Filtration Plant Research Articles

Improving the quality of irrigation water by vacuum treatment

The first stage of research of the water purification plant was carried out in laboratory conditions on a hydraulic model at the Department of Water Supply of the Volga State University, the second stage of tests for purification and activation of water was carried out at the experimental production site of the Volga State University “Innovative Village” before sowing tomatoes in the ground, on a plant with a capacity of 10 m3/ day. The second stage included the work performed in the following sequence: first, they achieved stable operation of the water purification unit by vacuum-ejection method, then they achieved stable operation of the water activation unit using a vacuum activator. The final tests were carried out at the start of both installations. The installations worked in semi-automatic mode. It should be noted that the vacuumejection unit includes a vacuum-ejection oxidizer and a semi-automatic sand filter, working as a single unit.

Study of water purification reactor operating modes

Wastewater treatment is one of the main problems of development and urbanization of the Arctic regions. This article is devoted to the development of a method for assessing the degree of water purification in order to determine the optimum operating parameters of treatment reactors for water treatment by ferrates from industrial and household waste resulting from the development of Arctic regions. Experiments reflecting the influence of the amount of air supplied to the purification plant on the processes of mixing and distribution of water were carried out and analyzed. Based on the experimental data, a method for determining the optimum operating parameters of a new mobile water purification plant has been developed and applied. The operation of the plant is based on the use of the ferrate method. equations and dependencies describing the relationship between the reactor volume, liquid flow rate and the degree of water purification are given. The degree of water pollution is estimated as its fraction which has left the reactor before the time required for complete treatment of the liquid from the moment it enters i the reactor. Optimal parameters of the ferrate reactor, such as volume and air supply, for a mobile water treatment plant were determined.

Flow cytometry for on-line microbial regrowth monitoring in a membrane filtration plant: pilot-scale case study for wastewater reuse

With the use of on-line flow cytometric fingerprinting, we confirmed that cell densities in a RO permeate were caused by bacterial regrowth in the piping, and that there was no problem with the integrity of the membrane and resulting water quality.

GIS-BASED ASSESSMENT OF GROUND WATER QUALITY FOR DRINKING PURPOSE BY WATER QUALITY INDEX APPROACHES IN BAHAWALPUR, PUNJAB

Groundwater pollution is a significant environmental issue globally, particularly in large cities, and trace heavy metals are the most significant groundwater pollutants. Pakistan is particularly affected by groundwater contamination, which poses a major threat to public health. Many industrial facilities in Pakistan discharge untreated wastewater into nearby drains, which has a direct impact on the quality of surface water, soil, and groundwater. Bahawalpur, the 11th most populous city in Pakistan, is the focus of this research, which examines how residential areas in the city affect groundwater. The research area was carefully studied, and groundwater sampling locations were collected from 45 distinct locations throughout Bahawalpur’s residential area. Groundwater samples were then analyzed for various parameters, including pH, turbidity, electrical conductivity, total dissolved solids, calcium, magnesium, iron, total hardness, total alkalinity, and chloride content. The results of these tests were compared to World Health Organization (WHO) recommendations, and the outcomes of the elements were displayed using ArcView GIS v10.7.1 and raster interpolation with IDW. The study found that the concentration of pollutants in groundwater exceeded the permitted level, and the water quality index for drinking water was determined to be only 65 percent in terms of pH, turbidity, electrical conductivity, iron, calcium, magnesium, total dissolved solids, total alkalinity, and total hardness. The characteristics of the groundwater did not comply with WHO standards. These findings suggest that there is a pressing need to address water pollution in Bahawalpur. The data collected and analyzed in this study could be used to design and construct a filtration plant facility to reduce water pollution in the area.

