Biomonitoring of urban wastewaters treated by an integrated system combining microalgae and constructed wetlands

Feasible cultivation of Verrucodesmus verrucosus on sterile raw wastewater for energy purposes: a case study in Mexico

In this study, wastewater from a sewage treatment plant was used to culture the microalga, Verrucodesmus verrucosus. The ability of microalgae to adapt to adverse environments and produce high lipid concentrations was evaluated using different media, including sterile and non-sterile media and a control medium. The analysis showed that the control medium (distilled water sample enriched with fertilizer) removed 80.35% ammonium, 32.71% phosphate, and 83.86% nitrate. The sterile raw effluent removed 78.91% of ammonium, 83.44% of phosphate, and 98.82% of nitrate. The optimal conditions for biomass production were sterile raw wastewater, which produced 383.3 mg L-1 of biomass, 2.5% of total lipids, and an average lipid production of 9.31 mg L-1. Microalgae can grow and consume inorganic nutrients under adverse environmental conditions such as in raw wastewater, which is of great importance because it is a pollutant that negatively affects the environment and society. However, wastewater may represent a viable alternative substrate, allowing the generation of high-value products, such as lipids. Furthermore, the specificity of microalgal morphotypes must be evaluated, because each has specific metabolic plasticity. Verrucodesmus verrucosus is a microalga that has not been evaluated in bioremediation processes of wastewater with and without the presence of biotic factors. Therefore, the present study provides a viable alternative for this biological process, with the potential to store metabolites of interest in the industry.

Phytotoxicity assessment of treated vegetable oily wastewater via environmentally coagulation/flocculation and membrane filtration technologies using lettuce (Lactuca sativa) seeds

The present investigation highlights the necessity of monitoring some basic physico-chemical water quality indicators and their phytotoxic effect using ecotoxicological bioassays such as "seed germination tests." The phytotoxicity of raw and treated vegetable oil refinery wastewater (VORW) using different treatment processes was assessed through some physiological responses (relative seed germination (RSG), seedling elongation, and germination index (GI)) using Lactuca sativa cultivar. Biotest results of different raw water samples revealed a noticeable correlation between the organic matter content and water phytotoxicity. In fact, VORW showed a very low RSG (17 ± 0.7 to -47 ± 0.58%) and high phytotoxic effects (GI < 50%). The use of coagulation/flocculation (CF) allowed a satisfactory phytotoxicity removal where RSG obtained ranged from 83 ± 1.58 to 90 ± 1.2%. However, the effluent still presents high to moderate phytotoxicity since GI remained below 80% which indicates the presence of toxic elements remaining after CF treatment. When VORW were treated using membrane processes, their phytotoxicity was gradually decreased with the decrease in the membrane pore size. The use of microfiltration membranes (MF), with pore size of 5 µm, 1.2 µm, 0.45 µm, and 0.22 µm, showed RSG values ranged from 37 ± 1.15 to 77 ± 1.68% and GI of less than 80% indicating a moderate to high phytotoxicity. However, the use of ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) of 100 kDa, 30 kDa, and 10 kDa made it possible to achieve an RSG of 100% and an IG exceeding 80% showing that the VORW-treated using UF does not exhibit any phytotoxicity effect. Hence, UF appears to be the most efficient and environmentally friendly technology that could be used for safely treated VORW irrigation purposes compared to CF and MF processes.

Algae-constructed wetland integrated system for wastewater treatment: A review

Integrating algae into constructed wetlands (CWs) enhances wastewater treatment, although the results vary. This review evaluates the role of algae in CWs and the performance of different algae-CW (A-CW) configurations based on literature and meta-analysis. Algae considerably improve N removal, although their impact on other parameters varies. Statistical analysis revealed that 70 % of studies report improved treatment efficiencies with A-CWs, achieving average removal rates of 75 % for chemical oxygen demand (COD), 74 % for total nitrogen and ammonium nitrogen, and 79 % for total phosphorus (TP). This review identifies hydraulic retention times, which average 3.1 days, and their varied impact on treatment efficacy. Mixed-effects models showed a slight increase in COD and TP removal efficiencies of 0.6 % every ten days in the A-CWs. Future research should focus on robust experimental designs, adequate algal storage and separation techniques, and advanced modeling to optimize the treatment potential of algae in CWs.

