Anaerobic Baffled Reactor Research Articles

Iron-modified biochar boosts anaerobic digestion of sulfamethoxazole pharmaceutical wastewater: Performance and microbial mechanism

The accumulation of volatile fatty acids (VFAs) caused by antibiotic inhibition significantly reduces the treatment efficiency of sulfamethoxazole (SMX) wastewater. Few studies have been conducted to study the VFAs gradient metabolism of extracellular respiratory bacteria (ERB) and hydrogenotrophic methanogen (HM) under high-concentration sulfonamide antibiotics (SAs). And the effects of iron-modified biochar on antibiotics are unknown. Here, the iron-modified biochar was added to an anaerobic baffled reactor (ABR) to intensify the anaerobic digestion of SMX pharmaceutical wastewater. The results demonstrated that ERB and HM were developed after adding iron-modified biochar, promoting the degradation of butyric, propionic and acetic acids. The content of VFAs reduced from 1166.0 mg L−1 to 291.5 mg L−1. Therefore, chemical oxygen demand (COD) and SMX removal efficiency were improved by 22.76% and 36.51%, and methane production was enhanced by 6.19 times. Furthermore, the antibiotic resistance genes (ARGs) such as sul1, sul2, intl1 in effluent were decreased by 39.31%, 43.33%, 44.11%. AUTHM297 (18.07%), Methanobacterium (16.05%), Geobacter (6.05%) were enriched after enhancement. The net energy after enhancement was 0.7122 kWh m−3. These results confirmed that ERB and HM were enriched via iron-modified biochar to achieve high efficiency of SMX wastewater treatment.

Greenhouse gas reduction of co-benefit-type wastewater treatment system for fish-processing industry: A real-scale case study in Indonesia

This study examined the application of co-benefit-type wastewater treatment technology in the fish-processing industry. Given that there was a dearth of information on fish-processing industrial wastewater in Indonesia, site surveys were conducted. For the entire fish-processing industry throughout the country, the dissemination rate of wastewater treatment facilities was less than 50%. Using a co-benefit approach, a real-scale swim-bed technology (SBT) and a system combining an anaerobic baffled reactor (ABR) with SBT (ABR–SBT) were installed in a fishmeal processing factory in Bali, Indonesia, and the wastewater system process performance was evaluated. In a business-as-usual scenario, the estimated chemical oxygen demand load and greenhouse gas (GHG) emissions from wastewater from the Indonesian fish-processing industry were 33 000 tons per year and 220 000 tons of equivalent CO2 per year, respectively. On the other hand, the GHG emissions in the co-benefit scenarios of the SBT system and ABR–SBT system were 98 149 and 26 720 tons per year, respectively. Therefore, introducing co-benefit-type wastewater treatment to Indonesia’s fish-processing industry would significantly reduce pollution loads and GHG emissions.

Pretreatment of septic tank wastewater by packed anaerobic baffled reactor: Pollutant degradation and microbial community succession in different compartments

Anaerobic baffled reactor (ABR) is widely used in rural sewage treatment due to its unique structure, strong impact load resistance, and low energy consumption. However, there is a lack of research on pollutant degradation patterns and microbial community succession patterns in each compartment of ABR. In this study, a packed anaerobic baffled reactor (PABR) was constructed. The effects of T and HRT on the pollutant removal performance of PABR were investigated, and the pollutant degradation and microbial community succession in different compartments of PABR were studied. The results show that the removal rates of COD, NH4+-N, and TN of PABR can reach 85.54 ± 1.08%, 16.94 ± 1.01%, and 5.64 ± 1.18% respectively, and PABR has a good pollutant removal effect. With the extension of HRT, the COD removal rate of PABR increases steadily, and the NH4+-N and TN removal rate of PABR increases to a certain extent. The recommended HRT is 72 h. T has a significant impact on the COD removal effect of PABR. The increase of T in a certain range is conducive to the removal of pollutants by PABR. The COD removal rate of PABR decreases gradually along the flow direction, and the removal of organic matter is mainly concentrated in the first compartment. PABR has good removal capacity for CODss and better nitrogen removal capacity compared with traditional ABR. The richness and diversity of the microbial community in PABR increased gradually along the flow direction. The bacterial species in each compartment were similar but the proportion was different, showing the characteristics of multi-stage and separated phase operation. This study provides a new reference for the application of ABR in rural sewage treatment.

