Dual removal of phosphate and ammonium from high concentrations of aquaculture wastewaters using an efficient two-stage infiltration system

Combining dredging with modified zeolite thin-layer capping to control nitrogen release from eutrophic lake sediment

Dredging is widely used to control internal sediment nitrogen (N) pollution during eutrophic lake restoration. However, the effectiveness of dredging cannot be maintained for long periods during seasonal temperature variations. This study used modified zeolite (MZ) as a thin-layer capping material to enhance dredging efficiency during a year-long field sediment core incubation period. Our results showed that dredging alone more effectively reduced pore water N, N flux, and sediment N content than MZ capping but showed more dramatic changes during the warm seasons. The N flux in dredged sediment in summer was 1.8 and 2.5 times that in spring and autumn, respectively, indicating a drastic N regeneration process in the short term. In contrast, the combination method reduced the extra 10% pore water N, 22% N flux, and 8% sediment organic N content compared with dredging alone and maintained high stability during seasonal changes. The results indicated that the addition of MZ to the surface of dredged sediment not only enhanced the control effect of dredging by its adsorption capacity but may also smooth the N regeneration process via successive accumulation (in the channel of the material) and activation of bacteria for months, which was evidenced by the variation in microbial diversity in the MZ treatment. As a result, the combination of dredging with modified zeolite simultaneously enhanced the efficiency and stability of the single dredging method in controlling sediment N content and its release, exhibiting great prospects for long-term application in eutrophic lakes with severe pollution from internal N loading.

Immobilization of phosphorus in water-sediment system by iron-modified attapulgite, calcite, bentonite and dolomite under feed input condition: Efficiency, mechanism, application mode effect and response of microbial communities and iron mobilization

Four kinds of iron-based materials, i.e., iron-modified attapulgite, calcite, bentonite and dolomite (abbreviated as Fe-ATP, Fe-CA, Fe-BT and Fe-DOL, respectively) were prepared and used to immobilize the phosphorus in the system of overlying water (O-water) and sediment under the feed input condition, and their immobilization efficiencies and mechanisms were investigated. The influence of application mode on the immobilization of phosphorus in the water-sediment system by Fe-ATP, Fe-CA, Fe-BT and Fe-DOL was researched. The effects of Fe-ATP, Fe-CA, Fe-BT and Fe-DOL on the concentration of labile iron in the water-sediment system and the microbial communities in sediment were also studied. The results showed that the Fe-ATP, Fe-CA, Fe-BT and Fe-DOL addition all can effectively immobilize the soluble reactive phosphorus (SRP), dissolved total phosphorus (DTP) and diffusive gradients in thin-films (DGT)-labile phosphorus in O-water under the feed input condition, and also had the ability to inactivate the DGT-labile phosphorus in the top sediment. Although the change in the application mode from the one-time addition to the multiple addition reduced the inactivation efficiencies of SRP and DTP in O-water in the early period of application, it increased the immobilization efficiencies in the later period of application. Although Fe-ATP, Fe-CA, Fe-BT and Fe-DOL had a certain releasing risk of iron into the pore water, they had negligible risk of iron release into O-water. The addition of Fe-ATP, Fe-CA, Fe-BT or Fe-DOL reshaped the sediment bacterial community structure and can affect the microorganism-driven phosphorus cycle in the sediment. Results of this work suggest that Fe-ATP, Fe-CA, Fe-BT and Fe-DOL are promising phosphorus-inactivation materials to immobilize the phosphorus in the water-sediment system under the feed input condition.

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.