Development and Application of An Integrated Urban Water Cycle System by Combining Water Cycle Elements

Smart city in water resources area attempts are being made by establishing an integrated urban water cycle model for a stable water supply and efficient water management in the city. Accordingly, the need for simulation and integrated management of water consumption in cities is increasing. If it is possible to predict and respond in advance to consumers' water consumption, more efficient urban water resource management will be possible based on river intake. Therefore, in this study, an integrated urban water cycle model was constructed that links river intake, water purification plants, retention tanks, water distribution, sewage pipe networks, sewage treatment plants, and river discharge of treated water. It was developed using C++, and was built by linking the modules of the water intake pump station, retention tank, water purification plant, sewage treatment plant, water supply pipe network, and the sewage pipe network. Among them, the water intake pumping station and retention tank were developed independently, and the other modules were linked with commercial software such as WaterFlow, MassFlow, EPANET, and SWMM. The model measures data such as water quality factors and flow rates for each module, displays the operation status, and enables linkage for each module, even when the measurement time interval is different. In addition, warnings and error messages were generated when a problem occurred during the operation of each module. To verify the applicability of the developed integrated model, the change in the water level of the retention tank was calculated by simulating consumer water consumption. As a result, it was confirmed that the water level change in the retention tank was proper, which meant that the operation changed from the intake pumping station. The developed model is expected to be used as an integrated urban water cycle model in the future.

Influence of the Stage Number on the Quality of Domestic Waste Water Treated with Typha domingensis Filter Plants

To achieve “good ecological status for water and aquatic environments”, extensive treatment techniques have been developed. The goal of this work is to study the two stages efficiency of filters planted with Typha domingensis. Two tanks in series of filters planted with reeds were used. Each tank consists of a tank of 1m3 in volume fitted with drainage pipes pierced with holes. Three different layers of gravel were laid over the drain pipes. From the comparison of the characterization of raw domestic wastewater and treated water, it appears that the reductions obtained at the outlet of the 2nd floor are more satisfactory than at the outlet of the 1st floor. The reductions at the exit of the 2nd floor are: 91.7% for total suspended solids; 98.3% for COD; 94.7% for BOD5; 79.9% for NTK and 49.8% for Pt.

Современные подходы к обработке различных типов вод (технологических, сточных, питьевых) на ТЭС

The article presents the types of new sorbents used in the industry from the point of view of their application for water purification for various purposes. A review of the literature and a selection of modern sorption materials of the new generation, which are raw materials of Russian production, for the purification of various types of water at thermal power plants to normalized indicators. Laboratory and industrial experiments were carried out to purify wastewater from petroleum products and drinking water from ammonium ions to normalized values using sorption materials APT-1, APT-2, APT-4 and BAU-A. At the Department of TOT of the MEI, work was carried out to study the properties of new sorption materials for the purification of technological, oil-containing wastewater and drinking-quality groundwater at thermal power plants. To determine the operability of sorbents for water purification from ammonium ions, a photocolorimetric analysis of filtrate samples was carried out. The sorption method of wastewater treatment is the most effective and environmentally acceptable method. A filter with a new sorbent should be installed as the last stage of purification of many types of water at thermal power plants to achieve the necessary water quality indicators: at a water purification plant from petroleum products; at a stormwater sewage treatment plant from petroleum products.

Identification of nitrate sources in tap water sources across South Korea using multiple stable isotopes: Implications for land use and water management

Stable nitrate isotopes (δ15N-NO3 and δ18O-NO3) in conjunction with stable water isotopes (δ18O-H2O and δD-H2O) were used to identify nitrogen (N) sources and N-biogeochemical transformation in tap water sources sampled from 11 water purification plants across South Korea. The raw water sources are taken from rivers within the water supply basins, which indicates the quality of tap water is highly dependent on surrounding the land use type. We estimated the proportional contribution of the various N sources (AD: atmospheric deposition; SN: soil nitrogen; CF: chemical fertilizer; M&S: manure/sewage) using Bayesian Mixing Model. As a result, the contribution of N sources exhibited large seasonal and spatial differences, which were related to the type of land use in the water supply basins. Commonly, the M&S and SN were the dominant N source during the dry and wet seasons in almost regions, respectively. However, in the regions with high N loading ratios from urban and industrial sources, the M&S was the dominant N source during both the wet and dry seasons. In addition, the regions were characterized by high NO3− concentrations due to the decreased dilution effect of precipitation during the dry seasons. In contrast, the SN was the dominant N source in the regions with high N loading ratios from agricultural areas during both the wet and dry seasons. The NO3−-N concentration during the wet season was significantly higher than those during the dry season in these regions due to the input of non-point sources with high concentrations. Meanwhile, denitrification and nitrification were observed in the watersheds. It is important to understand the isotope fractionation due to N-biogeochemical transformation for considering the potential misinterpretations of the origin and fate NO3−. Collectively, our findings provide a basis on N source control strategies to ensure tap water quality in complex land use areas.

