Tertiary Wastewater Treatment Research Articles

Impact of a natural disturbance on the performance and microbial communities in a full-scale constructed wetland for industrial wastewater treatment

Constructed Wetlands (CWs) are a cost-effective, versatile and sustainable choice for wastewater treatment. In these environments, microbial communities play a significant role in pollutant removal. However, little is known about how microbial communities in full-scale CWs contribute to maintaining water quality or how their dynamics change in response to pulse disturbances such as fire or freezes. Furthermore, few studies have examined the relationship between CW microbial community structure and performance in full-scale industrial operations. We characterized the water-column and leaf-litter layer microbial communities in a 110-acre free water surface CW that provides tertiary wastewater treatment to a plastics manufacturing plant. The CW’s sampling campaign was conducted over a 12-month period that included Winter Storm Uri, a 100-year freeze event. Analysis of 16S rRNA gene amplicon sequences revealed that the bacterial communities experienced a temporal shift. There was also a shift in microbial community structure between the influent and the first segment of the CW. However, no differences in microbial community structure were observed in the second segment of the CW. There was a negative association between microbial community diversity and chlorophyll a, as well as microbial community diversity and total suspended solids (TSS); demonstrating an increase in microbial biodiversity as water quality improved throughout the CW. Six months after the freeze, CW performance in terms of removal of water quality constituents began to return to former removal trends. Yet, there was still a significant difference in microbial community structure within the CW relative to the previous year. This suggests CW functional resilience despite a shift in microbial community structure in the wetland.

The role of coagulation on the fate of PFAS, brominated flame retardants and other trace contaminants in tertiary wastewater treatment for phosphorus control

Coagulant dosing to achieve low phosphorus concentrations in wastewater effluents may favour the removal of trace organics such as pharmaceuticals, plasticisers and flame retardants. Nevertheless, the behaviour of trace organics in coagulation processes is currently poorly understood because of the complex interactions between these compounds, the coagulants and dissolved organic matter (DOM). This study assessed the coagulation removal from synthetic secondary effluent of twenty-four compounds including ten PFAS and four brominated flame retardants. Testing involved two coagulants (alum, ferric chloride) and five DOM surrogates (resorcinol, benzoic acid, citric acid, tannic acid, humic acid); DOM surrogates had assorted molecular weights, structures, charges, and hydrophobicity. With coagulant doses of 14 mg Fe/L and 4 mg Al/L, ten trace organics were removed by >30 % in the presence of at least one DOM surrogate. Humic acid effected the highest removals owing to complexation of trace organics and subsequent co-removal by adsorption or sweep floc. For instance, removal extents for three brominated diphenyl ethers were 60 to 75 % with Al and 50 to 88 % with Fe (initial concentration 0.4 to 0.8 ng/L); PFTDA, a long-chain PFAS, was removed by 87 and 91 % with Fe in the presence of tannic or humic acid, respectively (initial concentration 0.03 μg/L). The varying coagulation performance of different treatment works in terms of trace substance removal can be explained because of the site-specific DOM characteristics. Addition of humic acids as complexing agents has the potential to improve the removal of hydrophobic trace substances, including some long-chain PFAS and brominated flame retardants.

Phycoremediation Processes for Secondary Effluent from Sewage Treatment Plants Using Photosynthetic Microorganisms: A Review

Taking into account the worrying scenario of water scarcity, it is essential to enable more efficient technologies for wastewater treatment. Wastewater may be treated by conventional biological processes that remove pathogenic organisms, particulate and soluble organic compounds, and other components. However, secondary effluents from treatment plants may still contain toxic elements or high concentrations of inorganic nutrients (mainly nitrogen and phosphorus), which enable the growth of photosynthetic microorganisms in water bodies, resulting in eutrophication. In this context, cultivation of photosynthetic microorganisms in secondary wastewater from sewage treatment allows the removal of nutrients from such wastewater, reducing the possibility of eutrophication. Moreover, microalgal biomass, produced in this tertiary wastewater treatment, may be harvested by different methods with the potential for different applications, such as fertilizer and biofuel.

