Large-scale Wastewater Treatment Plant Research Articles

An accurate and robust method for intensification of wastewater sludge pipe flow

Globally, environmental impacts and population growth are driving the process intensification of wastewater treatment plants (WWTPs) via transition from conventional (2–3 wt% solids) to highly concentrated (4–6 wt% solids) wastewater sludges (HCWS). This presents an industrial challenge as HCWS are complex, non-Newtonian materials whose viscosity increases nonlinearly with solids concentration. This viscosity increase is particularly relevant for sludge pipe flow as it leads to considerable pumping pressure that ultimately limits the feasibility of pipe flow transportation. Hence, process intensification demands accurate prediction of HCWS turbulent pipe flow to design and optimise pumping infrastructure and piping systems. Such prediction requires accurate rheological characterisation of HCWS and numerical prediction of HCWS turbulent pipe flow, neither of which has been achieved to date due to respective limitations associated with benchtop rheometry and numerical turbulence models. We address these challenges by first developing accurate methods for rheological characterisation of HCWS via laminar flow of digested sludge at various solids concentrations (2–5 %) in a fully instrumented pipe loop facility at a large-scale WWTP. These rheological parameters are used in direct numerical simulation (DNS) computations (that avoid turbulence models) of turbulent pipe flow of HCWS. These predictions are then validated against turbulent flow pipe loop data. This method yields accurate (2–15 % error) predictions of HCWS turbulent pipe flow, compared with up to ∼75 % error for conventional pipe flow correlations. This validation highlights the need for accurate rheological characterisation and numerical simulation to predict HCWS pipe flow and provides a sound basis for the intensification and optimisation of WWTP pipeline systems.

Reprocessing and Resource Utilization of Landfill Sludge—A Case Study in a Chinese Megacity

In the past, due to improper sludge treatment technology and the absence of treatment standards, some municipal sludge was simply dewatered and then sent to landfills, occupying a significant amount of land and posing a serious threat of secondary pollution. To free up land in the landfill area for the expansion of a large-scale wastewater treatment plant (WWTP) in Shanghai, in this study, we conducted comprehensive pilot research on the entire chain of landfill sludge reprocessing and resource utilization. Both the combination of polyferric silicate sulfate (PFSS) and polyetheramine (PEA) and the combination of polyaluminum silicate (PAS) and polyetheramine (PEA) were used for sludge conditioning before dewatering, resulting in dewatered sludge with approximately 60% moisture content. The combined process involved coagulation and sedimentation, flocculation, and oxidation to treat the leachate generated during dewatering. The treatment process successfully met the specified water pollutant discharge concentration limits for the leachate, with the concentration of ammonia nitrogen in the effluent as low as 15.6 mg/L. Co-incineration in a power plant and modification were applied to stabilize and harmlessly dispose of the dewatered sludge. The coal-generating system ran stably, and no obvious problems were observed in the blending process. In the modification experiment, adding 5% to 7% of the solidifying agent increased the sludge bearing ratio by 53% and 57%, respectively. This process effectively reduced levels of fecal coliforms and heavy metals in the sludge but had a less noticeable effect on organic matter content. The modified sludge proved suitable for use as backfill material in construction areas without requirements for organic matter. The results of this study provide valuable insights for a completed full-scale landfill sludge reclamation and land resource release project.

Restructuring anaerobic hydrolysis kinetics in plant-wide models for accurate prediction of biogas production

In this study, the effect of anaerobic hydrolysis rate on biogas production was investigated with mesophilic digesters in seven large-scale wastewater treatment plants. A linear correlation was determined between the percentage of primary sludge mass in the total sludge fed to the digester and the overall anaerobic hydrolysis rate. The anaerobic hydrolysis rate of primary sludge was determined to be three times higher than that of biological sludge. The reduction factors for anaerobic hydrolysis (ηHYD,ana) were identified in the range of 0.11–0.30 which is lower compared to the recommended range (0.30–0.50) given in the literature. This study proposes a new model approach where anaerobic degradation kinetics of influent originated (XB) and decay originated (XB,E) particulate biodegradable organics are separated. Current plant-wide models with a single kinetic expression required recalibration of the model for calculating biogas flowrate for each treatment facility with different primary and secondary sludge ratios fed to the digesters. The new model structure is able to predict biogas production of all wastewater treatment plants without any recalibration effort by segregating degradation kinetics of two particulate biodegradable organic fractions (XB, XB,E).