A Study on the Behavior Evaluation and Control of Midge Larvae in the Filtration Process

Recently, midge larvae, which are indicators of aquatic environmental pollution, have been detected in tap water in some areas, resulting in controversy. Therefore, the objective of this study is to analyze the behavioural features of midge larvae in sand, GAC (granular activated carbon) and GAC/sand processes, which are mainly operated in domestic water purification plants, and suggest effective operating methods for larval control. In this study, a pilot-scale square column (W300×L300×H3500~5000 mm) was used for the filtration experiment and was used with a filter height of 2.5 m as well as in the field. The water to be treated was the sand filtered from the water purification plant G, and midge larvae from the Han River were injected periodically and operated for an estimated 40 to 50 days. As a result, no larvae were detected during the first five operational days in the sand filter and GAC and 14 days in the case of GAC/sand. However, after backwashing, larvae were detected from the 9th day of operation for sand and GAC, and from the 15th day for GAC/sand. In the case of sand laying under the GAC, larvae detection was delayed by approximately 6 days compared to the operation of the GAC alone. Following examination of larval distribution in relation to the height of the activated carbon layer after approximately 50 days of operation, it was found that the larvae were distributed on 17% in the upper layer, 7% in the middle layer, 19% in the lower layer and 0.2% in the lower water collection device. Therefore, it is necessary to shorten the backwashing cycle from the initial stage of larval introduction and to increase the rate of expansion of GAC during the backwashing to quickly flush out the larvae. The results of this study also confirmed that when the backwash speed was 0.57 m/min or more, the rate of expansion of GAC was 30% or more, and larval rejection increased approximately twice when compared with a washing rate of 0.45 m/min. Consequently, as a method of effective functioning of the filtration process for larval control, in the case of sand filtration, when it is difficult to expand the filter media, it is necessary to increase the rinsing time, and in the case of GAC, it is necessary to quickly discard the larvae by increasing the backwashing rate and shortening the backwashing cycle.

An energy‐efficient two‐stage passively aerated trickling filter for high‐strength wastewater treatment and reuse

AbstractThis work aimed to assess the technical and energetic feasibility of a passively aerated laboratory‐scale trickling filter, configured as a two‐stage system, to produce urban wastewater (UWW) reusable in agriculture. The trickling filter was fed continuously with high‐strength UWW at four hydraulic retention times (HRTs), that is, 10, 5, 2 and 1 day, corresponding to organic loading rates (OLRs) of 0.1, 0.2, 0.5 and 0.9 kg COD/m3/d, respectively. The results revealed a good performance in organic load removal and nitrification at the four HRTs. The trickling filter showed high organic pollutant removal efficiencies of up to 93%, 94% and 98% for chemical oxygen demand (COD), BOD5 and total suspended solid (TSS), respectively, as well as high ammonia nitrogen removal above 96% at the shortest HRT of 1 day. All physicochemical parameters were significantly lower than the allowable limits set out in ISO 16075 for category C (non‐food crop irrigation) irrigation water. The reuse of treated UWW in irrigation led to germination indexes and growth parameters of triticale (Triticosecale Wittm.) almost equal to those obtained using tap water. Energy use was found to be about 0.2754 kWh/m3 of treated wastewater, making it competitive with trickling filter plants reported in the literature. The simplicity and energy efficiency of the developed trickling filter system, combined with its capacity for almost full nitrification, make it appealing for sewage treatment in small communities in developing countries.

Deep Learning Methods for Predicting Tap-Water Quality Time Series in South Korea

South Korea currently lacks a real-time monitoring and anomaly detection system for detecting continuous tap water quality changes from the water source to faucet and pre-diagnosing hazards that threaten tap water safety. In this study, we constructed an accurate water quality prediction model that could comprehensively cover all water treatment facilities supplying tap water nationwide and verified the model using an integrated approach. To address the uncertainty of continuously changing water quality, we collected five years (2017–2021) of hourly water quality data from 33 large water purification plants and applied various deep learning techniques to construct an optimal prediction model. We repeated water quality prediction and evaluation over the following 24 h through a time series cross-validation of an untrained dataset of the previous five months. The optimized deep learning model achieved average and maximum prediction accuracy of 98.78 and 99.98%, respectively, and showed excellent performance in terms of the root mean squared error (0.0006), mean absolute error (0.0003), and Nash–Sutcliffe efficiency (0.9894). Thus, deep learning technology greatly improved the accuracy and efficiency of water quality prediction. The proposed model could provide prompt and accurate water quality information for large-scale water supply facilities nationwide and improve public health through the early diagnosis of water quality anomalies.

