Biodegradation of gaseous toluene with mixed microbial consortium in a biofilter: steady state and transient operation

Identification of volatile biomarkers of Trichomonas vaginalis infection in vaginal discharge and urine

Trichomoniasis, a disease caused by Trichomonas vaginalis, is the most common non-viral sexually transmitted infection worldwide. The importance of its diagnosis lies in its ease of transmission and the absence of symptoms in most cases, as occurs in men, which have a significant role as asymptomatic carriers. The most widely used diagnostic methods are the fresh examination of vaginal or urethral secretions and molecular techniques. However, as they have some disadvantages and, sometimes, low sensitivity, new trichomoniasis diagnostic methods are necessary. Volatile organic compounds in clinical samples are effective in the diagnosis of different diseases. This work aimed to study, for the first time, those present in vaginal discharge and urine of patients with Trichomonas vaginalis infection to look for volatile biomarkers. The results showed that volatile compounds such as 2-methyl-1-propanol and cyclohexanone could serve as biomarkers in vaginal discharge samples, as well as 2-octen-1-ol and 3-nonanone in urine. Moreover, 3-hydroxy-2,4,4-trimethylpentyl 2-methylpropanoate found in vaginal discharge, highly correlated to positive patients, is also highly related to urines of patients with trichomoniasis. The biomarkers described in this study might be a promising diagnostic tool. KEY POINTS: • The incidence of Trichomonas vaginalis infection is increasing • Trichomonas vaginalis VOC study in vaginal discharge and urine was performed • The identification of volatile biomarkers could allow a new diagnostic method.

Effects of Water Content and Irrigation of Packing Materials on the Performance of Biofilters and Biotrickling Filters: A Review

Biofilters (BFs) and biotrickling filters (BTFs) are two types of bioreactors used for treatment of volatile organic compounds (VOCs). Both BFs and BTFs use packing materials in which various microorganisms are immobilised. The water phase in BFs is stationary and used to maintain the humidity of packing materials, while BTFs have a mobile liquid phase. Optimisation of irrigation of packing materials is crucial for effective performance of BFs and BTFs. A literature review is presented on the influence of water content of packing materials on the biofiltration efficiency of various pollutants. Different configurations of BFs and BTFs and their influence on moisture distribution in packing materials were discussed. The review also presents various packing materials and their irrigation control strategies applied in recent biofiltration studies. The sources of this review included recent research articles from scientific journals and several review articles discussing BFs and BTFs.

Effect of rhamnolipids on the fungal elimination of toluene vapor in a biotrickling filter under stressed operational conditions

The application of rhamnolipids in a fungal-cultured biotrickling filter (BTF) has a significant impact on toluene removal. Two BTFs were used; BTF-A, a control bed, and BTF-B fed with rhamnolipids. The effect of empty bed residence times (EBRTs) on toluene bioavailability was investigated. Removal of toluene was carried out at EBRTs of 30 and 60 s and inlet loading rates (LRs) of 23-184 g m^-3 h^-1. At 30 s EBRT, when inlet LR was increased from 23 to 184 g m^-3 h^-1, the removal efficiency (RE) decreased from 93% to 50% for the control bed, and from 94% to 87% for BTF-B. Increasing the EBRT simultaneously with inlet LRs, confirms that BTF-A was diffusion-limited by registering a RE of 62% for toluene inlet LR of 184 g m^-3 h^-1, whereas BTF-B, achieved RE > 96%, confirming a significant improvement in toluene biodegradability. Overall, the best performance was observed at 60 s EBRT and inlet LR of 184 g m^-3 h^-1, providing a maximum elimination capacity (EC) of 176.8 g m^-3 h^-1 under steady-state conditions. While a maximum EC of 114 g m^-3 h^-1 was observed under the same conditions in the absence of rhamnolipids (BTF-A). Measurements of critical micelle concentration showed that 150 mg L^-1 of rhamnolipids demonstrated the lowest aqueous surface tension and maximum formation of micelles, while 175 mg L^-1 was the optimum dose for fungal growth. Production rate of carbon dioxide, and dissolved oxygen contents highlighted the positive influence of rhamnolipids on adhesive forces, improved toluene mineralization, and promotion of microbial motility over mobility.

