Algae turf scrubber and vertical constructed wetlands combined system for decentralized secondary wastewater treatment

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.

Adaptive strategies to enhance water security and resilience in low- and middle-income countries: A critical review

The water sector is facing unprecedented pressures as increased environmental and anthropogenic challenges, such as climate change and rapid urbanization, impact the availability and predictability of safe drinking water. There is a need for practitioners and policymakers to integrate water security and resilience (WS&R) factors into programming to sustain investments in drinking water systems to support associated economic, security, and public health benefits. In response to intensifying impacts from WS&R risks, communities around the world are developing adaptive strategies, and a critical review of these strategies may provide lessons that can be implemented at scale. In this critical review, we systematically screened over 9000 peer-reviewed and grey literature articles and extracted data from relevant studies that propose, pilot, and/or evaluate adaptations in low- and middle-income countries (LMICs) and evaluated the suitability of each adaptation for different contexts. We created a portfolio of adaptive strategies from over 75 LMICs to inform practitioners and policymakers in enhancing the resilience of drinking water systems. Over 20 adaptations were identified, including strategies such as stormwater management, wastewater reuse, non-revenue water reductions, water pricing, and public awareness campaigns. We categorized adaptations by function (improving water management, augmenting existing supplies, reducing water demand) and scale (household, municipal, regional) to provide recommendations tailored to local needs. For each adaptation, we highlighted associated strengths, weaknesses, barriers to adoption, and enabling environments for successful implementation. We propose a novel decision-support tool, called STEP WS&R, that provides a consistent and replicable process for informing high-level investment and policy choices around WS&R. This critical review presents recommendations for practitioners and policymakers to invest in WS&R adaptations, catered to shared risks and contexts.

Using wastewater as a cultivation alternative for microalga Dunaliella salina: Potentials and challenges

Untreated or poorly treated wastewater still represents environmental issues world-widely. Wastewater, especially saline wastewater treatment, is still primarily associated with high costs from physical and chemical processes, as high salinity hinders biological treatment. One favourable way is to find the suitable biological pathways and organisms to improve the biological treatment efficiency. In this context, halophilic microorganisms could be strong candidates to address the economics and effectiveness of the saline wastewater treatment process. Dunaliella salina is a photoautotrophic microalga that grows in saline environments. It is known for producing marketable bio-compounds such as carotenoids, lipids, and proteins. A biological treatment based on D. salina cultivation offers the opportunity to treat saline wastewater, reducing the threat of possible eutrophication from inappropriate discharge. At the same time, D. salina cultivation could yield compounds of industrial relevance to turn saline wastewater treatment into a profitable and sustainable process. Most research on D. salina has primarily focused on bioproduct generation, leaving thorough reviews of its application in wastewater treatment inadequate. This paper discusses the future challenges and opportunities of using D. salina to treat wastewater from different sources. The main conclusions are (1) D. salina effectively recovers some heavy metals (driven by metal binding capacity and exposure time) and nutrients (driven by pH, their bioavailability, and functional groups in the cell); (2) salinity plays a significant role in bioproducts generation, and (3) wastewater can be combined with the generation of bioproducts.

Decentralized systems for the treatment of antimicrobial compounds released from hospital aquatic wastes

In many developing countries, untreated hospital effluents are discharged and treated simultaneously with municipal wastewater. However, if the hospital effluents are not treated separately, they pose concerning health risks due to the possible transport of the antimicrobial genes and microbes in the environment. Such effluent is considered as a point source for a number of potentially infectious microorganisms, waste antimicrobial compounds and other contaminants that could promote antimicrobial resistance development. The removal of these contaminants prior to discharge reduces the exposure of antimicrobials to the environment and this should lower the risk of superbug development. At an effluent discharge site, suitable pre-treatment of wastewater containing antimicrobials could maximise the ecological impact with potentially reduced risk to human health. In addressing these points, this paper reviews the applications of decentralized treatment systems toward reducing the concentration of antimicrobials in wastewater. The most commonly used techniques in decentralized wastewater treatment systems for onsite removal of antimicrobials were discussed and evidence suggests that hybrid techniques should be more useful for the efficient removal of antimicrobials. It is concluded that alongside the cooperation of administration departments, health industries, water treatment authorities and general public, decentralized treatment technology can efficiently enhance the removal of antimicrobial compounds, thereby decreasing the concentration of contaminants released to the environment that could pose risks to human and ecological health due to development of antimicrobial resistance in microbes.

