Development of a biofilter for turbid and nitrogen-rich irrigation water; B: Removal of phosphorus, algae and clay

Abstract

A biofilter made out of chopped wheat straw was shown to be an effective system to remove nitrogen from waste-water, both due to nitrogen immobilization as well as to a nitrification-denitrification sequence (Lowengart, A., Diab, S., Kochba, M. & Avinmelech, Y. 1993. Development of a biofilter for turbid and nitrogen-rich irrigation water. A: Organic carbon degradation and nitrogen removal processes Bioresource Technol. 44, 131-5). The tested laboratory scale biofilter was made out of wheat straw, a substrate that has excellent hydraulic characteristics. The pores are large and the substrate has a very high hydraulic conductivity and a very low sensitivity to clogging. Yet, it has, apparently, a high reactive and effective surface area. Thus, it can be easily used for the biofiltration of turbid water. The removal of phosphorus, clay and algae by the same biofilter is reported in this paper. Phosphorus was taken up by the growing microbial biomass, probably in parallel to the nitrogen immobilization process. Clay was removed very effectively from the water, due to its adsorption on the mucilaginous biofilm that developed on the degraded straw. The clay adsorption capacity was more than 170 mg clay/g straw. The removal of algae was also very effective. Moreover, the adsorbed algae provide an additional, ‘ever-lasting’ source of available organic carbon rich substrate, leading to the continual functioning of the biofilter. The straw biofilter seems to be an inexpensive, simple and efficient biofilter to reduce the levels of nitrogen, phosphorus, clay, algae and organic carbon in waste water used for irrigation.