Comparative study of the use of pure oxygen and air in the nitrification of a MBR system used for wastewater treatment.

A MBR (membrane bioreactor) was performed to quantify the improvement in nitrogen removal terms when pure oxygen and air were used to supply the aerobic conditions at different HRT (hydraulic retention time) and mixed liquid suspended solids concentrations. The improvement in the efficiency was 8.0% and 13.5% when pure oxygen was used with 12h and 18 h of HRT respectively. The ammonium utilization rates with HRT of 18 h with pure oxygen was 1.23 mg N(t)/(L h) and with air 0.66 mg N(t)/(L h) and with HRT of 12h was 1.14 mg N(t)/(L h) and 1.18 mg N(t)/(L h) respectively. Model simulation (DESSAS software) confirmed the validity for nitrogen removal, hydrolysis constant was increased (106% and 184%), decay constant was decreased and Monod's constant was increased (190.4% to 324.1%), and a multivariate analysis with CANOCO v4.5 demonstrated that temperature and HRT have the higher influence in kinetics.

Kinetic study and oxygen transfer efficiency evaluation using respirometric methods in a submerged membrane bioreactor using pure oxygen to supply the aerobic conditions.

The performance of a wastewater bench-scale ultrafiltration membrane bioreactor (MBR) treatment plant using pure oxygen to supply the aerobic conditions for 95 days was studied. The results showed the capacity of the MBR systems to remove organic material under a hydraulic retention time of 12h and a sludge retention time of 39.91 days. Aeration represents its major power input; this is why the alpha-factor of the aeration and kinetic parameters (design parameters) were determined when the mixed liquid suspended solids (MLSS) was increased from 3420 to 12,600 mg/l in order to understand the system. An alpha-factor in the range 0.462-0.022 and the kinetic parameters measured with the respirometric method (K(M) of 73.954-3.647 mg/l, k(d) of 0.0142-0.104 day(-1), k(H) of 0.1266-0.655 day(-1), and the yield mean coefficient of 0.941) were obtained. Our study suggested significant changes in the behaviour of the biological system when the concentration of MLSS was increased.

Water quality characterization in real biofilm wastewater treatment systems by particle size distribution.

This article analyses the relation between wastewater quality parameters and particle size distribution (PSD) in three real wastewater treatment plants with different biofilm technologies: submerged biofilter system, trickling filter system, and rotating biological contactor system. The main quality parameters, (suspended solids, turbidity and COD), and PSD in the influent and effluent water of each different biofilm treatment were analyzed during 1year. The PSD was fitted using the power law (n(d(p))= partial differentialN(d(p))/ partial differentiald(p)=A x d(p)(-)(b)(Log(d)(p)())) obtaining the coefficients A and b to define the particle distribution. Mathematical correlations between this coefficients and the rest of parameters studied were found (SS=0.0713 x A(0.585), turbidity=4.549 x 10(-4) x A(1.096), COD=0.0201 x A(0.774)). The relation with the average particle size by mass was also found, (d(pma)=60.3137 x b(-2.242)). Moreover a relation between PSD and the particle elimination efficiency of the secondary treatment was study, (eta=2.844-2.498 x b(relative)+0.0863 x A(relative)). These expressions are very useful to understand the behavior of the biofilm treatment system using PSD analyses.

Flux influence on membrane fouling in a membrane bioreactor system under real conditions with urban wastewater.

In order to evaluate the effect of flux on membrane fouling, the performance of a bench-scale submerged membrane bioreactor (MBR) equipped with ultrafiltration membranes (ZENON) was investigated under real conditions at different flux rates. The pilot plant was located at the wastewater treatment plant of the city of Granada (Spain). Influent used in the experiments came from the primary settling tank. Assays carried out under different operating conditions indicated that dTMP/dt increased in accordance with the increase in flux. The results showed a significant impact on the rate of transmembrane pressure, while the behavior of membrane fouling was logarithmic with respect to the flux. These findings could be of some importance for understanding the behavior of the membrane, since over 20.57 L m(-2) h(-1) the flux rate produced a significant increase in transmembrane pressure. The data therefore suggest that an increase in the net flux significantly affects membrane fouling.

Effect of the mixed liquor suspended solid on permeate in a membrane bioreactor system applied for the treatment of sewage mixed with wastewater of the milk from the dairy industry.

The performance of a bench-scale submerged membrane bioreactor (MBR) equipped with ultrafiltration membranes (ZENON) was investigated at different mixed liquor suspended solid (MLSS) concentrations (3069, 4314 and 6204 mg/L). The pilot plant was located in the wastewater treatment plant of the city of Granada (Puente de los Vados, Granada, Spain), which receives the wastewater of the milk from the dairy industry of Granada. The results showed the capacity of the MBR systems to remove organic material (COD and BOD5), suspended solids, turbidity, color and microbial indicators such as E. coli and coliphages. Therefore, the results suggest that the transmembrane pressure (TMP) was influence by the MLSS concentration assayed. However, an increase in the MLSS concentration increases the nitrification processes and consequently the amount of NO3- in permeate.

Study of biological aerated filters for the treatment of effluents from the citrus industry.

The primary objective of this research study was to test the applicability and optimize the design parameters of a system of biological aerated filters in order to obtain an optimal effluent from the citrus industry, which would allow its drainage into the municipal sewer system. Expanded clay was used as a support material. After experimenting with both countercurrent and cocurrent flows as well different aeration levels, it was found that cocurrent flow was more efficient. Backwashing was carried out on a daily basis. The results of our study showed that for an aeration of 10.47 Nm3/h/m2, the volumetric load should be less than 20 Kg. COD/m3/d in order to obtain an effluent with a maximum concentration of 600 mgCOD/L, and the hydraulic load should be less than 0.36 m/h.

Denitrifying activity of Xanthobacter autotrophicus strains isolated from a submerged fixed-film reactor.

Xanthobacter autotrophicus strains with the ability to reduce nitrate and nitrite to either nitrous oxide or molecular nitrogen were isolated from submerged fixed-film reactors. Isolated strains were Gram-negative rods able to grow on methanol, ethanol and sucrose. The yellow cellular pigmentation, pleomorphic appearance, and the presence of poly-beta-hydroxybutyrate granules suggest that the organisms might belong to the genus Xanthobacter. Comparison of 16S rDNA gene sequences demonstrated the affiliation of the strains to X. autotrophicus species. The results show that X. autotrophicus may play a role in inorganic nitrogen removal from a denitrifying submerged filter used for the treatment of contaminated groundwater. To our knowledge, no data on denitrifying activity in X. autotrophicus strains have been reported previously.

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 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.

Wastewater treatment with a double-layer submerged biological aerated filter, using waste materials as biofilm support.

The aim of this research was to determine the performance of a submerged biological aerated filter, composed of a double-layer bed. This bed is made up of a top layer of ceramic material and a bottom layer of plastic material (both from previously used waste material). Effluent concentrations are presented related to the volumetric and hydraulic loads applied. The results were very satisfactory. If effluent concentrations of under 20 mg TBOD5/L and 25 mg SS/L are to be achieved, 4.87 kg TBOD5/m3/d and 3.0 kg SS/m3/d could be applied, respectively. For that maximum TBOD5 volumetric load that can be applied, a very reasonable consumption value of 1.0 kg O2/kg TBOD5, eliminated was obtained. The counter-current flow system outperformed the co-current flow system with respect to TBOD5 and SS removal. The tests were performed at a pilot plant with full scale height. The influent used was primary effluent of a conventional treatment plant. A multivariant analysis (ANOVA) was applied to the results.