Energy is a major driving force for the economic development. Due to the scarcity of fossil fuels and negative impact on the environment, it is important to develop renewable and sustainable energy ...sources for humankind. Microalgae as the primary feedstock for biodiesel has shown great application potential. However, lipid yield from microalgae is limited by the upstream cost, which restrain the realization of large-scale biofuel production. The modification of lipid-rich microalgae cell has become the focus over the last few decades to improve the lipid content and productivity of microalgae. Carbon is a vital nutrient that regulates the growth and metabolism of microalgae. Different carbon sources are assimilated by microalgae cells via different pathways. Inorganic carbon sources are mainly used through the CO2-concentrating mechanisms (CCMs), while organic carbon sources are absorbed by microalgae mainly through the Pentose Phosphate (PPP) Pathway and the Embden-Meyerhof-Pranas (EMP) pathway. Therefore, the addition of carbon source has a significant impact on the production of microalgae biomass and lipid accumulation. In this paper, mechanisms of lipid synthesis and carbon uptake of microalgae were introduced, and the effects of different carbon conditions (types, concentrations, and addition methods) on lipid accumulation in microalgal biomass production and biodiesel production were comprehensively discussed. This review also highlights the recent advances in microalgae lipid cultivation with large-scale commercialization and the development prospects of biodiesel production. Current challenges and constructive suggestions are proposed on cost-benefit concerns in large-scale production of microalgae biodiesel.
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•The mechanism of carbon source on lipid synthesis was elucidated.•The effect of carbon source on algal biodiesel production was critically reviewed.•Reviewed and discussed carbon fixation efficiency of microalgae with selected carbon•Wastewater utilization could be cost-saving strategy for microalgal high-value products.
Dimethyl sulfoxide (DMSO) is one of the most commonly applied organic solvents in chemical transformations and is utilized widely in industrial processes as well. During the past decades, numerous ...procedures using DMSO as a reaction reagent have been developed and published. In this review, the main developments on the employment of DMSO as sources of Me, SMe, SO2Me, as an oxidant etc. have been summarized and discussed.
The potential effect of CO2 on environmental microbes has drawn much attention recently. As an important section of the nitrogen cycle, biological denitrification requires electron donor to reduce ...nitrogen oxide. Nicotinamide adenine dinucleotide (NADH), which is formed during carbon source metabolism, is a widely reported electron donor for denitrification. Here we studied the effect of CO2 on NADH production and carbon source utilization in the denitrifying microbe Paracoccus denitrificans. We observed that NADH level was decreased by 45.5% with the increase of CO2 concentration from 0 to 30,000ppm, which was attributed to the significantly decreased utilization of carbon source (i.e., acetate). Further study showed that CO2 inhibited carbon source utilization because of multiple negative influences: (1) suppressing the growth and viability of denitrifier cells, (2) weakening the driving force for carbon source transport by decreasing bacterial membrane potential, and (3) downregulating the expression of genes encoding key enzymes involved in intracellular carbon metabolism, such as citrate synthase, aconitate hydratase, isocitrate dehydrogenase, succinate dehydrogenase, and fumarate reductase. This study suggests that the inhibitory effect of CO2 on NADH production in denitrifiers might deteriorate the denitrification performance in an elevated CO2 climate scenario.
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•CO2 decreased NADH production during denitrification.•CO2 decreased cell growth, viability and carbon source utilization.•CO2 weakened carbon source transport by decreasing bacterial membrane potential.•CO2 downregulated the expression of key genes involved in intracellular carbon metabolism.
Solid and liquid organic substances as carbon sources for denitrification process were deeply explored. In this study, the effect of three carbon sources, referred to as poly ...(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly (lactic acid) (PHBV/PLA) polymer, glucose and CH3COONa, on denitrification performance, microbial community and functional genes were investigated. It was found that maximum denitrification rates of 0.37, 0.46 and 0.39gN/(L·d) were achieved in PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Meanwhile, Illumina MiSeq sequencing revealed that three carbon sources led to different microbial community structures. It can be seen that Brevinema/Thauera/Dechloromonas, Tolumonas/Thauera/Dechloromonas, Thauera dominated in the PHBV/PLA, glucose and CH3COONa supported denitrification systems, respectively. Transcriptome-based analysis further indicated that the glucose supported denitrification system showed the highest FPKM values (the fragments per kilobase per million mapped reads) of the genes participating in the dissimilatory nitrate reduction process, corresponding to the greatest effluent NH4+-N concentration. A better knowledge of effect of different carbon sources on denitrification process will be significant for nitrate removal in practice.
