The extensive production and use
of polyethylene terephthalate
(PET) have generated an enormous amount of plastic waste, which potentially
threatens the environment and humans. Enzyme biocatalysis is a promising
green chemistry alternative, relative to the conventional fossil-derived
production process, to achieve plastic waste treatment and recycling.
In this work, we created a biocatalyst, BIND-PETase, by genetically
engineering the curli of an Escherichia coli cell
with a functional PETase enzyme for biocatalytic degradation of PET
plastics. BIND-PETase could degrade PET to generate degradation products
at the concentration level of greater than 3000 μM under various
reaction conditions. The effects of key reaction parameters, including
pH, temperature, plastic substrate mass load, and surfactant addition
were characterized. BIND-PETase was reusable for PET degradation and
remained stable with no significant enzyme activity loss when stored
at both 4 °C and room temperature for 30 days (Student’s t test, p > 0.05). Notably, BIND-PETase
could enable the degradation of PET microplastics in wastewater effluent
matrix. Moreover, BIND-PETase could depolymerize highly crystalline
postconsumer PET waste materials under ambient conditions with degradation
efficiency of 9.1% in 7 days. This study provides a new horizon for
developing environmentally friendly biocatalytic approaches to solve
the plastic degradation and recycling challenge.
Petroleum-contaminated soil is considered among the most important potential anthropogenic atmospheric methane sources. Additionally, various rhizoremediation factors can affect methane emissions by altering soil ecosystem carbon cycles. Nonetheless, greenhouse gas emissions from soil have not been given due importance as a potentially relevant parameter in rhizoremediation techniques. Therefore, in this study we sought to investigate the effects of different plant and soil amendments on both remediation efficiencies and methane emission characteristics in dieselcontaminated soil. An indoor pot experiment consisting of three plant treatments (control, maize, tall fescue) and two soil amendments (chemical nutrient, compost) was performed for 95 days. Total petroleum hydrocarbon (TPH) removal efficiency, dehydrogenase activity, and alkB (i.e., an alkane compound-degrading enzyme) gene abundance were the highest in the tall fescue and maize soil system amended with compost. Compost addition enhanced both the overall remediation efficiencies, as well as pmoA (i.e., a methane-oxidizing enzyme) gene abundance in soils. Moreover, the potential methane emission of diesel-contaminated soil was relatively low when maize was introduced to the soil system. After microbial community analysis, various TPH-degrading microorganisms (Nocardioides, Marinobacter, Immitisolibacter, Acinetobacter, Kocuria, Mycobacterium, Pseudomonas, Alcanivorax) and methane-oxidizing microorganisms (Methylocapsa, Methylosarcina) were observed in the rhizosphere soil. The effects of major rhizoremediation factors on soil remediation efficiency and greenhouse gas emissions discussed herein are expected to contribute to the development of sustainable biological remediation technologies in response to global climate change.
Membrane-less, single-chamber, air-cathode, microbial fuel cells (ML-SC MFCs) have attracted attention as being suitable for wastewater treatment. In this study, the effects of nitrate and sulfate on the performance of ML-SC MFCs and their bacterial structures were evaluated. The maximum power density increased after nitrate addition from 8.6 mW·m to 14.0 mW·m, while it decreased after sulfate addition from 11.5 mW·m to 7.7 mW·m. The chemical oxygen demand removal efficiencies remained at more than 90% regardless of the nitrate or sulfate additions. The nitrate was removed completely (93.0%) in the ML-SC MFC, while the sulfate removal efficiency was relatively low (17.6%). Clostridium (23.1%), Petrimonas (20.0%), and unclassified Rhodocyclaceae (6.2%) were dominant on the anode before the addition of nitrate or sulfate. After the addition of nitrate, Clostridium was still the most dominant on the anode (23.6%), but Petrimonas significantly decreased (6.0%) and unclassified Rhodocyclaceae increased (17.1%). After the addition of sulfate, the amount of Clostridium almost doubled in the composition on the anode (43.2%), while Petrimonas decreased (5.5%). The bacterial community on the cathode was similar to that on the anode after the addition of nitrate. However, Desulfovibrio was remarkably dominant on the cathode (32.9%) after the addition of sulfate. These results promote a deeper understanding of the effects of nitrate or sulfate on the ML-SC MFCs' performance and their bacterial community.
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