Secondary Wastewater Research Articles

Enhancing sustainability through microalgae cultivation in urban wastewater for biostimulant production and nutrient recovery

Microalgae can produce biostimulants in form of phytohormones, which are compounds that, even if applied in low concentrations, can have stimulant effects on plants growth and can enhance their quality and their resistance to stress. Considering that microalgal biomass can grow recovering nutrients from wastewater, this circular approach allows to use residues for the production of high added value compounds (such as phytohormones) at low cost. The interest on biostimulants production from microalgae have recently raised. Scientists are focused on the direct application of these cellular extracts on plants, while the number of studies on the identification of bioactive molecules, such as phytohormones, is very scarce. Two cyanobacteria strains (Synechocystis sp. (SY) and Phormidium sp. (PH)) and a chlorophyte (Scenedesmus sp. (SC)) were cultured in laboratory-scale PBRs with a working volume of 2.5 L in secondary urban wastewater varying N:P ratio in the cultures to obtain the highest productivity. The variation of N:P ratio affects microalgae growth, and SY and PH presented higher productivities (73 and 48 mg L−1 d, respectively) under higher N:P ratio (> 22:1). Microalgal biomass was freeze-dried and phytohormones content was measured with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The three microalgae showed similar phytohormones profiles, being the auxin (indole-3-acetic acid, IAA) the most abundant (72 ng g−1DW in SY). Proteins were major macronutrient for all strains, reaching 48 %DW in PH culture. To optimize the biostimulants production, a balance between the production of such compounds, biomass productivity and nutrients removal should be taken into consideration. In this sense, SC was the most promising strain, showing the highest N and P removal rates (73 % and 59 %, respectively) while producing phytohormones.

3D nano-structured sepiolite dynamic membranes for enhanced ultrafiltration treatment and membrane fouling mitigation

The construction of replaceable dynamic membranes (DMs) on membrane surfaces is a promising strategy to effectively mitigate membrane fouling. Nevertheless, the efficiency of DMs in mitigating membrane fouling remains low due to the lack of microstructural configurations. Herein, we report a natural sepiolite (SEP) DM with a three-dimensional (3D) network structure for mitigating PES ultrafiltration (UF) membrane fouling. The abundant oxygen-containing groups on the surface of SEP nanofibers endowed SEP DM with good organic adsorption capacity, hindering the migration of contaminants such as humic acid (HA) and bovine serum albumin (BSA). Owing to the porous 3D network structure, SEP DM prevented the formation of a dense filter cake layer, which effectively mitigated the sharp rise in membrane resistance when filtering ideal HA and BSA solutions. For the actual secondary wastewater, SEP DM improved the removal of UV254 and DOC by 29.8% and 22.5%, respectively, over the pristine PES membrane. The decrease in membrane-specific flux was mitigated by about 20%. Notably, the dynamic nature of SEP DM allowed the contaminated DM layer to be replaced by hydraulic cleaning, resulting in 99% flux recovery (only 89% for the pristine PES membrane). These findings are beneficial in providing new ideas for the mitigation and control of UF membranes.

A new sulfur bioconversion process development for energy- and space-efficient secondary wastewater treatment

