Effect of temperature & salt concentration on salt tolerant nitrate-perchlorate reducing bacteria: Nitrate degradation kinetics

A systematic review of strategies to overcome barrier for nitrate separation systems from drinking water: Focusing on waste streams treatment processes

By 2030, the UN General Assembly issued the Sustainable Development Goal 6, which calls for the provision of safe drinking water. However, water resources are continuously decreasing in quantity and quality. NO3- is the most widespread pollutant worldwide, threatening both human health and ecosystems. NO3- separation systems (NSS) using IX and membrane-based techniques (MBT) are considered practical and efficient technologies, but the management of IX waste brine (IXWB) and concentrate streams for MBT (CSM), as well as the high salt requirements for IX regeneration, are challenging from both economic and environmental perspectives. It is essential to classify the different waste management strategies in order to examine the current state of research and identify the best option to address these issues. This review provides harmonized information on IXWB/CSM management strategies. This study is the first systematic review of all papers available in the Web of Science, Scopus, and PubMed databases published until February 2023. 75% of the studies focused on the use of biological denitrification (BD) and catalytic denitrification (CD). Although innovative technologies (bio-regeneration and direct CD) have advantages over indirect processes, they are not yet practical for large-scale plants because their reliability is unknown. Moreover, the generation of NH4+ is the major challenge for application large-scale of chemical reduction. An innovative work flow diagram, challenges, and future prospects are presented. The review shows that integrating modified NSS with IXWB/CSM treatment is a promising sustainable solution, as the combination could be economically and environmentally beneficial and remove barriers to NNS application.

Impacts of co-contaminants and dilution on perchlorate biodegradation using various carbon sources

This research investigates the biodegradation of perchlorate in the presence of the co-contaminants nitrate and chlorate using soluble and slow-release carbon sources. In addition, the impact of bio-augmentation and dilution, which results in lower total dissolved salts (TDS) and contaminant levels, is examined. Laboratory microcosms were conducted using actual groundwater and soils from a contaminated aquifer. The results revealed that both soluble and slow-release carbon sources support biodegradation of contaminants in the sequence nitrate > chlorate > perchlorate. Degradation rates, including and excluding lag times, revealed that the overall impact of the presence of co-contaminants depends on degradation kinetics and the relative concentrations of the contaminants. When the lag time caused by the presence of the co-contaminants is considered, the degradation rates for chlorate and perchlorate were two to three times slower. The results also show that dilution causes lower initial contaminant concentrations, and consequently, slower degradation rates, which is not desirable. On the other hand, the dilution resulting from the injection of amendments to support remediation promotes desirably lower salinity levels. However, the salinity associated with the presence of sulfate does not inhibit biodegradation. The naturally occurring bacteria were able to support the degradation of all contaminants. Bio-augmentation was effective only in diluted microcosms. Proteobacteria and Firmicutes were the dominant phyla identified in the microcosms.

Spatio-temporal patterns of Synechococcus oligotypes in Moroccan lagoonal environments

Synechococcus are unicellular cyanobacteria susceptible to environmental fluctuations and can be used as bioindicators of eutrophication in marine ecosystems. We examined their distribution in two Moroccan lagoons, Marchica on the Mediterranean coast and Oualidia on the Atlantic, in the summers of 2014 and 2015 using 16S rRNA amplicon oligotyping. Synechococcus representatives recruited a higher number of reads from the 16S rRNA in Marchica in comparison to Oualidia. We identified 31 Synechococcus oligotypes that clustered into 10 clades with different distribution patterns. The Synechococcus community was mainly represented by oligotype 1 (clade III) in Marchica. Cooccurring clades IV and I had an important relative abundance in Marchica in the summer of 2014, which is unusual, as these clades are widespread in cold waters. Moreover, Clades VII and subcluster "5.3" formed a sizeable percentage of the Synechococcus community in Marchica. Notably, we found low Synechococcus sequence counts in the Atlantic Lagoon. These results showed that the relative abundance of Synechococcus reads is not constant over space and time and that rare members of the Synechococcus community did not follow a consistent pattern. Further studies are required to decipher Synechococcus dynamics and the impact of environmental parameters on their spatial and temporal distributions.

