Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater.

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

Resourceful application and mechanism of oyster shell-microalgae synergistic system：Sustainable treatment of harsh low carbon nitrogen ratio actual wastewater.

Microalgal technology holds great promise for both low C/N wastewater treatment and resource recovery simultaneously. Nevertheless, the advancement of microalgal technology is hindered by its reduced nitrogen removal efficiency in low C/N ratio wastewater. In this work, microalgae and waste oyster shells were combined to achieve a total inorganic nitrogen removal efficiency of 93.85% at a rate of 2.05 mg L-1 h-1 in low C/N wastewater. Notably, over four cycles of oyster shell reuse, the reactor achieved an average 85% ammonia nitrogen removal extent, with a wastewater treatment cost of only $0.092/ton. Moreover, microbial community analysis during the reuse of oyster shells revealed the critical importance of timely replacement in inhibiting the growth of non-functional bacteria (Poterioochromonas_malhamensi). The work demonstrated that the oyster shell - microalgae system provides a time- and cost-saving, environmental approach for the resourceful treatment of harsh low C/N wastewater.

A pilot scale study on the treatment of rare earth tailings (REEs) wastewater with low C/N ratio using microalgae photobioreactor.

Microalgae appear to be a promising and ecologically safe way for nutrients removal from rare earth tailings (REEs) wastewater with CO2 fixation and added benefits of resource recovery and recycling. In this study, a pilot scale (50 L) co-flocculating microalgae photobioreactor (Ma-PBR) as constructed and operated for 140 days to treat REEs wastewater with low C/N ratio of 0.51-0.56. The removal rate of ammonia nitrogen (NH4+-N) reached 88.04% and the effluent residual concentration was as low as 9.91 mg/L that have met the Emission Standards of Pollutants from Rare Earths Industry (GB 26451-2011). Timely supplementation of trace elements was necessary to maintain the activity of microalgae and then prolonged the operation time. The dominant phyla in co-flocculating microalgae was Chlorophyta, the relative abundance of which was higher than 80%. Tetradesmus belonging to Chlorophyceae was the dominant genus with relative abundance of 80.35%. The results provided a practical support for the scaling-up of Ma-PBR to treat REEs wastewater.

Microalgae-bacteria tandem-type ponds simultaneously removing ammonia nitrogen and phosphorus towards municipal wastewater advanced treatment.

Low C/N municipal wastewater is difficult to be treated effectively via traditional biological methods, leading to concentrations of pollutants in effluent far exceeding increasingly strict standards. In this work, we propose a novel microalgae-bacteria tandem-type process to simultaneously remove ammonia nitrogen (NH4+-N) and phosphorus (P) from municipal wastewater. A 4.5 L microalgae-bacteria tandem-type reactor was constructed and operated stably for 40 days. The removal efficiencies of NH4+-N and P reached 97.5% and 92.9%, respectively, effluent concentrations were 0.53 and 0.17 mg/L on average, which met the Environmental quality standards for surface water in China (GB 3838-2002). Remarkably, microalgae ponds accounted for 69.3% and 76.3% of the overall NH4+-N and P removal via microalgae assimilation. Furthermore, 16 S rRNA gene amplicon sequencing revealed the abundance of bacteria changed, suggesting that the presence of microalgae leads to some species extinction and low-abundance bacteria increase. This work demonstrated that the microalgae-bacteria tandem-type processes can be efficient and widely applied in the advanced treatment of municipal wastewater.

A new microalgal negative carbon technology for landfill leachate treatment: Simultaneous removal of nitrogen and phosphorus.

Replete with ammonia nitrogen and organic pollutants, landfill leachate typically undergoes treatment employing expensive and carbon-intensive integrated techniques. We propose a novel microalgae technology for efficient, low-carbon simultaneous treatment of carbon, nitrogen, and phosphorus in landfill leachate (LL). The microbial composition comprises a mixed microalgae culture with Chlorella accounting for 82.58%. After seven days, the process with an N/P ratio of approximately 14:1 removed 98.81% of NH4+-N, 88.62 % of TN, and 99.55% of TP. Notably, the concentrations of NH4+-N and TP met the discharge standards, while the removal rate of NH4+-N was nearly three times higher than previously reported in relevant studies. The microalgae achieved a removal efficiency of 64.27% for Total Organic Carbon (TOC) and 99.26% for Inorganic Carbon (IC) under mixotrophic cultivation, yielding a biomass of 1.18 g/L. The treatment process employed in this study results in a carbon emissions equivalent of -8.25 kgCO2/kgNremoved, representing a reduction of 33.56 kgCO2 compared to the 2AO + MBR process. In addition, shake flask experiments were conducted to evaluate the biodegradability of leachate after microalgae treatment. After microalgae treatment, the TOCB (Biodegradable Total Organic Carbon)/TOC ratio decreased from 56.54% to 27.71%, with no significant improvement in biodegradability. It establishes a fundamental foundation for further applied research in microalgae treatment of leachate.

