Single Liners Research Articles

Are Corrosion and Material Loss a Threat for Titanium-Titanium Tapers in Total Hip Arthroplasty Modular Acetabular Components?

BackgroundExtensive research has reported on fretting corrosion and material loss for a variety of metal taper interfaces in orthopedic devices. For modular acetabular shell-liner constructs, the interfaces studied thus far have consisted of mixed-metal pairings, and the risk of fretting corrosion and material loss for the all-titanium (Ti) shell-liner taper junction in one ceramic-on-ceramic (COC) design remains poorly understood. We asked: do Ti shell-liner taper interfaces in COC total hip arthroplasty devices show in vivo evidence of (1) fretting and/or corrosion, and (2) quantifiable potential material loss? MethodsWe examined 22 shell-liner pairs and 22 single liners from retrieved COC components. The taper interface surfaces were assessed for fretting corrosion using a semiquantitative scoring method and imaged with scanning electron microscopy. A subcohort of components was measured with a coordinate measuring machine, and volumetric material loss and maximum wear depth were calculated. ResultsFretting corrosion at the taper interfaces was minimal to mild for 95% of liners and 100% of shells. Imaging revealed fretting marks within a band of corrosion on some implants and evidence of corrosion not in the proximity of mechanical damage. Estimated material loss ranged from 0.2 to 1.3 mm3 for liners, and 0.5 to 1.1 mm3 for shells. Maximum wear depth for all components was 0.03 mm or less. ConclusionsOur results indicate that, compared to other taper junctions in total joint arthroplasty, the risk of corrosion and material loss may be minimal for Ti shell-liner interfaces.

Estimation of fluorotelomer alcohol emissions from landfill cover systems

This paper presents analytical solutions for estimating emissions of fluorotelomer alcohol (FTOH), a precursor of per- and polyfluoroalkyl substances, from landfill single and composite cover liners. Single liners comprise a compacted clay liner (CCL), a geosynthetic clay liner (GCL) or a geomembrane barrier (GMB). Composite liners included a GMB underlain by a CCL or a GCL. This paper shows that for a single liner, an intact GMB reduces the FTOH emission flux by three orders of magnitudes compared with a CCL and by two orders of magnitude compared with a GCL. Also, a composite cover liner reduces FTOH emissions by at least one to three orders of magnitude relative to that of a single GMB, depending on the use of either a CCL or a GCL. The analytical solutions presented in this study can be used for the preliminary evaluation of different types of covers for mitigating FTOH emissions from landfills.

Evaluation of the suitability and optimal use of postharvest storage bag technologies and a combination thereof for maize storage in Nigeria.

The severity of postharvest losses varies considerably depending on storage method and prevalence of storage insect pests known to bore into storage bags. Polypropylene (PP) bags used by smallholder farmers in Nigeria do not provide effective protection for stored produce due to insect boring activities. Deltamethrin incorporated polypropylene, ZeroFly® (ZF) and ZeroFly® Hermetic Storage Bags are technologies with potential to improve protection of stored food commodities against insect attack. Therefore, a 12-month study was conducted in Ibadan, Nigeria to determine the suitability and potential of combined postharvest bag technologies involving ZeroFly® (hermetic and non-hermetic) bags for smallholder farmers when exposed to Sitophilus zeamais and Prostephanus truncatus infestation pressure. Cleaned but un-fumigated 50-kg lots of maize were used to fill bags in each of the following 8 treatments — PP and ZF bags alone, diatomaceous earth-treated maize in PP and ZF bags, single and double hermetic liners in ZF bags, single hermetic liner in PP bags and lastly PICS bags. Results obtained over a 12-month period showed infestation by S. zeamais, Tribolium castaneum, Cryptolestes ferrugineus and Liposcelis spp. and abundance of insect increased with storage period in PP and ZF bags without liner. The percentages of insect damaged kernels by number (IDK) were higher in PP and ZF bags without liner and were 5.4 and 16.9%, respectively; in ZeroFly bags with hermetic liners, these values were ~ 0.5%. The PP and ZF bags without liner also had higher weight loss values of 1.4 and 6.7%, respectively compared with ZeroFly bags with hermetic liners and PICS bags which had a relatively lower weight loss of =0.2%. These results indicate that the ZeroFly Hermetic bag mitigates insect infestations, thereby offering a suitable alternative towards achieving significant reduction in postharvest losses during storage.

Predicting Leachate Containing Nickel and Chromium Migration Through Single- and Double-liner System Landfill

The leachate produced in municipal solid waste landfills (MSWL) when mixed garbage decom-poses may contain heavy metals, such as nickel (Ni) and chromium (Cr), which are harmful to the environment. For this reason, it is necessary to provide landfills with liners that function as leachate barriers. In general, two liner systems are used in landfills: single and double liners. In order to calculate the capability of single and double liners to detain the migration of Ni and Cr, a description of Ni and Cr movement patterns in the liner of an MSWL is needed. Therefore, this research aimed to simulate the contaminant migration patterns of Ni and Cr. The initial concentrations of Ni and Cr above the liner layer were established as 4.5 mg/l and 7 mg/l, re-spectively. The study results indicate a significant decline in Ni and Cr concentrations after the contaminants pass through the semi-permeable layer of the liner. Meanwhile, other simulation results suggest that Ni and Cr concentrations in the natural soil increase slightly after a landfill has been operating for 15 years due to the accumulation of contaminants in the preceding years.