Enhancing robustness of halophilic aerobic granule sludge by granular activated carbon at decreasing temperature

High salinity seriously inhibits the growth and metabolism of microorganisms, resulting in poor settleability, excessive biomass loss and low treatment efficiency of biological wastewater treatment systems. The development of halophilic aerobic granular sludge (HAGS) is a feasible strategy for addressing this challenge. However, there are problems with the granulation of HAGS and the stability of granules at decreasing temperatures. In this study, granular activated carbon (GAC) with a large specific surface area and good biocompatibility was used to enhance the robustness of HAGS. The results showed that the addition of GAC shortened the granulation time from 60 d (control system) to 35 d (GAC-addition system). The proteins contents of extracellular polymeric substances (EPS) in the GAC-addition system was significantly higher (p < 0.05) than that in the control system during granulation. Satisfactory NH₄⁺-N and chemical oxygen demand (COD) removal efficiencies reached more than 96% in both systems at 18-26 °C. When the operating temperature was lower than 15 °C, the GAC-addition system exhibited better NH₄⁺-N removal performance (>80%) than the control system (<60%). Moreover, the abundance of almost all nitrogen metabolism-related genes in the GAC-addition system was higher than that in the control system. During the granulation process, the enrichment of functional microorganisms, including family Flavobacteriaceae, Rhodobacteraceae, and Cryomorphaceae, may promote the production of EPS by significantly upregulating (p < 0.05) the metabolic pathway "Signaling Molecules and Interaction" in the GAC-addition system. The overexpression of the nitrogen assimilation gene glnA in heterotrophic bacteria (Halomonas and Marinobacterium) may promote the conversion of inorganic nitrogen to extracellular proteins to adapt to the decreased operational temperature. Our findings confirm that GAC addition is a simple but effective strategy to accelerate granulation and enhance the robustness of HAGS in saline wastewater treatment.

Treatment try of simulated agricultural surface runoff pollution by using a novel biomass concentrator reactor

Increased agricultural surface runoff in rural watersheds is a leading cause of nonpoint source pollution. In this study, a new biomass concentrator reactor (BCR) is conducted to degrade simulated agricultural surface runoff for both start-up process and treatment process. The results show that both in the start-up phase and in the stable phase, BCR had a good degradation effect on simulated agricultural surface runoff. Within 13 days-15 days of completed start-up of BCR, degradation of COD can be considered to the first-order kinetics: lnC_t=lnC₀-0.1377t (R² = 0.78). During the stabilization phase, the average removal rate of COD, NH₄⁺-N, NO₃^--N, TN and TP from the effluents through the BCR membrane was 94.58%, 85.79%, 53.58%, 37.87%, and 60.62%, respectively, which was increased by 7.4%, 2.5%, 5.1%, 0.18% and 11.4%, respectively, compared to control experiment which the effluents without membrane. The pollutants degradation by BCR in stable phase show a partly relative model of Lawrence-McCarty equation, which the nitrogen and phosphorus degradation is v_N=(4.1+S)/(2.53×S) (R² = 0.69) and v_P=(8.78+S)/(3.0×S) (R² = 0.67), respectively. In the stable phase, the operation cost of BCR is about $0.08/(L•d). Future research on improved BCR maybe focus on the membrane pollution and cleaning, optimized operation conditions, new materials of membrane.

Sustainable treatment of nitrate-containing wastewater by an autotrophic hydrogen-oxidizing bacterium

Bacteria are key denitrifiers in the reduction of nitrate (NO₃ ^--N), which is a contaminant in wastewater treatment plants (WWTPs). They can also produce carbon dioxide (CO₂) and nitrous oxide (N₂O). In this study, the autotrophic hydrogen-oxidizing bacterium Rhodoblastus sp. TH20 was isolated for sustainable treatment of NO₃ ^--N in wastewater. Efficient removal of NO₃ ^--N and recovery of biomass nitrogen were achieved. Up to 99% of NO₃ ^--N was removed without accumulation of nitrite and N₂O, consuming CO₂ of 3.25 mol for each mole of NO₃ ^--N removed. The overall removal rate of NO₃ ^--N reached 1.1 mg L^-1 h^-1 with a biomass content of approximately 0.71 g L^-1 within 72 h. TH20 participated in NO₃ ^--N assimilation and aerobic denitrification. Results from ¹⁵N-labeled-nitrate test indicated that removed NO₃ ^--N was assimilated into organic nitrogen, showing an assimilation efficiency of 58%. Seventeen amino acids were detected, accounting for 43% of the biomass. Nitrogen loss through aerobic denitrification was only approximately 42% of total nitrogen. This study suggests that TH20 can be applied in WWTP facilities for water purification and production of valuable biomass to mitigate CO₂ and N₂O emissions.