Assessing the Degradation of Safety Management Performance in Large Construction Projects: An Investigation and Decision Model Based on Complex Network Modeling

Modern safety control theory suggests that the accumulation of safety management defects at the organizational level can lead to a degradation in the overall safety management performance. This problem is exacerbated by the increasing complexity of safety management in large construction projects. The theoretical frameworks proposed by existing studies can provide generalized guidance for identifying safety management defects, but they are not flexible enough to address the complexity of a safety management system (SMS) in specific large construction projects. This study proposed an investigation and decision model based on a complex network model of SMSs. The main purpose was to accurately assess the degradation of safety management performance through the comprehensive identification of safety management defects for large construction projects. The functional components and their interactions in SMSs were graphically represented in a complex network using the fuzzy DEMATEL technique. Based on this, deep-seated safety management defects were identified by tracing the path of influence between the functional components and their roots. Furthermore, the results of this identification were used to support the assessment of the degradation of the safety performance of the overall SMS. The proposed model was verified with a large-scale wastewater treatment plant construction project in Lanzhou City, China. The degradation of the functional components could be presented in a complex visual network map to facilitate an understanding of the weak points or risk-sensitive areas throughout the SMS. Especially in the case of false safety perceptions, deep-seated safety management defects can be identified in time to prevent a sudden collapse of the SMS through early warnings. In addition, it also facilitates timely short-term improvement strategies and systematic long-term improvement strategies for long-term sustainability and increased resilience.

Screening potential polyhydroxyalkanoate-producing bacteria from wastewater sludge.

We applied fluorescence staining of Nile red, polymerase chain reaction (PCR), and carbon substrate utilization and pressure tolerance analysis to execute three-stage screening for potential polyhydroxyalkanoate (PHA) producers in the sludge samples of 21 large-scale wastewater treatment plants of city and industrial parks in Taiwan area. Total 35,429 colonies were grown on 196 plates, the screened 30 strains were subjected to 16S rRNA analysis, and 18 identified genera belonged to Proteobacteria (67%), Firmicutes (17%), and Actinomycetota (16%). The PHA accumulation results revealed that nine genera (50% of 18 screened) produced PHAs by limiting the nitrogen source and excess single carbon sources of glucose in an aerobic status. The PHA accumulation percentage was 1.44-58.77% at dry cell weight, and the theoretical yield from glucose was 0.52-58.76%. Our results indicate that our triple-screening method is promising for identifying a high biodiversity of PHA-accumulating bacteria from activated sludge for future industrial applications.

The Current Status, Energy Implications, and Governance of Urban Wastewater Treatment and Reuse: A System Analysis of the Beijing Case

Wastewater treatment and reuse are important means of addressing water scarcity and protecting the aquatic environment in urban areas. However, it comes at the cost of energy consumption and greenhouse gas emissions. However, the issues of governance and provincial-scale research have largely been ignored in current urban wastewater treatment and reuse studies. This paper summarizes the current status of 175 wastewater treatment plants (WWTPs) in Beijing, explores energy-intensive processes, energy consumption ratios, and the overall energy intensity of WWTPs, and maps the structure of urban wastewater treatment and reuse governance. The results indicate that most WWTPs in Beijing are medium or small in scale, treating wastewater at less than 200 thousand tons/day. Then, five energy-intensive subprocesses are identified, and their energy consumption ratios vary with treatment technologies and management factors, which calls for individual WWTP analysis and plant-specific strategies. The energy intensity of WWTPs in Beijing varies with treatment capacity and membrane bioreactor treatment technology used. Large-scale WWTPs employing MBR technology have a higher average energy intensity. Furthermore, the current coordination group and the four-layer policy system provide sufficient executive power and promote efficiency in departmental collaborations. Finally, inconsistent data, reductions in energy consumption, and the normalization of the governance structure are discussed, and policy suggestions are proposed.

