Rotating Biological Contactor System Research Articles

Efficiency of Packed Cage RBC System for Treatment of Wastewater Containing Surfactants

Abstract The chemical oxygen demand (COD) and five-day biological oxygen demand (BOD5) removal efficiencies of a packed cage rotating biological contactor (RBC) system under a hydraulic retention time (HRT) of 16 h declined from 93.90% to 78.58% and 78.61% and 96.27% to 84.83% and 87.93%, respectively, with an increase of sodium dodecyl sulphate (SDS) and triton X-100 loading from 0.00 to 1.25 mg/m2·d. Reactor no. 1 of the system changed to anaerobic when the system was operated under an HRT of 8 h with surfactant loading of up to 2.55 mg/m2·d. However, reactor no. 2 of the system was aerobic and the dissolved oxygen was higher than 3.00 mg/L. The study showed that this type of packed cage RBC system could be applied for treating the cosmetic industry wastewater with surfactant loading of up to 2.55 mg/m2·d under an HRT of 8 h.

Rotating Biological Contactors: A Review

Rotating biological contactors (RBCs) offer an alternative treatment technology to the conventional activated sludge process. The principal advantages of the RBC stem from the fact that the interfacial area generated is very high and practically independent of the speed of rotation, unlike in the activated sludge process. In the present work, the process design aspects of RBCs are reviewed. The published literature on various aspects such as media employed in RBCs, hydrodynamic characteristics, power consumption, and mass-transfer characteristics is reviewed. The various models proposed for the design of RBC systems are reviewed. A stepwise procedure is given for the process design of an RBC system. The RBC system is compared with the other wastewater treatment facilities such as the activated sludge process and trickling filters in terms of its oxygen-transfer efficiency.

Oxygen-limited nitrogen removal in a lab-scale rotating biological contactor treating an ammonium-rich wastewater

A lab-scale Rotating Biological Contactor (RBC) was operated with the purpose of oxygen-limited (autotrophic) nitrification-denitrification of an ammonium-rich synthetic wastewater without Chemical Oxygen Demand (COD). Based on the field observations that RBCs receiving anaerobic effluents come to anoxic ammonium removal, the RBC was inoculated with methanogenic sludge. Some 100 days after the addition of the anaerobic sludge to the reactor as a possible means of a rapid initiation of the nitrogen (N) removal process, a maximum ammonium removal of 1,550 mg N m(-2) d(-1) was achieved. Batch tests with 15N labeled ammonium and nitrite indicated that a large part of that N was removed via oxygen-limited oxidation of ammonium with nitrite as the electron acceptor. The other part was removed via conventional denitrification, presumably with COD released from lysis of cells. Species identification of the most abundant microorganisms revealed that Nitrosomonas spp. were the dominant ammonium-oxidizers in the sludge. Thus far, the molecular characterization of the sludge could not show the presence of Planctomycetes among the most dominant species. Overall this experiment confirms the property of the RBC system to remove ammonium to nitrogen gas without the use of heterotrophic carbon source.

Design Criteria for a Rotating Biological Contactor System for Treatment of Urinal Wastewater

Various design criteria have been set for Rotating Biological Contactor (RBC) for treating urinal wastewater. The aim of treating urinal wastewater is to remove odour and color from it so that it can be recycled for flushing. In the present paper, significance of RBC system for treating urinal wastewater has also been elaborated. The setting up of design criteria is based on the assumption that the rate of nitrification is zero-order with respect to total Kjeldhal nitrogen concentration. Principles of bioprocess involved in wastewater treatment have also been described in relation to the composition of human urine.

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.

Dynamics of protozoan and metazoan communities in a full scale wastewater treatment plant by rotating biological contactors

