Isolation of a non-fermentative bacterium, Pseudomonas aeruginosa, using intracellular carbon for denitrification and phosphorus-accumulation and relevant metabolic mechanisms

High organic volumetric loading rates triggered heterotrophic nitrification in wastewater biological nutrient removal systems

This study confirmed the importance of a higher chemical oxygen demand (COD) volumetric loading rate (CODLR) for triggering heterotrophic nitrification in a lab-scale anoxic/microaerobic biological nutrient removal system for sewage treatment by analyzing the ammonia-oxidizing activities, nitrogen mass balance, and ammonia-oxidizing bacterial communities at four CODLR levels: 0.50 (Phase A), 0.75, 1.10, and 1.50 (Phase D) kg COD m-3 d-1. A higher CODLR led to a significant increase in the potential heterotrophic nitrification activity by 0.4, 0.9, 1.1, and 1.6 mg NH4±-N/g mixed liquor suspended solids h-1, respectively, contributing 7 %, 14 %, 17 %, and 21 % of the ammonia oxidization in the anoxic/microaerobic system. Furthermore, nitrogen balance analysis revealed that heterotrophic nitrifying bacteria contributed 4 % and 12 % of the ammonia oxidization in the anoxic/microaerobic system during Phases A and D, respectively, and that a more plentiful organic carbon supply in the microaerobic zone stimulated heterotrophic nitrification during Phase D.

Modeling and optimization of triclosan biodegradation by the newly isolated Bacillus sp. DL4: kinetics and pathway speculation

Triclosan is a widely used antibacterial agent and disinfectant, and its overuse endangered ecological safety and human health. Therefore, reducing residual TCS concentrations in the environment is an urgent issue. Bacillus sp. DL4, an aerobic bacterium with TCS biodegradability, was isolated from pharmaceutical wastewater samples. Response surface methodology (RSM) and artificial neural network (ANN) were carried out to optimize and verify the different condition variables, and the optimal growth conditions of strain DL4 were obtained (35 °C, initial pH 7.31, and 5% v/v). After 48 h of cultivation under the optimal conditions, the removal efficiency of strain DL4 on TCS was 95.89 ± 0.68%, which was consistent with the predicted values from RSM and ANN models. In addition, higher R2 value and lower MSE and ADD values indicated that the ANN model had a stronger predictive capability than the RSM model. Whole genome sequencing results showed that many functional genes were annotated in metabolic pathways related to TCS degradation (e.g., amino acid metabolism, xenobiotics biodegradation and metabolism, carbohydrate metabolism). Main intermediate metabolites were identified during the biodegradation process by liquid chromatography-mass spectrometry (LC-MS), and a possible pathway was hypothesized based on the metabolites. Overall, this study provides a theoretical foundation for the characterization and mechanism of TCS biodegradation in the environment by Bacillus sp. DL4.

Enhanced nitrogen removal via Yarrowia lipolytica-mediated nitrogen and related metabolism of Chlorella pyrenoidosa from wastewater

We investigated the optimum co-culture ratio with the highest biological nitrogen removal rate, revealing that chemical oxygen demand, total nitrogen (TN), and ammoniacal nitrogen (NH₃-N) removal was increased in the Chlorella pyrenoidosa and Yarrowia lipolytica co-culture system at a 3:1 ratio. Compared with the control, TN and NH₃-N content in the co-incubated system was decreased within 2-6 days. We investigated mRNA/microRNA (miRNA) expression in the C. pyrenoidosa and Y. lipolytica co-culture after 3 and 5 days, identifying 9885 and 3976 differentially expressed genes (DEGs), respectively. Sixty-five DEGs were associated with Y. lipolytica nitrogen, amino acid, photosynthetic, and carbon metabolism after 3 days. Eleven differentially expressed miRNAs were discovered after 3 days, of which two were differentially expressed and their target mRNA expressions negatively correlated with each other. One of these miRNAs regulates gene expression of cysteine dioxygenase, hypothetical protein, and histone-lysine N-methyltransferase SETD1, thereby reducing amino acid metabolic capacity; the other miRNA may promote upregulation of genes encoding the ATP-binding cassette, subfamily C (CFTR/MRP), member 10 (ABCC10), thereby promoting nitrogen and carbon transport in C. pyrenoidosa. These miRNAs may further contribute to the activation of target mRNAs. miRNA/mRNA expression profiles confirmed the synergistic effects of a co-culture system on pollutant disposal.