Alga-based dairy wastewater treatment scheme: Candidates screening, process advancement, and economic analysis

The common means of wastewater pre-treatment is impractical in large-scale wastewater treatment plants (WWTP). There is still a lack of suitable microalgae to treat raw dairy wastewater (DWW) with high organic matter concentration. For screening more diverse microalgae to treat raw DWW, the growth characteristics and metabolite production of ten algal strains cultured in undiluted DWW were studied in this paper, among which three were able to tolerate excessive chemical oxygen demand (COD) concentration and yielded high biomass concentration. Under the condition of 25 ± 1 °C and 55 μmol/m2/s, the most suitable strain were Scenedesmus SDEC-13, Chlorella pyrenoidosa SDEC-35, and Chlorella vulgaris SDEC-34, all of which had biomass concentrations above 1.2 g/L and protein contents above 45%. Based on the feasibility of cultivating microalgae with raw DWW, an alternative alga-based WWTP strategy was provided for the first time. The most important modification was the construction of the photobioreactor (PBR) to replace hydrolytic upflow sludge bed (HUSB) reactor and remove anaerobic-aerobic (AO) pond. The dairy WWTP with a PBR unit (1.68 × 104 m3) will yield a biomass production of 1.44 × 106 kg/year while capturing 2.59 × 106 kg CO2/year. Through carbon comparison and economic analysis, we believe that the use of microalgal PBRs for the treatment of wastewater from dairy plants presents a cost-effective and environmentally friendly alternative for the future. And future research should focus on pilot scale photobioreactor in the natural environment and large-scale treatment of dairy wastewater.

Integrating Reactive Chlorine Species Generation with H2 Evolution in a Multifunctional Photoelectrochemical System for Low Operational Carbon Emissions Saline Sewage Treatment.

Conventional wastewater treatment plants (WWTPs) suffer from high carbon emissions and are inefficient in removing emerging organic pollutants (EOPs). Consequently, we have developed a low operational carbon emissions multifunctional photoelectrochemical (PEC) system for saline sewage treatment to simultaneously remove organic pollutants, ammonia, and bacteria, coupled with H2 evolution. A reduced BiVO4 (r-BiVO4) photoanode with enhanced PEC properties, ascribed to constructing sufficient oxygen vacancies and V4+ species, was synthesized for the aforementioned technique. The PEC/r-BiVO4 process could treat saline sewage to meet local WWTPs' discharge standard in 40 min at 2.0 V vs Ag/AgCl and completely degrade carbamazepine (one of EOPs), coupled with 633 μmol of H2 production; 93.29% reduction in operational carbon emissions and 77.82% decrease in direct emissions were achieved by the PEC/r-BiVO4 process compared with large-scale WWTPs, attributed to the restrained generation of CH4 and N2O. The PEC system activated chloride ions in sewage to generate numerous reactive chlorine species and facilitate •OH production, promoting contaminants removal. The PEC system exhibited operational feasibility at varying pH and total suspended solids concentrations and has outstanding reusability and stability, confirming its promising practical potential. This study proposed a novel PEC reaction for reducing operational carbon emissions from saline sewage treatment.

Modelling and prediction of the effect of operational parameters on the fate of contaminants of emerging concern in WWTPs

Wastewater treatment plants (WWTPs) provide a barrier against the discharge of contaminants of emerging concern (CECs) into the environment. The removal of CECs is highly WWTP-specific and the underlying mechanisms are still poorly understood, hampering the optimization of biological treatment steps for their removal. To fill this knowledge gap, we assessed the influence of four operational parameters of activated sludge biological treatment, namely total suspended solids, temperature, pH and redox conditions, on the sorption and biodegradation of four CECs under controlled laboratory conditions. Design of Experiments was used to better address the factors influencing CECs removal and interactions among operational parameters. The derived statistical models showed results in concordance with previous studies and indicated how sorption and biodegradation of the investigated CECs depend on most tested parameters and few of their interactions. The predictions of the developed models have been compared with literature values, indicating how the tested parameters are responsible for most of the variability of sorption, while they could not reliably generalize biodegradation rates. The developed models were also implemented as an extension of a mechanistic biological treatment model, successfully describing the dynamic behaviour of a large-scale WWTP, which was observed during a three-day continuous monitoring campaign. Compared to a traditional modelling approach, the one including the developed models showed on average almost a three-fold uncertainty reduction, favouring its use to aid WWTP managers and regulators for improved assessment of CEC fate and removal. Finally, the models highlighted that, while higher temperatures and solids concentrations generically favoured CECs removal, removal efficiency vary significantly due to operational parameters and no globally optimum conditions for CECs removal exist. The use of these models opens the door to the combined dynamic management of both traditional contaminants and CECs in WWTPs.

