Municipal Wastewater Treatment Systems Research Articles

Generic and site-specific social life cycle assessment of municipal wastewater treatment systems in Spain: challenges and limitations of the method when applied to resource recovery systems

Abstract Purpose This work aims to provide insights on the application of social life cycle assessment (S-LCA) in evaluating the social impacts associated with municipal wastewater treatment (WWT). The study assesses the social risks and social performance of two municipal WWT systems in Catalonia, Spain: a conventional wastewater treatment plant (WWTP) (Reference System) and a novel system that recovers water and other valuable resources (Novel System). Methods S-LCA was conducted at Generic and Site-Specific levels using 1 m3 of wastewater treatment as the functional unit (FU). The Generic assessment was conducted via the Product Social Impact Life Cycle Assessment (PSILCA) database, while the Site-Specific assessment employed the Subcategory Assessment Method (SAM) with four-level reference scales to assess the social performance of the WWTP operator and its first-tier suppliers. Furthermore, activity variables were calculated based on organizations’ shares in the total costs per FU, and the Novel System’s multifunctionality was solved through economic allocation. Results were aggregated by (i) assigning equal weights to organizations and (ii) factoring in organizations’ weights and the allocation factor, leading to results per FU. Results and discussion The Generic analysis results indicated that the Novel System entailed fewer social risks than the Reference System. Most social risks in both systems occurred in the subcategories “Access to material resources,” “Fair salary,” “Freedom of association and collective bargaining,” “Contribution to economic development,” and “Corruption.” In the Site-Specific assessment, the Novel System presented better social performance than the Reference System per 1 m3 of wastewater treatment. The latter’s performance per FU did not meet the basic requirement in four out of eleven subcategories, mainly due to the performance and weight of a chemical supplier. Allocation greatly benefitted the Novel System’s results per FU compared to the results obtained when equal weights were applied. Conclusions Activity variables were used to connect organizations’ conduct with particular WWT systems, and multifunctionality was solved. This approach allowed for obtaining results per FU at both assessment levels. However, social performance was also evaluated by calculating the average social performance of each system without considering activity variables and the FU, leading to different results. The social performance of the Novel System per FU was satisfactory across all subcategories but required improvement in four subcategories based on the average results. Given the limitations of using activity variables and allocation in S-LCA, further research is necessary to appropriately evaluate and compare the social effects of novel resource recovery systems.

Comparative analysis of bioaerosol emissions: Seasonal dynamics and exposure risks in hospital vs. municipal wastewater treatment systems

Hospital wastewater is known to contain various pathogenic microorganisms and harmful substances. During the hospital wastewater treatment process, the bioaerosols released may encapsulate these pathogens, leading to human infection. This study undertook an investigation to compare the dispersion characteristics and seasonal variations of bioaerosols from hospital and municipal sewage. The results indicated that the airborne bacterial concentration from hospital sewage (119 ± 118 CFU/m3) was higher than municipal sewage (46 ± 19 CFU/m3), with the highest concentration observed in summer. The dominant bacterial genera present in bioaerosols from both sewages were alike, with the proportions varied by sewage types and the structure mainly influenced by seasonal factors. Bacteroides, Escherichia-Shigella and Streptococcus were identified as the most prevalent pathogenic genera in spring, summer and winter bioaerosols, respectively, while Pseudomonas and Acinetobacter were abundant in autumn. Although the non-carcinogenic risk associated with bioaerosols was low (<1), the presence of pathogenic species and their potential synergistic interactions elevated the overall exposure risk. The diffusion modeling results demonstrated that bioaerosol emissions from the surface of hospital sewage can reach up to 10570 CFU/m3 in summer and can spread more than 300 m downwind. The potential pathogenicity of bioaerosols was also highest in summer, which may pose a health hazard to populations located downwind. Therefore, the management and control of bioaerosols from sewage should be strengthened, especially in summer.

