Control of hydrogen sulfide emissions using autotrophic denitrification landfill biocovers: engineering applications

Hydrogen sulfide (H₂S) emitted from construction and demolition waste landfills has received increasing attention. Besides its unpleasant odor, longterm exposure to a very low concentration of H₂S can cause a public health issue. In the case of construction and demolition (C&D) waste landfills, where gas collection systems are not normally required, the generated H₂S is typically not controlled and the number of treatment processes to control H₂S emissions in situ is limited. An attractive alternative may be to use chemically or biologically active landfill covers. A few studies using various types of cover materials to attenuate H₂S emissions demonstrated that H₂S emissions can be effectively reduced. In this study, therefore, the costs and benefits of H₂S-control cover systems including compost, soil amended with lime, fine concrete, and autotrophic denitrification were evaluated. Based on a case-study landfill area of 0.04 km², the estimated H₂S emissions of 80900 kg over the 15-year period and costs of active cover system components (ammonium nitrate fertilizer for autotrophic denitrification cover, lime, fine concrete, and compost), ammonium nitrate fertilizer is the most cost effective, followed by hydrated lime, fine concrete, and yard waste compost. Fine concrete and yard waste compost covers are expensive measures to control H₂S emissions because of the large amount of materials needed to create a cover. Controlling H₂S emissions using fine concrete and compost is less expensive at landfills that provide on-site concrete recovery and composting facilities; however, ammonium nitrate fertilizer or hydrated lime would still be more cost effective applications.     

Integrating attachment style,vigor at work,and extra‐role performance

This paper presents and tests a model of the impact of secure and insecure attachment styles (secure, counterdependent, and overdependent) on citizenship behavior and workplace deviance behavior through vigor at work. Employees who exhibit secure attachment styles are proposed to exhibit more vigor at work because of more effective use of physical, emotional, and cognitive resources which translates into increased organizational citizenship behaviors (OCBs) and decreased deviance. Insecurely attached employees are hypothesized to exhibit the opposite pattern. In a sample of 331 repair generalists in a large building facilities and maintenance organization, results indicate that attachment styles indirectly predicted OCBs and deviance through vigor. Implications of these results for attachment style, vigor at work, OCBs, and deviance are discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Commentary: legal minimum tread depth for passenger car tires in the U.S.A.--a survey

Available tire traction is a significant highway safety issue, particularly on wet roads. Tire-roadway friction on dry, clean roads is essentially independent of tread depth, and depends primarily on roadway surface texture. However, tire-wet-roadway friction, both for longitudinal braking and lateral cornering forces, depends on several variables, most importantly on water depth, speed and tire tread depth, and the roadway surface texture. The car owner-operator has control over speed and tire condition, but not on water depth or road surface texture. Minimum tire tread depth is legislated throughout most of the United States and Europe. Speed reduction for wet road conditions is not.A survey of state requirements for legal minimum tread depth for passenger vehicle tires in the United States is presented. Most states require a minimum of 2/32 of an inch (approximately 1.6 mm) of tread, but two require less, some have no requirements, and some defer to the federal criterion for commercial vehicle safety inspections. The requirement of 2/32 of an inch is consistent with the height of the tread-wear bars built in to passenger car tires sold in the United States, but the rationale for that requirement, or other existing requirements, is not clear. Recent research indicates that a minimum tread depth of 2/32 of an inch does not prevent significant loss of friction at highway speeds, even for minimally wet roadways. The research suggests that tires with less than 4/32 of an inch tread depth may lose approximately 50 percent of available friction in those circumstances, even before hydroplaning occurs. It is concluded that the present requirements for minimum passenger car tire tread depth are not based upon rational safety considerations, and that an increase in the minimum tread depth requirements would have a beneficial effect on highway safety.