Ammonia removal from aqueous solution using natural Chinese clinoptilolite

Eco-Friendly Ammonia Adsorption from Aqueous Solutions Using Activated Madhuca indica Leaves Charcoal and Optimization of Parameters by RSM-BBD: A Sustainable Zero-Waste Approach

Ammonia separation from industrial effluents is a big concern for aquatic, plant, and human lives. Adsorption is best suited for separating ammonia from effluents due to its high effectiveness. In this paper, the activated Madhuca indica leaves charcoal (AMLC) adsorbent was synthesized and characterized using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX) to know the characteristics of the adsorbent before and after adsorption. Further, thermal gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) analysis were performed on the AMLC adsorbent, and a very high surface area of 964.252 m2/g was observed. The AMLC was utilized for adsorption experiments, and the adsorption parameters were optimized using response surface methodology-Box-Behnken design (RSM-BBD). The optimized parameters reported using RSM-BBD are a contact time of 123.19 min, an adsorbent dosage of 29.1 g/L, a pH of 10.33, an initial ammonia concentration of 312.28 mg/L, and a shaker speed of 82.70 rpm that gives the maximum ammonia removal efficiency of 100%. The adsorption equilibrium studies were analyzed using Langmuir, Freundlich, and Dubinin isotherms, with the Langmuir isotherm being the best fit for the data. The adsorption kinetics were modeled with pseudo-first-order (PFO), pseudo-second-order (PSO), and intraparticle diffusion (IPD) models, indicating that PSO best describes the rate of kinetics. In addition, adsorption thermodynamics is also studied. The change in enthalpy (ΔH) was positive, suggesting that the adsorption is an endothermic process. The negative energy of entropy (ΔS) indicated complex formation with the AMLC adsorbent. In contrast, the positive change in Gibb's free energy showed that adsorption was not spontaneous. The present study supports UN SDG Goal 6 by providing sustainable and cost-effective solutions to water treatment. It also promotes biomass use and reduces chemical usage toward an eco-friendly water purification process.

Adsorption and desorption of ammonium from treated wastewater by zeolite filled columns: An experimental study at the water resource recovery facility of Palermo University - Italy

Water scarcity and mineral fertilizer depletion are becoming recognised environmental challenges worldwide. Treated wastewater (TWW) could be a potential resource for reusing water and nutrients, such as nitrogen (N), for fertilizers. This study explores the possibility of adopting columns filled with zeolite to recover ammonium (NH4+) from real TWW. Specifically, this study aimed to evaluate zeolite's adsorption capacity with different particle sizes arranged in columns and various flow rates to determine the most efficient way of NH4+ adsorption from a real wastewater treatment plant's effluent. The same zeolite with two different size diameters (0.5-1.0 mm and 2.0-5.0 mm) was tested using three different flow rates (1.2, 1.6 and 2.4 L h-1) to evaluate their NH4+ adsorption capacity. After the adsorption test, a desorption trial assessed the zeolite's desorption ability. The results showed that the highest flow rate increased the adsorption capacity of both zeolites by about 29% more than the lowest flow rate. Moreover, the 0.5-1.0 mm zeolite adsorbed approximately 60 mg more NH4+ than the 2.0-5.0 mm zeolite, highlighting the influence of particle size on adsorption capacity. Furthermore, the zeolite was characterised by a rapid NH4+ release since 44-78% of the adsorbed NH4+ was released in the first 30 min. The desorption test with the lowest flow rate achieved the highest amount of desorbed NH4+, up to 123-148% more than the higher flow rates. Results have shown that due to its adsorption capacity, zeolite can be used to recover NH4+ from treated wastewater (TWW) and potentially recycle resources in the agriculture field, contributing to the circular economy.

Role of mordenite zeolite in improving nutrient and water use efficiency in Alfisols

Poor nutrient use efficiency (NUE) and water use efficiency (WUE) is a predominantly faced problem in semi-arid regions that limit the crop production. This problem can be addressed with the application of zeolite that is a naturally available mineral with very high cation exchange and water holding capacity, which aids in improving NUE and WUE. Moreover, zeolites are safe for the environment and living organisms, and their use in agriculture results in improving physical and chemical properties of soil. Yet, its study is very limited in semi-arid regions of India. Thus, a study was conducted with locally available zeolite at CRIDA, Hyderabad. Zeolite was further characterized using X-ray diffraction (XRD) and SEM, as the type of zeolite collected is unknown from local market. The results of XRD and SEM revealed that the zeolite collected was mordenite zeolite. Our study includes laboratory and pot experiment where laboratory includes sorption and leaching column study to evaluate the zeolite capacity to hold and release the nutrients especially NH4 +, P, and K. In this study, the adsorption behaviour of the natural mordenite was examined, and it was found that the maximum adsorption capacity for NH4 +, P, and K were estimated as 10.6, 1.08, and 2.15 mg g-1, respectively, suggesting the zeolite has good affinity for N. Furthermore, the column study revealed that there was 15.4% reduction in NH4 +-N loss with 10 tonnes zeolite ha-1 + N @ 100 kg ha-1 as compared to N alone, while the reduction was 39.6% with 10 tonnes zeolite ha-1 + N @ 500 kg ha-1 compared to N alone, suggesting that the zeolite could control the release of N as compared to the sole application of N, which was supplied through urea. In addition, pot experiment was carried out with three levels of fertiliser rates, four levels of zeolite, and two levels of moisture in randomised complete block design with three replications to evaluate the changes in soil available nutrients and their uptake in tomato. Results revealed that there was a significant positive impact on yield, water use efficiency, nutrient (N, P, and K) uptake, and soil available nutrients. Highest soil available N, P, and K, crop uptake, and yield were observed due to zeolite application @ 200 kg ha-1 along with 100% recommended dose of fertilization in Alfisols. Thus, zeolite application along with chemical fertilisers can improve the nutrient availability by reducing the leaching losses and improving nutrient use efficiency.

