The effect of grease on the activated sludge process in wastewater treatment

Abstract

The purpose of this paper is to introduce the major potentials and perspectives of applications of finite element analysis in solving the problems of shallow water wave equations. One‐dimensional and two‐dimensional shallow water wave equations will both be incorporated into the modeling procedures. For one‐dimensional flows, the models will cover the typical single channels, confluence channels system, division channels system, and natural river systems. As far as two‐dimensional flows are concerned, the overland flows are investigated. The simulation results are compared with the data obtained by physical modeling and field observation and with the results of other existing literature. The models were found to be very feasible in modeling the complex flow fields of shallow water wave equation problems.     

Study of the aerobic biodegradation of coke wastewater in a two and three-step activated sludge process

A laboratory-scale biological plant composed of two aerobic reactors operating at 35 degrees C was used to study the biodegradation of coke wastewater. The main pollutants to be removed are organic matter, especially phenols, thiocyanate and ammonium nitrogen. The concentrations of the main pollutants in the wastewater during the study ranged between 922 and 1,980 mg COD/L, 133 and 293 mg phenol/L, 176 and 362 mg SCN/L and 123 and 296 mg NH(4)(+)-N/L. The biodegradation of these pollutants was studied employing different hydraulic residence times (HRT) and final effluent recycling ratios in order to minimize inhibition phenomena attributable to the high concentrations of pollutants. During the optimisation of the operating conditions, the removal of COD, phenols and thiocyanate was carried out in the first reactor and the nitrification of ammonium took place in the second. The best results were obtained when operating at an HRT of 98 h in the first reactor and 86 h in the second reactor, employing a recycling ratio of 2. The maximum removal efficiencies obtained were 90.7, 98.9, 98.6 and 99.9% for COD, phenols, thiocyanate and NH(4)(+)-N, respectively. In order to remove nitrate, an additional reactor was also implemented to carry out the denitrification process, adding methanol as an external carbon source. Very high removal efficiencies (up to 99.2%) were achieved.     

Membrane bioreactors for wastewater treatment — operating experiences with the Kubota submerged membrane activated sludge process

A number of membrane systems have been developed for effluent treatment, however, few of these can treat the biological and solids loading of the effluent in one treatment stage. Operating and capital costs can be prohibitive for membrane systems used as a tertiary treatment stage (1), but by combining the biological and physical separation stages, membrane bioreactors promise to be compact and more economic in comparison.     

Solubilization of excess sludge in activated sludge process using the solar photo-Fenton reaction

The solubilization of excess sludge by the solar photo-Fenton reaction has been investigated for the reduction of excess sludge in the activated sludge process. The solubilization kinetics depended on the dosages of the Fenton reagents, Fe and H(2)O(2). Increases of initial Fe and H(2)O(2) concentrations in their ranges studied in this work continuously enhanced the sludge solubilization. Cell lysis by the photo-Fenton reaction caused the increase in dissolved chemical oxygen demand (COD) in the first step of sludge solubilization. The further oxidative decomposition of the discharged organic compounds by the photo-Fenton reaction led to the decrease in the dissolved COD as the second step of sludge solubilization. The increase of dissolved COD in the first step of sludge solubilization and the consumption of H(2)O(2) could be described by the pseudo-zero order kinetics based on the accumulated light energy. About 40% reduction of mixed-liquor suspended solids (MLSS) by the solar photo-Fenton reaction was found. It was found that solar light used as a light energy source instead of costly and hazardous artificial UV light was very effective. The dissolved COD for solar photo-Fenton reaction increased faster and by 1.5 times as compared with that by artificial UV light.     

Effects of nickel(II) addition on the activity of activated sludge microorganisms and activated sludge process

The effects of Ni(II) in a synthetic wastewater on the activity of activated sludge microorganisms and sequencing batch reactor (SBR) treatment process were investigated. Two parallel lab-scale SBR systems were operated. One was used as a control unit, while the other received Ni(II) concentrations equal to 5 and 10 mg/l. The SBR systems were operated with FILL, REACT, SETTLE, DRAW and IDLE modes in the time ratio of 0.5:3.5:1.0:0.75:0.25 for a cycle time of 6 h. The addition of Ni(II) into SBR system caused drastically dropped in TOC removal rate (k) and specific oxygen uptake rate (SOUR) by activated sludge microorganisms due to the inhibitory effects of Ni(II) on the bioactivity of microorganisms. The addition of 5 mg/l Ni(II) caused a slight reduction in TOC removal efficiency, whereas 10 mg/l Ni(II) addition significantly affected the SBR performance in terms of suspended solids and TOC removal efficiency. Termination of Ni(II) addition led to almost full recovery of the bioactivity in microorganisms as shown in the increase of specific oxygen uptake rate (SOUR) and SBR treatment performance.     

