Initial Nitrate Concentration Research Articles

Feasibility of in-situ sludge fermentation coupled with partial denitrification: Key roles of initial organic matters and alkaline pH

Achieving partial denitrification (PD) by using fermentation products extracted from waste activated sludge (WAS) rather than commercial organic matters is a promising approach for providing nitrite for anammox, while sludge reduction could also be realized by WAS reutilization. This study proposed an In-situ Sludge Fermentation coupled with Partial Denitrification (ISFPD) system and explored its performance under different conditions, including initial pH, nitrate concentrations, and organic matters. Results showed that nitrite production increased with the elevation of initial pH (from 6 to 9), and the highest nitrate-to-nitrite transformation ratio (NTR) reached 77% at initial pH 9. The PD rates and NTR were observed to be minimally influenced by initial nitrate concentrations. Acetate was preferred by denitrifying bacteria, while macromolecules such as proteins necessitated be hydrolyzed to be suitable for further utilization. The insights gained through this study paved the way for efficient nitrite production and sustainable WAS reutilization in harmony.

Unraveling the effect mechanism of sulfamethoxazole on nitrogen biotransformation in a PHBV supported denitrifying granular sludge

Sulfamethoxazole (SMX) is prevalent as one of the most frequently detected antibiotics in rivers worldwide, and is listed as one of the priority antibiotics in China based on the persistence, bioaccumulation, toxicity and resistance. Recently, the effect of SMX on aerobic granular sludge has attracted increasing interest. However, how SMX influences the biodegradable polymer supported denitrifying granular sludge is still obscure. Herein, two groups with or without exposure to 1 mg/L SMX with initial nitrate concentrations of 15, 30, and 50 mg/L were constructed. Results showed that there was a negligible difference on nitrate removal efficiencies between two groups under stable period (all exceeded 95 %) in batch bioreactors with an HRT of 24 h, supported by an insignificance difference (p > 0.05). However, the decline in the first-order decay kinetic constants of nitrate removal rate, NAR and NIR activities verified a slight inhibition of SMX on denitrification. Meanwhile, SMX also had an impact on the chemical and microbial properties on granular sludge. SMX boosted the EPS secretion with more humic acid, a delicate rise in PN/PS ratios and a decrease in zeta potential of EPS all favored the microbes' survival under SMX stress. SMX shifted the microbial compositions, namely, the microbes directly involving in PHBV degradation (Caldimonas, denitrificans Comamonas/Diaphorobacter) were enriched instead of some denitrifying microorganism that could not directly utilize PHBV (Denitratisoma, Azospira). Additionally, even though sul1 and sul2 were enriched, which was not readily accessible to receiving waters due to a good settling properties of granular sludge. This work contributes to a deeper understanding of the impact of SMX on this system, and is of great significance for the operation of granular sludge system for nitrate removal under antibiotic's stress.

Thauera sp. for efficient nitrate removal in continuous denitrifying moving bed biofilm reactor.

Thauera is the most widely found dominant denitrifying genus in wastewater. In earlier study, MBBR augmented with a specially developed denitrifying five-membered bacterial consortium (DC5) where Thauera was found to be the most abundant and persistent genus. Therefore, to check the functional potential of Thauera in the removal of nitrate-containing wastewater in the present study Thauera sp.V14 one of the member of the consortium DC5 was used as the model organism. Thauera sp.V14 exhibited strong hydrophobicity, auto-aggregation ability, biofilm formation and denitrification ability, which indicated its robust adaptability short colonization and nitrate removal efficiency. Continuous reactor studies with Thauera sp.V14 in 10 L dMBBR showed 91% of denitrification efficiency with an initial nitrate concentration of 620 mg L-1 within 3 h of HRT. Thus, it revealed that Thauera can be employed as an effective microorganism for nitrate removal from wastewater based on its performance in the present studies.