Effects of perfluoroalkyl substances on the operational efficiency, microbial communities, and key metabolic pathways of constructed rapid infiltration system with coke as filler layer

Influences of perfluoroalkyl substances on the performance and microbial metabolic pathways of constructed rapid infiltration systems are not fully understood. In this study, wastewater containing different concentrations of perfluorooctanoic acid (PFOA)/perfluorobutyric acid (PFBA) was treated in constructed rapid infiltration systems with coke as filler. The addition of 5 and 10 mg/L PFOA inhibited the removal of chemical oxygen demand (COD) (80.42%, 89.27%), ammonia nitrogen (31.32%, 41.14%), and total phosphorus (TP) (43.30%, 39.34%). Meanwhile, 10 mg/L PFBA inhibited TP removal of the systems. Based on X-ray photoelectron spectroscopy, the percentages of F^- within the PFOA and PFBA groups were 12.91% and 48.46%, respectively. PFOA transformed Proteobacteria (71.79%) into the dominant phyla of the systems, whereas PFBA enriched Actinobacteria (72.51%). The PFBA up-regulated the coding gene of 6-phosphofructokinase by 14.44%, whereas PFOA down-regulated it by 4.76%. These findings provide insights into the toxicity of perfluoroalkyl substances on constructed rapid infiltration systems.

Nutrients removal by Olivibacter jilunii immobilized on activated carbon for aquaculture wastewater treatment: ppk1 gene and bacterial community structure

In this study, immobilized biological activated carbon (IBAC) mediated with Olivibacter jilunii (strain PAO-9) was utilized to treat aquaculture wastewater for nutrients removal. IBAC with strain PAO-9 could load the greatest ppk1 gene copy numbers (129524.6) per gram on activated carbon at 28 °C for 2 d in 120 rpm of stirring speed and 2 d in stationary condition. Moreover, the results about the nutrients removal and microbiology community structure showed that strain PAO-9 on IBAC could alter the structure and diversity of microbial communities and then promoted to remove the total phosphorus and total nitrogen of eel aquaculture wastewater. The highest total phosphorus, chemical oxygen demand, ammonia and total nitrogen of the wastewater treated by strain PAO-9 on IBAC were 96.1 %, 98.0 %, 100.0 % and 97.4 %, respectively. In all, O. jilunii PAO-9 immobilized activated carbon was a potential and effective approach to remove the nutrients of eel aquaculture wastewater.

Valorization of wastewater: A paradigm shift towards circular bioeconomy and sustainability

Limitation in the availability of natural resources like water is the main drive for focussing on resource recovery from wastewater. Rapid urbanization with increased consumption of natural resources has severely affected its management and security. The application of biotechnological processes offers a feasible approach to concentrating and transforming wastewater for resource recovery and a step towards a circular economy. Wastewater generally contains high organic materials, nutrients, metals and chemicals, which have economic value. Hence, its management can be a valuable resource through the implementation of a paradigm transformation for value-added product recovery. This review focuses on the circular economy of "close loop" process by wastewater reuse and energy recovery identifying the emerging technologies for recovering resources across the wastewater treatment phase. Conventional wastewater treatment technologies have been discussed along with the advanced treatment technologies such as algal treatment, anammox technology, microbial fuel cells (MFC). Apart from recovering energy in the form of biogas and biohydrogen, second and third-generation biofuels as well as biohythane and electricity generation have been deliberated. Other options for resource recovery are single-cell protein (SCP), biopolymers as well as recovery of metals and nutrients. The paper also highlights the applications of treated wastewater in agriculture, aquaponics, fisheries and algal cultivation. The concept of Partitions-release-recover (PRR) has been discussed for a better understanding of the filtration treatment coupled with anaerobic digestion. The review provides a critical evaluation on the importance of adopting a circular economy and their role in achieving sustainable development goals (SDGs). Thus, it is imperative that such initiatives towards resource recovery from wastewater through integration of concepts can aid in providing wastewater treatment system with resource efficiency.