Unlocking the adsorptive effectiveness of naturally occurring heulandite zeolite for the removal of PO43- and NO3- anions from wastewater

The mitigation of high levels of phosphate (PO43-) and nitrate (NO3-) ions in water bodies, particularly in agricultural wastewater, holds paramount importance in curbing eutrophication within aquatic ecosystems. Herein, using experimental and computational techniques, the study explored the potential of naturally occurring South Africa heulandite (HEU) zeolite for the removal of PO43- and NO3- ions from synthetic wastewater in batch mode. The percentage removal of PO43- and NO3- was 59.15% and 51.39%, respectively, whereas the corresponding maximum adsorption capacity of the adsorbent was 0.0236 and 0.0206 mg/g. The adsorption kinetics of both anions by HEU fitted well in the pseudo-first-order (PFO) kinetic model indicating a physisorption-mediated rate-determining step. It was revealed that the adsorption process was multi-mechanistic spontaneous and exothermic. Molecular simulations using Monte Carlo (MC) and density functional theory (DFT) methods also provided insights into the adsorption mechanisms.

Benchmarking produced water treatment strategies for non-toxic effluents: Integrating thermal distillation with granular activated carbon and zeolite post-treatment

The management of produced water (PW) generated during oil and gas operations requires effective treatment and comprehensive chemical and toxicological assessment to reduce the environmental risks associated with reuse or discharge. This study evaluated a treatment train that included a low-temperature thermal distillation pilot system followed by granular activated carbon (GAC) and zeolite post-treatment for processing hypersaline Permian Basin PW. Our study provides a unique and comprehensive assessment of the treatment efficiency considering a targeted chemical scheme together with whole effluent toxicity (WET) tests across four trophic levels regarding aquatic critical receptors of concern (ROC): Raphidocelis subcapitata, Vibrio fischeri, Ceriodaphnia dubia, and Danio rerio. The distillate from the thermal distillation process met various numeric discharge standards for salinity and major ions. However, it did not meet toxicity requirements established by the United States National Pollutant Discharge Elimination System program. Subsequent post-treatment using GAC and zeolite reduced the concentration of potential stressors, including volatile organics, NH3, Cd, Cr, Zn, and Mn in the final effluent to below detection limits. This resulted in a consistent toxicity reduction across all WET tests, with no observable adverse effects for R. subcapitata, C. dubia, and D. rerio (no observed effect concentration >100%), and V. fischeri effects reduced to 19%. This study realizes the feasibility of treating PW to non-toxic levels and meeting reuse and discharge requirements. It underscores the importance of implementing integrated treatment trains to remove the contaminants of concern and provides a systematic decision framework to predict and monitor environmental risks associated with PW reuse.

An integrated physical-chemical system for concurrent carbon, nitrogen, and phosphorus removal in municipal wastewater treatment plants

A substantial quantity of suspended solids (SS) present in municipal wastewater leads to the swift depletion of the ion exchange (IE) capacity of natural zeolites like Clinoptilolite (CIO). This limitation has become the primary factor contributing to the limited adoption of the IE technique within municipal wastewater treatment plants (WWTPs). However, an extensive lab-scale and pilot-scale study conducted over approximately one year has made it possible to efficiently apply the IE system using CIO (main grain size of 0.5-1.0 mm) upstream of the primary sedimentation tank (PST). The primary treated wastewater (PTWW) was introduced to the IE system either by pre-straining or without any pre-treatment. The IE system's capabilities for removing total suspended solids (TSS), chemical oxygen demand (COD), and phosphorus (P) while primarily focusing on ammonium (NH4+) recovery were undergone for a detailed investigation. Frequent backwashing, involving intermittent water and air injection, was used to mitigate clogging as the main problem of the IE system for treating PTWW. The results revealed a mean removal efficiency of 85 %, 60 %, 50 %, and 30 % for NH4+, TSS, TCOD, and total phosphorus (TP), respectively, per cycle exclusively for the IE system. As the system scaled up, a substantial reduction was observed in the adsorption capacity, shifting from approximately 12 to 1 g NH4+ (kgCIO)-1. Despite this drawback, the study's finding showed that prolonged treatment of PTWW for NH4+ removal and recovery in municipal WWTPs, besides substantially reducing carbonaceous pollutants, is applicable. Implementing this application will not only decrease the biological treatment costs for municipal wastewater but also yield valuable by-products, such as NH4Cl, which can serve as a foundational material for the production of ammonium chloride fertilizer. Therefore, transitioning to IE systems in municipal WWTPs will diminish the reliance on resource-intensive methods like the Harber-Bosch procedure for producing nitrogen fertilizer.

Preparation of low-cost functionalized diatomite and its effective removal of ammonia nitrogen from wastewater

A low-cost functionalization method was used to treat diatomite, and an efficient adsorbent for ammonia nitrogen was prepared by optimizing the functionalization conditions. The functionalized diatomite (DTCA-Na) was characterized by SEM, EDS, BET, XRD, FT-IR, and TG. The results demonstrate that DTCA-Na has excellent adsorption performance after being modified with H2SO4 (60.00 wt.%), NaCl (5.00 wt.%), and calcination at 400 °C for 2 h. While studying the effect of adsorption factors on the removal of ammonia nitrogen, the kinetic and thermodynamic behaviors in the adsorption process were discussed. The removal efficiency of the simulated wastewater with the initial ammonia nitrogen concentration of 10.00 mg L-1 by the DTCA-Na was more than 80% when the contact time was 60 min, pH was 6-10, the dosage of adsorbent was 1.00 g, and the temperature was 25 °C. The adsorption process of ammonia nitrogen was conformed to the pseudo-first-order and Langmuir isothermal model. The removal efficiency of ammonia nitrogen was still above 80% after 5 times adsorption-desorption experiments. The DTCA-Na has a brighter prospect of application in the field of ammonia nitrogen wastewater treatment due to its excellent adsorption performance and low-cost advantage.

Machine learning approaches for data-driven process monitoring of biological wastewater treatment plant: A review of research works on benchmark simulation model No. 1(BSM1)

In the past decade, machine learning techniques have seen wide industrial applications for design of data-based process monitoring systems with an aim to improve industrial productivity. An efficient process monitoring system for wastewater treatment process (WWTP) ensures increased efficiency and effluents meeting stringent emission norms. Benchmark simulation model No. 1 (BSM1) provides a simulation platform to researchers for developing efficient data-based process monitoring, quality monitoring, and process control systems for WWTPs. The present article presents a review of all research works reporting applications of various machine learning techniques for sensor and process fault detection of BSM1. The review focuses on process monitoring of biological wastewater treatment process, which uses a series of aerobic and anaerobic reactions followed by secondary settling process. Detailed information on various parameters monitored, different machine learning techniques explored, and results obtained by different researchers are presented in tabular and graphical format. In the review, it was observed that principal component analysis (PCA) and its variants account for the maximum number of research works for process monitoring in WWTPs and there are very few applications of recently developed deep learning techniques. Following the review and analysis, various future scopes of research (such as techniques yet to be explored or improvement of results for a particular fault) are also presented. These information will assist prospective researchers working on BSM1 to take forward the research.