Microalgae as tertiary wastewater treatment: Energy production, carbon neutrality, and high-value products

In general, wastewater treatment plants (WWTPs) use basic effluent treatment (primary and secondary). However, including a tertiary treatment may enhance the quality of the treated effluent, making it reusable for different purposes. Several tertiary treatment techniques are available in the literature (e.g., coagulation, flocculation, filtration, and oxidation), but they are mainly focused on nutrients and contaminants remove (e.g., trace metals). However, when microalgae cultivation is applied as tertiary treatment, other possibilities could be explored. During the growth, microalgae incorporate nutrients present in the effluent in their biomass that could generate further high-value products such as biofuel, biochar, and carotenoids. In addition, during photosynthesis process they can fixed high CO2 rates, playing an important role in global climate mitigation under a carbon neutrality perspective. In this sense, we identified the potential of microalgae cultivation as a tertiary treatment, emphasizing its capacity of removal nutrients and also their potential reduce the WWTP's carbon footprint; while generating other high-value products.

Simultaneous Oxidation of Emerging Pollutants in Real Wastewater by the Advanced Fenton Oxidation Process

Since the conventional processes employed in most wastewater treatment plants (WWTPs) worldwide are not designed to entirely remove or oxidize emerging pollutants, which, due to their incidence and persistence, can cause damage to both the environment and human health, several options for their degradation and removal have emerged. Coupling the advanced Fenton oxidation process as a polishing or tertiary wastewater treatment alternative within conventional WWTP processes stands out among the treatment options. Therefore, the main objective of this research was to evaluate, at the laboratory level, the ability of the advanced Fenton oxidation process to oxidize triclosan, ibuprofen, DEET (N, N-diethyl-meta-toluamide), carbamazepine, caffeine, and acesulfame-K, which represent several groups of emerging pollutants in real wastewater from the second settling tank of a municipal WWTP. The compound used as a catalyst (Fe2+) supplier in the advanced Fenton oxidation process was ferrous sulfate heptahydrate (FeSO4•7H2O). The results obtained upon application showed that the advanced Fenton oxidation process could simultaneously oxidize and remove practically the total concentration of the above-mentioned emerging pollutants, except for DEET (85.21%), in conjunction with the chemical oxygen demand (COD), total suspended solids (TSS), and fecal coliforms (FC, pathogen group) in the effluent generated by the advanced Fenton oxidation process.

Risk Assessment of Trace Metals Using Chemical Speciation, Bioavailability, and Cluster Analysis Around Wadi EL Bey (Gulf of Tunis, Tunisia)

ABSTRACT The Wadi El Bey is one of the most vulnerable areas to pollution in the northeast of Tunisia, altered by anthropogenic and natural processes. This study uses the Community Bureau of Reference (BCR) approach and statistical tools, particularly the student’s t-test and the cluster analysis, to evaluate the danger of metals zinc (Zn), nickel (Ni), lead (Pb), cadmium (Cd), and copper (Cu) pose. This work is to assess the long-term evolution and mobility of heavy metals in the core soils of the Wadi El Bey River Bed. Heavy metals in SC1 followed the descending order Fe>Cu>Zn>Ni>Pb>Cd and in SC2 it was Fe>Cu>Zn>Ni>Cd>Pb. The (BCR) procedure showed that in soil cores SC1 and SC2, Ni was mainly associated with the exchangeable fractions (F1). However, the Zn and Cu were linked to the residual fractions (F4). The student’s t-test confirmed that the difference in vertical distribution between the SC1 and SC2 of Zn and Pb is statistically significant (p-value<.05) contrary to Ni (P = .06), Cd (P = .79), Cu (P = .38) demonstrated a common origin for these metals in the Wadi El Bey. The cluster analysis revealed that pH was the main responsible factor influencing the migration of Cu, Ni, and Zn toward the labile fractions in SC1. Whereas the total organic carbon influenced the Zn fixation in the most stable fraction in SC2. The use of pollution indices showed strong contamination by Ni, Cu, and Cd and moderate contamination by Zn and Pb. The risk assessment code (RAC) showed that Zn and Cu had a low to medium risk whereas medium to high risk for Ni. For better management and better control of heavy metal pollution in ecosystems with intermittent regimes, we advise a tertiary treatment of wastewater before evacuating it in Wadi el Bey.