Treatment of micro-polluted water with low C/N ratio by immobilized bioreactor using PVA/sintered ores@sponge cube: Performance effects and potential removal pathways

The widespread use of industrial products containing lead (Pb²⁺) and tetracycline (TC) medications led to the combined pollution of nitrate, Pb²⁺, and TC in water. A novel biomaterial containing polyvinyl alcohol (PVA) and sponge cube with sintered ores (PVA/sintered ores@sponge cube) was prepared to ensure the maximum NO₃^--N removal efficiency (96.21 %) of the bioreactor under the hydraulic retention time (HRT) of 7.0 h, pH of 6.0, and the carbon to nitrogen (C/N) of 1.5 that had the ability to remove TC and Pb²⁺ synergistically. Composite pollutants slightly decreased denitrification performance in the combined pollution system on account of the addition of sintered ores. Results of scanning electron microscopy (SEM) showed that the sintered ores in the biocarrier induced denitrification and the adsorption of bio‑iron oxides were involved in the removal of TC and Pb²⁺. The simultaneous removal of composite pollutants during denitrification was facilitated by extracellular polymeric substances (EPS) as revealed by Fourier transform infrared spectroscopy (FTIR) and fluorescence excitation-emission matrix (EEM). In addition, high-throughput sequencing results showed that Zoogloea had the highest proportion in the bioreactor.

Nutrient and organic pollutants removal in synthetic wastewater by Pseudomonas aeruginosa and Chryseobacterium sp./biofilter systems

Nutrient and organic pollution raise serious problems for aquatic ecosystems through the accumulation of organic carbon, the reduction of light penetration, and the loss of submerged aquatic vegetation. The over-enrichment of water with nitrogen and phosphorus leads to an imbalance in nutrient ratios, creating favorable conditions for toxic algal blooms, formation of oxygen-depleted water, etc. Thus, developing new technological solutions to reduce their amount is imperative. The present study investigates the capacity of Pseudomonas aeruginosa and Chryseobacterium sp. bacterial strains to form biofilm on solid support (biofilter), both individually and in tandem, using various analytical techniques. Also, the biofilm/biofilter systems' efficiency in removing nutrients such as nitrate, nitrite, ammonium, and phosphate ions from municipal wastewaters is assessed. The results showed a reduction of nutrient pollution of up to 91%, 98%, 55%, and 71% for nitrite, nitrate, ammonium, and phosphate ions. A reduction of about 78% of COD was also observed. The results were obtained in the absence of an additional aeration process, thus having a great potential for reducing total costs of wastewater treatment and developing ecological systems for wastewater management.

Nitrogen transformation in slightly polluted surface water by a novel biofilm reactor: Long-term performance and microbial population characteristics

This study proposes a modular floating biofilm reactor (MFBR) for in situ nitrogen removal from slightly polluted water in rivers using enriched indigenous microorganisms. Its main structure is a 60 cm × 60 cm × 90 cm rectangular reactor filled with hackettens. After a 96-day startup, the removal efficiencies of ammonia-N and total N (TN) reached 80% and 25%, respectively, with a hydraulic retention time (HRT) of 10 h, whereas those in a control reactor (without biofilm) were only 4.9% and 0.2%, respectively. The influences of HRT and dissolved oxygen (DO) were also investigated. As a key factor, HRT significantly affected the removal efficiencies of ammonia-N and TN. When HRT was close to the actual value for a river studied (2.4 min), the removal efficiencies of ammonia-N and TN were only 8.7% and 3.1%, respectively. Aeration increased the concentration of DO in water, which enhanced nitrification but inhibited denitrification. When HRT was 2.4 min, aeration intensity was 20 L/min; the ammonia-N and TN removal rates were 9.5 g/(m²·d) and 11.3 g/(m²·d), respectively. The results of microbial community analysis indicated that the microorganisms forming the biofilm were indigenous bacteria. The findings demonstrated a concept-proof of MFBR, which may be evaluated in scaling up investigation for developing a new methodology for nitrogen removal from slightly polluted surface water in plain river networks.

