Mass loading and the rate of clogging due to municipal solid waste leachate

The results of laboratory column tests conducted to assess the effect of th e mass loading on the clogging of porous media are presented. The tests wer e conducted using actual leachate from the Keele Valley Landfill under satu rated, anaerobic conditions. It is shown that clogging is greatest where th ere is the greatest mass loading (near the inlet in this case, but likely n ear the collection pipes in a field situation). An empirical relationship b etween the hydraulic conductivity and drainable porosity is presented. Even though it is shown that higher flow rates give rise to less efficient bior eactors, the columns with high flow still experience greater rates of clogg ing than those with low flow. The columns were found to be severely clogged when the drainable porosity had decreased to about 10% of the initial valu e. The bulk (wet) density of the clog material is found to range between 1. 6 and 2 Mg/m(3) and, on a dry mass basis, 27% of the clog is calcium and 47 % is carbonate. The columns were colonized by a diverse consortium of bacte ria including methanogens, sulfate-reducing, and denitrifying bacteria, wit h methanogens being dominant in the portion of the column where clogging wa s most severe.