Reduction of organic contaminants from industrial effluent using the advanced oxidation process, chemical coagulation, and green nanotechnology

Municipal wastewater treatment systems use the chemical oxygen demand test (COD) to identify organic contaminants in industrial effluents that impede treatment due to their high concentration. This study reduced the COD levels in tannery wastewater using a multistage treatment process that included Fenton oxidation, chemical coagulation, and nanotechnology based on a synthetic soluble COD standard solution. At an acidic pH of 5, Fenton oxidation reduces the COD concentration by approximately 79%. It achieves this by combining 10 mL/L of H2O2 and 0.1 g/L of FeCl2. Furthermore, the author selected the FeCl3 coagulant for the coagulation process based on the best results of comparisons between different coagulants. At pH 8.5, the coagulation dose of 0.15 g/L achieved the maximum COD removal efficiency of approximately 56.7%. Finally, nano bimetallic Fe/Cu was used to complete the degradation and adsorption of the remaining organic pollutants. The XRD, SEM, and EDX analyses proved the formation of Fe/Cu nanoparticles. A dose of 0.09 g/L Fe/Cu NPs, 30 min of contact time, and a stirring rate of 200 rpm achieve a maximum removal efficiency of about 93% of COD at pH 7.5. The kinetics studies were analyzed using pseudo-first-order P.F.O., pseudo-second-order P.S.O., and intraparticle diffusion models. The P.S.O. showed the best fit among the kinetic models, with an R2 of 0.998. Finally, the authors recommended that technique for highly contaminated industrial effluents treatment for agriculture or industrial purposes.

Hybrid machine learning modeling of nitrogen removal from wastewater using gas-liquid-solid circulating fluidized bed riser

Municipal wastewater generally contains high amounts of nitrogen (N), approximately 23–28 mg/L of total Kjeldahl Nitrogen (TKN), which causes eutrophication and pollution of groundwater. This article reports the generation of empirical models for estimating the nitrogen removal efficacy of two outputs (NH4-N and NO3-N) from the anoxic riser of a highly efficient municipal wastewater treatment system involving a gas-liquid-solid circulating fluidized bed (GLSCFB) bioreactor. To identify the important variables and discard irrelevant ones, the ReliefF algorithm is applied initially. Out of 10 independent variables, this method indicates that only three, such as flow rate, total Kjeldahl Nitrogen (TKN), and downer effluent of NO3-N, are meaningful for anoxic nitrogen removal. Then, a hybrid Bayesian Optimization Algorithm and Support Vector Regression (BOA-SVR) is implemented, considering only the essential variables. In this regard, real-life laboratory data are utilized to develop the models. The BOA approach and k-fold cross-validation technique are explicitly applied to optimize the model's hyperparameters and avoid overfitting. The established models provided sufficiently accurate predictions via their comparisons to the experimental observations. Besides, the BOA-SVR model outperforms the classical multiple linear regression (MLR). The BOA-SVR models' forecasted results for both the predicted amount of NH4-N and NO3-N are favorably compared with the laboratory trials (R2> 99 %). A comprehensive evaluation is further conducted to validate the performance of this model by calculating the root mean square error, mean absolute percentage error, fractional bias, and computational efficiency. Gaussian white noise is used to add three distinct noise levels (20 %, 40 %, and 60 %) to the testing data to evaluate the model's robustness. Moreover, the plots of relative deviations and residuals were dispersed across the zero-reference line with moderate fluctuations. Sensitivity analysis indicated the relative importance of the three independent variables on the anoxic nitrogen removal in the order of influent TKN > downer effluent NO3-N >flowrate. Overall, the developed tool has substantial potential in modeling other convoluted processes.