Constructing Randomly Lamellar HKUST-1@Clinoptilolite through Polyethylene Glycol-Assisted Hydrothermal Method and Coordinated Complexation for Enhanced Adsorptive Separation for CO2 and CH4

Clinoptilolite (CP) was successfully synthesized via a hydrothermal route in the presence of polyethylene glycol (PEG), and it was then delaminated by washing using Zn²⁺ containing acid. HKUST-1, as one kind of the Cu-based MOFs, showed a high CO₂ adsorption capacity owing to its large pore volume and specific surface area. In the present work, we selected one of the most efficient ways for preparing the HKUST-1@CP compounds via coordination between exchanged Cu²⁺ and ligand (trimesic acid). Their structural and textural properties were characterized by XRD, SAXS, N₂ sorption isotherms, SEM, and TG-DSC profiles. Particularly, the effect of the additive PEG (average molecular weight of 600) on the induction (nucleation) periods and growth behaviors were detailed and investigated in the hydrothermal crystallization procedures of synthetic CPs. The corresponding activation energies of induction (E_n) and growth (E_g) periods during crystallization intervals were calculated. Meanwhile, the pore size of the inter-particles of HKUST-1@CP was 14.16 nm, and the BET specific area and pore volume were 55.2 m²/g and 0.20 cm³/g, respectively. Their CO₂ and CH₄ adsorption capacities and selectivity were preliminarily explored, showing 0.93 mmol/g for HKUST-1@CP at 298 K with the highest selective factor of 5.87 for CO₂/CH₄, and the dynamic separation performance was evaluated in column breakthrough experiments. These results suggested an efficient way of preparing zeolites and MOFs composites that is conducive to being a promising adsorbent for applications in gas separation.

Advanced Hybrid System for Ammonium Valorization as Liquid Fertilizer from Treated Urban Wastewaters: Validation of Natural Zeolites Pretreatment and Liquid-Liquid Membrane Contactors at Pilot Plant Scale

This study evaluates a hybrid system combining zeolites as a sorption stage and a hollow fiber membrane contactor (HFMC) for ammonia (NH₃) recovery from treated urban wastewater. Ion exchange with zeolites was selected as an advanced pretreatment and concentration step before the HFMC. The system was tested with wastewater treatment plant (WWTP) effluent (mainstream, 50 mg N-NH₄/L) and anaerobic digestion centrates (sidestream, 600-800 mg N-NH₄/L) from another WWTP. Natural zeolite, primarily clinoptilolite, demonstrated effective desorption of retained ammonium using a 2% NaOH solution in a closed-loop configuration, resulting in an ammonia-rich brine that enabled over 95% NH₃ recovery using polypropylene HFMCs. A 1 m³/h demonstration plant processed both urban wastewaters, which were pretreated by ultrafiltration, removing over 90% of suspended solids and 60-65% of COD. The 2% NaOH regeneration brines (2.4-5.6 g N-NH₄/L) were treated in a closed-loop HFMC pilot system, producing 10-15% N streams with potential use as liquid fertilizers. The resulting ammonium nitrate was free of heavy metals and organic micropollutants, making it suitable for use as liquid fertilizer. This comprehensive N management solution for urban wastewater applications can contribute to local economies while achieving reduced N discharge and circularity goals.

Natural Zeolites for the Sorption of Ammonium: Breakthrough Curve Evaluation and Modeling

The excessive use of ammonium fertilizer and its associated leakage threatens aquatic environments around the world. With a focus on the treatment of drinking water, the scope of this study was to evaluate and model the breakthrough curves for NH₄⁺ in zeolite-filled, fixed-bed columns. Breakthrough experiments were performed in single- and multi-sorbate systems with the initial K⁺ and NH₄⁺ concentrations set to 0.7 mmol/L. Breakthrough curves were successfully modeled by applying the linear driving force (LDF) and Thomas models. Batch experiments revealed that a good description of NH₄⁺ sorption was provided by the Freundlich sorption model (R² = 0.99), while unfavorable sorption was determined for K⁺ (n_F = 2.19). Intraparticle diffusion was identified as the rate limiting step for NH₄⁺ and K⁺ during breakthrough. Compared to ultrapure water, the use of tap, river, and groundwater matrices decreased the treated bed volumes by between 25% and 69%-as measured at a NH₄⁺ breakthrough level of 50%. The concentrations of K⁺ and of dissolved organic carbon (DOC) were identified as the main parameters that determine NH₄⁺ sorption in zeolite-filled, fixed-bed columns. Based on our results, the LDF and Thomas models are promising tools to predict the breakthrough curves of NH₄⁺ in zeolite-filled, fixed-bed columns.

Development of Adsorptive Membranes for Selective Removal of Contaminants in Water

The presence of arsenic and ammonia in ground and surface waters has resulted in severe adverse effects to human health and the environment. Removal technologies for these contaminants include adsorption and membrane processes. However, materials with high selectivity and pressure stability still need to be developed. In this work, adsorbents and adsorptive membranes were prepared using nanostructured graphitic carbon nitride decorated with molecularly imprinted acrylate polymers templated for arsenate and ammonia. The developed adsorbent removed arsenate at a capacity and selectivity similar to commercial ion-exchange resins. Ammonia was removed at higher capacity than commercial ion exchange resins, but the adsorbent showed lower selectivity. Additionally, the prepared membranes removed more arsenate and ammonia than non-imprinted controls, even in competition with abundant ions in water. Further optimization is required to improve pressure stability and selectivity.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

The role of biochar on alleviating ammonia toxicity in anaerobic digestion of nitrogen-rich wastes: A review

This paper reviewed the mechanisms of biochar in relieving ammonia inhibition. Biochar affects nitrogen-rich waste's anaerobic digestion (AD) performance through four ways: promotion of direct interspecies electron transfer (DIET) and microbial growth, adsorption, pH buffering, and provision of nutrients. Biochar enhances the DIET pathway by acting as an electron carrier. The role of DIET in relieving ammonia nitrogen may be exaggerated because many related studies don't provide definite evidence. Therefore, some bioinformatics technology should be used to assist in investigating DIET. Biochar absorbs ammonia nitrogen by chemical adsorption (electrostatic attraction, ion exchange, and complexation) and physical adsorption. The absorption efficiency, mainly affected by the properties of biochar, pH and temperature of AD, can reach 50 mg g^-1 on average. The biochar addition can buffer pH by reducing the concentrations of VFAs, alleviating ammonia inhibition. In addition, biochar can release trace elements and increase the bioavailability of trace elements.