Smart instrumental Odour Monitoring Station for the efficient odour emission management and control in wastewater treatment plants

Odour emission assessment in wastewater treatment plants (WWTP) is a key aspect that needs to be improved in the plant management to avoid complaints and guarantee a sustainable environment. The research presents a smart instrumental odour monitoring station (SiOMS) composed of an advanced instrumental odour monitoring system (IOMS) integrated with other measurement units, for the continuous characterization and measurement of the odour emissions, with the aim of managing the potential odour annoyance causes in real time, in order to avoid negative effects. The application and on-site validation procedure of the trained IOMS is discussed. Experimental studies have been conducted at a large-scale WWTP. Fingerprint analysis has been applied to analyze and identify the principal gaseous compounds responsible for the odour annoyance. The artificial neural network has been adopted to elaborate and dynamically update the odour monitoring classification and quantification models (OMMs) of the IOMS. The results highlight the usefulness of a real-time measurement and control system to provide continuous and different information to the plant operators, thus allowing the identification of the odour sources and the most appropriate mitigation actions to be implemented. The paper provides important information for WWTP operators, as well as for the regulating bodies, authorities, manufacturers and end-users of odour monitoring systems involved in environmental odour impact management.

Redox environment inducing strategy for enhancing biological phosphorus removal in a full-scale municipal wastewater treatment plant

Phosphorus removal from wastewater is crucial for limiting water eutrophication. However, due to improper operating conditions, tremendous phosphorus removal chemicals addition or low C/N ratio in the influent, biological phosphorus removal (BPR) has been regarded as a difficult issue in real full-scale municipal wastewater treatment plants (WWTPs), especially in the membrane bioreactor (MBR) plants with long sludge retention time. Therefore, application of effective enhanced biological phosphorus removal (EBPR) technologies in WWTPs is of great significance to improve the BPR efficiency, reduce chemicals consumption and operating cost. Favorable redox environment, characterized by ORP is important for the growth and enrichment of phosphate-accumulating organisms (PAO), which is mainly responsible for BPR. In this study, a redox environment inducing strategy for EBPR was taken in a real full-scale MBR-WWTP (treatment capacity of 2 × 106 m3/d). The results indicated that the phosphorus release and uptake rate were rather low in the biochemical tank, which reflected the low phosphate-accumulating organisms (PAO) activity and poor BPR efficiency. This problem may be due to inappropriate redox environment, inhibition by phosphorus removal chemicals or low C/N in the influent. After EBPR, the contribution percentage of BPR increased by up to 18% and chemicals dosage reduced by up to 60%. Furthermore, the relative abundance of PAO (Dechloromonas, Thauera and OLB12) was significantly increased in anaerobic tank (4.62, 1.33 and 1.18%), in anoxic tank (4.85, 1.93 and 0.88%) and in oxic tank (5.17, 1.71 and 0.84%) for appropriate redox environment and relieved inhibition by less dosage of phosphorus removal chemicals. In addition, bacteria related to COD degradation and nitrogen removal were also enriched. The simultaneous enhancement of biological phosphorus removal, carbon removal and nitrogen removal was successfully realized in this research, which indicated that the strategy was effective in real large-scale WWTPs.

Predictive modeling of the primary settling tanks based on artificial neural networks for estimating TSS and COD as typical effluent parameters.