Application of encapsulated algae into MBR for high-ammonia nitrogen wastewater treatment and biofouling control

Low microbial activity and serious membrane biofouling are still critical problems that hinder the extensive application of membrane bioreactor (MBR) for industrial wastewater treatment. To address these bottlenecks, we report a new specialized microorganism encapsulation strategy for constructing a highly efficient MBR system. In our study, the algae-entrapping fiber macrospheres with polymeric coating were first coupled with membrane separation for treating refractory high-ammonia nitrogen wastewater. In comparison with traditional alginate beads, the developed macrocapsule (~0.5 cm) exhibited higher biomass harvesting and lower microbial leakage because of the confined micro-aerobic environment created by dual encapsulation of rigid inorganic macrosphere and porous polymeric layers. Application of algae-encapsulating macrocapsule to MBR presented excellent chemical oxygen demand (COD) and ammonia nitrogen (NH₃-N) removal efficiency of 62.23 and 97.38 %, respectively, which were higher than the corresponding values for algae/SA beads and free algae. The biodegradation performance of NH₃-N by encapsulated microalgae was similar or superior to that by free cells when the initial content of ammonia nitrogen ranged from 50 to 100 mg/L. The results well demonstrated that the GFS@polymer macrocapsule as a physical barrier reduced the inhibitory effect of higher concentration ammonia nitrogen on the bioactivity of living cells. Importantly, the encapsulated core-shell macrocapsules showed superior anti-biofouling capacity, which had a membrane resistance of 3-5 times lower than that of cell/alginate beads and free cells. This work will open a new avenue to develop a novel encapsulated MBR for various non-degradable wastewater treatments as an energy-saving and sustainable way.

Enhanced aerobic granulation at low temperature by stepwise increasing of salinity

High salinity and low temperature are generally considered to have negative effects on the formation, stability and performance of aerobic granular sludge (AGS). This study investigated whether and how salinity acclimation strategies can enhance aerobic granulation at low temperature (12 °C) in three sequencing batch reactors (SBRs). Stepwise increased concentrations of NaCl (2-10 and 4-20 g/L) were added to the influent of R1 and R2 with steps of 1 and 2 g/L per week respectively, while R0 was set as a control (salt-free). The granulation processes in R1 and R2 were rapidly started up within 9 days, and were completed within 21 and 18 days, respectively. By contrast, R0 took 25 days and 49 days to start and complete granulation. The salinity acclimation strategies improved sludge hydrophobicity, reduced repulsion barrier between cells, and stimulated EPS production during granulation processes, which simultaneously promoted the formation of AGS. When the influent salinity reached 14 g/L on day 35, granule hydrophobicity, density and size in R2 sharply decreased and granules began to disintegrate afterwards. When operated under salt-free condition, sludge bulking occurred in R0 since day 60. The treatment performance was thus impaired in these two reactors, especially in R2 with significant biomass loss. Conversely, the AGS developed in R1 maintained stable structure with high biomass concentration (8.0 gSS/L) and excellent treatment performance for COD (90%), ammonium (95%) and total nitrogen (70%). Genera Thauera, Azoarcus, and Nitrosomonas were more enriched, while Flavobacterium and Meganema were more suppressed in R1, which would have contributed to granule stability and treatment performance. In conclusion, great care has to be taken for cultivating and operating AGS at low temperature for treating saline wastewater. Increasing salinity with a lower salt gradient provides a possibility for rapid granulation of AGS with excellent treatment performance under such conditions.