Synergistic optimization of baffles and aeration to improve the Light/Dark cycle of microalgae photobioreactor for enhanced nitrogen removal performance: Computational fluid dynamics and experimental verification.

Microalgae photobioreactor (PBR) is a kind of efficient wastewater treatment system for nitrogen removal. However, there is still an urgent need for process optimization of PBR. Especially, the synergistic effect and optimization of light and flow state poses a challenge. In this study, the computational fluid dynamics is employed for simulating the optimization of the number and length of the internal baffles, as well as the aeration rate of PBR, which in turn leads to the optimal growth of microalgae and efficient nitrogen removal. After optimization, the Light/Dark cycle of the reactor B is shortened by 51.6 %, and the biomass increases from 0.06 g/L to 3.94 g/L. In addition, the removal rate of NH4+-N increased by 106.0 % to 1.56 mg L-1 h-1. This work provides a feasible method for optimizing the design and operational parameters of PBR aiming the engineering application.

Buffered loofah supported Microalgae-Bacteria symbiotic (MBS) system for enhanced nitrogen removal from rare earth element tailings (REEs) wastewater: Performance and functional gene analysis.

Rare earth element tailings (REEs) wastewater, which has the characteristics of high ammonia nitrogen (NH4+-N) and low COD. It can cause eutrophication and biotoxicity in water which is produced in high volumes, requiring treatment before final disposal. Microalgae-Bacteria symbiotic (MBS) system can be applied in REEs wastewater, but its low extent of nitrogen removal and instability limit its application. By adding biodegradable carrier as both carbon source and carrier, the system can be stabilized and the efficiency can be improved. In this work, the extent of NH4+-N removal reached 100% within 24 h in a MBS system after adding loofah under optimal conditions, and the removal rate reached 127.6 mg NH4+-N·L-1·d-1. In addition, the carbon release from loofah in 3 d reached 408.7 mg/L, which could be used as a carbon source to support denitrification. During 90 d of operation of the MBS system loaded with loofah, the effluent NH4+-N was less than 15 mg/L. At phylum level, Proteobacteria were dominant which accounted for 78.2%. Functional gene analysis showed that enhancement of microalgae assimilation was the main factor affecting NH4+-N removal. This work expands our understanding of the enhanced role of carbon-based carriers in the denitrification of REEs wastewater.

Enhanced ammonia nitrogen removal from actual rare earth element tailings (REEs) wastewater by microalgae-bacteria symbiosis system (MBS): Ratio optimization of microalgae to bacteria and mechanism analysis.

Microalgae-bacteria symbiosis system (MBS) appear to be a promising way for treating the rare earth elements (REEs) wastewater due to the natural symbiotic interactions between microalgae and bacteria. Herein, we investigated the effect of different inoculation ratios of microalgae and bacteria including 3:1 (MB_1), 1:1 (MB_2) and 1:3 (MB_3) on NH4+-N removal from REEs wastewater and analyzed the corresponding biological mechanism. The NH4+-N removal rate with MB_3 reached 17.69 ± 0.45 mg NH4+-N/L d-1, which was 2.58 times higher than that in single microalgae system. The results were further verified in continuous feeding photobioreactors and kept stable for 100 days. Metagenomic analysis revealed that the abundance of genes related to microalgae assimilation increased by 14 %-50 % in answer to photosynthesis and NH4+-N absorption, while that related to nitrification apparently dropped, indicating that MBS was a sustainable method capable of enhancing NH4+-N removal from REEs wastewater.

Enhancing nitrogen removal in mature landfill leachate by mixed microalgae through elimination of inhibiting factors.

