Cold-climate nitrification on plastic media trickling filters

Abstract

<p>The accuracy with which cold-climate nitrification performance in structured, plastic media trickling filters can be predicted and the ability to maintain stable operation are governed by the interaction of properties of the wastewater, properties of the media, and mechanical operating parameters;A pilot-scale investigation of cold-climate, separate-stage nitrification in structured, plastic media trickling filters was conducted at the Ames Water Pollution Control Plant (WPCP). Secondary effluent from the existing, overloaded WPCP was treated in the pilot-scale nitrifying biofilter. Pretreatment of the Ames WPCP secondary effluent for reduction of carbonaceous oxygen demand carryover was used in the latter half of the study;Nitrifying biofilter performance was observed for two wastewater application methods, continuous dosing and intermittent dosing, with average hydraulic loading rates ranging from 0.5 to 1.9 l/sq. m (.) s. Two types of cross-flow media were used: (1) 45 degree media with a specific surface area of 98 sq. m/cu. m in the pretreatment trickling filter and (2) 60 degree media with a specific surface area of 138 sq. m/cu. m in the nitrifying biofilter. Nitrification performance was monitored for various bulk liquid chemical oxgyen demand and dissolved oxygen conditions;Dissolved oxygen was shown to be a critical factor in nitrifying biofilter performance. Intermittent dosing and high hydraulic loading rates were shown to be detrimental to cold-climate nitrification performance. Filterable COD was shown to affect nitrification at lower hydraulic loading rates, but not at higher hydraulic loading rates. Transient, partial plugging of the 60 degree cross-flow media was suggested by erratic nitrification performance of individual segments of the nitrifying biofilter media for time periods up to six weeks;Study results were used to improve empirical design curves and to evaluate the implications of process flow schemes and operating parameters. The accuracies of two proposed methods of calculating the effective area of structured, plastic media were evaluated.</p>