Removal Efficiency Of NO3 Research Articles

Simultaneous removal of nitrate, manganese, zinc, and bisphenol a by a biofilm reactor with β-CD modified corn stover biochar and PU sponges: Performance and microbial community response

In the present study, a biofilm reactor with manganese (Mn) redox cycling was established to remove nitrate (NO3−-N), bisphenol A (BPA), zinc (Zn(II)), and Mn(II) using β-cyclodextrin (β-CD) modified corn stover biochar (BC) and polyurethane sponges loaded with Cupriavidus sp. HY129 and Pantoea sp. MFG10. At C/N = 2.0, HRT = 6 h, Mn(II) = 10.0 mg L−1, and BPA and Zn(II) concentrations = 1.0 mg L−1, the removal efficiencies of NO3−-N, Zn(II), BPA, and Mn(II) were 81.5%, 86.5%, 87.9%, and 75.5%, respectively. The outcomes demonstrated the success that the addition of β-CD could accelerate electron transfer activity and the denitrification process. The remediation of BPA and Zn(II) was mainly through the adsorption of bioprecipitation generated by reactor operation. The bioreactor could preserve the stability of the biological community and the expression of pertinent functional genes under the coercion of BPA and Zn(II).

Accelerating the production of formate radicals for nitrate purification via a redox-regulated photocatalysis route

The treatment of nitrate (NO3−) pollutants is crucial for human health in the context of environmental pollution. Synergistic photocatalytic redox technology is feasible for reducing low-concentrated NO3− to achieve environmental purification. As combined redox reactions proceed in one photocatalysis system, incorporating suitable oxidative reactions is one potential strategy to enhance photocatalytic NO3− reduction efficiency. Herein, almost 100 % removal efficiency of NO3− and superior N2 selectivity of 93.99±0.45 % is achieved through the precise matching of synergistic oxidative half-reactions. The crucial role of active radicals is revealed. Specifically, the conversion efficiency of NO3− is determined by the cooperation of formate radicals (•CO2−), which are generated from the selective oxidation of formaldehyde, acetaldehyde or glyoxal. Among them, the optimum yield of •CO2− radicals are reached from the formaldehyde oxidative reaction. It is clarified that this research will contribute to a deep understanding of the removal and purification of NO3− in wastewater.

Refractory degradable dissolved organic matter (R-DOM) driving nitrogen removal by the electric field coupled iron‑carbon biofilter (E-ICBF): Performance and microbial mechanisms

Researches on the advanced nitrogen (N) removal of municipal tailwater always overlooked the value of refractory degradable dissolved organic matter (R-DOM). In this study, a novel electric field coupled iron‑carbon biofilter (E-ICBF) was utilized to explore the performance and microbial changes with polyethylene glycol (PEG) as the representative R-DOM. Results demonstrated that the removal efficiencies of E-ICBF for nitrate nitrogen (NO3−-N), ammonia nitrogen (NH4+-N), and total nitrogen (TN) improved by 28.76 %, 12.96 %, and 28.45 %, compared to quartz sand biofilter (SBF). Moreover, removal efficiencies of NO3−-N and TN in E-ICBF with R-DOM went up by 12.11 % and 14.02 % compared to methanol. Additionally, both PEG and the electric field reduced the microbial richness and diversity. However, PEG promoted the increase of denitrifying bacteria abundance including unclassified_f_Comamonadaceae, Thauera, and unclassified_f_Gallionellaceae. The electric field improved the abundances of genes related to N removal (hao, nasC, nasA, nifH, nifD, nifK) and PEG further enhanced the effect. The abundances of key enzymes [EC:1.7.5.1], [EC:1.7.2.1], [EC:1.7.2.4], and [EC:1.7.2.5] decreased due to the addition of PEG and the electric field mitigated the negative influence. Additionally, the electric field changed relationships between microorganisms and pollutant removal, and improved interspecific relationships between denitrifying bacterial genera and other genera in E-ICBF.

