Treatment of Benzene and n-Hexane Mixtures in Trickle-Bed Air Biofilters

ABSTRACT

Trickle-bed air biofilters (TBABs) are suitable for treatment of hydrophilic volatile organic compounds, but they pose a challenge for hydrophobic compounds. Three laboratory-scale TBABs were used for the treatment of an airstream contaminated with different ratios of n-hexane and benzene mixtures. The ratios studied were 1:1, 2:1, and 1:3 n-hexane:benzene by volume. Each TBAB was operated at a pH of 4 and a temperature of 20 °C. The use of acidic-buffered nutrient solution was targeted for changing the microorganism consortium to fungi as the main biodegradation element. The experimental plan was designed to investigate the long-term performance of the TBABs with an emphasis on different mixture loading rates, removal efficiency with TBAB depth, volatile suspended solids, and carbon mass balance closure. n-Hexane loading rate was kept constant in the TBABs for comparison reasons and ranged from 4 to 22 g/(m³.hr). Corresponding benzene loadings ranged from 4 to 43 g/(m³.hr). Generally, benzene behavior in the TBAB was superior to that of n-hexane because of its higher solubility. n-Hexane showed improved performance in the 2:1 mixing ratio as compared with the other two ratios.

IMPLICATIONS The use of biofilters is a cheap and attractive option; however, their application is limited because of several challenges. One of them is the reluctance of hydrophobic compounds for biodegradation and the coexistence of other compounds in air emissions. This paper evaluated the impact of different mixing ratios of two hydrophobic compounds and the effect of increasing influent concentration. Finally, a comparison is provided on the best performance attained for these hydrophobic compounds as single solutes. The results of this study will aid in the design and operation of full-scale biofilters.     

Evaluation of trickle-bed air biofilter performance under periodic stressed operating conditions as a function of styrene loading

Trickle-bed air biofilters (TBABs) are suitable for treating volatile organic compounds (VOCs) at a significantly high practical loading because of their controlled environmental conditions. The application of TBAB for treating styrene-contaminated air under periodic backwashing and cyclical nonuse periods at a styrene loading of 0.64-3.17 kg chemical oxygen demand (COD)/m3 x day was the main focus of this study. Consistent long-term efficient performance of TBAB strongly depended on biomass control. A periodic in situ upflow with nutrient solution under media fluidization, that is, backwashing, was approached in this study. Two different nonuse periods were employed to simulate a shutdown for equipment repair or during weekends and holidays. The first is a starvation period without styrene loading, and the second is a stagnant period, which reflects no flow passing through the biofilter. For styrene loadings up to 1.9 kg COD/m3 x day, removal efficiencies consistently above 99% were achieved by conducting a coordinated biomass control strategy, that is, backwashing for 1 hr once per week. Under cyclical nonuse periods for styrene loadings up to 1.27 kg COD/m3 x day, stable long-term performance of the biofilter was maintained at more than 99% removal without employing backwashing. No substantial impact of nonuse periods on the biofilter performance was revealed. However, a coordinated biomass control by backwashing subsequently was unavoidable for attaining consistently high removal efficiency at a styrene loading of 3.17 kg COD/m3 x day. As styrene loading was increased, reacclimation of the biofilter to reach the 99% removal efficiency following backwashing or the nonuse periods was delayed. After the non-use periods, the response of the biofilter was a strong function of the biomass in the bed. No significant difference between the effects of the two different nonuse periods on TBAB performance was observed during the study period.     

Treatment of hydrophobic VOCs in trickling bed air biofilter: Emphasis on long-term effect of initial alternate use of hydrophilic VOCs and microbial species evolution