Response of the aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 to low temperature and zinc oxide nanoparticles stress

Performance and molecular changes of an aerobic denitrifying phosphorus accumulating bacteria Pseudomonas psychrophila HA-2 have been investigated under different temperatures and ZnO nanoparticles (NPs) exposures. Strain HA-2 removed 95.7% of total nitrogen (TN) and 24.6% of phosphorus at 10 °C, which was attributed to the joint up-regulation of intracellular energy metabolism and ribosome. Moreover, with the increase of ZnO NPs from 0 to 100 mg/L, TN and phosphurs removal efficiencies decreased from 95.7% to 44.5% and 24.6% to 6.8% at 10 °C, respectively, whereas phosphorus removal rate increased from 10.5% to 24.5% at 20 °C. Further transcriptomics and proteomics revealed that significant down-regulation of purine and amino acid metabolisms was the main reason for the inhibitory effect at 10 °C, while the up-regulation of antioxidant pathways and functional genes expressions was responsible for the promoted phosphorus accumulation at 20 °C. This study provides a potential solution for improving biological nutrients removal processes in winter months.

Pilot study on the treatment of low carbon and nitrogen ratio municipal sewage by A1/O2/A3/A4/O5 sludge-membrane coupling process with multi-point inflow

A new multi-point inflow pre-anoxic/oxic/anaerobic/anoxic/oxic (A1/O2/A3/A4/O5) sludge-membrane coupling process and pilot plant were developed and designed to solve the problem of nitrogen and phosphorus removal of low carbon and nitrogen (C/N) ratio domestic sewage in southern China. The removal effect and transformation rule of organic matter, nitrogen, and phosphorus in the system were studied by changing the distribution ratio of multi-point influent. The average C/N ratio of the influent was 2.09 and the influent distribution ratio was 1:1. When the temperature was 16-25 °C, the average concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺- N), total nitrogen (TN), and total phosphorus (TP) in the effluent were 21.31 (±2.65), 0.60 (±0.24), 12.76 (±1.09), and 0.34 (±0.05) mg/L, respectively, and their average removals are 87.3 (±1.2)%, 98.7 (±0.4)%, 74.1 (±1.3)%, and 88.1 (±0.4)% respectively. When the low temperature was 12-15 °C, the average removals were 78.6 (±1.1)%, 90.5 (±1.3)%, 73.7 (±1.13)%, and 86.6 (±1.7)%, respectively. Compared with the traditional anaerobic/anoxic/aerobic (A2O) process under the same conditions, the TN removal was increased by 15.4%, and the TP removal was increased by 22.2%. This system has obvious advantages in treating wastewater with low C/N ratio, thereby solving the problem wherein the effluent of biological phosphorus removal from low C/N ratio domestic sewage was difficult when it was lower than 0.5 mg/L.

Biological nitrogen and phosphorus removal by a phosphorus-accumulating bacteria Acinetobacter sp. strain C-13 with the ability of heterotrophic nitrification-aerobic denitrification

Strain C-13, identified as an Acinetobacter sp. by homology searches, exhibited efficient simultaneous heterotrophic nitrification-aerobic denitrification phosphorus removal (SNDPR) abilities by nitrogen balance analysis and further confirmation of successful amplification of functional genes ppk, napA, and nirS. In addition, strain C-13 could utilize NH₄⁺-N, NO₃^--N, and NO₂^--N as nitrogen sources, among which NH₄⁺-N was indicated to be an excellent nitrogen source for assimilation and heterotrophic nitrification. Besides, the optimum conditions for nutrient removal were determined as follows: sodium acetate as the sole carbon source, C/N/P ratio of 100/10/2, pH = 7.5, and temperature of 30 °C. Meanwhile, the strain also showed the traditional features, such as release and the excess uptake of phosphate under anaerobic/aerobic conditions, with the highest phosphorus content of 5.01% after cultivation. Strain C-13 presents promising prospects for application in biologicalnutrient removal in wastewater treatment.

