DEVELOPMENT AND EVALUATION OF A BIOFILTER FOR TURBID AND NITROGEN RICH IRRIGATION WATER

The biofilter system proposed and tested here, for upgrading irrigation water, is based upon the use of a carbonaceous material, such as wheat straw, as a substrate for microbial activity. Microorganisms degrading a carbon-rich and nitrogen-poor substrate are expected to take up nitrogen from the water. When wastewater flows along a column of the carbonaceous substrate, a sequence of nitrification and denitrification is also possible. Moreover, the biofilter may ''trap'' phosphorus, suspended matter and possibly soluble organic matter. Each biofilter (a l m3 PVC tank containing 50 kg of wheat straw) was fed by water from an oxidation pond at a rate of 60-65 l h-1. The biofilter system performed with no clogging or other hydraulic problems for a period of 63 days. The capacity of the filter was at least 2 m3 water for each kg of straw. The biofilter removed 50% of the ammonium from the input water, 65% of the suspended matter and 75% of the algal biomass. In addition, the leachates from the biofilter were more uniform than the raw pond water, the composition of which fluctuated within a wide range. Besides its smooth operation, the raw straw was enriched with protein during the operation of the filter. The initial protein content of the straw (about 3%) rising to 12-15% by the end of the experiment. It is anticipated that the spent straw may be used as a manure, or, probably following silage, as a valuable feed material.