Biological Wastewater Treatment Processes Research Articles

Dynamic alpha factor prediction with operating data - a machine learning approach to model oxygen transfer dynamics in activated sludge

Aeration is an energy-intensive process of aerobic biological wastewater treatment. An accurate model of oxygen transfer dynamics in activated sludge tanks would improve design and operation of aeration systems. Such a model should consider spatial and diurnal variation of α-factor as well as site-specific conditions that impact oxygen transfer. For this dynamic prediction a machine learning approach was used for the first time. The data-driven method was based on long-term ex-situ off-gas measurements with pilot-scale reactors (5.8 m height, 8.3 m3 vol) coupled to full-scale activated sludge tanks on the sites of two conventional and a two-stage activated sludge treatment plant. The ex-situ off-gas method allowed to quantify theoretical off-gas parameters in non-aerated zones and thus consider the whole activated sludge tank. We introduced the α0-factor to compare aerated and non-aerated zones under nonsteady-state conditions. Like the established α-factor for steady-state conditions, the α0-factor describes oxygen transfer inhibiting effects in activated sludge. α0-factor was lowest in upstream denitrification zones. This indicates an anoxic elimination of oxygen transfer inhibiting wastewater contaminants which improved oxygen transfer in subsequent aerobic zones. Random Forest models predicted α0-factor reliably in all examined activated sludge tanks even for stormwater events and seasonal variation. Model development only required online sensor data already available to operators. Our results suggest that machine learning models can dynamically predict α-factors in a variety of activated sludge processes, thus considering site-specific conditions in model training without manual calibration.

POSSIBLE USE OF LASERS FOR CLEAVAGE OF PHENOLS TILL BASE SUBSTANCES (REVIEW)

The purpose of this review article is to explain the hazards of phenol and phenol compounds to human health and the environment. To describe where and how phenol and its compounds occur, especially in industrial effluents. To study the possibility of using laser technologies for phenol cleavage, as well as for the treatment of industrial wastewater from phenol compounds. Removal of phenol and its compounds using biological wastewater treatment process is widely used worldwide. This method is cost-effective and environmentally friendly. On the other hand, exceeding the tolerable phenol concentration, which is individual for each biological treatment plant, may result in severe intoxication and lead to death of activated sludge system. Thus, the biological treatment process of industrial wastewater is halted until the phenol concentration is reduced to an acceptable level and the microorganisms have time to recover. Such a procedure can be time consuming and unpredictable due to the susceptibility of microorganisms to changing conditions. Based on this, sources of literature have been studied that could help to understand which laser equipment can be used to cleave a phenolic compound or benzene ring to simpler compounds.

Cupric ions inducing dynamic hormesis in duckweed systems for swine wastewater treatment: Quantification, modelling and mechanisms

Hormesis has attracted close attention of environmental and toxicological communities over the past decades. Most studies focused on the hormesis induced by stressors in the aspect of their biotoxicity to organisms, while little research was conducted on hormesis in the aspect of biological wastewater treatment process. In this study, removal of NH4+-N and Cu2+ by S. polyrrhiza under long-term Cu2+ exposure at environmentally relevant concentrations in swine wastewater was investigated. Removal efficiencies of NH4+-N by duckweeds at 0.0, 0.1, 0.5, 1.0, 2.0 and 4.0 mg/L Cu2+ were 81.6 %, 83.7 %, 89.4 %, 74.9 %, 61.8 % and 45.1 % on day 28, however, during the initial period of cultivation (0–4 days), such hormetic effect was not observed, indicating time-dependent feature of hormesis in NH4+-N removal. The modified logistic growth model was applied to describe long-term hormesis induced by Cu2+ on NH4+-N removal and it suggested that the optimal copper exposure for ammonium removal was 0.48 mg/L. More importantly, it was found that previous exposure to low doses of Cu2+ (0–1 mg/L) could enhance NH4+-N removal performance under the second exposure. Cu2+ above 1 mg/L could switch copper bioaccumulation pattern from the Langmiur-irreversible type to reversible one, indicating risk of secondary pollution. Six components including freshly-produced humic-like substances, lignin, fulvic acid-protein complex, free amino acid-like substances, tyrosine-like substance and soluble amino acid-like substances in duckweeds were detected by parallel factor (PARAFAC) model detected. Principle component analysis (PCA) conducted on PARAFAC components suggested that enhanced synthesis of protein and growth factors intracellularly at low dose stimulation improved ammonia uptake from the environment. This study provided a novel strategy to improve treatment performance of duckweeds for copper contaminated wastewater and helped understand biochemical responses and their roles in evolutionary adaptive strategies to stresses.