Insight into pharmaceutical and personal care products removal using constructed wetlands: A comprehensive review

Pharmaceutical and personal care products (PPCPs) were regarded as emerging environmental pollutants due to their ubiquitous appearance and high environmental risks. The wastewater treatment plants (WWTPs) became the hub of PPCPs receiving major sources of PPCPs used by humans. Increasing concern has been focused on promoting cost-effective ways to eliminate PPCPs within WWTPs for blocking their route into the environment through effluent discharging. Among all advanced technologies, constructed wetlands (CWs) with a combination of plants, substrates, and microbes attracted attention due to their cost-effectiveness and easier maintenance during long-term operation. This study offers baseline data for risk control and future treatment by discussing the extent and dispersion of PPCPs in surface waters over the past ten years and identifying the mechanisms of PPCPs removal in CWs based on the up-to-present research, with a special focus on the contribution of sediments, vegetation, and the interactions of microorganisms. The significant role of wetland plants in the removal of PPCPs was detailed discussed in identifying the contribution of direct uptake, adsorption, phytovolatilization, and biodegradation. Meanwhile, the correlation between the physical-chemical characteristics of PPCPs, the configuration operation of wetlands, as well as the environmental conditions with PPCP removal were also further estimated. Finally, the critical issues and knowledge gaps before the real application were addressed followed by promoted future works, which are expected to provide a comprehensive foundation for study on PPCPs elimination utilizing CWs and drive to achieve large-scale applications to treat PPCPs-contaminated surface waters.

Energy recovery by anaerobic digestion of algal biomass from integrated microalgae/constructed wetland wastewater treatment

The present study evaluated the potential for biogas generation from microalgae (MA) biomass and macrophytes used in vertical flow constructed wetlands (VFCW). The samples were obtained by separation and collection of MA after a hydraulic retention time of 14 days, frozen and taken to the laboratory, while the macrophytes of VFCW were obtained, by pruning, every 6 months. The obtained results presented reductions of 63.22% and 61.18% for COD and BOD₅, respectively, and removal efficiencies of 53.91% for TP and 99.98% de N-NH₃. Average biogas generation was 2322.51 NmL-gSV^-1 with 54.61% CH₄ (winter/2019), 4491.47 Nml-gSV^-1 with 57.17% CH₄ (spring/2019), 680.78 NmL-gSV^-1 with 16.04% CH₄ (summer/2020), and 681.0 NmL-gSV^-1 with 19.86% CH₄ (autumn/2020) for MA biomass and generation of biogas of 3826.70 NmL-gSV^-1 with 44.26% CH₄ for VFCW biomass in winter and spring/2019 and of 829.68 NmL-gSV^-1 with 17.06% CH₄ in summer and autumn/2020. Regarding electricity generation, the present work obtained 1.50 kWh/m³, therefore reaching similar values to other studies that used more traditional biomass sources.

Mechanisms and application of microalgae on removing emerging contaminants from wastewater: A review

This study reviews the development of the ability of microalgae to remove emerging contaminants (ECs) from wastewater. Contaminant removal by microalgae-based systems (MBSs) includes biosorption, bioaccumulation, biodegradation, photolysis, hydrolysis, and volatilization. Usually, the existence of ECs can inhibit microalgae growth and reduce their removal ability. Therefore, three methods (acclimation, co-metabolism, and algal-bacterial consortia) are proposed in this paper to improve the removal performance of ECs by microalgae. Finally, due to the high removal performance of contaminants from wastewater by algal-bacterial consortia systems, three kinds of algal-bacterial consortia applications (algal-bacterial activatedsludge, algal-bacterial biofilm reactor, and algal-bacterial constructed wetland system) are recommended in this paper. These applications are promising for ECs removal. But most of them are still in their infancy, and limited research has been conducted on operational mechanisms and removal processes. Extra research is needed to clarify the applicability and cost-effectiveness of hybrid processes.

