A critical review of municipal solid waste hydraulic conductivity: A mini review.

This study is a critical review of municipal solid waste (MSW) hydraulic conductivity that includes investigation of the influence of vertical stress, dry unit weight and degradation. A total of 56 studies were compiled that included laboratory-, pilot- and landfill-scale hydraulic conductivity experiments. Compacting waste and increasing vertical stress reduce MSW hydraulic conductivity via reshaping the pore networks throughout the waste matrix, reducing the void ratio and increasing tortuosity. However, the magnitude of reduction in hydraulic conductivity is dependent on stress, waste composition and decomposition. Solid waste decomposition can have opposing effects on hydraulic conductivity. Some studies have indicated that an increase in MSW decomposition results in particle size reduction and settlement that reduces the void ratio and decreases hydraulic conductivity. Conversely, some studies indicate that waste decomposition reduces the solid mass, which increases the void ratio and creates larger flow paths that increase hydraulic conductivity. The data compilation, observations and key findings from this study are beneficial for solid waste practitioners to improve design, analysis and operation of MSW landfills.

Influence of oil and gas exploration and production waste on municipal solid waste hydraulic conductivity.

This study evaluated the effects of addition of oil and gas exploration and production wastes (E&PW) on hydraulic behavior of municipal solid waste (MSW). A series of laboratory experiments were conducted to assess the impacts of vertical stress, waste composition, mixture ratio of MSW to E&PW based on total mass (e.g., 20% MSW + 80% E&PW), and mixing methods on hydraulic conductivity. Hydraulic conductivity (k) for MSW-E&PW mixtures with 20% and 40% E&PW contents reduced from 3 × 10-5 m/s to 10-7 m/s as vertical stress increased from 0 to 400 kPa. An increase in the mixture ratio above 60% resulted in an additional order-of-magnitude decrease in k to 10-8 m/s as vertical stress increased above 200 kPa. The addition of E&PW did not impact the available flow path, even though adding E&PW to MSW reduced the void spaces. This indicated that the waste matrix is capable of accepting E&PW while keeping the flow structure within the waste matrix. However, for vertical stress greater than 50 kPa, mixtures of MSW + 80% E&PW were observed to yield hydraulic conductivity < 10-9 m/s.

Association Between Pain Catastrophizing and Pain and Cardiovascular Changes During a Cold-Pressor Test in Athletes.

CONTEXT: Athletes are often exposed to pain due to injury and competition. Using preliminary evidence, researchers have shown that cardiovascular measures could be an objective measure of pain, but the cardiovascular response can be influenced by psychological factors, such as catastrophizing. OBJECTIVE: To use a painful cold-pressor test (CPT) to measure the relationship among catastrophizing, pain, and cardiovascular variables in athletes. DESIGN: Cohort study. SETTING: Laboratory. PATIENTS OR OTHER PARTICIPANTS: A total of 36 male rugby athletes (age = 24.0 ± 4.6 years, height = 180.0 ± 6.1 cm, mass = 90.5 ± 13.8 kg). MAIN OUTCOME MEASURE(S): We measured catastrophizing using the Pain Catastrophizing Scale and pain using a numeric pain rating scale. Cardiovascular measures were heart rate, systolic and diastolic blood pressure, and heart rate variability. RESULTS: During the CPT, participants experienced increases in pain (from 0 to 4.1 ± 2.2), systolic blood pressure (from 126.7 ± 16.5 to 149.7 ± 23.4 mm Hg), diastolic blood pressure (from 76.9 ± 8.3 to 91.9 ± 11.5 mm Hg), and heart rate variability (from 0.0164 ± 0.0121 to 0.0400 ± 0.0323 milliseconds; all P values < .001). In addition, we observed a decrease in heart rate after the CPT (P = .04). We found a correlation between athletes' pain catastrophizing and both pain intensity and change in heart rate during the CPT (P = .02 and P = .003, respectively). Linear regression indicated that pain and catastrophizing explained 29% of the variance in the change in heart rate (P = .003). CONCLUSIONS: Athletes who had catastrophizing thoughts were more likely to experience higher levels of pain and a greater cardiovascular response during a painful stimulus. The change in cardiovascular variables may be a good objective measure of pain in athletes in the future.

Hydraulic and mechanical behavior of municipal solid waste and high-moisture waste mixtures.

The objective of this study was to investigate how addition of high-moisture waste (HMW) affects the hydraulic and mechanical behavior of municipal solid waste (MSW). Direct shear and hydraulic conductivity tests were conducted on MSW, HMW, and MSW-HMW mixtures prepared with HMW contents ranging from 20% to 80% (by total mass). Direct shear tests were conducted at normal stress between 22 and 168 kPa and hydraulic conductivity tests were conducted at vertical effective stresses of approximately 50, 100, and 200 kPa. A threshold HMW content of 40% was identified corresponding to substantial change in friction angle and hydraulic conductivity of the mixtures. Municipal solid waste and MSW-HMW mixtures with less than 40% HMW had friction angles between 29° and 32° and hydraulic conductivities greater than or equal to 1.3 × 10-6 m/s. At HMW contents above 40%, the friction angle and hydraulic conductivity decreased with increasing HMW content. At 80% HMW, the hydraulic and mechanical behavior of the MSW-HMW mixture was comparable to HMW. The HMW had a friction angle of approximately 2° and hydraulic conductivity of 1.1 × 10-11 m/s at a vertical effective stress of 50 kPa. Additional direct shear tests conducted on MSW and MSW-HMW mixtures soaked in water to simulate subsequent wetting post disposal revealed a decrease in friction angle from approximately 29° to 24° for MSW mixed with 40% HMW.