An experimental study of Canal Water Purification in Chochocho Bushbuckridge Municipality Mpumalanga Province

Purpose: The purpose of this research is to evaluate the social, economic, and political feasibilities of providing water purification technologies to rural areas of Bushbuckridge Municipality, specifically Chochocho residents.
 Methodology: For this study, the following techniques were used: Questionnaire survey, simple survey, Observation, and group focus. Data was collected by fieldwork visiting the community members drinking polluted water and getting information utilizing calling individuals. Random sampling was done for this study from community members in Chochocho in Mpumalanga to collect data from known and unknown individuals and municipal officials. During the survey, we observed that residents were drinking polluted water.
 Main Findings: The study results show that Moringa oleifera powder cleans polluted water quicker and cheaper than paper filters and homemade filters.
 Implications of study: The results of this study can serve as a foundation for investors interested in entering the technological market. Therefore, Bushbuckridge municipality needs to develop a business strategy to assist the municipality in approaching water purification markets as a collective and social responsibility in the long term. The findings of this study can help the local municipality and the Department of water and sanitation to provide a water pipeline and erect a water purification plant to supply the community with clean water.
 Novelty of the study: The study will demonstrate knowledge and skills to the young generation through research, and residents and the young generation will gain more innovative ways how to treat polluted water in Chochocho and increase the good health and livelihoods of residents in Chochocho in Bushbuckridge Municipality.

A PLS-SEM Analysis to Check Public Willingness to Use Water from Filtration Plants Installed by Public Own Organizations; a Study of Psychological Behavior Toward Sustainable Development.

IntroductionWater is the basic need of human beings and there is no substitute for water. This research was conducted to analyze public willingness to use water from filtration plants installed by public own Organizations and which psychological factors may help them to decide to use safe water.MethodsThere ought to be some nudges in the right direction to encourage people to use water filters. A questionnaire was adopted from the literature for this research. PLS-SEM is used to evaluate data to check the connection among variables since it is the most recommended way for assessing and predicting explained variables to account for the largest latent variance, and PLS-SEM is one of the most effective approaches for predicting outcomes.ResultsPLS-SEM direct path analysis revealed that hypotheses H1-H6 were accepted and the gender and levels of education of the respondents as control variables, gender and education showed insignificant relationships with WUFWFP. Age showed a substantial relationship as a moderator variable between WQK*Age, and HC*Age with a willingness to use filter water from filtration plants=WUFWFP, while the rest of the variables showed an insignificant relationship.DiscussionAs per our results, H1a and H3a have a significant relationship as moderator variables between IV and DV, while H2a, H4a, H5a, and H6a did not show any relationship as moderator variables between IV and DV. Hence H1a and H3a were accepted while the rest of the moderator was rejected under this research. This study would be helpful for the decision-makers and planners to take proper sustainable measures to address the repercussions of urbanization and land use changes to protect the ecosystem.

LCL‐filter resonance suppression in grid‐connected inverter based on strictly real positive plant strategy

AbstractResonance is one of the most significant challenges in a voltage source inverter interfaced with the grid through an LCL filter. The capacitor current (CC) damping control methodology is considered due to its high‐quality of grid injected current feature. It is widely accepted that the proportional CC feedback compensation damping method becomes ineffective at critical resonance frequency due to control loop delays and may result in an unstable system under grid impedance or filter parameters variations. A suitable differential compensator placed in the CC feedback path can address this issue with a trade‐off between robustness and noise rejection capability. This paper offers a different design method called parallel feedforward compensation (PFC) method, which builds an almost strictly real positive (ASRP) plant and realized damping with enhanced stability features. In the proposed alternative, a compensator consisting of a damping gain and a sampled delay is placed across the filter plant and filter CC feedback loop and the joint output of this augmented plant is then transmitted back at the reference point on the input side of the inverter to attenuate the undesirable resonance peak. The control response and stability performance analysis show that the suggested methodology offers a wide damping region, high robustness, and improved control performance. Simulation and experimental results are presented to confirm the theoretical findings.

