Sludge Wastewater Treatment Process Research Articles

The effect of cadmium on a semi-self-sustaining microalgal-bacterial granular sludge process for wastewater treatment

Microalgal-bacterial granular sludge (MBGS) is an innovative and sustainable technology for wastewater treatment. This research investigated the effect of Cd2+ on the performance and characteristics of such semi-self-sustaining MBGS reactors (with additional intermittent aeration). After 30 days of exposure to 0, 2, and 10 mg·l−1 Cd2+, the three reactors consistently exhibited robust removal efficiencies, achieving 89 % removal for chemical oxygen demand (COD) and 99 % removal for NH4+-N. However, the MBGS in control exhibited better performance in T-N removal compared to MBGS exposed to 10 mg·l−1 Cd2+ (especially during the light phase), indicating a potential impact of Cd2+ on the N-assimilation process of microalgae. The high concentration of Cd2+ also negatively affected the MBGS structure and increased the production of extracellular polymeric substances. Further investigations of the dissolved oxygen profile were conducted under phototrophic conditions, the maximum oxygen production rate contributed to microalgae in the control group was 20.9 % and 46.4 % higher than that of groups with 2 and 10 mg·l−1 Cd2+. The results show that Cd2+ mainly impacts the microalgae in the outer layer of the structure, and additional aeration helps compensate for the decrease in oxygen production caused by Cd2+ in MBGS, thereby making the system more stable in removing COD and NH4+-N.

Analysing the influence of operating conditions on the performance of algal–bacterial granular sludge processes for wastewater treatment: A review

AbstractThis article discussed the effect of the main operating parameter involved in the operation of algal–bacterial granular sludge (ABGS) systems as promising biological processes for wastewater treatment. The focus was on the operational ranges reported in the literature capable of achieving better granule properties, good stability and high removal capacities. This review identified that hydraulic retention time (HRT), light intensity (LI) and light/dark periods were the most influential operating factors on the formation, stability, settleability and organic pollutant removal efficiency of ABGS. The discussion argued that ABGS systems enhance industrial and domestic wastewater treatment due to additional advantages that provide the symbiotic interactions to process performance, maintaining lesser operating costs concerning aerobic granular sludges (AGS) and microalgae consortia. This review will improve the understanding of the operation of ABGS systems and thus further expand possible operating combinations that help to enhance microbial interactions, microalgae growth and external aeration self‐sufficiency in further research with a focus on its scaling up.

Cultivation of algal-bacterial granular sludge and degradation characteristics of tetracycline.

Due to the increasing use of antibiotics, tetracycline was frequently detected in wastewater. As a novel technology, algal-bacterial granular sludge process is expected to be widely used in wastewater treatment. However, the degradation effect of tetracycline by algal-bacterial granular sludge process and its degradation path is still unknown. In this study, mature and stable algal-bacterial granular sludge was cultured and the degradation of tetracycline by it was investigated. The results showed that the removal amount of 1~25 mg/L tetracycline by algal-bacterial granular sludge was 0.09~1.45 mg/g VSS, in which the adsorption amount was 0.06~0.17 mg/g VSS and the degradation amount was 0.03~1.27 mg/g VSS. Tetracycline biosorption was dominant at its concentration of 1~3 mg/L, while biodegradation was predominant at 5~25 mg/L of tetracycline. At tetracycline concentration of 3~5 mg/L, the contribution of biosorption and biodegradation to tetracycline removal by algal-bacterial granular sludge process was almost equal. Algal-bacterial granular sludge could effectively degrade tetracycline through demethylation, dehydrogenation, deacylation and deamination or their combination. In addition, the degradation products were non-toxic and hardly pose a threat to environmental health. The research results of this paper provide a solid theoretical basis for tetracycline removal by algal-bacterial granular sludge, and a reference for the development of algal-bacterial granular sludge process for wastewater treatment in the presence of tetracycline.

