Standard Limit Research Articles

Water Quality of Lake Erhai in Southwest China and Its Projected Status in the near Future

The water quality of Lake Erhai has deteriorated in recent decades due to socioeconomic development in the lake basin. After the massive implementation of water environmental protection measures in Lake Erhai in 2016, the trend of water quality deterioration has been curbed and the intensity and frequency of algal blooms has decreased. However, water quality monitoring data show that pollutant concentrations in Lake Erhai still exceed acceptable values, and there is a risk of water quality standard limits being further exceeded in the future. Therefore, it is urgent to systematically study the variability characteristics of water quality in Lake Erhai to provide practical methods to predict the future evolution of water quality. Based on water quality monitoring data from 2009 to 2019, the current water quality characteristics of Lake Erhai were analyzed, and a two-dimensional hydrodynamic and water quality mathematical model was built to predict the water quality in 2025. The results showed that the total phosphorus (TP) concentration declined after 2016, mainly due to the significant reduction of TP entering the lake due to pollution interception. However, the concentrations of the potassium permanganate index (CODMn) and total nitrogen (TN) increased after 2016, demonstrating that the pollution control measures have had little effect on the improvement of CODMn and TN. The spatial and temporal distribution of pollutants showed that the water quality in winter and spring was better than in summer and autumn, and the water quality in the southern lake was better than in the northern lake. This analysis indicates that non-point source pollution remains the main source of pollution in Lake Erhai, and that rainfall is the main driving force of pollutants exceeding the water quality standard. According to the water quality predictions, without additional pollution control measures, pollutant concentrations in Lake Erhai will exceed the Class II water quality standard by 2025. This study analyzes the water quality characteristics, predicts the direction of future water quality changes, and provides a theoretical basis for the future water quality protection of Lake Erhai.

Microbiological analysis of broiler chicken slaughter products using “Subtiform” probiotic and establishment of safety and technological process criteria

Feeding broiler chickens a probiotic biopreparation containing bacteria of the genus Bacillus subtilis and Bacillus licheniformis leads to improved feed digestion, increased productivity, and immune status, as well as reduced insemination by opportunistic and pathogenic microorganisms of slaughter products. It enhances the level of prevention and treatment of various poultry diseases. The purpose of the work is to carry out a microbiological analysis of the slaughter products of broiler chickens after drinking the probiotic biological preparation “Subtiform” in doses of 0.5 g, 2.0, and 4.0 g per 10 dm3 of water. The material (major pectoral muscle and internal organs) was examined by bacteriological methods. It was established that the content of MAFAM in the control and experimental groups 1, 2, and 3 of the chilled slaughter products of broiler chickens for 1, 3, and 5 days of storage at a temperature of 0–4 °С was within the limits of standards (no more than 1.0×104 CFU/d). It was established that when broiler chickens were given 4.0 g/10 dm3 of water, the MAFAM content for one day of poultry meat storage decreased by 10.4 % (Р < 0.05); on the third day of storage, it decreased by 9.6 % (Р < 0.05); at the beginning of the fifth day of storage, the decrease was, respectively, by 11.3 % (Р < 0.01) compared to the indicators of the control group. The content of MAFAM in offal, in particular in the heart of broiler chickens, was reduced in experimental group 3 by 36.9 % (Р < 0.001); in the liver – by 33.6% (Р < 0.001); in the muscular part of the stomach – by 27.2 % (Р < 0.001); in the spleen and lungs, there was also a decrease in the content of MAFAM in experimental group 3, respectively, by 20.2 % (Р < 0.01) and 23.6 % (Р < 0.01) compared to the indicators of the control group of broiler chickens. It was established that opportunistic pathogenic microorganisms, in particular BGCP, bacteria of the genus Proteus, and pathogenic microorganisms, in specific bacteria of the genus Salmonella, bacteria of the species Staphylococcus aureus, Listeria monocytogenes in 25 grams of the large pectoral muscle of broiler chickens and internal organs (heart, spleen, liver, the muscular part of the stomach and lungs) were not detected. According to the results of the conducted research, an adverse effect of the probiotic biopreparation at a dose of 4.0 g/10 dm3 of water on the development of microorganisms in the large pectoral muscle and internal organs of broiler chickens was established. Therefore, the probiotic “Subtiform” at a dose of 4.0 g/10 dm3 of water during the drinking of broiler chickens can be recommended to increase productivity and obtain safe slaughter products. The practical value of the work consisted of establishing the microbiological indicators of poultry slaughter products after drinking probiotics, as well as establishing safety criteria and the technological process.

