The microbial synergy and response mechanisms of hydrolysis-acidification combined microbial electrolysis cell system with stainless-steel cathode for textile-dyeing wastewater treatment.

Microbial electrolysis cell (MEC) has been existing problems such as poor applicability to real wastewater and lack of cost-effective electrode materials in the practical application of refractory wastewater. A hydrolysis-acidification combined MEC system (HAR-MECs) with four inexpensive stainless-steel and conventional carbon cloth cathodes for the treatment of real textile-dyeing wastewater, which was fully evaluated the technical feasibility in terms of parameter optimization, spectral analysis, succession and cooperative/competition effect of microbial. Results showed that the optimum performance was achieved with a 12 h hydraulic retention time (HRT) and an applied voltage of 0.7 V in the HAR-MEC system with a 100 µm aperture stainless-steel mesh cathode (SSM-100 µm), and the associated optimum BOD5/COD improvement efficiency (74.75 ± 4.32 %) and current density (5.94 ± 0.03 A·m-2) were increased by 30.36 % and 22.36 % compared to a conventional carbon cloth cathode. The optimal system had effective removal of refractory organics and produced small molecules by electrical stimulation. The HAR segment could greatly alleviate the imbalance between electron donors and electron acceptors in the real refractory wastewater and reduce the treatment difficulty of the MEC segment, while the MEC system improved wastewater biodegradability, amplified the positive and specific interactions between degraders, fermenters and electroactive bacteria due to the substrate complexity. The SSM-100 µm-based system constructed by phylogenetic molecular ecological network (pMEN) exhibited moderate complexity and significantly strong positive correlation between electroactive bacteria and fermenters. It is highly feasible to use HAR-MEC with inexpensive stainless-steel cathode for textile-dyeing wastewater treatment.

Bioelectrochemical systems with a cathode of stainless-steel electrode for treatment of refractory wastewater: Influence of electrode material on system performance and microbial community.

The large-scale application of the bioelectrochemical system (BES) is limited by the cost-effective electrode materials. In this study, five kinds of stainless-steel materials were used as the cathode of the BES coupled with anaerobic digestion (BES-AD) for the treatment of diluted N, N-dimethylacetamide (DMAC) wastewater. Compared with a carbon-cloth cathode, BES-AD with a stainless-steel cathode had more engineering due to its low cost, although the operating efficiencies were slightly inferior. Stainless-steel mesh with a 100 µm aperture (SSM-100 µm) was the most cost-effective electrode and the implanted BES exhibited better COD removal efficiency, electrochemical performance and biodegradability. Analysis of microbial community revealed the synergetic effect between exoelectrogen and fermentative bacteria had been strengthened in the SSM-100 µm cathode biofilm. Function analysis of the microbial community based on PICRUSt predicted metagenomes revealed that the metabolic pathways of xenobiotics biodegradation and metabolism in the SSM-100 µm cathode were stimulated.

Revealing hydrodynamics and energy efficiency of mixing for high-solid anaerobic digestion of waste activated sludge.

Anaerobic digestion is a feasible and promising technique to deal with emerging waste activated sludge issues. In this work, the hydrodynamics and digestion performance of horizontal anaerobic systems equipped with double-bladed impeller and ribbon impeller were investigated. Simulation using computational fluid dynamics technique visually showcased the favorable mixing status implementing ribbon impeller. The mixing modes were considered as the major motivation for the difference of mixing efficiencies. Tracing experiment indicated that the minimum thorough mixing time with ribbon impeller was 20 min at a rotation speed of 50 rpm, whereas it was 360 min for the double-bladed impeller under similar conditions. The superior mixing performance of ribbon impeller resulted in better anaerobic digestion and energy efficiency outputs. The digester employing ribbon impeller obtained an ultimate biogas yield of 340.38 ± 15.91 mL/g VS (corresponding methane yield of 210.34 ± 7.55 mL/g VS) and produced a surplus energy of 16.23 ± 0.76 MJ/(m3·d). This study thus ascertained that ribbon impeller was proficient for high-solid anaerobic digestion and it will prominently benefit future system designs.