Granular Natural Zeolites: Cost-Effective Adsorbents for the Removal of Ammonium from Drinking Water

Increasing food demand has resulted in an ever increasing demand for nitrogen fertilizers. Ammonium is the main constituent of these fertilizers and is a threat to aquatic environments around the world. With a focus on the treatment of drinking water, the scope of this study was to investigate the influence of key parameters on the suitability of granular natural zeolites as adsorbents for ammonium. Sorption experiments were performed in artificial matrices by varying the grain size, contact time, ammonium concentration, pH, content of competing ions, and regeneration solutions used. Additionally, natural matrices and the point of zero charge (pzc) were investigated. With an initial ammonium concentration of 10 mgN/L, the grain size was shown to have no significant effect on the sorption efficiency (97–98%). The experimental data obtained was best described by the Langmuir adsorption model (R2 = 0.99). Minor effects on sorption were observed at different pH values and in the presence of competing anions. In addition, the pHPZC was determined to be between pH 6.24 and pH 6.47. Potassium ions were shown to be better than sodium ions for the regeneration of previously loaded zeolites, potassium is also the main competitor to ammonium sorption. The use of tap, bank filtrate, river, and groundwater matrices decreased the ammonium sorption capacity of granular natural zeolites by up to 8%. Based on our results, granular natural zeolites are promising cost-effective adsorbents for drinking water treatment, especially in threshold and developing countries.

Removal of ammonia nitrogen and phenol by pulsed discharge plasma combined with modified zeolite catalyst

In this work, the removal of ammonia nitrogen and phenol by pulsed discharge plasma (PDP) and modified zeolite was investigated. The Fe-zeolite and Mn-zeolite catalysts were prepared by the impregnation method. Catalysts' morphology, specific surface area, and chemical bond structure were characterized. Based on the pollutants removal experiments, Fe-zeolite (0.01) in the PDP system had better catalytic oxidation of phenol and adsorption effect of ammonia nitrogen. The removal efficiency of the pollutants increased with the increase of discharge voltage and solution conductivity, but decreased with the increase of discharge distance. During the plasma discharge process, the pH value in the solution decreased, and the solution conductivity gradually increased. After PDP/Fe-zeolite system treatment, the toxicity of the wastewater was significantly reduced. This study provided a new treatment method for inorganic and organic pollutants treated by PDP.

Remazol Brilliant Blue R (RBBR) dye and phosphate adsorption by calcium alginate beads modified with polyethyleneimine

This study concerns the preparation of novel adsorbent prepared from calcium alginate bead modified with polyethyleneimine (PEI-CaAlg). The adsorption capacity of the PEI-CaAlg was examined by Remazol Brilliant Blue R (RBBR) and phosphate adsorption. PEI-CaAlg showed high removal efficiencies for RBBR (90.48%) and phosphate (88.10%). The removal of both RBBR and phosphate onto the PEI-CaAlg followed the Freundlich isotherm and the second-order model. The adsorption was studied in terms of thermodynamic and found to be feasible and spontaneous in nature. The reusability of the modified alginate beads was also examined up to five cycles. The removal efficiency was 90.48% at the first cycle and decreased to 75.15% at the end of the fourth cycle. The adsorption of color and phosphate from real textile wastewater was also instigated. The removal efficiencies for color and phosphate ions reached 80.24% and 90.00%, respectively. Therefore, the prepared PEI-CaAlg can be considered as a novel, eco-friendly, and cost-effective adsorbent for simultaneous dye and phosphate adsorption. PRACTITIONER POINTS: This study aims to modify the surface of calcium alginate beads with polyethyleneimine (PEI). The adsorption of RBBR and phosphate by the modified alginate beads (PEI-CaAlg) was investigated. PEI is an organic polymer with a linear/branch shape, which can increase the active sites on the adsorbent surface. PEI has one nitrogen atom in every three atoms provides a positive charge that can complex with the negatively charged molecules. The adsorption of RBBR and phosphate were carried out onto PEI-CaAlg.

Removal of Ammonium Ions from Aqueous Solutions Using Weathered Halloysite

This study investigated the use of weathered halloysite as an ion exchange material for ammonium removal from water. The study was conducted under static and dynamic conditions. The influence of such parameters as the preliminary concentration of ammonium ions, dose of halloysite, and pH was examined in periodic studies. The ion exchange capacity of weathered halloysite under various regeneration conditions such as concentration, excess of regeneration solution and the pH at which the regeneration was performed was also determined. The effect of flow velocity, initial NH₄⁺-ions concentration was studied in column tests and the weathered halloysite’s ion -exchange capacity was also determined. The best results of ammonium ion removal were obtained at pH 6. The equilibrium isotherms were described using the Langmuir and Freundlich models. The results of periodic studies show a good fit for the data of both models, with Langmuir isotherms reflecting the removal of ammonium ions better. A good match for the data (R² > 0.99) was provided by a pseudo second-order kinetic model. The obtained results indicate that a properly prepared halloysite can be a useful mineral for the removal of dangerous substances, such as ammonium ions, present in natural waters.

Cation Exchange of Natural Zeolites: Worldwide Research

Research on natural zeolites (NZ) has increased over the years, showing potential in different areas, and many of them involve cation exchange (CE), considered one of the essential properties of NZ. This work aims to identify studies’ cognitive structure based on the cation exchange capacity (CEC) of NZ through bibliometric analysis to evaluate scientific production, growth trend, and visualization through bibliometric maps using the VOSviewer software. All types of documents and all languages indexed in Scopus from 1970 to 2020 were considered for the database, obtaining 703 documents. The results indicate an increasing trend in CE annual publications in NZ. This analysis shows the most influential authors such as Daković, Wang and Colella, while the countries that stand out are China, Turkey and the United States. Besides, the bibliometric maps made it possible to understand the intellectual structure of this academic discipline, identifying areas of current and potential interest in this field of studies such as its application in medicine, agriculture, catalysts, heavy metal removal, wastewater treatment (WWT), bioremediation and construction. Finally, these studies showed trends in science and technology studies favoring environmental remediation and human health.