Spatial distribution and hydrogeochemical evaluations of groundwater and its suitability for drinking and irrigation purposes in kaligonj upazila of satkhira district of Bangladesh

Groundwater is a significant water resource for drinking and irrigation in Satkhira district, Bangladesh. The depletion of groundwater resources and deterioration in its quality are the results of the confluence of factors such as industrialization, intensive irrigation, and rapid population growth. For this reason, this study focused on the evaluation of tubewell water of six unions of Kaligonj upazila in Satkhira district, which is situated in the coastal southwest part of Bangladesh. Major and trace elemental concentrations were assimilated into positive matrix factorization (PMF) to identify potential sources and their respective contributions. Principal component analysis (PCA) revealed that groundwater salinization and manmade activities were the primary causes of heavy metals in the coastal groundwater. Its average pH value was found to be 7.5, while Dissolved oxygen, Total dissolved solids, salinity, and conductivity, with values ranging from 1.18 to 7.38 mg/L, 0.5–4.88 g/L, 0.4–5%, and 0.95 to 8.56 mS/cm, respectively. The total hardness average value was 561.7 mg/L, classified into the very hard water categories, which is why 90% of the tubewell water samples were unfit for household purposes. All samples had an excessive level of arsenic present. The iron concentration of fifteen (15) samples crossed the standard limit according to WHO 2011 value. Around 63% of the samples were of the Na+-K+-Cl--SO42- type, and about 72% were sodium-potassium and alkali types. 98% of samples were covered in chloride and bicarbonate. The findings showed that 45.83% of the groundwater samples had negative Chloroalkaline index (CAIs), while 54.16% had positive. The permeability index (PI) was an average of 73%, and residual sodium carbonate (RSC) averaged 260.2 mg/L, and the findings clearly showed that 80% of the samples weren't appropriate for irrigation. According to the sodium adsorption ratio (SAR) value, 65% of the samples fell into the unsuitable category. These calculations indicated a high overall salinity hazard in the study area, which may be caused by the intrusion of sea water given that the study area is close to the coastal region. Findings compared to standards revealed that the majority of the samples were deemed unfit for drinking and irrigation purposes. Hence, additional attention must be paid to this area to ensure the availability of drinkable water and to preserve sustainable farming practices.

A robust hybrid receiver for binary phase-shift keying discrimination in the presence of phase noise

We address the problem of coherent state discrimination in the presence of phase diffusion. We investigate the role of the HYbrid Near-Optimum Receiver (HYNORE) we proposed in [J. Opt. Soc. Am. B 40 (2023) 705] in the task of mitigating the noise impact. We prove the HYNORE to be a robust receiver, outperforming the Displacement Photon-Number-Resolving (DPNR) receiver and beating the standard quantum limit in particular regimes. We introduce the maximum tolerable phase noise [Formula: see text]max as a figure of merit for the receiver robustness and show that HYNORE increases its value with respect to the DPNR receiver.

Engineering colloidal semiconductor nanocrystals for quantum information processing.

