Upflow Anaerobic Hybrid Research Articles

Hybrid bioreactor built-in with fixed bio-carriers for denitrification with low C/N ratio: Hydrodynamic optimization and microbial divergence

Hydrodynamics played an important role in the design and operation of bioreactors for wastewater treatment. In this work, an up-flow anaerobic hybrid bioreactor built-in with fixed bio-carriers was designed and optimized using computational fluid dynamics (CFD) simulation. The results indicated that the flow regime involving with vortex and dead zone was greatly affected by the positions of water inlet and bio-carrier modules. The ideal hydraulic features were obtained when the water inlet and bio-carrier modules located 9 cm and 60 cm above the bottom of reactor. Using the optimum hybrid system for nitrogen removal from wastewater with low carbon-to-nitrogen ratio (C/N = 3), the denitrification efficiency could reach 80.9 ± 0.4%. Illumina sequencing of 16S rRNA gene amplicons revealed that the microbial community divergence occurred among the biofilm on bio-carrier, the suspended sludge phase and the inoculum. Especially, the relative abundance of denitrifying genera Denitratisoma in the biofilm of bio-carrier reaches 5.73%, 6.2 times higher than that in the suspended sludge, implying the imbedded bio-carrier was conductive to enrich the specific denitrifiers to polish the denitrification performance with low carbon source. This work provided an effective method for the design optimization of bioreactor based on CFD simulation, and developed a hybrid reactor with fixed bio-carrier for nitrogen removal from wastewater with low C/N ratio.

Effects of temperature and HRT on biogas production in moving and fixed bed of a novel upflow anaerobic hybrid (UAHB) reactor

ABSTRACT The upflow anaerobic hybrid (UAHB) reactor combines the advantages of a upflow anaerobic sludge blanket (UASB-type) reactor and an anaerobic filter in a single compartment. A novel configuration of the UAHB reactor, composed of two three-phase separators (3PHS), was proposed to evaluate the biogas production in the moving and fixed bed in the treatment of synthetic sewage at a temperature range of 14–21 °C and hydraulic retention time (HRT) of 12, 10 and 8 h. The bench-scale reactor was operated in three different phases with organic loading rate (VOLR) of 0.6 (0.3–0.7), 0.7 ± 0.2, and 1.1 ± 0.1 kg COD m−3 d−1, respectively, for 225 days. The average removal efficiency of chemical oxygen demand (CODt) was 78 (42–89)%, and the total biogas yield was 3090 (1704–4782) mL d−1, with 66% of the lower 3PHS (moving bed) and 34% of the upper 3PHS (fixed bed). However, no significant difference was observed between the biogas yield on the 3PHS (p-value = 0.5048), thus confirming the influence of temperature in the biogas production. The average percentage of methane was 76 (60–82)% for both beds, and the filter media increased the production by 21%. Thus, it can be concluded that the fixed bed suppressed the instability of the moving bed regarding the biogas production and contributed to the final quality of the effluent.

Recovery of methane dissolved in the effluent of a novel upflow anaerobic hybrid reactor (UAHB) submitted to temperature variation

ABSTRACT Recent studies point out losses of 30–40% of the produced methane in the effluent of anaerobic reactors treating sewage, reducing the renewable energy potential and the environmental footprint. A novel bench-scale upflow anaerobic hybrid (UAHB) reactor combining a sludge blanket at the bottom and a filter media at the top, both with three-phase separators, was proposed to evaluate the recovery of dissolved methane. UAHB was operated with volumetric organic loading rate of 1.24 kg COD m−3 d−1 and hydraulic retention time of 8 h for 218 days to evaluate the influence of temperature (18°C, 23°C, and 28°C) in the methane dissolved in the effluent and collected from three-phase separators. Chemical oxygen demand (COD) and total suspended solids (TSS) removals efficiencies remained constant during the operation and equal to 90 and 95%, respectively, related to the activity of biomass retained in the filter media. Temperature increase influenced more the methane production in the sludge blanket rather than in the upper bed. The volume of recovered methane increased about 20% with the installation of the support media and the upper three-phase separator (3PHS). The loss of methane dissolved in the effluent was strongly influenced by the temperature, and higher with the decrease of this parameter. Non-statistically significant correlations were observed between the temperature and the methane production in the upper bed (p-value = 0.0943) and total (p-value = 0.0930). Thus, it can be concluded that the evaluated temperatures did not influence the global efficiency and the total methane yield of the UAHB reactor.