The effect of carbon source produced by modified corncob fermentation on denitrification

The advanced nitrogen removal is always limited by low carbon to nitrogen ratio (C/N), the feasibility of producing carbon source through fermenting corncob was evaluated in this study. The effect of initial pH, solid content and temperature on the production of volatile fatty acids (VFAs) by alkali pre-treated corncob were investigated, and the denitrification performance with anaerobic fermentation liquid (AFL) and sodium acetate (SA) was compared. The results showed that alkali pretreatment improved the mass transfer inside the corncob, and the solid content had a major impact on VFA production. The denitrification rate of the two systems was related to the influent NO3−-N concentration only when the C/N was 6:1 and 8:1, and the removal efficiency was bigger than 95 %. Nevertheless, the nitrite reduction of the AFL system was limited at a C/N of 4:1, and the removal efficiency of NO₃−-N was only 65.10 %. Moreover, the AFL system enriched a large number of genera involved in nitrogen removal and organic decomposition. The functional analysis showed that the denitrification activity and ability of the AFL system were slightly lower. However, the SA system enriched more pathogenic bacteria, the relative abundances of Arcobacter and Pseudomonas were 28.74 % and 11.85 %, respectively. This study provides a reference for optimizing the design and control of VFAs production by continuous fermentation from agricultural waste.

Coping with groundwater pollution in high-nitrate leaching areas: The efficacy of denitrification

The Ningxia Yellow River irrigation area, characterized by an arid climate and high leaching of NO3--N, exhibits complex and unique groundwater nitrate (NO3--N) pollution, with denitrification serving as the principal mechanism for NO3--N removal. The characteristics of N leaching from paddy fields and NO3--N removal by groundwater denitrification were investigated through a two-year field observation. The leaching losses of total nitrogen (TN) and NO3--N accounted for 10.81–27.34% and 7.59–12.74%, respectively, of the N input. The linear relationship between NO3--N leaching and N input indicated that the fertilizer-induced emission factor (EF) of NO3--N leaching in direct dry seeding and seedling-raising and transplanting paddy fields was 8.2% (2021, R2 = 0.992) and 6.7% (2022, R2 = 0.994), respectively. The study highlighted that the quadratic relationship between the NO3--N leaching loss and N input (R2 = 0.999) significantly outperformed the linear relationship. Groundwater denitrification capacity was characterized by monitoring the concentrations of dinitrogen (N2) and nitrous oxide (N2O). The results revealed substantial seasonal fluctuations in excess N2 and N2O concentrations in groundwater, particularly following fertilization and irrigation events. The removal efficiency of NO3--N via groundwater denitrification ranged from 42.70% to 74.38%, varying with depth. Groundwater denitrification capacity appeared to be linked to dissolved organic carbon (DOC) concentration, redox conditions, fertilization, irrigation, and soil texture. The anthropogenic-alluvial soil with limited water retention accelerated the leaching of NO3--N into groundwater during irrigation. This process enhances the groundwater recharge capacity and alters the redox conditions of groundwater, consequently impacting groundwater denitrification activity. The DOC concentration emerged as the primary constraint on the groundwater denitrification capacity in this region. Hence, increasing carbon source concentration and enhancing soil water retention capacity are vital for improving the groundwater denitrification capacity and NO3--N removal efficiency. This study provides practical insights for managing groundwater NO3--N pollution in agricultural areas, optimizing fertilization strategies and improving groundwater quality.

Deciphering the influencing mechanism of hydraulic retention time on purification performance of a mixotrophic system from the perspective of reaction kinetics.

