COD Loading Rate Research Articles

Kinetic analysis of dyestuff and COD removal from synthetic wastewater in an anaerobic packed column reactor

An anaerobic packed column reactor was operated continuously at different dyestuff loading rates, (0.05–0.4 g/(l day)) and COD loading rates (1–8 g/(l day)) in order to determine dyestuff and COD removal kinetic constants. The system was operated at room temperature (20 ± 1 °C) and at pH 7 using an immobilized anaerobic bacterial consortium called PDW. Synthetic wastewater containing textile dyestuff Reactive Red 195 was fed from the bottom of the reactor. Around 90% decolourization efficiency was obtained for dyestuff loading rates up to 0.15 g/(l day). COD removal efficiency was obtained between 5 and 35% for the applied loads. Modified Stover–Kincannon model was applied to the experimental data. Saturation value constant and maximum utilization rate constant of Stover–Kincannon model for dyestuff and COD were determined as K B = 17.8 g/(l day), U max = 19.5 g/(l day) and K B = 37.9 g COD/(l day), U max = 12.9 g COD/(l day), respectively. The predicted effluent dyestuff and COD concentrations were calculated using the constants and it was found that they are in good agreement with the observed ones.

Physicochemical and Microbial Monitoring of UASB Sludge during Start-Up of Mesophilic Reactor

Anaerobically digested sludge was seeded in a mesophilic UASB reactor and the sludge was monitored for seven months to better understand the start-up process of the reactor. The reactor was fed with synthetic wastewater containing glucose. As the COD loading rate increased stepwise (from 1 to 4 g COD l-1 d-1), the methane production rate increased. COD removal efficiency was maintained to be greater than 90% after day 36. Maximum value of the methane production rate (6.0-6.5 l d-1) was achieved from day 152 and remained stable afterward. Although the reactor showed steady performance in terms of COD removal efficiency and methane production under constant hydraulic retention time (HRT) or COD loading rates, physicochemical and microbial properties of UASB sludge kept changing during the initial 5 months of operation. Specific methanogenic activity was initially negligible but increased until day 150, and then remained constant (0.72 + 0.11 g CH4-COD g-1 VSS d-1) afterward. Sludge volume index showed that the settling ability of UASB sludge gradually improved until it reached a plateau in day 120. Improved settling-ability could provide a basis for keeping bed height constant despite shortened HRT. The mean diameter of the UASB sludge gradually increased until approximately day 150 and maintained a maximum value (0.48 mm) afterward. Confocal laser scanning microscopy revealed F420-based autofluorescence of physical and optical sections of UASB sludge, suggesting the locations of autofluorescent methanogens in the UASB sludge during the start-up period. During the initial operation of the reactor, autofluorescence showed random and uneven distribution inside the sludge. However, autofluorescence appeared as an inner layer near the edge of the sludge with time, suggesting more abundant or active methanogens in this layer. The highest autofluorescence was observed in the range of 20 to 28 µm depth from the surface of granule as determined by optical slicing of UASB sludge. The results obtained in this study provide insight into UASB sludge development that involves dynamic changes in physicochemical and microbial aspects during the start-up period.

Mixing Characteristics and Whey Wastewater Treatment of a Novel Moving Anaerobic Biofilm Reactor

A novel moving anaerobic biofilm reactor was used to treat whey wastewater. In this process, biofilm was grown on a plastic biofilm media module, which was vertically moved up and down in the bulk fluid. The objectives of the study were to investigate the mixing and performance characteristics of the new process in treating whey wastewater. The mixing efficiency was indicated by a dispersion number, D L /uL. D L /uL was up to 1.34, showing that the anaerobic reactor can be taken as a completely mixed reactor. At mesophilic conditions (35 ± 2°C), the admissible volumetric COD loading rate up to 11.6 kg COD m−3 day−1 was achieved with the COD removal efficiency of 89% and the hydraulic retention time (HRT) of 1 day. When the HRT was 0.6 days, the volumetric COD loading rate was 15.2 kg COD m−3 day−1, but COD removal efficiency decreased to 81%. The percentage of methane (CH4) in the biogas was 63% on average and the yield of methane was 333.4 L CH4 kg−1 COD removal at ambient conditions.

