Anaerobic Rotating Biological Contactor Research Articles

Novel insights into mechanism of biometal recovery from wastewater by sulfate reduction and its application in pollutant removal

Biological sulfate reduction is an emerging technique for both removal and recovery of heavy metals from wastewater. In this study, anaerobic biomass from three different sources were initially screened based on their metal removal and sulfate reduction efficiencies. The effect of metal loading on the removal of sulfate and chemical oxygen demand (COD) was further investigated to examine its toxic effect on sulfate reducing bacteria (SRB) present in the anaerobic biomass. At low metal loading conditions, biomass obtained from anaerobic rotating biological contactor (An-RBC) reactor treating metallic wastewater showed a maximum metal removal (95 ± 0.5%), sulfate reduction (90 ± 1.56%) and COD removal (80 ± 0.88%); the values decreased at a high metal concentration for all the biomass. Metals were then subsequently recovered from bioprecipitates in the form of nanopowder and the metal recovery efficiency was in the order Cu > Pb > Cd > Zn > Ni > Fe > Mn. Analysis of the bioprecipitates by field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX) confirmed that it was mainly composed of metal sulfide. Size, shape and crystallinity of the nanoparticles were determined by field emission transmission electron microscopy (FETEM) and X-ray diffractometer (XRD) which revealed its excellent potential for industrial reuse and application, particularly for treating toxic dye containing wastewater.

A new application of anaerobic rotating biological contactor reactor for heavy metal removal under sulfate reducing condition

This study evaluated the performance of a continuously operated laboratory scale anaerobic rotating biological contactor (An-RBC) reactor at 24h and 48h residence time (RT) for heavy metal removal from synthetic wastewater under sulfate reducing condition. A maximum removal of Cu(II) (97%) followed by Cd(II) (90%) and more than 77% removal in case of the other metals, viz Pb(II), Fe(III), Zn(II) and Ni(II) were obtained for a maximum inlet metal concentration in the range 50–175mg/L at 48h RT. Metal loading rates greater than 3.64mg/L·h in case of Cu(II) and 1.87mg/L·h, in case of Fe(III), Pb(II), Ni(II), Zn(II) and Cd(II) are toxic and inhibitory to SRB activity and are therefore, detrimental to the performance of the An-RBC reactor. The metal removal values were slightly reduced at 24h RT and the heavy metal removal was in the order: Cu>Cd>Pb>Fe>Zn>Ni at both the RTs. Sulfate removal results further confirmed that the heavy metal removal is due to sulfide generation in the reactor system. Field emission scanning electron microscopy (FESEM) images clearly revealed the immobilized sulfate reducing bacteria (SRB) onto the support material. Hence, this study demonstrated an excellent potential of the An-RBC reactor for treating metal containing wastewater even at high inlet concentration.

Comparative study of the performance of an anaerobic rotating biological contactor and its potential to enrich hydrogenotrophic methanogens

BACKGROUND Process upset due to volatile fatty acid accumulation is one of the major drawbacks of anaerobic treatment of wastewater. The performance of an anaerobic rotating biological contactor (AnRBC) was studied under normal operating conditions as well as shock loadings of propionic acid, for its ability to enhance the conversion of hydrogen to methane. These results were compared with those of a reactor lacking the enhanced gas-liquid hydrogen transfer mechanism, a conventional anaerobic digester. RESULT The AnRBC exhibited lower concentrations of hydrogen in the headspace (300–600 ppm) under both normal and shock loading conditions, and also showed more hydrogenotrophic methanogens on the denaturing gradient gel electrophoresis (DGGE) profile of 16S rRNA gene amplicons, both in terms of intensity and band numbers (4 in the AnRBC and 2 in the anaerobic digester). CONCLUSION This study showed that the AnRBC is able to maintain lower hydrogen partial pressure at both normal operating and shock loading conditions due to the abundance of hydrogenotrophic methanogens and good gas–liquid hydrogen transfer efficiency. This finding should encourage the commercial exploitation of AnRBC for the treatment of wastewaters, especially that containing easily acidifiable organic compounds, which causes instability in operation through souring. © 2014 Society of Chemical Industry

Rational immobilization of methanogens in high cell density bioreactors

Production of hydrogen sulphide by sulphate reducing bacteria (SRB) is a serious problem in anaerobic wastewater treatment, because it causes corrosion and reduces the value of methane in the biogas produced. The surface and adhesion characteristics of SRB as measured through the zeta potential are different from those of methanogens. We therefore tested the hypothesis that by choosing a carrier material with the proper surface characteristics (zeta potential) it should be possible to selectively immobilize methanogens while excluding SRB. In a series of batch tests with different support materials complete elimination of SRB was obtained on supports made of nylon, a result in line with our original hypothesis. Maximum preferential immobilization of methanogens was obtained at a temperature of 37 °C with media containing volatile fatty acids (VFA) as the carbon source. Preferential immobilization of methanogens was achieved in an anaerobic fluidized bed reactor (AFBR) with nylon granules as support and in an anaerobic rotating biological contactor (ARBC) with an acrylic disc as support. H2S-free biogas containing 63% and 38% methane were obtained from the AFBR and ARBC, respectively.