At present, eutrophication is increasingly serious, so it is necessary to effectively reduce nitrogen and phosphorus in water bodies. In this study, a pyrite/polycaprolactone-based mixotrophic denitrification (PPMD) system using pyrite and polycaprolactone (PCL) as electron donors was developed and compared with pyrite-based autotrophic denitrification (PAD) system and PCL-based heterotrophic denitrification (PHD) system through continuous flow experiment. The removal efficiency of NO3--N (NRE) and PO43--P (PRE) and the contribution proportion of PAD in the PPMD system were significantly increased by prolonging hydraulic retention time (HRT, from 1 to 48h). When HRT was equal to 24h, the PPMD system conformed to the zero-order kinetic model, so NRE and PRE were mainly limited by the PAD process. When HRT was equal to 48h, the PPMD system met the first-order kinetic model with NRE and PRE reaching 98.9 ± 1.1% and 91.8 ± 4.5%, respectively. When HRT = 48h, the NRE and PRE by PAD system were 82.7 ± 9.1% and 88.5 ± 4.7%, respectively, but the effluent SO42- concentration was as high as 152.1 ± 13.7mg/L (the influent SO42- concentration was 49.2 ± 3.3mg/L); the NRE by PHD system was 98.5 ± 1.7%, but the PO43--P could not be removed ideally. The concentrations of NO3--N, total nitrogen, PO43--P, and SO42- in the PPMD system also showed distinct changes along the reactor column. In addition, the microbial diversity analysis showed that prolonging HRT (from 24 to 48h) increased the abundance of autotrophic denitrifying microorganisms in the PPMD system, ultimately increasing the contribution proportion of PAD.

Simultaneous methanogenesis and denitrification in an anaerobic moving bed biofilm reactor for landfill leachate treatment: Ameliorative effect of rhamnolipids

In this study, an anaerobic moving bed biofilm reactor (AnMBBR) was developed for simultaneous methanogenesis and denitrification (SMD) to treat high-strength landfill leachate for the first time. A novel strategy using biosurfactant to ameliorate the inhibition of landfill leachate on the SMD performance was proposed and the underlying mechanisms were explored comprehensively. With the help of rhamnolipids, the chemical oxygen demand (COD) removal efficiency of landfill leachate was improved from 86.0% ± 2.9% to 97.5% ± 1.6%, while methane yields increased from 50.1 mL/g-COD to 69.6 mL/g-COD, and the removal efficiency of NO3−-N was also slightly increased from 92.5% ± 1.9% to 95.6% ± 1.0%. The addition of rhamnolipids increased the number of live cells and enhanced the secretion of extracellular polymeric substances (EPS) and key enzyme activity, indicating that the inhibitory effect was significantly ameliorated. Methanogenic and denitrifying bacteria were enhanced by 1.6 and 1.1 times, respectively. Analysis of the microbial metabolic pathways demonstrated that landfill leachate inhibited the expression of genes involved in methanogenesis and denitrification, and that their relative abundance could be upregulated with the assistance of rhamnolipids addition. Moreover, extended Deraguin - Landau - Verwery - Oxerbeek (XDLVO) theory analysis indicated that rhamnolipids reduced the repulsive interaction between biofilms and pollutants with a 57.0% decrease in the energy barrier, and thus accelerated the adsorption and uptake of pollutants onto biofilm biomass. This finding provides a low-carbon biological treatment protocol for landfill leachate and a reliable and effective strategy for its sustainable application.

Effects of anode materials on nitrate reduction and microbial community in a three-dimensional electrode biofilm reactor with sulfate

