Feed COD Research Articles

Ozonation of Procaine Penicillin G formulation effluent Part I: Process optimization and kinetics

Ozonation characteristics of synthetic Procaine Penicillin G (PPG) formulation effluent were investigated in a semi-batch ozone reactor at different pH (3, 7 and 12), ozone feed rates (600–2600 mg h −1) and COD values (200–600 mg l −1). Ozonation of aqueous PPG effluent resulted in 37 (82)% COD removal after 60 (120) min ozonation when the reaction pH was kept constant at pH = 7.900 mg l −1 (corresponding to 50% of the total introduced) ozone was absorbed during a reaction period of 1 h. The effects of increasing the applied ozone dose and the initial COD on the COD abatement rates of PPG effluent were also studied. Results have indicated that increasing the ozone dose and decreasing the COD content both have positive effects on COD removal rates. The significant contribution of the free radical ( OH) reaction pathway to PPG ozonation could be traced using tert-butyl alcohol as the OH probe compound at varying concentrations. The bimolecular reaction rate constants for the direct reaction of PPG with ozone were found as 152 and 2404 M −1 h −1 at pH = 3 and 7, respectively, using the gas phase ozone partial pressures determined from of the outlet gas stream analysis. It could be demonstrated that ozone decomposition to free radicals being triggered by increasing the pH from 3 to 7 is essential for the rate enhancement of PPG effluent ozonation.

Influence of filtration conditions on the performance of nanofiltration and reverse osmosis membranes in dairy wastewater treatment

Filtration performance and fouling of nanofiltration (NF) and reverse osmosis (RO) membranes in the treatment of dairy industry wastewater were investigated. Two series of experiments were performed. The first one involved a NF membrane (TFC-S) for treating the chemical-biological treatment plant effluents. The second one used a RO membrane (TFC-HR) for treating the original effluents from the dairy industry. The permeate flux was higher at higher transmembrane pressures and higher feed flowrates. The curves of permeate flux exhibited a slower increase while the feed flowrate decreased and the pressure increased. Membrane fouling resulted in permeate flux decline with increasing the feed COD concentration. Furthermore, the flux decline due to the COD increase was found higher at higher pressures for both NF and RO membranes.

Anaerobic digestion of dairy wastewater by inverse fluidization: The inverse fluidized bed and the inverse turbulent bed reactors

This paper describes the application of the inverse fluidization technology to the anaerobic digestion of dairy wastewater. Two reactors were investigated: the inverse fluidized bed reactor and the inverse turbulent reactor. In these reactors, a granular floating solid is expanded by a down‐flow current of effluent or an up‐flow current of gas, respectively. The carrier particles (Extendospheres(™)) were chosen for their large specific surface area (20,000 m2m−3) and their low energy requirements for fluidization (gas velocity of 1.5 mm s−1, 5.4 m h−1). Organic load was increased stepwise by reducing hydraulic retention time from more than 60 days to 3 days, while maintaining constant the feed COD concentration. Both reactors achieved more than 90% of COD removal, at an organic loading rate of 10–12 kgCOD m−3d−1, respectively. The performances observed were similar or even higher than that of other previously tested fluidized bed technologies treating the same wastewater. It was found that the main advantages of this system are: low energy requirement, because of the low fluidization velocities required; there is no need of a settling device, because solids accumulate at the bottom of the reactor, so they can be easily drawn out and particles with high‐biomass content can be easily recovered. Lipid phosphate concentration has been revealed as a good method for biomass estimation in biofilms since it only includes living biomass.

Low energy treatment system for brewery wastewater reuse

A pilot plant consisting of UASB, SBR and microfiltration in series was operated for 15 months to study a low energy treatment option for brewery effluent. The UASB was loaded up to 18 kg/kL.d. However for trouble free operation the loading had to be limited to 14 kg/kL.d. More than 80% of the feed COD was removed in the anaerobic process and a further 60% COD removal was observed in the aerobic process. An air backwashable microfiltration unit was used to remove suspended solids so that the treated water could be reused. The membrane unit was optimised by operating under dead-end, controlled flux conditions (permeate pumping) and air backwashing at set transmembrane pressure (TMP) (in practice the membranes are backwashed at set time interval). Operating energy cost calculations for the membrane system showed that the unit needs to be operated at low flux (say 20 to 30 L/m2.h) to have a low energy demand. However this necessitates a large membrane area. Optimisation for capital and energy cost indicates that the unit needs to be operated at more than 60 L/m2.h depending on the maximum TMP specified. The system energy balance was also calculated. The energy needed for the operation of all units less the energy gained from methane gas generated indicates that the system could yield a net energy of 2.5 kWh/kL water treated. The treated effluent had a turbidity of less than 1.2 NTU and the BOD5 less than 20 mg/L.