Effects of various COD/NO ratios on NOx removal performance and microbial communities in a BTF−ABR integrated system

In this study, we investigated the removal performance of NOx and stability of the biotrickling filter−anaerobic baffled reactor (BTF−ABR) integrated system at various chemical oxygen demand (COD)/NO ratios (12.18, 6.71, and 4.63 in stages 1, 2, and 3, respectively) under 3.5% O2 and 50 ± 0.5 °C conditions for the first time. The results showed that the maximum elimination capacity of NOx was 4.46, 8.16, and 11.58 g/(m3·h) in stages 1, 2, and 3, respectively. The minimum operating cost in terms of glucose was 4.79 g of glucose/g of NO. However, a COD/NO ratio of 12.18 resulted in a wastage of carbon sources, while a COD/NO ratio of 4.63 led to about 20 mg/m3 N2O emission at the end of the study. Highly bacteria diversity and positive co-occurrence networks at the COD/NO ratio of 6.71 were the main reasons for no intermediate accumulation or N2O emission. Analysis of real-time polymerase chain reaction (PCR) indicated that nirS and norB were more sensitive to the changes in the COD/NO ratios than other denitrifying genes, and the denitrifiers with nirS filled more ecological niches as the NOx increased. Furthermore, although the decrease in COD/NO ratio significantly impacted the microbial community structure, the NOx RE was stabilized at over 90% because the micro-aerobic environment produced by ABR combined highly diverse microbes and functions in BTF, as well as the coordinated expression of denitrifying genes. Achieving efficient, stable, and low-cost denitrification is feasible in this BTF−ABR integrated system.

The potential of decentralised wastewater treatment in urban and rural sanitation in South Africa: lessons learnt from a demonstration-scale DEWATS within the eThekwini Municipality

The design principles of decentralised wastewater treatment systems (DEWATS) make them a practical sanitation option for municipalities to adopt in fast-growing cities in South Africa. Since 2014, a demonstration-scale DEWATS with a modular design consisting of a settler, anaerobic baffled reactor (ABR), anaerobic filter (AF), vertical down-flow constructed wetland (VFCW) and horizontal flow constructed wetland (HFCW) has been in operation in eThekwini. A performance evaluation after the long-term operation was undertaken in 2019 by comparing the final effluent with national regulatory requirements. Despite limitations in characterising the raw wastewater, a comparison of the settler and final effluent quality indicated high (≥ 85%) removal efficiencies of total chemical oxygen demand (CODt), ammonium-N (NH4-N) and orthophosphate-P (PO4-P), 75% removal of total suspended solids (TSS) and 83.3% log10 removal of Escherichia coli. Lack of exogenous and endogenous carbon and high dissolved oxygen (DO) concentrations (> 0.5 mg‧L−1) inhibited denitrification in the HFCW, resulting in 12.5% of the effluent samples achieving compliance for nitrate-N (NO3-N). Moreover, mixed aggregate media and low residence times in the HFCW may have also contributed to poor NO3-N removal. During the COVID-19 lockdown, an unexpected shutdown and subsequent resumption of flow to the DEWATS indicated a 16-week recovery time based on achieving full nitrification in the HFCW. Although design modifications are necessary for the HFCW, the installation of urine diversion flushing toilets at the household will reduce the nutrient loading to the DEWATS and potentially achieve fully compliant effluent. Alternatively, the application of two-stage vertical flow constructed wetlands to improve denitrification should also be explored in the South African context. With an improved design, DEWATS has the potential to fill the gap in both urban and rural sanitation in South Africa, where waterborne sanitation is still desired but connections to conventional wastewater treatment works (WWTWs) are not possible.

Fate of ofloxacin in rural wastewater treatment facility: Removal performance, pathways and microbial characteristics

Ofloxacin (OFL) with high biological activity and antimicrobial degradation is a kind of the typical high concentration and environmental risk antibiotics in rural sewage. In this paper, a combined rural sewage treatment facility based on anaerobic baffled reactor and integrated constructed wetlands was built and the removal performance, pathway and mechanism for OFL and conventional pollutants were evaluated. Results showed that the OFL and TN removal efficiency achieved 91.78 ± 3.93 % and 91.44 ± 4.15 %, respectively. Sludge adsorption was the primary removal pathway of OFL. Metagenomics analysis revealed that Proteobacteria was crucial in OFL removal. baca was the dominated antibiotic resistance genes (ARGs). Moreover, carbon metabolism with a high abundance was conductive to detoxify OFL to enhance system stability and performance. Co-occurrence network analysis further elucidated that mutualism was the main survival mode of microorganisms. Denitrifers Microbacterium, Geobacter and Ignavibacterium, were the host of ARGs and participated in OFL biodegradation.