Harvesting organic matter from wastewater, chemical enhanced primary treatment for instance, is widely applied to maximize energy recovery; however, it limits the applicability of secondary treatment for acceptable effluent discharge into surface water bodies. To turn this bottleneck issue into an opportunity, this study developed oxygen-induced thiosulfatE production duRing sulfATe reduction (ERATO) to provide efficient electron donor for denitrification or partial denitrification anammox in wastewater treatment. Typical pretreated wastewater was synthesized with chemical oxygen demand of 110 mg/L, sulfate of 50 mg S/L, ammonium of 30 mgN/L, and varying dissolved oxygen (DO) and was fed into a moving-bed biofilm reactor (MBBR) with a short hydraulic retention time of 40 min. The ORP maintained at − 311 mV in the bioreactor, indicating that the influent DO was vanished immediately when it enters the bioreactor. In 349 days’ continuous operation, the surface-specific sulfate reduction rate reached 0.42 g S/(m2·d). Notably, the formation rate of thiosulfate reached 0.12–0.18 g S/(m2·d) with a high thiosulfate-Sproduced/sulfide-Sproduced ratio of 38–73% when influent DO was 2.7–3.6 mg/L, much higher than 0–17% obtained in previously reported sulfate-reducing process. Then, batch tests and metabolism analysis were conducted to confirm the oxygen effect on thiosulfate formation, and to explore the mechanism of oxygen-induced thiosulfate formation in ERATO. Results examined that oxygen supply promoted the thiosulfate-Sproduced/sulfide-Sproduced ratio from 4% to 24–26%, demonstrated that S0 and sulfate were critical for thiosulfate production, and indicated that oxygen induces thiosulfate formation mainly through: sulfide first oxidized to S0 which then reacts with sulfite derived from oxygen-regulated biological sulfate reduction (S0 + SO32−→S2O32−). The proposed compact ERATO process with high thiosulfate production, supporting space- and energy-efficient secondary wastewater treatment.

Process parameter study and kinetic of remazol dye adsorption onto local rice husk‐based organic porous materials

AbstractRemazol Brilliant Blue dye (RBB) is a harmful dye from the textile industry that can damage the environment and aquatic life. Since RBB is impossible to degrade in water by primary and secondary wastewater treatment, its removal is a challenge. An excellent treatment procedure is urgently anticipated to avoid the pollution spreading into the environment. Moreover, rice husk waste (RH) in Malaysia is abundant and generally dumped into landfills. Turning the waste into a value‐added product such as biochar as an effective adsorbent material for treating water pollutants is one of the initiatives in realizing the circular economy agenda. This study develops an organic porous material of biochar from RH and assesses the kinetic of RBB adsorption onto the rice husk biochar (RHB) in aqueous solution. The production of RHB was optimized by pyrolysis procedure at various temperatures, times, and particle sizes. The removal of RBB dye by RHB was investigated at different exposure times from 0 to 120 min under 100 rpm shaken and immersed conditions. The reduction of RBB concentrations using different RHB pyrolysis conditions has also been investigated. The dye removal efficiency by RHB increased with time and the highest removal efficiency (69.3%) was achieved by the smallest particle size of RHB which was produced at the highest pyrolysis temperature of 400°C (RHB‐400). The total pore volume and BET surface area of RHB‐400 were found to be 50.4827 m2/g and 0.00875 cm3/g, respectively. The adsorption kinetic study signifies that maximum adsorption has been completed within 90–120 min depending on the RHB conditions whereas two kinetic models such as pseudo‐first order and pseudo‐second order kinetic models were utilized to fit the experimental data and the results are more consistent with pseudo‐second order kinetic models. This study revealed that RHB can be used as adsorbent materials for dye removals, yet it is economical, environmentally friendly, and sustainable.

A novel catalytic membrane integrated with ozone process for secondary wastewater treatment: Micropollutant removal, membrane fouling control, and its mechanisms

The integration of membrane filtration and catalytic ozonation is increasingly investigated in micro-polluted wastewater treatment, whereas membrane fouling still inhibits its practical application. In the present study, a novel MnCe-catalytic membrane integrated with ozone process (O3/MnCe-CM) was established and applied to remove four micropollutants from the real secondary effluent in continuous operation. Efficient removal of four representative micropollutants with the removal rate ranging from 89.33 % to 99.49 % and superior performance on conventional pollutants, with the DOC, UV254, polysaccharide, and protein reduced by 30 %, 88 %, 32.5 %, and 24 %. The O3/MnCe-CM process had an improved TMP control effect, explicitly reducing the irreversible fouling resistance given a Rir/Rt of 10.17 % which is 42.9 % of that of the O3/CM process. After filtering for 70 days, the TMP only increased by 24.51 kPa. More importantly, the antifouling mechanism was proposed as the combined effects of the decrease of the membrane isoelectric point that elevated its repulsion towards pollutants and the catalytic ozonation that reduced the organic foulants accumulated on the membrane surface and inside the pores. In addition, ozonation in the membrane tank decreased the pollutant load passing through MnCe-CM. In all, the present study provides a novel O3/MnCe-CM process with a promising application perspective.

