Journal of Hazardous, Toxic, and Radioactive Waste

The objective of this paper is to evaluate the deformation behavior of clay-based landfill covers subjected to differential settlements through centrifuge model studies and finite-element analyses (FEA). A series of centrifuge tests were performed on model soil barriers subjected to continuous differential settlements through a motor-based differential settlement simulator by varying the thickness of the soil barrier with and without overburden equivalent to that of landfill coves at 40 gravities. In addition, a parametric study was carried out numerically by varying the thickness of the soil barrier and overburden pressure by using PLAXIS, a geotechnical finite-element code. The modeling considerations adopted in FEA were developed such that they are close to the centrifuge model tests in prototype dimensions. Differential settlements in FEA were assigned by using predefined displacement profiles. Results from centrifuge model tests deduce that both 0.6 and 1.2 m thick soil barriers were observed to experience full-depth cracks at the zone of maximum curvature and fail to serve the basic purpose of an effective hydraulic barrier. The results from FEA indicate the development of higher values of tensile stresses and strain extending throughout the thickness of the soil barrier at the zone of maximum curvature, which indirectly advocate the possibility of formation of tension cracking when the generated tensile stresses caused by deformation exceed the permissible tensile strength of the soil barrier material. The magnitude of the horizontal tensile stress along the top surface of the soil barrier at the zone of maximum curvature was found to be suppressed with an increase in the value of overburden pressure. When the soil barrier was subjected to an overburden pressure in the range of 50–75 kPa, there exists a complete transformation of tensile stresses to compressive stresses, which indirectly suggests that there can be no prospects of development of tension cracks even at a distortion level of 0.125.

The density of municipal solid waste (MSW) plays a significant role in the computation of landfill settlement. A methodology is developed to compute the primary and mechanical compression considering the landfill density to be constant or spatially and temporally variable. The primary and mechanical compression computed taking a constant density of refuse yields lower settlement values compared to variable density. The coefficient of compressibility was found highly sensitive in the model. The difference between constant and variable density was a decreasing rate for mechanical compression and an increasing rate for primary compression.

Disposal of hazardous and toxic waste arising out of combustible cartridge case (CCC)–based explosive munitions is an environmental issue of global concern. A large quantity of CCC waste is disposed of by open burning or detonation because there is no viable waste-disposal technology that is environmentally friendly and is found suitable for bulk treatment available at present. In the present study, the process of alkaline hydrolysis of CCC composition has been studied. It is found that CCCs waste can be suitably treated and neutralized by a simple chemical process (alkaline hydrolysis) that is eco-compliant. It is possible to recover a high proportion of nitrogen (87%) from this waste. The CCC hydrolysate can be suitably used as fertilizer for crop. Pot culture studies carried out using the hydrolysate as a fertilizer on wheat seed and plant give encouraging results of the main crop performance parameters like plant biomass, yield, plant growth, and chlorophyll content.

Batch adsorption studies were conducted to remove cutting oil from wastewater using activated lemon (species Citrus x limon) peels. The effect of various important parameters, namely, pH, dose of adsorbent, contact time, mixing speed, and initial oil concentration, and their optimum conditions for maximum sorption efficiency were studied. Batch studies indicated that adsorbent dosage of $5\mathrm{g}/\mathrm{L}$, contact time of 70 min, mixing rate of 45–50  revolutions/min, and pH of 2 provides maximum oil removal efficiency in the present study. Results indicated that the kinetics of sorption of cutting oil on powdered activated lemon peels closely follows Freundlich isotherms. A scanning electron microscope micrograph of powdered activated lemon peels before and after adsorption is presented to prove that the oil has been adsorbed by the adsorbent.

The treatment of a high-strength pharmaceutical wastewater (PW) has been carried out using two different electrochemical processes [i.e., electrocoagulation (EC) using aluminium and electrooxidation (EO) using carbon electrodes]. For EC, the main object was to study the adsorption capacity of electroflocs using the Freundlich isotherm ($R^2=0.8$) and the kinetics of adsorption by (Lagergren model) first-order ($R^2=0.88$) and second-order ($R^2=0.83$) kinetic models. For the EO process, the effect of current density (CD) in a range from 40 to $120\mathrm{A}/{\mathrm{m}}^2$ and initial pH from 3 to 11 on the treatment efficiency was studied. Under identical operating conditions (CD $80\mathrm{A}/{\mathrm{m}}^2$; pH 7.2), EC resulted in 24% after 25 min, whereas the EO yielded 35.6% chemical oxygen demand (COD) removal after 90 min of treatment. The kinetics of COD removal for EO was described by a two-stage, first-order kinetic model. Based on the cyclic voltammetric studies, the presence of chlorides was found to have an influence, resulting in indirect oxidation by the generation of chloride/hypochlorite oxidants. Response surface methodology (RSM) was found to be an effective optimization tool, which shows the optimum pH/CD/electrolysis time to be $6.56/76.06\mathrm{A}/{\mathrm{m}}^{-2}/86.89\min$ for achieving 30.89% COD removal by the EO process. The study has shown that electrooxidation treatment can be more effectively used as pre treatment to improve the biocompatibility of PW than as a direct biological treatment of PW.

The prior removal of uranium along with plutonium and neptunium from high-level waste (HLW) can simplify the subsequent actinide partitioning steps. In this context, extraction and stripping behavior of uranium, plutonium, and neptunium was investigated employing 1.1-M solutions of tri-n-butyl phosphate (TBP) and N,N-dihexyl octanamide (DHOA) dissolved in n-dodecane as extractants in the presence of $6\mathrm{g}/\mathrm{L}$ U relevant to pressurized heavy-water reactor (PHWR) high-level waste (HLW) conditions. Reductants such as acetohydroxamic acid (AHA) and hydroxyurea (HU) were evaluated for selective stripping of plutonium and neptunium over uranium from the loaded organic phases. These studies indicated the possibility of quantitative recovery of U(VI), Pu(IV), and Np(IV) from HLW solution employing either DHOA or TBP as extractant. Integration of this step in the minor actinide partitioning simplifies the treatment of HLW with the specially designed extractants like octyl(phenyl)- $N$, $N$-diisobutyl carbamoyl methyl phosphine oxide (CMPO), $N$, $N$, $N^{\prime }$, $N^{\prime }$-tetraoctyl diglycolamide (TODGA), and $N$, $N$, $N^{\prime }$, $N^{\prime }$-tetra(2-ethylhexyl) diglycolamide (TEHDGA).

This paper discusses for the first time the use of noninvasive and nondestructive microwave spectroscopy to analyze the effect of chemical treatment on the absorption properties of waste rubber aggregate material when it is reacted and heated with bitumen. Oxidation and cross-linking was used to treat the waste rubber aggregates. The surface properties of oxidized rubber were analyzed using scanning electron microscopy. The bitumen samples obtained from treated and untreated rubber-bitumen blends were analyzed using microwave spectroscopy. This technique was to measure instantaneously the reduction in absorption properties of rubber when it is reacted with bitumen after treatment, compared with the bitumen samples obtained from untreated rubber-bitumen blends before treatment. The results of the scanning electron microscopy analysis show that the surface properties of waste rubber have been changed, developing surface roughness after the oxidation process. This was consistent with the microwave spectroscopy results in which the chemical treatment successfully reduced the absorption of light fractions from bitumen to rubber. Thus, residual bitumen from treated rubber-bitumen blends is comparable with the pure bitumen in its behavior and operation. This finding will have a huge impact on industry for real-time measurement.