Bifunctional lighting/supporting substrate for microalgal photosynthetic biofilm to bio-remove ammonia nitrogen from high turbidity wastewater

Abstract

Treatment technologies based on microalgal biofilms have an enormous potential for dealing with water pollution because they can efficiently redirect nutrients from wastewater to renewable biomass feedstock. However, poor light transmittance is caused by the high turbidity of wastewater, which hinders the commercial application of microalgal biofilm-based wastewater treatment. Here, a bifunctional substrate with lighting and biofilm support functions was constructed using a light guide plate. In a biofilm photobioreactor (bPBR) with a bifunctional lighting/supporting substrate (BL/S substrate), light can directly irradiate the biofilm to avoid attenuation by the turbid wastewater. Direct irradiation of light onto the biofilm led to a 93.0% enhancement of microalgal photoconversion efficiency when compared to that of a supporting substrate without lighting (SO substrate). Meanwhile, the maximum growth rate of the microalgal biofilm on the BL/S substrate was 8.7 g m−2 d−1, which was increased by 60.3%. The removal rate of ammonia nitrogen (NH4+-N) from the digested wastewater contributed by the microalgal biofilm reached 22.6 mg L−1 d−1, which was higher than the previously reported that of NH4+-N from turbid digested wastewater by the biofilms. Furthermore, the BL/S substrate can facilitate the secretion of abundant extracellular polymeric substrates, which results in the stable adhesion of the biofilm onto the BL/S substrate. The optical density of the microalgae cells at the outlet of the bPBR with BL/S substrate was below 0.1, which was 94% lower than that of the bPBR with the SO substrate. The results indicated the BL/S substrate may avoid the loss of microalgal biomass, and almost all biomass could be easily harvested from the biofilm for algae-based biomass resources. Consequently, this study can offer a promising alternative with efficient treatment technologies for wastewater with high turbidity.