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•The maximum denitrification rate was lowest in PHBV/PLA supported system.•The relative abundance of denitrification bacteria was highest in CH3COONa system.•PHBV/PLA and glucose systems showed abundant hydrolysis and fermenting bacteria.•The FPKM value of functional genes for DNRA process was highest in glucose system.
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•Slurry is used to enhance nitrogen removal with an optimal HRT of 12 h.•Hydrogenophaga and Filimonas are confirmed as the key pollutant removal bacteria.•Hydraulic shear stress ...inhibits gene enrichment in carbon and nitrogen metabolism.•Microbial community under the condition of HRT 6 h has the highest pathogenic risk.
Insufficient carbon sources in low-carbon wastewater have consistently hindered nitrogen removal performance. This work utilized slurry after anaerobic digestion as an additional carbon source, and the optimal hydraulic retention time (HRT) parameters were obtained through adjustment. The findings revealed that, under HRT conditions of 24–12 h, the discharge standards of wastewater treatment plants (WWTPs) could be met. It had been proven that HRT 12 h was the more cost-effective parameter for application in WWTPs, and the removal efficiencies for COD, NH4+-N, NO3–-N, and TN reached impressive levels of 82.43%, 95.24%, 77.49%, and 86.70%, respectively. However, the HRT 6 h struggled to achieve efficient wastewater treatment. Mechanistic analysis demonstrated that shortening the HRT resulted in considerably higher microbial richness, diversity, and evenness, causing notable shifts in microbial community structure. Additionally, a shortened HRT reduced the enrichment abundance of key bacterial phyla (Proteobacteria, Bacteroidetes) and genera (Hydrogenophaga, Filimonas, Meganema) that played an important role in nitrogen and organic matter removal. Furthermore, a shortened HRT increased hydraulic shear forces, impeding the enrichment of carbon and nitrogen metabolism pathways, and reducing the abundance of essential genes associated with glycolysis (HK, pfkA, FBA, GAPDH) and nitrogen metabolism processes (narG, narH, narI, norB, nirS, nosZ). It was noteworthy that the microbial community under the HRT 6 h condition carried the highest risk of microbial pathogenicity. This work revealed the optimal parameters, and carbon and nitrogen metabolism mechanism of wastewater treatment systems with slurry as a carbon source for the first time, and provided novel ideas and insights for low-carbon wastewater treatment.
Fermented rice bran, when used as a carbon source in a biofloc system, can improve water quality, growth, and feeding efficiencies of cultured species. The present study delves into the effect of ...fermented rice bran as a carbon source on the growth and survival of Genetically Improved Farmed Tilapia (GIFT) fry. Additionally, the study investigated its impact on water quality, intestinal histology, proximate composition of fish and biofloc, total plate count of the experimental tank, and fish gut in the biofloc system. The study employed a completely randomized design with five different treatments: NFRB+BFT (Non-Fermented Rice Bran), FRBW+BFT (Fermented Rice Bran with Water), FRBP+BFT (Fermented Rice Bran with Probiotic), FRBY+BFT (Fermented Rice Bran with Yeast), and a clear-water system (with daily water exchange of 10%). The experimental duration was 60 days. The GIFT fry with an average weight of 1.04 ± 0.02 g were randomly distributed in High Density Polythene (HDPE) tanks of 110 L capacity at a stocking density of 250 individuals (ind.) m−3. Results indicated that the weight gain %, length gain %, Specific Growth Rate (SGR), and Protein Efficiency Ratio (PER) in FRBP+BFT and FRBY+BFT treatments were similar, with no significant differences (p > 0.05) and significantly higher (p < 0.05) than other treatments. At the end of the experiment, FRBP+BFT and FRBY+BFT treatments showed lower ammonia-N values. The histological study of GIFT showed a number of villi and villi length in FRBP+BFT and FRBY+BFT were similar with no significant differences (p > 0.05). The protein, lipid, and ash content of fish and biofloc were similar with no significant differences (p > 0.05) in FRBP+BFT and FRBY+BFT treatments. The total plate count of fish gut and water in FRBP+BFT and FRBY+BFT treatments was similar and significantly higher (p < 0.05) than the other treatments. Overall, the results indicate that rice bran fermented with both probiotic and yeast as a carbon source showed similar growth performance and improved water quality in rearing GIFT fry in a biofloc system.