Simultaneous removal of ammonia and volatile organic compounds from composting of dead pigs and manure using pilot-scale biofilter

Odor emission is one of the most common problems associated with dead animals composting. Biofiltration treatment for eliminating exhaust odors formed during dead pigs and manure composting has been studied. The composting and biofiltration process consisted of two series of tests. Composting experimental trials lasted 6 weeks, and composting was performed using six pilot-scale reactor vessels. A total of 37 kinds of volatile organic compounds (VOCs) present in the air were identified, and temporal variations were determined during the 42 days of composting. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), and trimethylamine (TMA) were identified as the main odors VOCs component according to odor active values (OAVs). Nine biofilter vessels containing mature compost were used in studying the effect of different (30, 60, and 100 s) empty bed retention times (EBRT) on the simultaneous removal efficiencies (REs) of NH₃, DMS, DMDS, DMTS, and TMA. Results indicated that the inlet concentration of NH₃ applied was 12-447 mg m^-3, and the average removal efficiencies were 85.4%, 88.7%, and 89.0% for EBRTs of 30, 60, and 100 s, respectively. The average REs of DMS, DMDS, DMTS, and TMA were 79.2%-95.4%, 81.9%-94.0%, 76.7%-99.1%, and 92.9%-100%, respectively, and their maximum elimination capacity (ECs) were 220, 1301, 296, and 603 mg m^-3 h^-1, respectively. The optimal EBRT for the stimulation removal of NH₃, DMS, DMDS, DMTS, and TMA was 60 s.Implications: Dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), and trimethylamine (TMA) were identified as the main odors VOCs component during dead pigs and manure composting. Biofilter with mature as media can be used to stimulation remove NH₃, DMS, DMDS, DMTS, and TMA, the optimal empty bed retention times EBRT was 60 s.

Removal of H2S by vermicompost biofilter and analysis on bacterial community

The vermicompost collected from dewatered domestic sludge as packing material in biofilter was investigated for hydrogen sulfide (H2S) removal. No nutrients or microbial inoculation was added throughout the experiment. The corresponding bacterial community characteristics in the vermicompost biofilter of different spatial levels were evaluated by Miseq high-throughput sequencing technique. The results showed that the vermicompost biofilter performed well during operation. The H2S removal efficiency reached nearly 100% under condition of the inlet concentration <350 mg m−3 and 0.25−0.35 m3 h−1 gas flow rate. The maximum elimination capacity of 20.2 g m−3 h−1 was observed at a flow rate of 0.35 m3 h−1. Furthermore, the amounts of biodegraded products and pH varied accordingly. In addition, the results from high-throughput sequencing revealed pronouncedly spatial variation of the vermicompost, and the Rhodanobacter, Halothiobacillus, Mizugakiibacter as well as Thiobacillus, which can play an important role in removing H2S, were predominant in the final vermicompost. These results imply that the vermicompost with diverse microbial communities has a good potential for eliminating H2S.

Experimental studies and neural network modeling of the removal of trichloroethylene vapor in a biofilter

In this study, bamboo carrier based lab scale compost biofilter was evaluated to treat synthetic waste air containing trichloroethylene (TCE) under continuous operation mode. The effect of inlet TCE concentration and gas flow rate and its removal was investigated. Maximum TCE removal efficiency was found to be 89% under optimum conditions of inlet 0.986 g/m³ TCE concentration corresponding to a loading rate of 43 g/m³ h and 0.042 m³/h gas flow rate at empty bed residence time (EBRT) of 2 min. For the first time, Artificial Neural Network (ANN) was applied to predict the performance of the compost biofilter in terms of TCE removal. The ANN model used a three layer feed forward based Levenberg-Marquardt algorithm, and its topology consisted of 3-25-1 as the optimum number for the three layers (input, hidden and output). An excellent match between the experimental and ANN predicted the value of TCE removal was obtained with a coefficient of determination (R²) value greater than 0.99 during the model training, validation, testing and overall. Furthermore, statistical analysis of the ANN model performance mediated its prediction accuracy of the bioreactor to treat TCE contaminated systems.