Enhancing Sewage Sludge Treatment with Hydrothermal Processing: A Case Study of Adana City

As a byproduct of municipal wastewater treatment systems, sewage sludge has traditionally been treated in low-value applications such as landfilling, posing significant environmental risks due to its pollutant content. However, there is a growing interest in utilizing the energy potential of sewage sludge through thermochemical conversion methods. Among these methods, hydrothermal liquefaction (HTL) has come to the fore as a promising green approach, offering an environmentally friendly means of extracting bio-oils and biochemicals from sewage sludge. In this study, the HTL method, regarded as an innovative approach among sewage sludge treatment methods apart from incineration, pyrolysis, and landfilling, is comparatively investigated in terms of greenhouse gas (GHG) emissions alongside other methods. In particular, this study analyzes the projected amount and various characteristics of sewage sludge that could potentially be generated by 2030 for the city of Adana, which currently produces approximately 185 tons of sewage sludge per day. The findings indicate that without intervention, sludge production is projected to reach 68,897 tons per year by 2030. Moreover, this research demonstrates that the utilization of HTL for sludge treatment results in a reduction of emissions by approximately 7-fold compared with incineration of sewage sludge.

A simulation-based DEA approach for multiple criterion decision-making problems with uncertain mixed-criteria values

In ex-ante decision scenarios, predicting criterion values accurately is difficult for decision makers (DMs). Inconsiderable work is normally required for measuring criteria by uncertain random values or ordinal values. However, in the classical data envelopment analysis (DEA) model, criterion values are the constants that limit the application of the classical DEA model in ex-ante decision scenarios. This paper presents a simulation-based DEA approach, which captures random and ordinal criterion values by a simple and direct simulation-based approach. The approach includes three steps. In the first step, Monte Carlo simulation methods are used to convert uncertain random values or ordinal values into cardinal data. In the second step, we use traditional DEA methods to compute the efficiency score of decision-making units (DMUs). In the third step, we ranked all DMUs by calculating the DEA-efficient acceptability of each DMU in multiple simulations and then selected the optimal DMU. The proposed approach is illustrated by experimental examples and a case study of a municipal wastewater treatment system.

Study on the Start-Up Phase of the Stabilization Lagoons System for Municipal Wastewater Treatment

Study on the Start-Up Phase of the Stabilization Lagoons System for Municipal Wastewater Treatment

A Novel Tiled Amplicon Sequencing Assay Targeting the Tomato Brown Rugose Fruit Virus (ToBRFV) Genome Reveals Widespread Distribution in Municipal Wastewater Treatment Systems in the Province of Ontario, Canada.

Tomato Brown Rugose Fruit Virus (ToBRFV) is a plant pathogen that infects important Solanaceae crop species and can dramatically reduce tomato crop yields. The ToBRFV has rapidly spread around the globe due to its ability to escape detection by antiviral host genes which confer resistance to other tobamoviruses in tomato plants. The development of robust and reproducible methods for detecting viruses in the environment aids in the tracking and reduction of pathogen transmission. We detected ToBRFV in municipal wastewater influent (WWI) samples, likely due to its presence in human waste, demonstrating a widespread distribution of ToBRFV in WWI throughout Ontario, Canada. To aid in global ToBRFV surveillance efforts, we developed a tiled amplicon approach to sequence and track the evolution of ToBRFV genomes in municipal WWI. Our assay recovers 95.7% of the 6393 bp ToBRFV RefSeq genome, omitting the terminal 5' and 3' ends. We demonstrate that our sequencing assay is a robust, sensitive, and highly specific method for recovering ToBRFV genomes. Our ToBRFV assay was developed using existing ARTIC Network resources, including primer design, sequencing library prep, and read analysis. Additionally, we adapted our lineage abundance estimation tool, Alcov, to estimate the abundance of ToBRFV clades in samples.

Synergistic denitrification mechanism of domesticated aerobic denitrifying bacteria in low-temperature municipal wastewater treatment

