Activated Sludge Wastewater Treatment Research Articles

Enhancement of activated sludge wastewater treatment with hydraulic selection

The slow settling rate of activated sludge (AS) in secondary clarifiers and batch reactors results in increased hydraulic retention time, AS with a higher water content pumped to the digesters, and higher suspended solids concentration in the clarified supernatant. Settling rates of AS can be improved through the removal of poor settling floc with a diameter less than 100 µm. Currently, the main technology used for the enhancement of AS settling is aerobic granular sludge reactors—very few of these reactors have been adopted into the United States market due to their cost and difficulty to integrate the technology into current wastewater treatment infrastructure. The objective of this study was to develop a technology that could enhance the settling properties of AS while maintaining nitrification/denitrification and that could easily be integrated into current wastewater treatment infrastructure. We have developed a hydraulic selection process that removes poor settling floc directly from the secondary clarifiers or batch reactors. The hydraulic selection process is a vacuum system that is suspended in the AS, the system then develops a unique pressure difference based on poor settling sludge density, floc diameter, and terminal settling velocity. The selection process captures and removes poor settling floc allowing the remaining floc to grow and increase the settling rate of AS. The hydraulic selection process was tested for 120 days in a 120 L batch reactor. Results from the experiment showed that the hydraulic selection process was successful, in 63 days the settling velocity increased from 0.2 to 20 m/hr, mean floc diameter increased from 62 to 430 µm, and sludge volume index decreased from 280 to 45 mL/g. Nitrification was maintained for nearly the entire duration of the experiments with the exception of a few days due to drastic changes in influent wastewater concentrations. Denitrification was only maintained for a limited period during the experiment due to an unfavorable carbon to nitrogen ratio.

Near Future Energy Self-sufficient Wastewater Treatment Schemes

Achieving energy self-sufficiency is critical for wastewater treatment plants (WWTPs) to comply with rapidly changing environmental regulatory standards in a sustainable manner. Currently, a small percentage of WWTPs around the world produce energy for beneficial use and only a handful of these plants are energy self-sufficient. We propose three energy-positive wastewater treatment schemes and use quantitative analysis to assess their potentials for carbon and nitrogen removal and energy generation from municipal wastewater. This research identifies potential challenges in the selection and implementation of energy recovery process configurations and proposes practically feasible energy-positive wastewater treatment process configurations. Energy self-sufficiency can be achieved through biogas production while simultaneously minimizing the energy consumption for treatment. Furthermore, energy recovery can be enhanced in the near future (i) by increasing the COD capture in primary treatment to enhance energy production; (ii) by replacing activated sludge process with other less energy-intensive biological treatment technologies; and (iii) by increasing energy production from digesting supplementary feedstock in anaerobic codigestion (AD) schemes. This paper presents a quantitative analysis of three process schemes that progressively build upon the concept of transforming the conventional activated sludge wastewater treatment plants (CAS-WWTP) into energy self-sufficient wastewater treatment facilities. These schemes also include a hypothetical but practically feasible WWTP configuration, which represents an alternative energy self-sufficient wastewater process scheme for future designs.

Energy Consumption and Internal Distribution in Activated Sludge Wastewater Treatment Plants of Greece

The high-energy consumption of wastewater treatment plants (WWTPs) is a crucial issue for municipalities worldwide. Most WWTPs in Greece operate as extended aeration plants, which results in high operational costs due to high energy needs. The present study investigated the energy requirements of 17 activated sludge WWTPs in Greece, serving between 1100–56,000 inhabitants (population equivalent, PE), with average daily incoming flowrates between 300–27,300 m3/d. The daily wastewater production per inhabitant was found to lie between 0.052 m3/PE·d and 0.426 m3/PE·d, with average volume of 0.217 ± 0.114 m3/PE·d. The electric energy consumption per volume unit (EQ (kWh/m3)) was between 0.128–2.280 kWh/m3 (average 0.903 ± 0.509 kWh/m3) following a near logarithmic descending correlation with the average incoming flowrate (Qav) (EQ = −0.294lnQav + 3.1891; R2 = 0.5337). A similar relationship was found between the daily electric energy requirements for wastewater treatment per inhabitant (EPE (kWh/PE·d)) as a function of PE, which varied from 0.041–0.407 kWh/PE·d (average 0.167 ± 0.101 kWh/PE·d)) (EPE = −0.073ln(PE) + 0.8425; R2 = 0.6989). Similarly, the daily energy cost per inhabitant (E€/PE (€/PE·d)) as a function of PE and the electric energy cost per wastewater volume unit (E€/V (€/m3)) as a function of average daily flow (Qav) were found to follow near logarithmic trends (E€/PE = −0.013ln(PE) + 0.1473; R2 = 0.6388, and E€/V = −0.052lnQav + 0.5151; R2 = 0.6359), respectively), with E€/PE varying between 0.005–0.073 €/PE·d (average 0.024 ± 0.019 €/PE·d) and E€/V between 0.012–0.291 €/m3 (average 0.111 ± 0.077 €/m3). Finally, it was calculated that, in an average WWTP, the aeration process is the main energy sink, consuming about 67.2% of the total electric energy supply to the plant. The large variation of energy requirements per inlet volume unit and per inhabitant served, indicate that there is large ground for improving the performance of the WWTPs, with respect to energy consumption.