Ammonia stripping using a continuous flow jet loop reactor: mass transfer of ammonia and effect on stripping performance of influent ammonia concentration, hydraulic retention time, temperature, and air flow rate

When wastewater containing ammonia is discharged into the receiving environment without any kind of treatment, it causes both environmental problems and negatively affects human health. In this study, the aim was to strip ammonia using air in a continuous flow jet loop reactor (JLR) and investigate the effects of ammonia concentration, hydraulic retention time (HRT), air flow rate, and temperature on ammonia removal within this scope. By changing the ammonia concentration in the influent, no significant change was observed in ammonia removal efficiency. With air flow rate 45 L min^-1, temperature 50 °C, pH 11, and HRT 7.5 h, mean 88.1% ammonia removal was achieved. Increasing the HRT, air flow rate, and temperature increased the ammonia removal efficiency. Later the ammonia stripping process in the continuous flow JLR was modeled and the volumetric mass transfer coefficient (K_La) for each parameter was calculated from the model equation. While the experimental parameters of air flow rate and temperature had a significant effect on the mass transfer coefficient, influent ammonia concentration and HRT were determined to have no effect.

A multilayer perceptron-based prediction of ammonium adsorption on zeolite from landfill leachate: Batch and column studies

In this study, multilayer perceptron (MLP) artificial neural network was used to predict the adsorption rate of ammonium on zeolite. pH, inlet ammonium concentration, contact time, temperature, dosage of adsorbent, agitation speed, and particle size in the batch experiments were used as independent variables while flow rate and particle size in column mode were investigated. In MLP application, different architecture structures were tried and the architecture structures with the highest predictive performance were determined. To comparatively evaluate the predictive capabilities of MLP based prediction tool, Response Surface Methodology (RSM) was utilized. When the results were evaluated with Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) values (<1%) for almost all experiments, it was seen that MLP-based prediction tool produces better predictions than RSM. The scatter plots showed that predictions and actual values were quite compatible. Both regression and determination coefficients were interpreted by creating a regression of the predictions against the actual values and these coefficients were obtained as pretty close to 1. The outstanding performance of MLP in out-of-sample data sets without the need for additional experiment demonstrate that MLP can be effectively and reliably used in cases where experimental setups are difficult or costly.

A highly activated iron phosphate over-layer for enhancing photoelectrochemical ammonia decomposition

Environmentally friendly ammonia (NH₃) decomposition has attracted a lot of interests in recent years to resolve the issue of water eutrophication from a wastewater and achieve a clean H₂ storage. Here, we report a novel strategy for solar-driven ammonia decomposition by introducing a highly-activated iron phosphate (FePi) over-layer on the surface of α-Fe₂O₃ nanorods photoanode (FePi/Fe₂O₃), and innovatively propose a photoelectrochemical (PEC) ammonia degradation system with enhanced performance. After a facile electrochemical (EC) activation, the FePi over-layer is converted into FeOOH. The EC-activated over-layer provides the efficient active sites for the ammonia adsorption process, which promotes the high catalytic kinetics for ammonia oxidation reaction (AOR). Due to the synergistic effect of the electrocatalytic and the photocatalytic process, the FePi/Fe₂O₃ exhibits the enhanced PEC AOR performance, which competes with water oxidation reaction (WOR). Comparing to the initial concentration of ammonia, the FePi/Fe₂O₃ achieves a 54.4% ammonia degradation rate within 3 h at 1.23 V vs. reversible hydrogen electrode (RHE) under 1 sun illumination, which demonstrates the reliable ammonia decomposition performance. This study confirms that it is feasible to achieve PEC ammonia decomposition in an aqueous solution without chloride mediators and provides a promising strategy for the harmless treatment of ammonia wastewater.

Effects of hydraulic loading rate and substrate on ammonium removal in tidal flow constructed wetlands treating black and odorous water bodies

The efficient removal of ammonium nitrogen (NH₄⁺-N) is vital to eliminating black and odorous water bodies. In this work, tidal flow constructed wetlands with gravel (TFCW-G) and with a mixture of zeolite and gravel (TFCW-Z) were set up to treat black and odorous water bodies at different hydraulic loading rates (HLRs). Results showed that zeolite significantly enhanced nitrogen removal, and the maximum NH₄⁺-N removal efficiency of 96.69% was achieved in TFCW-Z at HLR of 3 m·d^-1 with a flooding and drying cycle of 2 h. Zeolite addition changed the microbial community structure and the abundance of nitrification genes. Comammox Nitrospira was the only enriched strain accounting for NH₄⁺-N removal in TFCW-G, while the co-occurrence of comammox Nitrospira and the canonical and potential ammonia-oxidizing bacteria were identified in TFCW-Z. Summarily, high performance, together with low footprint and low maintenance cost, are characteristics that make the TFCW-Z a promising and competitive alternative.

Non-thermal plasma combined with zeolites to remove ammonia nitrogen from wastewater

In this work, non-thermal plasma combined with zeolites was used to remove inorganic pollutant ammonia nitrogen from wastewater. Ammonia nitrogen elimination performances at various operating parameters were investigated. Roles of active species in the removal of ammonia nitrogen were also discussed. The experimental results showed that 69.97% ammonia nitrogen can be removed from the plasma/zeolites synergistic system after 30 min treatment. The removal efficiency was 16.23% and 61.55% higher than that in sole zeolites adsorption system and that in sole discharge plasma system, respectively. Higher applied voltage, lower initial ammonia nitrogen concentration and weak acidic conditions were favorable for ammonia nitrogen removal. After the addition of zeolites, part of O₃ and H₂O₂ generated in the plasma/zeolites system were decomposed into other oxygen species (•OH and ¹O₂), which improved the oxidation degree of ammonia nitrogen. In addition, the reaction mechanism of ammonia nitrogen in water by plasma/zeolites process was discussed. After repeated use three times, the effect of the zeolites in the plasma/zeolites system remained stable. Characterization of the zeolites after reaction was analyzed through BET, SEM, XRD and FT-IR. The experiments have confirmed the applicability of the plasma/zeolites system for the further treatment of low-concentration ammonia nitrogen wastewater.

