Rotating Biological Contactor Reactor Research Articles

Residence time distribution studies and modeling of rotating biological contactor reactor for decolorization of Congo red from synthetic dye wastewater

A continuous study in a rotating biological contactor (RBC) reactor was carried out using polyurethane foam (PU) surface-immobilized live fungal biomass of Neurospora crassa with wheat bran adsorbent/substrate for the removal of Congo red (CR) color from aqueous solutions. Residence time distribution studies were conducted at various flow rates of water (1–6.5 mL min–1) using pulse input of tracer to explore the performance of mixing and type of flow behavior inside the reactor. It was found that the value of dispersion number at various flow rates of water such as 1, 3, and 6.5 mL min–1 was 4.36, 7.89, and 13.65, respectively, which indicates that the RBC reactor can be modeled as a mixed flow reactor. A model for a single stage RBC reactor for the decolorization of CR from synthetic dye wastewater has been developed using the principles of conservation of mass. Using the developed mathematical model and experimental data, the model parameters such as maximum specific growth rate of the attached active biomass (μmax), Monod kinetic constant (Ks ), rate constant for pseudo-second-order biosorption (K2 ), and effluent dye concentration at equilibrium (Se ) were estimated. The system of non-linear first-order ordinary differential mass balance equation was solved by the fourth-order Runge–Kutta method and the model parameters were evaluated using the Solver tool in Excel. The predicted and experimental values of effluent dye concentrations are then compared. The predicted values of effluent concentrations found from the theoretical model developed fitted well to the experimental data, suggests that the proposed model is valid for CR dye decolorization. The results reveal that the live fungal biomass of N. crassa with wheat bran is a suitable dual adsorbent for decolorization of CR from synthetic effluents using RBC reactor and it can be used effectively in wastewater treatment.

Rotating Biological Contactor Reactor with Biofilm Promoting Mats for Treatment of Benzene and Xylene Containing Wastewater

A novel rotating biological contactor (RBC) bioreactor immobilized with microorganisms was designed to remove volatile organic compounds (VOC), such as benzene and xylene from emissions, and its performance was investigated. Gas-phase VOCs stripped by air injection were 98 % removed in the RBC when the superficial air flow rate was 375 ml/h (1,193 and 1,226 mg/l of benzene and xylene, respectively). The maximum removal rate was observed to be 1,007 and 1,872 mg/m(3)/day for benzene and xylene, respectively. The concentration profile of benzene and xylene along the RBC was dependent on the air flow rate and the degree of microbial adaptation. Air flow rate and residence time were found to be the most important operational parameters for the RBC reactor. By manipulating these operational parameters, the removal efficiency and capacity of the bioreactor could be enhanced. The kinetic constant K (s) demonstrated a linear relationship that indicated the maximum removal of benzene and xylene in RBC reactor. The phylogenic profile shows the presence of bacterium like Pseudomonas sp., Bacillus sp., and Enterococcus sp., which belonged to the phylum Firmicutes, and Proteobacteria that were responsible for the 98 % organic removal in the RBC.

The use of the fungus Dichomitus squalens for degradation in rotating biological contactor conditions

Biodegradation potential of Dichomitus squalens in biofilm cultures and rotating biological contactor (RBC) was investigated. The fungus formed thick biofilms on inert and lignocellulosic supports and exhibited stable activities of laccase and manganese peroxidase to reach 40–62 and 25–32% decolorization of anthraquinone Remazol Brilliant Blue R and heterocyclic phthalocyanine dyes, respectively. The decolorization ceased when glucose concentration dropped to 1mmoll−1. In RBC reactor, respective decolorizations of Remazol Brilliant Blue R and heterocyclic Methylene Blue and Azure B dyes (50mgl−1) attained 99%, 93%, and 59% within 7, 40 and 200h. The fungus exhibited tolerance to coliform and non-coliform bacteria on rich organic media, the inhibition occurred only on media containing tryptone and NaCl. The degradation efficiency in RBC reactor, capability to decolorize a wide range of dye structures and tolerance to bacterial stress make D. squalens an organism applicable to remediation of textile wastewaters.

