Tertiary Wastewater Treatment Research Articles

Elemental sulfur–siderite composite filler empowers sustainable tertiary treatment of municipal wastewater even at an ultra-low temperature of 7.3 °C

Elemental sulfur–siderite composite filler empowers sustainable tertiary treatment of municipal wastewater even at an ultra-low temperature of 7.3 °C

Native Microalgae-Bacteria Consortia: A Sustainable Approach for Effective Urban Wastewater Bioremediation and Disinfection.

Urban wastewater is a significant by-product of human activities. Conventional urban wastewater treatment plants have limitations in their treatment, mainly concerning the low removal efficiency of conventional and emerging contaminants. Discharged wastewater also contains harmful microorganisms, posing risks to public health, especially by spreading antibiotic-resistant bacteria and genes. Therefore, this study assesses the potential of a native microalgae-bacteria system (MBS) for urban wastewater bioremediation and disinfection, targeting NH4+-N and PO43--P removal, coliform reduction, and antibiotic resistance gene mitigation. The MBS showed promising results, including a high specific growth rate (0.651 ± 0.155 d-1) and a significant average removal rate of NH4+-N and PO43--P (9.05 ± 1.24 mg L-1 d-1 and 0.79 ± 0.06 mg L-1 d-1, respectively). Microalgae-induced pH increase rapidly reduces coliforms (r > 0.9), including Escherichia coli, within 3 to 6 days. Notably, the prevalence of intI1 and the antibiotic resistance genes sul1 and blaTEM are significantly diminished, presenting the MBS as a sustainable approach for tertiary wastewater treatment to combat eutrophication and reduce waterborne disease risks and antibiotic resistance spread.

Nature-based solutions for antibiotics and antimicrobial resistance removal in tertiary wastewater treatment: Microbiological composition and risk assessment

This field-scale study evaluates the seasonal effectiveness of employing nature-based solutions (NBSs), particularly surface flow and horizontal subsurface flow constructed wetland configurations, as tertiary treatment technologies for the removal of antibiotics (ABs) and antibiotic resistance genes (ARGs) compared to a conventional treatment involving UV and chlorination. Out of the 21 monitored ABs, 13 were detected in the influent of three tertiary wastewater treatments, with concentrations ranging from 2 to 1218 ng·L-1. The ARGs sul1 and dfrA1 exhibited concentrations ranging from 1 × 105 to 9 × 106 copies/100 mL. NBSs were better at reducing ABs (average 69 to 88 %) and ARGs (2–3 log units) compared to the conventional tertiary system (average 36 to 39 % and no removal to 2 log units) in both seasons. Taxonomic compositions in influent water samples shifted from wastewater-impacted communities (Actinomycetota and Firmicutes) to a combination of plant rhizosphere-associated and river communities in NBS effluents (Alphaproteobacteria). In contrast, the conventional technology showed no substantial differences in community composition. Moreover, NBSs substantially reduced the ecotoxicological risk assessment (cumulative RQs). Furthermore, NBSs reduced the ecotoxicological risk (cumulative RQs) by an average of over 70 % across seasons, whereas the benchmark technology only achieved a 6 % reduction. In conclusion, NBSs present a robust alternative for minimizing the discharge of ABs and ARGs into surface water bodies.

Experimental soil matrix, vortex and oil skimming technology as a tertiary treatment of wastewater effluent