Key performance indicators (KPIs) comparison of food chain reactor and conventional oxidation ditch technology in industrial waste treatment

The oxidation process as the activated sludge (AS) system has been implemented widely in urban and industrial wastewater treatment. Oxidation ditch can be categorized as an advanced aeration activated sludge. I ntegrated Fix-Film Activated Sludge ( IFAS ) process has been already developed for decades that was a reasonable approach for technology to upgrade the activated sludge wastewater treatment plant (WWTP). IFAS processes are a combination of biofilm reactors and activated sludge processes, biofilm is introducing and retaining as the carrier media for microorganism growth. Both IFAS and AS processes can achieve similar percent removal of COD and ammonia. Current WWTP’s development was food chain reactor ( FCR ) which mainly IFAS process of engineered media that combining with natural plants with the plant roots submerging into the reactors. The references review and secondary data of the application in Jababeka’s WWTP-2 for both AS and FCR system showed that FCR is needless parameters to be controlled. In both AS and FCR have KPIs of flow rate (m 3 /day), F/M ratio, energy consumption (kWh/m 3 wastewater), Oxygen supply (kgO 2 / m 3 wastewater in each reactor, % removal of COD, BOD, TSS, NH 3 , TKN, NO 2 , and heavy metals, and pH, Dissolved Oxygen, microorganism performance in the reactor. Different from AS, the FCR system is not required to control the parameters of sludge retention time ( SRT ) , recirculated activated sludge ( RAS ) , sludge volume index ( SVI ), and mixed liquor suspended solids ( MLSS ) of activated sludge. Normal 0 false false false IN X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif"; mso-ansi-language:IN; mso-fareast-language:IN;} table.MsoTableGrid {mso-style-name:"Table Grid"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-priority:59; mso-style-unhide:no; border:solid windowtext 1.0pt; mso-border-alt:solid windowtext .5pt; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-border-insideh:.5pt solid windowtext; mso-border-insidev:.5pt solid windowtext; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif"; mso-ansi-language:IN; mso-fareast-language:IN;}

Environmental fate of Bacteroidetes, with particular emphasis on Bacteroides fragilis group bacteria and their specific antibiotic resistance genes, in activated sludge wastewater treatment plants

The aim of this study was to determine the effect of the activated sludge process on the abundance of anaerobic bacteria of the phylum Bacteroidetes, with special emphasis on Bacteroides fragilis group (BFG) bacteria, in twelve full-scale wastewater treatment plants. The composition of bacterial phyla and classes in wastewater samples were analyzed by next-generation sequencing. The presence of specific to BFG bacteria genes and the abundance of ARGs and genes encoding class 1 integrase in wastewater samples were determined by qPCR. Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were dominant bacterial phyla in wastewater samples. Next-generation sequencing revealed similar proportions of Bacteroidia (<1.0-8.2 % of all bacteria) in wastewater influents and effluents, which suggest that these microorganisms are not completely eliminated in the activated sludge process. The average copy numbers of specific to BFG bacteria gene, were 106, and 104 copies in 1 mL of wastewater influents and effluents, respectively. The results revealed a correlation between the abundance of BFG bacteria and BFG-specific genes encoding resistance to antibiotics. The observed changes in the prevalence of BFG-specific genes and ARGs in untreated and treated wastewater indicate that the activated sludge process decreases the number of gene copies in the effluent evacuated to the environment.