Improvement of aquaculture water quality by mixed Bacillus and its effects on microbial community structure

Microbial remediation, especially the application of probiotics, has recently gained popularity in improving water quality and maintaining aquatic animal health. The efficacy and mechanism of mixed Bacillus for improvement of water quality and its effects on aquatic microbial community structure remain unknown. To elucidate these issues, we applied two groups of mixed Bacillus (Bacillus megaterium and Bacillus subtilis (A0 + BS) and Bacillus megaterium and Bacillus coagulans (A0 + BC)) to the aquaculture system of Crucian carp. Our results showed that the improvement effect of mixed Bacillus A0 + BS on water quality was better than that of A0 + BC, and the NH₄⁺-N, NO₂^--N, NO₃^--N, and total phosphorus (TP) concentrations were reduced by 46.3%, 76.3%, 35.6%, and 80.3%, respectively. In addition, both groups of mixed Bacillus increased the diversity of the bacterial community and decreased the diversity of the fungal community. Microbial community analysis showed that mixed Bacillus A0 + BS increased the relative abundance of bacteria related with nitrogen and phosphorus removal, such as Proteobacteria, Actinobacteria, Comamonas, and Stenotrophomonas, but decreased the relative abundance of pathogenic bacteria (Acinetobacter and Pseudomonas) and fungi (Epicoccum and Fusarium). Redundancy analysis showed that NH₄⁺-N, NO₂^--N, and TP were the primary environmental factors affecting the microbial community in aquaculture water. PICRUST analysis indicated that all functional pathways in the A0 + BS group were richer than those in other groups. These results indicated that mixed Bacillus A0 + BS addition produced good results in reducing nitrogenous and phosphorus compounds and shaped a favorable microbial community structure to further improve water quality.

Electrochemical and Microbial Dissection of Electrified Biotrickling Filters

Electrified biotrickling filters represent sustainable microbial electrochemical technology for treating organic carbon-deficient ammonium-contaminated waters. However, information on the microbiome of the conductive granule bed cathode remains inexistent. For uncovering this black box and for identifying key process parameters, minimally invasive sampling units were introduced, allowing for the extraction of granules from different reactor layers during reactor operation. Sampled granules were analyzed using cyclic voltammetry and molecular biological tools. Two main redox sites [-288 ± 18 mV and -206 ± 21 mV vs. standard hydrogen electrode (SHE)] related to bioelectrochemical denitrification were identified, exhibiting high activity in a broad pH range (pH 6-10). A genome-centric analysis revealed a complex nitrogen food web and the presence of typical denitrifiers like Pseudomonas nitroreducens and Paracoccus versutus with none of these species being identified as electroactive microorganism so far. These are the first results to provide insights into microbial structure-function relationships within electrified biotrickling filters and underline the robustness and application potential of bioelectrochemical denitrification for environmental remediation.

Isolation, characterization and degradation performance of oxytetracycline degrading bacterium Planococcus sp. strain pw2

Oxytetracycline (OTC), is a widely used veterinary antibiotic for treatment and prophylaxis in aquaculture. As an emerging pollutant, OTC in the environment exerts selective pressure on aquatic organisms causing proliferation of antibiotic resistant genes. In the present study, an OTC tolerant isolate labelled as pw2 was selected among the 11 OTC tolerant isolates, isolated from the aquaculture effluent, for investigating its OTC degrading potential. The cell morphology, biochemical characteristics, and 16S ribosomal RNA (rRNA) gene sequence of the isolated strain indicated that it belonged to the genus Planococcus. The OTC removal percentage was estimated through measuring its residual concentration in the culture medium with high performance liquid chromatography. The strain exhibited maximum removal efficiency of 90.62%, with initial OTC concentration of 10 µg/ml. The optimum degrading conditions were 35 °C and pH 7. The degradation rate of OTC with (biotic) and without strain pw2 (abiotic) was 3.253 and 1.149 mg/l/d, respectively. The half-life was recorded to be 2.13 d in the presence of strain pw2, in contrast to 6.03 days recorded without strain pw2. The total (biotic + abiotic) OTC degradation efficiency was 75.74, 83.93, 90.62, and 86.47% for the initial OTC concentrations of 1 to 25 µg/ml, respectively. Addition of carbon and nitrogen did not influence the OTC removal which indicates Planococcus sp. pw2 use OTC as sole energy source. Thus, Planococcus sp. pw2 plays a vital role in reducing the OTC concentration in the environment, offering a promising method for treatment of aquaculture effluent containing OTC.