Empirical models for biological treatment of saline wastewater in rotating biodisc contactor

Biological treatment of saline wastewater in a rotating bio-disc contactor (RBC) was investigated under different operating conditions, such as A/ Q ratio, feed COD, COD loading and salt concentrations. COD removal efficiencies were determined and correlated with the aforementioned variables. The constants of the proposed empirical equation were determined using experimental data. Plots of COD removal efficiency as functions of these variables were established in order to estimate the performance of the system under different operating conditions.

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.

Comparison of performances of rotating perforated tubes and rotating biodiscs biofilm reactors for wastewater treatment

Wastewater treatment performance of a novel biofilm reactor named as rotating perforated tubes biofilm reactor (RPT) was investigated and compared with a rotating biodisc reactor (RBD) under the same conditions. The effects of major process variables such as feed wastewater flow rate, COD concentration and loading rate on COD removal performances of both reactors were evaluated. Rotating perforated tubes biofilm reactor was found to be more advantageous as compared to rotating biodisc system for COD removal efficiency. This difference becomes more significant at low A/ Q ratios. Empirical design equations were developed for both systems to quantify the systems' performance as a function of major process variables.

Modelling of a recycling sludge bed reactor using AQUASIM: reprint

The recycling sludge bed reactor (RSBR) allows for increased solids retention time, resulting in greater substrate conversion for all particulate degradation and biological reactions. The purpose of the RSBR is to hydrolyse primary settled sewage (PSS). Soluble products are then used for the biological treatment of acid mine drainage. A mathematical model has been developed that describes the anaerobic digestion of PSS and biological sulphate reduction in the RSBR. The hydrodynamic processes taking place in the RSBR have been simulated using a system of mixed reactors connected by water flow and mass flux streams. Trends obtained from varying the hydraulic retention time, the sludge recycle ratio, and the feed COD: SO42- ratio allow for identification of the critical biological processes taking place in the RSBR, as well as the influence of the operating parameters. Areas where there is a lack of understanding in the mechanism and kinetics have been identified, and these include the influence of sulphate reduction on the hydrolysis of particulate organic matter, as well as the mathematical influence of sulphide inhibition on the various biological groups. A sensitivity analysis shows that hydrolysis is the rate-limiting process, while sulphide inhibition is of importance when sulphate conversion increases. WaterSA Vol.28(1) 2002: 111-120

Wastewater Treatment Performance of Rotating Perforated Tubes Biofilm Reactor with Liquid Phase Aeration

A novel biofilm reactor named as `rotating perforated tubes biofilm reactor' was used for treatment of synthetic wastewaterwith and without liquid phase aeration. Effects of major processvariables such as feed wastewater flow rate, COD concentration and loading rate, liquid phase aeration on the rate and extent ofCOD removal were investigated. Liquid phase aeration was provento be advantageous especially for high strength wastewaters at highCOD loading rates. Kinetics of COD removal was investigated andkinetic constants were determined by using the experimental data.An empirical design equation was developed to quantify the system's performance as a function of major process variables.

Rotating-Perforated-Tubes Biofilm Reactor for High-Strength Wastewater Treatment

A rotating-perforated-tubes biofilm reactor was used for treatment of synthetic wastewater at different operating conditions. The biofilm reactor consisted of two sections each having 25 perforated tubes mounted on three perforated discs. The battery of the tubes was rotated with the aid of a shaft and a motor. Effects of major process variables such as feed wastewater flow rate and COD concentration on the system performance were investigated. Kinetics of COD removal was investigated and kinetic constants determined by using the experimental data. An empirical design equation was developed to quantify the system's performance as a function of major process variables.

Modelling of a falling sludge bed reactor using AQUASIM

The falling sludge bed reactor (FSBR) allows for increased solids retention time, resulting in greater substrate conversion for all particulate degradation and biological reactions. The purpose of the FSBR is to hydrolyse primary settled sewage (PSS). Soluble products are then used for the biological treatment of acid mine drainage. A mathematical model has been developed that describes the anaerobic digestion of PSS and biological sulphate reduction in the FSBR. The hydrodynamic processes taking place in the FSBR have been simulated using a system of mixed reactors connected by water flow and mass flux streams. Trends obtained from varying the hydraulic retention time, the sludge recycle ratio, and the feed COD: SO4 2- ratio allow for identification of the critical biological processes taking place in the FSBR, as well as the influence of the operating parameters. Areas where there is a lack of understanding in the mechanism and kinetics have been identified, and these include the influence of sulphate reduction on the hydrolysis of particulate organic matter, as well as the mathematical influence of sulphide inhibition on the various biological groups. A sensitivity analysis shows that hydrolysis is the rate-limiting process, while sulphide inhibition is of importance when sulphate conversion increases. WaterSA Vol.27(4) 2001: 445-454

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.