Feasibility Study of Anaerobic Baffled Reactor Coupled with Anaerobic Filter Followed by Membrane Filtration for Wastewater Treatment.

The performance of a Decentralized Wastewater Treatment System (DWTS) comprising an Anaerobic Baffled Reactor (ABR) and an Anaerobic Filter (AF) and Membrane Filtration (MF) module was studied for domestic wastewater treatment. The efficiency of the system was evaluated by running ABR at four different HRTs (14, 12, 10, and 8 h) resulting in COD removal efficiencies of 74, 72, 69, and 65%, respectively. The performance of AF using four different filtration media, i.e., PVC pipe (25 mm), PVC pipe (20 mm), PVC pipe (15 mm), and Kaldnes K3, was determined at optimized HRT (12 h). Among all the filtration media tested, the highest performance efficiency of the system was found with the PVC pipe (20 mm), which showed COD, TP, and TKN removal of 79, 32, and 63%, respectively. The efficacy of the system was proven via significant COD and turbidity removal of 94.6 and 87.2%, respectively, by the combined system.

Performance Evaluation of Modified Anaerobic Baffled Reactor (MABR) Treating High Strength Wastewater

Performance Evaluation of Modified Anaerobic Baffled Reactor (MABR) Treating High Strength Wastewater

Swine wastewater treatment using pilot-scale siphon-driven agitation anaerobic baffled reactor

Swine wastewater treatment using pilot-scale siphon-driven agitation anaerobic baffled reactor

Effect of Treated Wastewater from Anaerobic Digester Coupled with Anaerobic Baffled Reactor as Fertigation on Soil Nutrient Residues, Growth and Yield of Maize Plants

Water scarcity, wastewater management and growing food demand associated with global population increase, are among the drivers cited for water reuse in agriculture. The current study intends to contribute on the influence of treated wastewater from the anaerobic digester coupled with anaerobic baffled reactor (ABR) as a fertigation on soil nutrient residues, growth and yield attributes of maize plants by using surface drip irrigation system to apply the treated wastewater. The experiment consisted of experimental plots irrigated with treated wastewater and control plots irrigated with tap water; all with three replications. The treated wastewater was lightly alkaline with pH of 7.8±0.2 and high concentration of nutrients than tap water, but were within the acceptable levels. Fertigation with treated wastewater improved soil fertility evidenced by significant improvement (P≤0.05) in plant height, leaf area Index (LAI) and maize yield. Plant height was 1.5 times taller and LAI was about 2.5 times more in treatment than in control plots. Yield attributes in experimental plots including number of grains per cob, (97±11.3); weight of grains per cob, (80.7±7.9 g); mass of 100 grains, (35.0±3.5 g), and grain yield, (745.8±62.9 Kg/ha) were significantly higher (P≤0.05) compared to their counterpart control plots. The grain yield in experimental plots was about 37% higher than the yield in control plots. Therefore, fertigation with treated wastewater from the anaerobic digester coupled with ABR improves maize yield and is advisable in areas with water scarcity.

Municipal wastewater treatment with corrugated PVC carrier anaerobic baffled reactor.

The anaerobic baffled reactor (ABR) is a promising solution for decentralized wastewater treatment due to its low operation cost as compared to the activated sludge process, but it requires comparatively higher hydraulic retention time (HRT). This ultimately increases land requirement, capital and construction cost of treatment plant. This study investigates performance of ABR using polyvinyl chloride (PVC) corrugated pipe as carrier media to improve biomass retention capacity and treatment performance of reactor with the aim to reduce HRT. Comparative performance of two ABRs with and without carrier media was analyzed under mesophilic conditions (35 ± 1 °C) for organics and total suspended solids (TSS) removal at HRTs of 24, 18, 12, 8, 6 and 4 h. Results showed that at HRTs of 24-08 h, the organics removal performance of the carrier anaerobic baffled reactor (CABR) was better than ABR and was in the range of 77-81% for CABR as compared to 64-70% for ABR. However, on further decrease in HRT to 6 h, CABR sustained the treatment with organics removal of 80%, while ABR performance reduced to 58%, creating a performance difference of 38%. Average total suspended solids (TSS) removal was in the range of 76-83% at all HRTs for both reactors. Therefore, this study identified CABR with PVC carrier media as an effective low-HRT reactor for organics and SS removal with less land area requirement.