Evaluation and improvement of the WWTP performance of an agricultural cooperative by adsorption on inert biomaterial: case of orthophosphate, nitrate and sulfate ions

The study is carried out at the wastewater treatment plant (WWTP) of an agricultural cooperative that operates according to the activated sludge process. Dairy industry is enlisted as one of the top-most industries in the food industry. Dairy wastewater treatment is a big issue as dairy wastewater releases a high amount of chemical oxygen demand, inorganic and organic particles, biological oxygen demand, and nutrients. But, these processes partly degrade wastewater containing fats and nutrients as dairy wastewater. The aim of this study was to evaluate the purification performance of this treatment process. The qualitative analysis of decanted raw wastewater (DRWW) and purified wastewater (PWW) shows that the concentration of orthophosphate, nitrate and sulfate ions is slightly higher. Such contaminated water if not handled appropriately, it pollutes water bodies and largely affects our ecosystem and biodiversity. Hence, our proposal is to improve the WWTP performances by using the adsorption process onto dried Carpobrotus edulis as an inert biomaterial. This adsorption process is recognized as one of the best water treatment techniques, more and more works are oriented towards the search for new materials, cheaper and having a good adsorbent potential. This study opens the path for the use of natural and abundant local material to remove orthophosphate, nitrate and sulfate ions using the C. edulis plant particles shred. The surface micromorphology of the biomaterial was investigated using a scanning electron microscope; while the qualitative element composition was analyzed using energy dispersive X-ray and infrared spectroscopies. The found results of DRWW was about 57% for orthophosphates, 67% for sulfates and 73% for nitrates ions. For PWW, the percentage removal was found to be 62%, 73% and 84% for orthophosphates, sulfates and nitrates respectively. These results indicate that dried C. edulis plant, as an environmentally friendly adsorbent could be recommended for the removal of mineral pollutants. In conclusion, the C. edulis adsorbent can be integrated into the activated sludge process for wastewater treatment after identifying the optimal hydraulic loads, associated sizes, and shapes in continuous operations.

Auto-Control Technique Using Gradient Method Based on Radial Basis Function Neural Networks to Control of an Activated Sludge Process of Wastewater Treatment

Dissolved oxygen (DO) concentration is a key variable in the activated sludge wastewater treatment processes. In this paper, an auto control strategy based on Euler method and gradient method with radial basis function (RBF) neural networks (NNs) is proposed to solve the DO concentration control problem in an activated sludge process of wastewater treatment. The control purpose is to maintain the dissolved oxygen concentration in the aerated tank for having the substrate concentration within the standard limits established by legislation of wastewater treatment. For that reason, a new proposed control strategy based on gradient descent method and RBF neural network has been used. Compared with RBF neural network PI control, the obtained results show the effectiveness in terms of both transient and steady performances of proposed control method for dissolved oxygen control in the activated sludge wastewater treatment processes.

Gradient Descent Optimization Control of an Activated Sludge Process based on Radial Basis Function Neural Network

Most systems in science and engineering can be described in the form of ordinary differential equations, but only a limited number of these equations can be solved analytically. For that reason, numerical methods have been used to get the approximate solutions of differential equations. Among these methods, the most famous is the Euler method. In this paper, a new proposed control strategy utilizing the Euler and the gradient method based on Radial Basis Function Neural Network (RBFNN) model have been used to control the activated sludge process of wastewater treatment. The aim was to maintain the Dissolved Oxygen (DO) level in the aerated tank and have the substrate concentration Chemical Oxygen Demand (COD5) within the standard limits. The simulation results of DO show the robustness of the proposed control method compared to the classical method. The proposed method can be applied in wastewater treatment systems.

