Low-retention operation to enhance biomass productivity in an algal membrane photobioreactor

Response surface methodology to investigate the effects of operational parameters on membrane bioreactor

Performance modeling of wastewater treatment systems has now become an attractive area of investigation for the design, analysis, and optimization of operations. Mathematical modeling of membrane bioreactor (MBR) treatment is a powerful tool for predicting effluent quality. In this study, a bioreactor coupled with a membrane filtration process (MBR) was employed to treat municipal wastewater. An experimental design based on the response surface methodology (RSM) was applied to investigate the effects of operating conditions, such as hydraulic retention time (HRT), aeration rate (AR), and transmembrane pressure (TMP), on the removal efficiencies of chemical oxygen demand (COD), total suspended solids (TSS), and total nitrogen (TN). The results demonstrated a strong agreement between experimental data and model predictions. Furthermore, the RSM results display the effects of the operating parameters and their interactive effects on pollution removal. The maximum removal efficiency was achieved, exhibiting 95% of COD, 99.7% of TSS, and 93% of TN. These findings provide the effective use of statistical modeling to enhance MBR process performance, achieving sustainable and energy-efficient conditions.

A Study of Theoretical Analysis and Modelling of Microalgal Membrane Photobioreactors for Microalgal Biomass Production and Nutrient Removal

This study presents a theoretical and mathematical analysis and modelling of the emerging microalgal membrane photobioreactors (M-MPBRs) for wastewater treatment. A set of mathematical models was developed to predict the biological performances of M-MPBRs. The model takes into account the effects of hydraulic retention time (HRT), solid retention time (SRT), and the N/P ratio of influent on the biological performance of M-MPBRs, such as microalgal biomass production and nutrient (N and P) removals. The model was calibrated and validated using experimental data from the literature. This modelling study explained that prolonged SRT could promote biomass production and nutrient removal, while prolonging HRT exhibited a negative effect. Furthermore, biomass production could be improved by augmenting nutrient loading, and nutrient removal would be limited under insufficient conditions. The modelling results demonstrated that the best performance was achieved at HRT = 1 d and SRT = 40 d for typical municipal wastewater with an influent N concentration = 40 mg/L. The modelling results are in good agreement with the experimental results from the literature. The findings suggest that the proposed models can be used as a powerful mathematical tool to optimize these parameters to improve the removal of nutrients (N and P), as well as the productivity of biomass in M-MPBRs. This study provides new insights into the use of mathematical models for the optimal design and operation of the emerging M-MPBRs for sustainable wastewater treatment.

Influence of salinity on microalgae-bacteria symbiosis treating shrimp farming wastewater

Shrimp farming has strongly developed in recent years, and became an important economic sector that helps create jobs and increase incomes for Vietnamese. However, the aquatic environment has also been greatly affected by the development due to the amount of wastewater discharged from shrimp farms. Among biological processes used for treating shrimp farming wastewater, the application of microalgae-bacteria co-culture is considered high potential due to its treatment and energy saving. Consequently, a photobioreactor operated with microalgae-bacteria co-culture was employed to treat shrimp farming wastewater. The salinity of wastewater and the operating condition (ratio of biomass retention time and hydraulic retention time, BRT/HRT) are the major factors affecting pollutant removal. Thus, this study investigated the effects of salinities of 0.5-20 ppt and BRT/HRT ratios of 1.5-16 on the removal performance. The results indicated that the nutrient removal was reduced when PBR operated under salinity over than 10 ppt and BRT/HRT over 5.5. Particularly, the nitrogen and phosphorus removal rates were achieved 6.56 ± 1.33 gN m-3 d-1 and 1.49 ± 0.59 gP m-3 d-1, and the removal rates decreased by 2-4 times under a salinity >10 ppt and 2-6 times under a BRT/HRT ratio >5.5. Whereas, organic matter treatment seems not to be affected when the removal rate was maintained at 28-34 gCOD m-3 d-1 under various conditions.