First evidence of environmental bioaccumulation of pharmaceuticals on adult native anurans (Rhinella arenarum) from Argentina

The presence of pharmaceutically active compounds (PhACs) in surface water is well known, whereas their natural occurrence in biota is much less explored. The aim of this work was to evaluate the bioaccumulation of PhACs in adult toads of the neotropical species Rhinella arenarum. Three sites were selected in Buenos Aires (Argentina): a reference site (Site 1), a site with direct discharge from a secondary wastewater treatment plant (WWTP) (Site 2) and a site 300 m downstream of the WWTP discharge (Site 3). Surface water samples, as well as muscle, liver and fat bodies of toads were collected, extracted and analyzed by LC-MS/MS. Highly significant differences in total PhACs concentration in surface water (p < 0.005) were detected between Site 2 and the other sites. These concentrations ranged from 0.37 to 52.46 ng/L at Site 1, 0.71–6950.37 ng/L at Site 2, and 0.12–75.45 ng/L at Site 3. In general, bioaccumulation of PhACs in toad tissues was similar between sites and tissues of each site. The highest concentrations were detected in the muscle of toads from Site 3 (1.06–87.24 ng/g dw), followed by liver (1.77–38.10 ng/g dw) and fat bodies (0.68–20.59 ng/g dw) from Site 1. Ibuprofen (6950 ng/L), acetaminophen (3277 ng/L) and valsartan (2504 ng/L) were the compounds with the highest concentrations in surface water from Site 2, whereas acetaminophen (87.2 ng/g dw, muscle from Site 3), desloratadine (38.1 ng/g dw, liver from Site 1), and phenazone (25.9 ng/g dw, liver from Site 1) were the ones that showed the highest concentrations in biota. This is the first time a field study has examined the environmental bioaccumulation of PhACs in anurans, demonstrating their potential for monitoring the status of natural ecosystems.

Performance of membrane photobioreactor for integrated Spirulina strain cultivation and nutrient removal of membrane bioreactor effluent

Water reuse by wastewater treatment techniques is implemented to promote a circular economy strategy and alleviate water shortage. The microalgae-based wastewater treatment is an environmentally friendly tool to treat secondary or tertiary wastewater by removing the remaining nutrients, primarily dissolved nitrogen (N) and phosphorus (P). This research aimed to study the membrane photobioreactor (MPBR) performance to treat nitrate nitrogen (NO3-N) and phosphate (PO4) that remained in the membrane bioreactor (MBR) effluent by varying hydraulic retention times (HRTs) and solids retention times (SRTs). Bench-scale of MPBR (63 L) was continuously operated by cultivating Spirulina sp. TISTR 8875. The LED light intensity of 3000–5000 lux was provided 24 h daily. The experimental studies evaluated HRTs in the range of 6.4–9.7 days and SRTs at 20, 40, 60, and 80 days, and the microalgae cells were not removed (infinite SRT). The results showed that the HRT range of 7.7–7.8 days and SRT range of 60–80 days exhibited NO3-N and PO4 removal efficiencies of 39.3–40.9% and 43.8–46.6%, respectively, with the NO3-N and PO4 removal rates of 2.47–2.55 and 0.22–0.23 mg/L-d, respectively. In addition, iron (Fe) in the form of FeEDTA, has been added to the microalgae cultivation at a concentration of 0.07 g/L. It was found that Fe plays an essential role in the growth of microalgae and increases nutrient removal efficiency. The experimental results indicate that the cultivation of Spirulina sp. TISTR 8875 is expected to treat nutrients by the MPBR system as a promising water reuse and nutrient recovery potential.