Quantum information processing-which relies on spin defects or single-photon emission-has shown quantum advantage in proof-of-principle experiments including microscopic imaging of electromagnetic fields, strain and temperature in applications ranging from battery research to neuroscience. However, critical gaps remain on the path to wider applications, including a need for improved functionalization, deterministic placement, size homogeneity and greater programmability of multifunctional properties. Colloidal semiconductor nanocrystals can close these gaps in numerous application areas, following years of rapid advances in synthesis and functionalization. In this Review, we specifically focus on three key topics: optical interfaces to long-lived spin states, deterministic placement and delivery for sensing beyond the standard quantum limit, and extensions to multifunctional colloidal quantum circuits.

Observation of quantum-correlated twin beams in cascaded nonlinear interactions.

We report on the generation of twin beams through a cascaded process of optical parametric oscillation in a doubly resonant second-harmonic generation system. These bright beams exhibit strong quantum correlations, enabling the observation of up to 5 dB of noise reduction in their intensity difference below the standard quantum limit.

Assessment of Heavy Metals in Vegetables Grown on Irrigated Land in Butura, Bokkos LGA, Plateau State, Nigeria

Vegetables have positive antioxidative properties and are abundant in vitamins, minerals, and fiber. However, if consumed in large quantities, eating vegetables polluted with heavy metals may be harmful to human health. Therefore, this study assessed the effects of heavy metals on irrigated pepper, cabbage and Irish potatoes grown in Butura. Atomic absorption spectrophotometry (AA240FS) was used to analyze cadmium (Cd), cobalt (Co), nickel (Ni), lead (Pb), zinc (Zn), copper (Cu), chromium (Cr) and arsenic (As) levels. Three samples were selected from each of the vegetables grown on nine selected farms at distances of 0 m, 10 m, and 30 m. This forms a composite sample of vegetables at each farm. The study showed that the concentrations of cobalt, chromium, cadmium, copper, arsenic, zinc and nickel were within the standard limits set by the FAO/WHO, except for lead, which is higher than the allowable limits for vegetables. These patients may have behavioral problems, neurological complications and hematologic disorders. Thus, these findings could lead to a risk for the human population consuming these vegetables. It is recommended that irrigation water and agricultural soils be constantly monitored to determine the concentration of metals accumulated by crop plants to ensure that crop plants are safe for consumption by humans.

Assessment of Radio-Frequency Radiation Exposure from Selected Mobile Base Stations in Yenagoa, Bayelsa State, Nigeria

The antennas from mobile base stations radiate non-ionizing radio frequency radiation into space. The human body can experience negative health effects from prolonged exposure to radiofrequency (RF) radiation. Because base station installations and telecommunication networks are growing, there is a growing need to address the health risks connected with exposure to telecommunication masts. Using the Electrosmog Meter Cornet Model, power density from many telecom masts owned by various network operators was measured in this investigation. At 10-meter intervals, the RF radiation in seven (7) settlements in Yenagoa town, located in the Yenagoa Local Government Area of Bayelsa State, was measured within radial distances of 100 meters. With a mean value of 4.0569mWm-2, the measured values vary from 0.650mWm-2 to 9.810mWm-2. Still, values evolved. Nevertheless, additional factors, such as adjacent electromagnetic sources' wave interference or reference base station interference, caused readings to fluctuate. It was discovered that the greatest power density level was 9.810 mWm-2, and it was measured 20 meters away from the base station at site MBS1. As per the International Commission on Non-ionizing Radiation Protection (ICNIRP) and other regulatory authorities, the standard limit of 4.5Wm-2 for the 900 MHz system is not exceeded by the radiation exposure level, as the findings show. This shows that the exposure levels in these areas are low enough to not seriously jeopardize the health of those living in the research area.

