COD Fractions Research Articles

Kinetics of thermophilic, anaerobic oxidation of straight and branched chain butyrate and valerate.

The degradation kinetics of normal and branched chain butyrate and valerate are important in protein-fed anaerobic systems, as a number of amino acids degrade to these organic acids. Including activated and primary wastewater sludge digesters, the majority of full-scale systems digest feeds with a significant or major fraction of COD as protein. This study assesses the validity of using a common kinetic parameter set and biological catalyst to represent butyrate, n-valerate, and i-valerate degradation in dynamic models. The i-valerate degradation stoichiometry in a continuous, mixed population system is also addressed, extending previous pure-culture and batch studies. A previously published mathematical model was modified to allow competitive uptake of i-valerate, and used to model a thermophilic manure digester operated over 180 days. The digester was periodically pulsed with straight and branched chain butyrate and valerate. Parameters were separately optimized to describe butyrate, i-valerate, and n-valerate degradation, as well as a lumped set optimized for all three substrates, and nonlinear, correlated parameter spaces estimated using an F distribution in the objective function (J). Each parameter set occupied mutually exclusive parameter spaces, indicating that all were statistically different from each other. However, qualitatively, the influence on model outputs was similar, and the lumped set would be reasonable for mixed acid digestion. The main characteristic not represented by Monod kinetics was a delay in i-valerate uptake, and was compensated for by a decreased maximum uptake rate (k(m)). Therefore, the kinetics need modification if fed predominantly i-valerate. Butyrate (i- and n-) and n-valerate could be modeled using stoichiometry consistent with beta-oxidation degradation pathways. However, i-valerate produced acetate only, supporting the stoichiometry of a reaction determined by other researchers in pure culture. Therefore, lumping i-valerate stoichiometry with that of n-valerate will not allow good system representation, especially when the feed consists of proteins high in leucine (which produces i-valerate), and the modified model structure and stoichiometry as proposed here should be used. This requires no additional kinetic parameters and one additional dynamic concentration state variable (i-valerate) in addition to the variables in the base model.

Anaerobic treatability of high oil and grease rendering wastewater

This study evaluated the use of a new biosurfactant, BOD-Balance™, derived from cactus for the treatment of oil-and-grease-laden rendering wastewater anaerobically. Batch laboratory experimental results and preliminary full-scale data are presented. The biosurfactant affected a significant increase in the COD degradation rate for the raw wastewater. However, after reduction of the oil and grease (O&G) by dissolved air flotation, the biosurfactant did not exhibit any advantages. Modeling of the data indicated that various COD fractions, i.e. both soluble and particulate as well as total COD at various testing conditions conformed well to both zero-order and first-order models. The biosurfactant affected a 164–238 and 164–247% increase in COD and particulate COD biodegradation rate for the raw wastewater. The reduction of O&G concentration to <800 mg/l increased total and soluble COD degradation rates by 106%. Results from the full-scale mesophilic anaerobic digestion system indicated that the addition of the biosurfactant at doses of 130–200 mg/l decreased O&G concentrations from 66,300 to 10,200 mg/l over a 2-month-period.

Treatment of domestic sewage in a combined UASB/RBC system. Process optimization for irrigation purposes

