A study of Reactive Red 198 adsorption on iron filings from aqueous solutions

Nickel (Ni) phytotoxicity and detoxification mechanisms: A review

Scientists studying the environment, physiology, and biology have been particularly interested in nickel (Ni) because of its dual effects (essentiality and toxicity) on terrestrial biota. It has been reported in some studies that without an adequate supply of Ni, plants are unable to finish their life cycle. The safest Ni limit for plants is 1.5 μg g^-1, while the limit for soil is between 75 and 150 μg g^-1. Ni at lethal levels harms plants by interfering with a variety of physiological functions, including enzyme activity, root development, photosynthesis, and mineral uptake. This review focuses on the occurrence and phytotoxicity of Ni with respect to growth, physiological and biochemical aspects. It also delves into advanced Ni detoxification mechanisms such as cellular modifications, organic acids, and chelation of Ni by plant roots, and emphasizes the role of genes involved in Ni detoxification. The discussion has been carried out on the current state of using soil amendments and plant-microbe interactions to successfully remediate Ni from contaminated sites. This review has identified potential drawbacks and difficulties of various strategies for Ni remediation, discussed the importance of these findings for environmental authorities and decision-makers, and concluded by noting the sustainability concerns and future research needs regarding Ni remediation.

Phytoremediation of Toxic Metals: A Sustainable Green Solution for Clean Environment

Contamination of aquatic ecosystems by various sources has become a major worry all over the world. Pollutants can enter the human body through the food chain from aquatic and soil habitats. These pollutants can cause various chronic diseases in humans and mortality if they collect in the body over an extended period. Although the phytoremediation technique cannot completely remove harmful materials, it is an environmentally benign, cost-effective, and natural process that has no negative effects on the environment. The main types of phytoremediation, their mechanisms, and strategies to raise the remediation rate and the use of genetically altered plants, phytoremediation plant prospects, economics, and usable plants are reviewed in this review. Several factors influence the phytoremediation process, including types of contaminants, pollutant characteristics, and plant species selection, climate considerations, flooding and aging, the effect of salt, soil parameters, and redox potential. Phytoremediation’s environmental and economic efficiency, use, and relevance are depicted in our work. Multiple recent breakthroughs in phytoremediation technologies are also mentioned in this review.

Direct red 81 adsorption on iron filings from aqueous solutions; kinetic and isotherm studies

Direct Red 81 (DR-81) dye with a very high water solubility is widely used in many industries particularly textile industries. This study aimed to evaluate the practicability of using iron filings for the adsorption of DR-81 dye from the aqueous solutions. The effects of pH, adsorbent dose, initial DR-81 dye concentration, and adsorption time on adsorption process were also evaluated. The maximum of adsorption efficiency of DR-81 dye achieved in the optimum pH: 3, adsorbent dose: 2.5 g/L, contact time: 30 min, and initial dye concentration: 50 mg/L. The dye adsorption efficiency is increased by increasing the adsorbent dose and adsorption time. The kinetic and isotherm studies indicated that the adsorption process obeys a pseudo-first-order and Langmuir isotherm models. The experimental studies indicated that iron filings had the potential to act as an alternative adsorbent to remove the DR-81 dye from an aqueous solution.

The application of plant growth regulators to improve phytoremediation of contaminated soils: A review

Soil contamination is one of the most important environmental problems around the world. The transfer of organic contaminants and heavy metals to the food chain is a major threat to human health. Purging these contaminants often involves a lot of energy and complex engineering processes. Phytoremediation technology can be used in various environments, such as water, soil, and air, to reduce or eliminate different contaminants. The major mechanisms involved in phytoremediation include plant extraction, rhizofiltration, plant evaporation, plant stabilization, plant decomposition, and rhizosphere degradation. The efficiency of phytoremediation can be increased through using chelating and acidifying agents, applying electric current in the soil, using organic chemicals and fertilizers, planting transgenic plants, using bacteria, and applying plant growth regulators. Recently, the use of plant growth regulators has been investigated as a suitable method for improving the efficacy of phytoremediation. Effective plant growth regulators to improve phytoremediation include auxins, gibberellins, cytokinins, and salicylic acid. The activity of these materials depends on their concentration, environmental factors that affect their absorption, and the physiological state of the plant. Using these materials increases the biomass of the plant and reduces the negative effects of the presence of contaminants in the plant. The present study aimed to review the latest studies performed on the improvement of phytoremediation using plant growth regulators and their mechanisms.

Investigation of a new double-stage aerobic-anoxic continuous-flow cyclic baffled bioreactor efficiency for wastewater nutrient removal

Nitrogen and phosphorus are among the potential pollutants of receptive water sources entering into these water sources via sewage, which are not sufficiently treated. The purpose of this study is to investigate the efficiency of a new two-stage aerobic-anoxic continuous-flow baffled cycling reactor (CFBCR) to reduce nitrogen and phosphorus load from wastewater. Therefore, a double-stage baffled reactor was used in which the second part was integrated with the settling part causing the sludge to be spontaneously returned to the second reservoir. Additionally, the effect of different concentrations of chemical oxygen demand (COD) of 400-800 mg/L, ammonia of 40-60 mg/L, phosphate of 12-20 mg/L, internal rate of return of 100-200% and the retention time of 18-30 h was investigated. Furthermore, to investigate the performance of this reactor, four phases with different aeration and mixing conditions were designed. The percentage of ammonia removal with influent concentration of 40 mg/L in phase 2 with intermittent mixing and one-hour aeration time was 98.7%; effluent nitrate average concentration was 8.4 mg/L NO₃-N, and phosphate removal percent was 83%. The best nutrient removal efficiency was with the retention time of 24 h and internal return rate of 150%. In conclusion, CFBCR reactor with continuous influent and effluent and reduction of the need for sludge return, has the potential to be applied to remove nutrients from wastewater.

Removal of arsenic from aqueous solutions using waste iron columns inoculated with iron bacteria

Arsenic contamination of water resources is one of the serious risks threatening natural ecosystems and human health. This study investigates arsenic removal using a waste iron column with and without iron bacteria in continuous and batch phases. In batch experiments, the effects of pH, contact time, initial concentration of arsenic and adsorbent dose were investigated. Results indicated that the highest arsenate removal efficiency occurred at pH 7 (96.76%). On increasing the amount of waste iron from 0.25 to 1 g, the removal rate changed from about 42.37%-96.70%. The results of continuous experiments on the column containing waste iron showed that as the empty bed contact time increased from 5 to 60 min, the secondary arsenate concentration changed from 23 to 6 µg/l. In experiments involving a waste iron column with iron bacteria, an increase in residence time from 5 to 60 min decreased the secondary arsenate concentration from 14.97 to 4.86 µg/l. The results of this study showed that waste iron containing iron bacteria is a good adsorbent for removal of arsenic from contaminated water.