The effect of using seashells as cementitious bio-material and granite industrial waste as fine aggregate on mechanical and durability properties of green flowable sand concrete

The present work is a study of the feasibility of using seashell powder (SSP) combined with industrial granite waste (GW) to develop a new green flowable sand concrete (FSC). The GW was used to replace the natural sand at levels of 0, 10, 20, 30, 40, and 50% by volume, and the SSP has been used to substitute the cement at levels of 5, 10, and 15% by weight. Slump flow and V-funnel flow time tests have been used to investigate the fresh properties of FSC mixtures. Compressive strength, modulus of elasticity, ultrasonic pulse velocity (UPV), water absorption, porosity, and acid attack tests were used to assess the mechanical and durability properties of hardened FSC mixtures. XRD, TGA, and SEM analyses were performed to evolve the microstructure of hardened FSC. The results showed a decrease in the fresh properties of FSC mixtures with the substitution of sand by GW. Nonetheless, the inclusion of SSP as filler mitigated this adverse effect, and all FSC mixes were subsequently discovered to be within the standard limits. The combined use of 50 vol% GW and 10 wt% SSP developed FSC with the greatest compressive strength (67 MPa), modulus of elasticity (40 GPa), and UPV (4175 m/s), as well as the lowest porosity (2.9%) and absorption (2.4%) at 90 days, compared to the control FSC. Moreover, using up to 10 wt% SSP with a fineness of 8000 cm2/g may enhance the durability of GW-based FSC against acid attack. Microstructural analyses indicated denser microstructure, stronger ITZ, and weaker porosity. The developed eco-friendly FSC effectively showed a decrease in production costs and carbon emissions, reducing the level of waste and protecting natural resources, which provides an emerging approach for its application in advanced green concretes for future work.

Hazard-mapping and health risk analysis of iron and arsenic contamination in the groundwater of Sylhet district.

This study investigates groundwater contamination by arsenic and iron and its health implications within the Sylhet district in Bangladesh. Utilizing geographic information system (GIS) and inverse distance weighting (IDW) methods, hazard maps have been developed to evaluate contamination risk across various upazilas. The findings show significant arsenic and iron pollution, particularly in the northwestern part of the district. In about 50% of the area, especially in Jaintiapur, Zakiganj, Companiganj, and Kanaighat where arsenic levels surpass 0.05 mg/L which is the standard limit of Bangladesh. Iron levels peak at 13.83 mg/L, severely impacting 45% of the region, especially in Gowainghat, northeastern Jaintiapur, Zakigonj, and Golabganj. The study employs USEPA health risk assessment methods to calculate the hazard quotient (HQ) and hazard index (HI) for both elements via oral and dermal exposure. Results indicate that children face greater noncarcinogenic and carcinogenic risks than adults, with oral HI showing significant risk in Balagonj and Bishwanath. Dermal adsorption pathways exhibit comparatively lower risks. Cancer risk assessments demonstrate high carcinogenic risks from oral arsenic intake in all areas. This comprehensive analysis highlights the urgent need for effective groundwater management and policy interventions in the Sylhet district to mitigate these health risks and ensure safe drinking water.

'Environmental standard limit concentration' arsenic exposure is associated with anxiety, depression, and autism-like changes in early-life stage zebrafish

Arsenic is a worldwide environmental pollutant that can impair human health. Previous studies have identified mental disorders induced by arsenic, but the environmental exposure concentrations in the early life stages associated with these disorders are poorly understood. In the present study, early-life stage zebrafish were used to explore the effects on mental disorders under 'environmental standard limit concentrations' arsenic exposures of 5, 10, 50, 150, and 500 μg/L. The results showed that arsenic exposure at these concentrations changed the locomotor behavior in larval zebrafish and was further associated with anxiety, depression, and autism-like behavior in both larval and juvenile zebrafish. Changes were noted at benchmark dose limit (BMDL) concentrations as low as 0.81 μg/L. Transcriptomics showed that immediate early genes (IEGs) fosab, egr1, egr2a, ier2b, egr3, and jund were decreased after arsenic exposure in larval and juvenile zebrafish. Nervous system impairment and anxiety, depression, and autism-like behaviors in early-life stage zebrafish at 'environmental standard limit concentrations' may be attributed to the downregulation of IEGs. These findings in zebrafish provided new experimental support for an arsenic toxicity threshold for mental disorders, and they suggest that low levels of environmental chemicals may be causative developmental factors for mental disorders.