Graphite rod corrosion and peeling are serious problems in three-dimensional electrode biofilm reactors (3D-BERs). In this study, titanium rods, titanium suboxide-coated titanium rods and graphite rods were used as anodes to investigate the effect of anodic materials on the electrochemical and bioelectrochemical reduction of nitrate and sulfate. The results showed that the reactor with the titanium suboxide-coated titanium rod anode (3D-ER-T) exhibited a stable NO3−-N removal efficiency (46%–95%) with a current range of 160–320 mA in the electrochemical reduction process. In the bioelectrochemical reduction, the removal efficiencies of NO3−-N and SO42− and nitrogen selectivity in the 3D-BER with titanium suboxide-coated titanium rod anode (3D-BER-T) were higher than those in the 3D-BER with titanium suboxide-coated graphite rod anode (3D-BER-G). The removal efficiencies of NO3−-N and SO42− and nitrogen selectivity were 92%, 43% and 86%, respectively, in 3D-BER-T under 320 mA and HRT 12 h. Anode materials affected the microbial community. Hydrogenophaga and Dethiobacter were the dominant bacteria in 3D-BER-T, while OPB41 and Sulfurospirillum were dominant in 3D-BER-G. Nitrate and sulfate were effectively removed in 3D-BER-T by the synergistic work of electrochemical reduction, bioelectrochemical reduction and indirect electrochemical reduction. The resupply/reserve mode of the electron donor promoted the load of shock resistance of 3D-BER-T via the sulfur cycle. Titanium suboxide coating could significantly enhance the anti-corrosion ability of matrix anodes.

Microelectrolysis-integrated constructed wetland with sponge iron filler to simultaneously enhance nitrogen and phosphorus removal

Integrating sponge iron (SI) and microelectrolysis individually into constructed wetlands (CWs) to enhance nitrogen and phosphorus removal are challenged by ammonia (NH4+-N) accumulation and limited total phosphorus (TP) removal efficiency, respectively. In this study, a microelectrolysis-assisted CW using SI as filler surrounding the cathode (e-SICW) was successfully established. Results indicated that e-SICW reduced NH4+-N accumulation and intensified nitrate (NO3–-N), the total nitrogen (TN) and TP removal. The concentration of NH4+-N in the effluent from e-SICW was lower than that from SICW in the whole process with 39.2–53.2 % decrease, and as the influent NO3–-N concentration of 15 mg/L and COD/N ratio of 3, the removal efficiencies of NO3–-N, TN and TP in e-SICW achieved 95.7 ± 1.9 %, 79.8 ± 2.5 % and 98.0 ± 1.3 %, respectively. Microbial community analysis revealed that hydrogen autotrophic denitrifying bacteria of Hydrogenophaga was highly enriched in e-SICW.

Nitrogen removal from low-C/N-ratio wastewater using a three-dimensional bioelectrical reactor

A three-dimensional bioelectrical reactor (3D-BER) with a treatment capacity of 1 m3/d was constructed for the high-level denitrification of wastewater treatment plant effluent. The results indicated that with activated carbon and light ceramsite (volume ratio was 1:1) as the particle electrodes and applied current of 5 A, the removal efficiency of NO3−-N in the 3D-BER was 78.99 ± 4.10 %, the selectivity of nitrogen was 83.48 ± 4.20 %, and the energy consumption was 1.20 ± 0.13 kWh/m3. Nitrate and sulfate concentrations decreased rapidly based on the samples withdrawn at a reactor height of 47.5 cm, and they both decreased to their lowest values at a reactor height of 75 cm, indicating that nitrate reduction took place preferentially in the 3D-BER. Proteobacteria and Campilobacterota were selectively enriched in the 3D-BER compared with the inoculated sludge, and the microbial community composition of 3D-BER at 75 cm was significantly different from that at other heights. Sulfurimonas (20.96 %), Sulfuricurvum (5.32 %), Thauera (4.40 %) and Denitratisoma (3.87 %) were the dominant bacteria at 75 cm in the 3D-BER, and the relative abundance of bacteria with denitrifying functions was the highest at 75 cm. Fieldwork demonstrated the feasibility and sustainability of using a 3D-BER for nitrogen removal.