Evaluating the performance of anaerobic moving bed bioreactor and upflow anaerobic hybrid reactor for treating textile desizing wastewater

Performance and kinetic analysis of anaerobic moving bed bioreactor (AnMBBR) and upflow anaerobic hybrid reactor (UAHR) were investigated for the treatment of synthetic textile desizing wastewater (TDW) under organic loading rate (OLR) of 0.6–12 kgCOD/m3/day at thermophilic temperature (55 °C). The effects of increase in temperature (from 35 to 55 °C) on anaerobic treatment efficiency were studied. In the kinetic study for COD removal, first order substrate removal, Grau second order and modified Stover-Kincannon models were applied. By increasing temperature from 35 °C to 55 °C, COD removal, volumetric biogas production and methane content were increased 1.22, 2.58 and 1.08 times in AnMBBR. Whilst in the case of UAHR the increment for the aforementioned parameters were 1.10, 2.51 and 1.10 times, respectively. By increasing OLR from 0.6 to 6 kgCOD/m3/day, above 60% and 70% COD removal was observed, while the biogas increased from 0.12 to 0.97 L/L.day and 0.13–1.22 L/L.day for AnMBBR and UAHR, respectively. Up to an optimum OLR (6 and 8 kgCOD/m3/day for AnMBBR and UAHR) volumetric biogas production was also increased, simultaneously. Grau second order and modified Stover-Kincannon were found to be the best fit models (R2 =0.99). Biogas production and methane content in biogas were comparatively better in the case of real textile desizing wastewater due to lower sulfate concentration in the feed.

Treatment of slaughterhouse wastewater by upflow anaerobic hybrid reactor at pilot scale

Treatment of slaughterhouse wastewater by upflow anaerobic hybrid reactor at pilot scale

2-biofuels (H2 and CH4) production from anaerobic digestion of biscuits wastewater: Experimental study and techno-economic analysis

The up-flow anaerobic hybrid reactor (UAHR) was simultaneously employed for 2-biofuels (H2 and CH4) production from solely biscuits wastewater (BW) industry and a mixture of BW with domestic sewage (DS) at a mixing ratio of 3:1 respectively. The UAHR was fed with BW and operated at an organic loading rate (OLR) of 21.9 ± 1.7 gCOD/L/d., and hydraulic retention time (HRT) of 12.0 h. The module achieved volumetric hydrogen production rate (VHPR) and hydrogen yield (HY) of 0.95 ± 0.13 L/L reactor/d., and 118.6 ± 22.3 mL/gCODremoved respectively. A substantial deterioration in the H2 productivity was occurred after 94 days of continuous-feed operation, due to the inhibition effect of long-chain fatty acids (LCFAs). DS was integrated into the BW at mixing ratio of 3.0 (BW):1.0 (DS) where the UAHR was continuously operated at OLRs of 7.95 and 4.45 gCOD/L/d., achieving H2 and CH4 yields of 414.2 ± 38.1 and 318.5 ± 23.5 mL/gCOD removed, respectively. The payback periods for the production of biogas rich CH4 and H2 were 7.1 and 5.7 y respectively.

Performance evaluation and substrate removal kinetics in an up-flow anaerobic hybrid membrane bioreactor treating simulated high-strength wastewater

ABSTRACTThe prime objective of the present study is to evaluate the performance of novel up-flow anaerobic hybrid membrane bioreactor (An-HMBR) treating high-strength wastewater (synthetic) using polyurethane foam as filter media. Treatment efficiency of the entire An-HMBR varied from 88–97% corresponding to 0.67–3.90 d of hydraulic retention time (HRT) with organic loading rate of 6.4–1.06 kg COD m−3 d−1. The modified Stover–Kincannon model was the most appropriate model for An-HMBR and anaerobic hybrid bioreactor (excluding membrane). The suspended growth system in An-HMBR could be described by both modified Stover–Kincannon and Grau second order model. The attached growth system in An-HMBR followed conventional Monod’s kinetics. A novel combination of suspended, attached and membrane in single reactor increased the solid retention time to as high as 756 d at 3.9 d HRT which not only improved the COD removal efficiency but also enhanced the performance of the membrane.