A Rotating Biological Contactor (RBC) was fed with raw domestic wastewater or anaerobic effluents. The experiments were conducted at increasing operational temperatures viz. 11, 20 and 30 degrees C to assess the potential increase in removal efficiencies for the different COD fractions (COD(total), COD(suspended), COD(colloidal) and COD(soluble)), E. coli and in the nitrification rate. The results clearly show that, the RBC at HRT of 2.5 h and OLR of 47 g COD/m2 x d provided a very high residual COD(total) value of 228 mg/l when treating domestic wastewater. This was not the case as compared to the results obtained for the system when operated at the same HRT but at lower OLR's of 27, 20 and 14.5 g COD/m2 x d with a UASB effluent at operational temperatures of 11, 20 and 30 degrees C respectively. The residual COD(total) values amounted to 100, 85 and 72 mg/l in the final effluents. Moreover, a high removal of ammonia and low residual values of E. coli was found for the RBC when treating a UASB effluent at operational temperature of 30 degrees C as compared to the situation for treatment of domestic wastewater and UASB effluent at lower temperatures of 11 and 20 degrees C. It can be concluded that an efficient pre-treatment of sewage implies a substantial reduction of OLR applied to the RBC and consequently improves the residual of COD(total) ammonia and E. coli in the final effluent. Therefore, this study supports using a combined system UASB/RBC for treatment of domestic wastewater for reuse in irrigation.

Solubilization and Fermentation in a Modified VFA-Potential Method

The VFA-potential method is a fermentation technique for estimating the total volatile fatty acids (VFA) availability in wastewater. The VFA-potential was conceived as a measurement of the readily fermentable COD, because fermentation utilizes this COD as a substrate. However, anaerobic hydrolysis can also be a potential source of fermentable matter. In this work, the VFA-potential method has been modified and simplified to avoid nitrogen gas usage. In the modified method, several conventional BOD flasks are completely filled with wastewater and subsequently opened at scheduled times. This procedure keeps oxidation-reduction potential (ORP) at very low levels while reducing the laboratory equipment required. COD fractionation of initial wastewater was carried out. Analysis of total suspended solids (TSS), soluble phosphate, ammonia nitrogen, total and soluble COD, and individual VFA were obtained throughout the VFApotential test, to evaluate hydrolysis and fermentation. The mean ratio between VFA-potentia...

Biodegradability of slaughterhouse wastewater with high blood content under anaerobic and aerobic conditions

AbstractIn this work, the biodegradability of wastewater from a slaughterhouse located in Keşan, Turkey, was studied under aerobic and anaerobic conditions. A very high total COD content of 7230 mg dm−3 was found, due to an inefficient blood recovery system. Low BOD5/COD ratio, high organic nitrogen and soluble COD contents, were in accordance with a high blood content. A respirometry test for COD fractionation showed a very low readily biodegradable fraction (SS) of 2%, a rapidly hydrolysable fraction (SH) of 51%, a slowly hydrolysable fraction (XS) of 33% and an inert fraction of 6%. Kinetic analysis revealed that hydrolysis rates were much slower than these of domestic sewage. The results underlined the need for an anaerobic stage prior to aerobic treatment. Tests with an anaerobic batch reactor indicated efficient COD degradation, up to around 80% removal. Further anaerobic degradation of the remaining COD was much slower and resulted in the build up of inert COD compounds generated as part of the metabolic activities in the anaerobic reactor. Accordingly, it is suggested that an appropriate combination of anaerobic and aerobic reactors would have to limit anaerobic degradation to around 80% of the tCOD and an effluent concentration above 1000 mg dm−3, for the optimum operation of the following aerobic stage.© 2003 Society of Chemical Industry

Performance and membrane fouling in a pilot scale SBR process coupled with membrane

The performance of the pilot-scale submerged membrane coupled with sequencing batch reactor (SM-SBR) for upgrading effluent quality was investigated in this study. The reactor was operated with 3-hour cycle with alternating anoxic and aerobic conditions to treat organics, nitrogen and phosphate. Despite various influent characteristics, COD removal was always higher than 95%. Sufficient nitrification was obtained within a few weeks after start-up and during the stable period, complete nitrification occurred despite short aeration time. Total nitrogen (TN) removal efficiency was reached up to 85%. Membrane flux was critical for TN removal so that the decrease of flux by membrane fouling led to increase of HRT, and it caused the endogenous respiration of microorganisms such as nitrifying bacteria. The stirred cell test revealed the significant role of the soluble fraction in membrane permeability and dissolved solids played a major role in the short-term fouling mechanism. The cake resistance by the soluble COD fraction of supernatant or soluble microbial products (SMP) was investigated as a major part of total resistance.

