Nitrate removal from water via self-flocculation of genetically engineered bacteria

Optimizing aeration intensity to enhance self-flocculation in algal-bacterial symbiosis systems

Effectuating optimal wastewater treatment via algae-bacterial symbiosis (ABS) systems necessitates the precise selection of aeration intensity. This study pioneers an in-depth investigation into the interplay of aeration intensity on the microalgal-bacterial consortia's self-flocculation efficacy and the overall treatment performance within ABS systems. The research provides evidence for a direct association between aeration intensity and biomass proliferation, indicating enhanced pollutant removal efficiency with escalated intensities (1.0 and 1.5 L min-1), though the variance lacks statistical significance. The peak self-flocculation efficacy of the microalgal-bacterial consortium (82.39% at 30 min) was manifested at an aeration intensity of 1.0 L min-1. The meticulous analysis of biomass properties showed the complexity of self-flocculation capacity in the consortium, which involves a dynamic interplay of several pivotal factors, including floc size, zeta potential, and EPS content. In situations where these factors pose conflicting influences, the determining factor emerges as the dominant influencer. In this study, the optimal aeration intensity was identified as 1 L min-1, shedding light on the critical threshold for ABS system operation. This study not only enriches the understanding of microalgal-bacterial wastewater treatment mechanisms but also fosters innovative strategies to enhance the performance of such systems.

Lysozyme regulates the extracellular polymer of activated sludge and promotes the formation of electroactive biofilm

The formation of electroactive biofilm from activated sludge on electrode surface is a key step to construct a bio-electrochemical system, yet it is greatly limited by the poor affinity between the bacteria and the electrode interface. Herein, we report a new method to promote the formation of electroactive biofilm by regulating the extracellular polymeric substance (EPS) content in activated sludge with lysozyme. The investigation of the effect of lysozyme treatment on the content of extracellular polymers and the biofilm formation of electroactive bacteria suggests that lysozyme can improve the permeability of the positive bacterial cell membrane and thus increase the EPS content in the activated sludge. The characterizations of electrochemical activity, surface morphology and community structure of the anode biofilm indicate that increasing EPS content promotes the adhesion of the mixed bacteria in the activated sludge on the electrode and results in denser biofilms with better conductivities. The microbial fuel cell (MFC) inoculated with the sludge of high EPS content exhibits the power density up to 2.195 W/m², much higher than that inoculated with the untreated sludge (1.545 W/m²). The strategy of adjusting EPS content in activated sludge with a biological enzyme can effectively enhance the ability of the bacterial community to form biofilms and exhibits great application potentials in the construction of high efficiency bio-electrochemical systems.