A novel mechanistic model for nitrogen removal in algal-bacterial photo sequencing batch reactors

Algal-bacterial shortcut nitrogen removal model with seasonal light variations

The algal-bacterial shortcut nitrogen removal (ABSNR) process can be used to treat high ammonia strength wastewaters without external aeration. However, prior algal-bacterial SNR studies have been conducted under fixed light/dark periods that were not representative of natural light conditions. In this study, laboratory-scale photo-sequencing batch reactors (PSBRs) were used to treat anaerobic digester sidestream under varying light intensities that mimicked summer and winter conditions in Tampa, FL, USA. A dynamic mathematical model was developed for the ABSNR process, which was calibrated and validated using data sets from the laboratory PSBRs. The model elucidated the dynamics of algal and bacterial biomass growth under natural illumination conditions as well as transformation processes for nitrogen species, oxygen, organic and inorganic carbon. A full-scale PSBR with a 1.2 m depth, a 6-day hydraulic retention time (HRT) and a 10-day solids retention time (SRT) was simulated for treatment of anaerobic digester sidestream. The full-scale PSBR could achieve >90% ammonia removal, significantly reducing the nitrogen load to the mainstream wastewater treatment plant (WWTP). The dynamic simulation showed that ABSNR process can help wastewater treatment facilities meet stringent nitrogen removal standards with low energy inputs.

Light-introduced partial nitrification in an algal-bacterial granular sludge bioreactor: Performance evolution and microbial community shift

This objective of study was to evaluate the influence of light on the achievement of partial nitrification algal-bacterial granular bioreactor and its related nitrite accumulation mechanism. After 150-days operation, partial nitrification algal-bacterial granulation bioreactor was achieved under the 200 μmol/(m²·s) illuminance condition. The effluent NH₄⁺-N, NO₂^--N, NO₃^--N concentrations were average at 1.1, 61.7 and 8.0 mg/L (n = 21), respectively. The average sphericity of algal-bacterial aerobic granular sludge (AB-AGS) increased from 82.7% to 91.1%, accompanied by the significantly increased diameter. Additionally, extracellular protein increased by 1.5 times and 0.5 times higher in LB-EPS and TB-EPS of AB-AGS, respectively. According to typical cycles, N₂O emission amount reactor accounted for 2.4% of the removed nitrogen. Under the combined inhibition of light and free ammonia (FA), Nitrosomonas-related AOB (0.2% to 2.1%) were the predominant functional bacteria, whereas Nitrospira-related NOB (0.07% to below 0.01%) was fully inhibited.

Emerging biological wastewater treatment using microalgal-bacterial granules: A review

Aiming at deepening the understanding of the formation and evolution of emerging microalgal-bacterial granule (MBG)-based wastewater treatment systems, the recent advances regarding the formation processes, transfer phenomena, innovative bioreactors development and wastewater treatment performance of MBG-based systems are comprehensively reviewed in this work. Particularly, the successful establishments of MBG-based systems with various inocula are summarized. Besides, as the indispensable factors for biochemical reactions in MBGs, the light and substrates (organic matters, inorganic nutrients, etc) need to undergo complicated and multi-scale transfer processes before being assimilated by microorganisms within MBGs. Therefore, the involved transfer phenomena and mechanisms in MBG-based bioreactors are critically discussed. Subsequently, some recent advances of MBG-based bioreactors, the application of MBG-based systems in treating various synthetic and real wastewater, and the future development directions are discussed. In short, this review helps in promoting the development of MBG-based systems by presenting current research status and future perspectives.

Converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia: A critical review

Conventional wastewater treatment using activated sludge cannot efficiently eliminate nitrogen and phosphorus, thus engendering the risk of water eutrophication and ecosystem disruption. Fortunately, a new wastewater treatment process applying microalgae-bacteria consortia has attracted considerable interests due to its excellent performance of nutrients removal. Moreover, some bacteria facilitate the harvest of microalgal biomass through bio-flocculation. Additionally, while stimulating the functional bacteria, the improved biomass and enriched components also brighten bioenergy production from the perspective of practical applications. Thus, this review first summarizes the current development of nutrients removal and mutualistic interaction using microalgae-bacteria consortia. Then, advancements in bio-flocculation are completely described and the corresponding mechanisms are thoroughly revealed. Eventually, the recent advances of bioenergy production (i.e., biodiesel, biohydrogen, bioethanol, and bioelectricity) using microalgae-bacteria consortia are comprehensively discussed. Together, this review will provide the ongoing challenges and future developmental directions for better converting nitrogen and phosphorus wastewater into bioenergy using microalgae-bacteria consortia.

Comparing the nitrogen removal performance and microbial communities of flocs-granules hybrid and granule-based CANON systems

Flocs and granules tend to coexist in a single reactor. Granules can improve microbial retention capacity, however, the role of flocs in the CANON reactor remains unclear. The changes in the nitrogen removal performance and microbial communities between flocs-granules hybrid and granule-based systems were studied in this experiment. With a reduction in the flocs ratio (35% → 10%), the nitrogen removal performance deteriorated. The average nitrogen removal efficiency and rate dropped from 81.4% to 67.2% and from 0.225 to 0.174 kg/(m³·d), respectively. The contribution of heterotrophic denitrifying bacteria decreased from 13.5% to 1%, leading to changes in the nitrogen removal pathways between the systems. Furthermore, the activities of anaerobic and aerobic ammonium oxidizing bacteria declined dramatically, which weakened the nitrogen removal performance. Thus, the hybrid system with a flocs ratio near 35% is recommended for use in a CANON reactor.

Advances in the technologies for studying consortia of bacteria and cyanobacteria/microalgae in wastewaters

The excessive generation and discharge of wastewaters have been serious concerns worldwide in the recent past. From an environmental friendly perspective, bacteria, cyanobacteria and microalgae, and the consortia have been largely considered for biological treatment of wastewaters. For efficient use of bacteria‒cyanobacteria/microalgae consortia in wastewater treatment, detailed knowledge on their structure, behavior and interaction is essential. In this direction, specific analytical tools and techniques play a significant role in studying these consortia. This review presents a critical perspective on physical, biochemical and molecular techniques such as microscopy, flow cytometry with cell sorting, nanoSIMS and omics approaches used for systematic investigations of the structure and function, particularly nutrient removal potential of bacteria‒cyanobacteria/microalgae consortia. In particular, the use of specific molecular techniques of genomics, transcriptomics, proteomics metabolomics and genetic engineering to develop more stable consortia of bacteria and cyanobacteria/microalgae with their improved biotechnological capabilities in wastewater treatment has been highlighted.

Algal-Bacterial Symbiosis System Treating High-Load Printing and Dyeing Wastewater in Continuous-Flow Reactors under Natural Light

This study investigated the symbiotic structure relationship between mixed algae andactivated sludge while treating high-load printing and dyeing wastewater under natural light. Theeffects of hydraulic retention time (HRT) (12 h, 16 h and 20 h) and aeration rate (0.1–0.15, 0.4–0.5and 0.7–0.8 L/min) on algal–bacterial symbiosis (ABS) and conventional activated sludge (CAS)systems. Experimental results showed that the ABS system exhibited the best removal performancefor chemical oxygen demand (COD), ammonia nitrogen (NH4+-N) and total phosphorus (TP),which was increased by 12.5%, 23.1% and 10.5%, respectively, and reduced colour 80 timescompared with the printing and dyeing wastewater treatment plant. Algae growth could bepromoted under lower dissolved oxygen (DO), and the addition of algae could provide more DO tothe ABS system. The particle size distribution of sludge in the ABS system was stable, whichguaranteed a stable treatment effect. In addition, the COD and colour could be further degradedunder the conditions of no external carbon source and longer HRT. It is expected that the presentstudy will provide a foundation for the practical application of the ABS system, and new insightsfor the treatment of printing and dyeing wastewater.