Microscale Constructed Wetlands with Different Particulate Matters in their Substrates Exhibit Opposite Nitrogen Removal Performances

Excess suspended particulate matter (PM) in constructed wetland (CW) substrates may reduce the substrate porosity and thus affect pollutant removal performance. However, it remains unclear how different PMs affect the nitrogen removal performance in CWs. In this study, kaolin and polystyrene (PS) were selected as two model PMs added to CW substrates at a concentration of 100 mg/L. Four CWs were constructed, designated as C-CW without PM addition, K-CW with kaolin addition, M-CW with mixed addition of kaolin and PS, and PS-CW with PS addition. The CWs with or without PM addition showed no significant difference in terms of NH4+-N removal efficiency (p > 0.05), while the removal efficiency of NO3−-N and TN was significantly improved in PS-CW but, in contrast, was considerably inhibited in K-CW and M-CW (p < 0.05). The CWs with PM addition reduced the porosity of the substrates. There was no significant difference in the total solid quality among the CWs with PM addition (p < 0.05), but PS-CW had the highest volatile solid content. The addition of 100 mg/L PS significantly increased the activities of nitrite reductase (NIR) and nitrate reductase (NAR) with a much higher relative abundance of denitrifying bacteria, but it inhibited ammonia monooxygenase (AMO) and nitrite oxidoreductase (NXR) activities (p < 0.05). The activities of the four enzymes were improved to different degrees in K-CW and M-CW, in which the abundance of nitrifying bacteria was higher than that in C-CW. In conclusion, it was noteworthy that the effect of the PMs on the NO3−-N and TN removal performance were qualitatively different (i.e., enhanced vs. inhibited) with different types of PMs. This interesting and important new finding could provide valuable information for a better understanding and evaluation of the role of PMs in the nitrogen removal process during CW operation.

Simultaneous electrokinetic removal and in situ electrochemical degradation of a high nitrogen accumulated greenhouse soil

High nitrogen (N) concentration in farmland soil can easily cause the eutrophication of water bodies and a decline in soil fertility. As a new technology for quick in-situ nitrate restoration strategy, electrokinetic remediation has high efficiency, reliability, and competitive economic feasibility. However, the traditional electrokinetic remediation configuration will cause excessive acidification and alkalization of soil. The treatment of produced nitrogenous waste liquid was also necessary. In this study, the optimal design by the cation exchange membrane was adopted to solve the problems of soil over-acidification (pH<4) and over-alkalization (pH>10) caused by traditional electrokinetic remediation technology. Adding NaCl to the electrolyte, the anodic oxidation of ammonium was promoted, and the concentration of N in the electrolyte was reduced. Citric acid was added to stabilize pH and promote the conversion of NO3−-N. The removal efficiency of NO3−-N in the soil could reach 90%, 93%, and 97%, respectively, after 5, 10, and 15 days of electrokinetic treatment. The NO3−-N concentration in the processing solution was below 4 mg/L, the NH4+-N concentration was less than the method detection line, the total nitrogen concentration was not more than 8 mg/L, and the N in the waste liquid did not need secondary treatment. This study revealed the electrochemical behavior of nitrate on stainless steel electrodes, indicating that active chlorine can promote the anodic oxidation process of NH4+. At the same time, it was found that citric acid positively affected nitrate transformation. Based on the clarification of the transport and transformation mechanism, this study inspired optimizing our existing electric remediation technology to solve the problem of high N-accumulation in soils.

Enhanced nitrate and cadmium removal performance at low carbon to nitrogen ratio through immobilized redox mediator granules and functional strains in a bioreactor