HIGH RATE ANAEROBIC TREATMENT OF PALM OIL MILL EFFLUENT (POME) BY REVERSIBLE FLOW ANAEROBIC BAFFLED REACTOR (RABR)

A new reactor configuration called reversible flow anaerobic baffled reactor (RABR) was applied to palm oil mill effluent (POME) which contains high proportions of particulate COD. A laboratory-scale RABR having a working volume of 20 liters was operated under thermophilic condition (at 55°C) for 500 days. The reactor accommodated a volumetric COD loading rate of 20 kgCOD·m3·d-1, keeping soluble-COD removal of above 90% on average and overall-COD removal of 76% on average. There was no tendency for lipids to accumulate within the sludge bed over the entire period. Specific methanogenic activity tests revealed a uniform distribution of methanogenic sludge along the RABR compartment

Membrane bioreactors vs conventional biological treatment of landfill leachate: a brief review

AbstractA review of quality and biological treatment of landfill leachate is presented. Conventional ex‐situ treatment normally demands multistage process treatment schemes, which may encompass both aerobic and anaerobic technologies alongside chemical precipitation and/or oxidation. This is to be contrasted with the more recent membrane bioreactor technology, which generally demands much reduced pre‐ and post‐treatment and has a much reduced footprint compared with conventional biotreatment. Results are summarised in terms of the key determinant of COD removal for waters characterised in terms of BOD/COD ratio and age. Process operation is characterised with respect to COD strength and loading rate, hydraulic retention time and number of individual unit operations. Copyright © 2004 Society of Chemical Industry

Simultaneous Carbon and Nitrogen Removal in Anoxic-Aerobic Circulating Fluidized Bed Biological Reactor (CFBBR)

Biological nutrient removal (BNR) in municipal wastewater treatment to remove carbonaceous substrates and nutrients, has recently become increasingly popular worldwide due to increasingly stringent regulations. Biological fluidized bed (BFB) technology, which could be potentially used for BNR, can provide some advantages such as high efficiency and a compact structure. This work shows the results of simultaneous elimination of organic carbon and nitrogen using a circulating fluidized bed biological reactor (CFBBR), which has been developed recently for chemical engineering processes. The CFBBR has two fluidized beds, running as anoxic and aerobic processes to accomplish simultaneous nitrification and denitrification, with continuous liquid recirculation through the anoxic bed and the aerobic bed. Soluble COD concentrations in the effluent ranging from 4 to 20 mg l-1 were obtained at varying COD loading rates; ammonia nitrogen removal efficiencies averaged in excess of 99% at a minimum total hydraulic retention time (HRT) of 2.0 hours over a temperature range of 25 °C to 28 °C. Effluent nitrate nitrogen concentration of less than 5 mg l-1 was achieved by increasing effluent recycle rate. No nitrite accumulation was observed either in the anoxic bed or in the aerobic bed. The system was able to treat grit chamber effluent wastewater at a HRT of 2.0 hours while achieving average effluent BOD, COD, NH3-N, TKN, nitrates, total phosphate, TSS and VSS concentrations of 10 mg l-1, 18 mg l-1, 1.3 mg l-1, 1.5 mg l-1, 7 mg l-1, 2.0 mg l-1, 10 mg l-1 and 8 mg l-1 respectively. The CFBBR appears to be not only an excellent alternative for conventional activated sludge type BNR technologies but also capable of processing much higher loadings that are suitable for industrial applications.