•GIFT strain of Nile tilapia is favored in aquaculture.•Expansion of aquaculture is vital for increased production.•Biofloc system is an eco-friendly aquaculture technique.•Fermentation of rice bran enhances its solubility and efficiency in biofloc system.•Among five treatments, probiotic and yeast-fermented rice bran is a better source of carbon for rearing GIFT fry in a biofloc system.
Sludge hydrothermal treatment can achieve efficient reduction and resource utilization, and the hydrothermal liquid products (HLPs) generated in the hydrothermal process may be returned to beginning ...of the wastewater plant for resource utilization. In this study, dehydrated sludge was treated by a hydrothermal treatment process, and hydrothermal products were separated by centrifugation. Then the HLPs were returned to the front end of the anaerobic-oxic (A/O) reactor to explore their potential role as a source of denitrified carbon. Study focuses on the HLPs’ changes of Carbon (C), Nitrogen (N), and Phosphorus (P) speciation and distribution, and clarifying the organic matter forms and their impacts on the microbial community composition and functional expression in biological process after recirculation. The results show C and N components are dissolved to HLPs, existing in forms of easily biodegraded components, such as acetic acid (28.04 %), tryptophan, and humic substances, while P mainly precipitates in the solid residue, avoiding accumulation in the wastewater treatment system. The dominant bacteria Proteobacteria accounts for 30 %–40 % of the total sequence, and the abundance of metabolism-related genes maintain the highest level. The wastewater treatment process can withstand the shock of the recirculation of HLPs, and the microbial community composition remains stable.
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•Hydrothermal treatment promotes sludge reduction by 68.38 %.•The liquid product can partially play as a potential carbon source.•N and P in sludge migrates to the liquid product in NH3-N and ORP.•Recirculation don’t change Proteobacteria and Bacteroidota as dominant bacterial.
Microbial reductive dechlorination hosts great promise as an in situ bioremediation strategy for polychlorinated biphenyls (PCBs) contamination. However, the slow dechlorination in sediments limits ...natural attenuation. Short-chain fatty acids, as preferred carbon sources and electron donors for dechlorinating microorganisms, might stimulate PCB dechlorination. Herein, two sets of short-chain fatty acids, sole acetate and a fatty acid mixture (acetate, propionate, and butyrate), were amended periodically into Taihu Lake (China) sediment microcosms containing nine PCB congeners (PCB5, 12, 64, 71, 105, 114, 149, 153, and 170) after 24 weeks of incubation. Short-chain fatty acids facilitated the long-term PCB dechlorination and the promoting effect of the fatty acid mixture compared favorably with that of sole acetate. By the end of 108 weeks, the total PCB mass concentrations in acetate amended and fatty acid mixture amended microcosms significantly declined by 7.6% and 10.3% compared with non-amended microcosms (P < 0.05), respectively. Short-chain fatty acids selectively favored the removal of flanked meta and single-flanked para chlorines. Notably, a rare ortho dechlorination pathway, PCB25 (24-3-CB) to PCB13 (3-4-CB), was enhanced. Supplementary fatty acids significantly increased reductive dehalogenases (RDase) gene pcbA5 instead of improving the growth of Dehalococcoides. These findings highlight the merits of low cost short-chain fatty acids on in situ biostimulation in treating PCBs contamination.
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•The role of carbon source on long-term dechlorination of PCBs was investigated.•Short-chain fatty acids supplementation facilitated the long-term dechlorination of PCBs•The promoting effect of fatty acid mixture (acetate, propionate, and butyrate) outperformed sole acetate.•The flanked meta and single-flanked para dechlorination were enhanced, as well as a rare ortho dechlorination pathway.•PcbA5 was the main induced RDase gene under the biostimulation of carbon source.
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