Tubular membrane photoreactor for the tertiary treatment of urban wastewater towards antibiotics removal: application of different photocatalyst/oxidant combinations and ozonation

A tubular membrane photoreactor, operated in continuous mode and low residence times (τ from 3.9 to 12.2 s), was applied for the removal of 14 antibiotics (sulfonamides, fluoroquinolones, macrolides, cephalexin, and trimethoprim) in demineralized water (DW) and secondary-treated urban wastewater (UWW). In this setup, the oxidant (hydrogen peroxide (H2O2), persulfate (S2O82−) or ozone (O3)) is permeated through the membrane pores and delivered to the catalyst (titanium dioxide (TiO2) or silver molybdate (Ag2MoO4)), embedded in the membrane shell side, and to the annular reaction zone (ARZ) where the DW or UWW fortified with the target antibiotics (50 µg L−1 each) flows. The antibiotics removal in the tested processes - photolysis (UVC), photocatalysis (UVC/TiO2 or UVC/Ag2MoO4), photochemical oxidation (UVC/H2O2 or UVC/S2O82−), their combinations (UVC/TiO2/H2O2, UVC/TiO2/S2O82‾, UVC/Ag2MoO4/H2O2 and UVC/Ag2MoO4/S2O82‾) and O3 - were evaluated at steady-state conditions by ultra-high performance liquid chromatography followed by quadrupole time-of-flight high-resolution mass spectrometry (UHPLC-QTOF-HRMS). In the DW, the treatment efficiency followed the sequence: UVC < UVC/TiO2 ≈ UVC/Ag2MoO4 < UVC/H2O2 < UVC/TiO2/H2O2 ≈ UVC/Ag2MoO4/H2O2 < UVC/S2O82‾ < UVC/TiO2/S2O82‾ < UVC/Ag2MoO4/S2O82‾ < O3. In the UWW, the O3 process proved again to be the most efficient (12 antibiotics removed >90%), followed by UVC/Ag2MoO4/S2O82‾ (five antibiotics removed >60%). UHPLC-QTOF-HRMS tentatively identified seven by-products stemming from macrolides for O3 treatment. This is a pioneer study on the application of Ag2MoO4 combined with H2O2 or S2O82- for advanced treatment of UWW, laying the groundwork for future research. The membrane reactor proves to be an effective technological approach for the O3 process.

Insights into solid phase denitrification in wastewater tertiary treatment: the role of solid carbon source in carbon biodegradation and heterotrophic denitrification

The practical application of solid phase denitrification (SPD) was hindered by either poor water quality from natural plant-like materials or high cost of pure synthetic biodegradable polymers. In this study, by combining polycaprolactone (PCL) with new natural materials (peanut shell, sugarcane bagasse), two novel economical solid carbon sources (SCSs) named as PCL/PS and PCL/SB were developed. Pure PCL and PCL/TPS (PCL with thermal plastic starch) were supplied as controls. During the 162-day operation, especially in the shortest HRT (2 h), higher NO3−-N removal was achieved by PCL/PS (87.60%±0.06%) and PCL/SB (87.93%±0.05%) compared to PCL (83.28%±0.07%) and PCL/TPS (81.83%±0.05%). The predicted abundance of functional enzymes revealed the potential metabolism pathways of major components of SCSs. The natural components entered the glycolytic cycle by enzymatical generation of intermediates, while biopolymers being converted into small molecule products under specific enzyme activities (i.e., carboxylesterase, aldehyde dehydrogenase), together providing electrons and energy for denitrification.

Ex-situ magnetic activated carbon for the adsorption of three pharmaceuticals with distinct physicochemical properties from real wastewater.