Enhanced biosorptive incarceration of nitrate from aqueous solutions using novel green adsorbent: Performance optimization and mechanistic enlightenment

Excess nitrate contamination was lucratively addressed using the novel adsorbents prepared from waste seed pods of the Guilandina bonduc (L.) plant. Adsorbents BFP and EBFP (amino-grafted) were synthesized following a green pathway of thermo-chemical transformation. Adsorbents were successfully implemented for nitrate adhesion from natural and wastewater. The morphology of the adsorbents was studied using SEM-EDS, TGA, XRD, FTIR-ATR, and BET, including zeta potential and point of zero charges. The batch mode nitrate removal study was carried out using a colorimeter. The optimum efficiency in nitrate trapping was found to be 173.8 mg/g (EBFP) and 78.74 mg/g (BFP). The adsorption efficiency of the sorbents was further optimized using the RSM-CCD and found to be suitable. The batch sorption study was also supported by the column study with a breakthrough curve at 90% (EBFP) and 60% (BFP) for the regeneration study. The optimum value for EBFP was attained at an initial nitrate concentration of 110 mg/L, pH∼8, and a dosage of 12 g/L at room temperature within 75 minutes of contact. The Freundlich isotherm model and pseudo-second-order kinetics fit satisfactorily with the sorption trends followed by other isotherm and kinetic models. The influence of various competing ions e.g., PO43−, Cl−, HCO3−, SO42−etc., on nitrate adsorption study was investigated. The physicochemical sorption of nitrate was confirmed, and a plausible mechanism has been suggested accordingly. The field sample experiment, including the start-up opportunities with this work, has been highlighted. EBFP could be an excellent sorbent of choice at present that is ready for commercialization.

Response and Resilience of Scenedesmus rubescens Microalgae to ZnO Nanoparticles

Microalgae are microorganisms of great importance for aquatic ecosystems. The investigation of their interaction with potential environmental stressors like nanoparticles (NPs) is essential in order to assess their behavior and fate in aquatic ecosystems. The scope of this work is to investigate the response and potential toxic effects of the short-term exposure of Scenedesmus rubescens microalga to zinc oxide (ZnO) NPs with various initial nitrate concentrations in the culture medium. Scenedesmus rubescens was cultivated in four different compositions of modified BG-11 with a nitrate content varying from 0 to 300 mg/L, and it was exposed to four concentrations of ZnO NPs, ranging from 0.081 to 81 mg/L. S. rubescens was found to be resilient towards ZnO NP toxicity. The results also highlight the fact that the toxic effects of ZnO NPs on microalgae are highly dependent on the species tested. The nitrate content of the medium did not affect the toxicity of ZnO NPs but had a significant impact on cell concentration, as it was observed at an initial nitrate concentration of 300 mg/L. Further investigation should focus on studying the morphological and metabolic characteristics and mechanisms contributing to this species’ resilience.

Nitrate removal from aqueous solution by glucose-based carbonaceous adsorbent: Batch and fixed-bed column adsorption studies

In the present study, the glucose-based carbonaceous adsorbent was prepared from glucose, melamine and urea by using ZnCl2 activation and heated at 550°C under N2 flow. The sample was treated for the 1st, 2nd and 3rd activation process, and they were characterized by N2 adsorption and desorption isotherms, elemental analysis and X-ray photoelectron spectroscopy (XPS). The results showed that the content of nitrogen increased and that of oxygen decreased with the increasing of the number of activation process. The adsorbent obtained after the 2nd activation showed the best adsorption properties and was used in batch and fixed-bed column adsorption studies. In batch adsorption experiments, we investigated the factors affecting nitrate adsorption such as initial concentration, solution pH, adsorption isotherms and adsorption kinetics. The isotherm data and kinetic data were fitted well to the Langmuir isotherm model and pseudo-second-order model, respectively, and the maximum adsorption capacity calculated by Langmuir model was 1.58 mmol/g at pH 3. The adsorption performance of the adsorbent in industrial application mode was also investigated by fixed-bed column experiments. The breakthrough time of the packed column was 160 min for the initial nitrate concentration of 200 mg/L at pH 3. The saturated column could be regenerated by 1 mol/L HCl and reused for at least 5 adsorption-desorption cycles. The column showed good adsorption performance in both coexisting ions solution and real contamination water.