Kalman filter for updating the coefficients of regression models. A case study from an activated sludge waste-water treatment plant

A Kalman filter was developed to overcome the problems caused by process drifting. Different types of models were used to predict response variables of an activated sludge waste-water treatment plant. These models were constructed using MLR, PCR, and PLS. The MLR-type regression coefficients were calculated for both the PCR and PLS models. After that, the Kalman filter was used to estimate these coefficients, recursively. Both the PCR and PLS `inner relation' coefficient vectors were also estimated in this way and the results were then compared. The effect of the number of variables was also briefly studied. The testing was carried out using sequential process data. The prediction ability was measured by a Q²-value as a function of a lag in the updating of the coefficients.     

Parameter optimization of ferro-sonication pre-treatment process for degradation of bisphenol A and biodegradation from wastewater sludge using response surface model

In this study, the application of response surface model in predicting and optimizing the ferro-sonication pre-treatment for degradation of bisphenol A (BPA), an endocrine disrupter compound from wastewater sludge (WWS) was investigated. The ferro-sonication pre-treatment process was carried out according to central composite design (CCD) with four independent variables such as wastewater sludge solids concentration, pH, ultrasonication time and FeSO(4) concentration. The effect of ferro-sonication pre-treatment was assessed in terms of increase in sludge solids (suspended solids (SS) and volatile solids (VS)) and organic matter (chemical oxygen demand (COD) and soluble organic carbon (SOC)) solubilization and simultaneous BPA degradation from WWS. It was observed that among all the variables studied, ultrasonication time had more significantly affected the efficiency of the ferro-sonication pre-treatment process followed by FeSO(4) and solids concentration. Through this optimization process, it was found that maximum BPA degradation of 88% could be obtained with 163 min ultrasonication time, 2.71 mg/L FeSO(4) concentration, pH 2.81 with 22 g/L SS. Further, the effect of ferro-sonication pre-treatment on biodegradation of WWS was also studied. It was observed that ultrasonication time had significant effect and the higher biodegradation (32.48%) was observed at 180 min ultrasonication time.     

Effect of acclimatization of microorganisms to heavy metals on the performance of activated sludge process

Although selected heavy metals (HMs) stimulate biological reactions at low concentrations, all HMs are toxic to microorganisms (MOs) at moderate concentrations and can cause inhibitory effects on the biological processes. Therefore, MOs must be acclimated to HMs or other toxic substances present in wastewaters (WWs) before they are used in an activated sludge process (ASP). In this study, combined effect of Cu(2+) and Zn(2+) ions in a synthetic WW on the efficiency of a laboratory-scale ASP without recycle was investigated using acclimated MOs at different extents.A synthetic feed solution of 1222 mg L(-1) proteose-peptone (corresponding to 1300 mg COD L(-1)) served as a source of carbon. Cu(2+) and Zn(2+) ions at different concentrations (1.5, 4.5 and 9, 27 mg L(-1), respectively) were introduced in the feed to a continuously stirred activated sludge reactor at different hydraulic residence times (2-40 h) keeping pH, temperature and stock feed composition constant. The combined effects of copper and zinc ions were determined by mixing these metallic ions at the specified combinations of concentrations such as "1.5 mg L(-1) of Cu(2+)+9 mg L(-1) of Zn(2+)" and "4.5 mg L(-1) of Cu(2+)+27 mg L(-1) of Zn(2+)". It was observed that using seed MOs acclimatized to two times of the combined threshold concentration of these HMs for an unduly long period of time (1-4 months) caused adverse effects on the ASP performance. Besides, it was found that usual inhibition effects of these HMs were enhanced with increasing period of acclimation. Substantially lower substrate removal efficiencies were obtained with acclimatized MOs than those obtained with non-acclimatized MOs. At the higher initial substrate concentration of 2500 mg COD L(-1), substrate-inhibition occurred causing a decrease in the specific growth rate constant (k); however, HM inhibition was suppressed, resulting to about 20% increase in treatment efficiency of the ASP. It can be concluded that the time period necessary for acclimatization of seed MOs must be adjusted carefully with concentrations of HMs lower than their threshold concentrations to achieve an optimal operation of an aerobic biological process.     

