Removal of tetrachloroethene from polluted air by activated sludge

Mobilization pilot test of PCE sources in the transition zone to aquitards by combining mZVI and biostimulation with lactic acid

The potential toxic and carcinogenic effects of chlorinated solvents in groundwater on human health and aquatic ecosystems require very effective remediation strategies of contaminated groundwater to achieve the low legal cleanup targets required. The transition zones between aquifers and bottom aquitards occur mainly in prograding alluvial fan geological contexts. Hence, they are very frequent from a hydrogeological point of view. The transition zone consists of numerous thin layers of fine to coarse-grained clastic fragments (e.g., medium sands and gravels), which alternate with fine-grained materials (clays and silts). When the transition zones are affected by DNAPL spills, free-phase pools accumulate on the less conductive layers. Owing to the low overall conductivity of this zone, the pools are very recalcitrant. Little field research has been done on transition zone remediation techniques. Injection of iron microparticles has the disadvantage of the limited accessibility of this reagent to reach the entire source of contamination. Biostimulation of indigenous microorganisms in the medium has the disadvantage that few of the microorganisms are capable of complete biodegradation to total mineralization of the parent contaminant and metabolites. A field pilot test was conducted at a site where a transition zone existed in which DNAPL pools of PCE had accumulated. In particular, the interface with the bottom aquitard was where PCE concentrations were the highest. In this pilot test, a combined strategy using ZVI in microparticles and biostimulation with lactate in the form of lactic acid was conducted. Throughout the test it was found that the interdependence of the coupled biotic and abiotic processes generated synergies between these processes. This resulted in a greater degradation of the PCE and its transformation products. With the combination of the two techniques, the mobilization of the contaminant source of PCE was extremely effective.

Revealing the role of microalgae-bacteria niche for boosting wastewater treatment and energy reclamation in response to temperature

Conventional biological treatment usually cannot achieve the same high water quality as advanced treatment when conducted under varied temperatures. Here, satisfactory wastewater treatment efficiency was observed in a microalgae-bacteria consortia (MBC) over a wide temperature range because of the predominance of microalgae. Microalgae contributed more toward wastewater treatment at low temperature because of the unsatisfactory performance of the accompanying bacteria, which experienced cold stress (e.g., bacterial abundance below 3000 sequences) and executed defensive strategies (e.g., enrichment of cold-shock proteins). A low abundance of amoA-C and hao indicated that conventional nitrogen removal was replaced through the involvement of microalgae. Diverse heterotrophic bacteria for nitrogen removal were identified at medium and high temperatures, implying this microbial niche treatment contained diverse flexible consortia with temperature variation. Additionally, pathogenic bacteria were eliminated through microalgal photosynthesis. After fitting the neutral community model and calculating the ecological niche, microalgae achieved a maximum niche breadth of 5.21 and the lowest niche overlap of 0.38, while the accompanying bacterial community in the consortia were shaped through deterministic processes. Finally, the maximum energy yield of 87.4 kJ L^-1 and lipid production of 1.9 g L^-1 were achieved at medium temperature. Altogether, this study demonstrates that advanced treatment and energy reclamation can be achieved through microalgae-bacteria niche strategies.

Modified coir pith with glucose syrup as a supporter in non-external nutrient supplied biofilter for benzene removal by Bacillus megaterium

Coir pith glucose syrup beads were used as a supporter in a biofilter system. The modified coir pith beads provided a carbon source and controlled humidity for microorganism growth for long-term operation without external nutrient supplementation. For the screening, Bacillus spp. were immobilised on coir pith beads and used for benzene bioremediation. The result showed that coir pith beads immobilised with Bacillus megaterium can remove on average 85-100% of the benzene (215-day operation). In addition, B. megaterium presented the ability to transform benzene to catechol. For an up-scaled application, a 25-L biofilter system was developed and tested in a closed 24-m³ container re-injected with 0.6 ppm benzene for 8 cycles. The system presented the ability to remove 100% of the benzene. This biofilter has the potential to be applied in a real benzene-contaminated site.

A review and perspective of recent research in biological treatment applied in removal of chlorinated volatile organic compounds from waste air

Chlorinated volatile organic compounds (Cl-VOCs) waste air is a kind of typical recalcitrant organic compounds, which poses a great threat to the ecological environment and human health. At present, the biotechnology is considered as a potential strategy for the Cl-VOCs removal due to the advantages of low energy consumption and less possibility of secondary pollution. This work summarizes the recent researches on strains, bioreactors and technology integration. The dominant pure strains for biodegradation of Cl-VOCs are first outlined with a special focus on the co-metabolism of multi-components. It then summarizes two bioreactors (optimized airlift reactor (ALR) and two-phase partitioning bioreactor (TPPB)) and strategy (addition of surfactant) for improvement of biotrickling filter (BTF), which are benefit to achieve the mass transfer enhancement in the removal of hydrophobic Cl-VOCs from waste air. After that, the integration technologies, such as magnetic field (MF)-BTF, non-thermal plasma (NTP)/ultraviolet light (UV)-BTF, and microbial electrolytic cells (MEC), are elucidated, which provide opportunities for complete mineralization of Cl-VOCs in a more efficient, energy-saving and economical way. Finally, current challenges and a perspective of future research on biotechnology for Cl-VOCs removal are thoroughly discussed.

Enhancement of COD removal in constructed wetlands treating saline wastewater: Intertidal wetland sediment as a novel inoculation

This study investigated intertidal wetland sediment (IWS) as a novel inoculation source for saline wastewater treatment in constructed wetlands (CWs). Samples of IWS (5-20 cm subsurface sediment), which are highly productive and rich in halophilic and anaerobic bacteria, were collected from a high-salinity natural wetland and added to CW matrix. IWS-supplemented CW microcosms that are planted and unplanted Phragmites australis were investigated under salty (150 mM NaCl: PA+(S) and CT+(S)) and non-salty (0 mM NaCl: PA+ and CT+) conditions. The chemical oxygen demand (COD) removal potential of IWS-supplemented CWs was compared with that of conventional CWs without IWS (PA(S) and CT(S), PA, and CT). Results showed that the COD removal rate was higher in PA+(S) (51.80% ± 3.03%) and CT+(S) (29.20% ± 1.26%) than in PA(S) (27.40% ± 3.09%) and CT(S) (27.20% ± 3.06%) at 150 mM NaCl. The plants' chlorophyll content and antioxidant enzyme activity indicated that the addition of IWS enhanced the resistance of plants to salt. Microbial community analysis showed that the dominant microorganisms in PA+(S) and CT+(S), namely, Anaerolineae, Desulfobacterales, and Desulfuromonadales, enhanced the organic removal rates via anaerobic degradation. IWS-induced Dehalococcoides, which is a key participant in ethylene formation, improved the plants' stress tolerance. Several halophilic/tolerant microorganisms were also detected in the CW system with IWS. Thus, IWS is a promising inoculation source for CWs that treat saline wastewater.