Synergistic effect of LDHs/loofah composites for in-situ remediation of nitrate in contaminated groundwater

Permeable reaction barrier (PRB) is an innovative technology for in-situ remediation of nitrate-contaminated groundwater. In this study, layered double hydroxides (LDHs)/loofah composites were prepared and used as active fillers for PRB to facilitate nitrate removal from groundwater. Under the conditions of initial nitrate concentration of 5 mg/L, a hydraulic retention time (HRT) of 4 h, and without additional carbon source, the nitrate removal rates of the natural loofah, MgAl-LDHs, and CaMgAl-LDHs composite were 69.31 %, 85.35 %, and 97.82 %, respectively. The CaMgAl-LDHs composite exhibits the highest denitrification capacity, attributed to the presence of Ca2+and Mg2+. Ca2+ and Mg2+is an essential element for the structural integrity of microbial cells, which demonstrated that Ca2+ reduces the surface charge of bacteria, leading to hydrophobicity and facilitating biofilm formation. Electrochemical tests demonstrate that LDHs with distinctive two-dimensional layered structure, contribute to the augmentation of electron transfer during denitrification. LDHs can also promote the formation of highly active biofilms and the secretion of extracellular polymeric substances (EPS) on the surface of loofah, thereby enhancing the metabolic activity of microorganisms. Metagenomic analysis revealed that LDHs enhance the enrichment of denitrifying bacteria and the activity of key enzymes involved in denitrification. Therefore, the adsorption-biological coupled degradation of the LDHs/loofah composites have great potential to enhance the efficiency of biological denitrification, making it promising filling materials for PRB technology applied in groundwater remediation.

Assessment of nitrate contamination of domestic wells and remedial treatment by electrocoagulation

Natural water contaminated with nitrates can pose serious problems for human health and aquatic ecosystems. Thus, effective, and low-cost treatment systems that can be implemented on both large and small scales are needed. The main goals of this work were to quantify nitrate pollution of groundwater (i.e., underground well water used for drinking purposes), to identify its causes, to evaluate the performance of the electrocoagulation (EC) process in nitrate removal, optimizing the treatment procedure using synthetic water, and to estimate the process cost. A total of thirty domestic wells, located in Sidi Bel Abbes city in North-West Algeria, used for drinking water were subject to sampling. Results indicated that most of the wells had nitrate contents that exceeded the World Health Organization (WHO) guideline value as well as the Algerian permissible limit of 50 mg.L−1, with a maximum NO3- concentration of 162 mg.L−1. The pollution was presumed to be due to agricultural activity, human and animal waste, and the nature of the soil. The EC treatment tests with aluminum electrodes exhibited a high nitrate removal efficiency of 90% at a current density of 5.12 mA.cm−2, electrolysis time 15 min, pH 8.8, agitation speed 400 rpm and at an initial nitrate concentration of 50 mg.L−1. Under optimum operating conditions, nitrate removal was 88% for an initial [NO3-] of 87 mg.L−1 in groundwater. The operating cost was estimated at 0.27 US $/m3 or 0.12 US $/Kg nitrate removed. The findings from this study showed that EC is an economically viable technique for dealing with nitrate contamination for small-scale water treatment applications.

A novel combined system for efficient nitrate removal using a continuous flow electrocoagulation and sand filtration (FECF) reactor: Statistical analysis by Taguchi design.

In this study, a new hybrid bench-scale electrocoagulation-sand filtration (FECF) reactor was developed for purifying nitrate-contaminated samples. Before and after electrochemical treatment, two sand filters were included in this continuous system to facilitate the purification procedure, and the contaminated water flows horizontally through the entire system according to a specific hydraulic gradient within the reactor, resulting in water purification. Significant improvement in treatment performance was observed due to the presence of metal hydroxides in the second filter media that were not fully involved in the electrocoagulation treatment. Energy dispersive X-ray (EDX) analysis was performed to detect metal hydroxide species in the sand media, and the need for filter regeneration was evaluated by monitoring changes in the system flow rate. Moreover, an evaluation of the effects of different factors including operating time, current intensity, initial pH, type of anode and cathode, initial nitrate concentration, hydraulic head level inside the reactor, number of electrodes, and NaCl electrolyte concentration on the performance of nitrate removal was conducted through the Taguchi design. Further, ANOVA analysis verified the accuracy of the predicted model, and the variables were classified based on their relative importance in the FECF process. According to the regression model, 97% of nitrates were removed with Al electrodes as anode and Fe as cathode, 70 min purification time, current intensity of 3 A, 100 mg/l initial nitrate concentration, pH 8, electrolyte concentration of 1 g/l, electrode number of 6, and 1.5 cm head level.