The main research objective of this study is to enhance the removal of recalcitrant compounds that are not readily bioavailable due to limiting mass transfer rate between the liquid and gas phases. Four trickle-bed air biofilters (TBABs), loaded with pelletized diatomaceous earth support media, were run at an empty bed residence time (EBRT) of 120 sec. After an acclimation period at constant loading rate (LR) of n-hexane (13.2 g m^?3 hr^?1) and intermittent feeding of methanol, n-hexane influent LR was then increased in step-wise fashion to 47.7 g m^?3 hr^?1 for biofilters receiving acidic nutrients (pH 4), and to 36.3 g m^?3 hr^?1 for biofilters receiving nutrient at pH 7. The results have shown that for TBABs receiving nutrient at pH 4, greater elimination capacities were obtained as compared to TBABs working at pH 7. n-Hexane removal efficiency of more than 84% at LR up to 47.7 g m^?3 hr^?1 was obtained for pH 4 nutrient-fed biofilters, while for biofilters with nutrients fed at pH 7, the removal efficiency did not exceed 64% for n-hexane LR of 36.3 g m^?3 hr^?1. The microbial analysis revealed that no fungal community was detected in TBABs run at neutral pH. The fungi communities that were initially acclimating TBABs run at pH 4, namely, Aspergillus niger and Fusarium solani, were not detected at the end of the experiment, while Gibberella moniliformis (Fusarium verticillioides) genus became the dominant species. Gibberella moniliformis (Fusarium verticillioides) was present along all the biofilter media and sustained very high n-hexane elimination at steady-state condition.

Implications:With growing apprehension about sustainability and environmental protection, with limited resources available, and with the passage of the 1990 Amendments to the Clean Air Act, there is more need for using air pollution control techniques that are sound economically and proven environmentally friendly. Biofiltration systems, namely, trickle-bed air biofilters, were for decades recognized as efficient in treating air pollutants. Thus, the application of this technique over a wide industrial spectrum would certainly contribute to reduction of hazardous gas emissions.     

Evaluation of Trickle Bed Air Biofilter Performance as a Function of Inlet VOC Concentration and Loading,and Biomass Control

ABSTRACT

The 1990 Amendments to the Clean Air Act have stimulated strong interest in the use of biofiltration for the economical, engineered control of volatile organic compounds (VOCs) in effluent air streams. Trickle bed air biofilters (TBABs) are especially applicable for treating VOCs at high loadings. For long-term, stable operation of highly loaded TBABs, removal of excess accumulated bio-mass is essential. Our previous research demonstrated that suitable biomass control for TBABs was achievable by periodic backwashing of the biofilter medium. Backwashing was performed by fluidizing the pelletized biological attachment medium with warm water to about a 40% bed expansion. This paper presents an evaluation of the impact of backwashing on the performance of four such TBABs highly loaded with toluene. The inlet VOC concentrations studied were 250 and 500 ppmv toluene, and the loadings were 4.1 and 6.2 kg COD/m³ day (55 and 83 g toluene/m³ hr). Loading is defined as kg of chemical oxygen demand per cubic meter of medium per day. Performance deterioration at the higher loading was apparently due to a reduction of the specific surface of the attached biofilm resulting from the accumulation of excess biomass. For a toluene loading of 4.1 kg COD/m³ day, it was demonstrated that the long-term performance of biofilters with either inlet concentration could be maintained at over 99.9% VOC removal by employing a backwashing strategy consisting of a frequency of every other day and a duration of 1 hr.     

Removal of propylene and butylene as individual compounds with compost and wood chip biofilters

Propylene and butylene are highly reactive volatile organic compounds (HRVOCs) in terms of ground-level ozone formation. This study examined the effectiveness of biofiltration in removing propylene and butylene as separate compounds. Specific objectives were (1) to measure maximum removal efficiencies for propylene and butylene and the corresponding microbial acclimation times, which will be useful in the design of future biofilters for removal of these compounds; (2) to compare removal efficiencies of propylene and butylene for different ratios of compost/hard wood-chip media; and (3) to identify the microorganisms responsible for propylene and butylene degradation. Two laboratory-scale polyvinyl chloride biofilter columns were filled with 28 in. of biofilter media (compost/wood-chip mixtures of 80:20 and 50:50 ratios). Close to 100% removal efficiency was obtained for propylene for inlet concentrations ranging from 2.9 x 10(4) to 6.3 x 10(4) parts per million (ppm) (232-602 g/m3-hr) and for butylene for inlet concentrations ranging from 91 to 643 ppm (1.7-13.6 g/m3-hr). The microbial acclimation period to attain 100% removal efficiency was 12-13 weeks for both compounds. The lack of similar microbial species in the fresh and used media likely accounts for the long acclimation time required. Both ratios of compost/wood chips (80:20 and 50:50) gave similar results. During the testing, media pH increased slightly from 7.1 to 7.5-7.7. None of the species in the used media that treated butylene were the same as those in the used media that treated propylene, indicating that different microbes are adept at degrading the two compounds.     

