Temperature dependence of nitrification in a membrane-aerated biofilm reactor

Abstract

The membrane-aerated biofilm reactor (MABR) is a novel method for the biological treatment of wastewaters and has been successfully applied for nitrification. To improve the design and adaptation of MABR processes for colder climates and varying temperatures, the temperature dependence of a counter-diffusional biofilm's nitrification performance was investigated. A lab-scale MABR system with silicone hollow fibre membranes was operated at various temperatures between 8 and 30°C, and batch tests were performed to determine the ammonia oxidation kinetics. Biofilm samples were taken at 8 and 24°C and analysed with 16S rRNA sequencing to monitor changes in the microbial community composition, and a mathematical model was used to study the temperature dependence of mass transfer. A high nitrification rate (3.08 g N m^-2 d^-1) was achieved at 8°C, and temperature dependence was found to be low (θ = 1.024-1.026) compared to suspended growth processes. Changes in the community composition were moderate, Nitrospira defluvii remaining the most dominant species. Mass transfer limitations were shown to be largely responsible for the observed trends, consistent with other biofilm processes. The results show that the MABR is a promising technology for low temperature nitrification, and appropriate management of the mass transfer resistance can optimise the process for both low and high temperature operation.

Keywords: community composition; mass transfer; membrane-aerated biofilm; nitrification rate; temperature dependence; wastewater treatment.

FIGURE 1

Effect of temperature on the NH₄⁺-N removal rate of the MABR in the (A) high (10–20 mg/L) and (B) low (2.5–10 mg/L) initial NH₄⁺ -N concentration ranges.

FIGURE 2

Nitrite accumulation by the end of the batch experiments.

FIGURE 3

(A) Alpha biodiversity indicating species rarefaction curve and (B) beta biodiversity heat map (upper and lower values represent the unweighted and weighted Unifrac distance) of biomass samples from the MABR. E3 and E4 are duplicate samples taken at 24°C, F3 and F4 are duplicate samples taken at 8°C.

FIGURE 4

Relative abundance of top 10 taxa (A) phyla level and (B) genera level of biomass samples taken from the MABR at 8 and 24°C.

FIGURE 5

Relative abundance of (A) nitrification and (B) denitrification orthologues present in biomass samples at 24 and 8°C.

FIGURE 6

Temperature sensitivity of NH₄⁺-N removal rate at 35 mg/L () and 0.1–1.0 mg/L () NH₄⁺-N concentration at various combinations of biofilm thickness (Lf) and boundary layer thickness (LBL).

FIGURE 7

Sensitivity of NH₄⁺-N removal rate to the diffusivity constant of oxygen and ammonium at (A) 8°C and 35 mg/L, and (B) at 8°C and 0.1-1.0 mg/L NH₄⁺-N concentration.