Search Results (7)

The low solubility of CO₂ in water leads to massive CO₂ emission and extremely low CO₂ utilization in succinic acid (SA) biosynthesis. To enhance microbial CO₂ utilization, micro-nano bubbles (MNBs) were induced in SA biosynthesis by E. coli Suc260 in this study. The results showed that MNB aeration decreased CO₂ emissions and increased CO₂ solubility in the medium significantly. The CO₂ utilization of MNB aeration was 129.69% higher than that of bubble aeration in atmospheric fermentation. However, MNBs showed a significant inhibitory effect on bacterial growth in the pressurized environment, although a two-stage aerobic–anaerobic fermentation strategy weakened the inhibition. The biofilm-enhanced strain E. coli Suc260-CsgA showed a strong tolerance to MNBs. In pressurized fermentation with MNB aeration, the actual CO₂ utilization of E. coli Suc260-CsgA was 30.63% at 0.18 MPa, which was a 6.49-times improvement. The CO₂ requirement for SA synthesis decreased by 83.4%, and the fugitive emission of CO₂ was successfully controlled. The activities of key enzymes within the SA synthesis pathway were also maintained or enhanced in the fermentation process with MNB aeration. These results indicated that the biofilm-enhanced strain and CO₂-MNBs could improve carbon fixation efficiency in microbial carbon sequestration. Full article

This study investigates the impact of Aerated Subsurface Drip Irrigation (ASDI) on the growth and yield of mulched cotton, aiming to identify the optimal water-air combination pattern for ASDI in cotton cultivation. Conducted during 2021–2022, the experimental setup involved two aeration modes (aerated A₁ and unaerated A₀) and four irrigation quotas (W₁, W₂, W₃, and W₄), organized in a two-factor randomized block design resulting in eight distinct treatments. The findings revealed that ASDI significantly promoted soil moisture depletion from 0 to 40 cm during the cotton flowering and boll opening stages. Specifically, aerated A₁ reduced soil water content by 5.84% to 7.83% during the flowering stage and 7.45% to 13.39% during the boll opening stage compared to unaerated A₀. Additionally, both aerating and increasing irrigation quotas not only enhanced the cotton leaf area index (LAI) but also delayed leaf area decay, contributing to prolonged photosynthetic activity. Aerating also favorably influenced the distribution of above-ground biomass in cotton towards budding and boll stages, with the biomass share of buddings, flowers, and bolls averaging 62.98% under aerated conditions versus 62.27% under non-aerated conditions during the boll opening stage. Furthermore, aerating combined with increased irrigation quotas resulted in higher seed cotton yields, with aerated irrigation boosting yields by 1.79% in 2021 and 4.43% in 2022 compared to non-aerated irrigation. This approach also increased cotton’s water demand and average daily water consumption significantly (p < 0.01). Importantly, aerating improved IWUE, achieving 1.72 kg/m³ in 2021 and 1.62 kg/m³ in 2022 for ASDI, versus 1.69 kg/m³ and 1.57 kg/m³ for unaerated subsurface drip irrigation, respectively. In conclusion, from a water conservation and yield enhancement perspective, an irrigation quota of 337.4 mm during the reproductive stage under ASDI is recommended as an effective strategy for “one film three tubes and six rows” mulched cotton in Southern Xinjiang. Full article

Unnecessary discharge of nutrient-rich aquaculture wastewater is a significant threat to the environment, exacerbating massive resource wasting worldwide. Microalgae-based circular economy strategies utilize atmospheric CO₂ and aquaculture wastewater nutrients and convert them into valuable compounds. Lutein, a natural pigment, is a nutritional supplement for eye protection, anti-cancer and anti-inflammatory effects, and other health benefits. It is widely utilized in the food and pharmaceutical industries. The primary purpose of this study is to reuse aquaculture wastewater to grow microalgae and optimize conditions to achieve a high yield of lutein as well as the removal of nutrients from wastewater. When cultured in 1.0× BG11 nutrient-added aquaculture wastewater and aerated using 2% CO₂, the biomass concentration and lutein content of Chlorella sorokiniana NIES-2168 increased to 1.78 g L⁻¹ and 7.43 mg g⁻¹, respectively. A two-stage culture strategy further increased the lutein content and yield of microalgae. The highest lutein content of 13.95 mg g⁻¹ and lutein productivity of 3.63 mg L⁻¹ d⁻¹ in the second stage aligned with other phototrophic microalgae currently used for lutein production. C. sorokiniana NIES-2168 also showed exceptional nitrogen and phosphorus removal efficiency, with nitrate and phosphate removal rates reaching 96.07% and 96.75% during the two-stage culture process. Full article