Microalgae-based removal of pollutants from wastewaters: Occurrence, toxicity and circular economy

The natural and anthropogenic sources of water bodies are contaminated with diverse categories of pollutants such as antibiotics, pharmaceuticals, pesticides, heavy metals, organic compounds, and other industrial chemicals. Depending on the type and the origin of the pollutants, the degree of contamination can be categorized into lower to higher concentrations. Therefore, the removal of hazardous chemicals from the environment is an important aspect. The physical, chemical and biological approaches have been developed and implemented to treat wastewaters. The microbial and algal treatment methods have emerged as a growing field due to their eco-friendly and sustainable approach. Particularly, microalgae emerged as a potential organism for the treatment of contaminated water bodies. The microalgae of the genera Chlorella, Anabaena, Ankistrodesmus, Aphanizomenon, Arthrospira, Botryococcus, Chlamydomonas, Chlorogloeopsis, Dunaliella, Haematococcus, Isochrysis, Nannochloropsis, Porphyridium, Synechococcus, Scenedesmus, and Spirulina reported for the wastewater treatment and biomass production. Microalgae have the potential for adsorption, bioaccumulation, and biodegradation. The microalgal strains can mitigate the hazardous chemicals via their diverse cellular mechanisms. Applications of the microalgae strains were found to be effective for sustainable developments and circular economy due to the production of biomass with the utilization of pollutants.

Combined system for wastewater treatment: ozonization and coagulation via tannin-based agent for harvesting microalgae by dissolved air flotation

This study evaluated the performance of urban wastewater treatment in pilot-plant by an integrated system consisting of anaerobic reactor, microalgae cultivation, Venturi tube ozone recirculation, coagulation/flocculation with tannin-based agent natural coagulant, and dissolved air flotation (DAF). Ozone concentrations (without ozone, 0.13 and 0.25 mg O₃/mg of biomass) and tannin dosages (65, 85 and 105 mg/L) were evaluated regarding microalgae separation and their influences on wastewater treatment performance. During the experiments, it was verified that the treatment efficiency increased when ozone was applied and with higher tannin dosages. The best results were found with 0.13 mg O₃/mg of biomass and 105 mg/L of tannin, obtaining excellent removal of turbidity removal (99.4%), apparent colour at 420 nm (94.5%), TN (83.2%), N-NH₃ (100%), TOC (86.8%), BOD₅ (86.5%) and COD (100%), 47.6% reduction in electric conductivity, 46.1% in TDS, 66.4% TP removal for the integrated system and 84% microalgae biomass recovery were obtained. Our results showed that the system proved to be a viable alternative for the treatment of urban wastewater and the recovery of microalgae through the insertion of ozone via Venturi tube combined with tannin-based agent.

Hybrid constructed wetlands integrated with microbial fuel cells and reactive bed filter for wastewater treatment and bioelectricity generation

The present study aimed to develop a pilot-scale integrated system composed of anaerobic biofilter (AF), a floating treatment wetland (FTW) unit, and a vertical flow constructed wetland coupled with a microbial fuel cell (CW-MFC) and a reactive bed filter (RBF) for simultaneously decentralized urban wastewater treatment and bioelectricity generation. The first treatment stage (AF) had 1450 L and two compartments: a settler and a second one filled with plastic conduits. The two CWs (1000 L each) were vegetated with mixed plant species, the first supported in a buoyant expanded polyethylene foam and the second (CW-MFC) filled with pebbles and gravel, whereas the RBF unit was filled with P adsorbent material (light expanded clay aggregate, or LECA) and sand. In the CW-MFC units, 4 pairs of electrode chambers were placed in different spacing. First, both cathode and anode electrodes were composed of graphite sticks and monitored as open circuit. Later, the cathode electrodes were replaced by granular activated carbon (GAC) and monitored as open and closed circuits. The combined system efficiently reduced COD (> 64.65%), BOD₅ (81.95%), N-NH₃ (93.17%), TP (86.93%), turbidity (94.3%), and total coliforms (removal of three log units). Concerning bioenergy, highest voltage values were obtained with GAC electrodes, reaching up to 557 mV (open circuit) and considerably lower voltage outputs with closed circuit (23.1 mV). Maximum power densities were obtained with 20 cm (0.325 mW/m²) and 30 cm (0.251 mW/m²). Besides the electrode superficial areas, the HRT and the water level may have influenced the voltage values, impacting DO and COD concentrations in the wastewater.

