Reclaiming salt-affected soils using electro-remediation technology: PCPSS evaluation

Effect of experimental boundary conditions and treatment-time on the electro-desalination of soils

This study investigates the effect of boundary conditions and treatment-time on the electro-desalination of artificially-contaminated soil. The effect of ion exchange membranes (IEM), calcium chloride (CaCl2), and ethylenediaminetetraacetic acid (EDTA) on the removal of salt (i.e., Na+, Cl-, and Ca2+) and metal (i.e., Co2+ and Fe2+) ions from the soil by electrokinetic (EK) was studied. The outcomes demonstrate that an increase in treatment-time decreases the electroosmosis and ion removal rate, which might be attributed to the formation of acid-base fronts in soil, except in the IEM case. Because a high pH jump and electroosmotic flow (EOF) of water were not observed within the soil specimen due to the IEM, the removal of ions was only by diffusion and electromigration. The collision of acid-base fronts produced a large voltage gradient in a narrow soil region with a reduced electric field (EF) in its remaining parts, causing a decrease in EOF and ion transport by electromigration. The results showed that higher electroosmosis was observed by using CaCl2 and EDTA; thus, the removal rate of Co2+, Na+, and Ca2+ was greater than Cl- due to higher EOF. However, for relatively low EOF, the removal of Cl- exceeded that of Co2+, Na+, and Ca2+, possibly due to a lack of EOF. In addition, the adsorption of Fe2+ in soil increased with treatment-time due to the corrosion of the anode during all EK experiments except in the case of IEM, where an anion exchange membrane (AEM) was introduced at the anode-soil interface.

Impact of cellulose and lignin on restoration of vegetation and soil chemical properties for saline-alkali soil of songnen plain

To explore the effects of cellulose and lignin on stimulating vegetation restoration and improving soil chemical properties in saline-alkali soil, a large area test was carried out, and 2 treatments were set up: T (cellulose and lignin+ Planted seeds) and CK (Planted seeds). In this study, the species, quantity, plant height, above-ground biomass, biodiversity of vegetation in the treated plots, the determination of soil chemical nutrient content, and the effect of cellulose and lignin on vegetation restoration in saline-alkali land were investigated. The results showed that: 1) Cellulose and lignin contributed to vegetation growth. Compared with CK treatment, plant height and aboveground biomass of T increased by 158.73% and 240.13%, respectively; 2) Cellulose and lignin improved soil structure, and soil porosity, and decreased soil compaction (21.95%); 3) Compared with CK treatment, T treatment decreased soil pH by 0.5 units, total salt content decreased by 30.95%, exchangeable Na+ decreased by 63.00%, and exchangeable sodium percentage (ESP) decreased by 61.51%. Furthermore, cellulose and lignin effectively improved the physical and chemical properties of saline-alkali soil, promoted the recovery of ecological environment in saline-alkali soil, and improved regional biodiversity, which will provide new methods for soil remediation and improvement in saline-alkali areas.

Green synthesis of ZnO, MgO and SiO2 nanoparticles and its effect on irrigation water, soil properties, and Origanum majorana productivity

The synthesis of different metal oxide nanoparticles (NPs) (e.g., ZnO, MgO and SiO₂) using green methods is a promising alternative to traditional chemical methods. In this work, ZnO, MgO, and SiO₂ NPs were prepared using lemon peel extract. The synthesized NPs were characterized using Fourier transform infrared spectroscopy, UV–Visible spectroscopy, X-ray diffraction, and transmission electron microscopy. Also, the effects of the green synthesis of different NPs on the irrigation water quality, the availability of some heavy metals in soil and plants, and the productivity of Origanum majorana (marjoram) were studied in detail. The obtained results showed that the addition of the NPs resulted in noticeable variations in the removal percentages of Cu²⁺ and Fe³⁺ from aqueous solutions. The maximum values obtained for the adsorption of Cu(II) on ZnO, MgO, and SiO₂ NPs within the pH values of 3–5 were 89.9%, 83.3%, and 68.36%, respectively. Meanwhile, the maximum adsorption values of Fe(III) at pH 3.3 were 82%, 80%, and 65% for ZnO, MgO, and SiO₂ NPs, respectively. Clearly, the application of the NPs effectively reduced the available Cu²⁺ in the studied soil samples in the following order: Zn2 > Zn1 > Mg2 > Si2 > Mg1 > Si1 > C (control). The highest values of available Cu²⁺ were observed in the control treatment, whereas the lowest values were obtained when Zn2 was added. The same tendencies were observed with substantial concentrations of Fe. The addition of NPs to the soil samples positively affected the plants' Cu²⁺ uptake. The effects of NPs and the additions of Cu²⁺ and Fe³⁺ on the availability of nitrogen, phosphorus, and potassium (NPK) in the soil system were very completed and osculated from one treatment to another. The same tendencies were observed with the total concentration of NPK in plants.

