Condition optimization of iron-air fuel cell to treat phosphate-containing wastewater regarding sustainable development

Increasing use of phosphorus products and excessive exploitation of phosphorus resources become two major problems in perspective of phosphorus sustainable development. Phosphorus recovery is the shortcut to solve this dilemma. Combining electrochemistry, an iron-air fuel cell was adopted to recover phosphate and electricity from phosphate-containing wastewater in our previous studies. The present study focused on investigating the effects of catholyte/anolyte conductivity, external resistance, and anolyte pH on the performance of iron-air fuel cell, and obtaining the optimized conditions. Furthermore, the electrochemical methods of phosphate recovery were compared and assessed, and it is concluded that iron-air fuel cell has great potential for energy recovery. The phosphate removal efficiencies and vivianite yield roughly positively correlated with the catholyte conductivity and the anolyte pH, but negatively correlated with the external resistance and the anolyte conductivity. The electricity generation roughly positively correlated with the catholyte conductivity and anolyte conductivity, but showed limitations in the test range of anolyte pH and external resistance. To pursue high phosphate removal efficiencies and vivianite yield, the catholyte conductivity, external resistance, anolyte pH and anolyte conductivity were suggested to be 35 g-NaCl/L, 10 Ω, 8 and 0 g-NaCl/L. While if electricity generation was the primary goal, these parameters should be 35 g-NaCl/L, 220 Ω, 5 and 70 g-NaCl/L. The optimized conditions will help to improve the phosphate removal efficiency, vivianite yield and electricity generation, and to promote the development of iron-air fuel cell technology.

Fabrication and characterization of Ti/polyaniline-Co/PbO2-Co for efficient electrochemical degradation of cephalexin in secondary effluents

The traditional interlayer of PbO₂ electrode possessed many problems, such as short service lifetime and limited specific surface area. Herein, a novel and efficient Ti/polyaniline-Co/PbO₂-Co electrode was conctructed employing cyclic voltammetry to introduce a Co-doped polyaniline interlayer and anodic electrodeposition to synthetize a β-PbO₂-Co active layer. Compared with pristine PbO₂ electrode, Ti/polyaniline-Co/PbO₂-Co exhibited more compact crystalline shape and higher active sites amounts. Pratically, the electrochemical degradation of 5 mg L^-1 cephalexin in real secondary effluents was effectively achieved by the novel anode with 87.42% cephalexin removal and 71.8% COD mineralization after 120 min of 15 mA cm^-2 electrolysis. The hydroxyl radical production and electrochemical stability were increased by 3.16 and 3.27 times respectively. The cephalexin degradation pathway was investigated by combining a density functional theory-based theoretical approach and LC-QTrap-MS/MS. The most likely cleavage point of the β-lactam ring was the O=C-N bond, whose attack would produce small molecular compounds containing the thiazole and 4, 6-thiazine rings. Further oxidation produced inorganic ions; quantitative investigations indicated the amino groups to undergo decomposition to form aqueous NH₄⁺, which was further oxidized to NO₃^-. The accumulation of NO₃^- and SO₄^2-, combined with a decrease in toxicity toward Escherichia coli, demonstrated the efficient mineralization of cephalexin on the Ti/polyaniline-Co/PbO₂-Co electrode.

Extracellular expression of agarolytic enzymes in Clostridium sp. strain and its application for butanol production from Gelidium amansii

In this study, Clostridium sp. strain WK-AN1 carrying both genes of agarase (Aga0283) and neoagarobiose hydrolase (NH2780) were successfully constructed to convert agar polysaccharide directly into butanol, contributing to overcome the lack of algal hydrolases in solventogenic clostridia. Through the optimization by the Plackett-Burman design (PBD) and response surface methodology (RSM), a maximal butanol production of 6.42 g/L was achieved from 17.86 g/L agar. Further application of utilizing the butyric acid pretreated Gelidium amansii hydrolysate demonstrated the modified strain obtained the butanol production of 7.83 g/L by 1.63-fold improvement over the wild-type one. This work for the first time establishes a novel route to utilize red algal polysaccharides for butanol fermentation by constructing a solventogenic clostridia-specific secretory expression system for heterologous agarases, which will provide insights for future development of the sustainable third-generation biomass energy.

One-pot fermentation for erythritol production from distillers grains by the co-cultivation of Yarrowia lipolytica and Trichoderma reesei

A co-fermentation process involving Yarrowia lipolytica and Trichoderma reesei was studied, using distillers grains (DGS) as feedstocks for erythritol production. DGS can be effectively hydrolyzed by cellulase in the single-strain culture of T. reesei. One-pot solid state fermentation for erythritol production was then established by co-cultivating Y. lipolytica M53-S with the 12 h delay inoculated T. reesei Rut C-30, in which efficient saccharification of DGS and improved production of erythritol were simultaneously achieved. The 10:1 inoculation proportion of Y. lipolytica and T. reesei contributed to the maximum erythritol production of 267.1 mg/gds under the optimal conditions including initial moisture of 55%, pH of 5.0, NaCl addition of 0.02 g/gds and DGS mass of 200 g in 144 h co-cultivation. Being compared with the attempts to produce erythritol from other raw materials, the one-pot SSF with DGS is proposed to be a potential strategy for efficient and economical erythritol production.