Application of Natural Clinoptilolite for Ammonium Removal from Sludge Water

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c₀ = 967 mg/L NH₄-N, municipal wastewater; SW2: c₀ = 718–927 mg/L NH₄-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 g_CLI/mg_NH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.

Analysis of microbial community structure and degradation of ammonia nitrogen in groundwater in cold regions

Nitrogen pollution exceeding the standard because of intensive farming and cropping systems has been a widespread problem in Northeast China. This study investigated the characteristics of functional microorganisms in groundwater in the Bang River farming area. Metagenomic sequencing was used to analyze microbial community structures and Canoco was applied to reveal the response relationship between the microbial community and water environmental factors and to identify changes in the microbial population in response to the addition of electronic donors NH₄⁺-N, NO₂^--N, and NO₃^--N. The results showed that the dominant microorganisms in groundwater belong to the genera Exiguobacterium, Citrobacter, Acinetobacter, and Pseudomonas, which accounted for more than 40% of the total microbes in the study area. When combined with the results of a water chemical factor test, the dominant bacteria were found to be correlated with Fe²⁺, Mn²⁺, NH₄⁺, NO₃^-, NO₂^-, HCO₃^-, DOC, and pH in the water. However, the microbial population changed after the addition of the electron donor, with the genera Pseudomonas, Serratia, Enterobacter, Azomonas, and Ewingella accounting for 97.06% of the total sequences. Indigenous nitrogen-degrading bacteria suitable for low temperature, low oxygen, and oligotrophic groundwater were screened out. The total removal efficiency of NH₄⁺-N, NO₂^--N, and NO₃^--N in 120 h was 90.83%, 75.04%, and 73.35%, respectively. According to the experimental results, the degradation reaction kinetics followed a pseudo-second-order equation. The results presented herein provide an important scientific basis for the microbial remediation of groundwater contaminated by ammonia.

Positive effects of zeolite powder on aerobic granulation: Nitrogen and phosphorus removal and insights into the interaction mechanisms

Aerobic granular sludge is considered one of the most promising biological wastewater treatment technologies of the 21st century. However, the long granulation time and poor treatment effect on N and P have severely limited its popularity and large-scale application. In this study, we systematically examine the strengthening effects of zeolite powder on granulation, N and P removal, and their interaction mechanisms. The addition of zeolite powder decreased sludge granulation time to 18 d, and improved average N and P removal rates by 4.48% and 2.22%, respectively. The multi-pore and nutrient-rich environment of the zeolite powder is beneficial for maintaining microbial activity and granular stability. Moreover, its adsorption to N and P enriches their respective removal strains, improving their removal efficiency.

Removal of Ammonium from Aqueous Solutions Using Zeolite Synthesized from Electrolytic Manganese Residue

This paper carried out the study on removal of ammonium from aqueous solutions by zeolite derived from electrolytic manganese residue (EMR) via a fusion method. The variables of pH, contact time, EMRZ (EMR-based zeolite) dosage, initial ammonium concentration, and competitive cations and anions on the ammonium uptake capacity were systematically investigated in an attempt to illustrate adsorption performance of EMRZ. The results show that these influence factors had a remarkable impact on the ammonium uptake capacity of EMRZ. Maximum ammonium uptake capacity was achieved at pH value 8.0, EMRZ dosage 0.2 g/100 mL, contact time 100 min, initial ammonium concentration 200 mg/L, and temperature 35°C. Under optimized conditions, ammonium uptake capacity onto EMRZ was up to 27.89 mg/g. The competitive degree of cations in ammonium adsorption process follows the sequence of Na+>K+>Ca2+>Mg2+, and the sequence of anion effect on ammonium removal onto EMRZ is CO32− > Cl− > SO42− > PO43−. The adsorption kinetic was explored and best represented by pseudo-second-order kinetic model. And the adsorption isotherm experimental data had best fitness with the Freundlich and Koble–Corrigan model, suggesting that heterogeneous uptake was the principal mechanism adopted in the process of ammonium adsorption. Moreover, calculation of thermodynamic parameters such as change in free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) was carried out and it was determined to be −15.77∼−14.03 kJ·mol−1, +37.66 kJ·mol−1, and +173.38 J·mol−1·K−1, respectively. These parameters confirmed that ammonium uptake onto EMRZ was an endothermic and spontaneous process. Moreover, no obvious deterioration tendency was observed for the regenerated EMRZ compared with fresh EMRZ. These results indicate that EMRZ has wide application prospects in removing ammonium from wastewater.

Ultrasound-assisted electrochemical treatment for phenolic wastewater

With the rapid development of industry, especially the rapid rise of the chemical industry, the problem of water pollution is becoming more and more serious. Among them, the discharge of organic pollutants represented by phenolic substances has always been at the forefront. In this paper, ultrasound-assisted electrochemical treatment for phenolic wastewater is investigated. The effects of ultrasonic frequency, current, pH value and the amount of fly ash-loaded titanium TiO₂-Fe³⁺ particles on phenol removal from phenol-containing wastewater are investigated. The experimental results demonstrate that the removal rate of phenol in phenol-containing wastewater is the best when ultrasonic frequency is 45 kHz, power is 200 W, the current is 1.2 A, pH is 5 and the dosage of fly ash-loaded titanium TiO₂-Fe³⁺ particles is 3 g. In addition, microwave-assisted-Fenton reagent treatment for phenol wastewater is investigated. The effects of Fenton reagent dosage, initial pH value, microwave power density and radiation time on phenol degradation rate are investigated. The results show that microwave can accelerate the reaction rate, reduce the number of metal ions, save the process cost and reduce the difficulty of post-treatment. Finally, the research status of phenol wastewater treatment technology at the present stage is reviewed, and the future development direction is discussed.