Performance of a full-scale wastewater treatment plant by rotating biological contactors (RBC) system was monitored during a year by physico-chemical and microbial characterisation. Six points along wastewater treatment were selected in the plant: three points along the water line (influent, sedimentation tank and effluent) and three points along RBC system (RBC1, RBC2 and RBC3). Although a large seasonal change in the values of physico-chemical parameters was observed, operation of the plant was optimal during all year (90% of removal in BOD5 and SS influent content). Microbial characterisation was approached by determining the structure and dynamics of protozoan and metazoan communities. Protozoa were the most abundant in all stages in the plant, heterotrophic flagellates being the most representative group in the water line and ciliates in the RBC system. The same seasonal preference was only observed for heterotrophic flagellates in the water line and green flagellates in the RBC system, both groups having highest abundances in summer and spring, respectively. Identification of ciliated protozoa populations rendered 58 species of ciliates in the plant. Most of these species are typical of aerobic wastewater treatment systems except three of them, which are cited for the first time in this type of ecosystems: Chaenea stricta, Holosticha mancoidea and Oxytricha lanceolata. Along the water line 34 species were identified, and half of them only appeared occasionally (once in all the study), while along the RBC system biofilms 55 species were observed, and the majority appeared permanently in this system. Our results indicate that the type of habitat, rather than the physico-chemical water parameters, was the primary factor in determining the different distribution of protozoan and metazoan communities in the plant. In RBC biofilms, the structure of ciliate protozoa community was found to be quite sensitive to changes in physico-chemical parameters, mainly to organic loading (BOD5) variations.

Biofilm Communities and Operational Monitoring of a Rotating Biological Contactor System

A full scale rotating biologicalcontactor (RBC) system has been studied for a year.The main objective was to determine the distributionof protozoan and metazoan communities inhabiting theRBC biofilms, and to relate them to the BOD5content along RBC train. RBC system operatedefficiently as showed the removal of TBOD5 and TSSalong the plant. A weak nitrification process tookplace at last stages of the system. Orthophosphatesand pH average values were maintained quite similarthroughout the RBC stages. Microscopical countingindicated that communities were mainly made up ofciliated protozoa, although the abundance anddiversity of species varied widely along the differentRBC stages. A careful characterisation of ciliatespecies was carried out, with Vorticellaconvallaria, Epistylis entzii and Carchesiumpolypinum being the most abundant species in the wholesystem. Metazoa only reached a noticeable proportionin the last stages of the system. Spatial distributionof biofilm communities reflected the environmentalchanges observed as waste purification progresses.Associations between microorganisms and BOD5concentrations were studied by correlation analysis.Results chiefly revealed the importance of ciliatedprotozoa in this biological system. They showed a highabundance on the biofilms and some groups– cyrtophorids, hypotrichs, scuticociliates andpleurostomatids ciliates – were closely related to adecrease of BOD5 content.

Biodegradation of hydrocarbons by Prototheca zopfii in rotating biological contactors

The application of petroleum-degrading achlorophyllous micro-alga Prototheca zopfii cells to rotating biological contactors (RBCs) was investigated. The degradation activity of the biofilm, developed on the polycarbonate discs of the laboratory scale, single stage RBC was measured in batch operation at 25°C for 30 days. The volumetric biodegradation rate for n-alkanes (mixture of C 14, C 15 and C 16) as a model oil in the RBC system, was lower than that obtained for the bubble-column bioreactor, using immobilized biomass in polyurethane cubes. Abiotic attenuation of hydrocarbons by vaporization from the RBC rector during operation however, could be reduced significantly compared with the case of the bubble-column system. Mathematical modelling of the biodegradation characteristics of the RBC system was attempted, and validation of the model was confirmed. The model was extended to simulate the performance of the continuous biodegradation operation in the three RBCs in series.

Effect of Disc Rotating Velocity on the Nitrification Performance of RBC System and Biofilm Kinetics

Nitrification of high strength ammonia wastewaters in a rotating biological contactor (RBC) system was studied at 5 rpm, 15 rpm and 20 rpm disc rotating velocities. Effect of disc rotating velocities on the performance of the RBC system and biofilm kinetics was observed. Flow rates were changed from 19.6 to 103.5 l day−1 giving hydraulic retention times of 0.28 to 1.5 days. Influent NH4-N concentrations were changed from 100 to 550 mg l−1. For certain applied NH4-N loading rates and bulk NH4-N concentrations, rotating velocity of discs affected NH4-N removal rate and biofilm kinetics in the RBC system. If NH4-N removal efficiency and NO2-N concentration in the effluent were considered, RBC system was more efficient at 15 rpm disc rotating velocity at about 6 g NH4-N m−2 day−1 applied NH4-N loading rates. NH4-N removal rate of the RBC system at 5 rpm, 15 rpm and 20 rpm disc rotating velocities was nearly equal at applied NH4-N loading rates up to about 3.5 gNH4-N m−2 day−1.