Abstract Water is a necessary resource that must be carefully managed. Hazardous chemicals are produced with increased industrial activities and contamination has been detrimental to both people and the environment. An experimental investigation was performed to evaluate the efficiency of vortex technology, soil matrices, and oil skimmer separately for combination as a tertiary wastewater treatment in the design of a phytoremediation system. The objective of the study is to evaluate the performance of each component in removing oil and grease, reducing the concentration of ammonia, nitrate, and phosphate; quality control measures for dissolved oxygen, total dissolved solids, and chemical oxygen demand. One-way ANOVA, kinetics analysis, and adoption isotherm analysis were applied to determine the significance of the parameters. Analysis of results for the oil skimmer exhibited an efficiency of 96% in removing oil and grease after 5 hours of treatment. The vortex technology results were fluctuating with percentage removal of nitrates at 11% while ammonia with an initial concentration of 5.24 mg/L was reduced to 4.12 mg/L. Phosphate decreased after treatment from an initial of 0.87 mg/L to 0.809 mg/L. The analysis of pollutant concentration in the soil matrix after a 5-day period indicated a greater efficiency compared to the vortex technology in the removal of ammonia and phosphate. The ammonia concentration decreased from 18.7 mg/L and 21.4 mg/L to <0.1 mg/L. Similarly, phosphate concentration decreased from 15.5 mg/L to 1.13 mg/L and from 32.5 mg/L to 0.948 mg/L. The research finding underscores the efficiency of the soil matrix in removing ammonia and phosphate but recommends the need for additional intervention to lower nitrate. Overall, the three technologies showed potential and greater efficiencies in mitigating wastewater streams resulting in a notable reduction in oil and pollutant concentrations.

Combination of ultrafiltration, activated carbon and disinfection as tertiary treatment of urban wastewater for reuse in agriculture

In the present study, three ceramic ultrafiltration (UF) membranes UF1 (20nm), UF2 (50nm) and UF3 (100nm) were optimized using the Box-Behnken design (BBD) of response surface methodology (RSM) to determine the most adaptable membrane for reuse. The effectiveness of membranes was based on the retention capacity of chemical oxygen demand (COD), biochemical oxygen demand at 5 days (BOD5) and total suspended solids (TSS) as a function of transmembrane pressure (TMP), circulation velocity (CV) and volume concentration factor (VCF). In addition, the study investigated membrane fouling based on the variation in permeate flux under different operational conditions. Among the tested membranes, UF1 demonstrated superior retention efficiency compared to UF2 and UF3. Using granular activated carbon (GAC) and powdered activated carbon (PAC) with UF1 significantly improved water quality. Moreover, the combination of UF1 separately with GAC and PAC reduced amoxicillin residues by 60% and 69%, respectively. Furthermore, the UF1 membrane alone showed significant removal of bacterial loads, exceeding 90% removal of total coliforms, fecal coliforms and Escherichia coli, as well as complete (100%) elimination of helminth eggs. The treatment process ended with disinfection by sodium hypochlorite (NaOCl), providing total (100%) elimination of all remaining bacteria in the water.

Combination of ultrafiltration, activated carbon and disinfection as tertiary treatment of urban wastewater for reuse in agriculture

Combination of ultrafiltration, activated carbon and disinfection as tertiary treatment of urban wastewater for reuse in agriculture

Horizontal-flow constructed wetlands by phytoremediation using vetiver grass, common reed, and canna lily as tertiary wastewater treatment for the reduction of pollutant concentrations of ammonia, phosphates, and nitrates

Abstract The discharge of untreated wastewater into rivers and water bodies poses significant environmental and public health risks. High concentrations of contaminants like heavy metals and pharmaceuticals disrupt rivers, exacerbating waterborne diseases, and leading to unsafe water in the Philippines. This study proposed the use of horizontal-flow constructed wetlands as a tertiary treatment method utilizing the plants: vetiver grass, common reed, and canna lily, to reduce pollutant concentrations in wastewater. This is to ensure compliance with water quality guidelines and general effluent standards under the Class SB Category, water suitable for fishery, tourist zones, and recreational activities. The research investigated the efficiency of phytoremediation beds in removing pollutants from wastewater under fixed hydraulic retention times. The efficiency of reducing pollutants and adsorption isotherms (Freundlich and Langmuir) were calculated to analyze the results of the sampling. Phytoremediation bed 1 demonstra ted efficient ammonia removal by 64.64%. Phytoremediation bed 2 was proficient in reducing nitrates at 83.85%, while phytoremediation bed 3 effectively reduced phosphate to an average of 26.26%, achieved after a 6-hour retention time. In addition, Freundlich adsorption isotherm was observable in most parameters in phytoremediation bed 1 such as ammonia as nitrogen, TDS, COD, and DO. Phytoremediation bed 3 exhibited the same adsorption isotherm on ammonia as nitrogen. Conclusively, the phytoremediation system met the Department of Environment and Natural Resources - Updated Water Quality Guidelines and General Effluent Standard (GES) for all parameters tested.

