Removal Mechanisms of Slag against Potentially Toxic Elements in Soil and Plants for Sustainable Agriculture Development: A Critical Review

Potentially toxic element (PTE) pollution is a major abiotic stress, which reduces plant growth and affects food quality by entering the food chain, and ultimately poses hazards to human health. Currently, the use of slag in PTE-contaminated soils has been reported to reduce PTEs and toxicity in plants. This review highlights the role of slag used as a fertilizer for better crop production and sustainable agricultural development. The application of slag increased the growth, yield, and quality of crops under PTE toxicity. The mechanisms followed by slag are the immobilization of PTEs in the soil, enhancement of soil pH, changes in the redox state of PTEs, and positive changes in soil physicochemical and biological properties under PTE toxicity. Nevertheless, these processes are influenced by the plant species, growth conditions, imposition length of stress, and type of slag used. The current review provides an insight into improving plant tolerance to PTE toxicity by slag-based fertilizer application and highlights the theoretical basis for applying slag in PTE-contaminated environments worldwide.

Ammonium Cycling and Nitrification Stimulation during Oil Sludge Remediation by Gram-Positive Bacteria Lysinibacillus sphaericus Using Red Wiggler Earthworm Eisenia fetida

The performance of a mixture between L. sphaericus and E. fetida was evaluated for ammonium cycling and nitrifying bacteria stimulation during oil sludge remediation. The addition of E. fetida significantly increased ammonium concentration (p = 0.0218) and total Colony-forming units (CFU) count p = 0.02848). However, oil sludge with worms and L. sphaericus reached lower ammonium concentrations and CFU counts than sludge with worms alone. Sludge inoculated only with L. sphaericus presented higher ammonium concentration than sludge without inoculum, but the bacterial population reached a lower density during the final days. Final DNA and RNA extractions from all treatments amplified for L. sphaericus putative amoA and Gram-negative nitrifying bacteria amoA genes correlated with diminished ammonium concentrations during the final days of the experiment. Final RNA extractions for L. sphaericus amplified for Molybdenum transporter gene suggesting possible nitrogen fixation by L. sphaericus. The addition of Red Wiggler Earthworm to oil sludge remediation systems may provide better conditions for bacterial populations to carry out hydrocarbon degradation. The addition of E. fetida to a L. sphaericus crude oil biodegradation system may improve soil ammonium concentrations and nitrifying activity, and this could be crucial in oil sludge remediation because of bacterial inhibition due to high C:N ratios. The final product of this process may be used for soil enhancement due to its richness in nutrients and beneficial bacterial populations.

Utilization of Agricultural and Livestock Waste in Anaerobic Digestion (A.D): Applying the Biorefinery Concept in a Circular Economy

There has been intense debate over the depletion of fossil fuel reserves in recent decades as well as the greenhouse gas emissions that are causing climate change. At the same time, new legislation in Greece, national policies, European policies, and realistic needs, need effective waste management and the protection of national resources. As a result, it seems a necessity to exploit waste treatments, while expanding the use of renewable energy sources. In this study, an attempt is made to focus our interest and research on a specific biomass waste stream, namely the waste biomass from the agricultural-livestock sector. The possibility of processing these wastes through the technology of biomass biorefinery with anaerobic digestion as its central process will be studied. The technology of anaerobic digestion is a process widely used for the treatment of agricultural residues and livestock waste as well as for the exploitation of energy crops (energy development, soil enhancement) mainly in countries in Europe and globally. This study reviews the biorefinery biomass technology, the energy production technology, production of biofuels, and new materials from waste biomass at the behest of the circular economy and bioeconomy. Additionally, this research will be an introduction in maximizing the potential of the full utilization of agricultural and livestock waste, and the by-products that can be produced from these processes.

Effects of Xanthan Gum Biopolymers on Gypseous Soils Characteristics

Gypseous soils are problematic soils that cause large deformations in the constructions that are built on it. Therefore, many binders have been used to reduce this impact. Traditional soil binders like lime or cement have environmental problems in terms of sustainability. Thus, sustainable substances have attracted appreciable interest in recently soil enhancement. Biomaterials are being developed to enhance geotechnical engineering properties like hydraulic conductivity, strength, and slope stability of varied soil types. This study aims at evaluating the engineering characteristics of gypseous soil treated with xanthan gum biopolymer. The tests performed on three types of gypseous soil with various gypsum contents and different properties. Gypseous soils were mixed with various contents of xanthan gum with a percentage of 2, 4, and 6. The compaction results indicated that xanthan gum decreases the maximum dry density and increases the optimum moisture content. The treated gypseous soils exhibited a low collapse potential by more than 30% - 45% with xanthan gum. The direct shear results of biopolymer treated soils showed significant shear strength gains. The results of the current study imply xanthan gum biopolymer improvement as an environmentally friendly method to improve the engineering properties of gypseous soil.

Сontrolled breeding of the psychrophilic strain G-034 VIZR of Trichoderma asperellum for fast crop residues’ polymers utilization and soil enhancement

Genus Trichoderma strains as the natural plant residues’ biodestructors, highly active antagonists of soil phytopathogens and phytoregulators with the widest range of optimum conditions for their development, are widely used in biologics development. Of particular importance in Russia’s northern regions, especially in winter crop cultivation, is the ability of a microorganism’s strain used in agro-technologies to maintain viability and target biological activity at low temperatures. In this connection, this work purpose is to select a psychrotolerant strain of T. asperellum for the rapid crop residues’ polymer utilization and soil enhancement at low temperature, as well as to evaluate its activity under laboratory and field conditions. In the work process, the following tasks were addressed: selecting psychrotolerant strains of T. asperellum with high cellulolytic activity; further controlled breeding of psychrophilic strains capable of rapid growth, active colonization of plant substrates and high sporulation at 4–8 °C; evaluating the target activity of the selected psychrophilic strain as a cellulolytic as well as antagonistic activity against cereal pathogens; obtaining laboratory samples of bioformulations by deep-surface cultivation on non-sterile peat and multirecycled wastes from the edible mushrooms production and assessing their efficacy in field small-plot trials. The methods for inoculum cultivation, sporulation capacity determination, modified wet chamber, estimating antagonistic activity and biologics’ quality, field small-plot trials management, quantitative estimates of biomass losses, cellulose and lignin content were used in the work. The active psychrophilic strain for the rapid crop residues’ polymer utilization and soil enhancement controlled breeding was selected during a four-step screening of 29 T. asperellum strains from All-Russian Research Institute of Plant Protection (VIZR) State Microorganisms’ Collection with high cellulolytic and antagonistic activities. In terms of linear growth rate, antagonistic and hyperparasitic activities at 4–8 °С, a high rate of wheat and maize stubble residues’ colonization, a perspective psychrophilic strain G-034 of T. asperellum was selected for developing the laboratory samples of biologics and for running field trials. In small-plot trials, the active maize crop residues’ decomposition under the T. asperellum G-034 influence was revealed, resulting in the complete loss of plant intact state in 12 months due to more than 80 % cellulose and 20 % lignin biodestruction. The maximum loss of maize crop residues biomass for 12 months was more than 70 %. The T. asperellum strain G-034 was active after field hibernation in an amount of ×104 cfu/g, resulting in a titer increase with seasonal temperature rising and the trophic base bioavailability growth.