The operational costs of wastewater treatment plants (WWTPs) are mainly driven by electric power consumption, making the energy-efficient operation an all-time present target for engineers and operators. A well known approach to reduce the demand for purchased electricity is the operation of an anaerobic sludge stabilisation process. Although anaerobic digesters make it possible to recover large quantities of energy-rich methane gas, additional strategies are required to handle the increased internal return flow of nitrogen, which arises with the sludge dewatering effluent (SDE). SDE treatment increases the oxygen demand and in turn the energy required for aeration. In this study, different SDE treatment processes were compared with regard to the treatment in mainstream, sidestream nitritation, as well as nitritation combined with anammox for two-stage and single-stage WWTPs. Although SDE treatment in sidestream nitritation was found to have no effect on the energy demand of single-stage WWTPs, this concept allows the treatment capacity in the activated sludge tank to be raised, while contributing to a high nitrogen removal under carbon limitation. In contrast, SDE sidestream treatment showed great potential for saving energy at two-stage WWTPs, whereby sidestream nitritation and the further treatment in the first stage was found to be the most efficient concept, with a savings of approx. 11% of the aeration energy. Full article

The purification effect of a biological aerated filter (BAF) mainly comes from the microorganisms in the reactor. Understanding the correlation between microbial community characteristics and environmental factors along the filter has great significance for maintaining good operation and improving the removal efficiency of the filter. A two-stage BAF was employed to treat domestic sewage under organic loads of 1.02 and 1.55 kg/m³·d for 15 days each. 16S rDNA high-throughput sequencing technology and redundancy analysis were applied to explore the correlation between microbial community characteristics and environmental variables. The results showed that: (1) the crucial organic-degrading bacteria in the A-stage filter were of the genus Novosphingobium, which had a significant increase in terms of relative abundance at sampling outlet A3 (135 cm of the filling height) after the increase of organic load; (2) the microbial communities at different positions in the B-stage filter were similarly affected by environmental factors, and the main bacteria associated with nitrogen removal in the B-stage filter were Zoogloea and Rhodocyclus; and (3) to improve the pollutant removal performance of this two-stage biological aerated filter, a strategy of adding an internal circulation in the B-stage filter can be adopted. Full article

The newly-isolated strain Enterobacter sp. LU1, which has previously been shown to be an effective producer of succinic acid on glycerol with the addition of lactose, was used for further intensive works aimed at improving the production parameters of the said process. The introduction of an initial stage of gentle culture aeration allowed almost 47 g/L of succinic acid to be obtained after 168 h of incubation, which is almost two times faster than the time previously taken to obtain this amount. Furthermore, the replacement of glycerol with crude glycerin and the replacement of lactose with whey permeate allowed the final concentration of succinic acid to be increased to 54 g/L. Considering the high content of yeast extract (YE) in the culture medium, tests were also performed with a reduced YE content via its partial substitution with urea. Although this substitution led to a deterioration of the kinetic parameters of the production process, using the fed-batch strategy, it allowed a succinic acid concentration of 69 g/L to be obtained in the culture medium, the highest concentration ever achieved using this process. Furthermore, the use of microaerophilic conditions meant that the addition of lactose to the medium was not required, with 37 g/L of succinic acid being produced on crude glycerol alone. Full article

Hardwood spent sulfite liquor (HSSL) is a by-product from pulp industry with a high concentration of pentose sugars, besides some hexoses suitable for bioethanol production by Scheffersomyces stipitis. The establishment of optimal aeration process conditions that results in specific microaerophilic conditions required by S. stipitis is the main challenge for ethanol production. The present study aimed to improve the ethanol production from HSSL by S. stipitis through a two-stage aeration fermentation. Experiments with controlled dissolved oxygen tension (DOT) in the first stage and oxygen restriction in the second stage were carried out. The best results were obtained with DOT control at 50% in the first stage, where the increase of oxygen availability provided faster growth and higher biomass yield, and no oxygen supply with an agitation rate of 250 rpm, in the second stage allowed a successful induction of ethanol production. Fermentation using 60% of HSSL (v/v) as substrate for S. stipitis provided a maximum specific growth rate of 0.07 h⁻¹, an ethanol productivity of 0.04 g L h⁻¹ and an ethanol yield of 0.39 g g⁻¹, respectively. This work showed a successful two-stage aeration strategy as a promising aeration alternative for bioethanol production from HSSL by S. stipitis. Full article