Identification of β-lactam-resistant coding genes in the treatment plant by activated sludge process

Wastewater treatment plants are the most important release source of antibiotic-resistance genes (ARGs) into the environment. This study aimed to identify β-lactam-resistance genes in Qom province municipal wastewater and also to determine the effect of municipal wastewater treatment plants with different processes on reducing these pollutants. Sampling was performed according to the standard protocol and at constant temperature conditions. Nine genes resistant to the six groups of β-lactam antibiotics were selected, and polymerase chain reaction (PCR) test was performed to identify the presence/absence of ARGs. At the same time, real-time PCR test was also carried out to quantitatively measure three ARGs in wastewater and effluent samples. The obtained results showed that the highest and the lowest removal were related to blanps-1 (90.61%) and blaCTX-M-32 (65.93%), respectively; however, a decreasing trend in these two genes were showed in to blaoxa-1 with an increase in effluent unit (45.12%). The results showed that conventional biological wastewater treatment processes not only have little potential to reduce antibiotic-resistance genes during the treatment process but also these processes sometimes increase resistant genes. The results of the oxa-1 gene in this study are consistent with this trend. In addition, the sludge treatment unit was based on the results of sequencing Salmonella enterica and Klebsiella pneumoniae. Our study suggests that wastewater treatment plants using conventional chlorination do not favor the proliferation of antibiotic resistance bacteria and ARGs during wastewater treatment. Thus, equipping treatment plants with advanced processes will be efficient in reducing bacterial resistance.

The Potential of Heat Recovery from Wastewater Considering the Protection of Wastewater Treatment Plant Technology

Energy efficiency is extremely significant for industrial processes and technologies. Rising energy prices, depleting fossil fuels, as well as tightening regulations that impose the need to reduce GHG emissions incentivize companies to look for energy-efficient solutions. This also applies to wastewater treatment plants, which, on the one hand, are consumers of very large amounts of energy, and on the other hand, have significant potential to retrieve waste energy in the form of heat accumulated in wastewater. The authors of this publication have recognized the benefits of managing this heat. However, they have also pointed out several problems and difficulties associated with this process. By means of measured data, this publication provides a comprehensive analysis of the heat that can be recovered from wastewater treatment plants. As a result of the analyses, the locations of sites for collecting heat from wastewater have been determined, and potential technologies for this purpose have been identified. Moreover, the impact of the proposed heat recovery technology on the process of biological wastewater treatment has also been analyzed. As a result of the research, the authors developed generalized guidelines for selecting an optimal heat recovery site and the technological system designed for this purpose.

Integrated photocatalysis and moving bed biofilm reactor (MBBR) for treating conventional and emerging organic pollutants from synthetic wastewater: Performances and microbial community responses

Increasing concern for emerging organic pollutants (e.g. antibiotics) urges improvements in conventional biological wastewater treatment processes. This study examined the performance of an integrated photocatalysis and moving bed biofilm reactor (MBBR) system in treating synthetic wastewater containing sulfamethoxazole (SMX). It was found that the integrated system could remove over 80.5 % of SMX and 67.7–80.7 % of chemical oxygen demand (COD) with a hydraulic retention time of 24 h. The introduction of photocatalysis had no impact on COD removal and significantly enhanced SMX removal. High-throughput analysis indicated that microbial community greatly altered due to photocatalytic oxidation stress, with clostridiaceae and enterobacteriaceae becoming dominant families. Nevertheless, microorganisms maintained metabolic activity, which may be ascribed to the protection of carriers and microbial self-preservation by secreting extracellular polymeric substances and antioxidant enzymes. Collectively, this study sheds light on treating wastewater containing conventional and emerging organic pollutants by integrating photocatalysis with MBBR.