Heavy Metal Removal Investigation in Conventional Activated Sludge Systems

The combination of industrial and domestic wastewater in municipal WWTPs (waste water treatment plants) may be economically profitable, but it increases the difficulty of treatment, and also has some detrimental effects on the biomass and causes a low-quality final effluent. The present study evaluates the treatment process both in the presence and absence of heavy metals using ASM3 (activated sludge model no.3) so as to improve the model by means of incorporating other novel inhibitory kinetic and settler models. The results reveal that the presence of heavy metal, a case study for copper and cadmium at a concentration of 0.7 mgL−1 in a biological treatment system has a negative effect on heterotrophic bacteria concentration by 25.00 %, and 8.76 % respectively. Meanwhile, there are no important changes in COD (chemical oxygen demand), SS (total suspended solids) and TN (total nitrogen) in the final effluent in the conventional system. However, all these parameters are acceptable and consistent with EU Commission Directives. The results indicate that ASM3 can predict and provide an opportunity of the operation for an activated sludge wastewater treatment plant that receives the effluent from an industrial plant.

Energy saving for air supply in a real WWTP: application of a fuzzy logic controller.

An unconventional cascade control system, for the regulation of air supply in activated sludge wastewater treatment plants (WWTPs), was tested. The dissolved oxygen (DO) set point in the aeration tank was dynamically calculated based on effluent ammonia concentration, following a fuzzy logic based approach. First, simulations were conducted, according to the BSM2 protocol, for a general comparison with more conventional control strategies. It turned out that the effluent quality could be improved by 7-8%, based on the EQI parameter. Moreover, the aeration energy requirement could be reduced up to 13%. Subsequently, the system was installed in a full-scale WWTP. While stably complying with the ammonia effluent standard (10 mg/L), excess air supply was prevented, and a reduction of the specific power consumption (kWh/kgCODremoved) of 40-50% was recorded with respect to the previously installed PID controller (fixed DO set point).

Characterising and control of ammonia emission in microbial fuel cells

The serious ammonia (NH3) emission of air-cathode microbial fuel cells (MFCs) was reported but how to control and mitigate the emission hasn’t been well studied. Considering the importance of the issue for the application of MFCs in wastewater treatment, this study focused on understanding the NH3 emission process in MFCs and investigating mitigation approaches. The study found that when feeding with dairy wastewater the typical flat-cathode MFCs can emit NH3 of more than 0.82 mg-N/L. The NH3 emission reduced with the grown of cathode biofilm and the decrease of ammonium concentration in the influent. Combined experimental and theoretical results showed that the current density rather than the total current was the determined factor for ammonia emission. The novel Cu-blended 3D cathode developed in this study significantly decreased the NH3 emission to 0.037 mg-N/L (or 0.068% of the total removed ammonium), which was 6.3% of that in the activated sludge wastewater treatment plants (WWTP). In addition, the good power performance and high pollutants removal (14.4 W/m3, 88.1%-COD and 92.8%-TN removal) were also obtained by the Cu-blended 3D cathodes. This study unveiled the ammonia emission process and proposed effective mitigation methods, which will promote the practical application of MFCs for ammonium-rich wastewater treatment.

Enhancing treated wastewater effluent characteristics using hybrid biofilm/activated sludge process - a case study.

This paper documents the results of 12 months of monitoring of an upgraded hybrid moving bed biofilm reactor-conventional activated sludge wastewater treatment plant (MBBR-CAS WWTP). It also targets the assessment of the increment of the hydraulic load on existing treatment units with a zero construction and land cost. The influent flow to the plant was increased from 21,000 m3 d-1 to 30,000 m3 d-1, 40% of the existing CAS reactor volume was used for the MBBR zone with a carrier fill fraction of 47.62% and with Headworks Bio ActiveCell™ 515 used as media; no modifications were made for the primary and secondary tanks. The hybrid reactor showed high removal efficiencies for biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS), with average effluent values recording 33.00 ± 8.87 mg L-1, 52.90 ± 9.65 mg L-1 and 29.50 ± 6.64 mg L-1 respectively. Nutrient removals in the hybrid modified biological reactor were moderate compared with carbon removal despite the high C/N ratio of 12.33. Findings in this study favor the application of MBBR in the upgrading of existing CAS plants with the plant BOD5 removal efficiency recording an increase of about 5% compared with the plant before upgrade and effluent values well within the legal requirements.