A predictive model based on artificial neural networks (ANNs) for modeling primary settling tanks' (PSTs) behavior in wastewater treatment plants was developed in this study. Two separate ANNs were built using input data, raw wastewater characteristics, and operating conditions. The output data from the ANNs consisted of the total suspended solids (TSS) concentration and chemical oxygen demand (COD) as predictions of PSTs' typical effluent parameters. Data from a large-scale wastewater treatment plant was used to illustrate the applicability of the predictive model proposal. The ANNs model showed a high prediction accuracy during the training phase. Comparisons with available empirical and statistical models suggested that the ANNs model provides accurate estimations. Also, the ANNs were tested using new experimental data to verify their reproducibility under actual operating conditions. The predicted values were calculated with satisfactory results, having an average absolute deviation of <20%. The model could be adapted to any large-scale wastewater plant to monitor and control the operation of primary settling tanks, taking advantage of the ANNs' learning capacity.

Economic and ecological assessment of photovoltaic systems for wastewater treatment plants in China

The number of wastewater treatment plants (WWTPs) in China is fast growing as the country's urbanization accelerates. WWTPs, part of the high-energy-consumption industry, must use a lot of energy in wastewater treatment. PV projects in WWTPs are viable solutions for energy conservation, but PV project investors, WWTP owners, and government authorities need to conduct rigorous economic and ecological assessments. This article examines the PV potential, financial feasibility, energy savings, and emission reduction effect of large-scale WWTPs in China using the cable-supported system. Furthermore, China's total PV power potential for urban WWTPs has been assessed at 5.6 GW for the first time. According to economic feasibility analysis, 26 of the 31 WWTP-PV projects in China's various regions are economically viable. Moreover, the WWTP-PV projects can assist WWTP in reducing carbon emissions by 10%–40%. Further sensitivity analysis reveals that practically all WWTP-PV projects will be viable in the future, assuming that certain solar resource requirements are met, and appropriate investment strategies are implemented.

A comprehensive evaluation of process kinetics: A plant-wide approach for nutrient removal and biogas production

The present study investigated the deviations of operational parameters of a large-scale wastewater treatment plant (WWTP) from design basis through combining dedicated batch experiments with full-scale dynamic modeling results. The long-term process performance of a full-scale biological nutrient removal (BNR) plant equipped with anaerobic sludge digestion system was monitored to evaluate the process kinetics of both carbon and nutrient removal and anaerobic sludge digestion. In this respect, plant-specific characterization; chemical oxygen demand (COD) fractionation, batch kinetic studies and sludge settling velocity tests were performed together with plant-wide SUMO model simulation. Results showed that nitrification and anaerobic hydrolysis were found to be 30% and 70% lower than literature values, respectively. The anaerobic digestion test coupled with plant-wide model calibration showed that anaerobic hydrolysis was the bottleneck in biogas production. Correspondingly, performance of the anaerobic digestion in the full-scale plant was poor as low biogas production yields were observed. In addition, the degradation rate via anaerobic hydrolysis of primary sludge was found to be higher (∼2-2.5) compared to anaerobic hydrolysis of biological sludge. The results of this study provide insight into model-based experimental characterization as well as plant-wide modeling approach. Coupling model-based batch experiments with full-scale modeling enabled to reduce the number of kinetic parameters to be fine-tuned. Moreover, the information gathered from kinetic batch tests to the simulation platform yielded a satisfying prediction of long-term performance of the plant operation.

The structure of microbial communities of activated sludge of large-scale wastewater treatment plants in the city of Moscow

Microbial communities in wastewater treatment plants (WWTPs) play a key role in water purification. Microbial communities of activated sludge (AS) vary extensively based on plant operating technology, influent characteristics and WWTP capacity. In this study we performed 16S rRNA gene profiling of AS at nine large-scale WWTPs responsible for the treatment of municipal sewage from the city of Moscow, Russia. Two plants employed conventional aerobic process, one plant—nitrification/denitrification technology, and six plants were operated with the University of Cape Town (UCT) anaerobic/anoxic/oxic process. Microbial communities were impacted by the technology and dominated by the Proteobacteria, Bacteroidota and Actinobacteriota. WWTPs employing the UCT process enabled efficient removal of not only organic matter, but also nitrogen and phosphorus, consistently with the high content of ammonia-oxidizing Nitrosomonas sp. and phosphate-accumulating bacteria. The latter group was represented by Candidatus Accumulibacter, Tetrasphaera sp. and denitrifiers. Co-occurrence network analysis provided information on key hub microorganisms in AS, which may be targeted for manipulating the AS stability and performance. Comparison of AS communities from WWTPs in Moscow and worldwide revealed that Moscow samples clustered together indicating that influent characteristics, related to social, cultural and environmental factors, could be more important than a plant operating technology.