Математическое моделирование процесса биологической очистки сточных вод в аэротенке-вытеснителе

Приведены результаты теоретических исследований кинетики процессов биохимического окисления органических загрязнений сточных вод микроорганизмами активного ила. Показано, что величину среднедействующей удельной скорости окисления органических загрязнений сточных вод активным илом аэротенка-вытеснителя можно определить, используя теорему о среднем значении непрерывной функции f(L), интегрируемой в некотором промежутке изменения ее переменной от Lн до Lк. Интегрированием уравнения Михаэлиса–Ментен получена математическая модель, базирующаяся на фундаментальных закономерностях ферментативной кинетики, описывающая процесс биологического окисления органических загрязнений в аэротенке-вытеснителе. Использование предлагаемых уравнений позволит определять среднедействующие значения удельных скоростей окисления различных органических загрязнений (БПК, нефтепродуктов, ПАВ, фенолов и др.), расчетную продолжительность аэробных процессов и тем самым оптимизировать процессы проектирования и эксплуатации сооружений биологической очистки сточных вод в аэротенках-вытеснителях. The results of theoretical studies of the kinetics of the processes of biochemical oxidation of organic wastewater pollution by activated sludge microorganisms are presented. It is shown that the value of the average effective value of the specific rate of organic wastewater pollution oxidation by the activated sludge in a plug flow aeration tank can be determined using the theorem on the average value of the continuous function f(L) integrated in a certain range of its variable from Lн to Lк. By integrating the Michaelis–Menten equation, a mathematical model was obtained based on the fundamental regularities of enzymatic kinetics that describes the process of biological oxidation of organic pollutants in a plug flow aeration tank. The use of the proposed equations will provide for determining the average effective values of the specific oxidation rates of various organic pollutants (BOD, oil products, surfactants, phenols, etc.), the estimated duration of aerobic processes; and thereby, optimizing the design and operation of biological wastewater treatment facilities in plug flow aeration tanks.

A gas distributor capable of multiple injection directions to improve the gas–liquid dispersion performance in the airlift loop reactor

As the gas supply equipment, the gas distributor is one of the core components in the airlift loop bioreactor. The gas injection direction and the dynamic behavior of the bubbles significantly affect the gas–liquid dispersion performance in the bioreactor. Therefore, based on the previously designed airlift loop reactor, a new type of tubular convex gas distributor (TCD) with multi-angle gas injection capability was developed. Under the conditions of different superficial gas velocities, the gas–liquid flow in the reactor was numerically simulated by computational fluid dynamics. The results showed that TCD had better gas–liquid dispersion and mass transfer performance in this reactor than several other traditional types of distributors. Under the experimental conditions, the optimal gas–liquid two-phase flow in the reactor was observed when the angle of the TCD vent tube was 15°, the number was 12, and the diameter was 1 mm. It was found that the error between the experimental results and the simulation results was controlled within 10 %, which verified the accuracy of the simulation. The application of TCD in the airlift loop bioreactor improved the wastewater treatment and biomass accumulation, significantly. The TCD can provide design ideas for gas distributors in other types of bioreactors, and is beneficial to improving the process of biological wastewater treatment for industrial application.