Anaerobic Digestion of Synthetic Municipal Wastewater (MWW) in a Periodic Anaerobic Baffled Reactor (PABR): Assessment of COD Removal and Biogas Production

The benchmark approach for municipal wastewater treatment is based on biological oxidation. Due to high energy consumption, alternative treatment schemes are proposed, among which anaerobic digestion is the most promising. In this work, the direct anaerobic digestion of municipal wastewater in a high-rate system is examined. The reactor utilized for the study is the periodic anaerobic baffled reactor (PABR). Two distinct experimental cycles were conducted, during which the operational parameters of the PABR were consecutively modified: in the first cycle, six phases were conducted where the hydraulic retention time (HRT) varied from 10 to 1 days, the period T between 2.5 days and 0.25, while the OLR remained constant at values near 1.0 gsCOD/L/d. During the second cycle, four distinct phases were conducted with no switching imposed. The HRT varied from 4 to 1 d. The last experimental phase of both cycles was the most significant, due to feedstock resemblance to raw wastewater. The biogas and the biomethane production rates reached 66.8 L/d and 41.1 L/d, respectively, while the COD reduction rate reached 73.7%. Conclusively, the PABR is a high-rate AD system, capable of treating MWW under extreme operational conditions.

Performance of the anaerobic baffled reactor for primary treatment of rural domestic wastewater in Iraq

Abstract The purpose of this work is to evaluate the performance of the anaerobic baffled reactor (ABR) for on-site primary treatment of domestic wastewater in rural areas of Iraq. The performance of the three-chamber ABR has been investigated at four different hydraulic retention times (HRTs) ranging from 6 to 36 h. The results showed that the chemical oxygen demand (COD) removal efficiency is enhanced with increasing HRT, where it was recorded at 75, 71, 63, and 56% removals rate of COD at HRTs of 36, 24, 12, and 6 h, respectively. The mean steady-state removals of total suspended solids are 91, 78, 72, and 67% at HRTs of 36, 24, 12, and 6 h, respectively. Also, it was shown that there was low-nutrients removal within the ABR. Consequently, the effluent ABR wastewater needs to be post-treated before being discharged to the receiving water bodies. In general, it is concluded that the ABR could introduce a solution for on-site primary treatment of domestic wastewater in rural communities in Iraq.

Performance Effectiveness of Communal Wastewater Treatment Plant as an Effort to Control Pollution of the Gajah Wong River, Yogyakarta

The Gajah Wong River receives wastewater from the high population of Sleman Regency, including agricultural activities and home industries that contain organic pollutants. High organic pollutants cause dissolved oxygen depletion in waters that can threaten the lives of various aquatic biota. The construction of a communal wastewater treatment plant (WWTP) for handling domestic wastewater is an effort to control river pollution. The effectiveness of WWTP performance based on key parameters is continuously monitored, which is the purpose of this research. Surveys on 4 (four) communal WWTPs (Ngudi Mulyo, Wahana Bina Lingkungan, Tirto Mili, and Karya Asri Ambarukmo) were conducted in February – April 2021 with the key parameters observed were pH, BOD5, COD, and NH3. Sampling wastewater by grab sampling at each inlet and outlet of the WWTP using ABR (Anaerobic Baffled Reactor) and RBC (Rotating Biological Contactor) technology 6 times. The results provide an overview of the quality characteristics of wastewater that has been treated (outlet) at the Ngundi Mulyo WWTP (NH3 16.55 mg/L, BOD5 32.53 mg/L, COD 213.52 mg/L, pH 5) Wahana Bina Lingkungan (NH3 29.85 mg/L, BOD5 262.36 mg/L, pH 6-7), Tirto Mulyo (NH3 20.42 mg/L, BOD5 66.67 mg/L, COD 248.7 mg/L, pH 6-7) and Karya Asri Ambarukmo (NH3 21.60 mg/L, BOD5 252.64 mg/L, pH 6-7). These results reveal that the performance of the four WWTPs is still low and has not been effective in reducing COD and NH3 parameters, except that BOD5 reaches the required quality standard, and the processed wastewater still has the potential to reduce the water quality of the Gajah Wong River. This result is also a signal for WWTP managers to improve the processing process in each of these WWTPs.