Pharmaceuticals are able to evade conventional wastewater treatments and therefore, are recurrently found in the environment with proven potential to cause harm to human and wildlife. Adsorption onto activated carbon (AC) is a promising complement. However, AC production from non-renewable resources and its difficult after-use recuperation are prohibitive. Hence, a waste-based magnetic activated carbon (MAC) was produced from paper mill sludge, via an ex-situ synthesis, for the adsorptive removal of carbamazepine (CBZ), sulfamethoxazole (SMX) and ibuprofen (IBU) from ultrapure water and wastewater. The MAC was obtained through the promotion of electrostatic interactions between magnetic and activated carbon particles in a water suspension at controlled pH between the points of zero charge of both surfaces. The optimized condition (MACX3) presented remarkable properties regarding specific surface area (SBET=795m2 g-1) and saturation magnetization (MS=19emug-1). Kinetic and equilibrium adsorption studies were performed under batch conditions. Adsorption equilibrium was reached in up to 30min for all pharmaceuticals in both matrices, proving the low dependence on the adsorbate and the broad applicability of MACX3 in pharmaceutical adsorption. Regarding equilibrium experiments, high Langmuir maximum adsorption capacities (qm) were achieved in ultrapure water (up to 711 ± 40 µmol g-1). Equilibrium studies in wastewater revealed a decay in qm when compared to ultrapure water: 28% for CBZ (468 ± 20 µmol g-1 (111 ± 5 mg g-1)), 78% for SMX (145±10 µmol g-1 (37 ± 3 mg g-1)) and 62% for IBU (273 ± 8 µmol g-1 (56 ± 2 mg g-1)), attributed to the wastewater pH, which dictates the speciation of the pharmaceuticals and controls electrostatic interactions between pharmaceuticals and MAC, and to competition effects by organic matter. It was demonstrated the promising applicability of a waste-based ex-situ MAC, rapidly retrievable from water, as an alternative tertiary wastewater treatment for pharmaceuticals removal.

Nanofiltration as an efficient tertiary wastewater treatment for reuse in the aquaponic system in Tunisia

A tertiary treatment of the effluent received from five Tunisian wastewater treatment plants is implemented at GDA Sidi Amor for reuse in an aquaponic system. It includes a MBBR, a constructed wetland, sand and activated carbon filters, and a combined nanofiltration and reverse osmosis desalination system. The Results show that the post-treatment before desalination reduces the COD by 44 % which is mostly refractory, the orthophosphate by 33 %, and the ammonia by 95.6 %. The NF90 4040 removes 2/3 of the salts and micropollutants except for sodium, chloride and nitrate which are respectively 57 %, 45 %, 39 %. The micropollutants benzotriazole, and clarithromycin were removed by 17 %, and 8 % respectively. The optimum pressure for a conversion rate of around 80 % is 4.7 bar for the cold period and 7 bar for the summer period depending on water salinity and membrane fouling. After one year, membrane permeability decreases. After cleaning the conversion rate increases to 89 % at 5.2 bars and the hydraulic permeability increases by 39 %. Using the hybrid system NF-RO at 10 bars for RO BW30–4040 the amount of brine was reduced by 65 % and the permeate quality is improved. After five months, the total fish weight increases by 21 kg and the crops grow well.

Tertiary treatment of coke-oven wastewater using suspended and immobilized whole live cells of constructed bacterial-microalgal consortium: modeling and optimization using ANN-GA hybrid methodology.

