The role of loading rate, backwashing, water and air velocities in an up-flow nitrifying tertiary filter

Dynamic modeling of nitrogen removal for a three-stage integrated fixed-film activated sludge process treating municipal wastewater

The integrated fixed-film activated sludge (IFAS) process is being increasingly used to enhance nitrogen removal for former activated sludge systems. The aim of this work is to evaluate a numerical model of a new nitrifying/denitrifying IFAS configuration. It consists of two carrier-free reactors (anoxic and aerobic) and one IFAS reactor with a filling ratio of 43% of carriers, followed by a clarifier. Simulations were carried out with GPS-X involving the nitrification reaction combined with a 1D heterogeneous biofilm model, including attachment/detachment processes. An original iterative calibration protocol was created comprising four steps and nine actions. Experimental campaigns were carried out to collect data on the pilot in operation, specifically for modelling purpose. The model used was able to predict properly the variations of the activated sludge (bulk) and the biofilm masses, the nitrification rates of both the activated sludge and the biofilm, and the nitrogen concentration in the effluent for short (4-10 days) and long (300 days) simulation runs. A calibrated parameter set is proposed (biokinetics, detachment, diffusion) related to the activated sludge, the biofilm and the effluent variables to enhance the model prediction on hourly and daily data sets.

Investigation on evaluation criteria of backwashing effects for a pilot-scale BAF treating petrochemical wastewater

Parameters for evaluation criteria of air-water backwashing effects of a pilot-scale biological aerated filter (BAF) treating petrochemical wastewater were investigated. The parameters included the suspended solids (SS) and specific oxygen uptake rate (SOUR) of the backwashing effluent, recovery of the BAF after backwashing, and the removal of the biomass/bioactivity attached on the filter media after backwashing. Results showed that the weight of the total sludge produced in the backwashing effluent increased with the increase in water-backwashing intensity, while the total SOUR of backwashing effluent rose notably with the increase of air-backwashing intensity. The optimal backwashing intensity of 14 L/(m²_·s) for air and 4 L/(m²_·s) for water were obtained. When the BAF was backwashed on this condition, the BAF recovered with high average removal of chemical oxygen demand (COD) and ammonia nitrogen [Formula: see text] of 14.3% and 50.3%, respectively. High amount of biomass removal at 15.8% and low level of bioactivity removal at 8.8% attached on the filter media were also found. Concentrations of the benzene, toluene, ethylbenzene and (o-, m-, p-) xylenes (BTEX) and phenol in the backwashed sludge were analyzed, showing that the backwashing was essential to remove some aromatic compounds adsorbed in the microorganisms.

Understanding the contribution of biofilm in an integrated fixed-film-activated sludge system (IFAS) designed for nitrogen removal

The objective of this study is to improve knowledge on the integrated fixed-film-activated sludge (IFAS) system designed for nitrogen removal. Biofilm growth and its contribution to nitrification were monitored under various operating conditions in a semi-industrial pilot-scale plant. Nitrification rates were observed in biofilms developed on free-floating media and in activated sludge operated under a low sludge retention time (4 days) and at an ammonia loading rate of 45-70 gNH4-N/kgMLVSS/d. Operational conditions, i.e. oxygen concentration, redox potential, suspended solids concentration, ammonium and nitrates, were monitored continuously in the reactors. High removal efficiencies were observed for carbon and ammonium at high-loading rate. The contribution of biofilm to nitrification was determined as 40-70% of total NOx-N production under the operating conditions tested. Optimal conditions to optimize process compacity were determined. The tested configuration responds especially well to winter and summer nitrification conditions. These results help provide a deeper understanding of how autotrophic biomass evolves through environmental and operational conditions in IFAS systems.