Kinetics of catalytic oxidation of benzene, n-hexane, and emission gas from a refinery oil/water separator over a chromium oxide catalyst

With the advances made in the past decade, catalytic incineration of volatile organic compounds (VOCs) has become the technology of choice in a wide range of pollution abatement strategies. In this study, a test was undertaken for the catalytic incineration, over a chromium oxide (Cr2O3) catalyst, of n-hexane, benzene, and an emission air/vapor mixture collected from an oil/water separator of a refinery. Reactions were carried out by controlling the feed stream to constant VOC concentrations and temperatures, in the ranges of 1300-14,700 mg/m3 and 240-400 degrees C, respectively. The destruction efficiency for each of the three VOCs as a function of influent gas temperature and empty bed gas residence time was obtained. Results indicate that n-hexane and the oil vapor with a composition of straight- and branch-chain aliphatic hydrocarbons exhibited similar catalytic incineration effects, while benzene required a higher incineration temperature or longer gas retention time to achieve comparable results. In the range of the VOC concentrations studied, at a given gas residence time, increasing the operating temperature of the catalyst bed increased the destruction efficiency. However, the much higher temperatures required for a destruction efficiency of over 99% may be not cost-effective and are not suggested. A first-order kinetics with respect to VOC concentration and an Arrhenius temperature dependence of the kinetic constant appeared to be an adequate representation for the catalytic oxidation of these volatile organics. Activation energy and kinetic constants were estimated for each of the VOCs. Low-temperature destruction of the target volatile organics could be achieved by using the Cr2O3 catalyst.     

Volatile organic compounds (VOCs) in urban atmosphere of Hong Kong

The assessment of volatile organic compounds (VOCs) has become a major issue of air quality network monitoring in Hong Kong. This study is aimed to identify, quantify and characterize volatile organic compounds (VOCs) in different urban areas in Hong Kong. The spatial distribution, temporal variation as well as correlations of VOCs at five roadside sampling sites were discussed. Twelve VOCs were routinely detected in urban areas (Mong Kok, Kwai Chung, Yuen Long and Causeway Bay). The concentrations of VOCs ranged from undetectable to 1396 microg/m3. Among all of the VOC species, toluene has the highest concentration. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the major constituents (more than 60% in composition of total VOC detected), mainly contributed from mobile sources. Similar to other Asian cities, the VOC levels measured in urban areas in Hong Kong were affected both by automobile exhaust and industrial emissions. High toluene to benzene ratios (average T/B ratio = 5) was also found in Hong Kong as in other Asian cities. In general, VOC concentrations in the winter were higher than those measured in the summer (winter to summer ratio > 1). As toluene and benzene were the major pollutants from vehicle exhausts, there is a necessity to tighten automobile emission standards in Hong Kong.     

Bio-oxidation of airborne volatile organic compounds in an activated sludge aeration tank

An activated sludge aeration tank (40 x 40 x 300 cm, width x length x height) with a set of 2-mm orifice air spargers was used to treat gas-borne volatile organic compounds (VOCs; toluene, p-xylene, and dichloromethane) in air streams. The effects of liquid depth (Z), aeration intensity (G/A), the overall mass-transfer rate of oxygen in clean water (KLaO2), the Henry's law constant of the tested VOC (H), and the influent gaseous VOC concentration (C0) on the efficiency of removal of VOCs were examined and compared with a literature-cited model. Results show that the measured VOC removal efficiencies and those predicted by the model were comparable at a G/A of 3.75-11.25 m3/m2 hr and C0 of approximately 1000-6000 mg/m3. Experimental data also indicated that the designed gas treatment reactor with KLaO2 = 5-15 hr(-l) could achieve > 85% removal of VOCs with H = 0.24-0.25 at an aerated liquid depth of 1 m and > 95% removal of dichloromethane with H = 0.13 at a 1-m liquid depth.     

Sources of Volatile Organic Compounds in a University Building

A total of 34 volatile organic compounds (VOCs) were measured in the indoor of laboratories, offices and classrooms of the Chemical Engineering Department of Hacettepe University in Ankara in 2 week-day passive sampling campaigns. The average concentrations ranged from 0.77 to 265 μg m^?3 at the different indoor sites, with the most abundant VOC found to be toluene (119.6 μg m^?3), followed by styrene (21.24 μg m^?3), 2-ethyltoluene (17.11 μg m^?3), n-hexane (10.21 μg m^?3) and benzene (9.42 μg m^?3). According to the factor analysis, the evaporation of solvents used in the laboratories was found to be the dominant source.     

