Investigation into the kinetics of constructed wetland degradation processes as a precursor to biomimetic design

In this study, biomimetic principles were incorporated into a kinetic study of a pilot-scale, horizontal subsurface-flow constructed wetland (6.0 m × 1.0 m × 0.5 m) in Leipzig, Germany. The bed contained glacial gravel (4–8 mm) planted with Phragmites australis. Construction was completed in October 2013 and  experiments commenced in August 2015. During establishment, the system was fed with only municipal tap water (165 L·d−1). The Phragmites root system had penetrated to the bottom of the wetland within 18 months. To break into the constructed wetland ‘black box’, the system was divided into a three-dimensional grid of sample ports. Initially, the wetland was physicochemically characterized (prior to addition of nutrients from an external source) in order to quantify the natural, baseline state. Thereafter, an impulse-response tracer test was conducted, using a fluorometer, for continual measurement of uranine concentration. 100% tracer recovery was achieved. The RTD was multi-modal – indicating by-pass flow – and showed long tailing due to mixing, diffusive effects and dead zones. Kinetic performance was investigated via monitoring total organic carbon and total nitrogen degradation, with a continual feed of artificial domestic wastewater (110 mg·L−1 COD). 93% reduction in TOC and TN was achieved for 5 weeks (11 November – 08 December 2015), despite high inflow loading (69.9 g·m−3·d−1 TOC; 28.1  g·m−3·d−1 TN) and colder temperatures. There was a general decline in reaction rate and rate constant from late October to early December. The average rates of TOC and TN removal were 65.08 ± 2.16 g·m−3·d−1 and 26.22 ± 0.68 g·m−3·d−1, respectively (Tanks-In-Series model). These results are the first set in a series. Continual observation and repetition of these experiments into long-term operation will deepen understanding of the internal development and  performance of  constructed wetlands, as is in line with the biomimetic approach, and provide the basis of a framework for  improved wetland design.Keywords: constructed wetlands, baseline analysis, hydraulics, kinetics, biomimicr

Environmental pollution by wastewater from brown coal processing ¬ a remediation case study in Germany

The large scale of the contamination by the former carbo-chemical industry in Germany requires new and often interdisciplinary approaches for performing an economically sustainable remediation. For example, a highly toxic and dark-colored phenolic wastewater from a lignite pyrolysis factory was filled into a former open-cast pit, forming a large wastewater disposal pond. This caused an extensive environmental pollution, calling for an ecologically and economically acceptable strategy for remediation. Laboratory-scale investigations and pilot-scale tests were carried out. The result was the development of a strategy for an implementation of full-scale enhanced in situ natural attenuation on the basis of separate habitats in a meromictic pond. Long-term monitoring of the chemical and biological dynamics of the pond demonstrates the metamorphosis of a former highly polluted industrial waste deposition into a nature-integrated ecosystem with reduced danger for the environment, and confirmed the strategy for the chosen remediation management

Anoxic nitrogen cycling in a hydrocarbon and ammonium contaminated aquifer

Nitrogen fate and transport through contaminated groundwater systems, where N is both ubiquitous and commonly limits pollutant attenuation, must be re-evaluated given evidence for new potential microbial N pathways. We addressed this by measuring the isotopic composition of dissolved inorganic N (DIN = NH4+, NO2−, and NO3−) and N functional gene abundances (amoA, nirK, nirS, hszA) from 20 to 38 wells across an NH4+, hydrocarbon, and SO42− contaminated aquifer. In-situ N attenuation was confirmed on three sampling dates (0, +6, +12 months) by the decreased [DIN] (4300 - 40 μM) and increased δ15N-DIN (5‰–33‰) over the flow path. However, the assumption of negligible N attenuation within the plume was complicated by the presence of alternative electron acceptors (SO42−, Fe3+), both oxidizing and reducing functional genes, and N oxides within this anoxic zone. Active plume N cycling was corroborated using an NO2− dual isotope based model, which found the fastest (∼10 day) NO2− turnover within the N and electron donor rich central plume. Findings suggest that N cycling is not always O2 limited within chemically complex contaminated aquifers, though this cycling may recycle the N species rather than attenuate N

