E. Hontoria

Effect of dissolved oxygen concentration on nitrate removal from groundwater using a denitrifying submerged filter.

A unidirectional submerged filter system was employed to purify groundwater contaminated with nitrate by biological denitrification. The influence of the concentration of dissolved oxygen (DO) in the process was tested using ethanol, methanol and sucrose as carbon sources. Inorganic-nitrogen removal, growth of the biofilm, platable denitrifying bacteria and nitrate reducing bacteria in biofilm were studied. With regard to the type of electron donor used, the presence of oxygen decreased the removal efficiency of inorganic nitrogen and caused an increase of nitrite concentration in the treated water. These negative effects depended on utilised carbon source. Biological denitrification with alcohols such as ethanol and methanol was less affected by DO than with sucrose. The development of the biofilm was also influenced by the DO concentration as excess O(2) caused reduced biofilm growth. These biofilms developed in oxygen presence had a smaller bacterial density and a lower denitrifying bacteria versus nitrate reducing bacteria ratio, which led to an unfavorable inorganic nitrogen removal and presence of nitrite in the treated water. All these effects are more pronounced when sucrose is used as carbon source.

Gas chromatographic–mass spectrometric method for the determination of bisphenol A and its chlorinated derivatives in urban wastewater

The simultaneous determination of trace amounts of endocrine disruptors such as bisphenol A (BPA) and its monochloro, dichloro, trichloro and tetrachloro derivatives in wastewater has been developed using gas chromatography-mass spectrometry (GC-MS). Compounds were previously extracted from the aqueous samples using a liquid-liquid extraction procedure with a mixture of dichloromethane:carbon tetrachloride (25/75). After extraction, solvent was removed and a silylation step was carried out with N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA). The silylated compounds were identified and quantified by GC-MS using an HP1-MS column. The retention times were 6.64 min for BPA silylated, 7.26 min for Cl-BPA silylated, 7.99 min for Cl(2)-BPA silylated, 8.85 min for Cl(3)-BPA silylated and 9.95 min for Cl(4)-BPA silylated. A clean-up is not necessary using SIM mode. Deuterated anthracene (2H(10)-anthracene) was used as an internal standard. The detection limits obtained were 0.3, 0.6, 2.0, 4.5 and 13.0 ng L(-1) for silylated BPA, Cl-BPA, Cl(2)-BPA, Cl(3)-BPA and Cl(4)-BPA, respectively. The proposed method was applied satisfactory to the determination of these chemicals, in different types of wastewater previously spiked with different amounts of these chemicals at concentration levels ranging from 0.01 to 2.50 microg L(-1) for BPA, 0.05-2.50 micro L(-1) for Cl-BPA and 0.05-5.00 microg L(-1) for Cl(2)-BPA, Cl(3)-BPA and Cl(4)-BPA, respectively. The method was validated following standard addition methodology.

Influence of hydraulic loading and air flowrate on urban wastewater nitrogen removal with a submerged fixed-film reactor.

Nutrient disposal to sensitive areas, particularly nitrogen and phosphorus from wastewater treatment plants, provokes eutrophication reducing water quality. Fixed film technology is widely used for the removal of organic matter and nitrogen by the biological process of nitrification-denitrification. This paper studies a nitrification and post-denitrification lab-scale plant with a downflow aerobic submerged filter for removal of organic matter and nitrification, followed by an anoxic upflow biofilter for denitrification. Recycled construction material (clay shists) was employed as support material and methanol was used as carbon source. After 2 weeks of acclimation in which nitrification reached steady-state conditions, different hydraulic loadings (0.35-1.59 m(3)/m(2)h) and air flowrates (7.78-43.5 m(3)/m(2)h) were applied for 1 year. The highest hydraulic loading which complied with the EU regulation on nitrogen disposal was 0.71 m(3)/m(2)h (1.6 h). Hydraulic retention time (HRT), which corresponded to a nitrogen removal of 0.64 kg N/m(3) per day operating at an air flowrate of 25.6 m(3)/m(2)h. Concerning to organic matter removal efficiency, the aerobic reactor accepted a maximum chemical oxygen demand (COD) volumetric loading of 16.0 kg COD/m(3) per day with a 75% COD removal efficiency. For all the tests carried out, suspended solids (SS) concentration in the outlet water was less than 35 mg/l.