Treatment of Methanogenic Landfill Leachate to Remove Ammonia Using a Rotating Biological Contactor (RBC) and a Sequencing Batch Reactor (SBR)

The authors investigated the use of a pilot scale rotating biological contactor (RBC) and a pilot scale sequencing batch reactor (SBR) to nitrify landfill leachate with a mean ammonia nitrogen concentration of 202 mg L−1 and mean BOD5 concentration of 50 mg L−1. The research was conducted under field conditions over a 14 month period. The research showed that, for this type of leachate, the RBC ammonia removal was superior to the SBR ammonia removal. The result appeared to be due to the low solids generation potential of this type of leachate, and the impacts of low temperature on the SBR system. Mixed liquor solids concentration appeared to be the critical factor in determining SBR ammonia removal. Full ammonia removal was achieved at RBC loading rates up to 4.5 g m−2 day−1, a hydraulic retention time of 0.3 days and a temperature of 18 °C. Full ammonia removal was achieved in the SBR unit at ammonia loading rates up to 400 g m−3 day−1 (0.6 g g MLSS−1 day−1), a hydraulic retention time of 0.7 days, and 20 °C. The effect of temperature on the RBC ammonia removal was modeled using the Arrhenius Equation with Θ = 1.111 and R2 = 0.88. Ammonia was effectively removed by the RBC system at temperatures as low as 2 °C. At temperatures exceeding 20 °C, RBC performance appeared to be inhibited. Phosphorus limitation appeared to reduce RBC performance at effluent soluble PO4-P concentrations less than 0.2 mg L−1. RBC mass removal rate was affected by influent ammonia concentration. Artificially increasing the influent ammonia concentration resulted in increased ammonia removal. Neither system effectively removed BOD5, COD, colour or metals. Removal for these parameters ranged from less than 0 to 40%.

Rotating biological contactors for wastewater treatment in an equatorial climate

The purpose of the study was to investigate the use of the Rotating Biological Contactor (RBC) to treat high strength wastewater in an equatorial climate. Total Organic Carbon, BOD and COD were used as analytical parameters to determine the efficiency of treatment of the wastewater, using high influent concentrations and high loading rates with a laboratory scale rotating disk system operating under ambient temperatures in Singapore. The effect of recirculation of the effluent was also studied. The results indicated that the RBC system could produce high treatment efficiencies at high ambient temperatures, however there were problems with first stage due to the high reaction rate. The Stover-Kincannon relationship appeared to adequately model the process when TOC was used as the major analytical parameter for loading rates up to 20 g m−3 d−1. Higher loading rates produced first-stage problems and lower removal efficiencies. Recirculation had little effect on the treatment efficiency at low loading rates.

Rotating biological contactors for wastewater treatment in an equatorial climate

The purpose of the study was to investigate the use of the Rotating Biological Contactor (RBC) to treat high strength wastewater in an equatorial climate. Total Organic Carbon, BOD and COD were used as analytical parameters to determine the efficiency of treatment of the wastewater, using high influent concentrations and high loading rates with a laboratory scale rotating disk system operating under ambient temperatures in Singapore. The effect of recirculation of the effluent was also studied. The results indicated that the RBC system could produce high treatment efficiencies at high ambient temperatures, however there were problems with first stage due to the high reaction rate. The Stover-Kincannon relationship appeared to adequately model the process when TOC was used as the major analytical parameter for loading rates up to 20 g m-3 d-1. Higher loading rates produced first-stage problems and lower removal efficiencies. Recirculation had little effect on the treatment efficiency at low loading rates.

Sludge production in rotating biological contactors with supplemental aeration and an enlarged first stage

A full-scale rotating biological contactor (RBC) was used to study the effectiveness of supplemental aeration and an enlarged first stage in improving the performance of an RBC system. These experimental studies suggest that generally the sludge production was higher in the first stage because of the higher soluble COD (SCOD) removal rates. However, the sludge production in the first stage was significantly higher in the presence of supplemental air than without the air. At lower organic loadings, the first-stage sludge production was 1·09 kg SS/kg (2·40 lb SS/lb) and 0·572 kg SS/kg (1·26 lb SS/lb) SCOD removed with and without supplemental air, respectively. In addition, with supplemental air there was an increasing stabilization of volatile solids in the subsequent stages when the substrate was limiting in the succeeding stages. Overall sludge production was the same with and without supplemental aeration at low and high organic loading rates. However, overall sludge production decreased substantially with the use of an enlarged first stage, particularly with supplemental aeration, which results in lower operating costs for sludge stabilization and disposal. This occured despite higher first-stage sludge production rates with the use of supplemental air. Also, the overall performance of the RBCs receiving supplemental aeration was significantly better when compared to the RBCs receiving no supplemental air, both in terms of SCOD or SBOD 5 removal and ammonia nitrification.