Coke-oven wastewater (CW), containing an array of toxic pollutants above permissible limits even after conventional primary and secondary treatment, needs a tertiary (polishing) step to meet the statutory limit. In the present study, a suitable bacterial-microalgal consortium (Culture C) was constructed using bacterial (Culture B: Bacillus sp. NITD 19) and microalgal (Culture A: a consortium of Chlorella sp. and Synechococcus sp.) cultures at different ratios (v/v) and the potential of these cultures for tertiary treatment of CW was assessed. Culture C4 (Culture B:Culture A = 1:4) with inoculum size: 10% (v/v) was selected for the treatment of wastewater since the maximum growth (3.08 ± 0.57 g/L) and maximum chlorophyll content (4.05 ± 0.66 mg/L) were achieved for such culture in PLE-enriched BG-11 medium. During treatment of real secondary treated coke-oven effluent using Culture C4 in a closed photobioreactor, the removal of phenol (80.32 ± 2.76%), ammonium ions (47.85 ± 1.83%), fluoride (65.0 ± 4.12%), and nitrate (39.45 ± 3.42%) was observed after 24 h. In a packed bed bioreactor containing immobilized C4 culture, the maximum removal was obtained at the lowest flow rate (20 mL/h) and highest column bed height (20 cm). Artificial intelligence-based techniques were used for modeling and optimization of the process.

Ozonation and Granular Activated Carbon Adsorption for the Removal of Refractory Organic Matter and Decolorization During Wastewater Tertiary Treatment

This study investigated two different hybrid processes for the treatment of municipal secondary-treated biological effluents to meet the reuse of recycled water requirements for organic matter and color. The two hybrid treatment approaches were an oxidation-based treatment process (coagulation–sedimentation–deep-bed filtration [CSDF]–ozone oxidation) and an adsorption-based treatment process (CSDF-granular activated carbon [GAC] adsorption). The efficiencies of ozonation and GAC adsorption in removing chemical organic demand (COD), dissolved organic carbon (DOC), and color intensity were evaluated. The effect of CSDF as the pretreatment was also studied. Ozonation showed a much higher color removal efficiency (88%, 4.7 mg/L ozone dose) than GAC adsorption (23%). Organic matter with an apparent molecular weight of 2–3 kDa, being humus-like, might be the colored fraction in the secondary and CSDF effluents. Ozonation had a stronger ability to remove these substances than GAC adsorption, resulting in a visibly higher color removal efficiency. In addition, higher COD and DOC removal were achieved by ozonation when the average ozone dose was increased to 9.1 mg/L. Although both hybrid processes were reliable for reducing organic matter and color, the results show that ozonation is more suitable for simultaneously removing refractory organic matter and color.

Phototrophic Bioremediation of Municipal Tertiary Wastewater Coupling with Lipid Biosynthesis Using Scenedesmus dimorphus: Effect of Nitrogen to Phosphorous Ratio with/without CO2 Supplementation

Scenedesmus dimorphus was utilized for the tertiary treatment of municipal wastewater in an effort to remove nutrients from secondary treated wastewater. In addition to the concurrent generation of biomass containing lipids for biofuel production. The effect of nitrogen to phosphorous (N:P) ratios (1:1 to 8:1) in culture media without carbon dioxide (CO2) supplementation (air supply alone, Case 1) and with CO2 supplementation (2% CO2 in air, Case 2) was investigated through a series of systematic parametric batch experiments. Case 2 produces greater biomass at all N:P ratios than Case 1. In Case 1, the highest biomass output for a N:P ratio of 8:1 is 567 mg/L at pH 8.4. In Case 2, however, the maximum biomass yield is 733 mg/L when the N:P ratio is 2:1 and the pH is 7.23. Scenedesmus dimorphus is capable of absorbing nitrogen and phosphorous from wastewater in a CO2 environment and at the optimal N:P ratio. In Case 1, total nitrogen removal ranges from 28% to 100% and in Case 2, total nitrogen removal ranges from 60% to 100%, depending on the N:P ratio. For an initial concentration of 13 mg/L, the total phosphorous removal ranges from 37% to 57%, depending on the N:P ratio in both cases. Case 2 yields a maximum lipid content of 29% of the biomass dry weight when the N:P ratio is 1:1. These results suggest the viability of removing nutrients from secondary treated wastewater utilizing microalgae Scenedesmus dimorphus and lipid biosynthesis in the generated biomass.

