Secondary Settling Tank Research Articles

Development of a novel LED-IoT photoreactor for enhanced removal of carbamazepine waste driven by solar energy

This study introduces an innovative LED-IoT photoreactor, representing a significant advancement in response to the demand for sustainable water purification. The integration of LED-IoT installations addresses the challenge of intermittent sunlight availability, employing LEDs with a spectrum mimicking natural sunlight. Passive Infra-Red (PIR) sensors and Internet of things (IoT) technology ensure consistent radiation intensity, with the LED deactivating in ample sunlight and activating in its absence. Utilizing a visible light-absorbing photocatalyst developed through sol-gel synthesis and mild-temperature calcination, this research demonstrates a remarkable carbamazepine removal efficiency exceeding 95% under LED-IoT system illumination, compared to less than 90% efficiency with sunlight alone, within a 6-h exposure period. Moreover, the designed photocatalytic system achieves over 60% mineralization of carbamazepine after 12 h. Notably, the photocatalyst demonstrated excellent stability with no performance loss during five further cycles. Furthermore, integration with renewable energy sources facilitated continuous operation beyond daylight hours, enhancing the system's applicability in real-world water treatment scenarios. A notable application of the LED-IoT system at an operating sewage treatment plant showed nearly 80% efficiency in carbamazepine removal from sewage in the secondary settling tank after 6 h of irradiation, coupled with nearly 40% mineralization efficiency. Additionally, physicochemical analyses such as XPS and STA-FTIR confirm that the carbamazepine photooxidation process does not affect the surface of the photocatalyst, showing no adsorption for degradation products.

Investigating a batch-flow photocatalytic LED system for diclofenac removal in wastewater treatment plants: Assessing the influence of reaction conditions on photocatalytic efficiency

This work introduces an innovative batch-flow photocatalytic LED system aimed at efficiently removing diclofenac from wastewater. The study highlights the novelty of fabricating TiO2-loaded carbon fiber photocatalysts through a hydrothermal process, exhibiting a blue shift in their absorption spectrum and enhancing their photon absorption capability. A crucial design feature is the spectral matching between the LED light source and the photocatalyst, which is critical for achieving high photodegradation efficiency. A significant innovation of our study is the testing of the system under real conditions at an operational sewage treatment plant. Here, the designed system demonstrated high efficacy in degrading diclofenac across various treatment stages, highlighting its robustness and adaptability to changing environmental conditions. The highest degradation efficiency was achieved with sewage from the secondary settling tank, where nearly 90 % efficiency was observed after 6 h of irradiation. Moreover, the use of renewable energy sources emphasizes the system's sustainability, presenting a greener alternative to traditional wastewater treatment methods. The investigation not only showcases the system's effectiveness in diclofenac degradation but also its adaptability and stability under real-world conditions, marking a significant advancement in sustainable wastewater treatment technologies.

On-site monitoring of dissolved Sb species in natural waters by an automatic system using flow injection coupled with hydride generation atomic fluorescence spectrometer

Antimony (Sb) is a toxic and potentially carcinogenic element in the environment. The toxicity of Sb(III) is ten times that of Sb(V). Therefore, on-site monitoring technique for dissolved Sb species is crucial for the study of Sb environmental processes. In this study, an automated, portable, and cost-effective system was developed for field simultaneous analysis of Sb(III) and Sb(III + V) in natural waters. The system comprised a portable atomic fluorescence spectrometer equipped with a built-in electrochemical H2 generator to reduce the consumption of acid/borohydride solution and make the atomizer more stable for on-site analysis. Flow injection technique was also used to achieve on-line pretreatment of water samples, including filtration, acidification, pre-reduction, and hydride generation procedures. Under the optimal conditions, the limits of detection (3σ, n = 11) of the developed method were 0.015 μg/L and the linear ranges were 0.05–5.0 μg/L for both Sb(III) and Sb(III + V). The relative standard deviations (n = 11) of the spiked samples of Sb(V) were 3.2% (0.05 μg/L), 3.3% (0.2 μg/L), and 1.7% (0.5 μg/L), respectively. The spiked recoveries of lake water, treated wastewater, and seawater ranged from 97.0% to 108.5%. The novel system of flow injection coupled with hydride generation atomic fluorescence spectrometer (FI-HG-AFS) was applied to carry out an 18-h fixed-point monitoring at a secondary settling tank of a wastewater treatment facility in Xiamen University, and a 6-h real-time underway analysis in the surface seawater of Dongshan Bay, China, proving that the system was capable of long-term monitoring in the field.