Fate of parasites and pathogenic bacteria in an anaerobic hybrid reactor followed by downflow hanging sponge system treating domestic wastewater.

Treatment of domestic wastewater in a pilot-scale upflow anaerobic hybrid (AH) reactor (0.9 m(3)) in combination with downflow hanging sponge (DHS) system (1.3 m(3)) was investigated. The combined system was operated at a hydraulic retention time (HRT) of 6.0 h for AH and 3.2 h for DHS system. The total process achieved a substantial reduction of COD(total) resulting in an average effluent concentration of only 39 ± 12 mg/l. Moreover, 90 ± 7% of ammonia was eliminated in the DHS system. Nitrate and nitrite data revealed that 49 ± 3.2% of the ammonia removal occurred through nitrification process. The removal efficiency of total coliform (TC), fecal coliform (FC), and fecal streptococci (FS) was relatively low in the AH reactor. The major portion of TC, FC, and FS was removed in the DHS system resulting to an average count of 1.7 × 10(5) ± 1.1 × 10(2)/100 ml for TC, 7.1 × 10(4) ± 1.2 × 10(2)/100 ml for FC, and 7.5 × 10(4) ± 1.3 × 10(2)/100 ml for FS in the final effluent. Likely, the combined system was very efficient for the removal of protozoological species such as sarcodins (Entamoeba cysts), flagellates (Giardia cysts), and ciliates (Balantidium cysts). This was not the case for coccidia (Cryptosporidium oocysts), where 36.4 and 27.3% were detected in the effluent of AH and DHS system, respectively. Only 10% of intestinal nematode and cestode ova were recorded in the effluent of AH reactor and were completely removed in the DHS system.

A comprehensive review on utilization of wastewater from coffee processing.

The coffee processing industry is one of the major agro-based industries contributing significantly in international and national growth. Coffee fruits are processed by two methods, wet and dry process. In wet processing, coffee fruits generate enormous quantities of high strength wastewater requiring systematic treatment prior to disposal. Different method approach is used to treat the wastewater. Many researchers have attempted to assess the efficiency of batch aeration as posttreatment of coffee processing wastewater from an upflow anaerobic hybrid reactor (UAHR)-continuous and intermittent aeration system. However, wet coffee processing requires a high degree of processing know-how and produces large amounts of effluents which have the potential to damage the environment. Characteristics of wastewater from coffee processing has a biological oxygen demand (BOD) of up to 20,000 mg/l and a chemical oxygen demand (COD) of up to 50,000 mg/l as well as the acidity of pH below 4. In this review paper, various methods are discussed to treat coffee processing wastewaters; the constitution of wastewater is presented and the technical solutions for wastewater treatment are discussed.

High-rate anaerobic treatment of distillery spentwash using UASB and UAHR

Performance of upflow anaerobic sludge blanket and upflow anaerobic hybrid reactor in treatment of distillery spentwash was investigated under similar operating conditions. The reactors were initially fed with distillery spentwash having an average COD concentration of 1,22,000 mg L–1 with a HRT of 10 days and their performance was evaluated by operating at various HRTs viz., 10, 8, 7, 6, 5 and 4 days. Among the various HRTs, six days HRT was found to be ideal for the maximum reductions of COD, BOD and TS by 63.26, 70.80 and 57.20% respectively at OLR of 19.75 kg COD m–3 day–1 with UASB and 70.60, 78.50 and 62.45% at OLR of 19.25 kg COD m–3 day–1 with UAHR. The biogas yield of 0.30 and 0.31 m3 kg–1 COD removed was recorded in UASB and UAHR. Population of total anaerobic bacteria and methanogenic bacteria are also high in UAHR than in UASB. The study concludes that upflow anaerobic hybrid reactor is superior in reducing the pollution load of distillery spentwash as compared to UASB.

