Rotating Biological Contactor Unit Research Articles

Treatment of palm oil mill effluent using modified rotating biological contactor with organic loading rate variations

Indonesia is the world’s largest producer of palm oil or Crude Palm Oil (CPO). Palm oil production generates Palm Oil Mill Effluent (POME), which can harm the environment, if not properly treated. Untreated POME, with high Chemical Oxygen Demand (COD) levels, can lead to environmental degradations. Its high organic content and low acidity levels can also cause water pollution. This study modified the Rotating Biological Contactor (RBC) unit to treat POME, increasing the contact surface area between POME and microorganisms. It aimed to analyse the performance of the modified RBC unit, based on variations in organic loading rate (OLR). The study was conducted at a laboratory scale, with 2, 5, and 7 kgCOD/L/day organic loads. The results of this study revealed the highest percentage of removal obtained at an OLR variation of 7 kgCOD/L/day, with a removal rate of 70% for chemical oxygen demand (COD) concentration and 57% for ammonia concentration. Based on the research, the COD removal for organic loads of 7 kgCOD/L/day and 5 kgCOD/L/day decreased to 1900 mg/L and 2600 mg/L, respectively. Thus, the modified RBC unit would be more efficient with an organic load of 7 kgCOD/L/day. However, the COD concentration still did not comply with the water quality standards. Therefore, integrating the modified RBC unit with pre-treatment units, such as coagulation-flocculation, is necessary to achieve optimal effluent concentrations.

Treatment of Industrial Waste Water using Single-Stage Rotating Biological Contactor

This paper presents treatment of industrial waste water using a single-stage Rotating Biological contactor (RBC). A RBC unit typically consists of a series of closely spaced large flat or corrugated discs that are mounted on a common horizontal shaft and are partially or completely submerged in wastewater. The shaft continually rotates by a mechanical motor or a compressed air drive and a bio film is established onto the entire surface area of the media, which metabolizes the organic materials contained in the wastewater. Microorganisms get attached to and grow on these discs. The discs mounted on the surface of a rotating shaft are usually made up of different forms of plastic such as polypropylene or polyurethane. For this study, shaft of RBC is wrapped with polypropylene foam as bio-film medium. From the analysis of results obtained for the present study it has been found that, polypropylene foam as a bio-media can remove organic matter up to 91.2%, nitrate up to 86.2% and phosphate up to 96.3% for 48 hr of hydraulic retention time.

PENGOLAHAN AIR LIMBAH DENGAN SISTEM REAKTOR BIOLOGIS PUTAR (ROTATING BIOLOGICAL CONTACTOR) DAN PARAMETER DISAIN

A rotating biological contactor (or RBC) is a type of fixed media filter which removes both organic matter and ammonia from water. It can be added to a packaged plant for more efficient ammonia removal, replacing the aerator in both location and function.The RBC consists of a series of rotating discs. These discs are coated with a biological slime like the slime on rocks in a healthy stream. This slime is rotated through the air and and then through the wastewater so that it picks up oxygen in the air and breaks down B.O.D. in the wastewater. Since the discs rotate through the air, there is no need to pump air into the wastewater. And since the slime stays on the discs, there is no need to recycle sludge. The present study describes basic consideration of rotating biological contactor (RBC) system for wastewater treatment. The design of an RBC system must include the following consideration sach as organics and surface loading criteria, staging of RBC units, peripheral velocity, temperature, effluent characteritics and secondary clarifier. The RBC system have some advantages : smaller basin, less upset, high loading rate, nitrification/de-nitrification, high tolerance, low OM Cost, durable constructions, odorless, no noise, and stable sludge characteristics. Kata Kunci : Reaktor bioloigis putar, air limbah, parameter disain.