Comparative fate of CrAssphage with culturable and molecular fecal pollution indicators during activated sludge wastewater treatment

Wastewater treatment plants are typically monitored using fecal indicator bacteria to ensure adequate microbial water quality of the treated effluent. Fecal indicator bacteria exhibit poor correlation with virus fate in the environment, including during wastewater treatment. Viral-based microbial source tracking methods have the potential to overcome this limitation. The recently discovered human gut bacteriophage crAssphage is a promising viral human fecal indicator. In this current study, primary influent, primary effluent, secondary effluent, and final effluent of a conventional activated sludge wastewater treatment plant were analyzed for a suite of fecal indicators to evaluate the suitability of crAssphage as a wastewater process indicator for virus removal. CrAssphage was the most abundant fecal indicator measured through the wastewater treatment process. Culturable and molecular bacterial fecal pollution indicators showed higher removal than viral fecal pollution indicators, including crAssphage, confirming the necessity of a viral-specific fecal monitoring target. CrAssphage was strongly correlated with adenovirus and polyomavirus molecular indicators through the wastewater treatment process. Literature comparison demonstrated site-specific removal of molecular fecal indicators during wastewater treatment highlighting the need for local performance validation. The high abundance of crAssphage and correlation with pathogenic viruses suggests the potential suitability of crAssphage as a viral fecal pollution process indicator during wastewater treatment.

Comparative life cycle assessment of municipal wastewater treatment systems: lagoon and activated sludge

Providing health conditions, prevention of water pollution and wastewater reuse are needed to select the best wastewater treatment process before designing and implementing, according to regional climatic conditions. the aim of the present study was to evaluate the lagoon and activated sludge wastewater treatment systems using life cycle assessment and ISO14040 standards within four steps. Required data in the study systems were matter and energy inputs, including NH3-N, TP, TN, CL, O2 and electricity, as well as pollutant outputs involving BOD5, COD, SS, NH3-N, TP, TN, CL, CO2, and CH4. The data were obtained from treatment systems of Ardabil (aerated lagoon) and Tabriz (activated sludge), Iran. Some of the data were obtained by calculation and the eco-invent database was used to complete the information required. Data were analyzed by Simapro 8.0.1 software. The results of the study demonstrated that the lagoon system in comparison with the other systems had 100% negative impacts in every effect classes, while the activated sludge system on global warming (6.39%) and photochemical oxidation (7.14%) had the least impact. Therefore, the lagoon system was recognized as the environmentally-harmful system, while the activated sludge as the best wastewater treatment system.

Resource recovery assessment at a pulp mill wastewater treatment plant in Uruguay

Using a mathematical model, a resource recovery assessment was carried out at a pulp mill activated sludge wastewater treatment plant (WWTP) located in Uruguay. Through the evaluation of different scenarios, the potential production of methane from secondary sludge, with its inherent energy savings, and the recovery of phosphorus (P) as struvite were estimated. Considering the current WWTP configuration with a sludge retention time (SRT) of 32 days, and according to the model, which is a simplification of reality, the assessment indicates that the implementation of an anaerobic digester (AD) to treat the excess sludge can lead to a methane production of approximately 1736 m3 CH4 d−1, being a promising alternative to increase the WWTP treatment performance. Furthermore, the model predictions suggest that by shortening the SRT from 32 to 5 days, the methane production could increase by up to 5568 m3 CH4 d−1. If the methane produced is used to generate electrical energy to operate the WWTP, energy savings of about 88% can be achieved. Regarding the potential recovery of P as struvite, the addition of a struvite reactor could be an efficient option to recover approximately 1611 mg L−1 of struvite (corresponding to a load of about 433 kg d−1). By optimizing the process performance, these findings highlight the potential recovery of resources in pulp mill WWTP, while complying with stringent effluent discharge standards. In addition, further research activities such as pilot-test or detailed laboratory studies may be needed to validate the previous recommendations for industrial scale application.

Assessment of Full-Scale N2O Emission Characteristics and Testing of Control Concepts in an Activated Sludge Wastewater Treatment Plant with Alternating Aerobic and Anoxic Phases.