Upgrading of rotating biological contactor (RBC) systems to achieve higher effluent quality, including biological nutrient enrichment and reduction techniques

This paper explores RBC system mechanical and process upgrade alternatives. There may be multiple upgrade opportunities. Some process upgrades are proprietary while others are not. Mechanical and process upgrades describe many positive advantages for existing plants that need to be upgraded to meet more stringent effluent limits or for increased capacity. A case study was conducted to evaluate a process upgrade. Simple physical manipulation of existing process parameters within the treatment plant and the addition of a new process feature to facilitate secondary sludge recycle to the RBCs showed increased organic capacity and improvement in effluent quality. Also, a significant reduction in nutrients (N &amp; P) without the use of chemicals and a significant reduction in RBC shaft weight were other benefits. The easily settleable solids contained at least a doubling of the phosphorus content and dewatered well without chemical supplementation.

Activity of Biomass in RBC System Treating Pulp Industrial Wastewater

The activity of biomass in a longitudinal laboratory‐scale rotating biological contactor (RBC) system used for the treatment of evaporator condensate from a sulfite pulping process was determined by chemical parameters (TKN:SS and VSS:SS) and biological kinetic parameters (the rate of endogenous respiration, the maximum specific respiration rate, etc.) carried out in Warburg experiments. The results show that kinetic parameters are more effective in describing the activity of the biomass, both on the disks and in the basin of the RBC, than chemical parameters. The biomass on the disks at the transition phase of carbonaceous removal to beginning of nitrification has a high activity, which is comparable to that of activated sludge with high F/M ratio of 0.9 kg BOD5/kg MLSS/day. The biomass suspended in the basin of the RBC has only about one‐tenth of the metabolic activity of the disk biomass.

Improved Biological Nitrification Using Recirculation in Rotating Biological Contactors

The effect of recirculation on biological nitrification in rotating biological contactors (RBCs) was examined in an on-site pilot-scale RBC system which simulated full-scale plant RBC operations at the Longmont, Colorado, Wastewater Treatment Plant (LWWTP). Two LWWTP wastewater streams were used as pilot RBC influent. One wastewater stream, designated the “fresh” influent, was first stage trickling filter effluent. The second stream, designated the “recirculation” influent, was clarified secondary effluent. Three recirculation ratios, defined as the ratio of the recirculation influent to the fresh influent, were examined: 0 (no recirculation), 1 (50% of the flow is recirculation), and 3 (75% of the flow is recirculation). Each recirculation ratio was studied at three hydraulic loading rates. Recirculation improved nitrification at all hydraulic loading rates. Improved nitrification with recirculation was due to the dilution of influent biodegradable organic carbon (BOD5) which occurs as a result of mixing secondary plant effluent with first stage effluent. An unexpected and operationally significant result was that extremely low concentrations of influent organic carbon did not improve nitrification.

Evaluation of a small unsteady continuous flow RBC system

Abstract An unsteady state mathematical model of Rotating Biological Contactors (RBC) has been presented. The model was calibrated and tested in an operating RBC system. Under Steady State, the model was capable of predicting the performance of the operating plant by a standard error of 2,6% of the average steady state condition in the first stage of the system. Under unsteady condition, the standard deviation in model prediction of effluent quality measured within the range of 78‐ 132 mg/1 was found to be 7.8 mg/(BOD5). This observation indicated that the model may be utilized to simulate RBC system under unsteady state condition also.

Nitrification Kinetics and Its RBC Application

The surface reaction model for the mechanism of mass transfer-metabolism in the fixed-film nitrification process is investigated and discussed for the design of trickling filter systems and rotating biological contactor (RBC) systems. Two experimental studies are performed. The first study, using a stationary fixed-film reactor to simulate the trickling filter process, reveals that the surface reaction kinetics follow a pseudo-homogeneous model. The second study, using a bench-scale RBC unit, indicates that the pseudo-homogeneous model is also applicable to the rotating fixed-film process. The effective slime thickness of an RBC system can be estimated from this model by locating the optimum NH3-N removal rotating speed and finding the corresponding liquid film thickness at that rotating speed.