Feasibility studies on the treatment of dairy wastewaters with upflow anaerobic sludge blanket reactors

The feasibility of using upflow anaerobic sludge blanket (UASB) reactors for the treatment of dairy wastewaters was explored. Two types of UASBs were used––one operating on anaerobic sludge granules developed by us from digested cowdung slurry (DCDS) and the other on the granules obtained from the reactors of M/s EID Parry treating sugar industry wastewaters. The reactors were operated at HRT of 3 and 12 h and on COD loading rates ranging from 2.4 kg per m 3 of digester volume, per day to 13.5 kg m −3 d −1. At the 3 h HRT, the maximum COD reduction in the DCDS-seeded and the industrial sludge-seeded reactors was 95.6% and 96.3%, respectively, better than at 12 h HRT (90% and 92%, respectively). In both the reactors, the maximum, the second best, and the third best COD reduction occurred at the loading rates of 10.8, 8.6 and 7.2 kg m 3 d −1, respectively. At loading rates higher than 10.8 kg, the reactor performance dropped precipitously. Whereas in the first few months the reactors operating on sludge from EID Parry achieved better biodegradation of the waste, compared to the reactors operated on DCDS, the performance of the latter gradually improved and matched with the performance of the former.

Reactor performances and fate of aromatic amines through decolorization of Direct Black 38 dye under anaerobic/aerobic sequentials

The removal of aromatic amines was evaluated by decolorization of CI Direct Black 38 (DB 38) dye varying between 100 and 3200 mg l −1 using an anaerobic upflow anaerobic sludge blanket reactor and an aerobic completely stirred tank reactor system. The effect of increasing dye loadings from 6.1 to 213.0 g m −3 h −1 on decolorization and COD removal efficiency was investigated at constant glucose-COD (2000 mg l −1) concentrations in an UASB reactor. For 3200 mg l −1 of DB 38 and 2000 mg l −1 glucose-COD as co-substrate in the feed, 48.4% COD and 80% color removal efficiencies were observed at a maximum COD and dye loading rates of 5.37 kg COD m −3 per day and 213 g dye m −3 h −1, respectively at a hydraulic retention time (HRT) of 15 h in the UASB reactor. Sixty seven percentage remaining COD was removed at an HRT of 2.3 days and a maximum organic loading rate of 0.77 kg COD m −3 per day in the aerobic stage. Eighty four percentage COD, 86% color and 52.2% total aromatic amine (TAA) was removed at an HRT of 2.9 days and at an organic loading rate of 1.17 kg COD m −3 per day and a maximum DB 38 dye loading rate of 46.4 g dye m −3 h −1, respectively in a total system treating 3200 mg l −1 CI Direct Black 38 dye. The TAA produced under anaerobic conditions was ultimately removed in the aerobic stage and aromatic amine recoveries such as 45–50% were obtained in the aerobic reactor. The anaerobic/aerobic sequential process provides simultaneous color, COD and carcinogenic amine removal.

Swim-bed Technology as an Innovative Attached-growth Process for High-rate Wastewater Treatment

Swim-bed technology using the novel acryl-fiber biomass carrier--biofringe (BF) attachment material--demonstrated effective treatment of high-strength organic wastewater with 80% COD removal efficiencies at high volumetric loadings up to 12kg/m3/d with a hydraulic retention time of 3 h. BF material allowed for attachment of large amounts of biomass in a matrix that flexes with the wastewater flow, thus providing a high degree of contaminant-biomass contact in a fully retainable biofilm. As much as 133 g of biomass per meter of BF was retained for an equivalent 13.3 g/l with respect to the BF retention or reaction zone. Limited evidence for nitrification occurred only at low COD loading rates (ca.1.6 kg/m3/d) . In addition, filamentous biomass growth was very heavy at the lower loading rates, but was avoidable at COD loadings of 8kg/m3/d or greater. The levels of extracellular polymers--proteins in particular--in the biofilm were very high compared to levels reported for flocculent or granular sludges. While treatment in this study focused on industrial level applications, the possibility of using this technology in other treatment scenarios involving lower organic loadings was discussed.