This work aims to obtain full-scale N2O emission characteristics translatable into viable N2O control strategies and conduct full-scale testing of the proposed N2O control concepts. Data of a long-term monitoring campaign was first used to quantify full-scale N2O emission and probe into the seasonal pattern. Then trends between N2O production/emission and process variables/conditions during typical operating cycles were revealed to explore the dynamic N2O emission behavior. A multivariate statistical analysis was performed to find the dependency of N2O emission on relevant process variables. The results show for the first time that relatively low/high N2O emission took place in seasons with a decreasing/increasing trend of water temperature, respectively. Aerobic phase contributed to N2O production/emission probably mainly through the hydroxylamine pathway. Comparatively, heterotrophic bacteria had a dual role in the anoxic phase and could be responsible for both net N2O production and consumption. Incomplete denitrification might contribute mainly to the N2O production/emission in the anoxic phase and the accumulation of N2O to be significantly emitted in the following cycle due to the competition between different denitrification steps for electron donors. Therefore, properly extending the length of anoxic phase could serve as a potential control means to regulate N2O accumulation in the anoxic phase. The full-scale testing not only verified the efficacy of reduced dissolved oxygen set-point in reducing N2O emission by 60%, but also confirmed the proposed concepts of control over the aerobic and anoxic phases collectively.

The Phylogeny, Biodiversity, and Ecology of the Chloroflexi in Activated Sludge.

It is now clear that several of the filamentous bacteria in activated sludge wastewater treatment plants globally, are members of the phylum Chloroflexi. They appear to be more commonly found in treatment plants designed to remove nitrogen (N) and phosphorus (P), most of which operate at long sludge ages and expose the biomass to anaerobic conditions. The Chloroflexi seem to play an important beneficial role in providing the filamentous scaffolding around which flocs are formed, to feed on the debris from lysed bacterial cells, to ferment carbohydrates and to degrade other complex polymeric organic compounds to low molecular weight substrates to support their growth and that of other bacterial populations. A few commonly extend beyond the floc surface, while others can align in bundles, which may facilitate interfloc bridging and hence generate a bulking sludge. Although several recent papers have examined the phylogeny and in situ physiology of Chloroflexi in activated sludge plants in Denmark, this review takes a wider look at what we now know about these filaments, especially their global distribution in activated sludge plants, and what their functional roles there might be. It also attempts to outline why such information might provide us with clues as to how their population levels may be manipulated, and the main research questions that need addressing to achieve these outcomes.

Reconsideration and upgrading of sampling and analysis methods for avoiding measurement-related design and operation failures in wastewater treatment

Success of design and high operational efficiency may basically stand or fall on the quality of measured (or estimated) input data. Even small mistakes committed in the initial steps of sampling and analysis may become large once scaled up in the design process or during full-scale operation. The paper provides several experiment-based practical recommendations and easily implemented, powerful methods for appropriate sampling and analysis practice in wastewater treatment. Representative wastewater characterization is crucial for satisfactory design and cost-effective operation. The paper highlights hidden problems and challenges of sampling and analysis in activated sludge wastewater treatment which may strongly affect the quality of input data, and thus basically determine the modelling outputs. Full-scale results proved that wastewater quality may change significantly in the sampling tubing and vessels; during the sampling process even nitrification can happen. Regarding sludge settling measurements, effects of dilution, temperature, floc structure, nitrate and dissolved oxygen concentrations as well as current biochemical condition of the sludge sample have been studied and important recommendations provided. A combined comparative method including SVI and DSVI measurements has been elaborated for indication and early warning alert of undesired floc structure transformations. Influent BOD5 concentration is a key factor for describing biodegradability and denitrification capacity of wastewater to be treated. Results of the two most commonly used BOD testing methods were compared for preclarified wastewater. An electrochemical measurement technique provided significantly lower BOD5 concentrations compared to manometric analysis results with a difference of 23% and 15% on average for unfiltered and filtered samples, respectively. Effects of BOD-based fractionation deviations on predictable denitrification efficiency were studied at different inlet C/N ratios by simulating existing full-scale wastewater treatment plants resulting in remarkable differences in effluent nitrate concentrations. Based on the results, application of the manometric BOD measurement method proved to be preferable.

Time Series Genome-Centric Analysis Unveils Bacterial Response to Operational Disturbance in Activated Sludge.