Macroscale and microscale analysis of Anammox in anaerobic rotating biological contactor

Inoculated with conventional anaerobic activated sludge, the Anammox process was successfully developed in an anaerobic rotating biological contactor (AnRBC) fed with a low ratio of C/N synthetic wastewater. Operated in a single point feed mode, the AnRBC removed 92.1% in - 126) of the influent N at the highest surface load of 12 g/(m 2-day). The biomass increased by 25% and 17.1 g/(m 2-day) of maximum N removal surface load was achieved by elevating flow rate with another feed point. Fluorescence in situ hybridization and polymerase chain reaction analysis indicated that the Anammox genus Candidatus Kuenenia stuttgartiensis dominated the community. Both Anammox and denitrifying activity were detected in biofilm by the application of microelectrodes. In the outer layer of the biofilm (0-2500 μm), nitrite and ammonium consumed simultaneously in a ratio of 1.12/1, revealing the occurrence of Anammox. In the inner layer (> 2500 μm), a decrease of nitrate was caused by denitrification in the absence of nitrite and ammonium.

Treatment of winery wastewater with an anaerobic rotating biological contactor

Performances of an anaerobic rotating biological contactor (AnRBC) have been tested with winery wastewater. A 50 litres pilot has been used during a 4 month period. It was observed that the start-up took place in one month until the biofilm stabilized. Optimal performances were obtained with a COD removal close to 80%, with the following conditions: temperature of wastewater at 20 degrees C, volume load of 2 kg COD m(-3) d(-1), mass load of 0.3 kg COD kg MVS(-1) d(-1), surface load of 0.11 kg COD m(-2) d(-1). However, it is possible to enhance some experimental conditions to obtain better results, especially in increasing the total surface of the biodisk and in controlling temperature to the mesophilic optimal value (37 degrees C). In such conditions it is estimated that for 80% COD removal, volume load could approach 20 to 25 kg COD m(-3) d(-1).

Temperature Effects on the Performance of an Anaerobic Rotating Biological Contactor

Effects of temperature change in the mesophilic range (20 – 43°C) on the system performance of a four-stage anaerobic rotating biological contactor (AnRBC) for the treatment of high-strength organic wastewater were investigated. In the steady-state condition, the COD removal efficiency increased as the temperature increased in the range of 20 – 35°C. At a temperature of 43°C, the COD removal efficiency was lower than those of at 28 and 35°C but was higher than that of at 20°C. The AnRBC system appears to be an effective treatment process in the mesophilic range under appropriate organic loading rates. A theoretical evaluation on the temperature coefficient indicated that the temperature effects on the performance of AnRBC process are more significant at lower organic loading rates or in the latter stages. In addition, the θ values for the AnRBC process ranged from 1.03 to 1.08 which are in the typical range of some commonly used aerobic processes (1.0–1.10).

Performance of an anaerobic rotating biological contactor: Effects of flow rate and influent organic strength

The system performance of an anaerobic rotating biological contactor (AnRBC) for the treatment of high-strength synthetic wastewater was investigated under different flow rates and influent organic strengths. In the steady-state condition, the removal efficiencies of COD and BOD increased as the hydraulic retention time (HRT) increased or the influent organic strength decreased. The overall COD removal efficiencies ranged from 74 to 82% at an HRT of 32 h, from 56 to 61% at an HRT of 16 h, and from 44 to 53% at an HRT of 8 h. In view of these results, it was concluded that the AnRBC reactor is an effective treatment process at an HRT of 32 h and influent COD between 3248 and 12150 mg l −1. Most organic compounds were removed in the first two stages of the AnRBC indicating that a two-stage reactor may be sufficient in practical applications. The microscopic observations showed that the acetogenic microorganisms were predominant in the first two stages while the methanogenic microorganisms were predominant in the last two stages. The experimental observations were confirmed by performing a theoretical evaluation of the steady-state biofilm thickness, the mass balance analysis and the methane production to allow insight into the performance of an AnRBC process.

Effects of disc rotational speed and submergence on the performance of an anaerobic rotating biological contactor

Effects of disc rotational speed (ω) and disc submergence (Ω) on the system performance of a four-stage anaerobic rotating biological contactor (AnRBC) for treating high-strength organic wastewater were investigated to establish optimal operating conditions. Results of tracer study showed that the flow was more mixed when the AnRBC system was operated at a higher ω or at a lower Ω In the steady-state operating condition, the stage chemical oxygen demand (COD) removal efficiency increased as ω increased in the range of 0–12 rpm. The opposite trend was observed at ω values above 12 rpm. The optimal ω values are between 6 and 24 rpm with the overall COD removal efficiencies ranging from 70 to 78%. Results of disc submergence showed that the stage COD removal efficiency increased with an increase in Ω The overall COD removal efficiencies were 64, 70, and 78% for 40, 70, and 100% disc submergence, respectively. The AnRBC system appears to be an effective process for treating high-strength organic wastewaters under operating conditions of 12 rpm and 100% disc submergence.