Insight into hydraulic conductivity testing of geosynthetic clay liners (GCLs) exhumed after 5 and 7 years in a cover

Four geosynthetic clay liners (GCLs) serving as single liners were exhumed from below 0.7 m of silty sand on a 3:1 (horizontal:vertical) north-facing slope at the QUELTS site in Godfrey, Ontario, after 5 and 7 years. The 300 mm GCL overlaps with 0.4 kg/m supplemental bentonite were all physically intact. The exchangeable bound sodium was completely replaced with divalent cations. The GCL with the smallest needle-punched bundle size (average of 0.7 mm) and percentage area covered by bundles (4%) maintained low hydraulic conductivity (k) when tested under 0.07–1.2 m head with 10 mmol/L CaCl2solution as the permeant. For GCLs with larger bundles (1.1–1.6 mm) and higher percentage area covered by bundles (9%–14%), k was low when the head was low (0.07 m). Once the applied head increased, k increased by 1–4 orders of magnitude depending on the (i) hydraulic gradient, (ii) size and number of the needle-punched bundles, and (iii) structure and mass of the bentonite per unit area. The results suggest that the GCLs can perform effectively as a single hydraulic barrier in covers providing that the head above the GCL is kept low (e.g., by a suitable drainage layer above the GCL).

Long-term performance of contaminant barrier systems

This lecture describes the latest findings with respect to the long-term performance of modern municipal solid waste (MSW) landfill barrier systems. Field data relating to the clogging of leachate collection systems and the latest techniques for predicting their performance are examined. It is indicated that the primary leachate collection systems may have service lives that range from less than a decade to more than a century, depending on the design details, waste characteristics and mode of operation. Recent data indicate that landfill liner temperatures can be expected to reach at least 30–40°C for normal landfill operations. With recirculation of leachate the liner temperature increases faster than under normal operating conditions, and may be expected to exceed 40°C. Temperatures (up to 40–60°C) may occur at the base of landfills where there is a significant leachate mound. Temperature is shown to have a significant impact on both contaminant migration and the service life of the liner system. Field measurements and theoretical calculations show that composite liners are substantially better than single liners in terms of controlling leakage from landfills. Also, the leakage rates with a composite liner are very small, and diffusion will dominate as a transport mechanism for contaminants that can readily diffuse through a geomembrane (GM). Composite liners involving a GM over a geosynthetic clay liner (GCL) gave rise to substantially less leakage than those involving a compacted clay liner (CCL). The observed leakage through composite liners can be explained by the holes in, or adjacent to, wrinkles/waves in the GM, and this leakage can be calculated using simple equations. High-density polyethylene (HDPE) GMs provide an excellent diffusive barrier to ions. However, some organic compounds readily diffuse through HDPE GMs, and a combination of GM and an adequate thickness of liner and attenuation layer are required to control impact to negligible levels. The long-term performance of HDPE GMs is discussed. Based on the currently available data, the service life for HDPE GM in MSW landfill is estimated to be about 160 years for a primary liner at 35°C and greater than 600 years for a secondary GM provided it is at a temperature of less than 20°C. Clay liners are susceptible to both shrinkage and cracking during construction (due to heating by solar radiation or freezing) and after placement of the waste (due to temperature gradients generated by the waste). The former can be controlled by quickly covering the liner with a suitable protection layer. The latter can be controlled by appropriate design. The use of numerical models for predicting the service lives of engineered systems and long-term contaminant transport is demonstrated.

Geosynthetic clay liners

Over the past decade, geosynthetic clay liners (GCLs) have gained widespread popularity as a substitute for compacted clay liners in cover systems and composite bottom liners. They are also used as environmental protection barriers in transportation facilities or storage tanks, and as single liners for canals, ponds or surface impoundments. As a result, they are being investigated intensively, especially in regard to their hydraulic and diffusion characteristics, chemical compatibility, mechanical behaviour, durability and gas migration. In this paper, a review of the main findings is presented with the focus on the critical aspects affecting the service life of GCLs. From this work, a general insight is gained on the design implications for systems that incorporate GCLs.

Evaluation of Landfill‐Liner Designs

The effectiveness of landfill‐liner designs is evaluated in terms of the slope, drainage length, and saturated hydraulic conductivity of the lateral drainage layer, the saturated hydraulic conductivity of the soil liner, and the fraction of the area under a synthetic liner where leakage is occurring. The evaluation is performed using Version 1 of the Hydrologic Evaluation of Landfill Performance (HELP) model. The effectiveness is quantified by comparing the lateral drainage rate to the vertical percolation rate expressed as percentages of the total inflow. The two multiple‐liner systems specified in the Hazardous and Solid Waste Amendments (HSWA) minimum technology guidance are shown to have different leakage‐detection characteristics. One system detects significant leakage before leakage percolates out of the landfill, whereas the other system detects leakage only after significant leakage percolates out of the landfill. Four other designs were also examined—two with single liners and two with double liners. The two HSWA designs detected leakage at lower synthetic‐liner‐leakage fractions, but all designs with composite liners were nearly equally effective in reducing leakage from landfills.