Use of image analysis to determine algal and bacterial biomass in a high rate algal pond following Percoll® fractionation

This paper reports the results of work to allow a more accurate enumeration, and gravimetric determination, of the relative proportions of algae and bacteria within the floccular matrix present in a High Rate Algal Pond (HRAP). Methodology involving a combination of physical and chemical treatments was used and the resulting material was separated using density gradient centrifugation. The "fractions" were analysed using microscopical image analysis. Each "fraction" was categorised as containing bacteria only, algae only or an association of bacteria and algae, the relative proportions of which were then determined by image analysis to enable a "true" gravimetric determination of the algal and bacterial components of HRAP biomass for the first time. The biomass from HRAPs operated both outdoors and in a glasshouse was examined over complete operational seasons to investigate environmental effects as well as possible effects of variation in COD loading rate and retention time on cell biovolumes and cell quotients. In this study, the accurate assessment of both algal and bacterial biomass, determined as cell volume or dry matter, in addition to measurement of carbon and nitrogen has enabled the calculation of cell quotients. This allows a direct comparison between these values obtained from a nutrient-rich system and those published values obtained from systems with various nutrient status. Conversion factors obtained may also be of value for deriving inputs for computer models for the design and operation of high rate algal ponds.

Nutrient loading rate effects on nutrient removal in a five-step sequencing batch reactor

Nutrient removal from synthetic wastewater by sequencing batch operation was studied at different specific nutrient loading rates (SNLR). Nutrient removal in a sequencing batch reactor (SBR) was a five-step process consisting of anaerobic (An), anoxic (Ax), oxic (Ox), anoxic (An) and oxic (Ox) phases with hydraulic residence times (HRT) of 2/1/4.5/1.5/1.5 h, respectively. The settling step used at the end of the operation was 45 min for all experiments. The initial COD concentration was varied between 600 and 4800 mg l −1 at eight different levels with constant COD/N/P ratio of 100/3.33/0.7. Effects of SNLRs on COD, NH 4-N and PO 4-P removal were investigated. Percent nutrient removals decreased and effluent nutrient levels increased with increasing nutrient loading rates. The highest COD (99%), NH 4-N (99%) and PO 4-P (97%) removal efficiencies were obtained with the initial COD concentration of 600 mg l −1 at COD loading rate of nearly 40 mg COD (g biomass) −1 h −1. However, the sludge volume index (SVI) decreased with increasing COD loading rate resulting minimum SVI of 46 ml g −1 at COD loading rate of nearly 86 mg COD (g biomass) −1 h −1. Biomass concentration increased with increasing SNLR resulting in biomass concentration of 3.84 g l −1 at COD loading rate of 86 mg COD (g biomass) −1 h −1.

Performance of rotating perforated tubes biofilm reactor in biological wastewater treatment

A novel biofilm reactor named as ‘rotating perforated tubes biofilm reactor (RPT)’ was developed and used for biological treatment of synthetic wastewater. Effects of major process variables such as COD loading rate, specific biofilm surface area, number of tubes and the rotational speed (rpm) on COD removal performance of the reactor was investigated. COD removal efficiency increased with the specific biofilm surface area and the rotational speed, but decreased with increasing COD loading rate. Kinetics of COD removal was investigated and kinetic constants were determined by using the experimental data. An empirical design equation was developed to quantify the system’s performance as a function of the operating variables.

Who eats what? Classifying microbial populations based on diurnal profiles of rRNA levels

Identifying the relationships between various bacterial populations and the substrates they consume is central to the understanding of population dynamics and to the development of process control in activated sludge. However, linking a heterotrophic population to its activity in situ is difficult because ribosomal RNA (rRNA) techniques, while allowing the rapid identification of populations, provide little information about their heterotrophic activity. Activated sludge models describe biodegradation kinetics by classifying substrates into two types: readily and slowly degradable substrates. Assuming that bacterial populations specialize in degrading one type of substrate, their growth rate should be affected differently if the COD loading rate varies diurnally as for a municipal activated sludge system. Modeling results suggested that the growth rates of populations consuming readily degradable substrates vary according to variations in COD loading rate. On the other hand, the growth rates of populations consuming slowly degradable substrates do not change despite the variation in COD loading rate. Since the cellular rRNA level is positively correlated with the growth rate, we hypothesized that the rRNA levels of some populations in municipal activated sludge should increase throughout the day, while they should stay constant for other populations. This hypothesis was verified by monitoring the rRNA level of Acinetobacter (a model population consuming readily degradable substrates) and Gordonia (a model population consuming slowly degradable substrates) in the mixed liquor of a full-scale municipal activated sludge reactor for three weeks.

