (mesophilic and thermophilic) phases at 13 and 10 days. The two-phase systems had an efficient removal of pathogens and parasites, achieving values lower than those specified for Class A biosolids, according to the Mexican Standard NOM-004-SEMARNAT-2002. The first thermophilic phase achieved almost complete destruction of pathogens and parasites by itself. During the second steady state period, volatile fatty acids accumulated in the second methanogenic phases (HRT of 10 days and an organic load of 3 kg VS/m(3)d) indicating that the systems were overloaded, mainly the mesophilic digester. In this case, the accumulation of propionic acid may be related to a deficiency of micronutrients. The results show that the two-phase thermophilic/mesophilic anaerobic sludge digestion may be considered as an adequate option for the production of Class A biosolids.

Copper reduces striatal protein nitration and tyrosine hydroxylase inactivation induced by MPP+ in rats.

Striatal administration of 1-methyl-4-phenylpyridinium (MPP(+)), the active metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), causes nigrostriatal dopaminergic pathway damage similar to that observed in Parkinson's disease. Copper acts as a prosthetic group of several antioxidant enzymes and recent data show that copper attenuated MPP(+)-evoked neurotoxicity. We evaluated the effect of copper (as a supplement) upon proteins nitration (60 kDa) and tyrosine hydroxylase (TH) inactivation induced by MPP(+) (10 microg/8 microL) injection into the rat striatum. Copper pretreatment (10 micromol/kg i.p.) prevented both MPP(+)-induced proteins nitration and TH inactivation. Copper treatment also prevented the dopamine-depleting effect of MPP(+) injection. Those results were accompanied by a significant reduction of enzymatic activity of the constitutive nitric oxide synthase (cNOS), whereas, the protein levels of the three isoforms of NOS remained unchanged. Results indicate that the effect of copper against MPP(+)-induced proteins nitration and TH inactivation in the striatum of rat may be mediated by a reduction of cNOS activity.

Evaluation of an aerobic submerged filter packed with volcanic scoria.

An aerobic submerged filter (ASF) using volcanic scoria stones as packing media was evaluated. The wastewater used was a mixture of sewage with sugar to obtain organic matter concentrations between 28 and 3230 mg CODt/L, hydraulic rates up to 2.88 m3/m2 d and organic loading rates between 0.45 and 9.4 kg CODt/m3 d. The system removed 80% of CODt as average for organic loading rates between 0.45 and 3 kg CODt/m3 d and 54% at the higher rate (9.4 kg CODt/m3 d). It was not necessary to backwash the filters, a negligible pressure drop and a good biomass attachment in the volcanic scoria stones was observed. Nitrification and organic matter biodegradation were carried out simultaneously with a nitrate production of 90% up to 1.7kgCODt/m3 d. Tracer studies revealed a completed mixed hydraulic pattern which was not affected by the presence of biomass.

Stereospecific hydrolysis of a phosphoramidate as a model to understand the role of biotransformation in the neurotoxicity of chiral organophosphorus compounds.

Calcium-dependent and EDTA-resistant hydrolyses of R and S isomers of O-hexyl O-2,5-dicholorophenyl phosphoramidate (HDCP) were observed in serum and subcellular fractions of liver, kidney and brain from hen, rat and rabbit. In serum, the Ca(2+)-dependent hydrolysis was much higher in rabbit than in other species. Liver showed a higher activity than kidney and brain. The S-HDCP isomer was hydrolysed to a higher extent than the other isomer. The fact that this stereospecificity favours the S-isomer is more clearly observed in rabbit serum, and in rat and rabbit liver particulate fractions. In such tissues and species, the EDTA-resistant hydrolysis was not stereospecific. Soluble fractions of rat brain and of hen liver, kidney and brain, showed a lower total activity but with a higher proportion of EDTA-resistant activity and a higher hydrolysis of the R-HDCP isomer. The Ca(2+)-dependent stereoselective biodegradation of S-HDCP is dominant in the most active tissues in rabbit and rat. It can therefore be concluded that S-HDCP would be biodegraded faster than R-HDCP. Furthermore, R-HDCP is the isomer that will remain at a higher proportion to be available for interaction with the target of neurotoxicity.

Increasing microbial activity in thermophilic anaerobic digestion of physicochemical sludge.

Two thermophilic lab-scale reactors of 5 L were operated on a daily fed basis. Digester T1 received raw sludge (control) and digester T2 was fed with raw sludge plus metallic micronutrients and a bacilli additive. Raw sludge was obtained from a municipal chemically enhanced primary treatment plant. The effect of additives was clear on methane production, since on day 50, digester T2 produced 900 ml more methane than T1, an increase of 64%. On day 80, T2 reached twice the production of biogas of T1. Volatile solid removal (% VSR) in T2 increased to 29%; while T1 achieved only 15%. Acetic acid concentration in T2 diminished to 100 mg/L, which related to the higher biogas production. Based on the Mexican biosolids standard, the digested sludge reached Class A biosolids, in both digesters: fecal coliforms were reduced to less than 1000 MPN/gTS; Salmonella spp was totally eliminated and helminth egg counts were lower than one viable egg per gram of total solids.

Hydrogen sulfide removal by compost biofiltration: effect of mixing the filter media on operational factors.