Comparative Study on Startup Performance of UAHR and UASB Reactors in Anaerobic Treatment of Distillery Spentwash

In this paper, startup performance of Upflow Anaerobic Hybrid Reactor and Upflow Anaerobic Sludge Blanket reactors in anaerobic treatment of distillery spentwash has been studied under identical conditions of operation. Various effluent characteristics like pH, Electrical Conductivity, Chemical Oxygen Demand, Biochemical Oxygen Demand and Total Solids and other process parameters like biogas production and methane per cent in biogas were studied until the attainment of steady state. The startup of the reactors has been completed and steady state condition attained on 25th day of reactor operation in UAHR and 34th day in UASB reactor. The treated effluent characteristics of both reactors were fairly steady after attaining the steady state condition. The pH of treated effluent during steady state condition was almost neutral for both reactors even though the influent had an acidic pH. The maximum COD, BOD and TS removal efficiencies were as high as 79.60%, 87.39% and 69.96% in UAHR as compared with UASB of 72.98%, 81.34% and 66.23%, respectively during the steady state period. The maximum volumetric gas production of 149 L m-3 produced more in UAHR than in UASB reactor during steady state condition. The population of total anaerobic bacteria and methanogenic bacteria also more as that of the other parameters in UAHR than in UASB reactor and it were 55.2 x 103 ml-1 and 40.0 x 102 ml-1 respectively in UAHR. It is found that from an overall assessment the UAHR has proved superior in its performance compared to the UASB reactor during the startup process.

An integrated treatment system for coffee processing wastewater using anaerobic and aerobic process

The experiment was conducted to develop an integrated treatment system for coffee processing wastewater (CPWW) through the combination of biomethanation with aeration and wetland plants treatment. The biomethanation was carried out at different hydraulic retention times (HRTs) using upflow anaerobic hybrid reactor (UAHR) and 18 h of HRT was found to be optimum. The maximum biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total solids (TS) reduction were 66.0%, 61.0% and 58.0%, respectively with organic loading rate of 9.55 kg m −3 day −1. The reduction of pollution load of the wastewater by microbial action augmented by aeration resulted in the reduction of electrical conductivity (EC), BOD, COD, and total solids (TS). Continuous aeration of wastewater resulted in maximum reduction of BOD (74.6%), COD (68.6%) and TS (49.3%). The wetland plant, Typha latifolia reduced 85.4% and 78.0% of BOD and COD, respectively in biomethanated cum aerated CPWW.

High-rate anaerobic degradation of 5 and 6 carbon sugars under thermophilic and mesophilic conditions

In this research paper, a comparison between thermophilic and mesophilic anaerobic degradation of a variety of the simple sugar components of carbohydrate rich biomass is presented. In order to investigate the degradability of these basic sugars, three synthetic sugar based influents were supplied to two high rate upflow anaerobic hybrid reactors (UAHR) operated at 37 °C (R1) and 55 °C (R2). These influent streams were: d-glucose/sucrose; l-arabinose/ d-xylose and l-rhamnose/ d-galacturonic acid. The reactors were challenged in terms of influent composition rather than loading rate and were therefore operated at a maximum volumetric loading rate (VLR) of 4.5 gCOD l −1 d −1 during stable reactor performance. It was found that a switch from a d-glucose/sucrose synthetic influent to an influent composed of l-arabinose/ d-xylose resulted in failure of the mesophilic reactor while the thermophilic UAHR was able to tolerate the change of sugar influent at an unchanged VLR of 4.5 gCOD l −1 d −1. A subsequent phasing-in approach was used to introduce new sugar influent streams and proved highly successful. The physiology of the biomass was assessed and it was noted that thermophilic anaerobic digestion (AD) involved the formation of acetate and H 2, implying the involvement of homoacetogenic bacteria, while mesophilic AD proceeded via the formation of other intermediates.

ESTUDO DO DESEMPENHO DE UM SISTEMA HÍBRIDO NO TRATAMENTO DE ESGOTO SANITÁRIO

Simplified sewage treatment systems are a low cost alternative for regions lacking in basic sanitation. This work studied the applicability of an anaerobic hybrid reactor in real scale, consisting by an inferior compartment that it contained biomass in suspension, complemented by an superior compartment filled by biomass fixed in support media; this configuration is known as upflow anaerobic hybrid reactor (AHR). Physical-chemical characteristics of influent varied along monitoring because of sewage contributions and flow peaks during the day. Organic matter removal in terms of Biochemica Oxigen Demand (BOD) and Chemical Oxigen Demand (COD) reached 76 and 90% respectively and total solids removal was of 98%. Other parameters didn’t show considerable variations during the study.