To address the problems of low efficacy and low microbial activity in low-temperature municipal wastewater treatment, this study utilized an air-lift micro-pressure internal circulation integrated reactor (AMICIR). Through controlling the amount of aeration and dissolved oxygen (DO) in the reactor, AMICIR creates alternating aerobic and anaerobic environments, explores the enrichment conditions of aerobic denitrifying bacteria, examines the changes in pollutant removal efficiency and the characteristics of bacterial colony structure during the process of enrichment of aerobic denitrifying bacteria in the system, and reveals the mechanism of nitrogen removal by aerobic denitrifying bacteria cooperating with anaerobic denitrifying bacteria in the low-temperature municipal wastewater treatment system. Experimental results showed average removal rates of NH4+-N, chemical oxygen demand (COD), total phosphorus (TP), and total nitrogen (TN) reaching 93.85%, 89.30%, 92.75%, and 75.4%, respectively. The microorganisms secreted large amounts of proteins and polysaccharides, forming zoogloea and anaerobic microenvironments conducive to traditional denitrification reactions. IlluminaMiSeq sequencing analysis revealed the presence of anaerobic phyla. The system was enriched with a large number of microorganisms, and aerobic denitrifying bacteria (Flavobacterium, Rhodoferax, and Pseudomonas) were successfully cultured. Flavobacterium emerged as the dominant species, with relative abundance ranging from 18.56% to 22.60%. Functional gene prediction indicated high abundance of aerobic denitrification genes, such as napA. Aerobic denitrifying bacteria were successfully enriched in the system to improve nitrogen removal from municipal wastewater at low temperatures.

Factors affecting the enrichment of heterotrophic nitrifying aerobic denitrifying bacteria in municipal wastewater treatment systems and analysis of differences in nitrogen metabolism

In this study, a four-stage MPSR process was employed for the treatment of urban wastewater. Three different conditions were established by controlling dissolved oxygen (DO) concentration, organic load rate (OLR), and influent pH value to examine pollutant removal effects and the changes of the heterotrophic nitrification-aerobic denitrification (HN-AD) functional bacteria communities. The factors driving changes in the HN-AD bacterial community and differences in nitrogen metabolism were revealed in the urban wastewater treatment system. The results showed that by forming anoxic/aerobic alternate oxygen environments and increasing influent OLR and pH, various HN-AD bacteria (Pseudomonas, Aeromonas, Flavobacterium) were enriched in the system, leading to improved removal capacity for NH4+-N and TN. Under optimal condition, the removal rates of NH4+-N and TN were 94.0 % and 78.7 % respectively. The dominant species of HN-AD bacteria were influenced by OLR and pH. The HN-AD bacteria exhibited the capacity for heterotrophic nitrification and aerobic denitrification within the system. This study provides a technological basis for the application of HN-AD bacteria for wastewater treatment.

Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) enables effective phosphorus removal in a pilot-scale A-B stage shortcut nitrogen removal system for mainstream municipal wastewater treatment

While the adsorption/bio-oxidation (A/B) process has been widely studied for carbon capture and shortcut nitrogen (N) removal, its integration with enhanced biological phosphorus (P) removal (EBPR) has been considered challenging and thus unexplored. Here, full-scale pilot testing with an integrated system combining A-stage high-rate activated sludge with B-stage partial (de)nitrification/anammox and side-stream EBPR (HRAS-P(D)N/A-S2EBPR) was conducted treating real municipal wastewater. The results demonstrated that, despite the relatively low influent carbon load, the B-stage P(D)N-S2EBPR system could achieve effective P removal performance, with the carbon supplement and redirection of the A-stage sludge fermentate to the S2EBPR. The novel process configuration design enabled a system shift in carbon flux and distribution for efficient EBPR, and provided unique selective factors for ecological niche partitioning among different key functionally relevant microorganisms including polyphosphate accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs). The combined nitrite from B-stage to S2EBPR and aerobic-anoxic conditions in our HRAS-P(D)N/A-S2EBPR system promoted DPAOs for simultaneous internal carbon-driven denitrification via nitrite and P removal. 16S rRNA gene-based oligotyping analysis revealed high phylogenetic microdiversity within the Accumulibacter population and discovered coexistence of certain oligotypes of Accumulibacter and Competibacter correlated with efficient P removal. Single-cell Raman micro-spectroscopy-based phenotypic profiling showed high phenotypic microdiversity in the active PAO community and the involvement of unidentified PAOs and internal carbon-accumulating organisms that potentially played an important role in system performance. This is the first pilot study to demonstrate that the P(D)N-S2EBPR system could achieve shortcut N removal and influent carbon-independent EBPR simultaneously, and the results provided insights into the effects of incorporating S2EBPR into A/B process on metabolic activities, microbial ecology, and resulted system performance.