Organic Carbon Is Ineffective in Enhancing the Growth of Dunaliella

(1) Background: Mixotrophic growth is commonly associated with higher biomass productivity and lower energy consumption. This paper evaluates the impact of using different carbon sources on growth, protein profile, and nutrient uptake for Dunaliella tertiolecta CCAP 19/30 to assess the potential for mixotrophic growth. (2) Methods: Two experimental sets were conducted. The first assessed the contribution of atmospheric carbon to D. tertiolecta growth and the microalgae capacity to grow heterotrophically with an organic carbon source to provide both carbon and energy. The second set evaluated the impact of using different carbon sources on its growth, protein yield and quality. (3) Results: D. tertiolecta could not grow heterotrophically. Cell and optical density, ash-free dry weight, and essential amino acids index were inferior for all treatments using organic carbon compared to NaHCO3. Neither cell nor optical density presented significant differences among the treatments containing organic carbon, demonstrating that organic carbon does not boost D. tertiolecta growth. All the treatments presented similar nitrogen, phosphorus, sulfur recovery, and relative carbohydrate content. (4) Conclusions: Based on the results of this paper, D. tertiolecta CCAP 19/30 is an obligated autotroph that cannot grow mixotrophically using organic carbon.

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.

A comprehensive review on the use of algal-bacterial systems for wastewater treatment with emphasis on nutrient and micropollutant removal

The scarcity of water resources and environmental pollution have highlighted the need for sustainable wastewater treatment. Existing conventional treatment systems are energy-intensive and not always able to meet stringent disposal standards. Recently, algal-bacterial systems have emerged as environmentally friendly sustainable processes for wastewater treatment and resource recovery. The algal-bacterial systems work on the principle of the symbiotic relationship between algae and bacteria. This paper comprehensively discusses the most recent studies on algal-bacterial systems for wastewater treatment, factors affecting the treatment, and aspects of resource recovery from the biomass. The algal-bacterial interaction includes cell-to-cell communication, substrate exchange, and horizontal gene transfer. The quorum sensing (QS) molecules and their effects on algal-bacterial interactions are briefly discussed. The effect of the factors such as pH, temperature, C/N/P ratio, light intensity, and external aeration on the algal-bacterial systems have been discussed. An overview of the modeling aspects of algal-bacterial systems has been provided. The algal-bacterial systems have the potential for removing micropollutants because of the diverse possible interactions between algae-bacteria. The removal mechanisms of micropollutants - sorption, biodegradation, and photodegradation, have been reviewed. The harvesting methods and resource recovery aspects have been presented. The major challenges associated with algal-bacterial systems for real scale implementation and future perspectives have been discussed. Integrating wastewater treatment with the algal biorefinery concept reduces the overall waste component in a wastewater treatment system by converting the biomass into a useful product, resulting in a sustainable system that contributes to the circular bioeconomy.

Systematic review of the last 20 years of research on decentralized domestic wastewater treatment in Brazil: state of the art and potentials

A DEWATS (decentralized wastewater treatment system) is an alternative for expanding sanitation. In Brazil, DEWATS is acknowledged by law and is part of the National Sanitation Plan strategy for achieving the treatment of 85.6% of all the generated wastewater by 2033, improving the current treatment index of 49%. This review's aim is to identify DEWATS studies in Brazil and to verify their potential for narrowing the national wastewater treatment deficit. Hence, aspects such as cost, maintenance, and efficiency were assessed. The archival research method (ARM) was used to identify papers published in the last 20 years through the scientific databases of Scopus, Science Direct, and Web of Science. Data regarding the general characteristics of each study were collected and compared to Brazilian environmental regulation and sanitation status. The results showed the evaluation of different technologies such as DEWATS, highlighting their flexibility and potential use in 79% of Brazilian counties. However, although 81% of the studies conducted performance analysis, none covered the main parameters required by Brazilian law. Although legal gaps for DEWATS improvement and consolidation have been identified and the interest in studying DEWATS has been increasing in the last five years, many barriers to their widespread use remain.

