Nitrogen and phosphate adsorption on biofilms in reclaimed water

Abstract

Biofilms, abundantly attached on the surfaces of multiple media (such as pebbles and aquatic plants) in rivers or lakes reusing reclaimed water (RW), are of great significance to contaminants’ self-purification of water bodies. In this paper, the nitrogen and phosphate adsorption characteristics of such biofilms were studied by the batch method, using biofilms cultivated under an outdoor simulative process. Two types of RW treated by anaerobic-anoxic-oxic process (A²/O) and cyclic activated sludge technology (CASS), and surface water (NW) were chosen as the experimental water bodies. And the glasses of surface roughness of 0.1, 1.0, and 10 μm, respectively, were used as the substrates, where the biofilms adhere to them. The results indicated that the isothermal adsorption of biofilms for ammonia nitrogen and phosphates was proved to conform to the Langmuir and the Freundlich equation, whereas the adsorption capacity was significantly lower than that of soils and sediments limited by the pore structure and surface area. There were also significant differences between the adsorption behaviors. The distribution coefficients were ranked as K _dCASS > K _dNW > K ²_{dA /O}, and the maximum adsorption capacities (S _m), under these conditions were ranked as S ²_{mA /O} > S _mNW > S _mCASS, while other parameters did not change regularly. Extracellular polymers ($R^{ 2}_{\text{N}}$ = 0.95**, $R^{ 2}_{\text{p}}$ = 0.84**), iron oxides ($R^{ 2}_{\text{N}}$ = 0.86**, $R^{ 2}_{\text{p}}$ = 0.68*), and aluminum oxides ($R^{ 2}_{\text{N}}$ = 0.95**, $R^{ 2}_{\text{p}}$ = 0.81**) in the biofilms had a significant impact on the S _m for ammonia and phosphates. The roughness of media surfaces also had a considerable influence on the S _m, which was in the order of S _m10μm > S _m0.1μm > S _m1.0μm, whereas other parameters did not change regularly. The research aimed to provide theory reference for in situ decontamination of RW in rivers or lakes.