Distribution of antibiotic resistance genes and their association with bacteria and viruses in decentralized sewage treatment facilities.

The distribution of antibiotic resistance genes (ARGs) has been intensively studied in large-scale wastewater treatment plants and livestock sources. However, small-scale decentralized sewage treatment facilities must also be explored due to their possible direct exposure to residents. In this study, six wastewater treatment facilities in developed rural areas in eastern China were investigated to understand their risks of spreading ARGs. Using metagenomics and network analysis tools, ARGs and bacterial and viral communities were identified in the influent (INF) and effluent (EFF) samples. The dominant ARGs belonged to the bacitracin class, which are different from most of municipal wastewater treatment plants (WWTPs). The dominant hosts of ARGs are Acidovorax in bacterial communities and Prymnesiovirus in viral communities. Furthermore, a positive relationship was found between ARGs and phages. The ARGs significantly correlated with phages were all hosted by specific genera of bacteria, indicating that phages had contributed to the ARG’s proliferation in sewage treatment facilities. Paying significant concern on the possible enhanced risks caused by bacteria, viruses and their related ARGs in decentralized sewage treatment facilities is necessary.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s11783-021-1469-4 and is accessible for authorized users.

Life cycle assessment of prospective sewage sludge treatment paths in Germany

Due to the amendment of the sewage sludge ordinance, both a thermal post-treatment and a phosphorous recovery from sewage sludge will become mandatory for large-scale wastewater treatment plants in Germany. This study analyzed four prospective treatment paths for sewage sludge by means of life cycle assessment. In the realm of a gate-to-cradle approach, environmental impacts were quantified for all compartments of the ReCiPe Midpoint (H) 2016 method.The spreading of digested sludge on agricultural soils was considered as the base case (system: AD + spreading). It was compared to the centralized incineration of sludge (system: AD + I), a decentralized hydrothermal carbonization followed by centralized incineration (system: AD + HTC + I) and a decentralized pyrolysis of sludge followed by centralized incineration (system: AD + P + I). For all cases, phosphorous recovery from the ash was included. A comparative evaluation showed that AD + spreading resulted in least environmental impacts in most categories but was subject to a high local immission potential due to sewage sludge spreading. It was found to be only justifiable, if toxicity and eutrophication were not compromised. Alternatively, a thermal post-treatment step is required. Hereby, AD + I and AD + HTC + I showed the overall least environmental impacts, while AD + P + I was characterized by similar or higher environmental impacts throughout all impact categories.Alongside the comparative analysis, a hotspot analysis was carried out and mitigation potentials were identified. For all thermochemical post-treatment paths, it was derived that (i) the share of fossil external energy must be kept to a minimum, (ii) primary or secondary measures to control N2O emissions during the incineration and pyrolysis should be implemented and (iii) the technological approach to recover phosphorous must be carefully selected.

Investigation of the Prevalence of Antibiotic Resistance Genes According to the Wastewater Treatment Scale Using Metagenomic Analysis.

Although extensive efforts have been made to investigate the dynamics of the occurrence and abundance of antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs), understanding the acquisition of antibiotic resistance based on the WWTP scale and the potential effects on WWTPs is of relatively less interest. In this study, metagenomic analysis was carried out to investigate whether the WWTP scale could be affected by the prevalence and persistence of ARGs and mobile genetic elements (MGEs). As a result, 152 ARG subtypes were identified in small-scale WWTP samples, while 234 ARG subtypes were identified in large-scale WWTP samples. Among the detectable ARGs, multidrug, MLS (macrolide–lincosamide–streptogramin), sulfonamide, and tetracycline resistance genes had the highest abundance, and large and small WWTPs had similar composition characteristics of ARGs. In MGE analysis, plasmids and integrons were 1.5–2.0-fold more abundant in large-scale WWTPs than in small-scale WWTPs. The profile of bacteria at the phylum level showed that Proteobacteria and Actinobacteria were the most dominant bacteria, representing approximately 70% across large- and small-scale WWTPs. Overall, the results of this study elucidate the different abundances and dissemination of ARGs between large- and small-scale WWTPs, which facilitates the development of next-generation engineered wastewater treatment systems.