A review of autotrophic denitrification for groundwater remediation: A special focus on bioelectrochemical reactors

Groundwater is an important resource that can help in climate change adaptation. However, the pollution of these aquifers with nitrate is a widespread problem of growing concern. Biological denitrification using inorganic electron donors shows significant advantages in treating nitrate-polluted groundwater where organic matter presence is negligible. However, mass transfer limitations and secondary contamination seem to be the major hinderance to spread the use of these technologies. This could be solved by the use of bioelectrochemical systems (BES), which emerge as an attractive technology to solve these problems due to the reported low energy demand and high denitrification rates. However, technical and operational issues must be considered to replicate these results at full-scale. This review summarizes the biological basis of autotrophic denitrification and the key aspects of its application in bioelectrochemical systems. In addition, an estimation of the capital costs required for the implementation of a BES considering different population sizes and initial nitrate concentration in the groundwater is made.

Potential of algal oil production from secondary treated sewage: a study using Chlorella vulgaris and synthetic wastewater

ABSTRACTTo assess the potential of using the secondary treated wastewater for the production of algal biofuel, batch experiments were carried out in photobioreactors using indigenous Chlorella vulgaris isolated from the natural freshwater body. Secondary treated wastewater with partial nitrification was simulated using various proportions of NO3-N and NH4-N while keeping the total nitrogen the same. Experiments with similar concentrations of nitrate without the NH4-N were used for comparison. In the presence of only NO3-N in the concentration range of 9–37 mg/L, the growth and fatty acid methyl ester (FAME) production was similar to the literature reports. When NH4-N was present along with NO3-N, the biomass growth was adversely affected, indicating an impact on the metabolic activity. For the same initial concentrations of nitrate in the culture, the maximum biomass concentration was reduced by 50–60% in the presence of NH4-N. The FAME profile changed significantly and a new FAME was identified, suggesting an impact on the lipid synthesis pathway. Comparison and analysis with the help of existing literature indicated that the adverse effect due to NH4-N was a function of pH. The growth, biomass yield, and FAME production were unaffected by a wide range of phosphorus concentrations. Maximum fatty acid methyl ester (FAME) suitable for biodiesel production (fatty acid carbon chain length C16 to C18) was 381.01 mg/L (224.58 mg/g of dry biomass), produced at NO3-N concentration of 18.5 mg/L and initial nitrogen loading per unit biomass of 0.37 g NO3-N/g of dry biomass.

Experimental and theoretical studies on nitrate removal using epichlorohydrin-modified cross-linked chitosan derived from shrimp waste.

Nitrates level in water is a worldwide problem that represents a risk to the environment and people's health; efforts are currently devoted to the development and implementation of new biomaterials for their removal. In this study, chitosan (Ch) from shrimp waste and the related epichlorohydrin-modified crossover chitosan (Ch-EPI) were used to remove nitrates from aqueous solutions. The mechanism of selective nitrate removal was elucidated and validated by theoretical calculations. The physicochemical performance of Ch and Ch-EPI was investigated through the main parameters pH, adsorption capacity, contact time, initial nitrate concentration, coexisting anions, and temperature. The experimental data were fitted to widely used adsorption kinetic models and adsorption isotherms. The maximum percentage of nitrate adsorption was reached at an equilibrium pH of 4.0 at an adsorbent dose of 2.0 g/L after a contact time of 50 min. Competing anion experiments show that chloride and sulfate ions have minimal and maximal effects on nitrate adsorption by Ch-EPI. Experimental adsorption data are best fitted to pseudo-second-order kinetic and isothermal Langmuir models. The maximum adsorption capacities of Ch and Ch-EPI for nitrate removal were 12.0 mg/g and 38 mg/g, respectively.

Electrochemical reduction of aqueous nitrate using metallic silver particles as spatially suspended catalyst

Increasing nitrate concentrations in water sources is a serious concern. The current study demonstrates the electrochemical reduction of nitrate in the presence of silver metallic particles (AgMPs). Using Ti/RuO2 anode and a Ti cathode, nitrate removal in undivided and divided cells was limited to 18% and 77%, respectively, in the absence of AgMPs. Total Nitrogen (TN) removal in undivided and divided cells was nil and 29.5%, respectively, in the absence of AgMPs. Under identical conditions, the presence of 8 mM AgMPs increased nitrate removal to 63% and 99%, respectively, with significant improvement in nitrate conversion to N2. The effect of various parameters on nitrate removal and selectivity of products was studied using a divided cell: concentration of AgMPs, inter-electrode distance, cathode material, current density, initial nitrate concentration, and reusability of AgMPs. In the presence of 8 mM AgMPs, nitrate removal using different cathodes was Ti ≈ Fe > Cu > SS > Fe/Sn. The cathode type also affected the selectivity, with the maximum conversion to N2 achieved with the Ti cathode. Nitrate removal and conversion to N2 improved with the increase in current density up to 10 mA/cm2. Overall, the presence of AgMPs substantially improved nitrate removal and conversion to N2. The production of reductive species (AgHx) by the intercalation of nascent hydrogen on metallic silver appears to promote catalytic nitrate reduction. AgMPs could be reused up to 10 times with consistent performance. This work offers a new approach to nitrate reduction using an efficient and reusable catalyst.