A Study of Using Natural Sorbent to Reduce Iron Cations from Aqueous Solutions

Iron is an essential trace element, but at high doses, this element may pose a health risk. Wastewater from iron ore mining, steel production, and metal processing, among other heavy metals, also contains high concentrations of iron (Fe3+). The use of sorption on natural materials is a potential alternative to conventional methods for removing iron ions, also because of low cost. The methods presented in this article are based on the study of kinetic properties and the acquisition of adsorption isotherms, which are one of the most important characteristics of adsorption mechanisms. The course of sorption is analyzed according to the Freundlich sorption isotherm model. Isotherm parameters are evaluated using experimental results of ferric cation sorption. The results presented relate to the investigation of natural zeolite-clinoptilolite as a ferric cation sorbent, providing a measurement of the sorption kinetics as well as the observed sorption parameters of iron cations from aqueous media. The optimal time for equilibrium in the adsorption system is determined from the kinetic dependencies. The dependence of the achieved equilibrium concentration on the initial concentration of the solution was also expressed, both graphically and analytically. The new prediction model was compared with the traditional Freundlich model. Finally, adsorption isotherms tested under laboratory conditions for a practical application can be recommended for the preliminary examination of the possible technological use of natural zeolite in the wastewater treatment process.

Mineral sorbents for ammonium recycling from industry to agriculture

In tropical environments, nutrient-poor soils are commonly found, leading to high fertilizers application rates to support agricultural activities. In contrast, anthropogenic activities generate large amounts of effluents containing nitrogen. In this study, two minerals (natural zeolite and vermiculite) were tested to remove NH₄⁺ from an industrial effluent with high pH and contents in Na⁺ and K⁺. Afterwards, they were tested as an alternative slow-release fertilizer in the soil. To verify the best conditions to adsorb NH₄⁺, batch tests were conducted using synthetic solutions and an industrial effluent. In general, the efficiency of both minerals in removing NH₄⁺ was high (85% for zeolite and almost 70% for vermiculite) as well as the ability to decrease the industrial effluent pH. In this process, more NH₄⁺ and K⁺ ions were removed in comparison with Na⁺, which remained in solution. These minerals were tested as slow-release fertilizers by leaching with distilled water (both minerals releasing 2 mg L^-1 NH₄⁺) and with an acid solution (releasing 10 mg L^-1 NH₄⁺ from zeolite and 50 mg L^-1 NH₄⁺ from vermiculite-corresponding only to 12% of total NH₄⁺ retained by zeolite and 29% by vermiculite). During the test of soil incubation with zeolite-NH₄⁺, the NH₄⁺ ions of the exchangeable sites were retained for a longer period, minimizing their loss by leaching and biological nitrification. Consequently, soil acidification was prevented. Therefore, both minerals showed high efficiency in removing NH₄⁺ from solution which can then be slowly released as a nutrient in the soil.

Chitosan Modified Zeolite Molecular Sieve Particles as a Filter for Ammonium Nitrogen Removal from Water

Drinking water containing a high amount of ammonium-nitrogen (NH₄⁺-N) is not effectively removed by conventional treatment processes and can cause eutrophication. In this research, a composite adsorbent based on chitosan crosslink with zeolite molecular sieve (CTS-ZMS) was prepared for NH₄⁺-N removal through dynamic adsorption filter experiments. Effect of bed depth (30, 50 and 70 cm), flow rate (32, 49 and 65 mL/min), initial pH value (4.5, 6.5 and 8.5) and influent NH₄⁺-N concentration (3, 5 and 7 mg/L) was examined by using a filter column packed with CTS-ZMS particles. The Thomas model was applied to study the breakthrough curves and adsorption capacity. The optimal process parameters of the aforementioned factors were obtained at bed depth of 70 cm, flow rate of 32 mL/min, pH of 6.5 and initial NH₄⁺-N concentration of 7 mg/L. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FTIR) were investigated to analyze the structure and morphology of the CTS-ZMS adsorbents before and after 3 months running. The EDS and FTIR results showed Na⁺ and the active functional groups of -OH, -NH₂ and -COO⁻ on CTS-ZMS adsorbent particles reacted with ammonium nitrogen. The results of this study supported the use of CTS-ZMS to improve drinking water filtration processes by increasing ammonium nitrogen reductions.

Investigation of ammonia stripping with a hydrodynamic cavitation reactor

Ammonia is a commonly used compound in the domestic and industrial fields. If ammonia found in wastewater after use is not treated, even at low concentrations it may cause toxic effects in the receiving environment. In this study, a hydrodynamic cavitation reactor (HDC) was designed with the aim of removing ammonia. The effect of parameters like different cavitation numbers, airflow, temperature and initial concentration on NH₃ removal was researched. The potential of hydrodynamic cavitation for removal of volatile gases, like NH₃, was assessed with the aid of two film theory mathematical equations. Experimental studies were performed at fixed pH = 11. Under the conditions of 0.12 cavitation number, 25 L/min airflow, 30 °C temperature and 2500 mg/L initial concentration, in 24 h 98.4% NH₃ removal efficiency was achieved. With the same experimental conditions without any air, the HDC reactor provided 89.5% NH₃ removal at the end of 24 h. The HDC reactor is very effective for the removal of volatile gases from wastewater and it was concluded that even in the absence of aeration, the desired NH₃ removal efficiency was provided.

Revealing the effect of preparation parameters on zeolite adsorption performance for low and medium concentrations of ammonium

The effect of preparation parameters on the performance of zeolite for ammonium (20-300 mg N/L) adsorption from simulated wastewater is reported. It was found that the ratios of Na₂O/SiO₂ and Si/Al had a more important influence than crystallization time on zeolite adsorption properties. Relatively low Na₂O/SiO₂ ratios were beneficial for fabrication of zeolites with high proportions of micropore area and volume, which led to the surface adsorption mechanism being dominated by surface free energy and pore effects. However, with decreasing Si/Al ratios, the effect of ion-exchange was more prominent due to the high negative surface potential of zeolite. In addition, the concentration of weak acid sites on the zeolites was increased with lower ratios of Na₂O/SiO₂ and Si/Al, which may promote ammonium removal. Therefore, the most effective zeolite for ammonium removal, which was fabricated at Na₂O/SiO₂ = 1.375, Si/Al = 4 and crystallization time of 48 hr, exhibited the cooperative effects of adsorption, ion-exchange and a large amount of weak acid sites. The maximum ammonium adsorption capacity (35.06 ± 0.98 mg/g) and the removal efficiency (94.44% ± 4.00%) were obtained at the dosage of 4.0 g/L zeolite NaX at ammonium concentrations of 300 mg N/L and 20 mg N/L, respectively. The Freundlich isotherm and pseudo-first-order kinetics models provided excellent fitting for the ammonium adsorption process. In addition, zeolite NaX showed about 1.23-3.2 times the ammonium adsorption capacity of clinoptilolite. The stable and efficient reusability of zeolite NaX after five regeneration cycles demonstrated that this adsorbent has considerable potential for practical industrial applications.