Analytical Study of Pippalyadigana Vati - An Ayurvedic Formulation

In Ayurveda, the raw drugs are classified under various groups known as Gana, which contain substances with comparable qualities that can treat a particular ailment. Ganas are very crucial to making the treatment field simpler and more efficient. Acharya Sushrut made a truly remarkable contribution by classifying the drugs into 37 distinct categories for various ailments. Pippalyadi gana is one of the Ganas described by Acharya Sushruta and is specially mentioned for the management of Pratishyaya. Pratishyaya is one important disease of Urdhwajatrugata Roga. In Ayurveda, Kalka, Kawath, Churna and Vati are the most frequently used form of medication. Vati preparation is considered a secondary Kashaya Kalpana and offers an easy way to administer oral medication. In the present study, 14 drugs from Pippalyadi Gana were selected for Vati preparation and certain of them were used in Kwath form for Bhavna, while the drugs containing volatile oils were utilized in powder form. Vati Kalpana has been prepared according to general method of preparation Vati mentioned in API. Prepared Vati were tested by many parameters including physical and chemical ones, such as weight variation and disintegration time, and chromatographic tests, such as TLC fingerprinting, were used to standardize it. After the testing, all parameters were found to be within API standard limits. This kind of result indicates a good therapeutic property of Vati Kalpana which can be used as oral medication for Pratishyaya.

Isoelectric focusing technique enables protein detection beyond standard limits

The technique is an inexpensive and versatile means of enhancing existing detection methods.

A Comparative Study of Narrow/Ultra-Wideband Microwave Sensors for the Continuous Monitoring of Vital Signs and Lung Water Level.

This article presents an in-depth investigation of wearable microwave antenna sensors (MASs) used for vital sign detection (VSD) and lung water level (LWL) monitoring. The study looked at two different types of MASs, narrowband (NB) and ultra-wideband (UWB), to decide which one was better. Unlike recent wearable respiratory sensors, these antennas are simple in design, low-profile, and affordable. The narrowband sensor employs an offset-feed microstrip transmission line, which has a bandwidth of 240 MHz at -10 dB reflection coefficient for the textile substrate. The UWB microwave sensor uses a CPW-fed line to excite an unbalanced U-shaped radiator, offering an extended simulated operating bandwidth from 1.5 to 10 GHz with impedance matching ≤-10 dB. Both types of microwave sensors are designed on a flexible RO 3003 substrate and textile conductive fabric attached to a cotton substrate. The specific absorption rate (SAR) of the sensors is measured at different resonant frequencies on 1 g and 10 g of tissue, according to the IEEE C95.3 standard, and both sensors meet the standard limit of 1.6 W/kg and 2 W/kg, respectively. A simple peak-detection algorithm is used to demonstrate high accuracy in the detection of respiration, heartbeat, and lung water content. Based on the experimental results on a child and an adult volunteer, it can be concluded that UWB MASs offer superior performance when compared to NB sensors.

Development of non‐dairy creamer with modified fatty acid profile and high Omega‐3 and 6 at a non‐dairy creamer plant