Performance evaluation of pilot phyto-vortex integrated system in the reduction of wastewater pollutants

Abstract Wastewater pollution remediation connects to goal 6 of the United Nations 17 Sustainable Development Goals (SDG) ensuring availability and sustainable management of water and sanitation for all. Conventional and advanced wastewater treatment are quite expensive to operate to fully comply with regulatory standards in the country. Phyto-vortex integrated system is an alternative tertiary wastewater treatment system that interfaces with an oil and grease skimmer and vortex technology, relying on green plants and a variety of soil substrates to remediate wastewater. The research evaluated the potential of the Phyto-vortex system and its performance in the reduction of domestic wastewater pollutants. Plants and soil substrates were selected via Analytic Hierarchy Process (AHP) using one-way sensitivity analysis. Common reed, Vetiver grass, and Canna Lily were planted in constructed reed beds with various soil matrices using substrates laid at different levels. The beds operate continuously as a horizontal subsurface flow treating 5 m3 of a sewage treatment effluent per day with 1-3 days hydraulic retention time (HRT). The vortex unit aerates the water for further removal of gaseous pollutants. Samples were taken at designated points for 18 weeks. Analysis of the results shows a maximum reduction of 92% for biochemical oxygen demand (BOD), 60 % for chemical oxygen demand(COD), and 70 % for total suspended solids (TSS). Concentration of identified heavy metals in the influent are within the regulatory standards except for a rise in zinc concentration which was 97% reduced in the system. The percentage reduction of pollutants varies each week with nitrates decreasing in the range of 50% to 99%, phosphates from 8% to 39.5%, and ammonia from 45.65% to 99%. Varying environmental conditions such as monsoon rains and extreme heat caused algal blooms and plant disease affecting the results. Lower temperatures and lower humidity favor a decrease in the levels of the pollutants while higher temperature, higher humidity favor an increase in the levels of Nitrates, Phosphates, and Ammonia. The overall results show an effective integrated system of phytoremediation coupled with a vortex unit in the reduction of wastewater pollutants.

Real-time ozonation monitoring and control in wastewater tertiary treatment: An ultraviolet-visible monitoring approach

To address the challenge of refractory organics removal in wastewater tertiary treatment, this study investigates the application of ozonation, coupled with Ultraviolet-Visible (UV–Vis) spectroscopy, for enhanced tertiary treatment in a wastewater treatment plant (WWTP) in Qingdao, China. Our approach integrates ozonation with real-time UV–Vis spectral monitoring to precisely control ozone dosing, targeting the effective degradation of persistent organics characterized by high Chemical Oxygen Demand (COD) values. Through the deployment of mathematical models, including Linear Discriminant Analysis (LDA) and Support Vector Machine (SVM), we developed a robust two-step ozone dosing control model. The model's efficacy is validated by its ability to predict the need for ozonation with a high degree of accuracy (94.29 % for LDA), significantly optimizing the ozonation process. Key findings indicate that this method not only achieves substantial removal of recalcitrant organics (with COD removal rates varying between 16 % and 71 %) but also offers considerable energy savings and operational cost reductions by adjusting ozone dosing in real-time based on water quality data. This study presents a novel, sustainable approach to improving WWTP efficiency and compliance, showcasing the potential of integrating advanced oxidation processes with precision monitoring techniques for environmental protection and water reuse initiatives.

Efficient treatment of secondary treated refinery wastewater using sand biofiltration: Removal of hazardous organic pollutants