Characterization of Oxidation-Reduction Potential Variations in Biological Wastewater Treatment Processes: A Study from Mechanism to Application

Oxidation-reduction potential (ORP) sensors would constitute a robust surveillance and control solution for aeration and external carbon dosing in wastewater biological treatment processes if a clear correlation exists between the ORP values and process variables (e.g., dissolved oxygen (DO), nitrate, and chemical oxygen demand (COD). In this study, ORP values and other water quality variables were analyzed, and principal component analysis (PCA) and analysis of variance were used to study the relationships between ORP and main reactive substances under anoxic conditions. Mathematical models were then established using multiple regression analysis. The results showed that under anoxic conditions, ORP was positively correlated with nitrate, DO, and COD and negatively correlated with ammonia nitrogen, phosphate, and pH. COD had a low correlation with the ORP value change. PCA showed that the mathematical model of ORP can be established by using DO, nitrate, and phosphate, for which the adjusted R² value was 0.7195. The numeric relationships among ORP, COD, and nitrate were clearly established and applied to control external carbon dosing. A precise and clear relationship between ORP and COD offers the possibility to substitute COD monitoring for process control.

The impact of solids retention time on Greenhouse Gases Emissions from biological wastewater treatment processes

Biological wastewater treatment is linked to direct and indirect greenhouse gases (GHGs) emissions, thus new approaches on design and operation of wastewater treatment plants (WWTPs) must be adopted aiming towards GHGs emissions’ mitigation. This study evaluates the impact of solids retention time (SRT) on GHGs (CO2 and N2O) emissions of activated sludge (AS) wastewater treatment processes with nutrients removal operating at 10, 30 and 180 days SRT. The 180 days SRT represents the complete solids retention AS process (CRAS), which introduces a novel WWTP design and operation approach for excess sludge reduction. The evaluation of GHGs emissions and process performance via ASDM model and Bridle methodology showed that the total N2O emissions increased together with increasing dissolved oxygen and SRT. CRAS process achieved 97,4% and 96,2% excess sludge reduction compared to AS process with SRT of 10 d and 30 d respectively, with total direct emissions in CRAS process being respectively higher by 20,0% and 12,2%. The lower total indirect emissions in CRAS process compensate for the higher direct emissions. At high influent loads, the balance in GHGs emissions tilts in favour of CRAS process due to management of increased excess sludge quantities, rendering CRAS process a more sustainable choice.

MATHEMATICAL MODELING IN WATER TREATMENT PROBLEMS

Problem statement. Analysis of the treatment facilities efficiency in sewerage at the stage of their design is great importance. Also, at the stage of structures’ reconstruction or their operation adjustment under different load conditions, it is necessary to know the efficiency of water treatment in different areas of treatment facilities. Such information makes it possible to rationally operate facilities. For solving problems of this class, the most effective tool is the use of the numerical modeling method. The work considers development of numerical models set for solving problems of this class. Methodology. Two fundamental models are used to solve the velocity field determination of the wastewater flow in the sewage treatment plant. The first is a model of the vortex-free motion for an incompressible fluid. The second model is the Navier-Stokes equations written in Helmholtz variables. The mass transfer equation is used to determine impurity concentration fields in sewage treatment plants, which takes into account flow velocity, diffusion and the presence of impurity emission sources. Material balance equations for the substrate and activated sludge are used to calculate the process of biological wastewater treatment. Finite-difference schemes are used to build numerical models that allow calculating the hydrodynamics of the flow and the distribution of the impurity concentration in the facility. The Euler method is used for the numerical solution of the material balance equations. Results. Numerical models were built, which were used to develop a complex of computer programs. These computer programs allow real-time analysis of the water treatment efficiency in the facility. Scientific novelty. Numerical models have been developed that allow investigating the process of water treatment in facilities of the «settler» type and in aeration tanks, that is, for a significant class of treatment facilities used in practice. Practical value. The calculation time of the velocity field and the impurity concentration field in a water treatment plant with a complex geometric shape is few seconds. This allows usinge the developed numerical models for serial calculations in project organizations in daily work.