Combining tracer studies and biomimetic design principles to investigate clogging in constructed wetlands

In this study, we suggest a clogging maintenance strategy and design alteration for constructed wetlands. Such a system could benefit rural communities who rely solely on constructed wetland systems for provision of household and agricultural water and for whom regular system shut-down for maintenance is essentially not viable. A newly established, pilot-scale horizontal subsurface flow constructed wetland was investigated by means of step-change tracer experiments. Sampling was carried out at multiple points down the length of the wetland and at three depths for each location. The mean residence time datawere used to generate velocity profiles. This methodology enabled the development of a three-dimensional hydraulic model to identify dead zones and regions of short-circuiting within the system. Biomimetic principles were then incorporated to propose improvements to conventional constructed wetland design, which would potentially allow for better clogging management and continuous operation. In particular, modularizing the regions of the wetland most prone to clogging (those containing dead space) would accommodate isolation, removal and replacement of such sections, while still allowing treatment of wastewater in adjacent sections

Draft Genome Sequence of Magnetospirillum sp. Strain 15-1, a Denitrifying Toluene Degrader Isolated from a Planted Fixed-Bed Reactor

Here, we report the draft genome sequence of Magnetospirillum sp. 15-1. This strain was isolated from a planted fixed-bed reactor based on its ability to degrade toluene under anaerobic conditions. The genome assembly consists of 5.4 Mb in 28 contigs and 5,095 coding sequences containing the genes involved in anaerobic toluene degradation

High Stability and Fast Recovery of Expression of the TOL Plasmid-Carried Toluene Catabolism Genes of Pseudomonas putida mt-2 under Conditions of Oxygen Limitation and Oscillation▿ †

Pseudomonas putida mt-2 harbors the TOL plasmid (pWWO), which contains the genes encoding the enzymes necessary to degrade toluene aerobically. The xyl genes are clustered in the upper operon and encode the enzymes of the upper pathway that degrade toluene to benzoate, while the genes encoding the enzymes of the lower pathway (meta-cleavage pathway) that are necessary for the conversion of benzoate to tricarboxylic acid cycle intermediates, are encoded in a separate operon. In this study, the effects of oxygen availability and oscillation on the expression of catabolic genes for enzymes involved in toluene degradation were studied by using P. putida mt-2 as model bacterium. Quantitative reverse transcription-PCR was used to detect and quantify the expression of the catabolic genes xylM (a key gene of the upper pathway) and xylE (a key gene of the lower pathway) in cultures of P. putida mt-2 that were grown with toluene as a carbon source. Toluene degradation was shown to have a direct dependency on oxygen concentration, where gene expression of xylM and xylE decreased due to oxygen depletion during degradation. Under oscillating oxygen concentrations, P. putida mt-2 induced or downregulated xylM and xylE genes according to the O2 availability in the media. During anoxic periods, P. putida mt-2 decreased the expression of xylM and xylE genes, while the expression of both xylM and xylE genes was immediately increased after oxygen became available again in the medium. These results suggest that oxygen is not only necessary as a cosubstrate for enzyme activity during the degradation of toluene but also that oxygen modulates the expression of the catabolic genes encoded by the TOL plasmid

Aerobic toluene degraders in the rhizosphere of a constructed wetland model show diurnal polyhydroxyalkanoate metabolism