This study explored the potential of sand biofiltration for tertiary treatment of real refinery wastewater. The biofilter (2 cm (I.D.) x 15 cm (L)) operated on secondary treated refinery wastewater at flow rate of 1 mL/min had empty bed contact time (EBCT) of 47.12 min for one circulation. Maximum reduction in COD after 4, 8 and 12 times recirculation was 25 %, 52 % and 56 %; while the TOC reduction was 33 %, 43 % and 51 %, respectively, after biofilm development over 30 days. Quantification using two dimensional gas chromatography – time of flight mass spectrometry (GCxGC-TOF MS) revealed that several of the identified target compounds could not be detected in the wastewater after 12 recirculations. After 8 times recirculation, most of the compounds showed very high removal efficiency. For biofiltration over the flow rate range 2–10 mL/min, the reduction in COD and NH4+-N ranged from 62–73 % and 78–86 %, respectively, after 8 times recirculation. The nitrite concentration first increased and subsequently decreased, while the nitrate concentration continuously increased with increase in the number of recirculations. Solid phase micro-extraction (SPME) analysis of the aqueous phase using GCxGC-TOF MS and a semi-quantitative approach indicated that the removal of predominant classes of compounds was greater than 95 % after 8 times recirculation, with maximum reduction occurring in the first pass through the biofilter. Assimilable organic carbon (AOC) reduction was 98 % after 8 times recirculation. Metagenomic analysis revealed that Proteobacteria was the most dominant phylum in the biofilter. Many known polynuclear aromatic hydrocarbon (PAH) degraders, such as Sphingomonadales, Burkholderiales, Rhodobacterales and Rhodospirillales, were found in the biofilter leading to high removal efficiency of hazardous organic pollutants.

Tertiary treatment of dairy wastewater applying a microalga-fungus consortium

ABSTRACT This paper aimed to apply filamentous fungi (Penicillium oxalicum and Cunninghamella echinulata), the microalga Tetradesmus obliquus and their co-culture in advanced treatment (tertiary treatment) of cheese whey. The bioremediation process was carried out in agitated flasks and bubble column bioreactors with different concentrations of chemical oxygen demand (COD) (223–1663 mg L − 1), total nitrogen (TN) (13–61 mg L − 1), and total phosphorus (TP) (3–26 mg L − 1). The results obtained in shaken flasks showed a superiority of the consortium compared to the systems with separated species. In this sense, the treatment was carried out in a bubble column reactor, and the consortium formed by the microalga and the fungus C. echinulata showed a greater efficiency (at a light intensity of 100 µmol m − 2 s − 1), promoting by the symbiosis to reach removal efficiencies of up to 93.7, 78.8 and 93.4% for COD, TN and TP, respectively; meeting Brazilian and European standards for discharge into water bodies. In addition, no pH adjustment was required during the co-culture treatment, demonstrating the buffering effect of using these two types of microorganisms. Therefore, the use of the consortium formed by T. obliquus and C. echinulata as a remediator was highly promising to promote the advanced treatment of cheese whey.

Performance of bioretention systems by umbrella plant (Cyperus alternifolius L.) and common reed (Phragmites australis) for removal of microplastics

Domestic wastewater is one of the main sources of microplastic (MP) contamination in aquatic environment; however, most wastewater treatment plants (WWTPs) have not been designed for the removal of MPs. In this study, the release rate of MPs in the treated water from a WWTP into the river was estimated to be approximately 105 × 103 pcs/capita/day. Thus, bioretention systems are designed as tertiary wastewater treatment systems to reduce the number of MPs in water resources. The objective of this study was to evaluate the performance of bioretention systems using the umbrella plant (Cyperus alternifolius L.) and common reed (Phragmites australis) for MP removal. After 17 weeks, MPs were found in the common reed bioretention system. The common reed root system and substrate influence the MP retention process to a greater extent through physical filtration, substrate ratio, plant roots, and biofilms on the roots. Additionally, the common reed root system played an important role in the removal of low-density MPs. The accumulation of MPs in roots and root hairs inevitably impacts plants. The results showed that the common reed at a 3:2:9 ratio (gravel: sand: soil) had the highest relative height growth rate (RHGR) (1.8mmcm-1 week-1). These results show that the HSFs–3 at a ratio of 3:2:9 was able to reduce the number of MPs, with an average removal efficiency of 62.89% and 95.45% for sizes >1000µm, 89.21% for sizes 500–1000µm, and 44.16% for sizes <500µm. The highest average microbeads removal efficiency was 95.24%. Our results suggest that plant bioretention using Horizontal Subsurface Flow system is an effective treatment for removing MPs from wastewater.