Physical profile and chemical composition of a novel fabricated Kaolina as alternative growing media in aquaponics

The physical profile and chemical composition of growing media are vital in evaluating fish waste filtration efficiency and plant growth performance in aquaponics. The present study reported and compared the physical and chemical evaluation of the novel fabricated Kaolina, gravel, and commercially used lightweight expanded clay aggregate (LECA) as growing medias in aquaponics. Field emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FESEM-EDX) was utilized to analyze the growing media's chemical composition and structural characterization. The resultant effect of these growing medias on water quality and the growth performance of Clarias gariepinus and Lactuca sativa were also reported. Kaolina exhibited an excellent physical profile (42.95 ± 1.39%) in water absorption capacity as compared to LECA (35.90 ± 1.28%) and gravel (1.97 ± 0.25%), showing a significant difference at p < 0.05. The addition of 25% w/w Musa paradisiaca peel in the fabrication of Kaolina gives an added value of 88.0% of K and 100% of P elements, which show a significant difference (p < 0.05) compared to LECA. The results obtained reveal a better daily growth rate (DGR) and relative growth rate (RGR) of L. sativa at 0.57 ± 0.02 cm day−1 and 0.21 ± 0.00 g day−1, respectively. Results indicated that the porous structure of growing media could contribute to the high-water retention capability and slow the water desorption process. Hence, it could increase the ability of the growing media to hold nutrients for plant intake, resulting in higher removal percentage of nutrients in aquaponics system. Kaolina gives the highest nutrient removal percentage of TAN (96.86 ± 1.50%), NO2− (83.56 ± 1.27%), NO3−(77.55 ± 0.48%), and PO43− (79.46 ± 0.42%). The results also shown growing media has considerable impacts on nutrient removal, which contribute to the aquaponic productions.

Examining the Role of Clean Drinking Water Plants in Mitigating Drinking Water-Induced Morbidity

Access to clean drinking water is essentially required for human existence. It is a formalized fact that contaminated drinking water poses a serious threat to human life as the endowment of unpolluted drinking water to Pakistan’s inhabitants is the local government’s foremost duty. Thus, to conquer this purpose, the local government, with the coordination of the community development department (CD), fixed drinking water filtration plants at several places in Lahore. This study aimed to discover the health threats and health-associated costs endured by households in the target study areas and the effects of drinking water on infants’ and children’s health in areas having and lacking water filtration plants by employing the health lifestyle model. Moreover, this study compared waterborne disease incidence in households in targeted areas with and without local government filtration plants. For this purpose, a multistage random sampling technique was employed to collect the data from 300 households residing at different locations in Pakistan. This study revealed that people who make life choices to drink filtration plants’ water installed by the local government are less likely to contract waterborne diseases. Besides, class circumstances such as the size of the family, education of the family head, and plant water usage are highly correlated to the quality and use of drinking water and, ultimately, to the health-associated outcomes by improving a healthy lifestyle. In contrast, the age of the household head was found to be insignificant in making choices regarding drinking water choices and reducing waterborne illness. The more the education of the family head, the fewer family members found to indulge in practices for using plant water. Thus, infants/children and other people are less likely to contract waterborne incidents in areas equipped with these filtration plants. Moreover, the probability of contracting waterborne illness is higher in males than in females in areas lacking filtration plants.

