Understanding the influence of free nitrous acid on microalgal-bacterial consortium in wastewater treatment: A critical review

Plasma-Activated Water (PAW) Decontamination of Foodborne Bacteria in Shucked Oyster Meats Using a Compact Flow-Through Generator

This study explored the effectiveness of plasma-activated water (PAW), generated by a newly developed compact generator, for decontaminating foodborne bacteria in oyster meats. The generator effectively produced PAW with antibacterial activity when the water passed through the plasma reactor in a single cycle. The temperature of the PAW produced by the developed device did not exceed 40 °C, enabling its direct application to biological tissues immediately after production and discharge from the plasma reactor. The effects of flow rates and post-discharge times on key reactive species-including hydrogen peroxide, nitrite, and nitrate-were analyzed, along with pH and temperature. Freshly produced PAW can completely inhibit both E. coli and S. aureus in vitro, with a 5-log reduction within 5 min of treatment. Application to oyster meats led to an 86.6% and 87.9% inactivation of V. cholerae and V. parahaemolyticus, respectively. These research findings indicate that PAW generated using the developed compact flow-through generator holds promise as a food safety solution for households. The fact that complete foodborne pathogen elimination was not achieved emphasizes the need for further optimization.

Algae- and bacteria-based biodegradation of phthalic acid esters towards the sustainable green solution

Phthalic acid esters are widely used worldwide as plasticizers. The high consumption of phthalates in China makes it the world's largest plasticizer market. The lack of phthalic acid ester's chemical bonding with the polymer matrix facilitates their detachment from plastic products and subsequent release into the environment and causes serious threats to the health of living organisms. Thus, environmentally friendly and sustainable solutions for their removal are urgently needed. In this context, both natural and engineered bacterial and algal communities have played a crucial role in the degradation of various phthalic acid esters present in water and soil. When algae-bacteria co-culture is compared to a singular algae or bacteria system, this symbiotic system shows superior performance in the removal of dibutyl phthalates and diethyl phthalates from synthetic wastewater. This review provides an optimistic outlook for co-culture systems by in-depth examining single microorganisms, namely bacteria and algae, as well as algae-bacterial consortiums for phthalates degradation, which will draw attention to species co-existence for the removal of various pollutants from the environment. In addition, further development and research, particularly on the mechanisms, genes involved in the degradation of phthalic acid esters, and interactions between bacterial and algal species, will lead to the discovery of more adaptable species as well as the production of targeted species to address the environmental pollution crisis and provide a green, efficient, and sustainable approach to environmental protection. Discrepancies in knowledge and potential avenues for exploration will enhance the existing body of literature, enabling researchers to investigate this field more comprehensively.

Pathways, challenges, and strategies for enhancing anaerobic production of short-chain and medium-chain carboxylic acids from algal slurry derived from wastewater

Algal slurry (AS) generated from microalgae-based wastewater treatment processes holds significant potential for carboxylic acids production through anaerobic digestion (AD), which have emerged as promising products due to their high energy density, great economic value, and versatile applications. A comprehensive analysis of the pathways and optimization strategies for producing short-chain (SCCAs) and medium-chain (MCCAs) carboxylic acids using AS substrates is presented in this review. It begins by introducing and comparing two types of microalgae-based wastewater treatment processes: the microalgae process and the microalgal-bacterial consortia process. Afterwards, the review systematically examines the metabolic pathways involved in SCCAs and MCCAs production using AS substrates. Moreover, pretreatment strategies for enhancing the release of organic matter are critically discussed. Ultimately, specific emphasis is placed on addressing technical challenges and discussing future perspectives. This review provides a deeper understanding of the mechanisms and strategies involved in carboxylic acids production from wastewater-generated AS.