Characteristic Analysis on Temporal Evolution of Granulation in a Modified Anaerobic Digestion System

In the present study, the surface morphology, particle size distribution, sedimentation performance, and fractal characteristics of sludge flocs in a modified anaerobic baffled reactor (mABR) during start-up were analyzed by digital image analysis technology. The results showed that the special structure of mABR enabled successful start-up and granular sludge formation in a relatively short time. After the granular sludge was mature, the COD removal rate could quickly recover to the level before the change in organic loading rates (OLRs) within just six days, increasing from the lowest value of 76.8% to 80.2%, which indicated that the granular sludge could maintain a relatively stable micro-environment and make the metabolic process continue when the influent conditions changed suddenly. It was expected that this paper would be helpful for researchers to further develop a unified theory for anaerobic granulation and technology for expediting the formation of mABR granules.

The Dynamic Shift of Bacterial Communities in Hybrid Anaerobic Baffled Reactor (ABR)—Aerobic Granules Process for Berberine Pharmaceutical Wastewater Treatment

Because of its anticancer, anti-inflammatory, and antibiotic properties, berberine has been used extensively in medication. The extensive production of berberine results in the generation of wastewater containing concentrated residual berberine. However, to date, limited related studies on the biological treatment of berberine wastewaters have been carried out. A lab-scale anaerobic baffled reactor (ABR)–aerobic granular sludge (AGS) process was developed for berberine removal from synthetic wastewater. The system showed effective removal of the berberine. In order to better understand the roles of the bacterial community, the ABR–aerobic granular sludge system was operated in the state with the highest BBR removal rate in this study. The bacterial community dynamics were studied using the 16S rDNA clone library. The results showed that the hybrid ABR-AGS process achieved 92.2% and 94.8% overall removals of berberine and COD, respectively. Bacterium was dominant species in ABR, while the CFB group bacteria and Betaproteobacteria were dominant species in AGS process. The uncultured bacterium clone B135, Bacillus endophyticus strain a125, uncultured bacterium mle1-42, uncultured bacterium clone OP10D15, and uncultured bacterium clone B21.29F54 in ABR, and uncultured bacterium clone F54, uncultured bacterium clone ZBAF1-105, uncultured bacterium clone SS-9, and uncultured bacterium clone B13 in AGS process were identified as functional species in the biodegradation of berberine and/or its metabolites. Both anaerobic and aerobic bacterial communities could adapt appropriately to different berberine selection pressures because the functional species’ identical functions ensured comparable pollutant removal performances. The information provided in this study may help with future research in gaining a better understanding of berberine biodegradation.

Start-up of the combined anaerobic ammonium oxidation and solid phase denitrification process and microbial characterization analysis

To improve the nitrogen removal performance of anaerobic ammonia oxidation (anammox)-based processes, a modified anaerobic baffled reactor (ABR) equipped with a packed bed of poly-3-hydroxybutyrate-cohyroxyvelate (PHBV) was employed to start up the combined anammox and solid phase denitrification (SPD) process for the treatment of nitrogen-rich wastewater. Results showed that a stable removal of total inorganic nitrogen (TIN) of 98.5 % was achieved with a nitrogen loading rate of 0.46 kg·(m3·d)−1, decreasing the effluent TIN concentration to <2 mg·L−1. Throughout the operation period of 180 days, sludge granulation in three compartments of the ABR was promoted by a stepwise decrease in the hydraulic retention time. The anammox reaction and endogenous denitrification mainly occurred in the first two compartments with inorganic feeding and contributed >86 % of TIN removal. 16S rRNA gene amplicon sequencing showed that anammox communities, dominated by genera Candidatus Kuenenia and Candidatus Brocadiaceae, were enriched in granular sludges with symbiotic heterotrophic bacteria. Co-cultures of hydrolytic bacteria (Burkholderiales, Kapabacteriales, and Clostridium-sensu-stricto-7) and denitrifying bacteria (Comamonadaceae, Rhodocyclaceae, and Denitratisoma) were detected within the biofilm on the surface of PHBV particles. PHBV hydrolysate input effectively drove heterotrophic denitrification in the successive compartment and increased the complexity of microbial co-occurrence networks. These findings provide insight into the synergistic mechanisms between anammox and SPD and present a feasible combined process application for advanced biological nitrogen removal.

