Effect of illuviated deposits on inflitration rates and denitrification during sewage effluent recharge

Abstract

A column study was conducted to determine the interrelationships among nitrogen transformations, infiltration rates, and development of a black layer during sewage effluent recharge. Columns were packed with river sand and continuously flooded with sewage effluent for 28 days during the first trial, designated run 1. Run 2 lasted for 64 days and gravel was used in place of sand. For both runs infiltration rates and manometer readings were recorded daily and samples of the inflow and outflow were collected and analyzed for the various nitrogen compounds. Infiltration rates decreased rapidly upon application of the sewage, mainly due to clogging of the surface by suspended solids. A black layer developed within a few days, the thickness of which was inversely related to the infiltration rate. There was an average reduction in total nitrogen of 62.9% during run 1 and 15.9% during run 2. Black layer development was not a cause of reduced infiltration rates, but lower infiltration rates appeared to be an indirect cause of a thicker black layer within a given soil type. Total nitrogen reduction was apparently not related to black layer development. However, the percent of total nitrogen removal was greater for lower infiltration rates.