Nitrogen Removal and N2O Accumulation during Hydrogenotrophic Denitrification: Influence of Environmental Factors and Microbial Community Characteristics

Hydrogenotrophic denitrification is regarded as an efficient alternative technology of removing nitrogen from nitrate-polluted water that has insufficient organics material. However, the biochemical process underlying this method has not been completely characterized, particularly with regard to the generation and reduction of nitrous oxide (N₂O). In this study, the effects of key environmental factors on hydrogenotrophic denitrification and N₂O accumulation were investigated in a series of batch tests. The results show that nitrogen removal was efficient with a specific denitrification rate of 0.66 kg N/(kg MLSS·d), and almost no N₂O accumulation was observed when the dissolved hydrogen (DH) concentration was approximately 0.40 mg/L, the temperature was 30 °C, and the pH was 7.0. The reduction of nitrate was significantly affected by the pH, temperature, inorganic carbon (IC) content, and DH concentration. A considerable accumulation of N₂O was only observed when the pH decreased to 6.0 and the temperature decreased to 15 °C, where little N₂O accumulated under various IC and DH concentrations. To determine the microbial community structure, the hydrogenotrophic denitrifying enrichment culture was analyzed by Illumina high-throughput sequencing, and the dominant species were found to belong to the genera Paracoccus (26.1%), Azoarcus (24.8%), Acetoanaerobium (11.4%), Labrenzia (7.4%), and Dysgonomonas (6.0%).

Experimental studies and kinetic modeling of the growth of phenol-degrading bacteria in turbulent fluids

Understanding the interaction between microorganisms and fluid dynamics is important for aquatic ecosystems, though only sporadic attention has been focused on this topic in the past. In this study, particular attention was paid to the phenol-degrading bacterial strains Microbacterium oxydans LY1 and Alcaligenes faecalis LY2 subjected to controlled fluid flow under laboratory conditions. These two strains were found to be able to degrade phenols over a concentration range from 50 to 500 mg/L under different turbulence conditions ranging from 0 to 250 rpm. The time it took to reach total phenol degradation decreased when the turbulence was increased in both strains, with increasing energy dissipation rates ranging from 0.110 to 6.241 W/kg, corresponding to changes in the bacterial diffusive sublayer thickness (δ) and enhanced oxygen uptake. Moreover, the maximum specific growth rates of the two strains also increased with the enhancement of turbulence. A model integrating growth inhibition and fluid motion was proposed based on the self-inhibition Haldane model by introducing a turbulence parameter, α. The resulting modified Haldane model was designed to include fluid motion as a variable in the quantification of the physiological responses of microorganisms. This modified Haldane model could be considered a useful laboratory reference when modeling procedures for water environment bioremediation. Graphical abstract Cell nutrition uptake cartoon schematic diagram for M. oxydans LY1 under different turbulent condition (50 and 200 rpm).

Mathematical modelling and reactor design for multi-cycle bioregeneration of nitrate exhausted ion exchange resin

Nitrate contamination is one of the largest issues facing communities worldwide. One of the most common methods for nitrate removal from water is ion exchange using nitrate selective resin. Although these resins have a great capacity for nitrate removal, they are considered non regenerable. The sustainability of nitrate-contaminated water treatment processes can be achieved by regenerating the exhausted resin several times rather than replacing and incineration of exhausted resin. The use of multi-cycle exhaustion/bioregeneration of resin enclosed in a membrane has been shown to be an effective and innovative regeneration method. In this research, the mechanisms for bioregeneration of resin were studied and a mathematical model which incorporated physical desorption process with biological removal kinetics was developed. Regardless of the salt concentration of the solution, this specific resin is a pore-diffusion controlled process (XδD ¯CDr0(5+2α)<<1). Also, Thiele modulus was calculated to be between 4 and 12 depending on the temperature and salt concentration. High Thiele modulus (>3) shows that the bioregeneration process is controlled by reaction kinetics and is governed by biological removal of nitrate. The model was validated by comparison to experimental data; the average of R-squared values for cycle 1 to 5 of regeneration was 0.94 ± 0.06 which shows that the developed model predicted the experimental results very well. The model sensitivity for different parameters was evaluated and a model bioreactor design for bioregeneration of highly selective resins was also presented.