SummaryA study was conducted to develop non‐dairy creamer production with a modified fatty acid profile having high levels of omega‐3 and 6, by using raw materials collected from the Republic Foods industrial non‐dairy creamer plant. The non‐dairy creamer formulation aimed to maintain a balanced 1:1:1 ratio of polyunsaturated, monounsaturated and saturated fatty acids. The ingredients used included palm olein, stearin, RBD palm oil, rice bran oil, soybean oil, coconut oil and palm kernel oil. The mixture proportions tested were determined using Design Expert software, for in total 20 different formulations. From these, six formulations were selected based on their fatty acid profiles, which closely approximated the desired 1:1:1 ratio of polyunsaturated, monounsaturated and saturated fatty acids. To complement the physicochemical results, a quality control and research officer from Republic Foods industrial conducted a comprehensive evaluation of various properties of the non‐dairy cream samples intended for use in coffee. It is noteworthy that formulation number 20 received the highest scores across all tested properties. This formulation had 50.53% palm olein, 1.00% stearin, 1.00% RBD palm oil, 1.00% rice bran oil, 44.47% soybean oil, 1.00% coconut oil and 1.00% palm kernel oil. This combination results in a fatty acid ratio of 1:1:0.8 (PUFA:MUFA:SFA) at the least production cost. The developed non‐dairy creamer exhibited the highest total energy content, namely 519 kilocalories/100 g, when compared with commercial brands. However, after a storage period of 90 days, the peroxide value reached 6.18 ± 0.22 mEq kg−1 of fat, which is below the FDA standard limit of 10.0 mEq kg−1 fat. This trend in peroxide value increase over the 90‐day storage period aligns with the behaviour of TBA, which also showed an upward trend during storage.

A closed-form structural stress-strain relation and implications on plastic design limits in codes and standards

The deformation of elastic-perfectly plastic beam or plate under combined through-thickness membrane and bending stresses (i.e., structural stress) is analyzed in this paper. Closed-form solutions of “plane-remains-plane” strain (i.e., structural strain) distribution as a function of applied stress and yield strength is derived. The relationship between structural stress and structural strain is also revealed for gaining insights on not only the plastic collapse conditions, but also through-thickness deformation behaviors leading to limit state. Based on the closed-form strain solutions, four deformation modes are identified: (1) elastic, (2) one-side yielding, (3) two-side yielding, and (4) plastic collapse. A membrane-bending stress interaction diagram is constructed to depict four zones that are associated with the four deformation modes in the normalized membrane and bending stress space. Closed-form solutions of residual stress, residual strain, and structural stress range-strain range relation after a loading-unloading cycle are also derived. Based on the parabolic plastic collapse stress limit curve, parabolic design stress limit curves with coherent safety margins for any combinations of membrane and bending stresses are constructed. The new insights gained in this study offer a more consistent definition of design stress limit than those used in the current codes and standards, e.g., ASME BP&V Code.

First implementation of quality control procedures on selected X-ray machines in South of Benin

Abstract Introduction: The use of X-ray equipment for medical diagnostic radiography procedures has increased due to advances and complexity of radiological procedures. Achieving good image quality while keeping exposure of workers, public and patient exposure to an acceptable level has become a prerequisite for the radiology department in order to comply with best international practices. The aim of this study was to undertake quality control measurement of seven (7) diagnostic radiography equipment in the south of Benin, the first of its kind. Material and methods: Multifunction detector (Piranha) and beam alignment test tool were used to perform quality control tests on seven (7) X-ray units. The method used as well as the interpretation of the results was based on the American Association of Physicists in Medicine (AAPM), United States Food and Drug Administration (FDA), Healing Arts Radiation Protection (HARP), Institute of Physics and Engineering in Medicine (IPEM), International Atomic Energy Agency (IAEA) and Canadian Safety code 35 (S.C 35) recommendations. Results: The quality control results showed that all X-ray equipment investigated were within standard limits for accuracy of exposure time below 10 ms; reproducibility of kVp, exposure time and dose output; specific dose-kVp2 linearity; and specific dose-mAs linearity. Five (5) out of seven (7) diagnostic X-ray machines passed quality control tests such as X-ray beam alignment, exposure time above 10 ms and kVp accuracy. One (1) X-ray machine failed the quality control test of beam filtration at 70 kVp and above. Conclusions: The findings of this study have provided baseline data for other radiology departments to embark on similar QA/QC activities, and also explore options for optimization of patient dose. However, there is a need to extend the study to cover more diagnostic X-ray machines throughout the country. It is anticipated that this would ultimately assist in improving radiation protection and safety during medical diagnostic radiological procedures.