Novel biotechnologies for nitrogen removal and their coupling with gas emissions abatement in wastewater treatment facilities

Wastewaters contaminated with nitrogenous pollutants, derived from anthropogenic activities, have exacerbated our ecosystems sparking environmental problems, such as eutrophication and acidification of water reservoirs, emission of greenhouse gases, death of aquatic organisms, among others. Wastewater treatment facilities (WWTF) combining nitrification and denitrification, and lately partial nitrification coupled to anaerobic ammonium oxidation (anammox), have traditionally been applied for the removal of nitrogen from wastewaters. The present work provides a comprehensive review of the recent biotechnologies developed in which nitrogen-removing processes are relevant for the treatment of both wastewaters and gas emissions. These novel processes include the anammox process with alternative electron acceptors, such as sulfate (sulfammox), ferric iron (feammox), and anodes in microbial electrolysis cells (anodic anammox). New technologies that couple nitrate/nitrite reduction with the oxidation of methane, H₂S, volatile methyl siloxanes, and other volatile organic compounds are also described. The potential of these processes for (i) minimizing greenhouse gas emissions from WWTF, (ii) biogas purification, and (iii) air pollution control is critically discussed considering the factors that might trigger N₂O release during nitrate/nitrite reduction. Moreover, this review provides a discussion on the main challenges to tackle towards the consolidation of these novel biotechnologies.

In situ control of internal nutrient loading and fluxes in the confluence area of an eutrophic lake with combined P inactivation agents and modified zeolite

In this study, a field in situ inactivation experiment was carried out to control the confluence area sediment nutrient loading and fluxes using modified zeolite (MZ) in combination with poly aluminum chloride (PAC) and lanthanum-modified bentonite (LMB). The results indicated that PAC + MZ and LMB + MZ can reduce 76% and 75% of the P flux and 20% and 27% of the N flux, respectively. These results are based on a comparison with a control treatment over four months under the influence of external loading. However, their control efficiency on sediment nutrient fluxes decreased largely during the summertime algal blooming season. Both of the treatments lost their N control efficiency at this time. In contrast, LMB + MZ can still reduce 27% of the P flux compared to the control treatment. Surface sediment extractable ammonium increased substantially from the PAC + MZ and LMB + MZ treatments, which is 1.8 and 2.2 times more than the extractable ammonium in the control sediment after 210 days of remediation. The P fractionation analysis indicated that, in the PAC + MZ and LMB + MZ, both NaOH-rP and HCl-P increased greatly at a rate of 1.5 and 3.9 times, respectively, compared to the control sediment. PAC + MZ and LMB + MZ reduced the mobile P by 21% and 43%, respectively compared with the control sediment after 210 days of remediation. Bacteria richness and diversity in the PAC + MZ and LMB + MZ treatments had no obvious distinction when compared with the control treatment after 210 days of remediation but had a transient decrease in the LMB + MZ and recovered as it returned back to the same level found in control after 60 days. The results indicated that the control efficiency of nutrient fluxes in sediment might vary with types of inactivation agents and dosing methods and can be largely reduced under the influence of external loading and algal blooms.

Recycled Steel Slag as a Porous Adsorbent to Filter Phosphorus-Rich Water with 8 Filtration Circles

Steel slag is a secondary product from steelmaking process through alkaline oxygen furnace or electric arc furnace (EAF). The disposal of steel slag has become a thorny environmental protection issue, and it is mainly used as unbound aggregates, e.g., as a secondary component of asphalt concrete used for road paving. In this study, the characteristics of compacted porous steel slag disc (SSD) and its application in phosphorous (P)-rich water filtration are discussed. The SSD with an optimal porosity of 10 wt% and annealing temperature of 900 °C, denoted as SSD-P (10, 900) meets a compressive strength required by ASTM C159-06, which has the capability of much higher than 90% P removal (with the effluent standard < 4 mg P/L) within 3 h, even after eight filtration times. No harmful substances from SSD have been detected in the filtered water, which complies with the effluent standard ISO 14001. The reaction mechanism for P-rich water filtration is mediated by water, followed by two reaction steps-CaO in SSD hydrolyzed from the matrix of SSD to Ca2+ and reacting with PO43-. However, the microenvironment of water is influenced by the pH value of the P-rich water at different filtration times and the kind of P-rich water with different free positive ion that interferes the reactions of the release of Ca2+. This study demonstrates the application of circular economy in reducing steel slag deposits, filtering P-rich water, and collecting Ca3(PO4)2 precipitate into fertilizers.

