| Hydraulic design and operation of leachate injection pipes in bioreactor landfills were analyzed in this study. A conceptual framework that links the physical properties and hydraulic performance of the injection pipe with the overall design of the injection system was presented. A sensitivity analysis was completed for various literature reported pipe design and operation characteristics, showing that pipe diameter, perforation spacing and shape, pipe material, inlet flow rate and hydraulic head influence the perforation discharge along the pipe length. The sensitivity analysis suggested that long perforated pipes require high inlet flow rate and hydraulic head, resulting in high differences in perforation discharge between first and last perforation along the length of the pipe. This suggests that considerations should be given to design shorter length perforated pipes to overcome any pipe hydraulic limitations to uniformly discharge liquid along the length of the pipe.; Field studies of pipes used in leachate injection and collection systems have showed that leachate transmission pipes can clog with biological, chemical and soil materials over time. Clogging can impact the operating performance and service life of the injection system. Full-scale pipes were permeated leachate to provide insights into biological, chemical, and physical clogging mechanisms involved in clogging of leachate injection pipes under pressurized conditions. Two pipe external diameters (0.05 and 0.1 m) and three different average flow rates (0.25, 0.55 and 1.2 L/s) were tested. COD leachate concentrations and pH values between influent and effluent of the pipes did not change considerably during this laboratory study, indicating that not significant removal of organic acid occurred within the pipes. Calcium was removed, ranging from 25 to 50% within the pipes, which resulted in an increase in inorganic clog accumulation within the pipes. High influent leachate pH values of 8.3 to 9.4 where measured, with higher pH occurring as flow rate within the pipe increased. Clog material accumulated on the inner surface of the pipes was physically and chemically analyzed and was mainly comprised of organic and inorganic material. Magnesium, calcium and carbonate where the main inorganic clog constituents with hydromagnesite (Mg5(CO3)4(OH)24H2O) present as the sole phase mineral. More clog material, about 2 to 4.5 times, was accumulated within the small pipe diameter (0.05 m) for similar mass loads and flow rates compared to the larger pipe diameter (0.10 m), indicating that surface area has a direct effect on clog accumulation within the pipes. The experimental results showed that pipe physical characteristics and the hydraulic operation have a direct impact on changes in leachate composition and clog development within leachate injection pipes. |