Construction and analysis of an artificial consortium based on the fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 to produce the platform chemical 3-hydroxypropionic acid from CO2

BACKGROUND

Cyanobacterial carbohydrates, such as sucrose, have been considered as potential renewable feedstock to support the production of fuels and chemicals. However, the separation and purification processes of these carbohydrates will increase the production cost of chemicals. Co-culture fermentation has been proposed as an efficient and economical way to utilize these cyanobacterial carbohydrates. However, studies on the application of co-culture systems to achieve green biosynthesis of platform chemicals are still rare.

RESULTS

In this study, we successfully achieved one-step conversion of sucrose derived from cyanobacteria to fine chemicals by constructing a microbial consortium consisting of the fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 and Escherichia coli to sequentially produce sucrose and then the platform chemical 3-hydroxypropionic acid (3-HP) from CO₂ under photoautotrophic growth conditions. First, efforts were made to overexpress the sucrose permease-coding gene cscB under the strong promoter P _cpc560 in S. elongatus UTEX 2973 for efficient sucrose secretion. Second, the sucrose catabolic pathway and malonyl-CoA-dependent 3-HP biosynthetic pathway were introduced into E. coli BL21 (DE3) for heterologous biosynthesis of 3-HP from sucrose. By optimizing the cultivation temperature from 37 to 30 °C, a stable artificial consortium system was constructed with the capability of producing 3-HP at up to 68.29 mg/L directly from CO₂. In addition, cell growth of S. elongatus UTEX 2973 in the consortium was enhanced, probably due to the quick quenching of reactive oxygen species (ROS) in the system by E. coli, which in turn improved the photosynthesis of cyanobacteria.

CONCLUSION

The study demonstrated the feasibility of the one-step conversion of sucrose to fine chemicals using an artificial consortium system. The study also confirmed that heterotrophic bacteria could promote the cell growth of cyanobacteria by relieving oxidative stress in this microbial consortium, which further suggests the potential value of this system for future industrial applications.

Current states and challenges of salt-affected soil remediation by cyanobacteria

Natural and human activities lead to soil degradation and soil salinization. The decrease of farmlands threatens food security. There are approximately 1 billion ha salt-affected soils all over of world, which can be made available resources after chemical, physical and biological remediation. Nostoc, Anabaena and other cyanobacterial species have outstanding capabilities, such as the ability to fix nitrogen from the air, produce an extracellular matrix and produce compatible solutes. The remediation of salt-affected soil is a complex and difficult task. During the past years, much new research has been conducted that shows that cyanobacteria are effective for salt-affected soil remediation in laboratory studies and field trials. The related mechanisms for both salt tolerance and salt-affected soil remediation were also evaluated from the perspective of biochemistry, molecular biology and systems biology. The effect of cyanobacteria on salt-affected soil is related to nitrogen fixation and other mechanisms. There are complicated interactions among cyanobacteria, bacteria, fungi and the soil. The interaction between cyanobacteria and salt-tolerant plants should be considered if the cyanobacterium is utilized to improve the soil fertility in addition to performing soil remediation. It is critical to re-establish the micro-ecology in salt-affected soils and improve the salt affected soil remediation efficiency. The first challenge is the selection of suitable cyanobacterial strain. The co-culture of cyanobacteria and bacteria is also potential approach. The cultivation of cyanobacteria on a large scale should be optimized to improve productivity and decrease cost. The development of bio-remediating agents for salt-affected soil remediation also relies on other technical problems, such as harvesting and contamination control. The application of cyanobacteria in salt-affected soil remediation will reconstruct green agriculture and promote the sustainable development of human society.