Pressure retarded osmosis coupled with activated sludge process for wastewater treatment: Performance and fouling behaviors

A novel hybrid technology integrating pressure retarded osmosis with activated sludge process (denoted as PRO-MBR) was proposed in this study for wastewater treatment. Here, performance and fouling behaviors of PRO-MBR were investigated. Excellent contaminants removal and power production were simultaneously achieved in the PRO-MBR. A significant drop of water flux in the PRO-MBR was mainly due to the severe fouling of the support layer in forward osmosis (FO) membrane including internal fouling and external fouling. Although the external fouling was identified to be the major type of fouling, the internal fouling dominated the overall decline of water flux. In addition, organic foulants and biofoulants were the dominant foulants for the external fouling while inorganic foulants were equal to organic foulants and biofoulants for the internal fouling. According to the variations of water flux in the PRO-MBR, the development of support layer fouling was divided into three stages.

Benchmarking the scientific research on wastewater-energy nexus by using bibliometric analysis.

With an exponential increase in urbanization and industrialization, water pollution is an inevitable consequence of relatively lagging wastewater treatment facilities. The conventional activated sludge process for wastewater treatment primarily emphasizes the removal of harmful substances to maintain increasingly stringent effluent discharged standards, which is considered an energy-intensive technique. Therefore, innovative and sustainable wastewater treatment should pay more attention to energy and resource recovery in dealing with fossil fuel depletion, global-scale energy security, and climate change. A bibliometric analysis was applied to trace wastewater-energy nexus-related research during the period 1991 to 2015, with respect to the Science Citation Index EXPANDED (SCI-EXPANDED) database. Journal of Hazardous Materials, ranking 1st in h-index (79), was the most productive journal (431, 4.5%) during the same time, followed by International Journal of Hydrogen Energy (422, 4.4%) and Water Research (393, 4.1%) journal, the latter owning a topmost journal impact factor. Though, China (2154, 22.5%) was the most productive country, while the USA with highest h-index (88) was the favorest collaborative country. The Chinese Academy of Sciences, China (241, 2.5%) produced the maximum publications. A novel method called "word cluster analysis" showed that the emerging sustainable processes and novel renewable energy application are applied in response to the desire for a net wastewater-energy nexus system. Based on different wastewater types, the emerging energy and sources recovery treatment processes of Anammox, anaerobic digestion, and microbial fuel cells gained extensive innovation. Evaluation indicators including sustainability, life cycle assessment, and environmental impact were appropriately used to dissert feasibility of the novel treatment methods in regard of renewable energy utilization, energy savings, and energy recovery. The transformation of the new concept of "broaden income source, economize on expenditures and exploit inner potential" should be generalized in order to achieve an environmentally sustainable development of wastewater-energy nexus system.

Design of a modern automatic control system for the activated sludge process in wastewater treatment

The Activated Sludge Process (ASP) exhibits highly nonlinear properties. The design of an automatic control system that is robust against disturbance of inlet wastewater flow rate and has short process settling times is a challenging matter. The proposed control method is an I-P modified controller automatic control system with state variable feedback and control canonical form simulation diagram for the process. A more stable response is achieved with this type of modern control. Settling times of 0.48days are achieved for the concentration of microorganisms, (reference value step increase of 50mg·L−1) and 0.01days for the concentration of oxygen (reference value step increase of 0.1mg·L−1). Fluctuations of concentrations of oxygen and microorganisms after an inlet disturbance of 5×103m3·d−1 are small. Changes in the reference values of oxygen and microorganisms (increases by 10%, 20% and 30%) show satisfactory response of the system in all cases. Changes in the value of inlet wastewater flow rate disturbance (increases by 10%, 25%, 50% and 100%) are stabilized by the control system in short time. Maximum percent overshoot is also taken in consideration in all cases and the largest value is 25% which is acceptable. The proposed method with I-P controller is better for disturbance rejection and process settling times compared to the same method using PI controller. This method can substitute optimal control systems in ASP.