Integrated municipal wastewater treatment and lipid accumulation by a self-flocculating/floating microalga Limnothrix sp.

The present study evaluated the growth, self-flocculation, lipid content, and pollutants removal by Limnothrix sp. BASMWW-9 isolated from municipal wastewater treatment system and cultivated in municipal wastewater. The biomass yield and lipid content after 6 days of cultivation were 1.07 g dw/L and 27.34 %dw, respectively. In addition, its self-flocculating ability reached up to 90 % after harvesting time of 180 min. Moreover, COD,NH3-N, TN, and TP removalefficiencies were 71.65 %, 81.89 %, 74.64 %, and 80.16 %, respectively. The self-flocculation performance of Limnothrix sp. was greatly associated to its morphology and production of extracellular polymeric substances (EPS), with significant positive impact of the high calcium and magnesium content in municipal wastewater. Interestingly, blue light irradiation during harvest enhanced the aggregation and floc formation as a floating biomat, which was attributed to enhanced polysaccharides production. This study provides innovative harvest method for Limnothrix sp. BASMWW-9 cultivated in wastewater using blue light for enhanced lipid recovery.

Hydraulic retention time optimization achieved unexpectedly high nitrogen removal rate in pilot-scale anaerobic/aerobic/anoxic system for low-strength municipal wastewater treatment

Applications of post-denitrification processes are subjected to low reaction rates caused by a lack of carbon resources. To offer a solution for reaction rate promotion, this research found a pilot-scale anaerobic/aerobic/anoxic bioreactor treating 55–120 m3/d low-strength municipal wastewater for 273 days. A short hydraulic retention time (HRT, 5–6 h) and a high nitrogen removal rate (63.2 ± 9.3 g-N/m3·d) were achieved using HRT optimization. The effluent total nitrogen concentration was maintained at 5.8 ± 1.4 mg/L while operating at a high nitrogen loading rate of 86.2 ± 12.8 g-N/m3·d. The short aeration (1.25–1.5 h) minimized the Glycogen loss. The endogenous denitrification rate increased to above 1.0 mg/(g-VSS·h). The functional genus Ca. Competibacter enriched to 2.3 %, guaranteeing the efficient post-denitrification process. Dechloromonas rose to 1.1 %, aiding in the synchronous phosphorus removal. These findings offered fresh insights into AOA processes to achieve energy/cost-saving wastewater treatment.

Efficient nitrogen removal from municipal wastewater by an autotrophic-heterotrophic coupled anammox system: The up-regulation of key functional genes

The metabolic pathways based on key functional genes were innovatively revealed in the autotrophic-heterotrophic coupled anammox system for real municipal wastewater treatment. The nitrogen removal performance of the system was stabilized at 88.40 ± 3.39 % during the treatment of real municipal wastewater. The relative abundances of the nitrification functional genes ammonia oxidase (amoA/B/C), hydroxylamine oxidoreductase (hao), and nitrite oxidoreductases (nxrA/B) were increased by 1.2–2.4 times, and these three nitrification functional genes were mostly contributed by Nitrospira that dominated the efficient nitrification of the system. The relative abundance of anammox bacteria Candidatus Brocadia augmented from 0.35 % to 0.75 %, accompanied with the increased expression of hydrazine synthase (hzs) and hydrazine dehydrogenase (hdh), resulting in the major role of anammox (81.24 %) for nitrogen removal. The expression enhancement of the functional genes nitrite reductase (narG/H, napA/B) that promoted partial denitrification (PD) of the system weakened the adverse effects of the sharp decline in the population of PD microbe Thauera (from 5.7 % to 2.2 %). The metabolic module analysis indicated that the carbon metabolism pathways of the system mainly included CO2 fixation and organic carbon metabolism, and the stable enrichment of autotrophic bacteria ensured stable CO2 fixation. Furthermore, the enhanced expression of the glucokinases (glk, GCK, HK, ppgk) and the abundant pyruvate kinase (PK) achieved stable hydrolysis ability of organic carbon metabolism function of the system. This study offers research basics to practical application of the mainstream anammox process.

