A Model Based on Mechanics to Predict Settlements in Bioreactor Landfills

Prediction of waste settlement behavior during the construction phase of a landfill is vital to effective functioning of leachate recirculation systems and gas collection pipe network, yet prediction of waste settlement is complex and difficult to perform. Few models, are currently available which can be used to calculate landfill settlement of the entire waste thickness after closure without accounting for variation in density and other parameters with depth. By starting after closure, these models do not account for settlements during construction. The use of entire depth does not allow for the calculation of strains at different depths. When landfills are operated as bioreactors, waste decomposition and gas production are accelerated making the problem more complicated. Rapid degradation results in a significant impact on waste properties, settlement and stability. Accurate prediction of this rapid change in volume is of importance in estimating airspace, planning construction sequence, designing covers as well as planning for expansions. This paper focuses on the behavior of the density and settlements of waste with time and space and proposes a new mathematical model based on mechanics which is capable of computing settlements during construction of landfills. The impact of leachate recirculation and different waste types on settlement behavior of a landfill is also accounted in the proposed model

Leaching of heavy metals stabilized in asphalt matrix

Podle platné české legislativy je nutné nebezpečné odpady před uložením na skládku upravit tak, aby došlo ke snížení jejich nebezpečných vlastností. Jednou z metod úpravy odpadu je stabilizace/solidifikace. Pro stabilizaci odpadů můžeme použít například asfaltové emulze. Cílem stabilizace je snížení vyluhování kontaminantů do životního prostředí. Byl vypracován matematický model, který popisuje vyluhování těžkých kovů v závislosti na čase. Řídícím mechanismem je difúze kontaminantů ze stabilizovaného odpadu a jejich chemická interakce s extrakčním prostředím. V experimentální části se měřilo množství kontaminantů, které se vyluhovaly ze stabilizovaného odpadu do extrakčního činidla v závislosti na jeho pH. Na základě souvislostí mezí naměřenými hodnotami a matematickým modelem byl proveden střednědobý odhad množství vyluhovaných těžkých kovů z úložiště odpadu do životního prostředí.Long-term impact of stabilized/solidified hazardous waste on the environment was evaluated using a combination of long-term leaching tests and mathematical modelling. The waste used in this research is a dust collected from filters used in the production of nickel-cadmium accumulators. It contains nickel hydroxide, cobalt hydroxide and cadmium oxide, and based on Toxicity Characteristic Leaching Procedure (TCLP) test it is a hazardous waste. This waste was stabilized using two different aqueous anionic asphalt emulsions. Several extraction tests were used to evaluate the long-term leaching of stabilized waste. Then using a mathematical model, the long-term leaching test data was analyzed to obtain mass transport parameters for the contaminants in the stabilized wastes. From the leaching test results mathematical model parameters needed to estimate the transport and release of contaminants to the real environment under alkaline pH from the stabilized waste were obtained. The model simulation of the performance of the stabilized waste under the actual environmental conditions of the disposal site showed that there is insignificant release of the contaminants from the stabilized waste. Hence it was concluded based on the experimental and modelling data that if the environment is able to maintain an alkaline pH condition, then the stabilized waste will not damage the environment