Production and characterization of graphene oxide-engineered biochars and application for organic micro-pollutant adsorption from aqueous solutions.

In this study, conventional and Graphene Oxide-engineered biochars were produced and thoroughly characterized, in order to investigate their potential as adsorptive materials. Two types of biomass, Rice Husks (RH) and Sewage Sludge (SS), two Graphene Oxide (GO) doses, 0.1% and 1%, and two pyrolysis temperatures, 400°C and 600°C were investigated. The produced biochars were characterized in physicochemical terms and the effect of biomass, GO functionalization and pyrolysis temperature on biochar properties was studied. The produced samples were then applied as adsorbents for the removal of six organic micro-pollutants from water and treated secondary wastewater. Results showed that the main factors affecting biochar structure was biomass type and pyrolysis temperature, while GO functionalization caused significant changes on biochar surface by increasing the available C- and O- based functional groups. Biochars produced at 600°C showed higher C content and Specific Surface Area, presenting more stable graphitic structure, compared to biochars produced at 400°C. Micro-pollutant adsorption rates were in the range of 39.9%-98.3% and 9.4%-97.5% in table water and 28.3%-97.5% and 0.0%-97.5% in treated municipal wastewater, for the Rice Husk and Sewage Sludge biochars respectively. The best biochars, in terms of structural properties and adsorption efficiency were the GO-functionalized biochars, produced from Rice Husks at 600°C, while the most difficult pollutant to remove was 2.4-Dichlorophenol.

Engineering Hydroponic Systems for Sustainable Wastewater Treatment and Plant Growth

This study aimed to optimize hydroponic systems for simultaneous wastewater treatment/nutrient recovery and plant growth. Various hydroponic systems (geyser pump, full flow, ebb and flow, nutrient film techniques, aeroponics, misting) were constructed using 160 mm PVC waste pipes supported on a 200 L reservoir. Secondary wastewater was used to cultivate rice (Oryza sativa), ivy (Hedera helix), tomatoes (Solanum lycopersicum), and wheatgrass (Triticum aestivum). Parameters such as plant height, biomass, retention time, temperature, conductivity, pH, dissolved oxygen, ammonia, nitrite, nitrate, total phosphorus, COD, BOD, TDS, TSS, and TS were monitored. Results indicated minor variations in pH, EC, and TDS over time in systems with and without plants, with no significant differences. Turbidity decreased significantly (p ≤ 0.001) in all systems, while TOC levels reduced significantly (p ≤ 0.05) only in the presence of plants. BOD and COD levels exhibited similar reductions with and without plants. Ammonium levels decreased in plant systems, while nitrite levels remained unchanged. Nitrate levels increased significantly in plant systems, and phosphate levels showed no significant difference. Additionally, significant (p ≤ 0.001) plant length (12.84–46.75%) and biomass (31.90–57.86%) increases were observed in all hydroponic systems, accompanied by higher levels of dissolved oxygen (36.26–53.65%), compared to the control (4.59%). The hydroponic system that created a moist atmosphere, either through misting or aeroponics, thus allowing maximum access to oxygen, showed the greatest growth. This study confirmed the importance of oxygen availability to the rhizosphere for plant growth and wastewater treatment. It also identified limitations and investigated the impact of dissolved oxygen concentration on plant–microorganism interactions. Optimal oxygen availability was achieved when plant roots were exposed to a moist atmosphere created by the hydroponic system through aeroponics or misting. The findings have practical implications for hydroponic system design in urban vertical farms, benefiting wastewater treatment, mitigating eutrophication, and reducing food miles.