Determination of trace amounts of bisphenol F, bisphenol A and their diglycidyl ethers in wastewater by gas chromatography–mass spectrometry

A simple and sensitive method for the determination of trace amounts of bisphenol F, bisphenol A and their diglycidyl ethers in wastewater is proposed. The method involves a liquid‐liquid extraction (LLE) procedure using trichloromethane followed by a silylation step. Identification and quantification was performed by gas chromatography‐mass spectrometry (GC‐MS) using an HP1-MS column. The retention times were 6.59 and 7.02 min for BPF and BPA silylated, respectively, 8.30, 9.10 and 10.13 min for the three isomers of BFDGE and 11.12 min for BADGE. A clean-up is not necessary using SIM mode. Deuterated anthracene ( 2 H10-anthracene) was used as an internal standard. The detection limits obtained were 0.02, 0.006, 0.13 and 0.09m gl 1 for BPF, BPA, BFDGE and BADGE, respectively. The method was applied to the determination of these chemicals, as indicators of contamination by epoxy resins, in different types of spiked urban wastewater from Granada and Melilla (Spain) at concentration levels ranging from 0.06 to 2.50 m gl 1 for bisphenol F, 0.02 to 0.50m gl 1 for bisphenol A, 0.45 to 50.00m gl 1 for BFDGE and 0.30 to 50.00m gl 1 for BADGE.

Microbial community structure and dynamics in a pilot-scale submerged membrane bioreactor aerobically treating domestic wastewater under real operation conditions.

A pilot scale submerged ultra-filtration membrane bioreactor (MBR) was used for the aerobic treatment of domestic wastewater over 9 months of year 2006 (28th March to 21st December). The MBR was installed at a municipal wastewater facility (EMASAGRA, Granada, Spain) and was fed with real wastewater. The experimental work was divided in 4 stages run under different sets of operation conditions. Operation parameters (total and volatile suspended solids, dissolved oxygen concentration) and environmental variables (temperature, pH, COD and BOD(5) of influent water) were daily monitored. In all the experiments conducted, the MBR generated an effluent of optimal quality complying with the requirements of the European Law (91/271/CEE 1991). A cultivation-independent approach (polymerase chain reaction-temperature gradient gel electrophoresis, PCR-TGGE) was used to analyze changes in the structure of the bacterial communities in the sludge. Cluster analysis of TGGE profiles demonstrated significant differences in community structure related to variations of the operation parameters and environmental factors. Canonical correspondence analysis (CCA) suggested that temperature, hydraulic retention time and concentration of volatile suspended solids were the factors mostly influencing community structure. 23 prominent TGGE bands were successfully reamplified and sequenced, allowing gaining insight into the identities of predominantly present bacterial populations in the sludge. Retrieved partial 16S-rRNA gene sequences were mostly related to the alpha-Proteobacteria, beta-Proteobacteria and gamma-Proteobacteria classes. The community established in the MBR in each of the four stages of operation significantly differed in species composition and the sludge generated displayed dissimilar rates of mineralization, but these differences did not influence the performance of the bioreactor (quality of the permeate). These data indicate that the flexibility of the bacterial community in the sludge and its ability to get adapted to environmental changes play an important role for the stable performance of MBRs.

Removal and degradation characteristics of quinolone antibiotics in laboratory-scale activated sludge reactors under aerobic, nitrifying and anoxic conditions.

This work describes the removal of 6 quinolone antibiotics from wastewaters under different redox conditions (aerobic, nitrifying and anoxic) through batch experiments in laboratory scale activated sludge reactors using mixed liquor from a membrane bioreactor pilot plant (MBR). The main removal pathways for antibiotics from wastewaters involved in each treatment are described. Mass balances indicated that sorption on sludge played a dominating role in the elimination of antibiotics. Sorption potential depended on the redox conditions, being lower in nitrifying (Kd, 414-876 L kg(-1)) and anoxic (Kd, 471-930 L kg(-1)) sludge in comparison with aerobic sludge (Kd, 534-1137 L kg(-1)). Kd was higher for piperazinylic quinolones. Redox conditions also influenced biodegradation, a secondary pathway, which followed first-order kinetics with degradation rates constants ranging from 1.8·10(-3) to 8.2·10(-3) h(-1). Biodegradation rates under anoxic conditions were negligible. The experimental results have also demonstrated much higher removal efficiency by biodegradation (36.2-60.0%) under nitrifying conditions in comparison with aerobic conditions (14.9-43.8%). The addition of allylthiourea, an ammonia monooxygenase inhibitor, inhibited nitrification completely and reduced significantly the biodegradation of target antibiotics (16.5-29.3%). The residual biodegradation in the presence of allylthiourea may be due to the activity of heterotrophs in the enriched nitrifier culture. The removal of the selected antibiotics under the studied redox conditions depended significantly on the bacteria composition of the sludge. These results suggest that despite the known persistence of this group of antibiotics it is possible to enhance their degradation using nitrifying conditions, which at adequate working conditions as high SRT, typical in MBR, become a promising alternative for improving quinolones removal from environment.

Microbial enzymatic activities in a pilot-scale MBR experimental plant under different working conditions.