Decolourization of synthetic wastewater containing azo dyes by immobilized Phanerochaete chrysosporium in a continuously operated RBC reactor

A laboratory-scale rotating biological contactor (RBC) reactor with immobilized fungal biomass of Phanerochaete chrysosporium was investigated for its performance in decolourizing synthetic wastewater containing single or mixture of azo dyes, Direct Red-80 (DR-80) and Mordant Blue-9 (MB-9). Decolourization efficiency in the continuously operated bioreactor was studied by varying dye inlet concentration and disc rotation speed at two different wastewater hydraulic retention times (HRTs), i.e. 24 and 48 h. Results from the single dye-containing experiments showed that the system could completely decolourize the wastewater for a maximum inlet dye concentration within the range 25-200 mg L(-1) and 48 h HRT in the reactor; for an inlet dye concentration above 200 mg L(-1), the decolourization efficiency slightly reduced up to 85% for the same HRT. However, wastewater containing DR-80 was found to be decolourized more efficiently compared to that containing MB-9. Further, the effect of increase in the disc rotation speed from 2 to 6 rpm in the study revealed no large differences in the decolourization efficiencies of the wastewaters. Similar results were obtained with wastewater containing the dyes together at various concentration combinations as per the two-level factorial design of experiments. Enzyme activities of lignin peroxidase and manganese peroxidase by the fungus were also analysed in the study, and the results indicated that while DR-80 showed a large negative effect on both the enzymes, MB-9 affected mainly the MnP activity by the fungus.

Decolorization of Synthetic Wastewater Containing Azo Dyes in a Batch-Operated Rotating Biological Contactor Reactor with the Immobilized Fungus Phanerochaete chrysosporium

Biodecolorization of synthetic wastewater containing azo dyes, Direct Red-80 (DR-80) and Mordant Blue-9 (MB-9), both individually and together, using immobilized Phanerochaete chrysosporium in a batch-operated rotating biological contactor (RBC) reactor was investigated. Following initial startup of the RBC reactor, which took almost 1 month, results on dye decolorization and enzyme activities of lignin peroxidase (LiP) and manganese peroxidase (MnP) by the fungus were obtained. From experiments involving the individual dyes, decolorization efficiencies were found to be in the range of 94−100%, and from experiments in which the dyes were added together, the decolorization efficiencies of the dye mixture were between 77% and 97% at the end of 24 h. Results of LiP and MnP activities by the fungus revealed a strong role played by the enzymes in the dye decolorization process. As compared to the previous results obtained in batch shake flasks, the results in the present study revealed excellent performance of...

Performance of a three-stage aerobic RBC reactor in food canning wastewater treatment

Biological treatment using attached growth in a three-stage lab-scale rotating biological contactor (RBC) was implemented for wastewater from food cannery industries. The wastewater contained high level of organic compounds due to fish and fruit cleaning, cooking and filling processes. Nutrients available in the wastewater enhanced the growth of microorganisms and allowed the biological treatment to be effective. The RBC consisted of 54 parallel discs rotating in a reservoir and was arranged in three stages, i.e. 18 discs oriented in each stage. Effect of major operating and physical variables such as hydraulic retention time (HRT), disc submergence and disc rotational speed were examined in COD removal. For duration of 5 days, 96.4% BOD removal was achieved in batch experiment. BOD constant rate ( k) and ultimate BOD were determined respectively, 0.8198 day −1 and 6349 mg/l by Thomas graphical method. COD removal efficiency was increased from 85.3 to 97.4% while the HRT was increased from 24 to 48 h. The COD removal efficiency increased from 74.9 to 87.5% as the disc submergence was increased from 31 to 36%. At submergence level of 23.7%, removal efficiency was increased due to activation of second and third compartments. When the rotational speed was increased from 3 to 11 rpm, the COD removal efficiency was also increased from 62.7 to 93.7%, respectively. The stage COD removal efficiency was gradually decreased with an increase number of stage and about 88% of organic compounds were removed in the first stage of aerobic RBC, indicating that the single stage reactor may be sufficient in practical application.

Start-up of autotrophic nitrogen removal reactors via sequential biocatalyst addition.