Removal efficiency of antibiotic residues, antibiotic resistant bacteria, and genes across parallel secondary settling tank and membrane bioreactor treatment trains in a water reclamation plant

Antimicrobial resistance is recognized as a potent threat to human health. Wastewater treatment facilities are viewed as hotspots for the spread of antimicrobial resistance. This study provides comprehensive data on the occurrences of 3 different antibiotic resistant opportunistic pathogens (with resistance to up to 5 antibiotics), 13 antibiotic resistant genes and intI1, and 22 different antimicrobial residues in a large water reclamation plant (176 million gallons per day) that runs a conventional Modified Ludzack-Ettinger (MLE) reactor followed by a secondary settling tank (SST) and membrane bioreactor (MBR) in parallel.All the antibiotic resistant bacteria and most of the antibiotic resistance genes were present in the raw influent, ranging from 2.5 × 102–3.7 × 106 CFU/mL and 1.2× 10−1–6.5 × 1010 GCN/mL, respectively. MBR outperformed the SST system in terms of ARB removal as the ARB targets were largely undetected in MBR effluent, with log removals ranging from 2.7 to 6.8, while SST only had log removals ranging from 0.27 to 4.6. Most of the ARG concentrations were found to have significantly higher in SST effluent than MBR permeate, and MBR had significantly higher removal efficiency for most targets (p < 0.05) except for sul1, sul2, blaOXA48, intI1 and 16S rRNA genes (p > 0.05). As for the antibiotic residues (AR), there was no significant removal from the start to the end of the treatment process, although MBR had higher removal efficiencies for azithromycin, chloramphenicol, erythromycin, erythromycin-H2O, lincomycin, sulfamethoxazole and triclosan, compared to the SST system. In conclusion, MBR outperformed SST in terms of ARB and ARGs removal. However low removal efficiencies of most AR targets were apparent.

STUDY OF URBAN WASTEWATER TREATMENT PROCESSES IN THE SYSTEM OF BIOLOGICAL TREATMENT FACILITIES “AERATION TANK-MIXER – SECONDARY SEDIMENTATION TANK”

The paper examines the features of the biological purification process in the “aeration tank-mixer – secondary settling tank” system. Factors influencing the course of processes were determined, and an experimental study of this process was carried out. After processing the results, models are proposed that describe the course of the activated sludge regeneration process and directly the process of biological wastewater treatment. The results of the calculation were analyzed, the mutual influence of individual factors on the course of the biological purification process was investigated and analyzed. The models obtained in the work allow, without conducting additional experiments, to study the process of regeneration of activated sludge depending on the concentration of sludge and its consumption, as well as to study the process of wastewater treatment taking into account its characteristics (costs, concentrations of pollutants), the dose of sludge coming from the regenerator, concentrations dissolved oxygen. It is advisable to use the proposed models for the analysis of the process of biological wastewater treatment in the system “aeration tank-mixer – secondary settling tank” and for quick response to changes occurring in the treatment process. This will prevent insufficiently treated wastewater from entering the reservoir and reduce its negative impact on the environment.

Antibiotic Resistance in Metal-Tolerant Microorganisms from Treatment Facilities.

The study examines the antibiotic resistance of metal-tolerant bacteria isolated from the wastewater treatment plant of a large city to six antibiotics belonging to the β-lactam antibiotics, aminoglycosides and amphenicols. Resistance of bacteria from sewage sludge multitolerant to heavy metals to 18 antibiotics of the β-lactam antibiotics, tetracyclines, aminoglycosides, diaminopyrimidines, amphenicols and ansamycins was studied also. Out of 10, the metal-tolerant microorganisms isolated from wastewater treatment facilities only the Klebsiella pneumonia strain (tolerant to 3 mM Cu) from the sludge of a secondary settling tank did not show resistance to the studied antibiotics at the concentrations considered. Resistance to the maximum amount of antibiotics was typical for strains Serratia fonticola SS0-1, isolated from fresh sewage sludge and resistant to 5 mmol Cu and 3 mmol Pb, or Stenotrophomonas maltophilia SS0-5, also isolated from fresh sludge and resistant to 3 mmol Zn and Cu. It is possible that bacterial resistance to antibiotics develops not only as a result of the use of antibiotics themselves, but also as a result of environmental pollution with heavy metals, and vice versa.

