Performance and microbial diversity of an expanded granular sludge bed reactor for high sulfate and nitrate waste brine treatment

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.

Substrate competition and microbial function in sulfate-reducing internal circulation anaerobic reactor in the presence of nitrate

Nitrate and sulfate often coexist in organic wastewater. In this study, an internal circulation anaerobic reactor was conducted to investigate the impact of nitrate on sulfate reduction. The results showed that sulfate reduction rate dropped from 78.4% to 41.4% at NO₃^- /SO₄^2- ratios ranging from 0 to 1.03, largely attributed to the inactivity of acetate-utilizing sulfate-reducing bacteria (SRB) and preferential usage of nitrate of propionate-utilizing SRB. Meanwhile, high nitrate removal efficiency was maintained and COD removal efficiency increased with nitrate addition. Enhancement of propionate and butyrate degradation based on Modified Gompertz model and Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt2) analysis. Moreover, nitrate triggered the shift of microbial community and function. Twelve genera affiliated to Firmicutes, Bacteroidetes and Proteobacteria were identified as keystone genera via network analysis, which kept functional stability of the bacterial community responding to nitrate stress. Increased nitrate inhibited Desulfovibrio, but promoted the growth of Desulforhabdus. Both the predicted functional genes associated with assimilatory sulfate reduction pathway (cysC and cysNC) and dissimilatory sulfate reduction pathway (aprA, aprB, dsrA and dsrB) exhibited negative relationship with nitrate addition.

An appropriate technique for treating rural wastewater by a flow step feed system driven by wind-solar hybrid power

Most rural wastewater treatment facilities require aeration equipment to ensure sufficient dissolved oxygen (DO) during processing. Operation and maintenance are costly, and cannot be met in many areas with poor economic levels. This has led to further deterioration of the rural water environment and aroused much attention. This work reports a plug-flow step feed system utilizing wind and solar hybrid energy for rural wastewater treatment. Under certain climatic conditions, the wind energy and solar energy provided complimentary power generation, and an automatic control system (without batteries) was constructed. The corresponding control logic for multi-energy level operation was developed. Furthermore, the power generation efficiency of the system, the pollutant removal, and its mechanism on the bioreactor were also analyzed. According to the monitoring of meteorological conditions, wind and solar resources at the test site were abundant, and the electricity generated by the power generation was sufficient to meet the operational needs of the equipment. Energy efficiency can reach 80.0%. The characteristics of pollutant removal in each process section were studied on spatial and temporal dimensions. Results showed that the wastewater treatment process reached mean removal efficiencies of chemical oxygen demand (COD_cr), NH₄⁺-N, total nitrogen (TN) and total phosphorus (TP) were 90.2%, 94.3%, 61.4% and 63.1%, respectively. Analyses of microbial community richness and group changes in each anoxic/aerobic reaction chamber in the biofilm reactor showed that the population structure was relatively stable and that there were abundant functional bacteria capable of degrading pollutants in each aerobic and anoxic unit. This system can thus be a more sustainable treatment process than traditional techniques used for rural wastewater treatment, providing a new design approach for low-energy consumption and unattended rural wastewater treatment.

Expanded granular sludge blanket reactor treatment of food waste at ambient temperature: Analysis of nitrogen compositions and microbial community structure

The influent and effluent nitrogen compositions of an expanded granular sludge blanket (EGSB) reactor employed for treating food waste (FW) operated under ambient temperature was evaluated. Additionally, dynamic changes in the bacterial community structures and its metabolic functions were investigated. Results show that the EGSB reactor had a good effect on FW disposal and well resistance to variations in the organic loading rate. Furthermore, the COD concentration in the influent increased to about 10,000 mg/L and the COD removal rate stabilized at about 95%. The dissolved ammonia nitrogen (d-ammonia) content was the largest, accounting for approximately 70-80% of the dissolved nitrogen in the effluent. The amount of particulate organic nitrogen (PON) decreased by about 25%-33%. Amino acid, carbohydrate and lipid metabolism decreased at high organic loading rate (OLR). Meanwhile, the abundance of Methanothrix increased from 30.82% to 70.25%, whereas Methanobacterium decreased from 66.14% to 14.49%.

Preparation of LDHs Based on Bittern and Its Flame Retardant Properties in EVA/LDHs Composites