Effect of Ozonation on the Biological Treatability of a Textile Mill Effluent

Ozonation, applied prior to biological processes, has proved to be a very effective chemical treatment step mostly for colour removal when soluble dyes are used in textile finishing operations. Its impact on biological treatability however has not been fully evaluated yet. This study evaluates the effect of ozonation on the quality of wastewater from a textile mill involving bleaching and reactive dyeing of cotton and synthetic knit fabric. The effect of ozonation on COD fractionation and kinetic coefficients defining major biological processes is emphasised. The results indicate that the extent of ozone applied greatly affects the remaining organic carbon composition in the wastewater. The relative magnitude of different COD fractions varies as a function of the ozone dose. Ozonation does not however exert a measurable impact on the rate of major biological processes.

Advanced treatment of high strength opium alkaloid industry effluents

The purpose of this study was to investigate an effective treatment system which can be applicable to treat opium alkaloid industry (OAI) effluents characterised with high COD, TKN, dark color and non-biodegradable organic pollutants. In the first phase of the study, lab-scale anaerobic (UASBR) + aerobic (SBR) treatability studies were carried out on opium processing industry effluents. Effluent CODs from the two staged biological treatment system were relatively high (-700 mg l(-1)) and additional post treatment was required. Physico-chemical treatability studies previously carried out on the effluent of opium alkaloid wastewater treatment plant, were not effective in removing residual COD and color. In the second phase of the study, the refractory organics causing higher inert COD values in the SBR effluent were additionally treated by using Fenton's Oxidation. The batch tests were performed to determine the optimum operating conditions including pH, H2O2 dosage, molar ratio of Fe2+/H2O2 and reaction time. It was found that removal efficiencies of COD and color for 30 minutes reaction time were about 90% and 95%, respectively. The ratio of H2O2/FeSO4 was determined as 200 mg l(-1)/600 mg l(-1) for the optimum oxidation and coagulation process at pH 4. Experimental results of the present study have clearly indicated that the Fenton's oxidation technology is capable to treat almost all parts of the organics which consist of both soluble initial and microbial inert fractions of COD for opium alkaloid industry effluents. Effluents from the Fenton's Oxidation process can satisfy effluent standards for COD and color in general.

PHA storage from several substrates by different morphological types in an anoxic/aerobic SBR

An activated sludge was cultivated on a mixture of several soluble substrates (acetate, ethanol, glucose, glutamic acid, peptone, Tween 80, starch, yeast extract) in an anoxic/aerobic SBR. Highly dynamic conditions in the SBR (feast famine regime) caused fast removal of most COD in the anoxic phase (in particular acetate, ethanol, glutamic acid and glucose were totally removed) and relevant contribution of storage. In spite of that, filament abundance was always high, as is typical of bulking sludges. Filaments which developed in the reactor were characterized on a morphological basis and on the basis of their ability to grow and to store polyhydroxyalkanoates (PHAs). Three main filaments prevailed in the biocenosis, whose relative abundance was varyng with time: Nostocoida limicola II, (two different morphological types), Haliscomenobacter hydrossis and an unidentified one. It was found that maximum growth rate was higher for flocformers than for filaments on each of the tested substrates. Epifluorescence showed that storage ability was more widespread among flocformers than in the filaments. Only one type of Nostocoida limicola II was able to store PHAs. The obtained data show that aerobic growth on the little residual fraction of COD from the anoxic phase was enough to support high abundance of filamentous microorganisms.