Microbial community structure and functional prediction in five full-scale industrial park wastewater treatment plants

The development of industrial parks has become an important global trend contributing significantly to economic and industrial growth. However, this growth comes at a cost, as the treatment of multisource industrial wastewater generated in these parks can be difficult owing to its complex composition. Microorganisms play a critical role in pollutant removal during industrial park wastewater treatment. Therefore, our study focused on the microbial communities in five full-scale industrial park wastewater treatment plants (WWTPs) with similar treatment processes and capacities. The results showed that denitrifying bacteria were dominant in almost every process section of all the plants, with heterotrophic denitrification being the main pathway. Moreover, autotrophic sulfur denitrification and methane oxidation denitrification may contribute to total nitrogen (TN) removal. In plants where the influent had low levels of COD and TN, dominant bacteria included oligotrophic microorganisms like Prosthecobacter (2.88 % ~ 10.02 %) and hgcI_clade (2.05 % ~ 9.49 %). Heavy metal metabolizing microorganisms, such as Norank_f__PHOS-HE36 (3.96 % ~ 5.36 %) and Sediminibacterium (1.86 % ~ 5.34 %), were prevalent in oxidation ditch and secondary settling tanks in certain plants. Functional Annotation of Prokaryotic Taxa (FAPROTAX) revealed that microbial communities in the regulation and hydrolysis tanks exhibited higher potential activity in the nitrogen (N) and sulfur (S) cycles than those in the oxidation ditch. Sulfate/sulfite reduction was common in most plants, whereas the potential occurrence of sulfide compounds and thiosulfate oxidation tended to be higher in plants with a relatively high sulfate concentration and low COD content in their influent. Our study provides a new understanding of the microbial community in full-scale industrial park WWTPs and highlights the critical role of microorganisms in the treatment of industrial wastewater.

Intensification of wastewater treatment of the paper and cardboard factory using physical and chemical methods

The results of research on physical and chemical methods for the preliminary treatment of wastewater of a cardboard and paper factory in Khmelnytskyi region are presented. At the cardboard and paper factory, wastewater is treated at a sewage treatment plant, which includes sand traps, primary radial sedimentation tanks, aeration tanks with activated sludge regenerators, secondary radial sedimentation tanks, and bioponds. The use of coagulation and chlorination methods before biological treatment in aeration tanks was proposed. Alumofloc 18% was used as a coagulant, PAA was used as a flocculant, and sodium hydroxide was used as an alkalizing reagent. The study was conducted on a mixture of industrial and domestic wastewater with COD and BOD5 – 3200 and 1575 mg/dm3, respectively, and on industrial wastewater with COD and BOD5 – 4480 and 1960 mg/dm3, respectively. The effects of reducing COD and BOD5 indicators in the first case after coagulation were 30 and 40%, after chlorination - 37.82 and 43.18%, respectively, in the second after coagulation - 28.58 and 47.25%, respectively. It was established that a significant proportion of organic substances according to the COD indicator is in a dissolved state - 60-70%. It has been proven that as a result of chlorination, the maximum reduction of "pure" COD is achieved, therefore, the possibility and expediency of chlorination of water after the secondary settling tank with increased doses should be considered in the wastewater treatment technology of the cardboard and paper factory. The effects of wastewater treatment of a cardboard and paper factory using coagulation and oxidation methods, obtained as a result of research, will allow to reduce the concentration of organic substances according to COD and BOD indicators before the biological treatment of wastewater in aeration tanks and will ensure an increase in the efficiency of biological treatment.

Improving secondary settling tanks performance by applying CFD models for design and operation