Electrifying biotrickling filters for the treatment of aquaponics wastewater

This work aimed to study the electrification of biotrickling filters by means of Microbial electrochemical technologies (MET) to develop an easy-to-assemble and easy-to-use MET for nitrogen removal without external aeration nor addition of chemicals. Four different designs were tested. The highest ammonium and nitrate removal rates (94 gN·m^-3·d^-1 and 43 gN·m^-3·d^-1, respectively) were reached by combining an aerobic zone with an electrified anoxic zone. The standards of effluent quality suitable for hydroponics were met at low energy cost (8.3 × 10^-2 kWh·gN^-1). Electrified biotrickling filters are a promising alternative for aquaponics and a potential treatment for organic carbon-deficient ammonium-contaminated waters.

Deciphering pollutants removal mechanisms and genetic responses to ampicillin stress in simultaneous heterotrophic nitrification and aerobic denitrification (SHNAD) process treating seawater-based wastewater

Pollutants removal and genetic responses of simultaneous heterotrophic nitrification and aerobic denitrification (SHNAD) treating seawater-based wastewater were studied under ampicillin stress. Marine SHAND bacteria exhibited good tolerance to 10 mg/L ampicillin with nitrogen removal efficiency and organics removal efficiency of 94.5% and 82.6%, respectively. Besides, the half-inhibitory concentration of ampicillin on marine SHAND bacteria was 50 mg/L. The relative abundances of antibiotic resistance genes (ARGs) first decreased and then increased with ampicillin addition. The blaVIM played an important role to resist 25 mg/L ampicillin, which contributed to the recovery of pollutants removal. BlaSHV and blaTEM dominated ARG subtypes, which accounted for 96.6% of ARGs abundance. At 50 mg/L ampicillin, reactive oxygen species (ROS) production and cell numbers of apoptosis increased by 47.9% and 367.5%, respectively. The overproduction of ROS was stimulated by ampicillin, which caused bacterial cell apoptosis. Marine SHNAD bacteria produced more extracellular polymeric substances to resist ampicillin.

New progress of ammonia recovery during ammonia nitrogen removal from various wastewaters

The recovery of ammonia-nitrogen during wastewater treatment and water purification is increasingly critical in energy and economic development. The concentration of ammonia-nitrogen in wastewater is different depending on the type of wastewater, making it challenging to select ammonia-nitrogen recovery technology. Meanwhile, the conventional nitrogen removal method wastes ammonia-nitrogen resources. Based on the circular economy, this review comprehensively introduces the characteristics of several main ammonia-nitrogen source wastewater plants and their respective challenges in treatment, including municipal wastewater, industrial wastewater, livestock and poultry wastewater and landfill leachate. Furthermore, we introduce the main methods currently adopted in the ammonia-nitrogen removal process of wastewater from physical (air stripping, ion exchange and adsorption, membrane and capacitive deionization), chemical (chlorination, struvite precipitation, electrochemical oxidation and photocatalysis) and biological (classical and typical activated sludge, novel methods based on activated sludge, microalgae and photosynthetic bacteria) classification based on the ammonia recovery concept. We discuss the applicable methods of recovering ammonia nitrogen in several main wastewater plants. Finally, we prospect the research direction of ammonia removal and recovery in wastewater based on sustainable development.