The overall goal of this work was to determine the effect of mixing the filter media of a compost biofilter on H(2)S removal efficiency. The behavior of important operational factors such as moisture of filter media, pressure drop and sulfate accumulation were evaluated, considering mixing the media. Additionally, tracer studies were performed in order to determine the effect of mixing the media on gas distribution. H(2)S removal capacity decreased over time, from 100% to 90%. When bed mixing was carried out, the removal capacity remained constant, close to 100%, and moisture content and sulfates accumulation were better controlled at 50% and at 12 mg S-SO(4)/g dry media respectively. In addition, under this operational pattern, an improvement in gas and particle size distribution was observed inside the filter media, fitting the axial dispersion model and the Ergun equation.

Effect of biological additives and micronutrients on the anaerobic digestion of physicochemical sludge.

Two additives (lyophilized bacilli and enzymes) and a solution of micronutrients (Fe, Co, Ni and Mo) were tried separately and in combination, in order to assess their effect on the anaerobic digestion of waste sludge from an enhanced primary treatment (EPT) of municipal wastewater. Three batch tests were carried out in serological bottles. In the first test, addition of bacilli increased production of methane from day 11 and at day 1 7 the production was 95% greater than the control. In that experiment, the concentration of volatile fatty acids (VFAs) was 1,391 mg/L, 40% lower than the control. In the second test, the combination of micronutrients with bacilli, reached from the first days a better methane production than the control, 167% higher in day 17. At the end of the experiment, this combination achieved a lower concentration of VFAs and a greater percentage of volatile solid removal than the rest of the treatments. The third test was based on an experimental design in order to statistically determine the best doses of bacilli additive and micronutrients. The anaerobic thermophilic digestion of sludge from aluminium sulfate EPT will be improved with the addition of Fe: 4.5 mg/g VS, Ni: 0.75 mg/g VS, Co: 0.45 mg/g VS, Mo: 0.09 mg/g VS and bacilli additive: 12 mg/g VS.

Acclimation of mesophilic anaerobic sludge to thermophilic conditions: PCR genera detection methodology.

In Mexico, sludge from wastewater treatment plants is a public health problem, especially for the infant population due to the presence of pathogens and parasite eggs. Therefore, it is of great interest to apply proper treatment methods for those wastes. An option proposed for the removal of possible infectious sources is thermophilic anaerobic digestion, even though a limitation for its acceptance is the slow start-up of the reactors. The transformation of a mesophilic anaerobic sludge for its utilization as a thermophilic inoculum, by means of direct temperature increase up to 55 degrees C and feeding of the inoculum with synthetic medium was possible in two months. As a main part of the work and with the objective of evaluating the changes in the methanogenic microbial population during the sludge treatment, a specific detection technique for these bacteria has been developed and validated, based on the use of the polymerase chain reaction (PCR).

Effect of aluminium and sulphate on anaerobic digestion of sludge from wastewater enhanced primary treatment.

The combined and individual effects of aluminium and sulphate at concentrations of 1,000 mg/l as Al(OH)3, and 150 mgSO4(2-)/L as K2SO4, respectively, on the anaerobic digestion of sludge from enhanced primary treatment (EPT) were evaluated in 1 L capacity semi continuous reactors. It was found that at 59 days, aluminium inhibits the specific methanogenic activity (SMA) of methanogenic and acetogenic bacteria resulting in a 50% to 72% decrease. Sulphate also inhibits (48% to 65%) the SMA of the same type of bacteria. Methanogenic and acetogenic bacteria were able to adapt, to a different extent, to the assayed concentrations of aluminium and sulphate. However, the combination of aluminium and sulphate resulted in a higher inhibition, especially of the hydrogenophilic methanogenic bacteria. Indeed, this effect remained during the time of the experiment, maintaining an inhibition of 44% at 114 days. Feeding with EPT sludge led to a bigger decrease in SMA of each bacterial group, with respect to the other treatments with time. It is concluded that the acidification of anaerobic reactors fed with EPT sludge is due, among other causes, to the concurrent presence of aluminium and sulphate.

Pressure drop and gas distribution in compost based biofilters: medium mixing and composition effects.

The pressure drop and gas distribution in four different filter media for compost biofilters were studied as a function of three superficial loading rates of moist air and by carrying out the filter medium homogenization by mixing. The filter media used were compost, compost with cane bagasse, lava rock and aerobic sludge previously dried to 60% of water content. The pressure drop increased when lava rock and cane bagasse were used as bulking agents. The same trend was observed when water was added to the filter medium. Pressure drop tended to decrease with time as flow channels were formed inthe filter media. Tracer studies were carried out to quantify the gas distribution and the effect of channel formation. For the biofilters submitted to an airflow of 10, 40 and 70 l min(-1), an average normalized time of 0.96, 0.89 and 0.82, respectively were obtained. The results showed that channel formation was increased as the superficial loading rate was also increased. An operational practice that this work proposes and evaluates to improve gas distribution and medium moisture control is to carry out intermittent medium mixing. The medium moisture and void volume achieved under mixing condition were around 50% and 0.40, respectively with an average constant pressure drop of 11, 45 and 78 cm of water m(-1) for air velocities of 75, 300 and 525 m h(-1).