Performance of azotobacter supplemented activated sludge in biological treatment of nitrogen deficient wastewater

External addition of nitrogenous compounds is the most common practice used in biological treatment of nitrogen deficient wastewaters. However, this method adds an extra cost to the treatment. As an alternative for effective biological treatment of nitrogen deficient wastewaters, nitrogen fixing bacteria, Azotobacter vinelandii was used in activated sludge culture in this study. COD removal performance of Azotobacter-supplemented activated sludge was compared with Azotobacter-free activated sludge culture for biological treatment of nitrogen deficient synthetic wastewater. Effects of important process variables such as N/COD ratio, sludge age, hydraulic residence time, feed COD concentration and the COD loading rate on the COD removal performance were investigated. Kinetic constants of the system were determined. Azotobacter addition to the activated sludge in biological treatment of nitrogen deficient wastewater (N/COD<0.06) improved the COD removal performance significantly.

Oligonucleotide probe hybridization and modeling results suggest that populations consuming readily degradable substrate have high cellular RNA levels

Analyses based on ribosomal RNA (rRNA)-targeted hybridization performed in our laboratory identified two types of bacterial populations: a population with a high RNA level per biomass and a population with a low level of RNA per biomass. To extend these descriptions, the diurnal dynamics of the RNA pool were monitored by rRNA-targeted oligonucleotide probe membrane hybridization. Under the typical diurnal variation in COD loading rate experienced by municipal wastewater treatment plants, the RNA level of the bacterial population with a high level of RNA per biomass varied with changes in the COD loading rate. Under the same conditions, the RNA level of the population with low RNA level per biomass remained constant. A structured biomass model was developed to describe these data. Substrate COD was divided into a readily biodegradable and a slowly biodegradable COD fraction. It was assumed that two specialized populations coexist in municipal activated sludge treatment systems. One population consumes readily degradable COD and the other consumes slowly degradable COD. According to model simulations, the population consuming readily degradable COD has a high level of RNA per biomass under variable substrate concentrations. Comparatively, the population consuming slowly degradable COD has a low level of RNA level per biomass. Furthermore, model simulations reproduced the two diurnal RNA profiles observed in a full-scale municipal activated sludge system. Therefore, we suggest that two populations can be distinguished in municipal activated sludge systems: a population consuming readily degradable substrate and a population consuming slowly degradable substrate.

Performance of rotating biological disc system treating saline wastewater

Synthetic saline wastewater composed of diluted molasses, urea, KH 2PO 4 and different concentrations of salt (0–10%) was biologically treated in a rotating biodisc unit for COD removal. The performance of the system was evaluated under different operating conditions such as disc number (or surface area), COD loading rate (or feed COD) and salt concentration. COD removal efficiency increased with increasing number of discs ( N) or disc surface area ( A), but decreased with increasing COD loading rate ( L s) and salt concentration. Experimental results were correlated by an empirical polynomial equation in terms of COD removal efficiency as functions of disc number ( N) or disc surface area, feed COD and salt concentrations. Empirical constants were determined using the experimental data.

The feasible sequential control strategy of treating high strength organic nitrogen wastewater with sequencing batch biofilm reactor

The bio-kinetics and feasible sequential control strategy of treating high strength organic carbon and nitrogen wastewater were investigated by conducting the ABS manufacturing wastewater in a series of Sequencing Batch Biofilm Reactors (SBBRs). The on-line ORP, pH, and DO monitoring parameters were applied to identify the feature-points when ammonification, nitrification, and denitrification ends. The carbonaceous matter removal kinetics in the anaerobic and aerobic reaction stages can be expressed by the Michaelis-Menten equation. High efficiency of organic carbon removal and organic nitrogen ammonification in the anaerobic stage can eliminate the substrate competition and activation inhibition to nitrifying organisms in the following aerobic stage. In the sequencing nitrogen removal processes, the producing time and system ORP values of these feature-points have good function relationships with the influent COD loading rates of SBBR, which can be integrated into a set-point (set-time and set-ORP) sequential control strategy of nitrogen removal. The automatic control operation results revealed ORP was one of the major control parameters of the sequencing nitrogen removal process in SBBR system and high overall removal efficiency were obtained.

