Experiences from an investigation on the potential of packed bed reactors for high rate nitrification of mature landfill leachates

Due to high specific surface area, high biomass concentration and handling convenience, packed bed reactor technology is a highly competitive option for nitrification of landfill leachates. Nitrification would solve the problem of insufficient ammonia retention faced by the high pressure membrane systems at the Ihlenberg landfill, which aims to achieve clean water recoveries up to 95%. This study investigated the feasibility for ammonia removal using four lab-scale reactors packed with three different packing materials (coke, expanded clay beads and polyethylene carrier) over a period of about 400 days. The research work studied the nitrification of two process streams: reverse osmosis concentrate (RO) of raw leachate (having high dissolved organics content) and nanofiltration permeate of RO retentate (with a low concentration of organics), to identify advantages/disadvantages arising from the differences in their composition. The organics contained in the leachate were observed to cause inhibition. Due to this reason, the maximum nitrification rate obtained in the presence of organics was about 570 g N-NH4+/(m(3)d), whereas in their absence up to 1.2 kg N-NH4+/(m(3)d) could be achieved. Although coke packing because of its higher specific surface area and rugged surface favoured faster biofilm development; due to its ability to adsorb organics and thus also promoting the growth of heterotrophs, it was found to be more vulnerable to clogging.