Studies on SAGO wastewater treatment using anaerobic rotating biological contactor

Experimental studies were done in a laboratory scale Anaerobic Rotating Biological Contactor (RBC), for treatment of Synthetic sago wastewater. This paper describes the development and laboratory testing of an Anaerobic RBC process that couples the advantages of the fixed film horizontal flow RBC process with the high strength, starch degradation capabilities of anaerobic systems. The reactor was operated at ambient temperature and was subjected to organic and hydraulic loading rates. The reactor performance with respect to Chemical Oxygen Demand (COD) removal, alkalinity, volatile acids at each stage and biogas production were evaluated.

Hydraulic characteristics and startup of anaerobic rotating biological contactors

Abstract In this study the hydraulic characteristics and the start‐up of anaerobic rotating biological contactor (AnRBC) were investigated experimentally and theoretically. Results of tracer study showed that the AnRBC reactor is a well‐mixed reactor in the first and second stages. Start‐up of the AnRBC reactor was successfully carried out using high strength synthetic wastewaters at hydraulic retention time of 21.6 hours, organic surface loading of 111.4 g‐COD/m2•d, organic volumetric loading of 13.33 Kg‐COD/m3•d, disk rotational speed of 12 rpm and 100% disk submergence. In the steady‐state operating condition, the removal efficiencies of soluble COD and BOD could be up to 71% and 76% for the inlet COD and BOD concentrations of 12,000 and 7,267 mgL‐1, respectively. The microscopic observations after start‐up of the AnRBC reactor showed that the acetogenic bacteria are significant in the first two stages while the methanogenic bacteria predominate in the last two stages.

Treatment of high-strength organic wastewaters using an anaerobic rotating biological contactor

The removal of high strength organic compounds from the wastewater by an anaerobic rotating biological contactor (AnRBC) was studied experimentally and theoretically. In the steady-state operating condition, the removal efficiencies of soluble COD and BOD could be up to 71% and 76%, respectively, for the organic surface loading rate of 111.4 g COD/m 2·d and organic volumetric loading rate of 13.33 kg COD/m 3·d. A simple model that accounts for the simultaneous convective transport, dispersion in the axial direction, and substrate utilization by the attached biomass was developed to predict the system performance of the AnRBC reactor. Good agreement between model predictions and experimental data was obtained by comparing dimensionless soluble COD concentration profiles measured at the system effluent of earlier stages. The results presented herein are helpful in providing design and operational criteria for a full-scale AnRBC type system.

The effect of disc submergence level on the performance of a laboratory-scale anaerobic rotating biological contactor: implications for digester design and modelling

A hypothesis was advanced that an anaerobic rotating biological contactor (AnRBC) digester, if operated with its discs half rather than fully submerged, should show an enhanced capability to withstand shock loads. Laboratory-scale AnRBC digesters were constructed and their performance under 50% and 100% disc submergence conditions compared. In all cases, under otherwise comparable conditions the performance in the 50% disc submergence mode was better. From measurements, including biogas hydrogen concentration, pH and propionic acid content of the digester liquid, it was concluded that it was the markedly better hydrogen stripping capability of the digester operated with discs only half submerged that accounted for its superior performance. Implications for design and modelling of digesters are discussed. It is concluded that current models of anaerobic digester systems need to reflect more accurately the actual hydrodynamic conditions in digesters if good predictions of digester performance under dynamic conditions are to be realised.

An evaluation of a simple kinetic model for the treatment of domestic sewage by means of an anaerobic rotating biological contactor

Abstract In this study, the application of the mathematical model proposed by Andreadakis and Cailas to experimental data obtained in the treatment of domestic sewage is examined. A single-stage laboratory scale unit of an anaerobic rotating biological contactor (AnRBC) was used in the studies to produce kinetic parameters for the Andreadakis and Cailas model. The results demonstrated that a simple Monod-type expression can satisfactorily simulate the performance of an anaerobic rotating biological contactor and the model maintains its validity even with high-strength domestic wastewater.

Comparison of attached and suspended growth methanogenesis in a two phase system

Abstract Performance of an attached growth methane phase was compared to that of a completely mixed methane phase in a two‐phase anaerobic process. An anaerobic rotating biological contactor (AnRBC) and a completely mixed stirred tank reactor (CSTR) were used to study the attached growth and suspended growth phase systems, respectively. In the methane phase, the hydraulic retention time (HRT) was varied from 10 to 72 hours and the pH was maintained either at 6.0 or at 7.5. The attached growth methane system was observed to be more efficient than the suspended growth methane process In methane production per gram of total organic carbon (TOC) removed.