Removal of microplastics in wastewater by ceramic microfiltration

Microplastic (MP) pollution is a growing global concern affecting environmental water quality. Although primary and secondary treatment processes in conventional wastewater treatment plants (WWTPs) efficiently remove MPs, MPs <20 μm across are not removed effectively. The quality of final effluent should be enhanced by applying a tertiary treatment for reducing MP discharge from WWTPs. This study evaluated the effectiveness of ceramic membranes for this. Removal of MPs was assessed at laboratory scale by cross-flow filtration of a secondary wastewater effluent. The activated sludge process at a wastewater treatment plant removed MPs at moderate to high rates (45 %–98 %), and the ceramic membranes further removed >72 % of MPs. Although the activated sludge process removed variable rates of MPs, the total rates of removal by both processes was >96 %. This result suggests that the ceramic MF membrane treatment will contribute to stable MP removal.

Development of nature-based sustainable passive technologies for treating and disinfecting municipal wastewater: Experiences from constructed wetlands and slow sand filter

There is an urgent need to develop low-cost technology for effective wastewater treatment and its further disinfection to the level that makes it economically useful. This work has designed and evaluated the various types of constructed wetlands (CWs) followed by a slow sand filter (SSF) for wastewater treatment and disinfection. The studied CWs were, CWs with gravels (CW-G), free water surface-CW (FWS-CWs), and CWs integrated microbial fuel cell (MFC) with granular graphite (CW-MFC-GG) planted with Canna indica plant species. These CWs were operated as secondary wastewater treatment technologies followed by SSF for disinfection purposes. The highest total coliform removal was observed in the combination of CW-MFC-GG-SSF which achieved a final concentration of 172 CFU/100 mL, whereas faecal coliform removal was 100 % with the combinations of CW-G-SSF and CW-MFC-GG-SSF, achieving 0 CFU/100 mL in the effluent. In contrast, FWS-SSF achieved the lowest total and faecal coliform removal attaining a final concentration of 542 CFU/100 mL and 240 CFU/100 mL, respectively. Furthermore, E. coli were detected as negative/absent in CW-G-SSF and CW-MFC-GG-SSF, while it was positive for FWS-SSF. In addition, the highest turbidity removal was achieved in CW-MFC-GG and SSF combination of 92.75 % from the municipal wastewater influent turbidity of 82.8 NTU. Furthermore, in terms of overall treatment performance of CW-G-SSF and CW-MFC-GG-SSF, these systems were able to treat 72.7 ± 5.5 % and 67.0 ± 2.4 % of COD and 92.3 % and 87.6 % of phosphate, respectively. Additionally, CW-MFC-GG also exhibited a power density of 85.71 mA/m3 and a current density of 25.71 mW/m3 with 700 Ω of internal resistance. Thus, CW-G and CW-MFC-GG followed by SSF could be a promising solution for enhanced disinfection and wastewater treatment.

A downstream process control tool based on the redox dye resazurin for rapid and accurate measurement of microbial metabolic activity.

Many sophisticated water treatment plants need a reliable, fast, and economical microbial load detection method. We refined a colorimetric assay using the redox dye resazurin to assess viable microorganisms. Here, we have used a mixed bacterial suspension of significant multi-drug-resistant coliform bacteria isolated from hospital wastewater and constructed a resazurin reduction calibration curve which could accurately predict the level of microbial contamination. The number of viable microorganisms was calculated from calibration curve in terms of log colony forming units (CFU) per milliliter. Ultrasonication disinfection of bacterial suspension for a duration of 50min measured by resazurin assay depicted a reduction of 16.94%, 26.48%, and 37.69% at 410 W, 580 W, and 700 W, respectively. A synergistic effect of the combined methods of ultrasonication and heat disinfection treatments on raw wastewater and secondary wastewater effluent was observed and was also evaluated using both resazurin assay and standard plate count method. For raw wastewater, about 1.8 log reduction was observed for ultrasonication alone and 4 log CFU/mL reduction for thermosonication. In the secondary wastewater effluent, a reduction of 2.9 and 3.2 log CFU/mL was recorded for ultrasonication and thermosonication respectively. Resazurin microbial viability test results were highly comparable with conventional colony plate count for all treatment procedures, suggesting its appropriateness for quick and reliable wastewater sample microbial viability monitoring.