Abstract This study uses computational fluid dynamics (CFD) models for an improved performance of secondary settling tanks, taking as a case study the wastewater treatment plant (WWTP) of Souk-Ahras City, Northeastern Algeria. Unlike previous studies, which focused primarily on simulations of real-time clarifiers by independent measures, this study combines differentoperating criteria and geometric standards on clarifiers to estimate the ultimate capacity of secondary sedimentation tanks (SST). Numerical simulations were performed toassess the SST hydraulic performance under different conditions in order to (i) eliminate vortex zones; (ii) optimize the surface overflow rate (SOR) and predict sludge blanket height (SBH), and finally, (iii) estimate SST ultimate capacity. Based on the current configuration of the SST of Souk-Ahras WWTP, its hydraulic treatment capacity was found to be 49,000 m3/d. The results obtained, which were validated by field observations, showed that optimizing the different parameters yields a significantly improved SST performance. Furthermore, the tests consideredwere shown to be satisfactorily correlated with SOR. Validation using the receiver operating characteristic (ROC) curve analysis yielded anarea under curve (AUC) value of 90%, implying thereby a reasonably good performance. Indeed, optimization resulted in increased solidremoval efficiency and increased SOR to 1.4 m.h−1 (compared to 0.8 m.h−1 in literature) without overflow beyond the SBH.

Increasing of efficiency of fermentation process of organic substrates for intensification of methanogeneration

The prospects of increasing the efficiency of fermentation process of organic substrates to ensure the maximum yield of biogas and increase the economic efficiency of processing of organic sewage sludge are considered. Biogas, as an analogue of natural gas, is used in production of thermal and electrical energy, as transport motor fuel, as a raw material for chemical industry.&#x0D; An analysis of trends in intensification of methane fermentation processes was carried out. A promising way to increase productivity of methane generation process during processing of organic matter is to increase the energy saturation of an organic substrate and its preliminary treatment. One of the approaches aimed at intensifying methane generation is use of organic waste as an auxiliary substrate for fermentation of sewage sludge – a process known as co-fermentation.&#x0D; The sediments of primary and secondary settling tanks of the biological wastewater treatment complex were studied. According to results of tests, it was noted that ratio of carbon and nitrogen in the studied excess activated sludge is 4–5, in the mixture of primary and secondary sediment – 5–6, in sediment from sludge sites – 6–10, which is significantly less than desired ratio of 20:1, which limits the negative impact of increased nitrogen content in the organic substrate for methane fermentation. According to obtained data, it can be predicted that nitrogen-containing compounds present in sewage sludge will contribute to a microbiological process of formation of nitrogen-containing reduced products, which reduce output of methane during methanogenesis.&#x0D; The expediency of enriching the inoculated biocenosis with hydrolytic enzyme preparations or microorganisms with high hydrolytic activity is shown, given the fact that activated sludge has a lower hydrolytic activity than enzyme preparations isolated from the same sludge, as well as than some bacteria, and even more so microscopic fungi. This was caused by presence of inert organic and inorganic mass, dead microorganisms and those with low hydrolytic activity in the sludge biomass. It is also possible to increase speed of the first phase of sediment fermentation due to alkaline pretreatment of the substrate mixture.

Improving sludge settling performance of secondary settling tank and simultaneously adsorbing nitrate and phosphate with surfactant modified zeolite (SMZ) ballasted flocculation

Poor sludge settling characteristics limit the enhancement of treatment capacity of municipal wastewater treatment plants, and excessive nitrogen and phosphorus discharge will further aggravate water eutrophication, but the existing ballasting agents cannot promote sludge settling and adsorb nitrate and phosphate simultaneously. In this study, surfactant modified natural zeolite (SMZ) was used as a novel ballasting agent to improve settling performance of activated sludge and simultaneously adsorb nitrate and phosphate. The results of settling experiments showed that 75–150 µm size SMZ had the best effect in promoting sludge settling, and the zone settling velocity (ZSV) of sludge increased to 3.38 m/h at 1 g/L dosage, which reached 2.11 times of the original sludge. The results of microscopic observation, floc size determination, and density test demonstrated that finer particle size SMZ facilitated the formation of larger and denser flocs, thus promoting sludge settling, but excessively fine SMZ (45–75 µm) reduced the ability to promote sludge settling due to the lower density of the flocs formed. SMZ promoted sludge settling performance by attracting sludge to agglomerate through charge neutralization, forming larger and denser agglomerates. In addition, the SMZ removed 47.05% and 53.25% of nitrate and phosphate, respectively, while increasing the sludge settling velocity to more than twice that of the original sludge. This study expected to provide useful information for upgrading municipal wastewater treatment plants.