The responding mechanism of indigenous bacteria in municipal wastewater inoculated with different concentrations of exogenous microalgae

Indigenous bacteria popularly exist in real wastewater. Therefore, the potential interaction between bacteria and microalgae is inevitable in microalgae-based wastewater treatment systems. It is likely to affect the performance of systems. Accordingly, the characteristics of indigenous bacteria is worth serious concerning. Here we investigated the response of indigenous bacterial communities to variant inoculum concentrations of Chlorococcum sp. GD in municipal wastewater treatment systems. The removal efficiency of COD, ammonium and total phosphorus were 92.50%–95.55%, 98.00%–98.69%, and 67.80%–84.72%, respectively. The bacterial community responded differently to different microalgal inoculum concentrations, which was mainly affected by microalgal number, ammonium and nitrate. Besides, there were differential co-occurrence patterns and carbon and nitrogen metabolic function of indigenous bacterial communities. All these results indicated that bacterial communities responded significantly to environmental changes caused by the change of microalgal inoculum concentrations. The response of bacterial communities to different microalgal inoculum concentrations was beneficial for forming a stable symbiotic community of both microalgae and bacteria to remove pollutants in wastewater.

Cross-media migration behavior of antibiotic resistance genes (ARGs) from municipal wastewater treatment systems (MWTSs): Fugitive characteristics, sharing mechanisms, and aerosolization behavior

The municipal wastewater treatment systems (MWTSs) are the leading enrichment site of antibiotic resistance genes (ARGs), the occurrence of which in sewage and sludge significantly influences the ARGs burden of aerosols. However, the migration behavior and impact factors of ARGs in gas–liquid–solid phase are still unclear. This study collected gas (aerosol), liquid (sewage), and solid (sludge) samples from three MWTSs to explore the cross-media transport behavior of ARGs. The results showed that the main ARGs detected in the solid–gas-liquid phase were consistent, constituting the central antibiotic resistance system of MWTSs. Multidrug resistance genes dominated cross-media transmission (average relative abundance is 42.01 %). Aminocoumarin, fluoroquinolone, and aminoglycoside resistance genes (aerosolization index of 1.260, 1.329, and 1.609, respectively) were prone to migrating from the liquid to gas phase, resulting in long-distance transmission. Environmental factors (mainly temperature and wind speed), water quality index (mainly COD), and heavy metals may be the key factors affecting the trans-media migration of ARGs between the liquid, gas, and solid phase. Based on partial least squares path modeling (PLS-PM), the migration of ARGs in gas phase is primarily influenced by ARGs' aerosolization potential in liquid and solid phase, while heavy metals indirectly influences almost all categories of ARGs. Impact factors aggravated the migration of ARGs in MWTSs through co-selection pressure. This study clarified the key pathways and impact factors that form the cross-media migration behavior of ARGs, which can more specifically control ARGs pollution from different media.

Techno-economic and environmental assessment of different municipal wastewater treatment systems

A comprehensive economic evaluation and environmental assessment of wastewater treatment plants (WWTPs) is a precondition to ensure long-term economic, environmental, and social sustainability. In this study, a techno-economic feasibility analysis for different modern compact municipal wastewater treatment technologies including aerobic granular sludge (AGS), high rate activated sludge (HRAS) coupled with membrane bioreactor (MBR), HRAS + MBR process, was conducted. The findings were comparatively evaluated with the conventional anaerobic/anoxic/aerobic (A2O) process. Capital, operation and maintenance (O&M) costs for each system were investigated in detail. Environmental benefits for each system were assessed and an energy balance for each system was conducted. 21 % lower energy consumption was observed in the AGS system in comparison to the A2O system. This finding might be associated with the absence of mixers, return sludge pumping and recirculation of wastewater for nitrogen removal in AGS system. The unit total cost was found to be 0.113 €/m3, 0.091 €/m3, and 0.195 €/m3 for A2O process, AGS process, and HRAS + MBR process in order. Based on the energy balance and economic analysis, AGS system was found to have lower net energy consumption and total cost compared to A2O process and HRAS + MBR process. The results obtained from this study are of vital importance in the economic evaluation of the projected large new WWTPs.

