Chen Yiting,Yan Jun,Chen Mengli,Guo Fucheng,Liu Tao,Chen Yi
Constructed wetlands (CWs) are widely used as a tertiary treatment technology, and the addition of carbon sources can significantly improve advanced nitrogen removal. However, excessive carbon sources would lead to an increase in the effluent chemical oxygen demand in CWs, and microbial fuel cells (MFCs) can convert these into electricity. In this study, constructed wetland-microbial fuel cells (CW-MFCs) were built to achieve simultaneous nitrogen removal and electricity generation, using wetland plant litter fermentation broths as carbon sources. The total nitrogen removal in the groups with fermentation broth addition (FGs) reached 83.33%, which was 19.64% higher than that in the CG (group without fermentation broth), and the mean voltages in the FGs were at least 2.6 times higher than that of the CG. Furthermore, two main components of the fermentation broths, acetic acid (Ac) and humic acid (HA), were identified using a three-dimensional excitation emission matrix and gas chromatograph and added to CW-MFCs to explore the influence mechanism on the treatment performance. Denitrification and electrogenesis presented the same tendency: Ac&HA > Ac > CG’ (groups without Ac and HA). These results indicate that Ac and HA increased the abundance of functional genes associated with nitrogen metabolism and electron transfer. This study demonstrated that CW-MFC fermentation broth addition can be a potential strategy for the disposal of secondary effluent and bioelectricity generation.
The widespread use of neonicotinoid pesticides has caused environmental threat that has attracted scientific concern. This study developed a microalgae fuel cells (MFCs) with Chlorella sp. as the cathode synergistically enhanced the removal of imidacloprid (IMI). The MFCs were operated at open-circuit and closed-circuit. Under closed-circuit condition (with an external load), 57.20–61.66% of IMI (10–50 mg/L) was removed within 12 days. However, only 39.66–42.66% was removed in the open-circuit (without an external load). Additionally, a voltage of 200 mV was also detected in the closed-circuit MFCs, indicating the green bioenergy was produced during the degradation of IMI. Cyclic voltammetry revealed that the cathodic electroactivity was higher with the addition of IMI. Biomass accumulation (indicated by chlorophyll and dry cell weight) were significantly enhanced by IMI. On the 12th day, there was no difference in MDA content between the different IMI concentration (10–50 mg/L), while a significantly upregulated superoxide dismutase (SOD) of each group was also found at the same time. Six intermediates were detected and five major degradation pathways were proposed. Based on the identified products and microalgae growth, the degradation products of IMI were less toxic /non-toxic than IMI. Considering the efficient removal of IMI and energy production, the MFCs could be a promising technique for controlling IMI contamination by effective detoxification.
Chen Cai,Yu Hua,Huiping Li,Lei Li,Lingling Dai,Huiling Liu,Xiaohu Dai
Erythromycin fermentation residue (EFR) is a byproduct of bio-fermentation process for producing erythromycin, representing both an economic and environmental burden for the pharmaceutical industry. While hydrothermal treatment (HT) can solve the pollution and toxic problems, the impacts of HT on harmless performance and the bioresource properties of the complex EFR matrix remain unclear. In this study, the abatement of residual erythromycin, its associated antibiotic resistance genes and antimicrobial activity were investigated to evaluate the harmless performance of HT for EFR, and the feasibility of recycling hydrolysates as bioenergy was also assessed. The results showed that raising HT temperature significantly improved the harmless performance. The removal rate of residual erythromycin in EFR reached over 88% and the total absolute abundance of erythromycin resistance genes decreased by more than 3 logs with HT at 160°C for 60 min, but the hydrolysates still existed specific antimicrobial activity against S. aureus. . Additionally, the HT temperature remarkably influenced the bioresource properties of EFR-hydrolyzed products. The release of the protein-like polymers into the liquid phase was enhanced, while high HT temperature worsened the nutrient substances. The elevated drying property of solid products from EFR was observed along with the higher heating value of around 20 MJ/kg, indicating a potential of recycling solid products as biofuel. Total energy production from biogas conversion and biofuel incineration treating 1.0 kg raw EFR was 1875 kJ. Hydrothermal technology was proved to realize the harmless treatment of EFR and meanwhile to be promising for recycling EFR as bioenergy.
Bioconversion of biomass to bioenergy and recycle of cadmium wastewater are widespread and of significant economic importance. The development of an efficient and cost effective bioconversion process remains challenging. Here, recycling cadmium and un-pretreated biomass conversion were combined into a single operation. A modified consolidated bioprocessing (CBP) strategy of biomass and synthetic cadmium wastewater as mixed substrates for hydrogen generation through a couple of whole-cell catalysis with photocatalysis was established by Clostridium thermocellum . The process was accomplished by biotransformation of cadmium ions to cadmium sulfide (CdS) by C. thermocellum . The formed hybrid C. thermocellum -CdS complex converted biomass into hydrogen production through the integration of two reactions together, biocatalysis and photocatalysis. After optimization, the hydrogen production produced by C. thermocellum- CdS was remarkably increased by 36.1% if compared with that by C. thermocellum only . This exploration is expected to provide a novel strategy of collaborative disposal of cadmium wastewater and waste biomass, which would not only bring a great potential in the recycling and reusing of cadmium wastewater and waste biomass, but also provide new approach both for bioenergy recovery and environmental improvement.
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