Reactor performance in terms of COD and nitrogen removal and bacterial community structure of a three-stage rotating bioelectrochemical contactor

Integrating microbial fuel cell (MFC) into rotating biological contactor (RBC) creates an opportunity for enhanced removal of COD and nitrogen coupled with energy generation from wastewater. In this study, a three-stage rotating bioelectrochemical contactor (referred to as RBC–MFC unit) integrating MFC with RBC technology was constructed for simultaneous removal of carbonaceous and nitrogenous compounds and electricity generation from a synthetic medium containing acetate and ammonium. The performance of the RBC–MFC unit was compared to a control reactor (referred to as RBC unit) that was operated under the same conditions but without current generation (i.e. open-circuit mode). The effect of hydraulic loading rate (HLR) and COD/N ratio on the performance of the two units was investigated. At low (3.05 gCOD g−1N) and high COD/N ratio (6.64 gCOD g−1N), both units achieved almost similar COD and ammonia-nitrogen removal. However, the RBC–MFC unit achieved significantly higher denitrification and nitrogen removal compared to the RBC unit indicating improved denitrification at the cathode due to current flow. The average voltage under 1000 Ω external resistance ranged between 0.03 and 0.30 V and between 0.02 and 0.21 V for stages 1 and 2 of the RBC–MFC unit. Pyrosequencing analysis of bacterial 16S rRNA gene revealed high bacterial diversity at the anode and cathode of both units. Genera that play a role in nitrification (Nitrospira; Nitrosomonas), denitrification (Comamonas; Thauera) and electricity generation (Geobacter) were identified at the electrodes. Geobacter was only detected on the anode of the RBC–MFC unit. Nitrifiers and denitrifiers were more abundant in the RBC–MFC unit compared to the RBC unit and were largely present on the cathode of both units suggesting that most of the nitrogen removal occurred at the cathode.

Performance of an in-situ rotating biological contactor in a recirculating aquaculture system

The start-up and activation of a nitrifying rotating biological contactor (RBC) and its performance inside a culture tank of rainbow trout were studied. First, in a lab-scale operation, the system was fed with a synthetic medium containing a high ammonia concentration (567 mg NH(4)(+)-N L(-1)) and operated at a high hydraulic retention time (HRT) (6.5 days) to minimize the wash-out of the biomass and promote the biofilm formation. Then, both inlet ammonia concentration and HRT were decreased in order to obtain operational conditions similar to those of the culture tank. During this period, the RBC was able to treat an ammonia loading rate (ALR) of 0.64 g N-NH(4)(+) L(-1) d(-1) with a removal efficiency within 70-100%. Pilot-scale experiments were carried out in culture tanks of rainbow trout. The operation of a recirculating system with the RBC unit was compared with a recirculating system without biological treatment and with a flow-through system. The use of this in-situ nitrifying unit allowed working at a recirculation ratio of 90% without negative effects on either growth or the condition factor of fishes. Up to 70% of ammonia generated was removed and a removal rate of 1.41 g NH(4)(+)-N m(-2) d(-1) was reached.

Ensuring effluent standards by improving the design of Rotating Biological Contactors

The Rotating Biological Contactor (RBC) is used for both municipal and industrial wastewater treatment; however, the RBC has been plagued with mechanical deficiencies since its conception. The unpredicted loss of mechanical integrity results in loss of operation and the discharge, into the environment, of effluent that does not meet consent standards as set by governmental bodies. The consequence of the latter on aquatic life cannot be understated. Whilst maintaining an effluent standard is of vital importance this has to be balanced against the capital costs of RBC units. In addition to detailing reasons for defects associated with RBC’s this paper presents a novel design approach for shaftless RBC’s. This novel design takes cognisance of the mechanisms and reasons for mechanical failure, thereby reducing occurrence of loss operation of RBC units and ensuring that the effluent continually meets discharge standards. The added significance of the design is a 50% reduction in costs.

Enhanced biological phosphorus removal in RBC with SBR modification

The rotating biological contactor (RBC) system was operationally modified with a sequencing batch reactor to achieve biological phosphorus removal from a weak domestic sewage along with nitrogen removal. This study utilized three RBC units, of which two units were the main units to remove phosphorus and NH4N and the third RBC unit was used as the storage of wastewater for its minimal effect to the PAO activities in the anaerobic stage during the operation. It was noticed that the biofilm thickness in RBC must be controlled to be less than 1.8 mm in order to achieve more than 70% of P removal with about 60% of N removal. With a settled sewage representing 200 mg/L of COD and 5 mg/L of P, the predicted P content in biofilm was more than 3% and the effluent P concentration was about 1 mg/L. The %P content in biofilm decreased with an increase of influent COD/TP ratios. The COD requirement for anaerobic P release was similar to reported values for the suspended growth system, however, the overall requirement increased with thicker biofilm.