Application of high rate, high temperature anaerobic digestion to fungal thermozyme hydrolysates from carbohydrate wastes

The objective of this study was to examine the feasibility of using a two-step, fully biological and sustainable strategy for the treatment of carbohydrate rich wastes. The primary step in this strategy involves the application of thermostable enzymes produced by the thermophilic, aerobic fungus, Talaromyces emersonii, to carbohydrate wastes producing a liquid hydrolysate discharged at elevated temperatures. To assess the potential of thermophilic treatment of this hydrolysate, a comparative study of thermophilic and mesophilic digestion of four sugar rich thermozyme hydrolysate waste streams was conducted by operating two high rate upflow anaerobic hybrid reactors (UAHR) at 37 °C (R1) and 55 °C (R2). The operational performance of both reactors was monitored from start-up by assessing COD removal efficiencies, volatile fatty acid (VFA) discharge and % methane of the biogas produced. Rapid start-up of both R1 and R2 was achieved on an influent composed of the typical sugar components of the organic fraction of municipal solid waste (OFMSW). Both reactors were subsequently challenged in terms of volumetric loading rate (VLR) and it was found that a VLR of 9 gCOD l −1 d −1 at a hydraulic retention time (HRT) of 1 day severely affected the thermophilic reactor with instability characterised by a build up of volatile fatty acid (VFA) intermediates in the effluent. The influent to both reactors was changed to a simple glucose and sucrose-based influent supplied at a VLR of 4.5 gCOD l −1 d −1 and HRT of 2 days prior to the introduction of thermozyme hydrolysates. Four unique thermozyme hydrolysates were subsequently supplied to the reactors, each for a period of 10 HRTs. The applied hydrolysates were derived from apple pulp, bread, carob powder and cardboard, all of which were successfully and comparably converted by both reactors. The % total carbohydrate removal by both reactors was monitored during the application of the sugar rich thermozyme hydrolysates. This approach offers a sustainable technology for the treatment of carbohydrate rich wastes and highlights the potential of these wastes as substrates for the generation of second-generation biofuels.

Influence of media-packing ratio on performance of anaerobic hybrid reactors

In this study, the influence of media-packing ratio on the performances of anaerobic hybrid reactors (AHRs) at low, medium and high organic loading rates was evaluated by conducting COD profile, granulation and tracer studies. Four laboratory upflow anaerobic hybrid reactors, each with a total unpacked volume of 7.85 l, with varying packing depths, were operated at organic loading rates from 1 to 24 g COD/l d. The media-packing ratios were 75%, 60%, 40% and 20% of the total reactor height in the AHRs. Three types of soluble COD profiles along the reactor height were observed when the organic loading rate was gradually increased. When operated at 1 and 2 g COD/l d the COD profiles along the reactor height from bottom to top showed a plug-flow regime. From 4 to 12 g COD/l d the COD profiles were distorted in the reactors with 20%, 40% and 60% packing, while at 16 g COD/l d and above the COD profile indicated homogeneity in each reactor, suggesting a perfectly-mixed regime. The distorted COD profiles were considered to be caused by the non-ideal flow pattern prevalent in the reactors. The dead-space volume and the bypass flowrate due to short-circuiting were determined using the Cholette and Cloutier model. A `distortion index' (DI), which was calculated from the ratio of the average COD value of the sludge bed over the average COD value of the reactor, was used to describe distortion of the COD profile. The distortion index correlated well with the short-circuiting fraction.

Treatment characteristics of high strength fermentation wastewater consisting of high sulfate and ammonia by UAHB process

In this study, the formation process of granules and treatment characteristics were discussed for an Upflow Anaerobic Hybrid Blanket (UAHB) reactor, adding water absorbing polymer particles (WAP) for treating a fermentation process wastewater consisting of high sulfate and ammonia. Sulfide toxicity to methanogenic bacteria and the TOC/SO42− ratio that was usually used as an index of inhibition to methanogenesis were also examined. The results indicated that the granules could be developed in an UAHB process, in which a filter was installed in the upper part of reactor and WAP were also added into inoculum, for treating sulfide- and ammonia-rich wastewater, and inhibition caused by sulfide did not occurred when free hydrogen sulfide concentration was less than 200 mgl−1. Therefore, the UAHB process in the presence of adding WAP was shown to have a better stability for treating the refractory wastewater. The results also showed that total dissolved sulfide concentration had to be considered for inhibition assessment as well as the TOC/SO42− ratio.