Double-edged sword effects of sulfate reduction process in sulfur autotrophic denitrification system: Accelerating nitrogen removal and promoting antibiotic resistance genes spread

This study proposed the double-edged sword effects of sulfate reduction process on nitrogen removal and antibiotic resistance genes (ARGs) transmission in sulfur autotrophic denitrification system. Excitation-emission matrix-parallel factor analysis identified the protein-like fraction in soluble microbial products as main endogenous organic matter driving the sulfate reduction process. The resultant sulfide tended to serve as bacterial modulators, augmenting electron transfer processes and mitigating oxidative stress, thereby enhancing sulfur oxidizing bacteria (SOB) activity, rather than extra electron donors. The cooperation between SOB and heterotroph (sulfate reducing bacteria (SRB) and heterotrophic denitrification bacteria (HDB)) were responsible for advanced nitrogen removal, facilitated by multiple metabolic pathways including denitrification, sulfur oxidation, and sulfate reduction. However, SRB and HDB were potential ARGs hosts and assimilatory sulfate reduction pathway positively contributed to ARGs spread. Overall, the sulfate reduction process in sulfur autotrophic denitrification system boosted nitrogen removal process, but also increased the risk of ARGs transmission.

Potential of free nitrous acid (FNA) for sludge treatment and resource recovery from waste activated sludge: A review

The escalating production of waste activated sludge (WAS) presents significant challenges to wastewater treatment plants (WWTPs). Free nitrous acid (FNA), known for its biocidal effect, has gained a growing focus on sludge dewatering, sludge reduction, and resource recovery from WAS due to its eco-friendly and cost-effective properties. Nevertheless, there have been no attempts made to systematically summarize or critically analyze the application of FNA in enhancing treatment and resource utilization of sludge. In this paper, we provided an overview of the current understanding regarding the application potential and influencing factors of FNA in sludge treatment, with a specific focus on enhancing sludge dewatering efficiency and reducing volume. To foster resource development from sludge, various techniques based on FNA have recently been proposed, which were comprehensively reviewed with the corresponding mechanisms meticulously discussed. The results showed that the chemical oxidation and interaction with microorganisms of FNA played the core role in improving resource utilization. Furthermore, current challenges and future prospects of the FNA-based applications were outlined. It is expected that this review can refine the theoretical framework of FNA-based processes, providing a theoretical foundation and technical guidance for the large-scale demonstration of FNA.

Mg2+ addition: Unlocking optimized treatment performance and anti-fouling property in microalgal-bacterial membrane bioreactors

While microalgal-bacterial membrane bioreactors (microalgal-bacterial MBRs) have risen as an important technique in the realm of sustainable wastewater treatment, the membrane fouling caused by free microalgae is still a significant challenge to cost-effective operation of the microalgal-bacterial MBRs. Addressing this imperative, the current study investigated the influence of magnesium ion (Mg2+) addition on the biological dynamics and membrane fouling characteristics of the laboratory-scale submerged microalgal-bacterial MBRs. The results showed that Mg2+, important in augmenting photosynthetic process, yielded a biomass concentration of 2.92 ± 0.06 g/L and chlorophyll-a/MLSS (mixed liquor suspended solids) of 33.95 ± 1.44 mg/g in the RMg (Mg2+ addition test group). Such augmentation culminated in elevated total nitrogen and phosphorus removal efficiencies, clocking 81.73 % and 80.98 % respectively in RMg. Remarkably, despite the enhanced microalgae activity and concentration in RMg, the TMP growth rate declined by a significant 46.8 % compared to R0. Detailed characterizations attributed reduced membrane fouling of RMg to a synergy of enlarged floc size and reduced EPS contents. This transformation is intrinsically linked to the bridging action of Mg2+ and its role in creating a non-stressed ecological environment for the microalgal-bacterial MBR. In conclusion, the addition of Mg2+ in the microalgal-bacterial MBR appears an efficient approach, improving the efficiency of pollutant treatment and mitigating fouling, which potentially revolutionizes cost-effective applications and propels the broader acceptance of microalgal-bacterial MBRs. It also of great importance to promote the development and application of microalgal-bacterial wastewater treatment technology.