Triclosan in contact with activated sludge and its impact on phosphate removal and microbial community

Triclosan (TCS) is applied in a wide range of pharmaceutical and personal care products to prevent or reduce bacterial growth. In this study, the effects of TCS on phosphate removal and bacterial community shifts of activated sludge, especially on functional bacteria variation, were investigated. Compared with the control group (R-control), the treatment group (R-TCS) with 100 μg/L TCS inhibited the microbial growth. In addition, the phosphorus removal efficiency of PO₄^3--P and total phosphorus removal rates declined by 15.99% and 7.81%, respectively. Proteobacteria gradually dominated the microorganisms. The growths of Proteobacteria and Bacteroidetes were inhibited when 150 μg/L of TCS was added. Moreover, the differences in the microbial community structures of the R-control and R-TCS groups gradually expanded, no obvious difference was observed in the final stage, and the interrelationships of microbes in the latter weakened. The long-term addition of TCS impairs the growth of polyphosphate-accumulating organisms (PAOs).

Simultaneous nitrogen and phosphorus removal by interactions between phosphate accumulating organisms (PAOs) and denitrifying phosphate accumulating organisms (DPAOs) in a sequencing batch reactor

The identification of phosphate-accumulating organisms (PAOs), denitrifying phosphate-accumulating organisms (DPAOs) and their relationship is a key pathway for optimizing nitrate and phosphate removal efficiency in activated sludge. In this study, the acclimatization of microorganisms in sequencing batch reactor were performed with anaerobic/aerobic (A/O) and anaerobic/anoxic (A/A) cycles, the biomass changes of PAOs and DPAOs and the correlations were then discussed. The results indicated that after acclimatization, the nutrient removal efficiencies reached to 85.34% (COD), 93.64% (PO₄^3--P) and 92.34% (NO₃^--N), respectively, with NO₃^--N:PO₄³-P of 1.5:1. The successful enrichment of PAOs and DPAOs (reached 97.9%) was verified by the change of relative metabolic activities, which was further proved by the change of bacterial diversity. The number of Candidatus Accumulibacter, Zoogloea, and Dechloromonas all increased at A/O and A/A stages while the number of Acinetobacter only increased at A/O stage. So Accumulibacter sp. was DPAO while Acinetobacter sp. was only PAO in this process, and genera Accumulibacter, Dechloromonas and Zoogloea greatly coordinated in denitrification and accumulating phosphorous though RDA and chord plot. This was worthy of attention and development to explore enhanced biological phosphorus removal (EBPR) in practical wastewater treatment via improving identification of bacterial species and symbiosis of bacteria community.

Replacement of feed by fresh microalgae as a novel technology to alleviate water deterioration in aquaculture

The main aim of this work was to evaluate the feasibility of microalgae-assisted aquaculture and explore the relevant mechanisms. In this regard, our work explored the pollution problems in traditional aquaculture and studied the contribution of microalgae to eutrophication control, oxygen gas production and feed replacement. Besides, potential protection mechanisms of microalgae-assisted aquaculture were studied by bacterial community profile analysis and microscope observation. The results showed that microalgae performed well in nutrient assimilation and oxygen production, thus slowing down the eutrophication and preventing oxygen depletion in aquaculture. Study of the mechanisms revealed that microalgae-assisted aquaculture contained much fewer pathogens and a microalgal biofilm was formed to prevent the eutrophication caused by sludge degradation. It is expected that the findings in this work can support the further development of microalgae-assisted aquaculture and promote the industry upgrade.

Toxicity alleviation for microalgae cultivation by cationic starch addition and ammonia stripping and study on the cost assessment

Aiming at promoting microalgae-based anaerobically digested swine manure (AD-SM) treatment, this work evaluated the feasibility of removing turbidity and ammonia in swine manure by cationic starch addition and air bubbling-driven ammonia stripping. It was observed that turbidity and ammonia toxicity were two main factors limiting algae growth. Addition of cationic starch effectively reduced turbidity of AD-SM by 77.10% in 40 min. 6 L min⁻¹ air flow rate and 5 h stripping time were regarded as good conditions for ammonia stripping. An economic analysis was conducted to assess the feasibility of this pretreatment strategy in a pilot scale system and results indicated that unit energy input and freshwater consumption were 0.036 kW h g⁻¹ dry biomass and 0.76 L g⁻¹ dry biomass, respectively, much lower than those of a high dilution strategy. So it is a more promising and feasible way to pretreat AD-SM with low dilution by turbidity removal and ammonia stripping.