Chitosan-stabilized iron-copper nanoparticles for efficient removal of nitrate.

Chitosan-stabilized iron-copper nanomaterials (CS-nZVI/Cu) were successfully prepared and applied to the nitrate removal. Batch experiments were conducted to examine the effects of experimental parameters on nitrate removal, including Cu loading, CS-nZVI/Cu dosages, initial nitrate concentrations, and initial pHs. From the experimental date, it was concluded that CS-nZVI/Cu has a high nitrate removal efficiency, which can be more than 97%, respectively, at Cu loading = 5%, dosages of CS-nZVI/Cu = 3 g/L, initial nitrate concentrations of 30~120 mg/L, and initial pH values = 2~9. Additionally, the kinetic data for CS-nZVI/Cu were found to fit well with the first-order kinetic model with a rate constant of 0.15 (mg∙L)1-n/min, where n=1. The Langmuir model showed a good fit for NO3- removal, indicating that monolayer chemisorption occurred. The SEM and TEM analyses showed that the addition of chitosan resulted in improved dispersion of the CS-nZVI/Cu. The CS-nZVI/Cu nanomaterials have a more complete elliptical shape and are between 50 and 100 nm in size. The XRD analysis showed that the chitosan encapsulation reduced the oxidation of the iron component and the main product was Fe3O4. The FT-IR analysis showed that the immobilization of chitosan and the iron was accomplished by the ligand interaction. The nitrogen adsorption-desorption isotherm results showed that the CS-nZVI/Cu specific surface area and pore volume decreased significantly after the reaction. Adsorption, oxidation, and reduction are possible mechanisms for nitrate removal by CS-nZVI/Cu. The XPS analysis investigated the contribution of nZVI and Cu in the removal mechanism. Adding copper accelerates the reaction time and rate. In addition, nZVI played a vital role in reducing nitrate to N2. Based on these results, it looks like CS-nZVI/Cu could be a satisfactory material for nitrate removal.

Exposure pathways matter: Aquatic phototrophic communities respond differently to agricultural run‐off exposed via sediment or water

Abstract Small shallow ponds are widespread but understudied water bodies in agricultural landscapes. Agricultural run‐off (ARO) transports pesticides and nutrients into adjacent aquatic ecosystems where they occur dissolved in the water column or are bound to sediments. Consequently, aquatic communities are affected by ARO via different exposure pathways. We hypothesize that sediment‐bound ARO mainly affects submerged rooted macrophytes, while phytoplankton and periphyton are more prone to ARO in water. These primary producers compete for resources resulting in a regime shift between alternative stable states of macrophyte or phytoplankton dominance. We hypothesize that warming increases nutrient release from sediments and thereby facilitates the occurrence of phytoplankton dominance. Using a full‐factorial microcosm design, we exposed aquatic primary producers to either sediment or water application of a mixture of common pesticides (terbuthylazine, pirimicarb, tebuconazole and copper) and nitrate at two concentrations and two temperatures (22°C and 26°C) for 4 weeks. Initial and final concentrations of pesticides and nitrate, final biomass of macrophytes, periphyton and phytoplankton, pesticide accumulation in macrophytes and changes in carbon, nitrogen and phosphorus content and selected exoenzyme activities in the sediment were measured. We found lower final macrophyte biomass for both ARO treatments compared to controls, indicating a prevalence of negative effects by herbicides and competition for light with other phototrophs. In contrast, phytoplankton and periphyton biomass increased, but only when exposed to ARO via the water column, indicating a prevalence of positive effects by nutrient supply. Microbial carbon and nutrient cycling in sediments was not affected by ARO. Higher temperature mitigated ARO‐related effects on macrophytes under sediment exposure. Synthesis and application. ARO poses a strong risk of submerged macrophyte loss and establishment of turbid conditions with phytoplankton dominance in aquatic ecosystems. In conclusion, exposure pathways as well as indirect and interacting effects of multiple stressors need to be considered when designing appropriate mitigation measures. Under climate change, we suggest to prioritize local measures as buffer strips a reduced use of pesticides and fertilizers, and sediment removal as appropriate measures to protect these vulnerable but widespread aquatic systems, which are highly relevant for biodiversity in agricultural landscapes.