Methanol measurements in the lower troposphere near Innsbruck (047°16′N; 011°24′E), Austria

Diurnal variations on a time scale of minutes of the mixing ratios of methanol were measured using proton transfer reaction mass spectrometry (PTR-MS) technique during 67 days throughout the time span from November 1996 to July 1998 together with benzene and other volatile organic compounds at the western outskirts of Innsbruck, Austria. Comparison with the course of the mixing ratio of benzene, which served as marker for traffic emissions, as well as the observation of a seasonal variation allowed to distinguish between different sources for methanol release into the troposphere. Strong evidence for methanol removal via deposition on dew-wetted surfaces is obtained from the comparison of meteorological data with methanol mixing ratios. The mean volume mixing ratio of total methanol was 7.5 nmol mol⁻¹. Mixing ratios ranged from 0.03 up to 45 nmol mol⁻¹.     

Removal of ammonia from contaminated air by trickle bed air biofilters

A trickle bed air biofilter (TBAB) was evaluated for the oxidation of NH3 from an airstream. Six-millimeter Celite pellets (R-635) were used for the biological attachment medium. The efficiency of the biofilter in oxidizing NH3 was evaluated using NH3 loading rates as high as 48 mol NH3/m3 hr and empty-bed residence times (EBRTs) as low as 1 min. Excess biomass was controlled through periodic backwashing of the biofilter with water at a rate sufficient to fluidize the medium. The main goal was to demonstrate that high removal efficiencies could be sustained over long periods of operation. Ammonia oxidation efficiencies in excess of 99% were consistently achieved when the pH of the liquid nutrient feed was maintained at 8.5. Quick recovery of the biofilter after backwashing was observed after only 20 min. Evaluation of biofilter performance with depth revealed that NH3 did not persist in the gas phase beyond 0.3 m into the depth of the medium (26% of total medium depth).     

Characteristics of photocatalytic oxidation of toluene, benzene, and their mixture

The investigation of the photocatalytic oxidation (PCO) of multicomponent volatile organic compounds (VOCs) is very important to the application of PCO technology, because there is seldom a single VOC component in indoor air. In this paper, the characteristics of binary indoor VOCs, toluene and benzene, were experimentally studied using a mass transfer based method that we developed. The concentration ranges for toluene and benzene were 4.48-27.4 mg/m3 and 1.82-4.08 mg/m3, respectively. We found the following: (1) the PCO of each individual contaminant studied obeys the unimolecular form of the Langmuir-Hinshelwood (L-H) rate form; (2) the PCO of the binary contaminants follow the competitive adsorption L-H rate form; (3) the reaction-coefficient for PCO of individual contaminants differs from that in the competitive adsorption L-H rate form; and (4) the component impact factor of A to B, put forward in this paper, is a useful parameter describing the influence of A on the reaction coefficient of B, and it was found that the impact factor of toluene (a chemically active component) on benzene (a chemically stable component) is high, and the impact factor of benzene on toluene is low.     

Commuter exposure to volatile organic compounds under different driving conditions

The driving conditions that were tested for the in-vehicle concentrations of selected volatile organic compounds (VOCs) included transport modes, fuel distributions, vehicle ventilation conditions, driving routes, commute seasons, car models, and driving periods. This study involved two sampling seasons (winter and summer). The in-auto/in-bus/fixed site ratio of the wintertime mean concentrations was about 6/3/1 for total VOCs and 8/3/1 for benzene. On the median, the in-auto/in-bus exposure ratio ranged from 1.5 to 2.8 for the morning commutes, and ranged from 2.4 to 4.5 for evening commutes, depending on the target compounds. The wintertime in-auto concentrations were significantly higher (p<0.05), on the average 3–5 times higher, in a carbureted engine than in the three electronic fuel-injected cars. For the summertime in-auto concentrations of the target compounds except benzene, there were no significant differences between low and high ventilation conditions on the two urban routes. The urban in-auto benzene concentration was significantly higher (p<0.05) under the low ventilation condition. For the rural commutes, the in-auto concentrations of all target compounds were significantly higher (p<0.05) under the low ventilation condition. The in-auto VOC concentrations on the two urban routes did not differ significantly, and they were greater than the rural in-auto concentrations, with the differences being significant (p<0.05) for all target compounds. The summertime in-auto concentrations of benzene and toluene were greater than the wintertime in-auto concentrations, with the difference being significant (p<0.05), while the concentrations of the other target compounds were not significantly different between the two seasons. Neither car models nor driving periods influenced the in-auto VOC concentrations.     