Arbitrary polynomial chaos expansion for uncertainty analysis of the one-dimensional hindered-compression continuous settling model

Secondary settling tank (SST) models play a significant role in the simulation of a wastewater treatment system. They can estimate effluent and underflow quality and thus help with the design, management, and optimization of wastewater treatment systems. SST modeling consists of an empirical settling velocity function where parameter uncertainty could raise. The performance of an SST model could suffer from parameter uncertainty, which makes parameter uncertainty assessment valuable for SST modeling. Monte Carlo simulation (MCS) is a classical technique for assessing uncertainty, but it requires parameter distribution information and is computationally expensive. To overcome these limitations, arbitrary polynomial chaos expansion (aPCE), a novel approach has been adopted for the first time in this study. The well-recognized Bürger-Diehl SST model is used and the uncertainties originating from five essential model parameters are assessed by the novel aPCE method with the MCS technique being used as a benchmark. Probabilistic estimations of the model output, i.e., sludge blanket height (SBH), are generated by both aPCE and MCS. The comparison results between aPCE and MCS suggest that the aPCE approach can be as effective as MCS in quantifying the uncertainties associated with SST model parameters, while significantly reducing approximately 90 % computational requirements. This study explicitly quantifies the uncertainties associated with SST model parameters in an efficient manner, which can provide robust support for the design, management, and optimization of wastewater treatment systems.

WAYS TO IMPROVE THE EFFICIENCY OF WASTEWATER TREATMENT OF A CARDBOARD AND PAPER MILL

The results of research on physical and chemical methods for the preliminary treatment of wastewater of a cardboard and paper factory in Khmelnytskyi region of Ukraine are presented. At the cardboard and paper factory, wastewater is treated at a sewage treatment plant, which includes sand traps, primary radial sedimentation tanks, aeration tanks with activated sludge regenerators, secondary radial sedimentation tanks, and bioponds. The use of coagulation and chlorination methods before biological treatment in aeration tanks was proposed. Alumoflock 18% was used as a coagulant, polyacrylamide was used as a flocculant, and sodium hydroxide was used as an alkalizing reagent. The study was conducted on a mixture of industrial and domestic wastewater with COD and BOD5 – 3200 and 1575 mg/dm3, respectively, and on industrial wastewater with COD and BOD5 – 4480 and 1960 mg/dm3, respectively. The effects of reducing COD and BOD5 indicators in the first case after coagulation were 30 and 40%, after chlorination - 37.81 and 43.17%, respectively, in the second after coagulation - 28.57 and 47.24%, respectively. It was established that a significant proportion of organic substances according to the COD indicator is in a dissolved state - 60-70%. It has been proven that as a result of chlorination, the maximum reduction of "pure" COD is achieved, therefore, the possibility and expediency of chlorination of water after the secondary settling tank with increased doses should be considered in the wastewater treatment technology of the cardboard and paper factory.

An improved 1D reactive Bürger-Diehl settler model for secondary settling tank denitrification.

An improved 1D reactive settler model is pursued in order to increase the understanding of reactive settling processes and obtain a better prediction of the nitrogen mass balance in wastewater treatment systems. The developed model is based on the 1D Bürger-Diehl settler model with compression function and the Activated Sludge Model No. 1 biological reactions. Specific attention was paid in the model development phase to optimal selection of settling velocity functions and integration of the correct clarifier geometry. A unique measurement campaign was carried out with different operational scenarios to quantify the denitrification in a secondary settling tank. A detailed step-wise calibration effort demonstrated that by choosing an appropriate settling velocity function (power-law structure) and considering the true clarifier geometry allows to accurately capture the biomass concentration profile, total sludge mass, sludge blanket height, and the reaction rates. The resulting model is able to accurately describe total suspended solids (TSS) and nitrate concentration profiles throughout a settling tank under different operational conditions. As such the model can be applied in further scenario analysis and system optimization. PRACTITIONER POINTS: A unique measurement campaign was carried out to obtain detailed data for a reactive settler model development. A 1-D reactive settler model is developed based on the Bürger-Diehl framework including ASM1 biokinetics and the clarifier geometry. An extensive calibration and model selection effort was performed. The model accurately predicts measured concentration profiles in the settling tank. The developed model can be integrated in a plant-wide model to properly calculate the nitrogen mass balance of a WRRF.

