NITROGEN REMOVAL EFFICIENCY AND CAPACITY IN BIOFILMS WITH BIOLOGICALLY HYDROLYZED SLUDGE AS A CARBON SOURCE

The possibility of using biologically hydrolysed sludge as carbon source for the denitrification process in biofilms has been investigated. The goal of the biological sludge hydrolysis process is a high degree of solubilization of the organic matter in the sludge. The soluble organic matter is best dominated by readily biodegradable compounds, The biological hydrolysis of chemical/biological raw sludge resulted in a degree of solubilization (yield) of 11%, where about 84% of the soluble organic matter originated from protein materials. The solubililized nitrogen was found as ammonium-nitrogen. The sludge was composed of 70% chemical sludge and 30% biological sludge, On average 66% of the soluble organic matter was volatile fatty acids. Only the volatile fatty acids were utilized as carbon source in the denitrifying biofilm, The biofilms were around 1000 mu m thick, and the denitrification rate with respect to the concentration of volatile fatty acids could be described by a hyperbolic Monod-type function, The effect of the diffusion resistance in the biofilms was reflected by the use of an artificial ''half-saturation'' constant, K-CADVFA* = 3 mg CODVFA/1. The maximum denitrification rate was found to be r(NO3-N)(max) = 0.57 g NO3-N/g VS.d. The stoichiometric consumption ratio between soluble organic matter and nitrate was 4.5 g CODVFA/g NO3-N on average. A simulation example on the nitrogen removal capacity when the carbon source is provided by sludge hydrolysis is given.