Constructed wetlands (CWs) are successfully applied for the treatment of waters contaminated with aromatic compounds. In these systems, plants provide oxygen and root exudates to the rhizosphere and thereby stimulate microbial degradation processes. Root exudation of oxygen and organic compounds depends on photosynthetic activity and thus may show day-night fluctuations. While diurnal changes in CW effluent composition have been observed, information on respective fluctuations of bacterial activity are scarce. We investigated microbial processes in a CW model system treating toluene-contaminated water which showed diurnal oscillations of oxygen concentrations using metaproteomics. Quantitative real-time PCR was applied to assess diurnal expression patterns of genes involved in aerobic and anaerobic toluene degradation. We observed stable aerobic toluene turnover by Burkholderiales during the day and night. Polyhydroxyalkanoate synthesis was upregulated in these bacteria during the day, suggesting that they additionally feed on organic root exudates while reutilizing the stored carbon compounds during the night via the glyoxylate cycle. Although mRNA copies encoding the anaerobic enzyme benzylsuccinate synthase (bssA) were relatively abundant and increased slightly at night, the corresponding protein could not be detected in the CW model system. Our study provides insights into diurnal patterns of microbial processes occurring in the rhizosphere of an aquatic ecosystem. IMPORTANCE Constructed wetlands are a well-established and cost-efficient option for the bioremediation of contaminated waters. While it is commonly accepted knowledge that the function of CWs is determined by the interplay of plants and microorganisms, the detailed molecular processes are considered a black box. Here, we used a well-characterized CW model system treating toluene-contaminated water to investigate the microbial processes influenced by diurnal plant root exudation. Our results indicated stable aerobic toluene degradation by members of the Burkholderiales during the day and night. Polyhydroxyalkanoate synthesis in these bacteria was higher during the day, suggesting that they additionally fed on organic root exudates and reutilized the stored carbon compounds during the night. Our study illuminates microbial processes occurring in the rhizosphere of an aquatic ecosystem

Toward Biorecycling: Isolation of a Soil Bacterium That Grows on a Polyurethane Oligomer and Monomer.

The fate of plastic waste and a sustainable use of synthetic polymers is one of the major challenges of the twenty first century. Waste valorization strategies can contribute to the solution of this problem. Besides chemical recycling, biological degradation could be a promising tool. Among the high diversity of synthetic polymers, polyurethanes are widely used as foams and insulation materials. In order to examine bacterial biodegradability of polyurethanes, a soil bacterium was isolated from a site rich in brittle plastic waste. The strain, identified as Pseudomonas sp. by 16S rRNA gene sequencing and membrane fatty acid profile, was able to grow on a PU-diol solution, a polyurethane oligomer, as the sole source of carbon and energy. In addition, the strain was able to use 2,4-diaminotoluene, a common precursor and putative degradation intermediate of polyurethanes, respectively, as sole source of energy, carbon, and nitrogen. Whole genome sequencing of the strain revealed the presence of numerus catabolic genes for aromatic compounds. Growth on potential intermediates of 2,4-diaminotoluene degradation, other aromatic growth substrates and a comparison with a protein data base of oxygenases present in the genome, led to the proposal of a degradation pathway

Extracellular degradation of a polyurethane oligomer involving outer membrane vesicles and further insights on the degradation of 2,4-diaminotoluene in <i>Pseudomonas capeferrum</i> TDA1

The continuing reports of plastic pollution in various ecosystems highlight the threat posed by the ever-increasing consumption of synthetic polymers. Therefore, Pseudomonas capeferrum TDA1, a strain recently isolated from a plastic dump site, was examined further regarding its ability to degrade polyurethane (PU) compounds. The previously reported degradation pathway for 2,4-toluene diamine, a precursor and degradation intermediate of PU, could be confirmed by RNA-seq in this organism. In addition, different cell fractions of cells grown on a PU oligomer were tested for extracellular hydrolytic activity using a standard assay. Strikingly, purified outer membrane vesicles (OMV) of P. capeferrum TDA1 grown on a PU oligomer showed higher esterase activity than cell pellets. Hydrolases in the OMV fraction possibly involved in extracellular PU degradation were identified by mass spectrometry. On this basis, we propose a model for extracellular degradation of polyester-based PUs by P. capeferrum TDA1 involving the role of OMVs in synthetic polymer degradation