Biofilm formation and EPS production enhances the bioremediation potential of Pseudomonas species: a novel study from eutrophic waters of Dal lake, Kashmir, India

The present study was conducted with the aim of isolation and identification of the biofilm-forming denitrifying Pseudomonas bacterial strains from eutrophic waters of Dal lake, India, followed by the study of inter-relation of biofilm formation and denitrification potential of Pseudomonas strains. The bacterial strains were characterized by morphological observations and identified using 16S rDNA sequencing followed by the quantification of biofilm formation of these st by crystal violet (CV) assay using 96-well microtiter plate and extracellular polymeric substance (EPS) extraction. Lastly, the nitrate-reducing potential of all Pseudomonas species was studied. Our evaluation revealed that four different Pseudomonas species were observed to have the biofilm-forming potential and nitrate-reducing properties and the species which showed maximum biofilm-forming potential and maximum EPS production exhibited higher nitrate-removing capacity. Moreover, P. otitis was observed to have the highest denitrification capacity (89%) > P. cedrina (83%) > P. azotoform (79%) and the lowest for P. peli (70%). These results clearly signify a positive correlation of biofilm-forming capacity and nitrate-removing ability of Pseudomonas species. This study has for the first time successfully revealed the bioremediation potential of P. otitis, P. cedrina, P. azotoform, and P. peli species, thus contributing to the growing list of known nitrate-reducing Pseudomonas species. Based upon the results, these strains can be extrapolated to nitrate-polluted water systems for combating water pollution.

Harnessing the potential of microalgae-bacteria interaction for eco-friendly wastewater treatment: A review on new strategies involving machine learning and artificial intelligence

In the pursuit of effective wastewater treatment and biomass generation, the symbiotic relationship between microalgae and bacteria emerges as a promising avenue. This analysis delves into recent advancements concerning the utilization of microalgae-bacteria consortia for wastewater treatment and biomass production. It examines multiple facets of this symbiosis, encompassing the judicious selection of suitable strains, optimal culture conditions, appropriate media, and operational parameters. Moreover, the exploration extends to contrasting closed and open bioreactor systems for fostering microalgae-bacteria consortia, elucidating the inherent merits and constraints of each methodology. Notably, the untapped potential of co-cultivation with diverse microorganisms, including yeast, fungi, and various microalgae species, to augment biomass output. In this context, artificial intelligence (AI) and machine learning (ML) stand out as transformative catalysts. By addressing intricate challenges in wastewater treatment and microalgae-bacteria symbiosis, AI and ML foster innovative technological solutions. These cutting-edge technologies play a pivotal role in optimizing wastewater treatment processes, enhancing biomass yield, and facilitating real-time monitoring. The synergistic integration of AI and ML instills a novel dimension, propelling the fields towards sustainable solutions. As AI and ML become integral tools in wastewater treatment and symbiotic microorganism cultivation, novel strategies emerge that harness their potential to overcome intricate challenges and revolutionize the domain.

Potential interactive effect on biomass and bio-polymeric substances of microalgal-bacterial aerobic granular sludge as a valuable resource for sustainable development

The algal/bacterial biomass and extracellular polymeric substances (EPSs) existing in microalgal-bacterial aerobic granular sludge (MB-AGS) offer a promising bioresource. The current review-based paper presents a systematic overview of the compositions and interactions (gene transfer, signal transduction, and nutrient exchange) of microalgal and bacteria consortia, the role of cooperative or competitive partnerships of MB-AGS in the treatment of wastewater and recovery of resource, and the environmental/operational factors affecting their interactions and EPS production. Moreover, a brief notes is given on the opportunities and major challenges of utilizing the microalgal-bacterial biomass and EPS for phosphorus and polysaccharides chemical recovery, renewable energy (i.e. biodiesel, hydrogen, electricity) production. Overall, this compact review will pave the way for developing MB-AGS future biotechnology.