Integrated toxicity of secondary, tertiary, wetland effluents on human stem cells triggered by ERα and PPARγ agonists

Residual pollutants in discharged and reused water pose both direct and indirect human exposure. However, health effects caused by whole effluent remain largely unknown due to the lack of human relevant model for toxicity test. Effluents from four secondary wastewater treatment plants (SWTPs), a tertiary wastewater treatment plant (TWTP) and a constructed wetland (CW) were evaluated for the integrated toxicity of the organic extractions. Multiple-endpoint human mesenchymal stem cells (MSCs) assay was used as an in vitro model relevant to human health. The effluents caused cytotoxicity, oxidative stress and genotoxicity in MSCs. The osteogenic and neurogenic differentiation were inhibited and the adipogenic differentiation were stimulated by some of the effluent extractions. The SWTP, TWTP and CW treatments reduced integrated biomarker response (IBR) by 26.3 %, 17.5 % and 33.3 % respectively, where the IBR values of final CW (8.3) and TWTP (8.2) effluents were relatively lower than SWTPs (9.1). Among multiple biomarkers, the inhibition of osteogenesis was the least reduced by wastewater treatment. Besides, ozone disinfection in tertiary treatment increased cytotoxicity and differentiation effects suggesting the generation of toxic products. The mRNA expressions of estrogen receptor alpha (ERα) and peroxisome proliferator-activated receptor gamma (PPARγ) were significantly upregulated by effluents. The inhibitory effects of effluents on neural differentiation were mitigated after antagonizing ERα and PPARγ in the cells. It is suggested that ERα and PPARγ agonists in effluents were largely accountable for the impairment of stem cell differentiation. Besides, the concentrations of n-C29H60, o-cresol, fluorene and phenanthrene in the effluents were significantly correlated with the intergrated stem cell toxicity. The present study provided toxicological evidence for the relation between water contamination and human health, with an insight into the key toxicity drivers. The necessity for deep water treatment and the potential means were suggested for improving water quality.

Screening Disinfection Byproducts in Arid-Coastal Wastewater: A Workflow Using GC×GC-TOFMS, Passive Sampling, and NMF Deconvolution Algorithm.

Disinfection during tertiary municipal wastewater treatment is a necessary step to control the spread of pathogens; unfortunately, it also gives rise to numerous disinfection byproducts (DBPs), only a few of which are regulated because of the analytical challenges associated with the vast number of potential DBPs. This study utilized polydimethylsiloxane (PDMS) passive samplers, comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight mass spectrometry (TOFMS), and non-negative matrix factorization (NMF) spectral deconvolution for suspect screening of DBPs in treated wastewater. PDMS samplers were deployed upstream and downstream of the chlorination unit in a municipal wastewater treatment plant located in Abu Dhabi, and their extracts were analyzed using GC×GC-TOFMS. A workflow incorporating a multi-tiered, eight-filter screening process was developed, which successfully enabled the reliable isolation of 22 candidate DBPs from thousands of peaks. The NMF spectral deconvolution improved the match factor score of unknown mass spectra to the reference mass spectra available in the NIST library by 17% and facilitated the identification of seven additional DBPs. The close match of the first-dimension retention index data and the GC×GC elution patterns of DBPs, both predicted using the Abraham solvation model, with their respective experimental counterparts-with the measured data available in the NIST WebBook and the GC×GC elution patterns being those observed for the candidate peaks-significantly enhanced the accuracy of peak assignment. Isotopic pattern analysis revealed a close correspondence for 11 DBPs with clearly visible isotopologues in reference spectra, thereby further strengthening the confidence in the peak assignment of these DBPs. Brominated analogues were prevalent among the detected DBPs, possibly due to seawater intrusion. The fate, behavior, persistence, and toxicity of tentatively identified DBPs were assessed using EPI Suite™ and the CompTox Chemicals Dashboard. This revealed their significant toxicity to aquatic organisms, including developmental, mutagenic, and endocrine-disrupting effects in certain DBPs. Some DBPs also showed activity in various CompTox bioassays, implicating them in adverse molecular pathways. Additionally, 11 DBPs demonstrated high environmental persistence and resistance to biodegradation. This combined approach offers a powerful tool for future research and environmental monitoring, enabling accurate identification and assessment of DBPs and their potential risks.