Analyzing the secondary wastewater-treatment process using Faster R-CNN and YOLOv5 object detection algorithms

The activated sludge (AS) process is the most common type of secondary wastewater treatment, applied worldwide. Due to the complexity of microbial communities, imbalances between the different types of bacteria may occur and disturb the process, with pronounced economical and environmental consequences. Microscopic inspection of the morphology of flocs and microorganisms provides key information on AS properties and function. This is a time-consuming, highly skilled, and expensive process that is not readily available in all locations. Thus, most wastewater-treatment plants do not carry out this essential analysis, resulting in frequent operational faults. In this study, we develop a novel deep learning (DL) object detection algorithm to analyze and monitor the AS process based on a unique microscopic image database of flocs and microorganisms. Specifically, we applied YOLOv5 and Faster R-CNN algorithms as tools for segmentation and object detection to analyze the wastewater. The mean average precision (mAP) of the YOLOv5 was 0.67, outperforming the Faster R-CNN by 15%. Histogram equalization preprocessing of both bright-field and phase-contrast images significantly improved the results of the algorithm in all classes. In the case of YOLOv5, the mAP increased by 16.67%, to 0.77, where the AP of protozoa, filaments, and open floc classes outperformed the previous model by over 20%. These results demonstrate the potential of leveraging DL algorithms to enhance the analysis and monitoring of WWTPs in an affordable manner, consequently reducing environmental pollution caused by contaminated effluent. The fundamental challenge addressed herein has important global relevance, especially in an era in which the demand for high-quality wastewater reuse is expected to increase dramatically.

Organic carbon source excites extracellular polymeric substances to boost Fe0-mediated autotrophic denitrification in mixotrophic system

Fe0-mediated autotrophic denitrification (ADN) can be suppressed by iron oxide coverage resulting from Fe0 corrosion. The mixotrophic denitrification (MDN) coupling Fe0-mediated ADN with heterotrophic denitrification (HDN) can circumvent the weakening of Fe0-mediated ADN over operation time. But the interaction between HDN and Fe0-mediated ADN for nitrogen removal of secondary effluent with deficient bioavailable organics remains unclear. When the influent COD/NO3−-N ratio increased from 0.0 to 1.8–2.1, the TN removal efficiency was promoted significantly. The increased carbon source did not inhibit ADN, but promoted ADN and HDN synchronously. The formation of extracellular polymeric substances (EPS) was also facilitated concomitantly. Protein (PN) and humic acid (HA) in EPS increased significantly, which capable of accelerating electron transfer of denitrification. Due to that the electron transfer of HDN occurs intracellularly, the EPS with the capacity of accelerating electron transfer had a negligible influence on HDN. But for Fe0-mediated ADN, the increased EPS as well as corresponding PN and HA facilitated TN and NO3−-N removal significantly, while accelerated the electron release originating from Fe0 corrosion. The bioorganic-Fe complexes were generated on Fe0 surface after used, meaning that the soluble EPS and soluble microbial products (SMP) participated in the electron transfer of Fe0-mediated ADN. The coexistence of HDN and ADN denitrifiers demonstrated the synchronous enhancement of HDN and ADN by the external carbon source. From the perspective of EPS and related SMP, the insight of enhancing Fe0-mediated ADN by external carbon source is beneficial to implement high-efficiency MDN for organics-deficient secondary wastewater.

Biological Oxygen-dosed Activated Carbon (BODAC) filters – A bioprocess for ultrapure water production removing organics, nutrients and micropollutants