Effects and mechanisms of constructed wetlands with different substrates on N2O emission in wastewater treatment

Nitrous oxide (N₂O) emissions from constructed wetlands (CWs) are accompanying problems and have attracted much attention in recent years. CWs filled with different substrates (gravel, biochar, zeolite, and pyrite) were constructed to investigate the nitrogen removal performance and N₂O emissions, which named C-CWs, B-CWs, Z-CWs, and P-CWs, respectively. C-CWs showed the poorest nitrogen removal performance in all CWs. Although B-CWs exhibited the highest fluxes of N₂O emissions, the percentage of N₂O emissions in nitrogen removal (0.15%) was smaller than that of C-CWs (0.18%). In addition, microbiological analysis showed that compared with C-CWs, CWs filled with biochar, zeolite, and pyrite had higher abundance of nitrifying and denitrifying microorganisms and lower abundance of N₂O producing bacteria. In conclusion, biochar, zeolite, and pyrite were more favorable kinds of substrate than the conventional substrates of gravel for the nitrogen removal and reduction of N₂O emissions from CWs.

Algae-mediated antibiotic wastewater treatment: A critical review

The existence of continually increasing concentrations of antibiotics in the environment is a serious potential hazard due to their toxicity and persistence. Unfortunately, conventional treatment techniques, such as those utilized in wastewater treatment plants, are not efficient for the treatment of wastewater containing antibiotic. Recently, algae-based technologies have been found to be a sustainable and promising technique for antibiotic removal. Therefore, this review aims to provide a critical summary of algae-based technologies and their important role in antibiotic wastewater treatment. Algal removal mechanisms including bioadsorption, bioaccumulation, and biodegradation are discussed in detail, with using algae-bacteria consortia for antibiotic treatment, integration of algae with other microorganisms (fungi and multiple algal species), hybrid algae-based treatment and constructed wetlands, and the factors affecting algal antibiotic degradation comprehensively described and assessed. In addition, the use of algae as a precursor for the production of biochar is highlighted, along with the modification of biochar with other materials to improve its antibiotic removal capacity and hybrid algae-based treatment with advanced oxidation processes. Furthermore, recent novel approaches for enhancing antibiotic removal, such as the use of genetic engineering to enhance the antibiotic degradation capacity of algae and the integration of algal antibiotic removal with bioelectrochemical systems are discussed. Finally, some based on the critical review, key future research perspectives are proposed. Overall, this review systematically presents the current progress in algae-mediated antibiotic removal technologies, providing some novel insights for improved alleviation of antibiotic pollution in aquatic environments.

Microalgae-based technology for antibiotics removal: From mechanisms to application of innovational hybrid systems

Antibiotics contamination is an emerging environmental concern, owing to its potential risks to ecosystems and human health. Microalgae-based technology has been widely reported as a promising alternative to conventional wastewater treatment, since it is a solar-power driven, ecologically friendly, cost-effective, and sustainable reclamation strategy. This review provides fundamental insights into the major mechanisms underpinning microalgae-based antibiotics removal, including bioadsorption, bioaccumulation, and biodegradation. The critical role of extracellular polymeric substances on bioadsorption and extracellular biodegradation of antibiotics are also covered. Moreover, this review sheds light on the important factors affecting the removal of antibiotics by microalgae, and summarizes several novel approaches to improve the removal efficiency, including acclimation, co-metabolism and microbial consortium. Besides, hybrid systems (such as, microalgae-based technologies combined with the conventional activated sludge, advanced oxidation processes, constructed wetlands, and microbial fuel cells), and genetic engineering are also recommended, which will be feasible for enhanced removal of antibiotics. Finally, this review also highlights the need for further studies aimed at optimizing microalgae-based technology, with emphasis on improving performance and expanding its application in large-scale settings, especially in terms of technical, environmental-friendly and economically competitiveness. Overall, this review summarizes current understanding on microalgae-based technologies for removal of antibiotics and outlines future research directions.

Sustainable, Decentralized Sanitation and Reuse with Hybrid Nature-Based Systems

Nature (ecosystem) based processes for wastewater treatment include constructed wetlands (CWs), waste stabilization ponds, vegetated drainage ditches, buffer zones, instream or bankside river techniques, and mixotrophic systems, where light and CO2 are utilized, in addition to organic carbon compounds, by algal cultures. Algae-based systems can simultaneously remove organic matter, N, and P and may offer substantial energetic advantages compared to traditional biological treatment systems, require small spatial footprint, and contribute to biofuels production and CO2 emissions mitigation. Bioelectrochemical systems (BES) such as microbial fuel cells (MFCs) present characteristics compatible with the use in isolated realities for water and wastewater treatment with contextual energy recovery and may be combined with other nature-based process technologies to achieve good treatment and energy efficiencies. Despite that their application in real-scale plants has not been assessed yet, the most probable outcome will be the in situ/on site treatment (or pretreatment) of wastes for small “in house” plants not connected to the sewerage network. This paper focuses on the current practices and perspectives of hybrid nature-based systems, such as constructed wetlands and microalgae integrated phytoremediation plants, and their possible integration with microbial electrochemical technologies to increase recovery possibilities from wastes and positively contribute to a green economy approach.