Advanced Tertiary Wastewater Treatment for Enhanced Effluent Quality by Electrically Conducting Membranes Operated at Altered Potential for Simultaneous Mitigation of Scaling and Biofouling

Advanced Tertiary Wastewater Treatment for Enhanced Effluent Quality by Electrically Conducting Membranes Operated at Altered Potential for Simultaneous Mitigation of Scaling and Biofouling

Occurrence and Removal of Microplastics in Tertiary Wastewater Treatment Plants: A Case Study of Three Plants in Zhengzhou, China

Microplastics have been widely detected in wastewater treatment plants, but there is still a significant dearth of research data on the removal efficiency of microplastics in such plants. The present study focused on three wastewater treatment plants situated in Zhengzhou, China. On-site sampling and Raman spectrum detection techniques were employed to identify microplastics in both wastewater and sludge samples, while the removal efficiency of microplastics was quantified for each plant. Results showed that the abundance of microplastics in influent exhibited ranging from 147.5 ± 2.6 to 288.8 ± 11.8 n/L, while the range in sludge samples was from 12,024.7 ± 1737.0 n/kgdw to 20,818.4 ± 5662.0 n/kgdw. The removal efficiencies of microplastics in the three WWTPs ranged from 76.2% to 91.2%. The primary components of microplastics were generally identified as fibers ranging in size from 10 to 100 μm. The samples collectively exhibited a total of seven distinct colors, with the predominant proportion being transparent. Polypropylene was the polymer type with the highest proportion. The sludge in WWTPs plays a pivotal role in the accumulation of MPs from wastewater bodies, necessitating increased attention toward its proper disposal in future endeavors.

Scenario-based assessment of fecal pathogen sources affecting bathing water quality: novel treatment options to reduce norovirus and Campylobacter infection risks.

Wastewater discharge and runoff waters are significant sources of human and animal fecal microbes in surface waters. Human-derived fecal contamination of water is generally estimated to pose a greater risk to human health than animal fecal contamination, but animals may serve as reservoirs of zoonotic pathogens. In this study, quantitative microbial risk assessment (QMRA) tools were used to evaluate the hygienic impact of sewage effluents and runoff water from municipalities and animal farms on surface and bathing waters. The human-specific microbial source tracking (MST) marker HF183 was used to evaluate the dilution of fecal pathogens originating from the sewage effluent discharge to the downstream watershed. As novel risk management options, the efficiency of UV-LED disinfection and wetland treatment as well as biochar filtration was tested on-site for the contamination sources. According to the dilution pattern of the MST marker HF183, microbes from wastewater were diluted (2.3-3.7 log10) in the receiving waters. The scenario-based QMRA revealed, that the health risks posed by exposure to human-specific norovirus GII and zoonotic Campylobacter jejuni during the bathing events were evaluated. The risk for gastroenteritis was found to be elevated during wastewater contamination events, where especially norovirus GII infection risk increased (1-15 cases per day among 50 bathers) compared with the business as usual (BAU) situation (1 case per day). The noted C. jejuni infection risk was associated with animal farm contamination (1 case per day, versus 0.2-0.6 cases during BAU). Tertiary treatment of wastewater with wetland treatment and UV-LED disinfection effectively reduced the waterborne gastroenteritis risks associated with bathing. Based on the experiences from this study, a QMRA-based approach for health risk evaluations at bathing sites can be useful and is recommended for bathing site risk assessments in the future. In case of low pathogen numbers at the exposure sites, the MST marker HF183 could be used as a pathogen dilution coefficient for the watershed under evaluation. The full-scale implementation of novel tertiary treatment options at wastewater treatment plants (WWTPs) as well as on-site runoff water treatment options should be considered for infection risk management at locations where scenario-based QMRA implies elevated infection risks.