What removals of pathogen indicators can be expected within large-scale wastewater treatment facilities in the context of wastewater reuse in Paris conurbation?

The fate of pathogen indicators (Escherichia coli - EC, intestinal enterococci - IE, RNA-F bacteriophages and spores of sulfite reducing bacteria - SSR) was extensively studied in Parisian large-scale wastewater treatment plants (WWTPs), based on conventional activated sludge, biofiltration or membrane bioreactor (MBR) processes. Between 14 and 87 campaigns were performed between 2014 and 2018 in five WWTPs. High removals of 3 log for both EC and IE, and lower removals of 1-2 log for SSR and RNA-F bacteriophages, were observed in conventional activated sludge and biofiltration WWTPs. The MBR WWTP achieves notably greater removals of 4.5-5.5 log for faecal bacteria and 3-4 log for SSR and RNA-F bacteriophages. This WWTP is the only one already in compliance with reuse standards, the other ones being non-compliant because of SSR and RNA-F bacteriophages. The implementation of a micro-grain activated carbon process would increase the WWTP removals of 0.8 log for faecal bacteria, due to particles retention, with no significant effect on both other pathogens. Ozonation (0.9-1.3 g O3/g dissolved organic carbon) or performic acid (0.8-1.2 ppm) would have greater benefits with additional removals of 1.5-2.5 log for EC, 1-2 log for IE and 0.5-1 log for SSR and RNA-F bacteriophages. Correlations between pathogen indicator removals and initial concentrations were found, as well as a significant decrease of RNA-F bacteriophage concentrations in Parisian raw wastewater, below 2 log. Thus, RNA-F bacteriophages could be a real issue to evaluate the compliance of Parisian wastewater with reuse. The time evolution of removals demonstrated that SSR is the most problematic parameter regarding reuse in conventional activated sludge and biofiltration WWTPs, as its initial concentration is high (5 log) but removals insufficient (<2 log). In contrast, removals of RNA-F bacteriophages greater than 2 log can be obtained within WWTPs completed or not with a tertiary treatment when the initial concentration in raw wastewater is sufficient. Correlations were also found between the removals of pathogen indicators and the removals of physico-chemical parameters, but they are not good enough to allow performance predictions.

Biomass-Derived Adsorbents for Dye and Heavy Metal Removal from Wastewater

Wastewater has a high concentration of dyes and heavy metals, which are the two most significant contaminants. Due to their high toxicity and vulnerability, they possess a potential threat to human health as well as the ecosystem. There are many ways to eliminate these pollutants from water but adsorption has attained much interest because of its low cost, easy application, and no secondary pollutants. Biomass is considered an ecological burden and a reason for the reduction in the earth’s carrying capacity. These materials may be used as cost-effective adsorbents to remove dyes and heavy metals from wastewater. This paper highlights recent advances made in dye and heavy metal adsorption in the last 10 years. The prime focus of this review paper is on the direct application of these biomasses without any chemical or physical alteration. The removal efficiencies and adsorption capabilities of different biomass-derived adsorbents for the removal of dyes and heavy metals from wastewater are summarised in this study. Additionally, the adsorption mechanisms underlying the removal of dyes and heavy metals using biomass-derived adsorbents have been discussed, with a focus on two kinetic models: pseudofirst-order and pseudosecond-order. Furthermore, the Langmuir and Freundlich isotherms were utilised to verify the experimental findings and to quantify the amount and degree of adsorption favorability. Based on what has been covered in the literature, the conclusion has been drawn. The future research needs are proposed in the area of biomass-derived adsorbent development, their modification for improved efficiencies, and application on large-scale wastewater treatment plants.