A bibliometric analysis of published literature on membrane photobioreactors for wastewater treatment from 2000 to 2022

With the focus on limiting greenhouse gas emissions, microalgae-based technology is a promising approach for wastewater treatment, combining cost-effective operation, nutrient recovery, and assimilation of CO2. In addition, membrane technology supports process intensification and wastewater reclamation. Based on a bibliometric analysis, this paper evaluated the literature on membrane photobioreactors to highlight promising areas for future research. Specifically, efforts should be made on advancing knowledge of interactions between algae and bacteria, analysing different strategies for membrane fouling control and determining the conditions for the most cost-effective operation. The Scopus® database was used to select documents from 2000 to 2022. A set of 126 documents were found. China is the country with the highest number of publications, whereas the most productive researchers belong to the Universitat Politècnica de València (Spain). The analysis of 50 selected articles provides a summary of the main parameters investigated, that focus in increasing the biomass productivity and nutrient removal. In addition, microalgal-bacterial membrane photobioreactor seems to have the greatest commercialisation potential. S-curve fitting confirms that this technology is still in its growth stage.

Microalgae production in human urine: Fundamentals, opportunities, and perspectives

The biological treatment of source-separated human urine to produce biofuel, nutraceutical, and high-value chemicals is getting increasing attention. Especially, photoautotrophic microalgae can use human urine as media to achieve environmentally and economically viable large-scale cultivation. This review presents a comprehensive overview of the up-to-date advancements in microalgae cultivation employing urine in photobioreactors (PBRs). The standard matrices describing algal growth and nutrient removal/recovery have been summarized to provide a platform for fair comparison among different studies. Specific consideration has been given to the critical operating factors to understand how the PBRs should be maintained to achieve high efficiencies. Finally, we discuss the perspectives that emphasize the impacts of co-existing bacteria, contamination by human metabolites, and genetic engineering on the practical microalgal biomass production in urine.

Co-culture of microalgae-activated sludge in sequencing batch photobioreactor systems: Effects of natural and artificial lighting on wastewater treatment

Co-culture using microalgae-activated sludge in Sequencing Batch Photobioreactors (PBRs) was investigated for wastewater treatment performance. This study evaluated the effect of natural and artificial lighting conditons on treatment performance under consideration of energy consumption. The results found that the removal of nutrients and COD of natural lighting condition was only 10% and 13% lower than those of artificial lighting respectively. Generally, artificial lighting mode took an advantage in pollutants removal. However, standing at 0.294 kWh L^-1, the total energy consumption of natural lighting was over two times less than that of artificial lighting. It reveals the natural lighting system played a dominant role for cutting energy costs significantly compared to artificial lighting one (∼57%). As a practical viewpoint on energy aspect and treatment performance, a natural lighting PBR system would be a sustainable option for microalgae-activated sludge co-culture system treating wastewater.

Assessing the potential of purple phototrophic microbial community for nitrogen recycling from ammonia-rich medium and anaerobic digestate

Purple phototrophic bacteria (PPB) community, enriched from municipal wastewater, was characterized to assess their growth, tolerance, composition and potential for resource recovery from NH₄⁺-rich medium. Batch experiments were conducted in tissue culture flasks and glass bottles under anaerobic conditions with infra-red lights. PPBs showed remarkable tolerance to high concentrations of NH₄⁺-N and acetate. Below 1.5 g/L, growth was unaffected by NH₄⁺-N with optical density at 590 nm (OD₅₉₀) reaching 2.6-2.9, while they could tolerate 4.5 g/L NH₄⁺-N. Similarly, PPB growth was unaffected at acetate concentrations below 4 g/L and they could tolerate >20 g/L acetate. Taxonomic characterization showed that the community comprised of 37-52% PPBs (with 15-20% proteins) under different conditions, with Rhodobacter sp. over Rhodopseudomonas sp. dominating at higher NH₄⁺-N concentrations. PPBs showed growth and removal rates in anaerobic digestate and accumulated 26% proteins. These results indicated the potential of PPBs in resource recovery from NH₄⁺-rich wastewater.