Characterization of Extracellular Polymeric Substances in Rotating Biological Contactors and Activated Sludge Flocs

Extracellular polymeric substances (EPS) from biofilms of a rotating biological contactor (RBC) system and from activated sludge flocs were extracted using ultrasound and a cation exchange resin. In both wastewater treatment systems, the EPS matrix was mainly constituted of proteins, humic-like substances and polysaccharides, although other components - DNA and uronic-like substances- were also present. The composition of the biofilm EPS was different in the succesive RBC wastewater treatment stages: protein had its highest concentration in the first RBC unit, while humic substances and polysaccharides in the third RBC. Significant differences between biofilm and sludge floc EPS were also reported. The amount of proteins was 3.5 times higher for RBC biofilms than for sludge flocs, and quantities of humic substances and polysaccharides extracted from biofilms were twice as high than in sludges. Moreover, biofilm exopolymers were two times more hydrophobic than those of sludge flocs. Implications of wastewater chemistry and microbial growth strategies into EPS composition and properties are suggested.

Biodegradation of trichloroethylene in a rotating biological contactor

A laboratory scale study was carried out to treat synthetic wastewater containing 30 mg/l of trichloroethylene in a rotating biological contactor (RBC). A mixed culture of bacteria consisting of nitrifiers, heterotrophs and Thiosphaera pantotropha could be developed and acclimated to achieve 99.89% removal of trichloroethylene (TCE) from synthetic wastewater at TCE loading of 0.0039 m 3/m 2 d and HRT of 3.5 days. A substrate: CO substrate ratio of 1:100 and above was found to be optimum to avoid enzyme competition. C:N ratio of 100:20 was optimum for the biodegradation of TCE. The system could withstand TCE shock loadings up to 0.309 m 3/m 2 d. The volatilization losses of TCE were 4.8% from the RBC unit.

Performance of family-size sequencing batch reactor and rotating biological contactor units treating sewage at various operating conditions

Field trials were carried out using two types of package units designed for the treatment of domestic sewage from individual households. One of the units was a commercially available rotating biological contactor (RBC) system. The other was a newly developed sequencing batch reactor (SBR) system. Trials were carried at the site of a local sewage treatment plant where degritted raw sewage from a combined sewerage network was fed to the two units for a period of four months. Both units produced good effluent quality, well below 20/30 (BOD/SS) during steady-state performance. However, shorter start-up time was observed with the SBR unit together with better effluent quality (up to BOD<10 mg/l and SS<15 mg/l). Furthermore, the SBR unit produced effluents with ammonia nitrogen and total phosphorus levels of 3 mg/l and 2 mg/l respectively, for influent levels that varied from 20 to 60 mg N-NH3/l and from 15 to 17 mg/l of total phosphorus. On the other hand, significant nutrient removal did not seem tohave occurred in the RBC unit. During testing to meet the requirements of British Standard (BS 6297), it was observed that the SBR can tolerate shockloads and periods following zero flow better than the RBC unit.

Mechanical redesign of the rotating biological contactor

The principle of the Rotating Biological Contactor (RBC) was originated in the early part of the century and today there are many thousands of units operating world wide. However, the RBC has been plagued with mechanical deficiencies since its conception. This paper presents a brief insight into some of the major mechanical defects associated with RBCs. These findings have been accumulated over the past three years during a mechanical design audit, and encompass over two hundred and sixty RBC units visited operating on site. The reasons for mechanical failures are attributed to poor engineering design, low frequency corrosion fatigue and microbiologically influenced corrosion; evidence supporting these claims is presented. Having the benefit of a thorough understanding of the mechanisms and reasons for mechanical failure, a new approach to designing RBCs is encouraged. This has resulted in a new generation of RBC designs with a guaranteed operational life of twenty years.