Modeling and Experimental Prediction of Wastewater Treatment Efficiency in Oil Refineries Using Activated Sludge Process

In this study, activated sludge process for wastewater treatment in a refinery was investigated. For such purpose, a laboratory scale rig was built. The effect of several parameters such as temperature, residence time, effect of Leca (filling-in percentage of the reactor by Leca) and UV radiation on COD removal efficiency were experimentally examined. Maximum COD removal efficiency was obtained to be 94% after final testing. An artificial neural network (ANN) was applied to evaluate the effect of operational parameters on the efficiency as the next step. A two-layered ANN provided the best results, using Levenberg–Marquardt back propagation learning algorithm (trainLM) in which tansig and purelin used as transfer functions in the hidden and output layers. Furthermore, the application of three neurons in the hidden layer caused to gratify network training while overfitting was hindered. ANN model, provided a good estimation for correlation coefficient and the mean square error (MSE) which calculated 0.997  and 0.5 × 10-3 respectively.

Effects of the Filler Properties on Removal Nitrogen of Wastewater in Hybrid Biofilm-Activated Sludge Process

To develop the proper filler for improving removal efficiency of ammonia nitrogen in the activated sludge process of wastewater treatment, the effects of the filler properties and treatment conditions on removal efficiency of ammonia nitrogen in hybrid biofilm-activated sludge process were investigated by the lab-scale test and pilot-scale test. Moreover, the feasibility of simultaneous nitrification and denitrification (SND) was explored with biofilm treatment for chemical poor-biological wastewater. The results showed that SND occurred in the aerobic section. The effluent total basicity (TB) in biofilm process was more than 2mmol / L, higher than activated sludge process. Correspondingly, the effluent TB in activated sludge process was about 0.1mmol / L, and nitrate produced by activated sludge process was 30 mg/L higher than biofilm process. Under the condition of HRT of 24 h for hydrolysis-acidification tank, HRT of 4 h for anoxic tank and HRT of 16 h for aerobic tank, effluent NOˉx-N with combination type of filler in biofilm process was 20mg/L less than that with the activated sludge process. TB with combination type of filler in biofilm process was 2mmol/L less than that with the activated sludge process. Nitrogen removal efficiency was 10.46% with SJ-1 type of filler (made in Jiangsu Suzhou Purification Group Co.,Ltd) more than with combination type of filler. The effluent NOˉx-N concentrations was less than.15mg/L in biofilm process with SJ-1 type of filler. A practical mathematical model with the A/O process was developed for predicting removal effects, which can provide a theoretical guidance for wastewater treatment and engineering design.

Control of an ideal activated sludge process in wastewater treatment via an ODE–PDE model

The activated sludge process (ASP), found in most wastewater treatment plants, consists basically of a biological reactor followed by a sedimentation tank, which has one inlet and two outlets. The purpose of the ASP is to reduce organic material and dissolved nutrients (substrate) in the incoming wastewater by means of activated sludge (microorganisms). The major part of the discharged flow through the bottom outlet of the sedimentation tank is recirculated to the reactor, so that the biomass is reused. Only two material components are considered; the soluble substrate and the particulate sludge. The biological reactions are modelled by two nonlinear ordinary differential equations and the continuous sedimentation process by two hyperbolic partial differential equations (PDEs), which have coefficients that are discontinuous functions in space due to the inlet and outlets. In contrast to previously published modelling-control aspects of the ASP, the theory for such PDEs is utilized. It is proved that the most desired steady-state solutions can be parameterized by a natural control variable; the ratio of the recirculating volumetric flow to the input flow. This knowledge is a key ingredient in a two-variable regulator, with which the effluent dissolved nutrients concentration and the concentration profile in the sedimentation tank are controlled. Theoretical results are supported by simulations.