Tertiary treatment of wastewater by coupling anodic oxidation processes using solar energy and the coagulation–flocculation processes

Tertiary treatment of wastewater by coupling anodic oxidation processes using solar energy and the coagulation–flocculation processes

Integrated genotoxicity of secondary and tertiary treatment effluents in North China

Genotoxic effects on aquatic organisms caused by wastewater discharging have raised extensive concerns. However, the efficiency of various wastewater treatment processes to reduce effluent genotoxicity was not well known. Genotoxic effects of effluents from four secondary wastewater treatment plants (SWTPs) and a tertiary wastewater treatment plant (TTP) in north China on Chinese rare minnows (Gobiocypris rarus) were evaluated and the toxicity reduction efficiency of various treatment techniques was compared. SWTPs and TTP final effluents disturbed the antioxidant system and lipid peroxidation, with malondialdehyde (MDA) contents in the fish livers and gills increasing to 1.4–2.4 folds and 1.6–3.1 folds of control, respectively. Significant increases in erythrocytes micronucleus (MN) frequency were induced by effluent, and liver DNA damage caused by final SWTPs effluent was 29–54 % lower than TTP effluent. Further, DNA repair gene atm and growth arrest gene gadd45a were remarkably upregulated by SWTP and TTP final effluents to 1.8–12 folds and 4.1–15 folds, respectively, being consistent with the chromosomal aberration and DNA damage in liver tissue. Integrated biomarker response (IBR) of the tertiary effluent was 49 %–69 % lower than the secondary effluents. However, the final ozone disinfection at TTP caused an increase in the DNA damage, suggesting the generation of genotoxic by-products. UV disinfection at secondary treatment removed part of genotoxicity, with a reduction in IBR of 0 %–47 %. The total semi-volatile organic compounds (SVOCs) detected in the final effluent contained 5 %–56 % potential genotoxic substances, removal of which was 9 %–51 % lower than non-genotoxic compounds. Microfiltration and reverse osmosis process exhibited good performance in removing both the integrated genotoxicity and the potential genotoxic SVOCs. Our finding shows that TTP is superior than SWTP for wastewater treatment due to higher genotoxicity removal, but ozone disinfection needs improvement by optimizing performance parameters or adding post-treatment processes, to achieve better protection for aquatic organisms against genotoxic contaminants.

Tertiary Wastewater Treatment Processes Can Be a Double-Edged Sword for Water Quality Improvement in View of Mitigating Antimicrobial Resistance and Pathogenicity.

Despite the high removal efficiency for chemical pollutants by tertiary wastewater treatment processes (TWTPs), there is no definite conclusion in terms of microbial risk mitigation yet. This study utilized metagenomic approaches to reveal the alterations of antibiotic resistance genes (ARGs), virulence factor genes (VFGs), their co-occurrence, and potential hosts during multiple TWTPs. Results showed that the TWTPs reduced chemical pollutants in wastewater, but the denitrifying biofilter (DB) significantly increased the absolute abundances of selected antibiotic-resistant bacteria and ARGs, and simultaneously elevated the relative abundances of ARGs and VFGs through the enrichment of multidrug resistance and offensive genes, respectively. Moreover, the co-occurrence of ARGs and VFGs (e.g., bacA-tapW, mexF-adeG) was only identified after the DB treatment and all carried by Pseudomonas. Then, the ultraviolet and constructed wetland treatment showed good complementarity for microbial risk reduction through mitigating antibiotic resistance and pathogenicity. Network and binning analyses showed that the shift of key operational taxonomic units affiliating to Pseudomonas and Acinetobacter may contribute to the dynamic changes of ARGs and VFGs during the TWTPs. Overall, this study sheds new light on how the TWTPs affect the antibiotic resistome and VFG profiles and what TWTPs should be selected for microbial risk mitigation.