Denitrification Assays for Testing Effects of Xenobiotics on Aquatic Denitrification and Their Degradation in Aquatic Environments

We developed, tested, and optimized two laboratory denitrification assays for both managers and scientists to assess the effects of xenobiotics on the denitrification process over 7 days (short batch assay, SBA) and 28 days (long semi-continuous assay, LSA). The assays facilitate (1) measuring the efficiency of nitrate removal under the influence of xenobiotics, (2) determining the removal of the tested xenobiotics via adsorption or biotic decomposition, and (3) testing the influencing parameters for optimizing the denitrification process. The adsorption of the xenobiotics was assessed by inhibiting all biological processes through the addition of HgCl2. Our tests demonstrate that the ratio of the initial nitrate concentration to the amount of bioavailable organic matter provided is essential to avoid organic carbon or nitrate limitation. While a pH < 7 resulted in decreased denitrification, a pH > 8 led to nitrite accumulation, indicating incomplete denitrification. Over durations of more than a week, weekly replenishments of the nitrate and HgCl2 and weekly purging with argon gas to reduce the oxygen concentrations are needed. The assays provide information about the accumulation of xenobiotics in the bioreactors that is necessary for the environmentally friendly treatment of the bioreactor fillings and provide insight into the potential of the bioreactors to remove pesticides from polluted water resources.

Unusual, hierarchically structured composite of sugarcane pulp bagasse biochar loaded with Cu/Ni bimetallic nanoparticles for dye removal

Biochar-supported nanocatalysts emerged as unique materials for environmental remediation. Herein, sugarcane pulp bagasse (SCPB) was wet-impregnated with Cu(NO3)23H2O and Ni(NO3)26H2O, then pyrolyzed at 500 °C, under N2, for 1 h. We specifically focused on sugarcane pulp instead of SCB and biochar materials. The metal nitrate to biomass ratio was set at 0.5, 1, and 2 mmol/g, with Cu/Ni initial ratio = 1. The process provided hierarchically structured porous biochar, topped with evenly dispersed 40 nm-sized CuNi alloy nanoparticles (SCPBB@CuNi). The biochar exhibited an unusual fishing net-like structure induced by nickel, with slits having a length in the 3–12 μm range. Such a fishing net-like porous structure was obtained without any harsh acidic or basic treatment of the biomass. It was induced, during pyrolysis, by the nanocatalysts or their precursors. The CuNi nanoparticles form true alloy as proved by XRD, and are prone to agglomeration at high initial metal nitrate concentration (2 mmol/g). Stepwise metal loading was probed by XPS versus the initial metal nitrate concentration. This is also reflected in the thermal gravimetric analyses. The SCPBB@CuNi/H2O2 (catalyst dose: 0.25 g/L) system served for the catalyzed removal of Malachite Green (MG), Methylene Blue (MB), and Methyl Orange (MO) dyes (concentration = 0.01 mmol/L). Both single and mixed dye solutions were treated in this advanced oxidation process (AOP). The dyes were removed in less than 30 min for MG and 3 h for MB, respectively, but 8 h for MO, therefore showing selectivity for the degradation of MG, under optimized degradation conditions. The catalysts could be collected with a magnet and reused three times, without any significant loss of activity (∼85%). AOP conditions did not induce any nanocatalyst leaching.To sum up, we provide a simple wet impregnation route that permitted to design highly active Fenton-like biochar@CuNi composite catalyst for the degradation of organic pollutants, under daylight conditions.