Treatment characteristics of high strength fermentation wastewater consisting of high sulfate and ammonia by uahb process

In this study, the formation process of granules and treatment characteristics were discussed for an Upflow Anaerobic Hybrid Blanket (UAHB) reactor, adding water absorbing polymer particles (WAP) for treating a fermentation process wastewater consisting of high sulfate and ammonia. Sulfide toxicity to methanogenic bacteria and the TOC/SO42- ratio that was usually used as an index of inhibition to methanogenesis were also examined. The results indicated that the granules could be developed in an UAHB process, in which a filter was installed in the upper part of reactor and WAP were also added into inoculum, for treating sulfide- and ammonia-rich wastewater, and inhibition caused by sulfide did not occurred when free hydrogen sulfide concentration was less than 200 mgl−1. Therefore, the UAHB process in the presence of adding WAP was shown to have a better stability for treating the refractory wastewater. The results also showed that total dissolved sulfide concentration had to be considered for inhibition assessment as well as the TOC/SO42-ratio.

Effect of feed composition and upflow velocity on aggregate characteristics in anaerobic upflow reactors

Two upflow anaerobic hybrid reactors treated lactose and a mixture of ethanol, propionate and butyrate, respectively, at a volumetric loading rate of 3.7 kg chemical oxygen demand (COD) m−3day−1, a hydraulic retention time of 5 days and a liquid upflow velocity of 0.01 m/h. Under steady-state conditions, the lactose-fed sludge had much higher (20%–100%) specific methanogenic conversion rates than the volatile-fatty acid␣(VFA)/ethanol-fed sludge for all substrates tested, including VFA. In both reactors, a flocculant sludge developed, although a much higher content of extracellular polysaccharide was measured in the lactose-fed sludge [1900 μg compared to 305 μg uronic acid/g volatile suspended solids (VSS)]. When the liquid upflow velocity of a third, VFA/ethanol-fed reactor was increased to 0.5 m/h, granulation of the sludge occurred, accompanied by a large increase (200%–500%) in the specific methanogenic conversion rates for the syntrophic and methanogenic substrates studied. Granulation reduced the susceptibility of the sludge to flotation. Glucose was degraded at a high rate (100 mg glucose gVSS−1h−1) by the sludge from the third reactor, despite not having been exposed to a sugar-containing influent for 563␣days.

Anaerobic treatment of thermal sludge conditioning liquor with granular sludge

ABSTRACT: Thermal sludge conditioning liquor was successfully treated by a pilot‐scale upflow anaerobic hybrid system with an effective volume of 10.4 m3. The reactor was similar to the HYAN reactor in Lakeview but without a recirculation system. A gas‐solid separator was installed above a filter packed with polypropylene pall rings. The organic loading rate was increased stepwise to 30 kg chemical oxygen demand (COD)/m3 · d. The hydraulic retention time was only 6 hours at the target loading rate. More than 70% of soluble COD in the influent was removed, even at an organic loading as high as 30 kg COD/m3 · d. Soluble 5‐day biochemical oxygen demand (BOD5) removal efficiency at the loading rate exceeded 95%. Volatile fatty acids concentration in the effluent was consistently less than 60 mg/L after the day when stable treatment had been obtained. The methane production fluctuated between 0.3 and 0.4 L/g COD removed. Solids production including effluent suspended solids (SS) was between 0.16 and 0.24 kg SS/kg COD removed. The inside of the reactor consisted of two zones, a sludge blanket zone with less than 1% solids concentration and a sludge bed zone with 47% solids concentration. Although the reactor was seeded with an anaerobically digested sludge, granular sludge was produced in the reactor. The ratio of granules to the solids remaining in the reactor increased to approximately 70% at the end of the experiments. Most of the granules had diameters of less than 1 mm and their settling velocity was 0.6 cm/s or more. The granules were composed of bacteria like Methanothrix according to SEM observations. The methane production rate was between 0.8 and 1.1 kg methane as COD/kg SS · d in an acetate solution. According to substrates distribution in the reactor and tracer tests, the bed zone in the reactor worked similarly to a continuously stirred tank reactor (CSTR). Evaluation of soluble COD removal rates in the reactor indicated that the rate could be simulated by a Monod type reaction.