Breakthrough tests on preferential flow in municipal solid waste

The municipal solid waste (MSW) is characterized by large pores, so the water flow in MSW often takes the form of preferential flow. The fundamental rules of the preferential flow in MSW has not been revealed thoroughly at present, and parameters in numerical analysis still need to be studied further. The solute breakthrough tests are carried out by using Cl^- as a tracer to investigate the preferential flow in MSW. The influences of depth and age, sample heights and infiltration rates on the preferential flow are considered. The regression analysis is performed using the log-normal probability distribution model and bimodal probability density model. The results show that 55% to 70% of the total solute is transported through large pores, indicating that the preferential flow is obvious in MSW. The proportion of pores that participates in solute movement increases as the depth and ages increase, but the proportion of solute movement through large pores decreases, such that the degree of preferential flow decreases. As heights of the MSW sample increase, the connectivity of large pores in MSW decreases and the proportion of solute movement through large pores decreases, so the degree of preferential flow decreases. As the infiltration rate increases, the proportion of solute movement through large pores increases and the degree of preferential flow increases. The bimodal probability density model is more suitable than the log-normal probability distribution model to characterize the preferential flow in MSW. The analysis helps to determine the parameters in two-domain model in analysis of water movement in MSW.