Determination of chromium in foodstuffs by using novel adsorbent in vortex assisted-dispersive solid phase micro-extraction method: An application of multivariate techniques

A new graft copolymer composed of polystyrene and polylinoleic acid (PLinas) with the sodium salt of iminodiacetate (Ida) was synthesized and used as an adsorbent. The vortex-assisted dispersive solid-phase micro-extraction (VA-dSPµE) method was used for the extraction and pre-concentration of chromium. Multivariate methodologies, such as factorial design and 3D surface plots, were applied for screening and optimizing effective extraction parameters. The influence of diverse analytical parameters, such as pH, sample volume, and interfering ions, on the extraction of chromium was studied. The calibration standard curve exhibited a linear range from 0.01 to 0.50 μg L−1. The relative standard deviation and limit of detection were found to be 1.65 % and 0.003 μg L−1, respectively. Extraction recoveries were found in the range of 96 to 99 % by using certified reference materials (CRMs). The adsorbent capacity of PLinas-Ida was found to be 112 mg g−1. The VA-dSPµE method demonstrated its effectiveness in the pre-concentration and determination of chromium within samples of foodstuffs by graphite furnace-atomic absorption spectrometry (GF-AAS).

Evaluation of some physical and chemical characteristics of the drinking water collected after winter and autumn seasons from Kosti and Rabak Cities, White Nile State, Sudan

Drinking water quality is a very important issue in the health sector and it involve the check of some physical, chemical and biological parameters through some standard methods and limits. The current study aimed to determine some physical and chemical parameters of the drinking water collected from White Nile after autumn and winter seasons. The drinking water samples were collected from Kosti and Rabak Cities, White Nile State, Sudan, in clean disposable plastic bottles from random sites of each city. The determinations of the physiochemical tests were performed within one week after sample collection at University of Gezira Laboratories. The results of this study show that, the drinking water that collected after winter season showed good physical quality, as same as that collected after autumn season except the slight problem in color (less transparent). The tested chemical parameters of Kosti and Rabak drinking water that collected after winter season showed good quality except, those of sulphate, carbonate (0 mg/L) and chloride of 28.4 and 31.95 (ppm) as same as that collected after autumn season, except hardness (500 mg/L) which seemed to be an autumn problem of Rabak city. Although there were some signs of physical and chemical pollutions, serious steps towards treatment of their causes should be done.

Enhanced ammonia removal in tidal flow constructed wetland by incorporating steel slag: Performance, microbial community, and heavy metal release

Utilizing alkaline solid wastes, such as steel slag, as substrates in tidal flow constructed wetlands (TFCWs) can effectively neutralize the acidity generated by nitrification. However, the impacts of steel slag on microbial communities and the potential risk of heavy metal release remain poorly understood. To address these knowledge gaps, this study compared the performance and microbial community structure of TFCWs filled with a mixture of steel slag and zeolite (TFCW-S) to those filled with zeolite alone (TFCW-Z). TFCW-S exhibited a much higher NH4+-N removal efficiency (98.35 %) than TFCW-Z (55.26 %). Additionally, TFCW-S also achieved better TN and TP removal. The steel slag addition helped maintain the TFCW-S effluent pH at around 7.5, while the TFCW-Z effluent pH varied from 3.74 to 6.25. The nitrification and denitrification intensities in TFCW-S substrates were significantly higher than those in TFCW-Z, consistent with the observed removal performance. Moreover, steel slag did not cause excessive heavy metal release, as the effluent concentrations were below the standard limits. Microbial community analysis revealed that ammonia-oxidizing bacteria, ammonia-oxidizing archaea, and complete ammonia-oxidizing bacteria coexisted in both TFCWs, albeit with different compositions. Furthermore, the enrichment of heterotrophic nitrification-aerobic denitrification bacteria in TFCW-S likely contributed to the high NH4+-N removal. In summary, these findings demonstrate that the combined use of steel slag and zeolite in TFCWs creates favorable pH conditions for ammonia-oxidizing microorganisms, leading to efficient ammonia removal in an environmentally friendly manner.