The coexistence of multiple pollutants and lack of carbon sources are challenges for the biological treatment of wastewater. To achieve simultaneous removal of nitrate (NO3−-N) and cadmium (Cd2+) at low carbon to nitrogen (C/N) ratios, 2-hydroxy-1,4-naphthoquinone (HNQ) was selected from three redox mediators as an accelerator for denitrification of heterotrophic strain Pseudomonas stutzeri sp. GF2 and autotrophic strain Zoogloea sp. FY6. Then, halloysite nanotubes immobilized with 2-hydroxy-1,4-naphthoquinone (HNTs-HNQ) were prepared and a bioreactor was constructed with immobilized redox mediator granules (IRMG) as the carrier, which was immobilized with HNTs-HNQ and inoculated with the two strains. The immobilized HNQ and the inoculated strains jointly improved the removal ability of NO3−-N and Cd2+ and the removal efficiency of NO3−-N (25.0 mg L−1) and Cd2+ (5.0 mg L−1) were 92.81% and 93.94% at C/N = 1.5 and hydraulic retention time (HRT) = 4 h. The Cd2+ was removed by adsorption of iron oxides (FeO(OH) and Fe3O4) and IRMG. The electron transport system activity (ETSA) of bacteria was improved and the composition of dissolved organic matter in the effluent was not affected by HNQ. The HNQ promoted the production of FeO(OH) and up-regulated the proportion of Zoogloea (54.75% in the microbial community), indicating that Zoogloea sp. FY6 was dominant in the microbial community. In addition, HNQ influenced the metabolic pathways and improved the relative abundance of some genes involved in nitrogen metabolism and the iron redox cycle.

A novel constructed wetland based on iron carbon substrates: performance optimization and mechanisms of simultaneous removal of nitrogen and phosphorus.

In recent years, the combination of iron carbon micro-electrolysis (ICME) with constructed wetlands (CWs) for removal of nitrogen and phosphorus has attracted more and more attention. However, the removal mechanisms by CWs with iron carbon (Fe-C) substrates are still unclear. In this study, the Fe-C based CW (CW-A) was established to improve the removal efficiencies of nitrogen and phosphorus by optimizing the operating conditions. And the removal mechanisms of nitrogen and phosphorus were explored. The results shown that the removal rates of COD, NH4+-N, NO3--N, TN, and TP in CW-A could reach up to 84.4%, 94.0%, 81.1%, 86.6%, and 84.3%, respectively. Wetland plants and intermittent aeration have dominant effects on the removal of NH4+-N, while the removal efficiencies of NO3--N, TN, and TP were mainly affected by Fe-C substrates, wetland plants, and HRT. XPS analysis revealed that Fe(0)/Fe2+ and their valence transformation played important roles on the pollutants removal. High-throughput sequencing results showed that Fe-C substrates and wetland plants had considerable impacts on the microbial community structures, such as richness and diversity of microorganism. The relative abundance of autotrophic denitrification bacteria (e.g., Denitatsoma, Thauera, and Sulfuritalea) increased in CW-A than CW-C. The electrons and H2/[H] produced from Fe-C substrates were utilized by autotrophic denitrification bacteria for NO3--N reduction. Microbial degradation was the main removal mechanism of nitrogen in CW-A. Removal efficiency of phosphorus was enhanced resulted from the reaction of phosphate with iron ion. The application of CWs with Fe-C substrates and plants presented great potential for simultaneous removal of nitrogen and phosphorus.

Enhanced denitrification of dispersed swine wastewater using Ca(OH)2-pretreated rice straw as a solid carbon source

In a pilot-scale packed bed reactor, the denitrification performance and microbial community structure of the dispersed swine wastewater treatment using calcium hydroxide (Ca(OH)2) pretreated rice straw as a carbon source were investigated. In a Ca(OH)2-pretreated rice straw supported denitrification system (Ca(OH)2-RS), the removal efficiency of NO3−-N was 96.39% at an influent NO3−-N load of 0.04 kg/(m3•d). Meanwhile, there was no obvious accumulation of NO2−-N or chemical oxygen demand (COD) in the effluent of Ca(OH)2-RS. The contents of soluble microbial byproduct-like substances and tryptophan-like substances in the effluent of Ca(OH)2-RS were reduced by 46.2% and 43.4%, respectively, compared with the influent. Overall, the Ca(OH)2-pretreated rice straw system had a strong resistance to fluctuations in water quality conditions, such as influent NO3−-N and COD concentrations. According to the microbial assay results, the Ca(OH)2 pretreatment enriched more denitrifying bacteria. Among them, Proteobacteria (42.33%) and Bacteroidetes (35.28%) were the dominant bacteria. Moreover, the main denitrifying functional bacteria, generanorank_f_Saprospiraceae (13.32%), norank_f_Porphyromonadaceae (4.22%), and Flavobacterium (3.25%), were enriched in Ca(OH)2-RS. This suggested that using Ca(OH)2-pretreated rice straw as a carbon source was a stable and efficient technology to enhance the denitrification performance of dispersed swine wastewater.