A procedure for start-up of oxygen-limited autotrophic nitrification-denitrification (OLAND) in a lab-scale rotating biological contactor (RBC) is presented. In this one-step process, NH4+ is directly converted to N2 without the need for an organic carbon source. The approach is based on a sequential addition of two types of easily available biocatalyst to the reactor during start-up: aerobic nitrifying and anaerobic, granular methanogenic sludge. The first is added as a source of aerobic ammonia-oxidizing bacteria (AAOB), the second as a possible source of planctomycetes including anaerobic ammonia-oxidizing bacteria (AnAOB). The initial nitrifying biofilm serves as a matrix for anaerobic cell incorporation. By subsequently imposing oxygen limitation, one can create an optimal environment for autotrophic N removal. In this way, N removal of about 250 mg of N L(-1) d(-1) was achieved after 100 d treating a synthetic NH4+-rich wastewater. By gradually imposing higher loads on the reactor, the N elimination could be increased to about 1.8 g of N L(-1) d(-1) at 250 d. The resulting microbial community was compared with that of the inocula using general bacterial and AAOB- and planctomycete-specific PCR primers. Subsequently, the RBC reactor was shown to treat a sludge digestor effluent under suboptimal and strongly varying conditions. The RBC biocatalyst was also submitted to complete absence of oxygen in a fixed-film bioreactor (FFBR) and proved able to remove NH4+ with NO2- as electron acceptor (maximal 434 mg of NH4+-N (g of VSS)(-1) d(-1) on day 136). DGGE and real-time PCR analysis demonstrated that the RBC biofilm was dominated by members of the genus Nitrosomonas and close relatives of Kuenenia stuttgartiensis, a known AnAOB. The latter was enriched during FFBR operation, but AAOB were still present and the ratio planctomycetes/AAOB rRNA gene copies was about 4.3 after 136 d of reactor operation. Whether this relates to an active role of AAOB in the anoxic N removal process remains to be solved.

Posttreatment of upflow anaerobic sludge blanket-treated industrial wastewater by a rotating biological contactor.

The performance of a rotating biological contactor (RBC) for posttreatment of the slaughterhouse effluent from an upflow anaerobic sludge blanket (UASB) reactor was investigated in this study. The 280-L, six-stage RBC pilot plant was operated at different organic loading rates (OLRs) and biodisk speeds. The overall removal efficiencies for soluble biochemical oxygen demand (SBOD), total biochemical oxygen demand (TBOD), and total chemical oxygen demand (TCOD) decreased with increasing OLRs. Disk rotational speed did not have a significant effect on performance in the range studied. The results showed that satisfactory posttreatment to meet regulatory requirements for agricultural purposes (effluent biochemical oxygen demand of 100 mg/L) can be achieved at an OLR of 5.3 +/- 2.9 g SBOD x m(-2) x d(-1), with an SBOD removal efficiency of 85 +/- 3%. Most of the organics were removed in the first three stages, with minimal contribution from the remaining stages of the RBC reactor. There was a decrease in SBOD removal efficiency to 74 +/- 3% at an OLR value of 17.8 +/- 2.1 g SBOD x m(-2) x d(-1). The results for elimination capacity indicated a linear relationship with first-stage OLRs without any signs of limitation at the range of loading rates investigated in this study. However, average first-stage elimination capacity rates of 4.8 and 3.8 g x m(-2) x d(-1) at OLR values of 17.8 and 11 g SBOD x m(-2) x d(-1) were relatively lower than previous studies of RBC performance using domestic or industrial wastewater without anaerobic pretreatment. It was suggested that the lower elimination capacity rates were due to the fact that a smaller fraction of UASB effluent was biodegradable as reflected in TBOD/TCOD ratios of 0.47 +/- 0.04.

Polycyclic aromatic hydrocarbon removal from soil by surfactant solubilization and Phanerochaete chrysosporium oxidation.

Surfactant soil washing can remove polycyclic aromatic hydrocarbons (PAHs) from contaminated soil, and the white rot fungus, Phanerochaete chrysosporium Burdsall in Burdsall & Eslyn, can oxidize PAHs. The objective of this study was to develop a novel bioremediation technology using a combination of abiological surfactant soil washing followed by PAH biological oxidation in soil washwater using P. chrysosporium in a rotating biological contactor (RBC) reactor. Soil used for experimentation was an 11-month aged contaminated soil spiked with a total of nine PAHs: acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, benzo(a)pyrene, dibenz(a-h)anthracene, and benzo(ghi)perylene. After 11 months of aging, recovery percentages of high molecular weight PAHs [i.e., from chrysene to benzo(ghi)perylene] were greater than 86%, while those of low molecular weight PAHs (i.e., from acenaphthene to pyrene) were less than 19%. Total removal efficiency for any of the nine PAHs was greater than 90% using a combination of surfactant soil washing and P. chrysosporium oxidation of soil washwater in the RBC reactor when used in batch operation, and greater than 76% when used in continuous operation. The treatment of PAH-contaminated soil using a combination of surfactant soil washing and subsequent PAH removal from the resultant washwater in an RBC reactor, in the presence of immobilized P. chrysosporium, permits (i) a rapid abiological cleanup of soil for compliance with relevant soil quality standards and (ii) PAH biological removal in soil washwater for compliance with aqueous discharge standards.