A comparison study of the Boussinesq and the variable density models on buoyancy-driven flows

When density variations are sufficiently small the Boussinesq approximation is valid. The approximation is introduced to reduce the degree of the complexity of density variations and implies that density effects are considered only in the buoyancy force term of the momentum equation. Because of its simplicity in practical implementations, the approximation is widely used. Although there are many studies related to the approximation, some important characteristics are still missing. In this article, we compare the Boussinesq approximation and variable density models for the two-dimensional (2D) Rayleigh–Taylor instability with a phase-field method. Numerical experiments indicate that for an initially symmetric perturbation of the interface the symmetry of the heavy and light fronts for the Boussinesq model can be seen for a long time. However, for the variable density model, the symmetry is lost although the flow starts symmetrically.     

Sludge reduction potential of the activated sludge process by integrating an oligochaete reactor

An oligochaete reactor linked to an integrated oxidation ditch with vertical cycle (IODVC) was used to investigate the sludge reduction potential induced by worms. The presence of Tubificidae was observed in the worm reactor throughout the operational period after its inoculation, and Tubificidae was occasionally found in the IODVC. Free-swimming worms, Aeolosoma hemprichi, Nais elinguis, and Aulophorus furcatus, were found in both the IODVC and the worm reactor, but A. hemprichi was dominant. A. hemprichi reached its maximum, 322 and 339 Aeolosoma/mL mixed liquor on day 49 in the worm reactor and the IODVC, respectively. The presence of oligochaetes or the integration of worm reactor with the IODVC had little effect on sludge yield, but the worm growth was helpful for improving sludge settling characteristics. The average sludge yield and sludge volume index (SVI) in the IODVC were 0.33 kgSS/kgCOD(removed) and 78 mL/g, respectively. The worm presence had little impact on effluent quality of the IODVC, but it caused phosphorus release into the effluent. The average COD, NH(4)(+)-N, and SS concentrations in the effluent of the IODVC were 49.06, 12.82, and 58.25 mg/L, respectively. No total nitrogen (TN) release into the effluent of the IODVC occurred.     

Distribution of extractable fractions of heavy metals in sludge during the wastewater treatment process

Sludge samples were collected from different treatment steps of Gaobeidian wastewater treatment plant (WWTP) of Beijing City, PR China, to investigate the distributions of total and chemical fractions of Fe, Mn, Ni, Cu, Zn, Cr, Pb, and Mo in different sludges. The highest total concentrations were found for Fe, Mn, Pb, and Mo in digested sludge (DS), Ni and Cr in thickened sludge (TS), Zn in dewatering sludge (DWS), and Cu in active sludge (AS). The lowest concentrations were observed in AS, except for Cu in TS. Significant differences of total metal concentration were observed between AS and TS (or DS), suggesting that sludge thickening and digesting treatments significantly influenced the total metal concentrations. Fe, Cu, Ni, Cr, Mo, and Pb distributed principally in the residual fraction in all sludges, while Zn and Mn presented in a highly available fraction. For same metal in different sludges, the portion of easily mobile fraction decreased significantly along the wastewater treatment process, and metals in AS presented in the highest available fraction. Organic matter contents, TN, and TP of sludges exhibited a significant positive correlation with the concentrations of exchangeable and reducible fraction of Pb, Mo, Cr, Cu, and Fe, while sludge pH demonstrated significant negative correlations with the concentrations of these metals.     

A study of operational and testing reliability in software reliability analysis

Software reliability is an important aspect of any complex equipment today. Software reliability is usually estimated based on reliability models such as nonhomogeneous Poisson process (NHPP) models. Software systems are improving in testing phase, while it normally does not change in operational phase. Depending on whether the reliability is to be predicted for testing phase or operation phase, different measure should be used. In this paper, two different reliability concepts, namely, the operational reliability and the testing reliability, are clarified and studied in detail. These concepts have been mixed up or even misused in some existing literature. Using different reliability concept will lead to different reliability values obtained and it will further lead to different reliability-based decisions made. The difference of the estimated reliabilities is studied and the effect on the optimal release time is investigated.     