Electrocatalytic Reduction of Nitrate via Co3O4/Ti Cathode Prepared by Electrodeposition Paired With IrO2-RuO2 Anode.

Nitrate pollution is already a global problem, and the electrocatalytic reduction of nitrate is a promising technology for the remediation of wastewater and polluted water bodies. In this work, Co3O4/Ti electrodes were prepared by electrodeposition for the electrocatalytic reduction of nitrate. The morphology, chemical, and crystal structures of Co3O4/Ti and its catalytic activity were investigated. Then, the electrocatalytic nitrate reduction performance of Co3O4/Ti as the cathode was evaluated by monitoring the removal efficiencies of nitrate (NO3 −-N) and total nitrogen (TN), generation of reduction products, current efficiency (CE), and energy consumption (EC) at different operating conditions. Under the catalysis of Co3O4/Ti, NO3 − was reduced to N2 and NH4 +, while no NO2 − was produced. After the introduction of chloride ions and IrO2-RuO2/Ti as the anode, NH4 + was selectively oxidized to N2. The removal efficiencies of NO3 −-N (at 100 mg/L) and TN after 2 h were 91.12% and 60.25%, respectively (pH 7.0; Cl− concentration, 2000 mg/L; current density, 15 mA/cm2). After 4 h of operation, NO3 −-N and TN were completely removed. However, considering the EC and CE, a 2-h reaction was the most appropriate. The EC and CE were 0.10 kWh/g NO3 −N and 40.3%, respectively, and electrocatalytic performance was maintained after 10 consecutive reduction cycles (2 h each). The cathode Co3O4/Ti, which is prepared by electrodeposition, can effectively remove NO3 −-N, with low EC and high CE.

Physical filtration of nutrients utilizing gravel-based and lightweight expanded clay aggregate (LECA) as growing media in aquaponic recirculation system (ARS)

The aquaponic recirculation system (ARS) combined aquaculture and hydroponic systems in a mutually beneficial environment. In this study, African catfish, Clarias gariepinus with Butterhead lettuce, Lactuca sativa were cultivated to evaluate gravel-based media and lightweight extended clay aggregate (LECA) as a physical filtration in the nutrient's removal. The performance of both tested growing media was assessed through the reduction of nutrient concentrations in the circulated water, which were total ammonia nitrogen (TAN), nitrite-nitrogen (NO2--N), nitrate-nitrogen (NO3--N), and phosphorus (PO43--P). Statistically, there were significant differences in the percentage of nutrient removal between gravel-based media and LECA treatment for TAN, NO2--N, NO3--N, and PO43--P. TAN removal efficiency achieved 92.47 ± 1.03% in LECA compared to 61.26 ± 2.69% in gravel-based media. For NO2--N, the removal efficiency was 77.25 ± 1.47% and 22.43 ± 6.84% in LECA and gravel-based media. The removal efficiency of NO3--N on LECA was two times more than gravel-based, 60.03 ± 1.58% and 30.77 ± 1.54%. The removal efficiency of PO43--P was 64.29 ± 1.82% for LECA while 27.43 ± 1.62% for gravel-based media. In addition, L. sativa yield was significantly higher in LECA with 64,961.71 ± 1295.61 g/m² as compared to 31,0582.82 ± 877.07 g/m² in gravel-based media. Significantly higher SGR of C. gariepinus in LECA with 3.94 ± 0.11%/day compared to 3.10 ± 0.12%/day in gravel-based media. LECA is an adsorptive substrate with a high removal capacity for phosphorus and nitrogen in aquaculture wastewater, increase its use as growing media in ARS or hydroponics.