Removal of surfactant solubilized polycyclic aromatic hydrocarbons by Phanerochaete chrysosporium in a rotating biological contactor reactor

White rot fungi can oxidize surfactant solubilized polycyclic aromatic hydrocarbons (PAH). The objective of this study was to evaluate the performance of immobilized white rot fungus, Phanerochaete chrysosporium, to remove surfactant Tween 80 solubilized PAH i.e. phenanthrene, pyrene and benzo(α)pyrene in a rotating biological contactor (RBC) reactor. Results indicated that the immobilized P. chrysosporium in the RBC reactor system in continuous operation could effectively remove the three tested PAH at specific hydraulic loading rates and concentrations tested for each individual PAH. Batch operation of RBC reactor showed that the immobilized P. chrysosporium was stable and effective for the eight successive batch treatments of PAH in solution medium i.e. PAH removal was greater than 90% after 60 h, although only low levels of ligninolytic enzyme activity were detected. The removal of phenanthrene and pyrene in solution medium has been found to be a first order reaction in batch operation. A mass balance calculation indicated that biological oxidation was the main factor for removal of benzo(α)pyrene i.e. 95.7% in the RBC reactor. However, for phenanthrene and pyrene, both biological oxidation (i.e. 49 and 56%, respectively) and RBC disc foam adsorption (i.e. 44 and 34%, respectively) made a significant contribution to the removal of PAH.

Phenol biodegradation by rotating biological contactor

This study presents the removal performance of phenol in a three-stages cross flow laboratory-scale rotating biological contactor (RBC). The impact of major process and operating variables, such as input hydraulic loading (HL), input COD loading, and temperature of wastewater on the total removal efficiency of the system were examined. It was observed that the phenol removal performance worsened when the HL increased, and optimum total phenol removal efficiency of 99.9% was observed at loading of 4×10 −3 m −3 m −2 per day and COD concentration of 800 mg dm −3. On the basis of overall treatment of phenol containing wastewater in the RBC, the optimal removal performance was noted at the end of second stage inclusive the first one, but the third stage has not significant influence on phenol removal efficiency. The effect of temperature on improving the removal efficiency was significant in the temperature range of 13–43 °C, whose operating condition at 36 °C was optimum. The study of different phenol removal mechanism shows that about 10% of phenol was removed by physical adsorption and evaporation in RBC reactor.

Oxygen-Limited Nitrification and Denitrification in a Lab-Scale Rotating Biological Contactor

Rotating Biological Contactors (RBC) treating highly nitrogenous wastewaters are known to give rise to nitrogen losses, generally assumed to be due to concomitant nitrification and denitrification. In this study, a lab-scale nitrifying RBC reactor was shown to bring about losses of nitrogen of the order of 10 to 20% at ammonium loading rates of up to 2129 mg N m−2 d−1, when no extra carbon source was added. These higher removal values could be due to Oxygen-Limited Autotrophic Nitrification and Denitrification (OLAND), because the reactor was operated at oxygen limitation. When methanol was added as a soluble organic carbon source to further diminish oxygen transfer into the deeper parts of the biofilm, the RBC achieved 84% nitrogen removal (loading rate 2300 mg N m−2 d−1) at a COD/N ratio of 3.1. The latter also suggests that the OLAND process was occurring parallel to conventional denitrification.

Treatment of anaerobically pre-treated domestic sewage by a rotating biological contactor

The performance of a rotating biological contactor (RBC) for the post-treatment of the effluent of an up-flow anaerobic sludge blanket (UASB) was the subject of this study. Different hydraulic and organic loading rates have been investigated. The removal efficiencies of COD total, COD suspended, COD colloidal and COD soluble increased at a higher hydraulic retention time (HRT) and a lower influent organic loading rate. The results obtained indicated that a two-stage RBC reactor at an HRT of 10 h and an organic loading rate of 6.4 g COD m −2 d −1 represents an effective post-treatment process. Most COD suspended and COD colloidal were removed in the first stage while nitrification proceeded in the second stage. The overall nitrification efficiency was 92% at an ammonia loading rate of 1.1 g m −2 d −1. Total E. coli removal at HRTs of 10, 5 and 2.5 h were 99.5%, 99.0% and 89.0%, respectively. The major part of suspended E. coli (>4.4 μm) was removed by sedimentation or by adsorption in the biofilm of the first stage of RBC (99.66%). However, E. coli in the colloidal fraction (<4.4 to >0.45 μm) was eliminated in the second stage of RBC (99.78%). A comparison of the performance of a one-stage versus two-stage RBC system, operated at the same total loading rate, revealed an improvement in the effluent quality of the two-stage effluent as compared to the one-stage effluent. The two stages RBC were used to examine the effect of hydraulic shock loads on reactor performance in terms of COD, nitrification and E. coli removal.