Investigation, biokinetic calculation, and modelling of a real combined industrial wastewater biological treatment process by activated sludge models

Background: Treatment of combined industrial wastewater from industrial parks is one of the most complex and difficult wastewater treatment processes. Also, the accuracy of biological models for the prediction of the performance of these processes has not been sufficiently evaluated. Therefore, in this study, the International Association on Water Quality (IAWQ(-Activated Sludge Model No. 1 (ASM1) was implemented for the Jey industrial park in Isfahan province, Iran. Methods: The Jey IPWWTP process is a combination of anaerobic and aerobic biological processes. To evaluate the overall performance of IPWWTP, organic compounds, suspended solids, nutrients, attached biomass, and some operating parameters were measured during 6 months. Then, the biokinetic coefficients of aerobic processes were determined using Monod equations. Finally, the aerobic processes were modeled using ASM1 implemented in STOAT software. Results: The values of the biokinetic coefficients K, Y, Ks, Kd, and µmax were calculated as 2.7d- , 0.34 mg VSS/mg COD, 133.36 mg/L COD, 0.03d- , and 0.93d- , respectively. Based on the default coefficients and conditions of the ASM model, the difference between the experiments and model prediction was about 2 to 98%. After calibrating the ASM model, the difference between the experiments and prediction in all parameters was reduced to less than 10%. Conclusion: Investigations showed that the default coefficients and operation conditions of the ASM1 model do not have good predictability for complex industrial wastewaters and the outputs show a low accuracy compared to the experiments. After calibrating the kinetic coefficients and operating conditions, the model performance is acceptable and the predictions show a good agreement with the experiments.

Potential of food waste-derived volatile fatty acids as alternative carbon source for denitrifying moving bed biofilm reactors

Fossil-based materials such as methanol are frequently used in the denitrification process of advanced biological wastewater treatment as external carbon source. Volatile fatty acids (VFAs) produced by anaerobic digestion of food waste, are sustainable compounds with the potential to act as carbon sources for denitrification, reducing carbon footprint and material costs. In this study, the effectiveness of food waste-derived VFAs (AD-VFA) was investigated in the post-denitrification process in comparison with synthetic VFA and methanol as carbon sources. Acetic acid had the highest rate of disappearance among single tested VFAs with a denitrification rate of 0.44 g NOx-N removed/m2/day, indicating a preferential utilization pattern. While AD-VFA had a denitrification rate of 0.61 mg NOx-N removed/m2/day, sVFA had a rate of 0.57 mg NOx-N removed/m2/day, indicating that impurities in AD-VFA did not play substantial role in denitrification. AD-VFA proved to be promising carbon source alternative for denitrification in wastewater treatment plants.

Toxic Effects of Xenobiotic Compounds on the Microbial Community of Activated Sludge

AbstractThe presence of xenobiotic compounds in biological wastewater treatment processes with activated sludge may reduce microbial communities, disrupt microbial diversity, and diminish system performance. Shock loads and unusual operating events in these biological systems have negative impacts on their efficiency and reliability for pollutant degradation, thereby posing high risk to microorganisms and water quality of receiving treated water bodies. The severity and characteristics of the occurring damage are determined by the toxic contaminant's degree, nature and mode of application. This review highlights the effects of metabolic uncouplers, heavy metals, carbon nanotubes, pharmaceuticals and personal care products, nanoparticles, and phenolic compounds stress on microbial biomass in activated sludge systems. The synergistic, antagonistic, and shock load toxic effects of hybrid substances exposure in an activated sludge sequential batch reactor (SBR) system on organic and nutrient removal, system efficiency, and toxicants biodegradation are discussed. The findings can be used to provide a theoretical foundation and professional assistance for optimizing the shock impacts of these toxic substances on biological wastewater treatment systems, which will help to reduce their negative effects on treatment system efficiency.