Ozonation application in activated sludge systems for a textile mill effluent

The study investigates the effect of partial ozonation of textile wastewater, both at the inlet (pre-ozonation) and the outlet (post-ozonation) of biological treatment, for the optimization of COD and color removals, both typical polluting parameters associated with the textile industry. Pre-ozonation provides at optimum contact time of 15 minutes 85% color removal, but only 19% COD reduction. Removal of the soluble inert COD fraction remains at 7%, indicating selective preference of ozone for simpler compounds. Post-ozonation is much more effective on the breakdown of refractory organic compounds and on color removal efficiency. Ozonation after biological treatment results in almost complete color removal and a 14% soluble inert COD reduction. The polishing effect of post-ozonation also proves quite attractive from an economical standpoint, involving approximately 50% of the ozone utilization at the same ozone flux rate and contact time, yet providing a lower soluble residual COD level.

Dairy wastewater treatment in a moving bed biofilm reactor

Dairy raw wastewater is characterised by high concentrations and fluctuations of organic matter and nutrient loads related to the discontinuity in the cheese production cycle and machinery washing. The applicability of a Moving Bed Biofilm Reactor (MBBR) filled with FLOCOR-RMP plastic media to the treatment of dairy wastewater was evaluated in a pilot-plant. COD fractionation of influent wastewater, MBBR performance on COD and nutrient removal were investigated. A removal efficiency of total COD over 80% was obtained with an applied load up to 52.7 gCOD m-2 d-1 (corresponding to 5 kgCOD m-3d-1). The COD removal kinetics for the MBBR system was assessed. The order of the kinetics resulted very close to half-order in the case of a biofilm partially penetrated by the substrate. The nitrogen removal efficiency varied widely between 13.3 and 96.2% due to the bacterial synthesis requirement. The application of a MBBR system to dairy wastewater treatment may be appropriate when upgrading overloaded activated sludge plants or in order to minimise reactor volumes in a pre-treatment.

Treatment of anaerobically treated domestic wastewater using rotating biological contactor

A small-scale pilot plant consisting of a three-stage RBC has been investigated for the removal of E. coli, COD fractions and ammonia from the effluent of an UASB reactor treating domestic wastewater. The results obtained reveal that a three-stage system operated at a HRT of 3.0 h represents an effective posttreatment process. The remaining COD in the final effluent was only 51 (+/- 7) mgl(-1). Ammonia concentration was reduced by 67 (+/- 7.6) %. The overall E. coli reduction was 1.39 log10 at an influent count of 6.5 log10 corresponding to an overall removal efficiency of 95.8 (+/- 4.7) %. However, according to prevailing standards, residual E. coli counts are still high for unrestricted reuse for irrigation purposes. When the system was operated at a HRT of 10 h, overall E. coli removal and ammonia reduction were 99.9 (+/- 0.05)% and 92 (+/- 6.5) % respectively. At a HRT of 10 h, recirculation of the 3rd stage effluent to the 1st stage reduced the residual of E. coli in the final effluent from 2 x 10(3) to 9.8 x 10(2)/100ml. Moreover, the recirculation of nitrified effluent from the 3rd stage to the 1st stage increased ammonia removal in the stage 1 from 23 to 43%. This relatively high ammonia removal likely can be attributed to the supply of nitrifiers from 3rd stage to the 1st one.

Experience with guidelines for wastewater characterisation in The Netherlands

In this paper experiences and results are presented with guidelines for wastewater characterisation that are standardised in The Netherlands for modelling purposes with ASM. The wastewater characterisation is based on a physical-chemical method to characterise the soluble and particulate fractions, combined with a BOD-analysis for characterising the biodegradable fraction of the influent COD. By following the guidelines, a sufficiently detailed and practical characterisation is obtained, and the results can be used for simulation studies on treatment plants for process optimisation, trouble-shooting and design assistance. At present, five years of experience is gained with the guidelines and they were used for the simulation of circa 100 treatment plants. The guidelines are evaluated as simple and easy to implement in routine analysis programs.

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.