Toxic effects on respiratory activities of phenol‐oxidizing cultures grown from various conditions

This study examined the toxic effects on respiratory activities of three cultures of phenol‐oxidizing bacteria grown with two chemostats at mean cell retention times (MCRT) of 3.8 and 18.7 days, respectively, and one with rotating biological contactors (RBC) at MCRT of 71.0 days. Bacterial activity was evaluated by measuring specific oxygen uptake rates (SOUR) for the three cultures when subjected to various concentrations of phenol (within 1000 mg l‐1), and two concentrations of trichloroethylene (2, and 20 mg l‐1). Phenol exposure data were also modeled using Haldane kinetics and then solved by nonlinear regression routine. According to those results, cells from the chemostat with 3.8 MCRT have the highest respiratory activities, while those from RBC reactor are least active. When exposed to 2 mg l‐1 of TCE, all of the cultures exhibited no significant toxic effect. However, increasing the TCE dosage to 20 mg l‐1 obviously inhibited the cell's respiratory activities, particularly for the cultures with a RBC reactor.

A study on microbiology of biological film layer in rotating biological contactors

Experimental studies were carried out for upgrading the secondary treated domestic sewage effluent using the Rotating Biological Contactors (RBC) as an unit process in the premises of the existing water reclamation plant of Satellite Centre Building Complex of Indian Space Research Organisation at Bangalore. As part of these studies, a brief study was carried out on the microbiological aspects of the biological slime layer developed in the RBC. This study included observations on the development of the biological film on wetted disc surfaces of RBC, measurement of the thickness of the biological film, a discussion on significance of biofilm thickness in substrate removal, effect of wastewater characteristics on the thickness of biofilm and determination of MLSS/MLVSS ratio of biological film obtained in RBC reactor used for upgrading the secondary effluent. The results of these studies are presented in this paper. The results of identification of species of micro-organisms predominant in the biological slime layer in the RBC used for upgradation of secondary treated effluent are discussed separately in another paper.

Hydraulics of bench-scale rotating biological contactor

The hydraulic characteristics of a four-stage bench-scale rotating biological contactor (RBC) were studied using its three major operating parameters: (i) liquid flow rate, (ii) rotational speed of disc and (iii) degree of submergence. The liquid flow rate and the degree of submergence have been combined to obtain the dimensionless parameter Reynolds number ( Re), whereas the liquid flow rate and the rotational speed have been grouped together, leading to another dimensionless parameter, Modified Froude number ( Fr). Moreover, the different stages of RBC have been expressed in terms of dimensionless length ( L R ). The overall dispersion number ( d = D UL , where D is the dispersion coefficient, U is the velocity of liquid and L is the length of liquid flow path) of the flow regime in the RBC has been formulated by a hydraulic model based on multiple linear regression analysis through a package of 96 observations on tracer response data in the RBC operating at flow rates of 0.04–21.90 m 3/day, rotational speeds of 1–15 rpm and degrees of submergence of 32–60%, resulting in Re values in the range of 51–2500 and Fr values in the range of 5.61 × 10 −6 to 1.26 × 10 −3. The overall value of d has reduced significantly, by 76%, from the first stage (2.48) to the fourth and final stage (0.60). It increased with the increase of Re and Fr values. The range (0.048-8.24) of the observed values of d shows insignificant deviation from the corresponding values predicted by the following proposed hydraulic model for a multi-stage RBC reactor. The model with a multiple correlation coefficient value of 95% is d p = D UL = 0.32(Fr) 0.57(Re) 0.75 (L R 1.1