Effect of potassium ferrate on disintegration of waste activated sludge (WAS)

The activated sludge process of wastewater treatment results in the generation of a considerable amount of excess activated sludge. Increased attention has been given to minimization of waste activated sludge recently. This paper investigated the effect of potassium ferrate oxidation pretreatment on the disintegration of the waste activated sludge at various dosages of potassium ferrate. The results show that potassium ferrate pretreatment disintegrated the sludge particle, resulting in the reduction of total solid content by 31%. The solubility (SCOD/TCOD) of the sludge increased with the increase of potassium ferrate dosage. Under 0.81g/g SS dosage of potassium ferrate, SCOD/TCOD reached 0.32. Total nitrogen (TN) and total phosphorous (TP) concentrations in the solution all increased significantly after potassium ferrate pretreatment. The sludge particles reduced from 116 to 87μm. The settleability of the sludge (SVI) was enhanced by 17%, which was due to the re-flocculation by the by-product, Fe(III), during potassium ferrate oxidation and the decrease of the viscosity. From the result of the present investigations, it can be concluded that potassium ferrate oxidation is a feasible method for disintegration of excess activated sludge.

Effects of dissolved oxygen on biological nitrogen removal in integrated fixed film activated sludge (IFAS) wastewater treatment process

The objective of this research was to determine the effects of dissolved oxygen on the biological nitrogen removal in the Integrated Fixed Film Activated Sludge (IFAS) and Modified Ludzack-Ettinger (MLE) systems. The carbonaceous and nitrogen removals were investigated at the COD/Nitrogen (C/N) ratios of 4, 6, and 10, and the dissolved oxygen (DO) concentrations of 2, 4, and 6 mg/L. The experimental results indicate that the C/N ratios of 4, 6, and 10 and the DO concentrations of 2, 4, and 6 affected insignificantly on the chemical oxygen demand (COD) removal, but significantly on the nitrogen removal as the consequences of different nitrification and denitrifcation rates in both systems. The COD removal was nearly completed throughout this study because glucose was used as a primary carbon source in the wastewater and both systems were operated at high SRT relative to the minimum SRT requirement for COD removal. The experimental conditions used in this study apparently led to nitrite accumulation in both IFAS and MLE systems. It is suggested that there is no benefit of installing media in the IFAS system at the C/N ratio of 10 because the system was underloaded with the nitrogen. The lower DO concentration, the greater denitrification in the anoxic zone was achieved because nitrite nitrogen was used as an electron acceptor. At the C/N ratios of 4 and 6, the IFAS system was higher in capacity for nitrification as a result of attached biomass on the support media in the aerobic zone. The DO concentration of 6 mg/L is required to maximize the nitrification rates in the systems under these experimental conditions resulting in greater oxidized nitrogen for denitrification in the anoxic zones. The denitrification in the aerobic zone of the IFAS system is not evaluated due to unavailability of nitrite information. The optimal DO concentrations for biological nitrogen removal in the IFAS system at the C/N ratios of 4, 6, and 10 in this study were 6, 6, and 2 mg/L, respectively.

Mesophilic anaerobic digestion of waste activated sludge: influence of the solid retention time in the wastewater treatment process

The performance of mesophilic anaerobic digesters of four large Italian wastewater treatment plants without primary sedimentation were studied. Only the waste activated sludge is stabilised by means of the mesophilic (35–37 °C) anaerobic digestion process. The anaerobic digesters generally worked with a hydraulic retention time in a range of 20–40 days and an organic loading rate of some 1 kg VS/ m reactor 3 day. The solids content of the sludge fed to the digesters was in the range 2.6–3.9% and the gas produced per kilogram of volatile solids added was in the range 0.07–0.18 m 3/kg VS fed. The specific gas production per kilogram of volatile solids destroyed was in the range 0.5–0.9 m 3/kg VS destroyed and the reduction of the volatile solids concentration was in the range 13–27% (average 18%). These figures are particularly significant when designing anaerobic digesters for the treatment of waste activated sludge as single substrate. Moreover, it was observed that the higher the applied solid retention time in the activated sludge process for wastewater treatment, the lower the gas production. In particular, the specific gas production decreased from 0.18 to 0.07 m 3/kg VS fed when increasing the solid retention time in the wastewater treatment line from 8 to 35 days. Finally, a mathematical model for the prediction of biogas production on the solid retention time applied in the wastewater treatment process was developed.