Optimal operation for timely adaptation of activated sludge plants to changes in the surfactant composition of wastewater

The composition of a textile industry wastewater is highly variable, as the industrial process has to follow fashion and season trends. Surfactants represent one of the largest COD fractions in a typical textile wastewater. Therefore, it was the aim of this paper to model the acclimatisation behaviour of an activated sludge system when subjected to composition variations in the surfactant containing feed. The model was based on data obtained in SBR experiments in which a linear alkyl ethoxylate as sole carbon source in the feed was replaced by another with a longer ethoxylate chain. A previously developed model (Fractionated Degradation Model) was applied to each of the 21 SBR cycles carried out in this study. The resulting best-fit parameters were investigated and sub-models were further developed, to create an acclimatisation model, able to predict the sludge acclimatisation level. Using the information given by this model, it was possible to propose an optimal operation scheme to pre-acclimatise the sludge before a surfactant replacement is made in the textile process. A cost analysis was carried out to compare different scenarios, with and without the application of this operation scheme. It was concluded that the proposed pre-acclimatisation process may be cost effective as compared to other scenarios if a cheap surfactant-containing product was employed.

Removal of molecular weight fractions of COD and phenolic compounds in an integrated treatment of olive oil mill effluents.

Previous works (Beccari et al. 1999b; Beccari et al. 2001a; Beccari et al. 2001b) on the anaerobic treatment of olive oil mill effluents (OME) have shown: (a) a pre-treatment based on the addition of Ca(OH)2 and bentonite was able to remove lipids (i.e. the most inhibiting substances present in OME) almost quantitatively; (b) the mixture OME-Ca(OH)2-bentonite, fed to a methanogenic reactor without providing an intermediate phase separation, gave way to high biogas production even at very low dilution ratios; (c) the effluent from the methanogenic reactor still contained significant concentrations of residual phenolic compounds (i.e. the most biorecalcitrant substances present in OME). Consequently, this paper was aimed at evaluating the fate of the phenolic fractions with different molecular weights during the sequence of operations (adsorption on bentonite, methanogenic digestion, activated sludge post-treatment). The results show that a very high percentage (above 80%) of the phenolic fraction below 500 D is removed by the methanogenic process whereas the phenolic fractions above 1,000 D are significantly adsorbed on bentonite; the 8-day activated sludge post-treatment allows an additional removal of about 40% of total filtered phenolic compounds. The complete sequence of treatments was able to remove more than the 96% of the phenolic fraction below 500 D (i.e. the most toxic fraction towards plant germination). Preliminary respirometric tests show low level of inhibition exerted by the effluent from the methanogenic reactor on aerobic activated sludges taken from full-scale municipal wastewater plants.

Treatment of domestic sewage in a two-step anaerobic filter/anaerobic hybrid system at low temperature

The treatment of domestic sewage at low temperature of 13°C was investigated in a two-step system consisting of an anaerobic filter (AF) +an anaerobic hybrid (AH) reactor operated at different hydraulic retention times (HRTs). The AF reactor was efficient in the removal of suspended COD, viz. 81%, 58% and 57% at an HRT of, respectively, 4, 2 and 3 h. For optimisation of the removal of suspended COD and dissolved COD, an HRT of 4+4 h is required for the AF+AH system. For additional optimisation of colloidal COD removal, the AH reactor needs an HRT of 8 h. The AF+AH system operated at an HRT of 4+8 h at 13°C provided a high removal efficiency for all COD fractions. The achieved total COD removal was as high as 71% which is similar to values found in tropical areas. Moreover, 60% of the removed COD was converted to methane.