Treatment of phenolic wastewater in RBC reactor

The removal performance of phenol in a four-stage cross-flow laboratory-scale rotating biological contactor (RBC) reactor was investigated in the present study. The impacts of major process and operating variables, viz. input phenol concentration ( PH i), input phenol loading ( PH.L), input hydraulic loading ( HL), temperature of wastewater ( T), and rotational speed of discs (ω) on the removal efficiency of the system were examined. A first-order reaction with an average rate constant ( K e ) value of 0.10–0.13 h −1 at a temperature range of 20.5–27.0°C was obtained for the biodegradation of phenolic wastewater. On the basis of overall treatment of phenolic wastewater in the RBC reactor, the optimal removal performance was noted at the end of the second stage inclusive of the first one. It was observed that the phenol removal performance improved at higher input phenol concentrations, while at the increased level of input hydraulic loading, the removal performance worsened. The effect of temperature in improving the removal efficiency was significant in the temperature range of 13–36°C. The temperature activity coefficient (ϑ) value of the VantHoff-Arrhenius equation was computed as 1.04 in the stated range of temperature. The positive role of rotational speed of discs in the treatment of phenolic wastewater was more pronounced in the range of 3.7–10 rpm. The major group of microbes, responsible for the microbial treatment of phenol in the acclimatized concentration up to 420 g m −3, was identified as Pseudomonas and the corresponding species were detected as stutzeri and Putida.

Phenol‐ and Thiocyanate‐Based Wastewater Treatment in RBC Reactor

A laboratory-scale investigation at ambient temperature was performed to examine the applicability of a four-stage across-the-flow rotating biological contactor (RBC) reactor for the treatment of synthetic waste-water containing phenol and thiocyanate. The composition was so maintained that the phenol to thiocyanate ratio approximated that usually found in coal carbonization effluent. In the combined treatment of the toxicants, it was noted that the toxicants were removed in sequence. Phenol was mostly removed in the earlier (first and second) stages, while thiocyanate-fed microbes acted more efficiently in the latter stages (third and fourth). The overall reaction rate coefficient for phenol biodegradation (K{sub PH}) varied in the range of 10.20--3.50 g/m{sup 2}{center_dot}d in presence of 0--240 g/m{sup 3} of influent thiocyanate concentration. The same coefficient for thiocyanate biodegradation (K{sub TH}) was found to be in the range of 8.20--0.30 g/m{sup 2}{center_dot}d in presence of 0--240 g/m{sup 3} of influent phenol concentration. The effects of various operating and process parameters such as disk rotational speed, temperature of the reactor liquid, and substrate load on the removal of phenol and thiocyanate were also examined. The microbes, predominantly found in the earlier stages, were identified as Pseudomonas putida, Pseudomonas stutzeri and Candida tropicalis, whereas in themore » latter stages, Thiobacillus thioparus and Nocardia sp. populations predominated.« less

Nitrate removal from groundwater using an anoxic-aerobic rotating biological contactor

The removal of nitrate-nitrogen from groundwater was investigated using two rotating biological contactors (RBC) in series. The first pilot plant RBC reactor was operated under anoxic condition to remove nitrate-nitrogen. A fraction of effluent of the anoxic RBC was fed to a bench scale aerobic RBC to study the degradation of residual organic carbon and oxidation of nitrite-nitrogen. The first reactor achieved a nitrate removal efficiency of 90 percent for a loading rate of 76 mg/m2.h. The corresponding effluent nitrate, nitrite and residual carbon sources concentrations amounted to 3.3, 0.34 and 3.9 mg/l, respectively. The optimum ethanol to nitrate-nitrogen (E/N) ratio was found to be 2.35. No residual ethanol and nitrite-nitrogen were observed in the final effluent under optimum conditions. Dissolved oxygen in the final effluent was found to be greater than 7 mg/l. The results of the study suggest that using a continuous anoxic-aerobic RBC is a convenient and reliable process for removal of nitrate, residual organic carbon and nitrite.

Nitrate removal from groundwater using an anoxicaerobic rotating biological contactor

The removal of nitrate-nitrogen from groundwater was investigated using two rotating biological contactors (RBC) in series. The first pilot plant RBC reactor was operated under anoxic condition to remove nitratenitrogen. A fraction of effluent of the anoxic RBC was fed to a bench scale aerobic RBC to study the degradation of residual organic carbon and oxidation of nitrite-nitrogen. The first reactor achieved a nitrate removal efficiency of 90 percent for a loading rate of 76 mg/m2.h. The corresponding effluent nitrate, nitrite and residual carbon sources concentrations amounted to 3.3, 0.34 and 3.9 mg/l, respectively. The optimum ethanol to nitrate-nitrogen (E/N) ratio was found to be 2.35. No residual ethanol and nitrite-nitrogen were observed in the final effluent under optimum conditions. Dissolved oxygen in the final effluent was found to be greater than 7 mg/l. The results of the study suggest that using a continuous anoxic-aerobic RBC is a convenient and reliable process for removal of nitrate, residual organic carbon and nitrite.