Behavior of Suction Pressure and Membrane Filtration Resistance in Submerged Membrane Activated Sludge Process of Wastewater Treatment

Behavior of Suction Pressure and Membrane Filtration Resistance in Submerged Membrane Activated Sludge Process of Wastewater Treatment

Applications of the deep-shaft activated sludge process in wastewater treatment

The deep-shaft activated sludge process is a unique modification of the activated sludge system. The main objective of this system is to increase the amount of dissolved oxygen available for biological activity. This can be achieved by increasing the rate of oxygen transfer from the gas phase to the liquid phase. The deep-shaft configuration increases the partial pressure of oxygen, thereby causing a high saturation concentration in the reactor. In the deep-shaft process, owing to high oxygen availability, a higher organic loading can be accommodated with a comparatively low air supply. This reduces the energy and area requirements and lowers the overall cost of treatment. This technology has been successfully applied for the high-rate treatment of strongly polluted wastewater, as well as for the treatment of wastewater containing toxic or slowly biodegradable pollutants. This paper presents different applications of the deep-shaft activated sludge process, along with their relative performances.

Steady state analysis of the coupling aerator and secondary settling tank in activated sludge process

The steady state analysis of coupling the function of aerator and secondary settling tank in activated sludge process for wastewater treatment is carried out to obtain appropriate responses of output variables and to decide optimum operating parameters. To consider the effect of the secondary settling tank, limit flux theory is applied and the aerator is assumed to be a continuous flow stirred tank reactor. By using sludge recycle ratio and sludge waste ratio as the operating parameters, the responses of the output variables—biomass concentration in aerator, dissolved pollutant and solid concentration in effluent—are represented as response surfaces and isoresponse curves. Acceptable operating zone can be obtained from the curves and optimum parameters can be determined. Coupling the function of aerator and secondary settling tank is important to consider the appropriate control of an activated sludge process.

Experimental procedures characterizing transformations of wastewater organic matter in the Emscher river, Germany

The Emscher river in the Ruhr district, Germany, is at present acting as a large wastewater collector receiving untreated and mechanically treated wastewater. Before the Emscher flows into the river Rhine, treatment takes place in a biological wastewater treatment plant. The transformations of the organic matter in the Emscher affect the river catchment, the subsequent treatment and the river quality. This paper focuses on evaluation of methods for quantification of the microbial transformations of wastewater in the Emscher with emphasis on characterization of wastewater quality changes in terms of biodegradability of organic matter and viable biomass. The characterization is based on methods taken from the activated sludge process in wastewater treatment. Methods were evaluated on the basis of laboratory investigations of water samples from the Emscher. Incubation in batch reactors under aerobic, anoxic and anaerobic conditions were made and a case study was performed. The methods described will be used in an intensive study of wastewater transformations in the Emscher river. This study will be a basis for future investigations of wastewater quality changes in the Emscher.

An adaptive algorithm for external carbon addition to an alternating activated sludge process for nutrient removal from waste water

The paper deals with a means to improve nitrogen removal in an alternating activated sludge waste water treatment process by automatic control. A control strategy is formulated involving the on demand increase in denitrification rate by the addition of a readily metabolizable carbon source to the point in the process where denitrification occurs. An algorithm is presented which automatically adjusts the carbon addition rate to match current process conditions. Two models are employed: a prediction model based on mass balances to determine the needed denitrification rate; and an experimentally determined, empirical relational model describing the denitrification rate as a function of carbon addition rate. An adaptive technique is employed to continually update estimates for the slowly changing parameters of the relational model. The algorithm is illustrated with a simulated example and two pilot plant demonstrations.