Critical review on arsenic: Its occurrence, contamination and remediation from water and soil

With the increasing pollution in today’s world, importance is being given to solve a problem and do it in a sustainable, eco-friendly manner. Arsenic is a class-1 carcinogen and also causes many other side effects to humans, plants and animals. The utilization of arsenic as wood preservatives, pesticides, or its historical overuse by some military units for rice killing operations has led to the increase in the toxic effects of arsenic like its carcinogenicity, decreased immune response etc. Although conventional methods like coagulation, lime softening, adsorption, membrane technology are effective, they have their disadvantages like additional waste generation, causing increased pollution and are expensive. The better alternative is phytoremediation. Appropriate plants like Brassica juncea, Hydrilla verticilata, Pteris vittata L., Vallisneria natans, can be chosen based on the method of the remediation like phytoextraction, phytostabilization and phytofiltration or phytovoltalization. This review provides the list of a few plants which can be likely chosen for the purpose of both water and soil remediation. Advancements are occurring in bioremediation studies with the development of transgenic plants like transgenic tobacco, transgenic Arabidopsis thaliana for better phytoremediation. Understanding the mechanism employed by the plant for its uptake/detoxification can aid in the enhancement of the process of remediation with the external supply of phosphorus. Along with this, the proper and safe disposal of plants is crucial for the remediation process. In addition, awareness of this solution to the general public is to be made for its effectiveness.

Swelling behaviours of compacted lime-softening sludge for application in landfill liners

The objective of this study was to investigate the swelling potential of compacted lime-softening sludge for application in landfill liners. The study involved the assessment of the effect of compaction and moulding moisture content (30–40%), corresponding to the Proctor standard compaction test. One-dimensional oedometer swell tests were conducted using distilled water, tap water, and municipal landfill leachate, resulting in the determination of the expansion indices. Moreover, changes in the moisture content and dry density during the swelling process were investigated. The expansion index was significantly influenced by the initial moisture content and liquid chemistry. Subsequently, these factors also affected the sludge dry density decrease, and its moisture content increase, whereas the impact of the initial dry density on expansion was of low importance. An increase in the sludge moulding moisture content, limited swelling in all liquids used. The highest expansion, dry density, and moisture content changes due to swelling were identified for leachate at w < wopt. It should be underlined that the effect of liquid on the swelling potential faded away along with a further increase in the moisture content w > wopt. The novelty of the work lies in identifying a significant plunge of the expansion index at w ≈ wopt for the leachate swelling test. The lime-softening sludge non-swelling moisture content was defined as wnon ≈ (wopt + 4.0%) − (wopt + 4.5%). For practical engineering implications, the moisture content between (wopt + 2.0%) and (wopt + 4.0%) was provided for the most suitable sludge application in landfill liners.

Hydraulic Conductivity of Compacted Lime-Softening Sludge Used as Landfill Liners

The research goal was to investigate the hydraulic conductivity of compacted lime-softening sludge as a material to be applied to landfill liners. In doing so, the effect of compaction and moulding moisture content on the sludge hydraulic conductivity was assessed. An approximate polynomial k10mean at hydraulic gradients ≥30 for degree of compaction (0.95–1.05) and moulding moisture content (28%–36%) was determined. The results of short-term tap water permeation tests revealed that all hydraulic conductivity values were less than 2.5•10–8 m/s. A lowest hydraulic conductivity of 6.5•10–9 m/s, as well as a corresponding moisture content of 31% were then established. The long-term hydraulic conductivity was measured with tap water, distilled water, NaOH and HCl solutions and municipal waste leachate. The factors of permeating liquids and permeation time significantly affected the initial hydraulic conductivity. The long-term hydraulic conductivity increased for NaOH and HCl solutions and decreased for tap and distilled water. A significant reduction of hydraulic conductivity was observed for leachate permeation. The investigated material met the requirements for the liner systems of inert landfill sites regardless of pH and the limit value for hazardous and non-hazardous waste landfills.