Nitrogen removal from landfill leachate (LL) using microalgae is a promising method and can realize CO2 mitigation. But the performances are usually inhibited by high chromaticity, high free ammonia (FAN) and some complex macro molecular organic matter (MOM) in the LL. To achieve efficient nitrogen removal from LL, this study firstly pretreated the mature LL with ozone, decolorizer and activated sludge (AS) respectively, and then inoculated with mixed microalgae. The results showed that the synergistic effect of ozonation and microalgae was the best among the three, with 99.7% ammonia removal, 0.77 g/L (dry weight) microalgae biomass, and a maximum growth rate of 160 mg/L/d. Ozonation pretreatment significantly reduced the chromaticity and macromolecular organic matter of LL, with the chromaticity reduced from 2225 to 225 times and the 3D fluorescence intensity representing MOM reduced from 4089 a.u. to 986.1 a.u.. And it was found that the mixed microalgae grown after pretreatment by three different methods all were mostly Chlorella and very few Microcystis, and the density of microalgal populations (number of cells per unit volume) after ozonation was up to 10,650 cells/µL. This work provides a feasible and an economical way to remove ammonia nitrogen (NH+ 4-N) from landfill leachate.

Corncob biocarriers with available carbon release for Chlamydopodium sp. microalgae towards enhanced nitrogen removal from low C/N rare earth element tailings (REEs) wastewater.

Low nitrogen (N) removal efficiency limits the potential of microalgae technology for the treatment of high nitrogen and low carbon rare earth tailings (REEs) wastewater. In this study, waste corncob was utilized as a biocarrier immobilizing Chlamydopodium sp. microalgae to realize high-efficient treatment of the REEs wastewater. In only 2.5 d, corncob-immobilized microalgae allowed the residual concentrations of N lower than the emission standards, and ammonia nitrogen (NH4+-N) removal rate is 83.3 mg L-1·d-1, total inorganic nitrogen (TIN) removal rate is 86.7 mg L-1·d-1, which was 18.5 times that of the previously-reported microalgae (4.68 mg L-1·d-1). Compared with other microalgae immobilization carriers, corncob possesses the ability to release available carbon sources for microalgae. Composition analysis and sugar verification experiments showed that the main content of TOC released by corncob was monosaccharide, and in a certain range, the removal rate of N was positively correlated with the TOC concentration. The utilization of biomass wastes with dual functions as biological carriers has great potential to improve the performance of microalgae, and is conducive to the development of engineering applications.

Degradation of pesticide wastewater with simultaneous resource recovery via ozonation coupled with anaerobic biochemical technology.

The effective treatment of pesticide wastewater with high organic content, complex composition and high-toxicity has attracted enormous attention of researchers. This work proposes a new idea for removing the pesticide wastewater with simultaneous resource recovery, which is different from the traditional view of mineralization of pesticide wastewater via composite technology. This novel strategy involved a sequential three-step treatment: (a) acidic Ozonation process, to remove the venomous aromatic heterocyclic compounds; (b) hydrolysis and ozonation in alkaline conditions, enhancing the biodegradability of pesticide wastewater, mainly due to the dehalogenation, elimination of C=C bonds and production of low molecular-weight carboxylate anions; (c) the final step is anaerobic biological reactions. Based on the characterizations, this two-stage acidic-alkaline ozonation can efficiently degraded the virulence of pesticide wastewater and enhance its biodegradability from 0.08 to 0.32. The final anaerobic biochemical treatment can stably remove the residuals and convert the low molecular-weight organics into CH4, achieving the resource recovery. This work explored the pH-dependent of ozonized degradation of pesticide wastewater and gives a new perspective of wastewater treatment.

Resourceful treatment of harsh high-nitrogen rare earth element tailings (REEs) wastewater by carbonate activated Chlorococcum sp. microalgae.

The discharge of rare earth element (REE) tailings wastewater results in serious ecological deterioration and health risk, due to high ammonia nitrogen, and strong acidity. The low C/N ratio makes it recalcitrant to biodegradation. Recently it has been shown that microalgal technology has a promising potential for the simultaneous harsh wastewater treatment and resource recovery. However, the low nitrogen removal rate and less biomass of microalgae restricted its development. In this work, Chlorococcum sp. was successfully isolated from the rare earth mine effluent. The microalgae was capable of enhancing nitrogen contaminants removal from REEs wastewater due to the carbonate addition, which simulated the activity increase of carbonic anhydrase (CA). The total inorganic nitrogen (TIN) removal rate reached 4.45 mg/L h-1, which compared to other microalgal species, the nitrogen removal rate and biomass yield were 7.8- and 4.9-fold higher, respectively. Notably, high lipid contents (mainly triglycerides, 43.85% of dry weight) and a high biomass yield were obtained. Meanwhile, the microalgae had an excellent settleability attributed to higher extracellular polymeric substance (EPS) formation, leading to easier resource harvest. These results were further confirmed in a continuous-flow photobioreactor with a stable operation for more than 30 days, indicating its potential for application.