Evaluation of Monoraphidium contortum for the tertiary treatment of dairy industry wastewater and biomass production with nitrogen supplementation

The present study sought to evaluate the secondary wastewater from dairy industry as a culture medium for Monoraphidium contortum, in bench-scale tubular photobioreactor, aiming at tertiary wastewater treatment and microalgae biomass production. Since the used secondary wastewater contained residual phosphorus (P) but negligible residual nitrogen (N), we also evaluated the nitrogen supplementation, following Redfield ratio (N:P = 16:1) and the same N:P proportion of Bold Medium (N:P = 1.71:1). These cultures were compared to secondary wastewater without N and Bold Medium (control). Secondary wastewater without N addition provided lower values of maximum biomass concentration, indicating the importance of this supplementation. The nitrogen supplementation following Bold Medium represented the best protocol, since biomass productivity was higher than that in control culture, but with lower nitrogen addition (in comparison with the supplementation following Redfield proportion). The biomass of M. contortum showed to be an excellent candidate for oil production, which could be employed as feedstock for biodiesel, for example.

Green synthesis of AgNPs, alginate microbeads and Chlorella minutissima laden alginate microbeads for tertiary treatment of municipal wastewater

The present study included a tertiary treatment of municipal wastewater to eliminate bacterial count, nitrite, nitrate, ammonia and phosphorus using AgNPs, free and Chlorella minutissima laden alginate microbeads. The green synthesis of AgNPs (size range = 5–20 nm) was by using the Rumex dentatus plant extract. The UV–Vis spectroscopy analysis indicates the presence of two peaks at 360 and 486 nm representing the AgNPs with different sizes. The free and alginate immobilized AgNPs (0.068 g.L−1) record a highly significant bactericidal effect of 100 % growth elimination till 48 h treatment. The removal efficiency of nitrogen and phosphorus pollutants by free and C. minutissima immobilized alginate microbeads was time-dependent, with the highest removal efficiencies (38–82 %) after 12 h and (55–100 %) after 24 h. As most of the water resources are closed systems, the results of the present study could help improve the wastewater quality before runoff in receiving water system.

Tertiary wastewater treatment combined with high dilution rates fails to eliminate impacts on receiving stream invertebrate assemblages

The amount of wastewater processed in treatment plants is increasing following more strict environmental regulations. Treatment facilities are implementing upgrades to abate the concentrations of nutrients and contaminants and, thus, reduce their effects on receiving systems. Although many studies characterized the chemical composition and ecotoxicological effects of treated wastewater, its environmental effects are still poorly known, as receiving water bodies are often subjected to other stressors. We performed a field manipulative experiment to measure the response of invertebrate assemblages to one year of tertiary-treated wastewater discharges. We poured treated wastewater from an urban wastewater treatment plant into the lower-most 100-m of a previously unpolluted stream (3.6 % daily flow on average) while using another upstream reach as control. The positive correlation between effect sizes of abundance changes and IBMWP scores suggested assemblage modifications were following taxa tolerance to ecological impairment. The treatment increased the temporal variability of SPEARorganic, EPT relative abundance, and invertebrate functional redundancy. Our results show that even in this best-case scenario of tertiary-treated and highly diluted wastewater, the abundance of the most sensitive taxa in the aquatic assemblages is reduced. Further improvements in wastewater treatments seem necessary to ensure these effluents do not modify receiving water ecosystems.

Microalgae Harvesting after Tertiary Wastewater Treatment with White-Rot Fungi.

Tertiary wastewater treatment with microalgae incorporates environmental sustainability with future technologies and high exploitation costs. Despite the apparent ecological benefits of microalgae-assisted wastewater treatment/biomass-based resource production, technological improvements are still essential to compete with other technologies. Bio-flocculation instead of mechanical harvesting has been demonstrated as an alternative cost-effective approach. So far, mostly filamentous fungi of genus Aspergillus have been used for this purpose. Within this study, we demonstrate a novel approach of using white-rot fungi, with especially high potential of algae-Irpex lacteus complex that demonstrates efficiency with various microalgae species at a broad range of temperatures (5-20 °C) and various pH levels. Harvesting of microalgae from primary and secondary wastewater resulted in 73-93% removal efficiencies within the first 24 h and up to 95% after 48 h. The apparent reuse potential of the algae-I. lacteus pellets further complements the reduced operating costs and environmental sustainability of bio-flocculation technology.