Phyco-remediation of swine wastewater as a sustainable model based on circular economy

Pork production has expanded in the world in recent years. This growth has caused a significant increase in waste from this industry, especially of wastewater. Although there has been an increase in wastewater treatment, there is a lack of useful technologies for the treatment of wastewater from the pork industry. Swine farms generate high amounts of organic pollution, with large amounts of nitrogen and phosphorus with final destination into water bodies. Sadly, little attention has been devoted to animal wastes, which are currently treated in simple systems, such as stabilization ponds or just discharged to the environment without previous treatment. This uncontrolled release of swine wastewater is a major cause of eutrophication processes. Among the possible treatments, phyco-remediation seems to be a sustainable and environmentally friendly option of removing compounds from wastewater such as nitrogen, phosphorus, and some metal ions. Several studies have demonstrated the feasibility of treating swine wastewater using different microalgae species. Nevertheless, the practicability of applying this procedure at pilot-scale has not been explored before as an integrated process. This work presents an overview of the technological applications of microalgae for the treatment of wastewater from swine farms and the by-products (pigments, polysaccharides, lipids, proteins) and services of commercial interest (biodiesel, biohydrogen, bioelectricity, biogas) generated during this process. Furthermore, the environmental benefits while applying microalgae technologies are discussed.

Antibiotic resistance in wastewater treatment plants: understanding the problem and future perspectives

Antibiotics residues (AR), antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG) are a new class of water contaminants, due to their adverse effects on aquatic ecosystems and human health. Contamination of water bodies occurs mainly by the excretion of antibiotics incompletely metabolized by humans and animals and is considered the main source of contamination of antibiotics in the environment. Given the imminent threat, the World Health Organization (WHO) has categorized the spread of antibiotics as one of the top three threats to public health in the twenty-first century. The Urban Wastewater Treatment Plants (UWWTP) bring together AR, ARB, ARG, making the understanding of this peculiar environment fundamental for the investigation of technologies aimed at combating the spread of bacterial resistance. Several methodologies have been employed focusing on reducing the ARB and ARG loads of the effluents, however the reactivation of these microorganisms after the treatment is widely reported. This work aims to elucidate the role of UWWTPs in the spread of bacterial resistance, as well as to report the efforts that have been made so far and future perspectives to combat this important global problem.

Toxicity evaluation of hospital laundry wastewaters treated by microbial fuel cells and constructed wetlands

Hospital laundries generate high wastewater volumes with the presence of several contaminants. Nevertheless, few studies have investigated the toxicity of these effluents and looked for treatment alternatives that might reduce this eventual toxicity. So, the present study assessed the performance of an integrated system combining a microbial fuel cell (MBFC) and a constructed wetland (CW) to reduce toxic effects of wastewaters generated at a hospital laundry. After collection, raw effluents remained 7 days at the first unit (MBFC) of integrated system. Afterward, they were transferred to the second unit (CW) unit where remained more 7 days totaling a hydraulic detention time of 14 days. The toxicity evaluation involved three different organisms: Daphnia magna (acute ecotoxicity), Lactuca sativa (phytotoxicity) and Allium cepa (phytotoxicity, cytotoxicity, mutagenicity, and genotoxicity). Got results revealed an extremely acute ecotoxicity against D. magna, high phytotoxic effects in the L. sativa and A. cepa assays, and genotoxicity in the A. cepa assay for the untreated effluents. Furthermore, no significant incidence of micronuclei was observed in the raw wastewaters. Regarding the treatment, after the first stage, it was possible to verify that MBFC reduced the toxicity of the wastewaters only in some tested assays (endpoints) while after the CW (second stage) the effluents presented a complete absence of toxicity of the investigated bioassays. Therefore, the use of the integrated system combining two environmentally friendly technologies can be considered promising, since both MBFC and CW presented a complimentary effect with excellent results regarding the reduction of the overall toxicity of hospital laundry wastewaters.