Pollution prevention and waste phycoremediation by algal-based wastewater treatment technologies: The applications of high-rate algal ponds (HRAPs) and algal turf scrubber (ATS)

Following the escalating human population growth and rapid urbanization, the tremendous amount of urban and industrial waste released leads to a series of critical issues such as health issues, climate change, water crisis, and pollution problems. With the advantages of a favorable carbon life cycle, high photosynthetic efficiencies, and being adaptive to harsh environments, algae have attracted attention as an excellent agent for pollution prevention and waste phycoremediation. Following the concept of circular economy and biorefinery for sustainable production and waste minimization, this review discusses the role of four different algal-based wastewater treatment technologies, including high-rate algal ponds (HRAPs), HRAP-absorption column (HRAP-AC), hybrid algal biofilm-enhanced raceway pond (HABERP) and algal turf scrubber (ATS) in waste management and resource recovery. In addition to the nutrient removal mechanisms and operation parameters, recent advances and developments have been discussed for each technology, including (1) Innovative operation strategies and treatment of emerging contaminants (ECs) employing HRAPs, (2) Biogas upgrading utilizing HRAP-AC system and approaches of O₂ minimization in biomethane, (3) Operation of different HABERP systems, (4) Life-cycle and cost analysis of HRAPs-based wastewater treatment system, and (5) Value-upgrading for harvested algal biomass and life-cycle cost analysis of ATS system.

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.

Microalgal and duckweed based constructed wetlands for swine wastewater treatment: A review

Constructed wetlands for swine wastewater treatment have been one of the most exciting research topics. Usually hydrophytes based constructed wetlands could not adapt well to high concentration of ammonia nitrogen in swine wastewater, while microalgal and duckweed based constructed wetlands are promising for the nutrient removal. In this critical review, the important roles of microalgae and duckweeds played in wastewater treatment in constructed wetlands were first summarized. Performances including biomass growth, nutrient removal capacities and mechanisms of microalgal and duckweed based constructed wetlands were reviewed for swine wastewater treatment. Challenges for the applications of constructed wetlands including microalgal and duckweed based ones were discussed which includes a better understanding and utilization of synergistic effects among microalgae and duckweeds, difficulty and costs in harvesting biomass, applications in various field conditions including low temperatures, and selections of various types of microalgal and duckweed species. Future research needs were also proposed accordingly.

Influence of rain events on the efficiency of a compact wastewater treatment plant: a case study on a university campus aiming water reuse for agriculture

In this study, the efficiency of contaminant removal from a compact wastewater treatment plant (CWTP) in a university campus under different rain conditions was evaluated. Wastewater samples were collected weekly for 1 year and the physicochemical parameters were monitored. Removal efficiency higher than 77%, reaching values above 95% for samples with lower wastewater flow rates, was found for biological oxygen demand (BOD) and total and fecal coliforms. The pH values remained in the range of 6.0-8.0. However, pH values below 6.8 impaired the nitrification rate and, therefore, the removal of total Kjeldahl nitrogen (TKN) and ammonia was lower than the expected, with concentration values above those set by the Brazilian regulation for wastewater discharge. The results show that the flow rate of wastewater at the entrance of the CWTP is directly related to the rain events, thus affecting its efficiency, mainly in the removal of total solids, turbidity, and organic matter. The assessment of the treated wastewater reuse on site for agricultural purposes showed to be a prominent and more sustainable alternative regarding the discharge of wastewater into water bodies.

Distributed treatment systems

This section presents a review of the scientific literature published in 2019 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics. PRACTITIONER POINTS: Highlights changes and innovation in removal techniques and technologies in water treatment. Reviews management systems of distributed treatment systems. Discusses point-of-use treatment systems.