Tertiary Wastewater Treatment Technologies: A Review of Technical, Economic, and Life Cycle Aspects

The activated sludge process is the most widespread sewage treatment method. It typically consists of a pretreatment step, followed by a primary settling tank, an aerobic degradation process, and, finally, a secondary settling tank. The secondary effluent is then usually chlorinated and discharged to a water body. Tertiary treatment aims at improving the characteristics of the secondary effluent to facilitate its reuse. In this work, through a literature review of the most prominent tertiary treatment methods, a benchmarking of their technical efficiency, economic feasibility, and environmental impact was carried out. The photo-Fenton method proved to be the most technically efficient process, significantly reducing the microbial load and pharmaceutical content (by 4.9 log and 84%, respectively) of the secondary effluent. Chlorination and UV irradiation exhibited the lowest treatment costs (0.004 EUR/m−3) and the lowest global warming potential (0.04 and 0.09 kg CO2eq. m−3, respectively). After all the data were aggregated, a decision-making tool was constructed in the form of a ternary diagram, which indicates the most appropriate tertiary treatment method according to the weight-per-process aspect (technical, economic, and environmental) selected by the user, with chlorination, UV irradiation, ozonation, microalgae cultivation, and constructed wetlands prevailing in the final results.

A model of reactive settling of activated sludge: Comparison with experimental data

A non-negligible part of the biological reactions in the activated sludge process for treatment of wastewater takes place in secondary settling tanks (SST) that follow biological reactors. It is therefore of interest to develop models of so-called reactive settling that describe the spatial variability of reaction rates caused by the variation of local concentration of biomass due to hindered settling and compression. A reactive-settling model of an SST is described by a system of nonlinear partial differential equations and a numerical scheme is introduced for the simulation of hindered settling of flocculated particles, compression at high concentrations, dispersion of the flocculated particles in the suspension, dispersion of the dissolved substrates in the fluid, and the mixing that occurs near the feed inlet. The model is fitted to experiments from a pilot plant where the SST has a varying cross-sectional area. For the reactions, the Activated Sludge Model No. 1 (ASM1) is used with temperature-adjusted standard coefficients. The constitutive functions for hindered settling and compression are calibrated to a series of conventional batch settling experiments after the initial induction period of turbulence and reflocculation has been transformed away. The overall conclusion is thus that a careful treatment of batch-settling data to calibrate the sedimentation-compression model is sufficient to ensure good predictability of the reactive sedimentation process in a pilot SST, while the optional inclusion of hydrodynamic dispersion (modelled with two parameters) or a term modelling the mixing of the suspension near the feed inlet at most marginally improve predictability.

Sewage sludge dewatering by electric field

During the cleaning and further treatment of municipal wastewater, sediments are formed, which are extremely dangerous from a sanitary and hygienic point of view, poorly dewatered, have high humidity (over 90%), large volumes (up to 3% of wastewater consumption), contain organic substances, pathogens, heavy metals, etc. In Ukraine, at most wastewater treatment plants, sewage sludge is mostly piled up on sludge sites after minimal treatment. Effective processing and disposal of sewage sludge in order to reduce the negative impact on the environment, as well as the use of sewage sludge as secondary raw materials, is an actual, complex and urgent task. The key link in the existing process of treatment and disposal of sewage sludge is their dewatering. When designing facilities for the treatment and disposal of sewage sludge, advanced technologies should be used, the use of which is based on scientific and technical research. The article reviews the results of research on the intensification of existing mechanical methods of sewage sludge. One of the most effective methods of intensifying the process of dewatering sewage sludge is electro-dewatering, which involves the application of an electric field during mechanical dewatering of sludge. Electro-dewatering technology makes it possible to reduce the humidity of sediments to 20...40%, reduce the concentration of heavy metals and pathogens in sediments, etc. The purpose of this work is to study the possibility of electro-dewatering of activated sludge from secondary settling tanks of municipal wastewater treatment plants in Lviv. Empirical research methods were used. A laboratory scale has been designed for electro-dewatering of sewage sludge. Activated sludge with a moisture content of 98% was studied. It is shown that the effect of activated sludge dewatering, depending on the duration of its treatment, is an S-shaped curve that resembles a kinetic autocatalytic reaction with three periods: induction, main, and fading. The possibility of electro-dewatering of sewage sludge with a maximum dewatering effect of 60% has been proven. Therefore, it is proposed to carry out mechanical dewatering of city sewage sludge using an electric field.