Anaerobic treatment for C and S removal in “zero-discharge” paper mills: effects of process design on S removal efficiencies

Stringent environmental laws in Europe and Northern America lead to the development towards closure of the process water streams in pulp and paper mills. Application of a "zero-discharge" process is already a feasible option for the board and packaging paper industry, provided in-line treatment is applied. Concomitant energy conservation inside the mill results in process water temperatures of 50-60 degrees C. Thermophilic anaerobic treatment complemented with appropriate post-treatment is considered as the most cost-effective solution to meet re-use criteria of the process water and to keep its temperature. In the proposed closed-cycle, the anaerobic treatment step removes the largest fraction of the biodegradable COD and eliminates "S" as H2S from the process stream, without the use of additional chemicals. The anaerobic step is regarded as the only possible location to bleed "S" from the process water cycle. In laboratory experiments, the effect of upward liquid velocity (Vupw) and the specific gas loading rate (Vgas) on the S removal capacity of thermophilic anaerobic bio-reactors was investigated. Acidifying, sulphate reducing sludge bed reactors were fed with partly acidified synthetic paper mill wastewater and were operated at 55 degrees C and pH 6. The reactors were operated at organic loading rates up to 50 g COD.l-1.day-1 at COD/SO4(2-) ratios of 10. The effect of Vupw was researched by comparing the performance of a UASB reactor operated at 1.0 m.h-1 and an EGSB reactor, operated at 6.8 m.h-1. The Vupw had a strong effect on the fermentation patterns. In the UASB reactor, acidification yielded H2, acetate and propionate, leading to an accumulation of reducing equivalents. These were partly disposed of by the production of n-butyrate and n-valerate from propionate. In the EGSB reactor net acetate consumption was observed as well as high volumetric gas (CO2 and CH4) production rates. The higher gas production rates in the EGSB reactor resulted in higher S-stripping efficiencies. The effect of Vgas was further researched by comparing 2 UASB reactors which were sparged with N2 gas at a specific gas loading rate of 30 m3.m-2.day-1. In contrast to the regular UASB reactors, the gas-supplied UASB showed a more stable performance when the organic loading rates were increased. Also, the H2S stripping efficiency was 3-4 times higher in the gas-supplied UASB, reaching values of 67%. Higher values were not obtained owing to the relatively poor sulphate reduction efficiencies.

Characterization and modelling of denim‐processing wastewaters for activated sludge

AbstractThe study involved characterization of denim‐processing wastewaters, mainly to generate the necessary experimental data for the modelling and evaluation of the activated sludge process. The striking feature of the wastewater quality was the excessive suspended solids content requiring effective removal before biological treatment. COD fractionation was, however, typical for a textile effluent in general, with a biodegradable fraction of 90%, a readily biodegradable COD ratio of 20%, a predominantly soluble slowly biodegradable fraction of 55–60% and negligible particulate inert COD. Hydrolysis was identified as the significant step in the biodegradation kinetics with rate coefficients quite specific to plant operation. Evaluation of the hydrolysis kinetics showed that the magnitude of the slowly biodegradable COD could be reduced with a higher hydraulic detention time, effectively improving the quality of the soluble effluent.© 2001 Society of Chemical Industry

Full-scale application of the IAWQ ASM No. 2d model

In the framework of the EU-funded TTP-UPM project (Technology Transfer Project--Urban Pollution Management) the waste water treatment plant (WWTP) of Tielt was modelled with the recently issued IAWQ ASM No. 2d model. Up to 41 % of the total COD load is originating from a textile industry. A measurement campaign was conducted during a period with industrial discharge and a period with only domestic sewage. The stop of the industrial discharge resulted in a highly dynamic response of the system. Based on an expert-approach the calibration was obtained changing only four parameters (anaerobic hydrolysis reduction factor etafe, reduction factor for denitrification etaNO3, the decay rate of autotrophs bAUT and the decay rate of the bio-P organism building blocks bPAO, bPHA, bPP). Influent fractionation remains a critical step within the model calibration. A proven procedure to characterise the influent determinants by standard physical chemical analysis failed to assess the influent COD fractions when the textile waste water is discharged to the WWTP. Selected bench-scale experiments, instead, succeeded in providing the adequate influent characterisation accuracy. For characterising the readily biodegradable COD fraction respirometry is to be preferred.