Effect of free nitrous acid on nitritation process: Microbial community, inhibitory kinetics, and functional biomarker

This work comprehensively deciphered the effect of free nitrous acid (FNA) on the microbial community, inhibitory kinetics, and nitrifiers in nitritation process. Nitritation was first successfully achieved through selective inhibition of free ammonia (FA) on nitrite oxidizers (NOB). Then, batch tests clearly showed that FNA significantly inhibits the ammonia oxidation rate (r_su) and the growth rate (μ) of ammonia oxidizers (AOB), which was well described by the Hellinga model (K_I = 0.222 mg·L^-1). The structural equation model indicated that FNA was significantly and negatively associated with r_su, μ, Nitrosomonas, Commamons, Nitrospira, and Nitrotoga and positively correlated with Paracoccus. Furthermore, Nitrosomonas significantly drove the ammonia utilization and growth of AOB and was identified as the most important functional biomarker indicating the nitritation in response to FNA levels using random forest model. This study provides helpful information on the kinetics of the mechanism underlying the FNA inhibition on nitrification.

Artificial intelligence and machine learning-based monitoring and design of biological wastewater treatment systems

Artificial intelligence (AI) and machine learning (ML) are currently used in several areas. The applications of AI and ML based models are also reported for monitoring and design of biological wastewater treatment systems (WWTS). The available information is reviewed and presented in terms of bibliometric analysis, model's description, specific applications, and major findings for investigated WWTS. Among the applied models, artificial neural network (ANN), fuzzy logic (FL) algorithms, random forest (RF), and long short-term memory (LSTM) were predominantly used in the biological wastewater treatment. These models are tested by predictive control of effluent parameters such as biological oxygen demand (BOD), chemical oxygen demand (COD), nutrient parameters, solids, and metallic substances. Following model performance indicators were mainly used for the accuracy analysis in most of the studies: root mean squared error (RMSE), mean square error (MSE), and determination coefficient (DC). Besides, outcomes of various models are also summarized in this study.

Effect of free ammonia shock on Chlorella sp. in wastewater: Concentration-dependent activity response and enhanced settleability

The unstable microbial activity and unsatisfactory settling performance impede the development and implementation of microalgal wastewater treatment, especially in high-ammonium wastewater in the presence of free ammonia (FA). The shock of FA due to the nutrient fluctuation in wastewater was demonstrated as the primary stress factor suppressing microalgal activities. Recent study has clearly revealed the inhibition mechanism of FA at a specific high level (110.97 mg/L) by inhibiting the genetic information processing, photosynthesis, and nutrient metabolism. However, the effects of various FA shock concentrations on microalgal activities and settling performance remain unknown, limiting the wastewater bioremediation efficiencies improvement and the process development. Herein, a concentration-dependent shock FA (that was employed on microalgae during their exponential growth stages) effect on microalgal growth and photosynthesis was observed. Results showed that the studied five FA shock concentrations ranging from 25 to 125 mg/L significantly inhibited biomass production by 14.7-57.0%, but sharp reductions in photosynthesis with the 36.0-49.0% decreased Fv/Fm values were only observed when FA concentration was above 75.0 mg/L. On the other hand, FA shock enhanced microalgal settling efficiency by 12.8-fold, which was believed to be due to the stimulated intra- and extracellular protein contents and thereby the enhanced extracellular polymer substances (EPS) secretion. Specifically, FA shock induced 40.2 ± 2.3% higher cellular protein content at the cost of the decreased carbohydrates (22.6 ± 1.3%) and fatty acid (39.0 ± 0.8%) contents, further improving the protein secretion by 1.21-fold and the EPS production by 40.2 ± 2.3%. These FA shock-induced variations in intra- and extracellular biomolecules were supported by the up-regulated protein processing and export at the assistance of excessive energy generated from fatty acid degradation and carbohydrates consumption. In addition, FA shock significantly decreased the biomass nutritional value as indicated by the 1.86-fold lower essential amino acid score and nearly 50% reduced essential to non-essential amino acids ratio, while slightly decreased the biodiesel quality. This study is expected to enrich the knowledge of microalgal activities and settling performance in response to fluctuant ammonium concentrations in wastewater and to promote the development of microalgal wastewater treatment.