Trimethylamine abatement in algal-bacterial photobioreactors.

Trimethylamine (TMA) is an odorous volatile organic compound emitted by industries. Algal-based biotechnologies have been proven as a feasible alternative for wastewater treatment, although their application to abate polluted air emissions is still scarce. This work comparatively assessed the removal of TMA in a conventional bacterial bubble column bioreactor (BC) and a novel algal-bacterial bubble column photobioreactor (PBC). The PBC exhibited a superior TMA abatement performance compared to the conventional BC. In this sense, the BC reached a removal efficiency (RE) and an elimination capacity (EC) of 78% and 12.1 g TMA m-3 h-1, respectively, while the PBC achieved a RE of 97% and a EC of 16.0 g TMA m-3·h-1 at an empty bed residence time (EBRT) of 2 min and a TMA concentration ~500 mg m-3. The outstanding performance of the PBC allowed to reduce the operating EBRT to 1.5 and 1 min while maintaining high REs of 98 and 94% and ECs of 21.2 and 28.1 g m-3·h-1, respectively. Moreover, the PBC improved the quality of the gas and liquid effluents discharged, showing a net CO2 consumption and decreasing by ~ 30% the total nitrogen concentration in the liquid effluent via biomass assimilation. A high specialization of the bacterial community was observed in the PBC, Mumia and Aquamicrobium sp. being the most abundant genus within the main phyla identified. GraphicalAbstract.

Removal of dimethyl sulphide via a bio-scrubber under anoxic conditions.

The removal performance of dimethyl sulphide (DMS) by anoxic laboratory-scale bio-scrubber was studied under different operation conditions for 315 days. DMS removal in bio-scrubber system was performed by controlling and changing the operation parameters, including inlet concentration, empty bed residence time (EBRT) and spraying density (SD) of irrigation. Best conditions in the system were achieved for SD of 0.18 m3/m2 h within EBRT of 40 s at an inlet gas concentration of 150 mg/m3 in which 93% of waste gas stream was removed in the bio-scrubber column and bio-degradation in the bio-reactor tank led to 89% of DMS removal from the transferred bio-reactor, while 91.5% of input chemical oxygen demand (COD) was successfully removed. The use of closer values of the average experimental yield to the theoretical value (YNO3/NO3 -) of 0.74 led to the production of elemental sulphur (S°) and other sulphur forms rather than sulphate (SO42-) , which was also was recognized as a pale-yellow coloured substance of S° that appeared within the biomass.

Removal of ethanethiol using a biotrickling filter with nitrate as an electron acceptor.

Many studies have discussed the biotreatment of ethanethiol (ET) under aerobic conditions. However, O2 free conditions offer bio-conversion of ET gas into elemental sulphur and/or sulphate using [Formula: see text] as electron acceptor, and this has been not studied. In this study, an anoxic biotrickling filter was tested in lab-scale conditions with ET/[Formula: see text] ratio 0.74 and 0.34 mole/mole to remove malodorous ET waste gas. The study examined the effect of three operational parameters: ET inlet concentrations (150, 300, 800, and 1500 mg/m3), trickling velocities (0.12, 0.18, 0.24, 0.3, and 0.45 m/h), and empty bed residence times (30, 60, 90, and 120 s). It found that the effect of trickling velocity on removal efficiency depended on inlet concentrations; 0.24 m/h trickling velocity resulted in efficient ET removal (higher than 90.8% for 150 mg/m3 of inlet concentration) while 0.45 m/h trickling velocity could only achieve a removal of 80.6% for 1500 mg/m3 of inlet concentration at fixed EBRT 60 s. Increasing the EBRT up to 60 s was adequate to achieve removal efficiency, i.e. 92 and 80% for ET inlet concentrations 150 and 1500 mg/m3 respectively, and the maximum elimination capacity was 75.18 g/m3/h at 0.45 m/h. Overall, the anoxic conditions enhanced the low oxidation rates of ET in an anoxic biotrickling filter despite mass transfer limitations and poor solubility of ET.

Ethanethiol gas removal in an anoxic bio-scrubber.

