Civil & Environmental Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2221
Browse
4 results
Search Results
Item Effects of Slope Ratio, Straw Mulching, and Compost Amendment on Vegetation Establishment and Runoff Generation(2020) Owen, Dylan; Davis, Allen P; Aydilek, Ahmet; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soil erosion management is a major environmental challenge facing highway construction. This study was undertaken to evaluate the effectiveness of compost use in lieu of topsoil for final grade turfgrass establishment on highway slopes. Two compost types, biosolids and greenwaste, and four compost/topsoil blends were compared with a topsoil standard (TS; with straw and fertilizer application) in their ability to reduce soil and nutrient loss and improve vegetation establishment. A series of greenhouse studies and field tests were conducted to analyze the effects of slope ratio, straw mulching, and compost mixing ratio on runoff by observing green vegetation (GV) establishment, runoff volume generation, and nutrient and sediment export. GV was measured using an innovative image segmentation and classification algorithm coupled with machine learning approaches with varying block size and classification acceptance thresholds. Algorithm classifications were compared to manual coverage classifications with R-squared values of 0.86 for GV, 0.87 for straw/dormant vegetation, and 0.96 for exposed soil, respectively. Straw mulching (≥95% straw cover) reduced evaporation rates and soil sealing and increased soil roughness and field capacity (FC), which significantly reduced volume runoff (34-99%) and mass export of sediment and nutrients (81-91%). With mulching, no statistical differences were found in GV establishment among the compost and TS treatments (≥95% cover in 60 days) while non-mulched media cover reached a maximum of 35%, due to limited moisture availability. Composted material (excluding 2:1 compost: topsoil mixtures) had higher hydraulic conductivity, FC, and shear strength than TS which, combined with straw mulching, reduced total runoff volume by 33-72%. This led to sediment and nutrient mass reductions of 57-97% and 6-82%, respectively, from standard TS. A general increase in runoff generation and decrease in GV was seen with slope ratio increase (41-96% more nutrient and sediment export and 81-97% lower GV from 20:1 to 2:1 slopes). However, benefits displayed at 25% slope were reduced at shallower slopes and enhanced at greater slopes. The use of compost as an additive or replacement to TS, with straw mulching, was seen to reduce runoff generation and improve runoff quality from the TS standard and is suggested as possible alternatives.Item HYDRAULIC COMPATIBILITY OF GEOTEXTILE-COMPOST SYSTEMS IN LANDFILL COVERS(2019) Ryoo, Sung Chun; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As annual generation of municipal solid waste increases every year, sustainable practices must be promoted in landfill construction. Landfill covers are required by federal regulation to cap the municipal solid waste and to prevent leachate formation. The use of compost as the vegetative layer in landfill final covers is one way to improve the sustainability of landfills. Current literature on compost shows it to be a superior vegetative facilitation material compared to the traditional topsoil material. In order to successfully use compost in landfill cover applications, hydraulic compatibility of the compost and underlying geotextile filters must be adequate. The hydraulic compatibility of various compost, topsoil, and geotextiles have been explored by performing long-term filtration (LTF) tests. Upon completion of the LTF tests, particle size analysis, permittivity tests, piping measurements, and image analysis were conducted to determine clogging and retention performances. When the clogging ratios and piping measurements were considered, every compost-geotextile and topsoil-geotextile combinations yielded acceptable clogging and retention performance. A parametric study was conducted to determine if different characteristic pore size and grain sizes influenced the laboratory observed clogging ratios; currently, no relationships exist. Existing filter selection criteria successfully predicted retention behavior and failed to predict clogging behavior. Conducting more soil-geotextile compatibility tests will be needed to propose a new filter criterion for clogging. Based on limited LTF data, compost is not likely to promote clogging in geotextiles; however, additional leaching and geotechnical tests are required to assess the nutrient leaching and shear behavior of compost layers on landfill cover slopes.Item Nutrient Leaching from Bioretention Amended with Source-Separated Compost(2016) Owen, Dylan; Davis, Allen P; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bioretention has been noted to be an effective stormwater control measure (SCM). Compost addition to bioretention could be beneficial, but could also act as a source for excess nutrients. This project analyzed possible nitrogen (N) and phosphorus (P) leaching from bioretention soil media (BSM) amended with source-separated compost. Columns were mixed with compost and BSM at volumes of 30%, and 15%. A final column had 15% compost and an additional 4% water treatment residual (WTR). Synthetic stormwater was applied to each column and the effluent was analyzed for N and P. The 30% column increased the mass exported for both nutrients. Both 15% columns had a net zero effect on nitrogen, but the 15%+WTR column reduced the exported phosphorus load. All compost columns discharged more nutrients than standard BSM. Compost addition should be minimized in bioretention, less than 15% by volume, and WTR should be added to control phosphorus leaching.Item Mitigation of High Alkalinity in Leachates of Aged Steel Slag(2015) Ozkok, Enes; Davis, Allen P; Aydilek, Ahmet H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Steel slag, an abundant by-product of the steel-making industry, after it is aged, has a huge potential for use as an aggregate in road construction. However, the high pH of steel slag seepage (pH≥12) is a major impediment in its beneficial use. Analyses on aged steel slag samples demonstrated that the alkalinity producing capacity of aged steel slag samples strongly correlated to Ca(OH)2 dissolution and that prolonged aging periods have marginal effects on overall alkalinity. Treatment methods that included bitumen-coating, bathing in Al(III) solutions and addition of an alum-based drinking water treatment residual (WTR) were evaluated based on reduction in pH levels and leachate alkalinity. 10% (wt./wt.) alum-based drinking water treatment residual (WTR) addition to slag was determined to be the most successful mitigation method, providing 65−70% reduction in alkalinity both in batch-type and column leach tests, but final leachate pH was only 0.5−1 units lower and leachates were contaminated by dissolved Al(+III) (≥3−4 mM). Based on the interpretation of calculated saturation indices and SEM and EDX analyses, formation of calcium sulfoaluminate phases (i.e., ettringite and monosulfate) was suggested as the mechanism behind alkalinity mitigation upon WTR-modification. The residual alkalinity in WTR-amended slag leachates was able to be completely eliminated utilizing a biosolids compost with high base neutralization capacity. In column leach tests, effluent pH levels below 7 were maintained for 58−74 pore volumes worth of WTR-amended slag leachate using 0.13 kg compost (dry wt.) per 1 kg WTR-amended slag on average; also, dissolved Al(+III) was strongly retained on the compost.