A scheduling system for the steelmaking-continuous casting process. A case study from the steel-making industry

This paper describes the models, algorithms and implementation results of a computerised scheduling system for the steelmaking-continuous casting process of a steel plant in Austria. The basis for the scheduling task is a preliminary production schedule for the continuous casters (sequence of charges that must be consecutively cast and their allocation to the continuous casters). The scheduling task can be structured as four sub-problems: (1) scheduling the continuous casters. (2) Allocation of the charges to the parallel facilities at the upstream stages (converter and refining facilities). (3) Sequencing the charges at the converters and refining facilities. (4) Exact timing of all operations. The heuristic algorithm consists of three planning levels: (1) scheduling the continuous casters, considering the capacity restrictions at the upstream stages and the limited availability of hot metal. (2) Scheduling of the converter and refining facilities according to priorities, performing allocation and sequencing. (3) Improving the schedule by means of an LP model. The system visualises the schedules as Gantt charts. Extensive numerical tests with real-life data and more than two years of experience with the implementation demonstrate that the system produces reasonable schedules and is accepted by the planners.     

On the occasional biodegradation of pharmaceuticals in the activated sludge process: the example of the antibiotic sulfamethoxazole

Sulfamethoxazole, a common antibiotic, was found to be biodegradable under aerobic conditions. The fate of sulfamethoxazole in the activated sludge process was studied using a Sequencing Batch Reactor (SBR). Aerobic biomass was acclimated to sulfamethoxazole and a series of kinetic experiments were conducted to investigate the impact of other carbon and nitrogen sources on the degradation of the antibiotic. It was found that sulfamethoxazole serves both as carbon and nitrogen source for the enriched consortium. It was degraded whenever there was a depletion of carbon or nitrogen or both in the feeding medium, while in the presence of acetate and ammonium nitrogen (alternative carbon and nitrogen sources, respectively), sulfamethoxazole remained intact.     

Ecotoxicity tests in the environmental analysis of wastewater treatment plants: case study in Portugal

A global evaluation of wastewaters should include ecotoxicological tests to complement the chemical characterization, with advantages especially in the case of complex wastewaters. A European project developed in Tranc?o River Basin (Portugal), integrated the ecotoxicological and physicochemical studies of wastewater samples from two municipal sewer networks and respective wastewater treatment plants. Wastewater samples were analysed for physicochemical parameters, ecotoxicological acute and chronic tests performed and the potential for endocrine disruption evaluated. Organic load parameters and total suspended solids showed significant correlations with Microtox and ThamnoToxKit test results. Data analysis showed that treated treatment plant effluent samples are associated with less organic contamination and less toxicity in ThamnoToxKit test. Chronic toxicity test and endocrine disruption assay of treatment plant effluent samples indicated that, in a long term, potential population effects could arise in the receiving waters. A test battery to monitor this type of wastewaters is proposed, including tests with a bacterium, an alga and a crustacean. In a screening phase the most sensitive test, Microtox, can be used. The use of an ecotoxicological approach can have added value to hazard and risk assessment of discharges to the receiving waters and can contribute to the environmental management of the treatment plant.     

Elimination of Cu(II) toxicity by powdered waste sludge (PWS) addition to an activated sludge unit treating Cu(II) containing synthetic wastewater

Copper(II) ion toxicity onto activated sludge organisms was eliminated by addition of powdered waste sludge (PWS) to the feed wastewater for removal of Cu(II) ions by biosorption before biological treatment. The synthetic feed wastewater containing 14 or 22 mgl(-1) Cu(II) was mixed with PWS in a mixing tank where Cu(II) ions were adsorbed onto PWS and the mixture was fed to a sedimentation tank to separate Cu(II) containing PWS from the feed wastewater. The activated sludge unit fed with the effluent of the sedimentation tank was operated at a hydraulic residence time (HRT) of 10h and sludge age (SRT) of 10 days. To investigate Cu(II), COD and toxicity removal performance of the activated sludge unit at different PWS loadings, the system was operated at different PWS loading rates (0.1-1 gPWSh(-1)) while the Cu(II) loading rate was constant throughout the operation. Percent copper, COD and toxicity removals increased with increasing PWS loading rate due to increased adsorption of Cu(II) onto PWS yielding low Cu(II) contents in the feed. Biomass concentration in the aeration tank increased and the sludge volume index (SVI) decreased with increasing PWS loading rate due to elimination of Cu(II) from the feed wastewater by PWS addition. PWS addition to the Cu(II) containing wastewater was proven to be effective for removal of Cu(II) by biosorption before biological treatment. Approximately, 1 gPWSh(-1) should be added for 28 mgCuh(-1) loading rate for complete removal of Cu(II) from the feed wastewater to obtain high COD removals in the activated sludge unit.     