Biological phosphorus and nitrogen removal in a sequencing batch moving bed biofilm reactor

Biological phosphorus and nitrogen removal in biofilm processes have a potential advantage compared to activated sludge processes, because of less vulnerability with respect to sludge loss and because biofilm processes, in general, are more compact with a smaller footprint. Experiments have been carried out in a moving bed biofilm reactor operated as a sequencing batch reactor (SBR), with simultaneous nitrification, phosphorus uptake and denitrification in the aerobic phase. In order to achieve good phosphorus and nitrogen removal, the length of the anaerobic period should be tuned to achieve near complete removal of easily biodegradable COD in the anaerobic period, and the length of the aerobic period should be long enough for complete nitrification. The total COD-loading rate must be at the same time be kept high enough to achieve a net growth of biomass in the reactor.

Long-term impact of dissolved O2 on the activity of anaerobic granules

The impact of influent dissolved O(2) on the characteristics of anaerobic granular sludge was investigated at various dissolved O(2) concentrations (0.5-8.1 ppm) in 1- and 5-L laboratory-scale upflow anaerobic sludge bed (UASB)-like anaerobic/aerobic coupled reactors with a synthetic wastewater (carbon sources containing 75% sucrose and 25% acetate). The rate of dissolved O(2) supplied to the coupled reactor was as high as 0.40 g O(2)/L(rx).d, and the anaerobic/aerobic coupled reactors maintained excellent methanogenic performances at a COD loading rate of 3 g COD/L(rx).d even after the reactors had been operated with dissolved O(2) for 3 months. The activities of granular sludge on various substrates (glucose, propionate, and hydrogen) were not impaired, and acetate activity was even improved over a short term. However, after 3 months of operation, slight declines on the acetoclastic activities of granules were observed in the coupled reactor receiving the recirculated fluid containing 8.1 ppm dissolved O(2).Methane yield in the anaerobic control reactor and anaerobic/aerobic coupled reactors revealed that a significant aerobic elimination (up to 30%) of substrate occurred in the coupled reactors, as expected. The presence of dissolved O(2) in the recirculated fluid resulted in the development of fluffy biolayers on the granule surface, which imposed a negative impact on the settleability of granular sludge and caused a slightly higher sludge washout. This research shows that the anaerobic/aerobic coupled reactor can be successfully operated under O(2)-limited conditions and is an ideal engineered ecosystem integrating oxic and anaerobic niches. (c) 1996 John Wiley & Sons, Inc.

Anaerobic Gasification of Liquefied Okara

It is necessary to utilize Okara which is a byproduct of soybean processing. For this purpose, an anaerobic methane fermentation system is proposed to transform Okara to biogas which is used as recycling energy. In thisexperiment, a bench scale anaerobic contact process which is composed of CSTR's was experimentally used to treat the supernatant of liquefied Okara from the liquefaction reactors in the steady state. Four experimental runs with COD loading rates from 1980 to 3440 mg/L/d were conducted at 30 days of HRT. It was found that the gasification process worked and showed the VS removal ratio from 72 to 80 % as long as its pH was controlled within the range of neutrality. Obtained Vmax and Ks as apparent kinetic parameters based on the material balance and the growth model for the process were 0.55 mg-COD/mg-VSS/d and 5400 mg-COD/L respectively. They indicated that the phase separation of methane fermentation activated the microbial growth and the reactors required the improvement in the mixing method. The simulation based on the energy yields in this experiment revealed that the feasibility of the anaerobic methane fermentation system to produce the recycling energy from Okara would be best improved by increasing the VA yield for the liquefaction rather than trying to improve the methane yield for the gasification