Characterization of dissolved organic matter during the O3-based advanced oxidation of mature landfill leachate with and without biological pre-treatment and operating cost analysis

In this study, the organic matter in an O₃-based advanced oxidation process (AOP) for treating raw leachate (RL) and bio-treated leachate (BTL) was characterized. The optimal conditions for COD removal in RL and BTL treatment were as follows: initial pH of 6.0 and H₂O₂ dosage of 9 mL 30% H₂O₂ L^-1 leachate, and initial pH of 12 without H₂O₂ addition, respectively. H₂O₂ addition had little influence on COD removal in the BTL treatment as sufficient hydroxyl radicals may not be produced at extremely high pH levels. The differences in the alkalinity between RL and BTL caused differences in the optimum pH of the AOPs. Overall, the initial pH more affected COD removal than the H₂O₂ dosage. O₃-based AOP converted organics with high molecular weight fractions into low ones. Meanwhile, it preferentially degraded hydrophobic substances over hydrophilic substances. The organic matter in the BTL contained more refractory and hydrophobic fractions; therefore, higher COD removal was achieved in the treatment of RL. The organics in the treatment of RL and BTL were identified by excitation-emission matrix spectroscopy combined with parallel factor analysis, and their degradation decreased in the following order: terrestrial humic-like > microbial humic-like > combination of tryptophan and humic-like components. O₃-based AOP significantly enhanced biodegradability. According to the economic analysis results, as an intermediate treatment, O₃-based AOP is a cost-effective strategy of ensuring that leachate effluent meets the discharge standards, with the lowest operating cost of $4.62 m^-3. This study provides a reference for the application of O₃-based AOP in full-scale landfill leachate treatment.

Co/Sm-modified Ti/PbO2 anode for atrazine degradation: Effective electrocatalytic performance and degradation mechanism

In this work, Ti/PbO₂-Co-Sm electrode has been successfully prepared using electrodeposition and further applied for the electrocatalysis of atrazine (ATZ) herbicide wastewater. As expected, Ti/PbO₂-Co-Sm electrode displays highest oxygen evolution potential, lowest charge transfer resistance, longest service lifetime and most effective electrocatalytic activity compared with Ti/PbO₂, Ti/PbO₂-Sm and Ti/PbO₂-Co electrodes. Orthogonal and single factor experiments are designed to optimize the condition of ATZ degradation. The maximum degradation efficiency of 92.6% and COD removal efficiency of 84.5% are achieved in electrolysis time 3 h under the optimum condition (current density 20 mA cm^-2, Na₂SO₄ concentration 8.0 g L^-1, pH 5 and temperature 35 °C). In addition, Ti/PbO₂-Co-Sm electrode exhibits admirable recyclability in degradation progress. The degradation of ATZ is accomplished by indirect electrochemical oxidation and ∙OH is tested as the main active substance in ATZ oxidation. The possible degradation mechanism of ATZ has been proposed according to the degradation intermediates detected by LC-MS. This research suggests that Ti/PbO₂-Co-Sm is a promising electrode for ATZ degradation.

Optimization of submerged fermentation of Thelephora ganbajun zang

The effects of the fermentation conditions on both the biomass yield and the organic selenium yield of Thelephora ganbajun zang were studied. The components most suitable for the submerged fermentation medium were examined using the orthogonal array method; they comprised sucrose at 30 g L(-1) , carbamide 1 g L(-1) , corn steep liquor 8 g L(-1) , MgSO4 ·7H2 O 0.3 g L(-1) , KH2 PO4 0.5 g L(-1) , and NaCl 5 g L(-1) . The optimum cultivation conditions that resulted in maximal biomass yield were obtained using the response surface methodology (RSM). The conditions were as follows: initial pH, 5.84; temperature, 26.16 °C; and rotation speed, 170 rpm. Feeding sucrose led to a higher biomass yield, with a maximum of 21.20 g L(-1) . The biomass yield and the organic Se yield of T. ganbajun could reach 10.8 g L(-1) and 3256.07 mg kg(-1) , respectively, in a culture medium supplemented with 200 mg L(-1) sodium selenite (Na2 SeO3 ), which was added to the medium at 36 h after inoculation. Application of the orthogonal array method and RSM gave rise to a significant enhancement in the biomass yield of T. ganbajun. The results of these experiments indicate that T. ganbajun is a promising microorganism for selenium enrichment.