Biological oxygen-dosed activated carbon (BODAC) filters in an Ultrapure water plant were demonstrated to have the potential to further treat secondary wastewater treatment effluent. The BODAC filters were operated for 11 years without carbon regeneration or replacement, while still functioning as pre-treatment step to reverse osmosis (RO) membranes by actively removing organic micropollutants (OMPs) and foulants. In this study, the removal of nutrients and 13 OMPs from secondary wastewater treatment effluent was investigated for 2 years and simultaneously, the granules’ characterization and microbial community analysis were conducted to gain insights behind the stable long-term operation of the BODAC filters. The results showed that the BODAC granules' surface area was reduced by ∼70 % of what is in virgin carbon granules and covered by biofilm and inorganic depositions. The BODAC filters reduced the concentration of soluble organics, mainly proteins, performed as an effective nitrification system, and almost completely removed manganese. During the 2 years of observation, the filters consistently removed some OMPs such as hydrochlorothiazide, metoprolol, sotalol, and trimethoprim by at least 70 %. Finally, through microbial community analysis, we found that nitrifying and manganese-oxidizing bacteria were detected in high relative abundance on BODAC granules, supporting BODAC performance in removing OMPs and manganese as well as converting nitrogenous species in the water.

Infilling missing data and outliers for a conventional sewage treatment plant using a self-organizing map: a case study of Kauma Sewage Treatment Plant in Lilongwe, Malawi

Abstract Data availability is key for modeling of wastewater treatment processes. However, process data are characterized by missing values and outliers. This study applied a self-organizing map (SOM) to fill in missing values and replace outliers in wastewater treatment data from Kauma Sewage Treatment Plant in Lilongwe, Malawi. We used primary and secondary wastewater data and executed the SOM algorithm to fill missing values and replace outliers in effluent pH, biochemical oxygen demand, and dissolved oxygen. The results suggest that the SOM algorithm is reliable in filling gaps in wastewater time series data with less than 50% missing values with correlation coefficient (R) values of &amp;gt;0.90. The SOM algorithm failed to reliably fill gaps and replace outliers in time series data with &amp;gt;50% missing values. For instance, high mean square error (MSE) values of 3,655.57, 10.62, and 2,153.34 for pH, DO, and BOD, respectively, were registered in datasets with more than 50% missing values, while very small MSE values (MSE ≈ 0) were associated with effluent pH, BOD, and DO data with missing values of &amp;gt;50%. Practitioners can use this approach to improve the planning and management of wastewater treatment facilities where available data records are riddled with missing observations.

Microplastic emission trends in Turkish primary and secondary municipal wastewater treatment plant effluents discharged into the Sea of Marmara and Black Sea

Wastewater Treatment Plants (WWTPs) are recognized as one of the primary sources of microplastics, a class of contaminants that has lately gained attention. The quantity of MP that WWTPs release into the environment depends on several factors, including the treatment type, season, and population serviced. MP abundance and characterization were explored in 15 WWTP effluent waters, 9 discharged to the Black Sea from Türkiye and 6 to the Marmara Sea, with varying population densities and treatment methods. The mean MP abundance in primary treatment WWTPs (76.25 ± 49.20 MP L−1) was found to be substantially greater than that in secondary treatment WWTPs (20.57 ± 21.56 MP L−1) (p<0.05). MPs in WWTP effluent waters showed significant seasonal and spatial differences (Two Way ANOVA, Tukey, p<0.05). However, no positive correlation was detected between the population serviced and MP abundance in effluent waters. While the fiber was the dominant shape (49.5%) among MPs in effluent waters, ≈80% of the length was <1000 μm. MPs are classified into polymer types as follows: polyethylene terephthalate (34.9%) > polypropylene (32.4%) > polyethylene (19.9%) > polyamide (11%) > polystyrene (1.2%) > polyvinyl chloride (0.6%). With effluent waters from the WWTPs tested, we calculated that 1.24x1010 daily MPs are discharged into the Black Sea while 4.95x1010 MPs are into the Marmara Sea, for a combined annual discharge of 2.26x1013 MPs highlighting that WWTPs are key contributors of MP in Turkish coastal waters.