Impact of saline valorization in contaminated municipal wastewater on the treatment performance and bacterial community dynamics of a membrane bioreactor

AbstractBackgroundDue to salt intrusion and the improper use of seawater for cleaning and flushing in food shops along coastal regions, the aerobic biological wastewater treatment process may have an adverse effect on treatment performance. This study demonstrates membrane bioreactor (MBR) performance for treating saline‐contaminated municipal wastewater. The aim of this study is to determine how much salt affects the efficiency of the process and how the functional bacterial community evolves in an MBR for treating actual municipal wastewater.ResultsAn MBR was applied for actual municipal wastewater treatment by increasing the NaCl concentration from 0 to 20 g L−1 with a hydraulic retention time of 12 h and complete sludge retention. High removal efficiencies of chemical oxygen demand (COD) (ranging from 80.3 to 82.8 mgL−1) and ammonium‐N (ranging from 40.8 to 44.4 mgL−1) were found at salinity concentrations of up to 7.8 ± 0.8 g L−1. However, the removal efficiency of COD was below 50% at high salinity concentrations of 17.9 ± 1.3 g L−1, whereas the removal rate of ammonium‐N had slightly changed with the value of 90%. In terms of bacterial composition, the largest dominant bacterial communities were Proteobacteria and Planctomycetota, both of which may be the predominant halotolerant/halophilic bacteria group. Additionally, Rhizobiales, Planctomycetales, Pirellulales, and Gemmatales (all of which are members of these phyla) were increased, suggesting that they played an important role in the biodegradation process.ConclusionThe MBR operation showed a good performance for treating municipal wastewater with high salinity concentrations, with a salt tolerance threshold of 7.8 g L−1. The experimental results indicate that the MBR system can be applied for treating municipal wastewater that is occasionally contaminated with seawater. © 2022 Society of Chemical Industry (SCI).

Impacts of dibutyl phthalate on biological municipal wastewater treatment in a pilot-scale A2/O-MBR system

Dibutyl phthalate (DBP) is a typical contaminant in pharmaceutical wastewater with strong bio-depressive properties which potentially affects the operation of municipal wastewater treatment systems. Based on a year-round monitoring of the quality of influent and effluent of a full-scale pharmaceutical wastewater treatment plant in Northeast China, the DBP was found to be the representative pollutant and its concentration in the effluent ranged 4.28 ± 0.93 mg/L. In this study, the negative effects of DBP on a pilot-scale A2/O-MBR system was investigated. When the influent DBP concentration reached 8.0 mg/L, the removals of chemical oxygen demand (COD) and total nitrogen (TN) were significantly inhabited (P < 0.01), with the effluent concentration of 54.7 ± 2.6 mg/L and 22.8 ± 3.7 mg/L, respectively. The analysis of pollutant removal characteristics of each process unit showed that DBP had the most significant effects on the removals of COD and TN in the anoxic tank. The α- and β-diversity in the system decreased significantly when the influent DBP concentration reached 8.0 mg/L. The impacts of DBP on known nitrifying bacteria, such as Nitrospira, and phosphorus accumulating organisms (PAOs), such as Cadidatus Accumulibacter, were not remarkable. Whereas, DBP negatively affected the proliferation of key denitrifying bacteria, represented by Simplicispira, Dechloromonas and Acinetobacter. This study systematically revealed the impacts of DBP on the pollutants removal performance and the bacterial community structure of the biological municipal wastewater treatment process, which would provide insights for understanding the potential impacts of residues in treated pharmaceutical wastewater on biological municipal wastewater treatment.

Recovery Strategies for Heavy Metal-Inhibited Biological Nitrogen Removal from Wastewater Treatment Plants: A Review

Biological nutrient removal is an integral part of a wastewater treatment plant. However, the microorganism responsible for nutrient removal is susceptible to inhibition by external toxicants such as heavy metals which have the potential to completely inhibit biological nutrient removal. The inhibition is a result of the interaction between heavy metals with the cell membrane and the deoxyribonucleic acid (DNA) of the cell. Several attempts, such as the addition of pretreatment steps, have been made to prevent heavy metals from entering the biological wastewater systems. However, the unexpected introduction of heavy metals into wastewater treatment plants result in the inhibition of the biological wastewater treatment systems. This necessitates the recovery of the biological process. The biological processes may be recovered naturally. However, the natural recovery takes time; additionally, the biological process may not be fully recovered under natural conditions. Several methods have been explored to catalyze the recovery process of the biological wastewater treatment process. Four methods have been discussed in this paper. These include the application of physical methods, chelating agents, external field energy, and biological accelerants. These methods are compared for their ability to catalase the process, as well as their environmental friendliness. The application of bio-accelerant was shown to be superior to other recovery strategies that were also reviewed in this paper. Furthermore, the application of external field energy has also been shown to accelerate the recovery process. Although EDTA has been gaining popularity as an alternative recovery strategy, chelating agents have been shown to harm the metal acquisition of bacteria, thereby affecting other metabolic processes that require heavy metals in small amounts. It was then concluded that understanding the mechanism of inhibition by specific heavy metals, and understanding the key microorganism in the inhibited process, is key to developing an effective recovery strategy.