Understanding ecosystem response to disturbances and identifying the most critical traits for the maintenance of ecosystem functioning are important goals for microbial community ecology. In this study, we used 16S rRNA amplicon sequencing and metagenomics to investigate the assembly of bacterial populations in a full-scale municipal activated sludge wastewater treatment plant over a period of 3 years, including a 9-month period of disturbance characterized by short-term plant shutdowns. Following the reconstruction of 173 metagenome-assembled genomes, we assessed the functional potential, the number of rRNA gene operons, and the in situ growth rate of microorganisms present throughout the time series. Operational disturbances caused a significant decrease in bacteria with a single copy of the rRNA (rrn) operon. Despite moderate differences in resource availability, replication rates were distributed uniformly throughout time, with no differences between disturbed and stable periods. We suggest that the length of the growth lag phase, rather than the growth rate, is the primary driver of selection under disturbed conditions. Thus, the system could maintain its function in the face of disturbance by recruiting bacteria with the capacity to rapidly resume growth under unsteady operating conditions.IMPORTANCE Disturbance is a key determinant of community assembly and dynamics in natural and engineered ecosystems. Microbiome response to disturbance is thought to be influenced by bacterial growth traits and life history strategies. In this time series observational study, the response to disturbance of microbial communities in a full-scale activated sludge wastewater treatment plant was assessed by computing specific cellular traits of genomes retrieved from metagenomes. It was found that the genomes observed in disturbed periods have more copies of the rRNA operon than genomes observed in stable periods, whereas the in situ mean relative growth rates of bacteria present during stable and disturbed periods were indistinguishable. From these intriguing observations, we infer that the length of the lag phase might be a growth trait that affects the microbial response to disturbance. Further exploration of this hypothesis could contribute to better understanding of the adaptive response of microbiomes to unsteady environmental conditions.

Aeration system to be used in wastewater treatment

The main purpose of the authors is to develop an improved aeration system to be used in wastewater treatment that will reduce the energy consumption by 20% for conventional activated sludge wastewater treatment plants (WWTPs) and by 40% for Moving Bed Biofilm Reactor (MBBR) WWTPs. A new type of aeration system based on fine-bubble diffusers with high endurance and reliability made from corrosion resistant metals is developed. The paper presents the innovative aeration systems with holes smaller than Ø 1 mm. An ultrasound system is used to clean the diffusers for clogging prevention. Ultrasound systems are used in WWTPs, but in the treatment process and not as an additional solution for anticlogging.

Bubble generation by micro-orifices with application on activated sludge wastewater treatment

We studied the initial gas dispersion performance of diffuser concepts based on micro-orifices and needles with very fine orifice diameters in the range from 37 μm to 225 μm, as such diffusers are currently in discussion for energy-efficient wastewater treatment plants. To evaluate the performance of these micro-orifices, we compared them with industrial rubber membrane diffusers with respect to Sauter mean bubble diameter, pressure drop, frequency of bubble formation, oxygen transfer rate, and power demand for air compression. Our study revealed that, in comparison with current state of the art of rubber membrane diffusers, bubbles generated from the micro-orifices transfer up to 22% more oxygen content into the continuous phase at up to 51% less power demand. Moreover, these micro-orifices are able to produce bubble sizes in the same range as the needle diffusers at 60% less pressure drop and 60% higher bubble generation frequency.

A nonlinear observer for activated sludge wastewater treatment process: Invariant observer

AbstractAn activated sludge wastewater treatment process model is concerned in this paper. In order to estimate the variables that cannot be measured online, an invariant observer for activated sludge wastewater treatment process is presented. The invariant observer can measure biomass concentration, substrate concentration and dissolved oxygen concentration in high accuracy and rapidity. Meanwhile it can be structured by means of typical form, and its robust convergence property is verified by theoretical analysis and numerical simulations (MATLAB).

Decision tree for identification and prediction of filamentous bulking at full-scale activated sludge wastewater treatment plant

This study attempted to model sludge bulking in a full-scale wastewater treatment plant operated as a 3-stage Phoredox process. Principal component analysis and a regression tree model were employed to describe the correlations between influent wastewater characteristics and operational conditions (as inputs) and sludge volume index (SVI) as an output. A classification tree model was used to determine the environmental factors that affected the proliferation of filamentous microorganisms. Fluorescent in situ hybridisation analysis identified filamentous species of Microthrix parvicella, Thiothrix I & II, and Eikelboom Types 0041, 0092, and 021 N. It was found that SVI increased with an increment in sludge retention time, but it negatively correlated with soluble chemical oxygen demand (sCOD) and ammonium-nitrogen. The dominance of Microthrix parvicella was observed with a decline in temperature below 15.5 °C, causing an increase in SVI during the winter and spring seasons. The overgrowth of Thiothrix could be linked to the unbalanced ratio between readily biodegradable COD and nutrient species. The filament Type 0092 contributed to high SVI, and it prevailed with a decrease in food-to-microorganisms ratio below 0.08 1/d. Based on the satisfactory training, validation, and generalization procedures, the proposed models could be applied for the prediction of sludge bulking episodes.