Role of supplemental aeration in improving overloaded first-stage RBC performance

A study was conducted to evaluate the effectiveness of supplemental aeration in improving the performance of an rotating biological contactor (RBC) treatment system whose first and second stages were overloaded resulting in very low dissolved oxygen conditions and heavy beggiatoa growth thereby deteriorating process performance. A four-stage RBC having two parallel trains and treating combined municipal and industrial dairy wastewater was used to conduct the research. One train was provided with supplemental air in all stages and the other train, without supplemental air, was used as a control. Daily 24-hour compositie samples were collected at the influent to the RBC and at the end of each stage. Dissolved oxygen, pH, and temperature levels were measured in each stage. Samples were analyzed for soluble COD, ammonia nitrogen, total and volatile suspended solids. Samples were also analyzed for soluble BOD5 and oxygen uptake rate once a week. The biomass thickness on the discs was measured and growth conditions were noted. The experimental results indicate that RBC units with supplemental aeration demonstrated remarkable performance and ability to adapt to differing organic loading rates. In addition, beggiatoa growth was completely eliminated with supplemental air thereby establishing thinner and active aerobic biomass.

Mineralogical characteristics of residues produced in microbiological treatment of acidic mine drainages

Abstract Inorganic residues produced on the disks of rotating biological contactor (RBC) wastewater treatment units during microbiological oxidation of the ferrous iron in both natural and synthetic acidic mine drainages were analyzed using x‐ray energy‐dispersive microanalysis, x‐ray diffraction, and scanning electron microscopy. The predominant mineral forms were x‐ray amorphous ferric hydroxysulfates. In addition, jarosites were detected in RBC units which treated natural mine drainages, and magnetite was detected in solids generated during treatment of a synthetic acidic mine drainage. Bacteria were observed on the surface of the inorganic residues and in gelatinous films seen microscopically following chemical dissolution of the iron crust.

Operational design and power economy of a rotating biological contactor

A method to estimate power economy, defined as the amount of BOD removed per unit power consumption of the rotating biological contactor (RBC) was developed. The characteristic value of the power economy as a function of operating conditions was evaluated and discussed. While the power economy of RBC under practical operating conditions is much higher than that of the activated sludge process, the BOD removal rate of RBC per unit floor area is rather small, only about one-third of the latter in its practical use. This renders the RBC not well suited for use in large scale wastewater treatment, but rather only for small scale treatment where the floor area of the RBC is not an important factor to reckon with in the plant. Since the influent fluctuation of wastewater reduces considerable power economy, in order to keep its high value the use of a flow balancing tank with the RBC unit is recommended.

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.

Kinetic considerations on the performance of activated sludge reactors and rotating biological contactors

This study compares the performance characteristics of laboratory-scale activated sludge and rotating biological contactor (RBC) units treating an industrial effluent. It is found that, within the range of hydraulic detention time examined (0.3–1.7 days), the two plants show very similar BOD 5 removal kinetics. These results indicate that an RBC unit with a geometrical area of the discs of 1340 cm 21 −1 of aeration reactor is equivalent to an activated sludge plant with an MLVSS concentration of about 2000 mg 1 −1. Experimental data from the two units are also analyzed by two steady-state kinetic models. It is proved that the kinetic constants of suspended microbial growths may be used successfully for fixed biological films. At the same time, a simplified design equation for RBC systems is verified and an estimation procedure for the effective surface area of the biofilm developed.

Operational performance of an RBC unit in conjunction with a septic tank

A rotating biological contactor (RBC) unit in series with a septic tank for primary solids removal and sludge storage was monitored for 21 months. The results of that monitoring are summarized in this paper. The treatment configuration produced an effluent that met federal guidelines of 20 mg/L for BOD5, and 25 mg/L for suspended solids. When solids were allowed to accumulate in the septic tank beyond 12 months, there was a marked increase in loading of the RBC with a resultant decrease in effluent quality. A linear relationship could be shown between clarified effluent BOD5 and applied BOD5. The data from this monitoring program suggest that surface area requirements of RBC units utilizing septic tanks for primary solids removal are three times those utilizing conventional primary treatment. When high levels of nitrate were in the unit, feed denitrification occurred concurrently with carbonaceous oxidation.