A case study on process optimization using the gradient loss function

This paper focuses on studies where the goal is to optimize the key quality characteristics of a specific product or process. In order to do that, the process parameters must be adjusted in such a way that deviations from target are minimized while robustness to noise and to process parameter fluctuations are maximized. Since this is a multi-response, multi-objective problem, the optimum solution is a compromise. In this paper we present a gradient loss function which captures all the desired objectives, and propose a general methodology to perform the optimization analysis. This methodology is then carried out experimentally on a cosmetic product and the results are discussed.     

Applying the TOC thinking process in manufacturing: A case study

A case study is presented to illustrate the application of the Theory of Constraints thinking process logic tools in a manufacturing environment. The study firm performs design activities related to meeting future product requirements while concurrently meeting existing production schedules for the current design of the product. Current approaches to managing the firm's limited productive capacity do not allow for both design and production activities to occur simultaneously while meeting the customer's current product delivery schedule. Thus, despite their desire to satisfy their customer's future design requirements, management uses the majority of its production capacity to meet its customer's current product delivery schedule. This case study demonstrates how a team of employees used thinking process logic diagrams to document reality, identify a core conflict and problem, develop proposed changes to address the core problem, and create several detailed action plans to implement changes within the study organization. Initially, scenarios associated with some undesirable effects are used to understand how prevailing policies and behaviours result in less than desired production line performance. Then, a current reality tree is constructed to link the core problem or system constraint with the previously identified undesirable effects. Next, two major injections are developed to address the core problem in managing the production line as logically documented in a future reality tree. Finally, three transition trees are presented to guide the implementation of change at the study organization.     

A comparative study of the adsorption of humic acid, fulvic acid and phenol onto Bacillus subtilis and activated sludge

The adsorption of humic acid and fulvic acid onto Bacillus subtilis cells and activated sludge biomass was studied as a function of pH and incubation time. The adsorption of humic and fulvic acids was strongly pH-dependent and followed the same trend on both surfaces, increasing in a sigmoidal way with decreasing pH over the 2-10 pH range. This behaviour is explained in terms of hydrophobic interactions between the uncharged biomass and the uncharged humic and fulvic acids. In contrast, the adsorption of phenol onto B. subtilis cells and activated sludge biomass showed in both cases an optimum pH at around 7.0. This optimum value may be interpreted in terms of a combination of hydrophobic interactions and hydrogen bonds between undissociated phenol and polar groups on the cell walls. Kinetic studies on the adsorption of humic acid, fulvic acid and phenol onto B. subtilis cells and sludge biomass pointed to a rapid uptake of the substances, with an equilibrium time of about 30 min. In all cases, the kinetic curves were acceptably fitted by non-linear regression to an exponential function, suggesting a first-order kinetic phenomenon. The specific adsorption values collected at optimum pH revealed that with the materials used in this work both B. subtilis and activated sludge follow the same adsorption trend: humic>fulvic>phenol. The lower adsorption of fulvic acid as compared with humic acid may be explained in terms of its lower hydrophobicity rather than its lower molecular size. On comparing the specific adsorption values of activated sludge versus B. subtilis, similar but lower figures were found for the three organic compounds studied. This similar behaviour suggests that both types of biomass base their adsorption capacity on the general characteristics of the bacterial cell wall, and the lower adsorption by the sludge would be due to a lower specific area due to clustering of the cells. This is remarkable, since sludge is a heterogeneous and cheap material in comparison with cultured bacterial cells.     

Demonstration of statistical approaches to identify component's ageing by operational data analysis—A case study for the ageing PSA network

The paper presents some results of a case study on “Demonstration of statistical approaches to identify the component's ageing by operational data analysis”, which was done in the frame of the EC JRC Ageing PSA Network. Several techniques: visual evaluation, nonparametric and parametric hypothesis tests, were proposed and applied in order to demonstrate the capacity, advantages and limitations of statistical approaches to identify the component's ageing by operational data analysis. Engineering considerations are out of the scope of the present study.