Response of the reactor performances and bacterial communities to the evolution of sulfide-based mixotrophic denitrification processes from nitrate-type to nitrite-type

An up-flow biofilm reactor was set up to study the effect of the gradually changing ratio of NO3− to NO2− on the reactor performance, bacterial community and metabolic pathways in the mixotrophic desulfurization-denitrification process. With NO3−/NO2− decreasing, the removal efficiencies of NO3−, NO2− and S2−, and the generating efficiency of S0 increased. The top dominant desulfurization-denitrification genera changed from Rhodobacter (5.6 %) to Thiovirga (11.0 %), and the top dominant Sulfate-Reducing Bacteria changed from Clostridium (1.7 %) to Desulfovibrio (7.2 %). The relative abundance of sulfide oxidation gene sqr, twelve sulfate reduction genes and fifteen denitrification genes had the overall trend towards increasing, but that of sulfur oxidation gene sox decreased. The electron acceptor’s evolution from NO3− to NO2− screened the functional bacteria suitable living in NO2− environment to promote the bioreactor’s optimization. The main degradation pathway of the contaminants was predicted that: NO3− tended to utilize organics to release NO2−, while NO2− tended to utilize S2− and S32− to generate N2; after NO3− was entirely consumed, NO2− began to react with organics, S32− and S0. The results obtained in this work can be used as a practical reference for development, optimization and control of NO2−-type mixotrophic desulfurization-denitrification process.

An integrated permeable reactive barrier and photobioreactor approach for simultaneous removal of nitrate, phosphate and hexavalent chromium: A combined batch and continuous flow study

In this study, simultaneous removal of nitrate (NO3–), phosphate (PO43−) and hexavalent chromium (Cr(VI)) from wastewater was investigated using a novel integrated filtration unit consisting of adsorbent based permeable reactive barrier (AB-PRB) and biosorption based photobioreactor (BSB-PBR). AB-PRB was comprising a mixture of low-cost adsorbents in an optimum proportion, whereas BSB-PBR carried C. vulgaris microalgae cultivated in controlled environment. The batch analysis for AB-PRB showed maximum removal efficiency of 95.7% and 98.0% for NO3– and PO43−, at pH-6, whereas 84.0% for Cr(VI) at pH-4. However, continuous flow study showed decreasing trend in removal efficiency of NO3–, PO43− and Cr(VI) with increasing flow rate from 10 ml min−1 to 30 ml min−1. Further, in BSB-PBR, maximum removal of 98.2% was achieved for Cr(VI) of 1.0 mg L−1 initial concentration at 3.3 days of hydraulic retention time (HRT). This study provides a novel integrated remediation approach for efficient removal of unlike contaminants.

Enhanced Benzofluoranthrene Removal in Surface Flow Constructed Wetlands with the Addition of Carbon.

Polycyclic aromatic hydrocarbons (PAHs), as hazardous pollutants, could be removed by constructed wetlands (CWs). While the traditional substrate of CWs has a weak adsorption capacity for PAHs, in this study, the carbonous fillers—activated carbon (AC) and biochar—were added into the substrate of surface flow CWs to improve the removal performance of benzofluoranthrene (BbFA), a typical PAH. The results showed that the BbFA removal efficiencies in CWs with the addition of AC and biochar were 11.8 and 1.2% higher than those in the Control group, respectively. Simultaneously, the removal efficiencies of NO3––N were 42.8 and 68.4% in these two CWs, while the BbFA content in the substrate and plants with the addition of carbon was lower than that in the Control group. The addition of carbonous filler reduced the absorption of PAHs by plants in CWs and enhanced microbial degradation. The microbial community results showed that the relative abundance of Proteobacteria, especially γ-proteobacteria, was higher with the addition of fillers, which related to PAH degradation.