Effective discharge method of pulsed energy in industrial effluents by DBD and EHPD technique

This manuscript proposes a method for effective discharging method of pulsed energy in industrial effluents. The proposed approach is based on the dielectric barrier discharge (DBD) and Electro hydraulic Plasma Discharge (EHPD). The objective function of the proposed approach is minimizing the concentration of the ethylene blue (MB) dye in the industrial waste water. Using DBD and EHPD technique, treating such industrial effluents before mixing to the running water can effectively prevent polluting the water bodies and human health. It is one of the tertiary waste water treatments, which can also degrade biological substances. DBD technique is one of the advanced oxidation technique to de-color MB dye and the EHPD reactor is a strong and extremely efficient method for the degradation of MB. By then, the proposed model is implemented in the MATLAB platform and the implementation is calculated with the present procedure. The study concludes that the DBD and EHPD method outperforms other methods in terms of degradation efficiency. De-colorization of methylene blue (MB) took just 15 s using a 3 KV, 50μs pulse.

Enhancing urban wastewater treatment: Chlorella vulgaris performance in tertiary treatment and the impact of anaerobic digestate addition

The rising urban wastewater discharge into waterways resulted in harmful environmental effects. Microalgae can bioremediate wastewaters by removing contaminants such as nitrogen and phosphorus and can be rather tolerant to toxic compounds. Managing the anaerobic digestate resulting from sludge treatment in wastewater treatment plants faces some obstacles related to its high contaminant content. This work aims to study the ability of the microalga Chlorella vulgaris to perform the tertiary treatment of urban wastewater, assessing its growth, nutrient removal and the effect of the addition of digestate at different concentrations in this treatment phase. A secondary effluent was supplied with 1% (M1), 5% (M5) and 10% (M10) (v/v) of anaerobic digestate and used to culture microalgae. An assay using only secondary effluent was also performed (S). C. vulgaris grew successfully in all effluents except for the M10, and the highest specific growth rate was obtained in the M1 assay, 0.35 ± 0.01 d−1. Ammonium-nitrogen was completely removed in the S, M1 and M5 assays (>99.9%). Microalgae successfully removed phosphate-phosphorus from the tested effluents, achieving a negligible concentration in the M1 assay and a removal efficiency of 96.2 ± 0.2%, 51 ± 2%, and 43 ± 3% in S, M5 and M10, respectively. These results showed that microalgal cultures could efficiently remediate the secondary effluent and its mixture with 1% (v/v) of anaerobic digestate, achieving nutrient concentrations below the current legislation limits and the more restrictive limits predicted for future legislation.

Toxicity removal from contaminated water by constructed wetlands assessed using multiple biomarkers in human stem cell assays

Constructed wetlands (CWs) have been developed rapidly as a sustainable water treatment technique. However, the capability of CWs for remediating the contaminated water based on toxicity assessment remains largely unknown. Four surface flow CWs and two integrated surface-subsurface flow CWs, from five cities in central and eastern region of China were evaluated, concerning the adverse effects of effluents and the toxicity reduction efficiency. Human bone marrow mesenchymal stem cells (hBMSCs) were employed as a human relevant in vitro model. The influent extractions caused cytotoxicity in a dose-dependent manner. The non-cytotoxic dilutions of the influents enhanced the genotoxicity marker γ-H2AX and reactive oxygen species levels. In addition, the influent repressed the osteogenic and neurogenic differentiation, and stimulated the adipogenic differentiation. Cytotoxicity of the contaminated water was reduced by 54 %–86 % after treatment with CWs. CWs were effective to remove part of the sub-lethal effects, with lower reduction than cytotoxicity. The integrated biomarker response (IBR) value of the effluents from the six CWs is lower than that of four secondary and one tertiary wastewater treatment plants. The IBR of the six CWs influents were in the range of 8.6–10.6, with a reduction of 15–50 % after the pollution restoration in CWs. The two integrated surface-subsurface flow CWs achieved higher IBR removal than the four surface flow CWs, possibly due to improved treatment effects by the combined systems. Cytotoxic and genotoxic effects of polar fractions in the CW effluents were stronger than the medium-polar and the non-polar fractions. Besides, PPARγ agonists present in the effluents played crucial roles and ERα agonists may make modest contributions. The present study enhances understanding of the role of CWs in achieving safe wastewater reclamation and provides evidence for further improving toxicity reduction in CWs performance.