Effects of ionic strength on the production of short chain volatile hydrocarbons by Dunaliella salina (Teodoresco)

The effect of ionic strength on the production of short chain volatile hydrocarbons was studied in cultures of Dunaliella salina. Axenic cultures of D. salina were grown at three different ionic strengths 0.5, 2 and 3 M of NaCl in Johnson (J/1) culture medium [Journal of Bacteriology 95 (1968) 1461] under the following laboratory growth conditions: a 12:12 h photoperiod, 300 micromolm(-2)s(-1) of photosynthetic active radiation (PAR) provided by a fluorescent lamp of 40 W combined with a 100 W incandescent lamp at 20 +/- 1 degrees C at pH 7.5. C1 to C5 hydrocarbons were detected using a head space technique and GC-FID. Cell numbers and growth rate was greatest at 2 M NaCl 4.3 x 10(6) cellml(-1) after a 15 days period of culture. Maximum hydrocarbon production was measured in the concentration of 0.5 NaCl with lower production rates in the more concentrated solutions. The principal hydrocarbon was pentane at 0.5 M but was ethane in 2 and 3 M solutions. Production rates for individual compounds ranged between 0.13 and 22 x 10(-15) microgCcell(-1)h(-1). It is suggested that the ability to produce and release volatile organic compounds of D. salina is related to osmotic conditions established by the ionic strength of growth solution.     

Assessment of indoor air concentrations of VOCs and their associated health risks in the library of Jawaharlal Nehru University,New Delhi

The present work investigated the levels of total volatile organic compounds (TVOC) and benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene (BTEX) in different microenvironments in the library of Jawaharlal Nehru University in summer and winter during 2011–2012. Carcinogenic and non-carcinogenic health risks due to organic compounds were also evaluated using US Environmental Protection Agency (USEPA) conventional approaches. Real-time monitoring was done for TVOC using a data-logging photo-ionization detector. For BTEX measurements, the National Institute for Occupational Safety and Health (NIOSH) standard method which consists of active sampling of air through activated charcoal, followed by analysis with gas chromatography, was performed. Simultaneously, outdoor measurements for TVOC and BTEX were carried out. Indoor concentrations of TVOC and BTEX (except benzene) were higher as compared to the outdoor for both seasons. Toluene and m/p-xylene were the most abundant organic contaminant observed in this study. Indoor to outdoor (I/O) ratios of BTEX compounds were generally greater than unity and ranged from 0.2 to 8.7 and 0.2 to 4.3 in winter and summer, respectively. Statistical analysis and I/O ratios showed that the dominant pollution sources mainly came from indoors. The observed mean concentrations of TVOC lie within the second group of the Molhave criteria of indoor air quality, indicating a multifactorial exposure range. The estimated lifetime cancer risk (LCR) due to benzene in this study exceeded the value of 1?×?10^?6 recommended by USEPA, and the hazard quotient (HQ) of non-cancer risk came under an acceptable range.     

A fungal vapor-phase bioreactor for the removal of nitric oxide from waste gas streams.

Ground-level O3 formation is becoming a major concern in many cities due to recent tightening of O3 regulations. To control O3 formation, more efficient treatment processes for O3 precursors, such as NOx and volatile organic compounds (VOCs), are needed. One promising new technology for removing both NOx and VOCs from off-gas streams is biofiltration, a simple process whereby contaminated air is passed through a biologically active packed bed. In this study, a toluene-degrading fungal bioreactor was used to treat an aerobic gas stream contaminated with NO. The fungal bioreactor removed 93% of the inlet 250-ppmv NO at an empty bed contact time (EBCT) of 1 min when supplied with 90 g/m3/hr toluene. The presence of NH4+ concentrations greater than 0.4 mg NH3/g dry packing medium, however, resulted in poor NO removal. The bioreactor achieved a maximum toluene elimination capacity of 270 g/m3/hr and maintained greater than 95% toluene removal efficiencies over the 175-day study period.     

