Particle size and clogging of granular media permeated with leachate

The effect of particle size (4-, 6-, and 15-mm nominal sizes) on the rate o f clogging of columns of porous media permeated with municipal solid-waste leachate is examined. Clogging is shown to be more localized over a small v olume of the porous media near the influent end of the column for smaller p articles than for larger particles, where clogging was more uniformly distr ibuted along the column. This is attributed to the greater surface area per unit volume of smaller particles allowing greater biofilm growth per unit volume. This increased the reduction in chemical oxygen demand (COD) and ca used greater deposition of inorganic clog material per unit length of colum n than for larger particles. The distribution of methanogenic bacteria was found to closely correspond to the zones of most severe clogging. The bulk density of clog material is shown to be between 1.6 and 1.8 Mg/m(3). The ch emical composition of the clog material is essentially independent of parti cle size, with calcium representing 26% of the dry mass of the clog materia l and CaCO3 being the main component of the clog. An examination of the yie ld of CaCO3 relative to COD indicates that the carbon in the CaCO3 represen ts <4% of the organic carbon represented by the drop in COD. Finally, the d ata from the column test is used to predict the expected time to clog for a n actual landfill and were found to give results consistent with what was o bserved in the field.