Synchronous removal of ammonium and phosphate from swine wastewater by two agricultural waste based adsorbents: Performance and mechanisms

Two agricultural wastes, Chinese medicinal herbal residue and spent Pleurotus ostreatus substrate, were developed to remove ammonium and phosphate from swine wastewater. These adsorbents were mesoporous materials with abundant smooth layered pores, and rough protuberances and grooves, respectively. Their adsorption capacities were 1131.65 and 1631.79 mg N g^-1, and 63.41 and 62.58 mg P g^-1 at pH 8.0, dosage of 0.2 g L^-1 and contact time of 360 min. And kinetics data of ammonium and phosphate fitted best with the intra-particle diffusion and pseudo-second-order models, respectively. Based on the point of zero charge, FTIR and XPS analyses, ammonium was removed mainly by electrostatic attraction, ion exchange and surface precipitation, while phosphate was by ligand exchange, surface complexation and precipitation. Therefore, the two agricultural wastes have great potential to synchronously remove ammonium and phosphate from swine wastewater.

Effects of Hydraulic Retention Time and Influent Nitrate-N Concentration on Nitrogen Removal and the Microbial Community of an Aerobic Denitrification Reactor Treating Recirculating Marine Aquaculture System Effluent

The effects of hydraulic retention time (HRT) and influent nitrate-N concentration on nitrogen removal and the microbial community composition of an aerobic denitrification reactor treating recirculating marine aquaculture system effluent were evaluated. Results showed that over 98% of nitrogen was removed and ammonia-N and nitrite-N levels were below 1 mg/L when influent nitrate-N was below 150 mg/L and HRT over 5 h. The maximum nitrogen removal efficiency and nitrogen removal rate were observed at HRT of 6 or 7 h when influent nitrate-N was 150 mg/L. High-throughput DNA sequencing analysis revealed that the microbial phyla Proteobacteria and Bacteroidetes were predominant in the reactor, with an average relative total abundance above 70%. The relative abundance of denitrifying bacteria of genera Halomonas and Denitratisoma within the reactor decreased with increasing influent nitrate-N concentrations. Our results show the presence of an aerobically denitrifying microbial consortium with both expected and unexpected members, many of them relatively new to science. Our findings provide insights into the biological workings and inform the design and operation of denitrifying reactors for marine aquaculture systems.

Removal of ammonium ion from aqueous solutions by using unmodified and H2O2-modified zeolitic waste

In the petroleum industry during a catalytic cracking process, the used zeolitic catalyst becomes waste. This article investigated the sorption capacities of ammonium ions from aqueous solutions onto the previously mentioned zeolitic waste by batch experiments. Three types of zeolitic waste were used: unmodified zeolitic waste with two different particle size distributions and H2O2-modified zeolitic waste. Several techniques, including X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET) multilayer adsorption theory measurements, and X-ray fluorescence analysis (XRF) were used to demonstrate experimentally that the zeolitic waste could be used as a sorbent for the water decontamination of NH4+ ions. The morphology of zeolitic waste investigated by scanning electron microscopy (SEM) revealed particles with a spherical shape. The nitrogen adsorption-desorption isotherms showed an isotherm mixture of types I (pure microporous) and IV (mesoporous). This suggested that the investigated zeolitic materials were mesoporous (4.84 nm) and microporous (0.852 nm), as well as containing slit/cylindric pores, according to a quench solid density functional theory (QSDFT) adsorption branch model. Zeolitic waste from the oil industry showed good NH4+ sorption properties (removal efficiency of 72%), thus becoming a potential adsorbent to be used in the treatment of contaminated aqueous effluents polluted with ammonium ions. Simultaneous waste and water decontamination can be achieved, providing a new tool and enhanced capabilities for environmental remediation.