Aiming at promoting microalgae-based anaerobically digested swine manure (AD-SM) treatment, this work evaluated the feasibility of removing turbidity and ammonia in swine manure by cationic starch addition and air bubbling-driven ammonia stripping.

A novel approach of using zeolite for ammonium toxicity mitigation and value-added Spirulina cultivation in wastewater

Owning to the ammonium toxicity, some ammonium-rich wastewater may not be used for algae cultivation. To overcome this problem, herein, a novel approach of using zeolite to mitigate ammonium toxicity in wastewater for value-added Spirulina production was proposed. Synthetic zeolite was used as medium for ammonium adsorption in wastewater and subsequently as slow-releaser providing nitrogen to Spirulina growth. The optimal conditions for ammonium adsorption include pH value of 8.0, zeolite dose of 300 g/L, and adsorption time of 9 h. The results showed that in terms of biomass production and ammonium recovery, zeolite-based pretreatment has great advantages over some conventional pretreatment technologies. After algae-assisted desorption treatment, ammonium adsorption capacity of zeolite increased back to 1.21 mg/g. In a real-world application, this work will provide a feasible and sustainable approach to remediate ammonium-rich wastewater, produce value-added Spirulina biomass, and recycle used zeolite, further promoting the industrialization of algae-based wastewater remediation.

Single-stage denitrifying phosphorus removal biofilter utilizing intracellular carbon source for advanced nutrient removal and phosphorus recovery

Advanced nutrient removal of municipal wastewater has insufficient carbon source, and resource recovery is neglected. In this study, a single-stage biofilter based on denitrifying phosphorus removal (DPR) was proposed for advanced nutrient removal and phosphorus recovery, which was operated under alternating anoxic/anaerobic mode with no extracellular carbon source in anoxic period. The results showed that the biofilter achieved efficient and stable performance with low carbon consumption (C/N ≈ 3.7). The average removal efficiency of NO₃^--N, TN and PO₄^3--P were 74.81%, 71.08% and 91.15%, respectively. DPR primarily occurred in the middle of the filtration bed and nutrient removal was driven by intracellular polymers, which was the main carbon source. High-throughput sequencing indicated that Dechloromonas was enriched and contributed to DPR while Zoogloea was responsible for endogenous denitrification. Denitrifying polyphosphate accumulating organisms and endogenous denitrifiers synergistically enhanced the nutrient removal capacity. The study further provides research perspectives for improving nutrient removal.

Development of denitrifying phosphate accumulating and anammox micro-organisms in anaerobic hybrid reactor for removal of nutrients from low strength domestic sewage

Low strength domestic sewage was treated in an Anaerobic Hybrid Reactor. The first phase was focused on the enhancement of denitrifying phosphate accumulating organisms (DPAOs) for the concurrent removal of nitrogen and phosphate. 16S rRNA gene confirmed the presence of Flavobacterium spp. and Pseudomonasalcaligenes spp. which are dominant DPAOs. The second phase was the anaerobic ammonium oxidation (anammox) enrichment phase, and it exhibited much higher chemical oxygen demand (87%) and nitrogen removal (90%) as compared to the first phase. However, it had failed to remove the phosphate from the system. In case of anammox, the dominant specie detected was Candidatus Brocadia, along with minor counts of Candidatus Jettenia and Anammoxoglobus Propionicus. Apart from that, ammonia oxidizing bacteria (Nitrosomonas europaea, Nitrosomonas nitrosa) and methanogens (Methanosaeta, Methanobacterium) were also detected in the system. This study showed the feasibility of anammox species over DPAOs in treating domestic sewage.

Enhancement of the adaptability of anammox granules to zinc shock by appropriate organic carbon treatment

Heavy metals, which are commonly present in high ammonia-containing wastewater, can cause inhibitory effects to anammox reaction. This study proposes a novel approach to enhance the adaptability of anammox granules to heavy metal [Zn(II)] shock by organic carbon (sodium acetate, NaAc) treatment, paying special attention to optimization of the treatment dosage and duration. For granules treated with 200 mg chemical oxygen demand (COD)/L NaAc for 2 d, the activity recovery (six cycles) efficiency after Zn(II) (40 mg/L) shock reached 127.4%. The extracellular polymeric substance (EPS) production increased by 168% and heterotrophic bacteria mildly proliferated (increased by 14%) in such granules compared with the control. The dramatic recovery capacity was likely due to the entrapment and barrier function of EPS and the outer-layer proliferated heterotrophic bacteria. This finding offers a useful process to enable maximum adaptability of anammox granules from heavy metals shocks, allowing anammox technology to be more widely applied.