Evaluation of an anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system in treatment of black wastewater from a closed recirculating aquaculture system

This study focused on evaluating the nitrogen and solids removal performance of a laboratory-scale anaerobic baffled reactor (ABR) – downflow hanging sponge (DHS) system for treating black wastewater from a closed recirculating aquaculture system (RAS) under a salinity of 15‰. The system was investigated under a controlled temperature (35 °C) with total organic carbon/total nitrogen (TOC/TN) ratios of 1.8, 2.5, 0.3, and 3.0, which corresponded to Phases 1, 2, 3, and 4, respectively, for 500 days. The ABR achieved a nitrate removal efficiency of 95–99 % at TOC/TN ratios higher than 1.8. The nitrate removal efficiency significantly decreased from 98 % to 12 % when the TOC/TN ratio decreased from 3.0 to 0.3. The highest TN removal efficiency (94 ± 4 %) was achieved with a TOC/TN ratio of 3.0. The ABR could remove 97 ± 6 % of the suspended solids during the entire experimental period. The DHS reactor achieved a nitrification efficiency of 70 % with short hydraulic retention times of 0.11–0.28 min. Total ammonia nitrogen in the DHS effluent was less than 1.0 mg N/L in the stable condition. The denitrifying Thauera genera predominant in the ABR reactor led to a high degree of denitrification. Methanogenic organisms such as Methanobacterium and Methanosaeta contributed to methane production of 0.8 ± 0.4 L/d in the ABR at a TOC/TN ratio of 3.0. Microbial community structure analysis showed that nitrifying microorganisms, such as Nitrosomonas, Nitrospira, and Candidatus Nitrosopumilus, were detected in the DHS-retained sludge. These results indicate that the ABR–DHS system evaluated could be applied for the removal of nitrogen and solids from RAS derived black wastewater to meet the water quality level needed for production-scale RAS.

Small-Scale Operation of an Integrated Anaerobic Baffled Reactor and Biofilter: Factors Affecting Its Performance

Small-Scale Operation of an Integrated Anaerobic Baffled Reactor and Biofilter: Factors Affecting Its Performance

Biohydrogen production from brewery wastewater in an Anaerobic baffled reactor. A preliminary techno-economic evaluation

The study aimed to optimise the dark fermentation (DF) process for producing biohydrogen from brewery effluent using an anaerobic baffled reactor (ABR). Temperature, pH, and retention time were considered as the operating parameters. The output parameters were hydrogen production rate (HPR), chemical oxygen demand (COD) removal efficiency, and total volatile fatty acids (tVFA). The maximum HPR was 18.16 mL/h, and the lowest was 0.94 mL/h, all at 35°C, even though the operating pH in both cases was different, pH 5 and 2.5, respectively. Under pH conditions ranging between 4 and 7, high COD removal was more prominent, with 60.81% COD removal found at a pH of 6.5. pH played a pivotal role in the process's general performance; at the same retention time (10.0 h) and temperature (35 ºC), a hydrogen yield of 2.77 mmol/gCOD at pH of 2.5 and 30.98 mmol/gCOD at pH of 5 were recorded. The Design-Expert software was used to design the experimental runs. The model produced predicted an optimum operating temperature of 36℃, pH of 5.6, retention time of 10.2 h and 17.05 mL/h HPR, 49.88% COD removal efficiency and 683 mg/L VFA concentration in the effluent were predicted. A techno-economic evaluation was conducted to assess the feasibility of scaling up the dark fermentation of brewery wastewater at the optimum conditions specified in this research. A 40 million litre per annum dark fermentation system was preliminarily designed, and about 5.5 GL/yr of hydrogen was expected under normalised conditions. The hydrogen cost was US$ 7.35/kg, with a payback period of 5.9 years and a return on the interest of 25.59%.