Bittern, as a byproduct of salt manufacture, is abundant in China. The researches and developments for seawater bittern have mainly focused on the reuse of magnesium, calcium, lithium, and boron. However, the utilization rate is less than 20%. The large amount of unused bittern has become a challenge that attracts much attention in academic and industry areas. In this paper, three kinds of layered double hydroxides (LDHs) were synthesized from bittern using a coprecipitation method and characterized by X-ray diffraction (XRD). The XRD results showed that the three kinds of LDHs(MgAl-LDHs, MgFe-LDHs and MgAlFe-LDHs) were successfully synthesized. Then, the flame retardant properties and thermal properties of the three LDHs in ethylene vinyl acetate (EVA)/LDHs composites had been tested by cone calorimeter test (CCT), limiting oxygen index (LOI), smoke density test (SDT), and thermogravimetry-Fourier transform infrared spectrometry (TG-IR). The CCT results showed that the heat release rate (HRR) of all three kinds of EVA/LDHs composites significantly decreased compared with that of pure EVA, and the EVA/MgAl-LDHs composites had the lowest PHRR value of 222.65 kW/m2. The LOI results showed that EVA/MgAl-LDHs composites had the highest LOI value of 29.8%. The SDT results indicated that MgAl-LDHs were beneficial to smoke suppression. TG-IR results showed that EVA/MgAl-LDHs composites had a better thermal stability.

Biological treatment of selenium-laden wastewater containing nitrate and sulfate in an upflow anaerobic sludge bed reactor at pH 5.0

This study investigated the removal of selenate (SeO₄^2-), sulfate (SO₄^2-) and nitrate (NO₃^-) at different influent pH values ranging from 7.0 to 5.0 and 20 °C in an upflow anaerobic sludge blanket (UASB) reactor using lactate as an electron donor. At pH 5.0, the UASB reactor showed a 20-30% decrease in reactor performance compared to operation at pH 5.5 to 7.0, reaching removal efficiencies of 79%, 15%, 43% and 61% for NO₃^-, SO₄^2-, Se_total and Se_diss, respectively. However, the reactor stability was an issue upon lowering the pH to 5.0 and further experiments are recommended. The sludge formed during low pH operation had a fluffy, floc-like appearance with filamentous structure, possibly due to the low polysaccharide (PS) to protein (PN) ratio (0.01 PS/PN) in the soluble extracellular polymeric substances (EPS) matrix of the biomass. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) analysis of the sludge confirmed Se oxyanion reduction and deposition of Se⁰ particles inside the biomass. Microbial community analysis using Illumina MiSeq sequencing revealed that the families of Campylobacteraceae and Desulfomicrobiaceae were the dominant phylotypes throughout the reactor operation at approximately 23% and 10% relative abundance, respectively. Furthermore, approximately 10% relative abundance of both Geobacteraceae and Spirochaetaceae was observed in the granular sludge during the pH 5.0 operation. Overall, this study demonstrated the feasibility of UASB operation at pH values ranging from 7.0 to 5.0 for removing Se and other oxyanions from wastewaters.

Functional bacterial and archaeal diversity revealed by 16S rRNA gene pyrosequencing during potato starch processing wastewater treatment in an UASB

Microbial community structure of sludge sampled from an UASB treating potato starch processing wastewater (PSPW) was investigated. Operational taxonomic units revealed at 97% sequence identity tolerance was 2922, 2869 and 3919 for bottom, middle and top sections of the reactor, respectively. Overall abundant phylum observed within the UASB was low-G+C-Gram-positive bacteria affiliated to Firmicutes (26.01%) followed by Chloroflexi (16.70%), Proteobacteria (12.71%), Cloacimonetes (10.72%), Bacteroidetes (7.87%), Synergistetes (9.02%) and Euryarchaeota (8.82%). Whiles Firmicutes had dominated the bottom and top section by 34.01% and 28.64%, respectively, middle section was predominantly Euryarchaeota (24.32%) with major dominance in methanogens affiliated to genus Methanosaeta. The results demonstrated substantial stratification of the microbial community structure along the reactor height with various functional bacterial groups which subsequently allowed degradation of organics in PSPW in sequential mode. The findings herein would provide guidance for optimizing the anaerobic process and operation of the UASB.

Illumina MiSeq sequencing reveals the key microorganisms involved in partial nitritation followed by simultaneous sludge fermentation, denitrification and anammox process

A combined process including a partial nitritation SBR (PN-SBR) followed by a simultaneous sludge fermentation, denitrification and anammox reactor (SFDA) was established to treat low C/N domestic wastewater in this study. An average nitrite accumulation rate of 97.8% and total nitrogen of 9.4mg/L in the effluent was achieved during 140days' operation. The underlying mechanisms were investigated by using Illumina MiSeq sequencing to analyze the microbial community structures in the PN-SBR and SFDA. Results showed that the predominant bacterial phylum was Proteobacteria in the external waste activated sludge (WAS, added to the SFDA) and SFDA while Bacteroidetes in the PN-SBR. Further study indicated that in the PN-SBR, the dominant nitrobacteria, Nitrosomonas genus, facilitated nitritation and little nitrate was generated in the PN-SBR effluent. In the SFDA, the co-existence of functional microorganisms Thauera, Candidatus Anammoximicrobium and Pseudomonas were found to contribute to simultaneous sludge fermentation, denitrification and anammox.

The effect of magnetite on the start-up and N2O emission reduction of the anammox process

A reactor combined with magnetite could enhance the anammox performance and enrich morePlanctomycetesbacteria.