Food waste based biochars for ammonia nitrogen removal from aqueous solutions

Biochar derived from waste has been increasingly considered as a potential green adsorbent due to its significant ability and affordable production costs. This study prepared and evaluated 7 types of food waste-based biochars (FWBBs) (including meat and bone, starchy staples, leafy stemmed vegetables, nut husks, fruit pericarp, bean dreg and tea leaves). The impacts of raw materials, pyrolysis temperatures (300, 400, 500, 600 and 700 °C), and residence time (2 h and 4 h) on the removal of ammonia nitrogen at different ammonia nitrogen concentrations (5, 10, 20, 50, 100, 150 mg/L) were investigated. The batch equilibrium and kinetic experiments confirmed that a FWBB dosage of 3 g/L at 25 °C could remove up to 92.67% ammonia nitrogen. The Langmuir isotherm model had the best fit to equilibrium experimental data with a maximum adsorption capacity of 7.174 mg/g at 25 °C. The pseudo-second order kinetic model well describes the ammonia nitrogen adsorption.

Rapid removal of ammonia nitrogen in low-concentration from wastewater by amorphous sodium titanate nano-particles

An amorphous sodium titanate (ST) nano-particle was prepared via the facile hydrolytic process with the addition of sodium hydroxide and firstly used for ammonia nitrogen (NH₃-N) removal from wastewater. ST exhibited satisfactory adsorption efficiency for NH₃-N simulative wastewater (20 mg·L^-1) at a wide range of pH 3.0-9.0, within a minimum contact time of 10 min. The Langmuir isotherm showed that the maximum adsorption capacity (298 K) of the adsorbent was reach up to 44.54 mg·g^-1. Concentrated competing cations had some interferences with NH₃-N adsorption at the order of Ca²⁺ > K⁺ > Mg²⁺ > Na⁺ according to their competition on adsorption sites. During the adsorption process, cation exchange between Na⁺ and NH₄⁺ played a powerful role for the NH₃-N removal and the contribution of Ti-OH groups was also involved in the adsorption. The regeneration test showed that the saturated adsorbents could be conveniently regenerated just by NaOH or NaCl solution treatment and there was no obvious decline of the adsorption capacity after reused for five times. The facile method of fabrication and regeneration, the rapid adsorption process and the satisfactory adsorption efficiency make sodium titanate a promising adsorbent for low concentration NH₃-N minimization.

Performance of physical and chemical methods in the co-reduction of internal phosphorus and nitrogen loading from the sediment of a black odorous river

The continuous release of nutrients from sediment is a major barrier to the remediation of black odorous rivers. This study used a long-term laboratory incubation experiment to investigate the effectiveness of sediment dredging, intermittent aeration, and in situ inactivation with modified clays to reduce the internal loading of sediment from a seriously polluted river. The results indicated that intermittent aeration and in situ inactivation were effective in reducing the TN and NH₄⁺ concentrations in the water column. However, sediment dredging did not consistently reduce the TN and NH₄⁺ concentrations in the water column. In contrast, the three methods were all effective in controlling the TP and PO₄^3- concentrations in the water column. Except for dredging, >30% of NH₄⁺ and 40% of PO₄^3- fluxes from sediment were reduced when compared with a control sample after 120 days of remediation. Dredging induced a significant release of NH₄⁺ from sediment. Dredging and aeration made nearly no change to the amount of extractable nitrogen in the sediment. However, inactivation may increase sediment-extractable ammonium in deep sediment layers with time due to vertical transportation of clay by intensive bioturbation. Dredging is the most effective way to reduce surface mobile phosphorus over time while the transported clays can reduce a large percentage of the mobile phosphorus in deeper sediment. The relative abundance of Nitrospira in the surface sediment increased significantly with each remediation measure, creating favorable conditions for the reduction of the ammonium released from sediment. Altogether, the results of this study indicated that clay inactivation is the best method for controlling the internal loading of both phosphorus and nitrogen in seriously polluted river sediment.