Carbon-dependent alleviation of ammonia toxicity for algae cultivation and associated mechanisms exploration

Ammonia toxicity in wastewater is one of the factors that limit the application of algae technology in wastewater treatment. This work explored the correlation between carbon sources and ammonia assimilation and applied a glucose-assisted nitrogen starvation method to alleviate ammonia toxicity. In this study, ammonia toxicity to Chlorella sp. was observed when NH₃-N concentration reached 28.03mM in artificial wastewater. Addition of alpha-ketoglutarate in wastewater promoted ammonia assimilation, but low utilization efficiency and high cost of alpha-ketoglutarate limits its application in wastewater treatment. Comparison of three common carbon sources, glucose, citric acid, and sodium bicarbonate, indicates that in terms of ammonia assimilation, glucose is the best carbon source. Experimental results suggest that organic carbon with good ability of generating energy and hydride donor may be critical to ammonia assimilation. Nitrogen starvation treatment assisted by glucose increased ammonia removal efficiencies and algal viabilities.

Exploration of a mechanism for the production of highly unsaturated fatty acids in Scenedesmus sp. at low temperature grown on oil crop residue based medium

The ability of algae to produce lipids comprising of unsaturated fatty acids varies with strains and culture conditions. This study investigates the effect of temperature on the production of unsaturated fatty acids in Scenedesmus sp. grown on oil crop residue based medium. At low temperature (10°C), synthesis of lipids compromising of high contents of unsaturated fatty acids took place primarily in the early stage while protein accumulation mainly occurred in the late stage. This stepwise lipid-protein synthesis process was found to be associated with the contents of acetyl-CoA and α-KG in the algal cells. A mechanism was proposed and tested through simulation experiments which quantified the carbon flux allocation in algal cells at different cultivation stages. It is concluded that low culture temperature such as 10°C is suitable for the production of lipids comprising of unsaturated fatty acids.

Pretreatment of brewery effluent to cultivate Spirulina sp. for nutrients removal and biomass production

Due to the low concentration of nitrate and high contents of organics, brewery effluent was not suitable for the cultivation of Spirulina sp. This work changed the nutrient profile of brewery effluent effectively by dilution, addition of nitrate, and anaerobic digestion. The result showed that the optimum dilution rate and NaNO₃ addition for brewery effluent were 20% and 0.5 g/L, respectively. Spirulina sp. grown in pretreated brewery effluent produced 1.562 mg/L biomass and reduced concentrations of nutrients to reach the permissible dischargeable limits. In addition, Spirulina sp. grown in pretreated brewery effluent had much higher protein content and oil content. So the appropriate treatment converted brewery effluent into a nutrient balanced medium for algae cultivation and alleviated the potential environmental problems. Pretreatment procedure developed in this work is an effective way to realize the sustainable utilization of brewery effluent and produce algal biomass with valuable nutrients.

Isolation of a bacterial strain, Acinetobacter sp. from centrate wastewater and study of its cooperation with algae in nutrients removal

Algae were able to grow healthy on bacteria-containing centrate wastewater in a pilot-scale bioreactor. The batch experiment indicated that the co-cultivation of algae and wastewater-borne bacteria improved the removal efficiencies of chemical oxygen demand and total phosphorus in centrate wastewater to 93.01% and 98.78%, respectively. A strain of beneficial aerobic bacteria, Acinetobacter sp., was isolated and its biochemical characteristics were explored. Synergistic cooperation was observed in the growth of algae and Acinetobacter sp. Removal efficiencies of some nutrients were improved significantly by the co-cultivation of algae and Acinetobacter sp. After treatment, residual nutrients in centrate wastewater reached the permissible discharge limit. The cooperation between algae and Acinetobacter sp. was in part attributed to the exchange of carbon dioxide and oxygen between the algae and bacteria. This synergetic relationship between algae and Acinetobacter sp. provided a promising way to treat the wastewater by improving the nutrients removal and biomass production.