Removal of Ammonia from the Municipal Waste Treatment Effluents using Natural Minerals

Due to various ecological problems, it is required to remove the ammonia nitrogen from wastewater. Industrial wastewater that was not subjected to any purification was used in this study, while most processes described in the literature were carried out using synthetically prepared solutions. The study investigated the removal of ammonium ions using ion exchange on various commercial minerals, in 3 h long batch ion-exchange experiments. Furthermore, research on the sodium chloride activation of the selected mineral was conducted. The screening of the mineral with the highest removal potential was conducted taking into account the adsorption capacity (q) and maximal removal efficiency (E), based on the NH₄⁺ ions changes determined using the selective electrode and spectrophotometric cuvette tests. The highest adsorption capacity (q = 4.92 mg/g) of ammonium ions with the maximum removal efficiency (52.3%) was obtained for bentonite, with a 0–0.05 mm particle size. After pretreatment with a 1 mol/L NaCl solution, maximum efficiency increments were observed (55.7%). The Langmuir adsorption isotherm corresponds well with the equilibrium adsorption data (R² from 0.97 to 0.98), while the Freundlich model was found to be mismatched (R² = 0.77). Based on these results it was concluded that natural sorbents may be effectively applied in wastewater treatment. It can be observed that as the size of sorbent particles gets lower, the adsorption capacity, as well as the removal efficiency, gets higher. The bentonite pretreatment with the NaCl solution did not result in the expected efficiency improvement. The 2 mol/L solution affected about 3.5% of the removal efficiency yield.

Potential of agro-waste sugarcane bagasse ash for the removal of ammoniacal nitrogen from landfill leachate

Ammoniacal nitrogen is considered as one of the major pollutants of the leachate generated from the landfill site and has the potential to deteriorate the environment as well as health. Considering this, locally available agricultural waste, i.e., sugarcane bagasse ash, was employed as an adsorbent for the removal of ammoniacal nitrogen from landfill leachate. Batch-mode experiments were conducted to see the effect of dose (2-60 g L^-1), pH (2-12), and temperature (20-60 °C) on ammoniacal nitrogen adsorption. Application of sugarcane bagasse ash showed 60% removal of ammoniacal nitrogen (50 mg L^-1 strength) at an optimum dose of 20 g L^-1 and 180 min of contact time with an adsorption capacity of 0.31 mg g^-1. The Langmuir adsorption model was found to be best fit at 40 °C with R² = 0.944, depicting a monolayer coverage of ammoniacal nitrogen onto sugarcane bagasse ash. According to the result, solute uptake rate could be well described by the pseudo-second-order model (R² = 0.928), whereas the intraparticle diffusion model and Boyd plot indicated that the overall adsorption rate is governed by the external mass transfer. Thermodynamic studies revealed that adsorption is feasible, spontaneous, and endothermic in nature. Hence, the study shows that sugarcane bagasse ash could turn out to be a cost-effective adsorbent for the removal of ammoniacal nitrogen from leachate.

Long-Term Performance of a Pilot-Scale Gas-Sparged Anaerobic Membrane Bioreactor under Ambient Temperatures for Holistic Wastewater Treatment

Concerns regarding ambient temperature operation, dissolved methane recovery, and nutrient removal have limited the implementation of anaerobic membrane bioreactors (AnMBRs) for domestic wastewater treatment. This study addresses these challenges using a pilot-scale gas-sparged AnMBR, with post-treatment recovery of dissolved methane and nutrients. Operating under ambient temperatures for 472 days, the AnMBR achieved an average effluent quality of 58 ± 27 mg/L COD and 25 ± 12 mg/L BOD₅ at temperatures ranging from 12.7 to 31.5 °C. The average total methane yield was 0.14 ± 0.06 L-CH₄/g-COD fed, with 42% of the total methane dissolved in the permeate. Dissolved methane removal using a hollow fiber membrane contactor achieved an average removal efficiency of 70 ± 5%, producing effluent dissolved methane concentrations of 3.8 ± 0.94 mg/L. The methane recovered from gaseous and dissolved fractions could generate an estimated 72.8% of the power required for energy neutrality. Nutrient recovery was accomplished using coagulation, flocculation, and sedimentation for removal of sulfide and phosphorus, followed by a clinoptilolite ion-exchange column for removal of ammonia, producing effluent concentrations of 0.7 ± 1.7 mg-S/L, 0.43 ± 0.29 mg-P/L and 0.05 ± 0.05 mg-N/L. The successful integration of AnMBRs in a treatment train that addresses the critical challenges of dissolved methane and nutrients demonstrates the viability of the technology in achieving holistic wastewater treatment.

Pollutant Removal from Synthetic Aqueous Solutions with a Combined Electrochemical Oxidation and Adsorption Method

Eliminating organic and inorganic pollutants from water is a worldwide concern. In this study, we applied electrochemical oxidation (EO) and adsorption techniques to eliminate ammonia, phenols, and Mo(VI) from aqueous solutions. We analyzed the first stage (EO) with response surface methodology, where the reaction time (1⁻3 h), initial contaminant concentration (10⁻50 mg/L), and pH (3⁻6) were the three independent factors. Sodium sulfate (as an electrolyte) and Ti/RuO₂⁻IrO₂ (as an electrode) were used in the EO system. Based on preliminary experiments, the current and voltage were set to 50 mA and 7 V, respectively. The optimum EO conditions included a reaction time, initial contaminant concentration, and pH of 2.4 h, 27.4 mg/L, and 4.9, respectively. The ammonia, phenols, and Mo elimination efficiencies were 79.4%, 48.0%, and 55.9%, respectively. After treating water under the optimum EO conditions, the solution was transferred to a granular composite adsorbent column containing bentonite, limestone, zeolite, cockleshell, activated carbon, and Portland cement (i.e., BAZLSC), which improved the elimination efficiencies of ammonia, phenols, and molybdenum(VI) to 99.9%. The energy consumption value (8.0 kWh kg−1 N) was detected at the optimum operating conditions.