Action of oxytetracycline (OTC) degrading bacterium and its application in Moving Bed Biofilm Reactor (MBBR) for aquaculture wastewater pre-treatment

In this study, the characteristics of biodegradation of oxytetracycline (OTC) by strain Ochrobactrum sp. KSS10 were studied under various environmental conditions, including initial OTC concentrations, variable temperature, initial pH, and diverse carbon sources. The capability of this bacterial strain for performing simultaneous OTC degradation and nitrate reduction was also explored under aerobic conditions. An OTC degradation ratio of 63.33% and a nitrate removal ratio of 98.64% were obtained within 96 h. In addition, removal of OTC and ammonia from synthetic aquaculture wastewater by a Moving Bed Biofilm Reactor (MBBR) and changes in the resistant genes of microbial communities were also investigated. The results demonstrated that the strain KSS10 was the dominant contributor in OTC and ammonia removal in the MBBR chamber. It removed almost all ammonia and approximately 76.42% of OTC. The abundances of genes tetL, tetX and intI1 were reduced by the MBBR, but the abundance of tetG and tetM were increased due to horizontal and vertical gene transfers. Such a result can potentially be used by the strain KSS10 for removing antibiotics and nitrogen from aquaculture wastewater during pre-treatment.

Adsorption of phosphate on iron oxide doped halloysite nanotubes

Excess phosphate in water is known to cause eutrophication, and its removal is imperative. Nanoclay minerals are widely used in environmental remediation due to their low-cost, adequate availability, environmental compatibility, and adsorption efficiency. However, the removal of anions with nanoclays is not very effective because of electrostatic repulsion from clay surfaces with a net negative charge. Among clay minerals, halloysite nanotubes (HNTs) possess a negatively charged exterior and a positively charged inner lumen. This provides an increased affinity for anion removal. In this study, HNTs are modified with nano-scale iron oxide (Fe₂O₃) to enhance the adsorption capacity of the nanosorbent. This modification allowed for effective distribution of these oxide surfaces, which are known to sorb phosphate via ligand exchange and by forming inner-sphere complexes. A detailed characterization of the raw and (Fe₂O₃) modified HNTs (Fe-HNT) is conducted. Influences of Fe₂O₃ loading, adsorbent dosage, contact time, pH, initial phosphate concentration, and coexisting ions on the phosphate adsorption capacity are studied. Results demonstrate that adsorption on Fe-HNT is pH-dependent with fast initial adsorption kinetics. The underlying mechanism is identified as a combination of electrostatic attraction, ligand exchange, and Lewis acid-base interactions. The nanomaterial provides promising results for its application in water/wastewater treatment.

Zeolite as a Potential Medium for Ammonium Recovery and Second Cheese Whey Treatment

The efficiency of natural zeolite to remove ammonium from artificial wastewater (ammonium aqueous solutions) and to treat second cheese whey was examined, aiming to recover nitrogen nutrients that can be used for further applications, such as slow-release fertilizers. Sorption experiments were performed using artificial wastewater and zeolite of different granulometries (i.e., 0.71–1.0, 1.8–2.0, 2.0–2.8, 2.8–4.0, and 4.0–5.0 mm). The granulometry of the zeolite had no significant effect on its ability to absorb ammonium. Nevertheless, smaller particles (0.71–1.0 mm) exhibited quicker NH4+-N adsorption rates of up to 93.0% in the first 10 min. Maximum ammonium removal efficiency by the zeolite was achieved at ammonium concentrations ranging from 10 to 80 mg/L. Kinetic experiments revealed that chemisorption is the mechanism behind the adsorption process of ammonium on zeolite, while the Freundlich isotherm model fitted the experimental data well. Column sorption experiments under batch operating mode were performed using artificial wastewater and second cheese whey. Column experiments with artificial wastewater showed high NH4+-N removal rates (over 96% in the first 120 min) for all granulometries and initial NH4+-N concentrations tested (200 and 5000 mg/L). Column experiments with second cheese whey revealed that natural zeolite can remove significant organic loads (up to 40%, 14.53 mg COD/g of zeolite) and NH4+-N (about 99%). For PO43−-P, the zeolite appeared to saturate after day 1 of the experiments at a removal capacity of 0.15 mg P/g of zeolite. Desorption experiments with water resulted in low NH4+-N and PO43−-P desorption rates indicating that the zeolite could be used as a substrate for slow nitrogen release in soils.