生物滴滤器处理味精厂挥发性恶臭废气的试验研究

报道了采用以沸石为填料的生物滴滤器净化处理味精厂内挥发性恶臭废气的试验结果。在一定的试验条件下,当高强度恶臭废气的进气量<3.0m3/h时,系统除臭效果显著,这为净化以味精厂内恶臭废气为代表的多组分复杂气体提供了切实可行的新技术,具有很好的市场应用前景。此外,研究表明,在净化氨氮臭气取得良好效果的生物膜基础之上,加入特定菌液能较快地培养出适宜处理味精厂内恶臭废气的微生物种群,且能获得满意的净化效果。     

Air quality modeling of interpollutant trading for ozone precursors in an urban area

Emission trading is a market-based approach designed to improve the efficiency and economic viability of emission control programs; emission trading has typically been confined to trades among single pollutants. Interpollutant trading (IPT), as described in this work, allows for trades among emissions of different compounds that affect the same air quality end point, in this work, ambient ozone (O3) concentrations. Because emissions of different compounds impact air quality end points differently, weighting factors or trading ratios (tons of emissions of nitrogen oxides (NO(x)) equivalent to a ton of emissions of volatile organic compounds [VOCs]) must be developed to allow for IPT. In this work, IPT indices based on reductions in O3 concentrations and based on reductions in population exposures to O3 were developed and evaluated using a three-dimensional gridded photochemical model for Austin, TX, a city currently on the cusp of nonattainment with the National Ambient Air Quality Standards for O3 concentrations averaged over 8 hr. Emissions of VOC and NO(x) from area and mobile sources in Austin are larger than emissions from point sources. The analysis indicated that mobile and area sources exhibited similar impacts. Trading ratios based on maximum O3 concentration or population exposure were similar. In contrast, the trading ratios did exhibit significant (more than a factor of two) day-to-day variability. Analysis of the air quality modeling indicated that the daily variability in trading ratios could be attributed to daily variations in both emissions and meteorology.     

Treatment of N,N-dimethylacetamide waste gas by a trickle-bed air biofilter.

The system performance of a trickle-bed air biofilter (TBAB) for treating N,N-dimethylacetamide (DMAC) waste gas was investigated under different gas flow rates and influent concentrations. In the pseudo-steady-state conditions, the DMAC elimination capacity increased but the removal efficiency decreased as the influent loading increased. More than 90% and 80% DMAC removal efficiencies are achieved for influent loadings below 20.2 and 34.5 g DMAC/m3/h, respectively. The TBAB appears to be an effective treatment process for controlling DMAC emission with low-to-medium loadings and the effectiveness could be maintained over a long-period operation.     

Biological treatment of a contaminated gaseous emission from a leather industry in a suspended-growth bioreactor

A suspended-growth bioreactor (SGB) was operated for the treatment of a gaseous stream mimicking emissions generated at a leather industrial company. The main volatile organic compounds (VOCs) present in the gaseous stream consisted of 1-methoxy-2-propanol, 2,6-dimethyl-4-heptanone, 2-butoxyethanol, toluene and butylacetate. A microbial consortium able to degrade these VOCs was successfully enriched. A laboratory-scale SGB was established and operated for 210-d with an 8h cycle period and with shutdowns at weekends. Along this period, the SGB was exposed to organic loads (OL) between 6.5 and 2.3 x 10(2) g h(-1) m(-3). Most of the compounds were not detected at the outlet of the SGB. The highest total VOC removal efficiency (RE) (ca 99%) was observed when an OL of 1.6 x 10(2) g h(-1) m(-3) was fed to the SGB. The maximum total VOC elimination capacity (1.8 x 10(2) g h(-1) m(-3)) was achieved when the OL applied to the SGB was 2.3 x 10(2) g h(-1) m(-3). For all the operating conditions, the SGB showed high levels of degradation of toluene and butylacetate (RE approximately equal to 100%). This study also revealed that recirculation of the gaseous effluent improved the performance of the SGB. Overall, the SGB was shown to be robust, showing high performance after night and weekend shutdown periods.