Methanogenic community development in anaerobic granular bioreactors treating trichloroethylene (TCE)-contaminated wastewater at 37 °C and 15 °C

Four expanded granular sludge bed (EGSB) bioreactors were seeded with a mesophilically-grown granular sludge and operated in duplicate for mesophilic (37 °C; R1 & R2) and low- (15°; R3 & R4) temperature treatment of a synthetic volatile fatty acid (VFA) based wastewater (3 kg COD m⁻³ d⁻¹) with one of each pair (R1 & R3) supplemented with increasing concentrations of trichloroethylene (TCE; 10, 20, 40, 60 mg l⁻¹) and one acting as a control. Bioreactor performance was evaluated by % COD removal efficiency and % biogas methane (CH₄) content. Quantitative Polymerase Chain Reaction (qPCR) was used to investigate the methanogenic community composition and dynamics in the bioreactors during the trial, while specific methanogenic activity (SMA) and toxicity assays were utilized to investigate the activity and TCE/dichloroethylene (DCE) toxicity thresholds of key trophic groups, respectively. At both 37 °C and 15 °C, TCE levels of 60 mg l⁻¹ resulted in the decline of % COD removal efficiencies to 29% (Day 235) and 37% (Day 238), respectively, and in % biogas CH₄ to 54% (Day 235) and 5% (Day 238), respectively. Despite the inhibitory effect of TCE on the anaerobic digestion process, the main drivers influencing methanogenic community development, as determined by qPCR and Non-metric multidimensional scaling analysis, were (i) wastewater composition and (ii) operating temperature. At the apical TCE concentration both SMA and qPCR of methanogenic archaea suggested that acetoclastic methanogens were somewhat inhibited by the presence of TCE and/or its degradation derivatives, while competition by dechlorinating organisms may have limited the availability of H₂ for hydrogenotrophic methanogenesis. In addition, there appeared to be an inverse correlation between SMA levels and TCE tolerance, a finding that was supported by the analysis of the inhibitory effect of TCE on two additional biomass sources. The results indicate that low-temperature anaerobic digestion is a feasible approach for the treatment of TCE-containing wastewater.     

Outlier detection in UV/Vis spectrophotometric data

UV/Vis spectrophotometers have been used to monitor water quality since the early 2000s. Calibration of these devices requires sampling campaigns to elaborate relations between recorded spectra and measured concentrations. In order to build robust calibration data sets, several spectra must be recorded per sample. This study compares two approaches – principal component analysis and data depth theory – to identify outliers and select the most representative spectrum (MRS) among the repetitively recorded spectra. Detection of samples that contain outliers is consistent between the methods in more than 70% of the samples. Identification of spectra as outliers is consistent in more than 95% of the cases. The identification of MRS differs depending on the approach used. In their current form, both of the proposed approaches can be used for outlier detection and identification. Further studies are suggested to combine the methods and develop an automated ranking and sorting system.     

Influence of Guiding Curves in the Optimal Management of a Hydropower System

Optimal operating policies for hydropower generation in a system of dams were obtained by means of a modified algorithm of stochastic dynamic programming that incorporates the guiding curve concept and other operating requirements defined by the Mexican agency in charge of electricity generation. These operating policies were used to simulate the long term system behavior and to analyze the influence of the guiding curves in the energy generation, the volume spilled and the possible deficit. The results show that by trying different curves it is possible to obtain a range of results that will enable decision makers to choose those that best fit their needs.     

Factors influencing the choice of nonrequired mathematics courses.

1,418 high school students comprised 3 samples of Ss currently enrolled in their last semester of required mathematics or already enrolled in nonrequired mathematics courses. Results show that a factor involving encouragement from significant others and subjective value placed on mathematics was the best predictor of taking nonrequired mathematics courses across samples and for both sexes. Ss who intended to enroll in optional mathematics and later did so were compared with Ss who intended to enroll but did not. Results show that Ss who acted inconsistently with their intentions attributed the same subjective value to mathematics but had less confidence in their mathematical ability. Factors that influence the initial decision to participate in optional mathematics were found to be similar to factors influencing later decisions to continue participation. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Engine Performance and Exhaust Emission Tests of Sulfate Turpentine and No:2 Diesel Fuel Blend

Environmentally friendly, biobased fuel additives become more important when environmental concerns all around the world are considered. In this study, sulfate turpentine is investigated as a candidate diesel fuel additive. Engine performance tests were conducted on a 53 kW, 4000 rpm Peugeot XD 3P 157 type diesel engine for 3:97 turpentine and No:2 diesel fuel blend and similar results to No:2 diesel fuel were obtained. Significant reduction in exhaust emissions were observed as a result of using turpentine and No:2 diesel fuel blend.