Study on a sequencing batch membrane bioreactor for wastewater treatment

This study investigated the effect of MLSS concentration in a sequencing batch membrane bioreactor on COD and nitrogen removal as well as flux. Two values of MLSS (5 g/l and 10 g/l) were investigated in this study. The strength of the feed was varied to achieve a target F/M ratio of 0.5 based on COD. Accordingly, the concentration of COD was determined as 3.5 and 7.0 g/l for the 5 and 10 g/l MLSS targets, respectively. The test results showed that an average COD removal of 98.5% was achievable. However, it was noted that nitrification inhibition occurred. Nitrification inhibition occurred because of two factors, namely high NH4+–N concentration and high DO demand. High NH4+–N in the feed led to the inhibition of nitratation and thus high nitrites are found in the effluent. High DO demand due to high feed COD concentration led to an extended period with low DO levels inside the reactor thus retarding the conversion of NH4+–N. The increase in the MLSS concentration from 5 to 10 g/l led to a decrease in the average flux from11.1 l/m2 · h to 9.6 l/m2 · h. An increase in aeration, from 2.0 to 8.0 l/min, did not lead to any significant improvement in terms of fouling.

Nitrogen removal in a modified anaerobic baffled reactor (ABR): 1, denitrification

In order to achieve nitrogen removal within a single reactor unit, an eight compartment anaerobic baffled reactor (ABR) was modified to accommodate an in-situ aerobic stage in the penultimate compartment, which allowed ammonia oxidation to nitrite and nitrate via nitrification. In theory, the nitrite/nitrate may be recycled to the inlet of the ABR and be reduced via denitrification. This paper deals with the anoxic denitrification of a nitrate feed, while a later paper examines nitrification in the aerobic stage. Denitrification occurred almost exclusively in the front two compartments of the anaerobic baffled reactor, with rates of 0.335 (82% reduction) and 0.085 kg NO 3/kg VSS.d (96% reduction) in compartments 1 and 2, respectively. Denitrification had several positive effects on overall reactor performance, and this was due to the following factors: the utilisation of an oxidisable electron donor in the form of the feed COD; increased system pH at the reactor inlet thus improving environmental conditions; a high hydrogen demand during dissimilatory nitrate reduction to ammonium, therefore improving conditions for syntrophic bacteria; and, the generation of ammonium from dissimilatory reduction which provided slowly growing bacteria at the front of the ABR with a reduced nitrogen source. The overall effect of these influences was improved hydrogenotrophic methanogenesis. Denitrification also increased the residual COD in the first two compartments, and this was attributed to faster growth/decay rates of denitrifying bacteria. Nitrate reduction also influenced the ratio of volatile fatty acids produced and catabolised, with a significant reduction in propionate and butyrate, while acetate levels increased.

Salt Inhibition Effects in Biological Treatment of Saline Wastewater in RBC

Design and operation of saline wastewater treatment systems are difficult because of adverse effects of salt on microbial flora. Quantification and modeling of salt inhibition effects are essential in designing biological treatment processes for saline wastewater. Synthetic wastewater containing 0–10% salt (NaCl) was treated in a rotating biodisc contactor (RBC) unit operating in a continuous mode. Effects of important process variables such as the A/Q ratio, COD loading rate, and salt concentration on COD removal rate and efficiency were investigated. The system's performance improved with an increasing A/Q ratio; however, performance decreased with an increasing COD loading rate and salt content. The liquid phase was aerated to keep suspended cells active at high feed COD concentrations such as S0 = 5,000 mg/L. A mathematical model was developed to describe the system's behavior. Model parameters were determined by using the experimental data. Salt inhibition was found to be significant for salt concentrations larger than 2% NaCl. The experimental results and mathematical model may be used in design of RBC units treating saline wastewater.

