Innovative inbuilt moving bed biofilm reactor for nitrogen removal applied in household aquarium

Abstract

An innovative inbuilt moving bed biofilm reactor (MBBR) was created to protect fish from nitrogen in a household aquarium. During the 90 experimental days, the ammonia nitrogen (NH₄⁺-N) concentration in the aquarium with the inbuilt MBBR was always below 0.5 mg/L, which would not threaten the fish. Concurrently, nitrite and nitrate nitrogen concentrations were always below 0.05 mg/L and 4.5 mg/L, respectively. However, the blank contrast aquarium accumulated 1.985 mg/L NH₄⁺-N on the 16th day, which caused the fish to die. The suspended biofilms could achieve the specific NH₄⁺-N removal rate of 45.43 g/m³/d. Biofilms presented sparsely with filamentous structures and showed certain degrees of roughness. The bacterial communities of the suspended biofilms and the sediment were statistically different (p < 0.05), reflected in denitrifying and nitrifying bacteria. In particular, the relative abundance of Nitrospira reached 1.4%, while the genus was barely found in sediments. The suspended biofilms showed potentials for nitrification function with the predicted sequence numbers of ammonia monooxygenase [1.14.99.39] and hydroxylamine dehydrogenase [EC:1.7.2.6] of 220 and 221, while the values of the sediment were only 5 and 1. This study created an efficient NH₄⁺-N removal inbuilt MBBR for household aquariums and explored its mechanism to afford a basis for its utilization.

Keywords: ammonia; biofilm; moving bed biofilm reactor; nitrification; wastewater treatment.

Figure 1

Schematic of the inbuilt MBBR in the household aquarium: application scenarios (A) and details of the composition (B).

Figure 2

COD, NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N concentrations of blank contrast aquarium (A) and the aquarium with the inbuilt MBBR (B).

Figure 3

NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N concentration variations during the nitrification performance test for the suspended biofilms.

Figure 4

Morphology scanned by type microscope for the new carriers (A) and the bio-carriers in the aquarium (B), by the SEM for the suspended biofilms (C) and the sediment (D) in the aquarium, and by the LSCM for the bio-carriers in the aquarium (E).

Figure 5

Heatmap for the relative abundance of the top 30 genera (A); PCA for the bacterial community (B); and collinear network analysis (C) of the suspended biofilms and sediment in the aquarium.

Figure 6

Heatmap for sequence numbers of the potential functions for nitrogen removal of the suspended biofilms and sediment in the aquarium.