Evaluating the potential of off-line methodologies to determine sludge filterability from different municipal wastewater treatment systems

This study aimed to evaluate the capability of different methodologies for determining sludge filterability and estimate filtration resistance during real filtration processes. Three filterability methods were applied during this study: capillary suction time (CST), time to filter (TTF), and specific resistance to filtration (SRF). These methods were evaluated using three different sludge sources: aerobic activated sludge, supernatant from a primary settler further concentrated by ultrafiltration membranes (PSE), and digestate from the anaerobic co-digestion of microalgae and primary sludge. These sludge sources were taken from systems treating municipal wastewater entering to a full-scale wastewater treatment facility. The capability of CST, TTF and SRF to estimate total suspended solids (TSS) and soluble microbial products (SMP) concentrations was also assessed, while validating the results obtained with the real filtration process of the operated membrane-based systems. The results suggested that both TSS and SMP concentrations significantly affect filterability. However, each sludge filterability was mainly dominated by one of these parameters (TSS or SMP), being the biological sludge more influenced by the SMP content, while the PSE filterability was mainly controlled by the TSS concentration. SRF method resulted in poor correlations between filterability and TSS and SMP concentrations, especially regarding SMP. CST method resulted in good correlations for all treated sludge regardless the TSS and SMP concentration. However, when treating sludge without an important biological activity (e.g. PSE), TTF method was identified as the best option due to its better correlation with the experimentally determined sludge filtration resistance.

Ultra-high anammox-based nitrogen removal contribution and robust bacterial abundance in a pure-biofilm anoxic/oxic system for real municipal wastewater treatment

For municipal wastewater treatment via partial-denitrification/anammox (PD/A) in the anoxic zone, the primary challenge is effective enrichment of anaerobic ammonium oxidation (anammox) bacteria with a stable autotrophic nitrogen removal performance. This long-term study investigated a pure-biofilm anoxic/oxic reactor using real municipal wastewater with an ammonia concentration of 49.1 ± 3.6 mg N/L, achieving a total inorganic nitrogen concentration of 11.2 ± 3.5 mg N/L in the effluent, resulting in a removal efficiency of 77.4 ± 7.2%. Driven by partial denitrification, the anammox contribution to total nitrogen removal represented an ultra-high level over 55%, and was considerable in the first anoxic zone. Candidatus Brocadia, the only anammox genus detected by 16S rRNA gene sequencing, reached robust abundances of 5.46, 6.49 and 5.79% in the three sequentially connected anoxic zones. Metagenomic sequencing further identified that the main species was Ca. Brocadia sapporoensis, which is inhibited by nitrite but not by acetate, supporting its high-level enrichment under acetate conditions in the anoxic zone. Batch tests indicate that heterotrophic denitrification activity decreased while anammox activity increased along the anoxic zones, and that excessive heterotrophic denitrifying activity was not conducive to increasing the anammox contribution. This study achieved robust anammox bacterial abundance using a pure-biofilm system, shedding fresh light on the application of mainstream anammox in municipal wastewater treatment.

New concept regarding the selection of sewerage systems and natural treatment of municipal wastewaters

The article contains a review of methods and procedures of the municipal wastewater treatment, with the discussion of their specifics. A new concept is proposed related to the selection of municipal sewerage and wastewater treatment systems, considering the local/decentralized, semicentralized or centralized systems, especially those suitable to rural and suburban localities, in dependence on the advantages and disadvantages of these systems and local specifics. The concept of phytofilters is proposed for the biological treatment of wastewater in small towns. This technology is simple, inexpensive and requires relatively little maintenance. Biological ponds in the Republic of Moldova have proven to be very suitable for advanced wastewater treatment, being a cheap and natural purification system with a good potential for implementation. When choosing a sewer system, priority must be given to its functionality and practical considerations.