Constructed Wetlands in Latin America and the Caribbean: A Review of Experiences during the Last Decade

The review aims to report the state-of-the-art constructed wetlands (CW) in the Latin America and Caribbean (LAC) region not limited to national and local conditions. The aim is with a broader view, to bring updated and sufficient information, to facilitate the use of the CW technology in the different countries of LAC. Thus, 520 experiences extracted from the 169 reviewed documents in 20 countries were analyzed. According to the data, horizontal subsurface flow wetlands are the most reported CW in the region (62%), the second most common CW technology in the region is free water surface CW (17%), then vertical flow systems (9%), followed by intensified constructed wetlands (8%), and finally French systems (4%). The performance for nutrient removal is analyzed, finding that the mean of Chemical Oxygen Demand (COD), Total Nitrogen (TN), and Total Phosphorous (TP) removal efficiencies varies from 65% to 83%, 55% to 72%, and 30% to 84%, respectively. The results suggest a generally good performance for COD and TN removal, but a low performance for TP removal. Regarding plant species used for CWs, 114 different plant species were reported, being until now the most extensive report about plant species used in CWs in the LAC region.

Acute ecotoxicity and genotoxicity assessment of two wastewater treatment units

Water contamination by discharge of untreated or poorly treated wastewater into water bodies is a current issue that may cause harm to humans. Water quality assessment targets general parameters, which often misleads to underestimation of their implication in the environment. Acute and genotoxicity assays using Daphnia magna is a reliable tool for testing deleterious effects of wastewater exposure. This paper aimed at evaluating acute ecotoxicity as well as genotoxicity of a biological treatment system composed by an anaerobic bioreactor (AR), algal turf scrubber (ATS), followed by two downflow constructed wetlands (CW). The university's wastewater treatment plant (WWTP) composed by an equalization tank (ET), an upflow anaerobic sludge blanket (UASB), followed by an aerobic bioreactor (AB) was also assessed for acute and genotoxicity. Our results showed the acute ecotoxicity ranged from moderately to extremely toxic, and from nontoxic to moderately toxic for ET and AB. For AR, most samples were moderately toxic. The outflow from ATS and CW's tanks completely eliminated acute toxicity and genotoxicity evidencing that the proposed system combining ATS and vertical CWs is suitable for treating sanitary wastewater.

Wastewater Biofilm Photosynthesis in Photobioreactors

Photosynthetic performance of algal-bacterial biofilms from an Italian wastewater treatment plant was studied in a flow-lane photobioreactor at different irradiances, temperatures, and flow regime to evaluate the effects of these environmental parameters on biofilms’ functioning, in view of application of these communities in wastewater biological treatment. Pulse amplitude modulated fluorescence was used to estimate the effective quantum yield of PSII (ΔF/F_m’) of the light-acclimated biofilms and to perform rapid light curves (RLCs) for the determination of the photosynthetic parameters (rel.ETR_max, α, I_k). Chl a, ash free dry weight (AFDW), and dry weight (DW) were measured to assess phototrophic and whole biofilm biomass development over time. From the analysis of photosynthetic parameter variation with light intensity, temperature and flow rate, it was possible to identify the set of experimental values favoring biofilm photosynthetic activity. Biomass increased over time, especially at the highest irradiances, where substrata were fastly colonized and mature biofilms developed at all temperatures and flow conditions tested.

Combined system for the treatment and reuse of urban wastewater: the efficiency of anaerobic reactors + hybrid constructed wetlands + ozonation

The research developed a combined system in batch flow and in pilot scale for the treatment and reuse of urban effluents. The system was fed raw effluent from a university campus in Brazil and composed of four anaerobic reactors, three constructed wetlands (CWs) and an ozonation unit. The three sequential hybrid constructed wetlands were composed of a floating treatment wetland, an aerobic-anoxic baffled constructed wetland (CW) and a saturated vertifcal flow CW. Later, during the last trimester, weekly samples of the treated effluent were ozonated by bubbling with an application rate of 240 mg.h-1 O3. The system presented high removal rates efficiencies in terms of carbonaceous organic matter (78.9%), nitrogen (91.0%), color (96.7%) and turbidity (99.1%). In addition, it worked well for disinfection and acute ecotoxicity, but P was only efficiently (75%) removed in the first 8 months, with removing efficiency declining after this period. Ozonation provided significant color removal and an increased pH. The combination of floating, alternated upflow and downflow and saturated vertical flows improved the treatment of wastewater. This was due to the presence of both aerobic and anaerobic zones, as well as the filter substrate, through an integrated system with simple construction and operation and increased lifespan.