Phosphatases, glucosidase, protease, esterase and dehydrogenase activities in a MBR (membrane bioreactor) system equipped with ultrafiltration membranes for the treatment of real urban wastewater were measured at different volatile suspended solid (VSS) concentrations, total suspended solid (TSS) concentrations, hydraulic retention times (HRT), temperatures and inflow rates. The results showed the capacity of the MBR system to remove COD and BOD(5) at TSS between 7200 and 13,300 mg/L; HRT values of 8.05 and 15.27 h; inflow rates of 14.67 and 27.81 L/h; and temperatures between 4 and 27 degrees C. The enzymatic activities are influenced by increases in VSS and TSS concentrations. These results suggest that the ability to get adapted to environmental changes of the bacterial populations and their microbial enzymatic activities is essential to understand the biological processes that occur in MBR systems and crucial for proper urban wastewater treatment when using MBR technologies.

Influence of ethanol concentration on biofilm bacterial composition from a denitrifying submerged filter used for contaminated groundwater.

The influence of the ethanol concentration on the composition and activity of a developed biofilm in a denitrifying submerged unidirectional filter was studied. Process yields (represented as inorganic nitrogen removal), total platable bacteria, denitrifying bacteria, nitrate- and sulphate-reducing bacteria and denitrifying activity (N2O production) were compared at different ethanol concentrations (0 to 46.74 mg l(-1)). The biofilm exhibited a diverse bacterial composition and higher microbial development at the entrance of the unidirectional biofilter. The number of cells per gram of dry weight of biofilm was increased when the ethanol concentration increased, with the exception of nitrate reducers, for which the number of cells decreased per gram of biofilm in relation to height. Five different species of denitrifying bacteria were isolated from the biofilm, all of which were gram-negative rods. All of the species manifested an increase in denitrifying activity when the ethanol concentration was increased. In this sense, the number of denitrifying bacteria in the biofilm was positively correlated with the ethanol concentration. Both nitrate- and sulphate-reducing bacteria were present in the biofilm in the lower and higher part of the column. Nitrate-nitrogen removal in the submerged filter showed a high correlation with the influent ethanol concentration.

Effect of ciprofloxacin antibiotic on the partial-nitritation process and bacterial community structure of a submerged biofilter

A partial-nitritation bench-scale submerged biofilter was used for the treatment of synthetic wastewater containing a high concentration of ammonium in order to study the influence of the antibiotic ciprofloxacin on the partial-nitritation process and biodiversity of the bacterial community structure. The influence of ciprofloxacin was evaluated in four partial-nitritation bioreactors working in parallel, which received sterile synthetic wastewater amended with 350 ng/L of ciprofloxacin (Experiment 1), synthetic wastewater without ciprofloxacin (Experiment 2), synthetic wastewater amended with 100 ng/L of ciprofloxacin (Experiment 3) and synthetic wastewater amended with 350 ng/L of ciprofloxacin (Experiment 4). The concentration of 100 ng/L of antibiotics demonstrated that the partial-nitritation process, microbial biomass and bacterial structure generated by tag-pyrosequencing adapted progressively to the conditions in the bioreactor. However, high concentrations of ciprofloxacin (350 ng/L) induced a decay of the partial-nitritation process, while the total microbial biomass was increased. Within the same experiment, the bacterial community experienced sequential shifts with a clear reduction of the ammonium oxidation bacteria (AOB) and an evident increase of Commamonas sp., which have been previously reported to be ciprofloxacin-resistant. Our study suggests the need for careful monitoring of the concentration of antibiotics such as ciprofloxacin in partial-nitritation bioreactors, in order to choose and maintain the most appropriate conditions for the proper operation of the system.

Structure of archaeal communities in membrane-bioreactor and submerged-biofilter wastewater treatment plants.

A cultivation independent approach (PCR-TGGE) was used to evaluate the occurrence of Archaea in four wastewater treatments based on technologies other than activated sludge, and to comparatively analyze their community structure. TGGE fingerprints (based on partial archaeal 16S-rRNA amplicons) were obtained from sludge samples taken from a pilot-scale aerated MBR fed with urban wastewater and operated under two different sets of conditions (MBR1 and MBR2 treatments), and also from biofilms sampled from two pilot-scale submerged biofilters (SBs) consisting of one aerated and one anoxic column each, fed with urban (USB treatment) or industrial (ISB treatment) wastewater, respectively. Analysis of TGGE fingerprints revealed clear and significant differences of the community structure of Archaea between the wastewater treatments studied, primarily according to wastewater origin and the type of technology. Thirty-two different band classes were detected among the 23 sludge and biofilm samples analyzed, from which five were selected as dominant or distinctive of the four treatments studied. Sixteen predominant TGGE bands were identified, revealing that all of them were related to methanogenic Archaea. Neither other Euryarchaeota groups nor Crenarchaeota members were identified amongst the 16S-rRNA fragments sequenced from separated TGGE bands.