Simultaneous nitrification-denitrification in a fluidized bed reactor

This paper describes simultaneous nitrification-denitrification (SND) in a fluidized bed reactor (FBR) without physical separation of the aerobic and anoxic zones. Continuous reactor SND trials demonstrated successful SND over distinct periods. Control was achieved by varying the reactor dissolved oxygen and the feed COD, although optimal performance could not be consistently maintained. Batch studies, using cultures from different vertical sections, demonstrated that variation of the bulk parameters successfully stratified the reactor bed into zones that predominantly either nitrified or denitrified. Evidence also indicated that both types of activity occurred throughout the FBR.

Saline Wastewater Treatment By Halophile-Supplemented Activated Sludge Culture in an Aerated Rotating Biodisc Contactor

Synthetic wastewater containing 0–10% salt (NaCl) was treated in a rotating biodisc unit operating in continuous mode. Salt tolerant, Halobacter halobium-supplemented activated sludge culture was used in order to alleviate salt inactivation effects. Effects of important process variables such as inclusion of Halobacter, A/Q ratio, COD loading rate, and salt concentration on the COD removal rate and efficiency were investigated. The system performance improved with increasing A/Q ratio; however, it decreased with increasing COD loading rate and salt content. The liquid phase was aerated in order to keep suspended cells active at feed COD concentrations of 5,000 mg l −1. A mathematical model was developed to describe the system behavior. Model parameters were determined by using the experimental data. Salt inhibition was found to be significant for salt contents larger then 3% NaCl.

Production of Soluble Microbial Products (SMP) in an Anaerobic Baffled Reactor: Composition, Biodegradability, and the Effect of Process Parameters

The composition and biodegradability of effluents from biological treatment plants is of increasing interest due to tightening effluent standards. One of the main constituents of effluents are soluble microbial products (SMPs) produced in the reactor during metabolism and endogenous decay. The objective of this preliminary work was to examine the influence of operating parameters such as temperature, hydraulic retention time (HRT), and organic loading rate (OLR) on the production of SMPs in a compartmentalised anaerobic baffled reactor (ABR) fed a simple sucrose-nutrients substrate. In addition, in order to gain greater insight into the SMPs produced, the composition and anaerobic biodegradability of various molecular weight fractions were analysed. It was found that decreasing operating temperature resulted in slight increases in SMP production, a decreased rate of degradation, and hence increases in effluent SMPs. In addition, decreasing HRTs, and increasing OLRs, also resulted in increased effluent SMPs. Quantitatively, between 26 and 48% of the incoming feed COD was converted to SMPs in the first compartment of the ABR, more than double that previously reported. Molecular weight (MW) fractionation revealed a bimodal distribution with 25% > 100kDa, and 30% < 1kDa, and all MW fractions were between 62 and 82% degradable. Analysis revealed most of the high MW fraction to be primarily an excreted heteropolysaccharide.

Simultaneous nitrification-denitrification in a fluidized bed reactor

This paper describes simultaneous nitrification-denitrification (SND) in a fluidized bed reactor (FBR) without physical separation of the aerobic and anoxic zones. Continuous reactor SND trials demonstrated successful SND over distinct periods. Control was achieved by varying the reactor dissolved oxygen and the feed COD, although optimal performance could not be consistently maintained. Batch studies, using cultures from different vertical sections, demonstrated that variation of the bulk parameters successfully stratified the reactor bed into zones that predominantly either nitrified or denitrified. Evidence also indicated that both types of activity occurred throughout the FBR.

Anaerobic treatment of olive mill effluents

The anaerobic treatability of olive mill effluent was investigated using a laboratory scale upflow anaerobic sludge blanket reactor (UASBR) operated for about six months. The effects of various operating conditions including pH, feed strength and hydraulic retention time on the performance of the anaerobic treatment process were determined. In the first part of this study, the reactor was operated with feed COD concentrations from 5000 to 19,000 mg/l and a retention time of 1 day, giving organic loading rates from 5 to 18 kg COD/m3d. Soluble COD removal was around 75% under these conditions. In the second part of the study, feed CODs were varied from 15,000 to 22,600 mg/l while retention times ranged from 0.83 to 2 days; soluble COD removal was around 70%. A methane conversion rate of 0.35 m3 per kg COD removed was achieved during the study. The average volatile solids (VS) concentration in the reactor had increased from 12.75 g l−1 to 60 g l−1 by the end of the study. Sludge volume index (SVI) determinations performed to evaluate the settling characteristics of the anaerobic sludge in the reactor indicated excellent settleability with SVI values of generally less than 20 ml g−1. Sludge granules ranging from 3 to 8 mm in diameter were produced in the reactor. The second order substrate removal kinetics was applied by assuming that hydraulic conditions in the UASBR are approximately completely mixed and the model fitted well to the steady state operating results.