Experimental and theoretical insight into carbamazepine degradation by chlorine‐based advanced oxidation processes: Efficiency, energy consumption, mechanism and DBPs formation

Chlorine has been widely used in different advanced oxidation processes (AOPs) for micropollutants removal. In this study, different chlorine-based AOPs, namely medium pressure (MP) UV/chlorine, low pressure (LP) UV/chlorine, and in-situ chlorination, were compared for carbamazepine (CBZ) removal efficiency, energy consumption, and disinfection by-products (DBPs) formation. All three processes could achieve nearly 100% CBZ removal, while the reaction time needed by in-situ chlorination was double the time required by UV/chlorine processes. The energy consumed per magnitude of CBZ removed (EE/O) of MP UV/chlorine was 13 times higher than that of LP UV/chlorine, and relative to that of in-situ chlorination process. Accordingly, MP and LP UV/chlorine processes generated one to two orders of magnitude more hydroxyl radicals (•OH) and reactive chlorine species (RCS) than in-situ chlorination. Besides, RCS were the dominant reactive species, contributing to 78.3%, 75.6%, and 71.6% of CBZ removal in MP, LP UV/chlorine, and in-situ chlorination, respectively. According to the Gibbs free energy barriers between CBZ and RCS/•OH calculated based on density functional theory (DFT), RCS had more reaction routes with CBZ and showed lower energy barrier in the main CBZ degradation pathways like epoxidation and formation of iminostilbene. When applied to secondary wastewater effluent, UV/chlorine and in-situ chlorination produced overall DBPs ranging from 104.77 to 135.41 µg/L. However, the production of chlorate during UV/chlorine processes was 15 times higher than that during in-situ chlorination.

Recirculating packed-bed biofilm photobioreactor combined with membrane ultrafiltration as advanced wastewater treatment

Packed-bed biofilm photobioreactor combined with ultrafiltration membrane was investigated for intensifying the process for secondary wastewater effluent treatment. Cylindrical glass carriers were used as supporting material for the microalgal-bacterial biofilm, which developed from indigenous microbial consortium. Glass carriers allowed adequate growth of the biofilm with limited suspended biomass. Stable operation was achieved after a start-up period of 1000 h, where supernatant biopolymer clusters were minimized and complete nitrification was observed. After that time, biomass productivity was 54 ± 18 mg·L−1·day−1. Green microalgae Tetradesmus obliquus and several strains of heterotrophic nitrification–aerobic denitrification bacteria and fungi were identified. Combined process exhibited COD, nitrogen and phosphorus removal rates of 56 ± 5%, 12 ± 2% and 20 ± 6%, respectively. Membrane fouling was mainly caused by biofilm formation, which was not effectively mitigated by air-scouring aided backwashing.

Novel self-sustained flow-through electrochemical advanced oxidation processes using nano-Fe0 confined B, N co-doped carbon nanotubes/graphite felt cathode: Higher mineralization efficiency under wider pH

To improve the mineralization efficiency of pollutants under wide pH ranges by self-sustained electrochemical advanced oxidation processes (EAOPs) without any reagent addition, a flow-through system based on the bifunctional cathode of B, N-doped carbon nanotubes embedded with nano-Fe0 particles that loaded on graphite felt (Fe@BN-C/GF) was developed. Dominant by 1O2 oxidation, the sulfamethazine (SMT) degradation rate and TOC removal in this recirculated flow-through system were 2.6 ∼ 3.3-folds and 1.4 ∼ 2.4-folds that of the batch system under the pH ranges of 3 ∼ 11, respectively. The SMT degradation performance was found not affected in the presence of HCO3–, NO3–, Cl-, K+, or humic acid (HA). The Fe@BN-C/GF cathode had more potential to treat enlarged wastewater by 5-folds during 10 h operation, and the SMT and TOC removal was 99% and 70.31%, respectively. The total phosphorus (TP), ammonia nitrogen (NH3-N) and TOC in reverse osmosis concentrate and secondary wastewater effluent could be simultaneously removed to <0.01 mg L-1 and 8 mg L-1 by this flow-through system with a low electric energy consumption (EEC) of 0.022 and 0.18 kWh gTOC-1, respectively. This EAOPs based on the flow-through Fe@BN-C/GF cathode was self-sustained, and had very promising application prospect of high mineralization of pollutants even for low-conductivity wastewater.