A hindered settling velocity model related to the fractal dimension and activated sludge flocs characteristics: Application to a sludge with a previous fragmentation and flocculation process

The modelling of the activated sludge hindered settling velocity as a function of the flocs characteristics and the incorporation of these models to the secondary settling tanks simulation is a hardly studied subject. Commonly used empirical models cannot describe the changes in the settling velocity caused by changes in the flocs characteristics. In this paper, a model for the hindered settling velocity as a function of the fractal dimension and other flocs characteristics is proposed. The model was used to describe the settling velocity after a flocculation process originated by activated sludge fragmentation. The model reproduces the observed abrupt decrease of hindered settling velocity in a small range of suspended solids concentration. It also enables to relate the flocs characteristics and the settling velocity to the fragmentation and sludge aggregation mechanisms.

Long-term effects of hydrocyclone operation on activated sludge morphology and full-scale secondary settling tank wet-weather operation in long sludge age WWTP

This paper presents the study concerning long-term effects of a full scale hydrocyclone unit implemented in a continuous flow long sludge age system, on sedimentation, treatment efficiency and sludge morphology. The research concentrates on identifying the mechanisms of sludge behaviour within the system. The gravimetric selection of activated sludge via a hydrocyclone is a recent development for enhancing sludge separation, where heavier flocs are retained in the system, and lighter ones are discarded as waste sludge. The effects of implementing hydroclyclones were analysed with the use of SEM imagining and fractal dimensioning through the frequent assessment of sludge settling capabilities, effluent quality, and floc properties. Over the course of 60 weeks of hydrocyclone operation, sedimentation efficiency varied significantly. Sludge volume index values of 40 mL/g, achieved during the warm season, were not sustained when the temperature decreased and an overgrowth of filamentous bacteria occurred. Good settling efficiency was also observed in batch tests, where settling velocity of experimental sludge was app. 1 m/h higher than for the reference train at the same concentrations. This was confirmed during wet weather, as the experimental train sustained safe sludge blanket height in secondary clarifiers. SEM imaging and fractal dimension analysis revealed that the underflow that returned to the system had a more compact and spherical shape, which led to an increased content of granule-like particles in the reactor. The presence of flocs with a diameter exceeding 900 μm in the underflow, which is not observed in the feed, indicated agglomeration within the hydrocyclone. This is contradictory to most of the literature data coming from laboratory experiments. This phenomenon was attributed to differences in the size and geometry of the used hydrocyclones, and the potential process mechanism was presented.

IMPROVEMENT OF THE MODE OF OPERATION OF BIOLOGICAL WASTEWATER TREATMENT FACILITIES

Despite the strict requirements for wastewater quality, intensive pollution and accumulation of industrial pollution, potentially hazardous substances, continues in the places of wastewater discharge. Therefore, the aim of the study is to improve the operation of biological wastewater treatment plants to ensure compliance with environmental requirements. To achieve this goal, the features of wastewater treatment are analyzed and it is found that the treatment process depends on the concentration of activated sludge, the amount of air and the properties of the wastewater entering the treatment. With this in mind, it is proposed to adjust the ratio of "sewage active sludge air" to ensure compliance with environmental requirements. Factors influencing the cleaning process are also identified. Such factors are the consumption of wastewater coming for treatment, oxygen saturation of the mixture of activated sludge and wastewater, the quantity and quality of activated sludge fed into the aeration tank. In addition, the peculiarities of the processes occurring in different parts of the buildings are taken into account, and it is proposed to divide the cleaning process into two stages. The first stage takes place in the first corridor of the aeration tank (regenerator), where the activated sludge enters for regeneration. The second stage covers the second or third corridors of the aeration tank and the secondary settling tank, where the wastewater is first mixed with activated sludge, then the mixture is discharged to the secondary settling tank. An experimental study of the cleaning process was carried out, as a result of which the necessary data for the mathematical description of the processes were obtained. After processing the experimental data, regression equations were obtained that describe the purification processes in the system "aeration tank-displacer - secondary settling tank", namely the change in the concentration of activated sludge at the outlet of the regenerator and the change in the concentration of contaminants in the purified water. The adequacy of the equations was checked according to Fisher's test. It was found that the equations are adequate to real processes within the accepted conditions and assumptions. Analytical solutions of the obtained equations allow to analyze the course of purification processes at different stages, to determine the influence of factors on the process. A procedure for the use of equations is proposed, which allows without additional experiments to choose the mode of operation of biological treatment facilities, which will ensure compliance with environmental requirements.