Short-Term Toxicity of ZnO Nanoparticles on Microalgae at Different Initial Nutrient Concentrations

The aim of this work was to investigate the combined short-term toxic effect of zinc oxide (ZnO) nanoparticles (NPs) and nitrate concentration of the medium on freshwater microalgae. For this purpose, freshwater microalgae Chlorococcum sp. was cultivated in modified Blue-Green medium (BG-11) containing nitrate concentrations ranging from 0 to 300 mg/L, and exposed to ZnO NPs in different concentrations (0.081 to 810 mg/L) for a period up to 96 h. The experimental results revealed that algal growth was affected by the exposure time, NPs concentrations, and mainly the initial nitrate concentration. Differences in microalgae growth rates were observed. The toxic effect of ZnO NPs was higher on microalgae cultured in modified BG-11 with low and high nitrate concentrations. During the 4-day exposure, the highest growth rates were observed at 24 h at an initial nitrate concentration of 50 mg/L; 1.94 d−1 and 0.22 d−1 for 0 and 810 mg/L ZnO NPs, respectively. Nitrate uptake by algal biomass reached up to 40.1% after 96 h of operation in the control culture with an initial nitrate concentration of 50 mg/L. Finally, the results of this study showed the need for the investigation of ZnO NPs toxicity on microalgae under optimum and stressful nutrient conditions for microalgae growth.

A Promising, Highly Effective Nitrate Sorbent Derived from Solid Olive Mill Residues

Olive mill residues have been valorized by chemical modification with amines to improve their adsorption capacity and to be used as a low-cost bioadsorbent for nitrate removal. The Taguchi method was used to optimize the process. By performing a three-factor analysis with three levels, it was possible to significantly reduce the number of experiments to be performed and to obtain the best working conditions. The results of the Taguchi method showed that the highest adsorption capacity was 110 mg·g−1 with a functionalized biomass dose of 1 g·L−1 using an initial nitrate concentration of 500 mg·L−1. Field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) were used to characterize the surface morphology and study the chemical changes that occurred in the biomass. For the best conditions of the Taguchi approach, the kinetic and equilibrium aspects of the adsorption process were analyzed. The adsorption isotherms obtained were successfully fitted to the Freundlich (R2 = 0.98) and Langmuir (R2 = 0.97) models. The kinetics of the process were studied, and the data obtained fit very well to the pseudo-second-order model (R2 = 0.99). The adsorption values obtained suggest that it is a bioadsorbent with great potential for nitrate retention in aqueous solutions.

End-of-pipe treatment of secondary treated coke-oven wastewater for removal of fluoride, cyanide, phenol, ammoniacal-N and nitrate using waste material: Experiment, modelling and optimization

The present investigation focused on End-of-pipe treatment of secondary treated coke-oven wastewater to remove cyanide, phenol, ammoniacal-N, nitrate and fluoride using earthen tea pot (ETP), a local market waste. The effect of parameters like adsorption time (0–10 h), particle size (1–3 mm) and adsorbent dose (10–30 gL−1) was tested for removal of pollutants from synthetic BOD treated coke-oven wastewater (SBTCW) and maximum removal was obtained as cyanide (95.46 ± 0.004%), phenol (99.70 ± 0.005%), ammoniacal-N (47.88 ± 6.31%), nitrate (61.03 ± 2.12%), and fluoride (92.35 ± 0.09%) at adsorption time 10 h, particle size 1 mm and adsorbent dose 10 gL−1. Kinetic study showed that the fluoride removal data fit satisfactorily to the Pseudo 2nd order kinetic model, whereas the Pseudo 1st order model was found to be fitted well to the kinetic data of all other pollutants. Adsorption isotherm study portrayed that the Freundlich isotherm model holds good to represent equilibrium data for the removal of pollutants. Response Surface Methodology (RSM) was used to optimize the removal efficiencies of all five pollutants. The optimum removal condition as shown by RSM study was contact time: 7.3 h, and initial concentrations (ICs) of cyanide, phenol, ammoniacal-N, nitrate and fluoride are 0.71, 10, 400, 100 and 10.1 mgL−1, respectively, and the removal of five pollutants (cyanide, phenol, ammoniacal-N, nitrate and fluoride) were predicted as 40.58%, 90.00%, 41.63%, 96.00% and 45.29%, respectively. Artificial Neural Network model was developed based on experimental points which indicated that the model can calculate abatement of five different pollutants for various operating conditions with reasonably high accuracy. Genetic Algorithm was then used to optimize the removal process of the five pollutants. Regeneration study was conducted to assess the efficacy of the regenerated adsorbent in next cycle of the End-of-pipe treatment of SBTCW. Finally, real secondary treated coke-oven wastewater was collected and treated with the present adsorbent.