The performance of ethanethiol removal in an anoxic lab-scale bio-scrubber was investigated under different operating parameters and conditions for 300 days. The removal efficiency (RE) of ethanethiol was examined as a function of inlet concentration, empty bed residence time (EBRT) and spray density of irrigation. The results showed the best operation conditions and operation characteristics of the bio-scrubber for this study were at an inlet concentration of 150 mg/m3, a spray density of 0.23 m3/m2 h and an EBRT of 90 s. An average RE of 91% and elimination capacity (EC) of 24.74 g/m3 h was found for all inlet ethanethiol concentrations. Variations in spray density higher than 0.23 m3/m2 h had no effect on ethanethiol RE at different ethanethiol concentrations. The average experimental yield values were closer to the YET/NO3- theoretical value of 0.74 when the main product was elemental sulphur (So). This indicates that So and other forms of sulphur were formed rather than sulphate (SO42-) as the end product. Furthermore, growth kinetics for bio-degradation were evaluated in batch culture experiments using the Monod model, and bio-kinetic parameters of µmax, Ks, Yxs and qmax were obtained as 0.14 1/h, 1.17 mg/L, 0.52 gx/gs and 0.26 gs/gx h, respectively.

Anoxic denitrification of BTEX: Biodegradation kinetics and pollutant interactions.

Anoxic mineralization of BTEX represents a promising alternative for their abatement from O2-deprived emissions. However, the kinetics of anoxic BTEX biodegradation and the interactions underlying the treatment of BTEX mixtures are still unknown. An activated sludge inoculum was used for the anoxic abatement of single, dual and quaternary BTEX mixtures, being acclimated prior performing the biodegradation kinetic tests. The Monod model and a Modified Gompertz model were then used for the estimation of the biodegradation kinetic parameters. Results showed that both toluene and ethylbenzene are readily biodegradable under anoxic conditions, whereas the accumulation of toxic metabolites resulted in partial xylene and benzene degradation when present both as single components or in mixtures. Moreover, the supplementation of an additional pollutant always resulted in an inhibitory competition, with xylene inducing the highest degree of inhibition. The Modified Gompertz model provided an accurate fitting for the experimental data for single and dual substrate experiments, satisfactorily representing the antagonistic pollutant interactions. Finally, microbial analysis suggested that the degradation of the most biodegradable compounds required a lower microbial specialization and diversity, while the presence of the recalcitrant compounds resulted in the selection of a specific group of microorganisms.

Anoxic biodegradation of BTEX in a biotrickling filter.

Emissions of BTEX (benzene, toluene, ethylbenzene and xylene) from the petrochemical industry are characterized by a low pollutants concentration and the absence of oxygen. Biodegradation of these pollutants using nitrate as the electron acceptor is of key interest to reuse the residual gas for inertization purposes. However, the biological mineralization of BTEX is often limited by their recalcitrant nature and the toxicity of the secondary metabolites produced. The potential of an anoxic biotrickling filter for the treatment of a model O2-free BTEX-laden emission at inlet individual concentrations of ~700mgm-3 was here evaluated. A UV oxidation step was also tested both in the recycling liquid and in the inlet gas emission prior to biofiltration. Removal efficiencies >90% were achieved for both toluene and ethylbenzene, corresponding to elimination capacities (ECs) of 1.4±0.2gm-3h-1 and 1.5±0.3gm-3h-1, respectively, while ~45% of xylene (EC=0.6±0.1g m-3h-1) was removed at a liquid recycling rate of 2mh-1. Benzene biodegradation was however limited by the accumulation of toxic metabolites in the liquid phase. The oxidation of these intermediates in the recycling liquid by UV photolysis boosted benzene abatement, achieving an average EC of 0.5±0.2gm-3h-1 and removals of ~40%. However, the implementation of UV oxidation as a pretreatment step in the inlet gas emission resulted in the deterioration of the BTEX biodegradation capacity of the biotrickling filter. Finally, a high bacterial diversity was observed throughout the entire experiment, the predominant phyla being Proteobacteria and Deinococcus-thermus.