Storage and reactivation of aerobic granular sludge: A review

Aerobic Granular Sludge (AGS) is a biological wastewater treatment process. This technology offers both low land use and cost efficiency. However, the long start-up time is one of the main problems the AGS is facing; to overcome this challenge, several methods have been proposed. Storing and then reactivating AGS is one of the methods proposed. It considerably reduces the start-up time due to skipping most of the granulation procedures. This method collects mature AGS from a running AGS bioreactor, stores it in different forms and environments (depending on the techniques used), and then reactivate the stored AGS when needed. This review summarizes the previously-proposed granules storage techniques such as soaking in different mediums, freezing, and drying. Additionally, the storing techniques are analysed discussing their advantages and disadvantages. The review result indicated that the AGS storage and reactivation method is successful in shortening the lengthy start-up period of the AGS technology. Moreover, storing AGS in dried form using a combination of air drying and dehydration solutions showed a high potential for recovering the removal performance after reactivation. The stored-then-reactivated AGS not only shortens the lengthy start-up period, but it may also lead to an AGS stocking business with further investigation.

Biological Activated Sludge from Wastewater Treatment Plant before and during the COVID-19 Pandemic.

The COVID-19 pandemic and the related measures brought a change in daily life that affected the characteristics of the municipal wastewater and further, of the biological activated sludge. The activated sludge process is the most widely used biological wastewater treatment process in developed areas. In this paper, we aim to show the situation of specific investigations concerning the variation of the physicochemical parameters and biological composition of the activated sludge from one conventional wastewater treatment plant from a metropolitan area. The investigations were carried out for three years: 2019, 2020 and 2021. The results showed the most representative taxa of microorganisms: Microtrix, Aspidisca cicada, Vorticella convallaria, Ciliata free of the unknown and Epistylis and Rotifers. Even if other microorganisms were found in the sludge flocs, their small presence did not influence in any way the quality of the activated sludge and of the wastewater treatment process. That is why we conclude that protozoa (especially Flagellates and Ciliates) and rotifers were the most important. Together with the values and variation of the physicochemical parameters, they indicated a good, healthy, and stable activated sludge, along with an efficient purifying treatment process, no matter the loading conditions.

The effects of light regime on carbon cycling, nutrient removal, biomass yield, and polyhydroxybutyrate (PHB) production by a constructed photosynthetic consortium

Microalgae can add value to biological wastewater treatment processes by capturing carbon and nutrients and producing valuable biomass. Harvesting small cells from liquid media is a challenge easily addressed with biofilm cultivation. Three experimental photobioreactors were constructed from inexpensive materials (e.g. plexiglass, silicone) for hybrid liquid/biofilm cultivation of a microalgal-bacterial consortia in aquaculture effluent. Three light regimes (full-spectrum, blue-white, and red) were implemented to test light spectra as a process control. High-intensity full-spectrum light caused photoinhibition and low biomass yield, but produced the most polyhydroxybutyrate (PHB) (0.14 mg g−1); a renewable bioplastic polymer. Medium-intensity blue-white light was less effective for carbon capture, but removed up to 82 % of phosphorus. Low-intensity red light was the only net carbon-negative regime, but increased phosphorus (+4.98 mg/L) in the culture medium. Light spectra and intensity have potential as easily-implemented process controls for targeted wastewater treatment, biomass production, and PHB synthesis using photosynthetic consortia.