Electrochemical approach toward reduced graphene oxide-based electrodes for environmental applications: A review.

Graphene has shown great potential in various application fields due to its excellent carrier transportation, ultra-high specific surface area, good mechanical properties, and light transmittance. However, pure graphene still exhibits some insurmountable defects, such as difficulty in simple and large-scale preparation, and limitations in application. The electrochemical method is a simple, clean, and environmentally friendly method. The rapid and simple preparation of graphene and its derivatives by electrochemical methods has important environmental significance. Moreover, rGO-based nanohybrids can be prepared by convenient and quick electrodeposition or cyclic voltammetry (CV), or to change the morphology and structure of graphene and its derivatives to achieve the purpose of improving material properties. This work mainly summarizes electrochemically related graphene from four aspects: (i) the method of electrochemical exfoliation of graphene; (ii) types of electrodeposition rGO-based nanohybrids; (iii) electrochemical regulation of the structure of rGO-based mixtures; (iv) environmental applications of rGO-based nanohybrids prepared by electrodeposition. This article critically discusses the advantages and disadvantages of electrochemical-related graphene, outlines future challenges, and provides insightful views and references for other researchers.

Evaluating the adsorptivity of organo-functionalized silica nanoparticles towards heavy metals: Quantitative comparison and mechanistic insight.

Organo-functionalized SiO2 nanoparticles are regarded as promising adsorbents for capture of heavy metals. However, actual adsorptivity of a specific functional group onto SiO2 surface is unclear, thus extending a debate on which type of organic group possesses a better affinity toward heavy metals. Herein, surface functionalization of SiO2 with different groups (i.e., -EDTA (ethylenediamine triacetic acid), -COOH, -SO3H, -SH and -NH2) were achieved by a facile silylating reaction. Batch experiments indicated that adsorption capacity of SiO2 was remarkably improved by surface functionalization. Quantitative analysis manifested that one mole of EDTA grafted onto SiO2 surface can adsorb 1.51 mol of Pb(II) ions, which was 7.7, 17.1, 28.4 and 50.2-fold larger than those of COOH-, SO3H-, SH- and NH2-functionalized SiO2, respectively. This is first time to evaluate adsorptivity of functionalized SiO2 on the basis of per effective functional group, which may repair deficiency of conventional assessment method that calculated on the basis of per unit mass. Further, adsorption mechanism of these functionalized SiO2 were identified and uncovered by experimental and theoretical studies. This work not only develops an efficient adsorbent for heavy metal remediation but also provides a valuable insight for evaluation and design of novel SiO2-based materials.

Successful isolation of a tolerant co-flocculating microalgae towards highly efficient nitrogen removal in harsh rare earth element tailings (REEs) wastewater.

Acidic rare earth element tailings (REEs) wastewater with high nitrogen and low COD is the most serious and yet unsolved environmental issue in the rare earth mining industry. The effective and cheap remediation of NH4+-N and NO3--N from the REEs wastewater is still a huge challenge. This harsh wastewater environment results in the difficulty for common microbes and microalgae to be survived. In this work, a novel highly tolerant co-flocculating microalgae (the combination of Scenedesmus sp. and Parachlorella sp.) was successfully isolated from the rare earth mine effluent through three-year cultivation. The removal efficiency of total inorganic nitrogen (TIN) by the co-flocculating microalgae cultivation was as high as 90.9%, which is 1.9 times than the average removal efficiency (47.9%) of previously-reported microalgae species in the wastewater with COD/N ratio ranging from 0 to 1. Thus, the residual concentrations of NH4+-N and TIN could reach the Emission Standards of Pollutants from Rare Earths Industry (GB 26451-2011). Along with the high N removal performance, other related characteristics of the co-flocculating microalgae were also revealed, such as high tolerance towards high NH4+-N and strong acid, rapid growth and sedimentation, and simultaneous removal of NH4+-N and NO3--N. These algae characteristics were ascribed to the specific co-flocculating community structure covered by extracellular polymeric substances.