Effects of photoperiod on nutrient removal, biomass production, and algal-bacterial population dynamics in lab-scale photobioreactors treating municipal wastewater.

This review focuses on the potential advantages and challenges of submerged membrane photobioreactors (MPBRs) for microalgae cultivation and wastewater treatment. MPBR technology combines a conventional photobioreactor (PBR) with a membrane process to grow microalgae, enabling complete retention of algal biomass. Microalgae populations in MPBRs are affected by a number of factors, including wastewater characteristics and operational conditions. Although the wastewater types used in previous MPBR studies varied significantly in terms of composition, especially nitrogen (7.5 to 25 mg/L) and phosphorus (0.15 to 20 mg/L) concentrations, general trends and some optimised operating conditions can now be defined. Individual parameters, including hydraulic retention time (HRT), solids retention time (SRT), lighting, aeration, temperature, and pH were all found to be important factors affecting process efficiency; furthermore, there is evidently complex inter-relationships between these parameters, which should not be overlooked during MPBR design. Membrane fouling is still considered an operational challenge, with previous studies focusing on the relationship between membrane performances and algal organic matter. Applying immobilised microalgal technology to MPBRs has the potential to enhance productivity and mitigate fouling.

Simultaneous microalgae cultivation and wastewater treatment in submerged membrane photobioreactors: A review

A novel shortcut nitrogen removal process using an algal-bacterial consortium in a photo-sequencing batch reactor (PSBR).

Evaluation of wastewater treatment in a novel anoxic-aerobic algal-bacterial photobioreactor with biomass recycling through carbon and nitrogen mass balances.

The economic factor of the microalgae harvesting step acts as a barrier to scaling up microalgae-based technology designed for wastewater treatment. In view of that, this study presents an alternative microalgae-bacteria system, which is proposed for eliminating the economic obstacle. Instead of the microalgae-bacteria (activated algae) flocs, the study aimed to develop activated algae granules comprising the microalgae Chlorella sp. as a target species. The presence of the filamentous microalgae (Phormidium sp.) was necessary for the occurrence of the granulation processes. A progressive decrease in frequency of the free Chlorella sp. cells was achieved once with the development of the activated algae granules as a result of the target microalgae being captured in the dense and tangled network of filaments. The mature activated algae granules ranged between 600 and 2,000 µm, and were characterized by a compact structure and significant settling ability (21.6 ± 0.9 m/h). In relation to the main aim of this study, a microalgae recovery efficiency of higher than 99% was achieved only by fast sedimentation of the granules; this performance highlighted the viability of the granular activated algae system for sustaining a microalgae harvesting procedure with neither cost nor energy inputs.

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Overcoming Microalgae Harvesting Barrier by Activated Algae Granules.

Assessing carbon and nitrogen removal in a novel anoxic–aerobic cyanobacterial–bacterial photobioreactor configuration with enhanced biomass sedimentation

I. de Godos

Papers

Assessing carbon and nitrogen removal in a novel anoxic–aerobic cyanobacterial–bacterial photobioreactor configuration with enhanced biomass sedimentation