Allergy Diagnostics 2021

Allergic diseases are among the most common diseases worldwide. For appropriate management knowledge of the allergy trigger is crucial. The clinical picture of allergic diseases is diverse and correct diagnosis is often a challenge. The allergist needs to distinguish intolerances from allergies and infectious diseases from non-infectious triggers. Test results have to be interpreted accordingly to differentiate sensitizations from allergies. In this review current state of the art diagnostic measures to diagnose type I and type IV allergies are described and discussed.Immediate type allergies such as allergic rhinoconjunctivitis, asthma and anaphylaxis are mediated by allergen-specific IgE antibodies detectable both in serum and tissue. Typical triggers are pollen, mites, animal epithelia, food, insect toxins and pharmaceuticals. In everyday practice, diagnostics are based on three complementary pillars: the allergy-specific anamnesis as a prerequisite of correct interpretation of subsequent diagnostic tests like skin testing and serological immunoglobulin detection. These can be supplemented as required and available by provocation tests to prove clinical reactivity and cellular assays to demonstrate the cellular immune response.Type IV allergic reactions are mediated by T cells causing contact allergy with a local eczematous reaction with a latency of several hours to days. Some 3,500 triggers, often from occupational environment, are known; e. g., nickel, chromium, cobalt, fragrances, rubber, plastics, preservatives, dyes, neomycin, benzocaine, sulfonamides, quinidine, wool wax, perubalsam, eye therapeutics, light filter substances, disinfectants, pesticides, technical oils or plants. Diagnosis of contact allergy combines the history of cutaneous exposure with associated symptoms and patch testing, with detection of a late phase clinical reaction after 6 to 48, up to a maximum of 96 hours after antigen contact.

Analysis of particle size distribution in municipal wastewaters

Innovative membrane filtration plants for municipal wastewaters are being developed and need the support of reliable filtration models in the designing phase. In the past, semi-empirical filtration models for membrane processes have been proposed. At present, the most prominent works point out the importance of particle poly-dispersity in the development of reliable models but fail into the implementation of probability density functions (PDFs) capable of an accurate fitting of the experimental particle size distribution (PSD). We report the experimental PSDs of two different municipal wastewater samples, obtained through the laser diffraction technique. The experimental results show that the laser diffraction technique can characterize wastewater particle dimensions both in the colloidal and supra-colloidal regions. The experimental study is complemented by a comparative analysis in which many PDFs are used to fit the experimental PSDs through a least-squares approach. Some of these PDFs are proposed here for the first time to fit experimental wastewater PSDs. Among the PDFs considered for the statistical modeling, the three-parameter lognormal and the Burr PDFs are demonstrated to provide satisfactory fitting, whereas the other considered functions fail. This result is confirmed by the analysis of both the available wastewater samples. • Experimental data of particle size distribution in municipal wastewaters. • Experimental data from laser diffraction technique. • Fitting of probability density functions to experimental data through a least-squares approach. • Several probability density functions tested. • Burr and three-parameter lognormal densities capture well the experimental data.

정수장 침전슬러지 배출 성능향상을 위한 연구

The characteristics of sludge generated in the process of producing drinking water are closely related to the water purification process. However, sludge discharge and treatment facilities often tend to be treated as separate issues from the water purification process. The sludge accumulated inside the hopper is often not sufficiently discharged when the sludge draw-off valve is opened, and improvement studies have been conducted. In this study, the discharge flow characteristics of draw-off valves such as a gate valve, a full ball valve, and a segment ball valve have been predicted according to the opening degree by numerical methods, and the discharge flow characteristics have been analyzed for the actual valve operation time. Based on the method of the design of experiments, tests have been conducted for various valve operating conditions to find the optimal operating conditions, and the improvement effect has been analyzed through repeated tests in a water purification plant.

Drugs of abuse in tap water from eight European countries: Determination by use of supramolecular solvents and tentative evaluation of risks to human health.

Recent research findings have confirmed the presence of illicit drugs in tap water from some European Union (UE) member states. Contaminants in tap water come directly from drinking water sources such as rivers or lakes owing to inefficient removal at wastewater treatment and water purification plants. This work was aimed at setting a starting point for assessing the health risks of exposure to twelve drugs of abuse through consumption of tap water in the European population. For this purpose, a method using supramolecular solvents (SUPRAS) was developed to extract drugs in the opioid, amphetamine, cocaine and cannabinoid groups from tap water for their determination by liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 119 tap water samples were collected from eight EU countries for analysis. Seven drugs were found at concentrations from 0.3 to 340ng/L in 72 of the samples (60.5%). The mean exposure to the drugs through consumption of tap water was calculated to be 0.0064-3.531ng/kg·day for adults and 0.0247-6.7580ng/kg·day for children, whereas that resulting from dermal contact was estimated to be 4-7 orders of magnitude lower. Exposure values were compared with the minimum required performance levels (MRPL) for the drugs in urine set by the World Anti-Doping Agency (WADA). Based on the results, a need clearly exists for further research into the adverse effects on health of inadvertent, sustained exposure to low doses of drugs of abuse.