Sustainable Wastewater Treatment Technology Research Articles

Constructed Wetland for Sustainable and Low-Cost Wastewater Treatment: Review Article

There is a growing need for more sustainable wastewater treatment technologies to provide non-conventional water sources. Constructed Wetland systems (CW) are viewed as a low-cost treatment technology with proven treatment efficiency. CWS can treat a variety of contaminants using low energy and natural systems by altering various design parameters. There are two configuration types of constructed wetlands: vertical (VF) and horizontal flow CW (HF). Both configurations have been widely adopted in both large and pilot scale studies with proven records of reasonable wastewater treatment efficiency. The current article reviews the recent development of CW technology and highlights the main achievements and successful applications for wastewater treatment at various locations. The review has indicated that a considerable removal efficiency is attained while using engineered CW systems with variable treatment rates for various pollutants. The treatment efficiency is a function of various parameters including wastewater type, scale dimensions, applied plant and the retention time. The review compared the treatment efficiency for both VF and HF and has revealed that various removal rates of BOD, COD, TSS, TN, TP and NH₄ was attained using both configurations. Yet, the removal efficiency in the case of VF was slightly higher compared with the HF with an average treatment level of 77% and 68% was achieved in both systems, respectively. The review revealed that the CW is an effective and sustainable technology for wastewater treatment with the initial influent level, microbial biofilm, detention time, plant species and configuration among the most dominating parameters that are directly controlling the removal rates.

An integrated decision making approach for selecting a sustainable waste water treatment technology

Growing global energy demand and the depletion of fossil fuels have highlighted the need for alternate and environmentally benign energy sources. The volume of untreated waste water being disposed of straight into fresh water is becoming a major concern. An integrated treatment method can address the problems of bio-energy generation and wastewater management as both processes can use wastewater as a substrate. Linear diophantine fuzzy sets help handle the uncertainty and difficulties that arise while deciding on an effective treatment technique. The use of control parameters makes these fuzzy sets unique and superior to other existing fuzzy sets. A modified strategy incorporating the Pivot pairwise relative criteria importance assessment and Interactive multi-criteria decision making methodologies is proposed for the linear diophantine fuzzy environment. The applicability and effectiveness of the developed model are established by choosing an appropriate wastewater treatment technology in the context of linear diophantine fuzzy sets. In addition, sensitivity analysis is used in this study to determine the stability of the developed framework. Further, comparison analysis is also addressed to assess the validity of the acquired results.

Photocatalytic oxidation of simulated and real hazardous medical wastewater: decolorization, mineralization and toxicity evaluation

AbstractBACKGROUNDLiquid hazardous medical wastes (LHMW) originating from health‐care laboratory services present a global environmental hazard as most sustainable wastewater treatment technologies fail to address this particularly demanding issue. In this study, heterogeneous and homogeneous photocatalytic oxidation of simulated and real LHMW has been performed at bench scale, investigating their potential to decompose and detoxify such effluents.RESULTSA simulated LHMW of 0.4 g L−1 DOC0 was photocatalytically treated in the presence of TiO2 P25. The addition of H2O2 was necessary to achieve mineralization, while the optimal concentration of P25 for this purpose was 1.0 g L−1. In the case of photo‐Fenton, under optimal conditions (0.056 g L−1 Fe3+, 3 g L−1 H2O2, UV‐A, pH 3.0) complete mineralization was accomplished in 600 min of illumination, while phytotoxicity was eliminated or significantly reduced, depending on the employed plant species. Photocatalytic processing of real LHMW (400 mg L−1 DOC0, 1.0 g L−1 TiO2 P25, 2.5 g L−1 H2O2, UV‐A or 0.056 g L−1 Fe3+, 3.0 g L−1 H2O2, UV‐A, pH 3.0) led to mineralization rates ranging from 55.5% to 95% after 900 min. Variations in ecotoxicity followed the mineralization profile for most samples. Partial mineralization failed to reduce toxicity in most samples, suggesting the generation of toxic intermediates; however, when mineralization exceeded 85%, ecotoxicity was in most cases efficiently removed.CONCLUSIONLaboratory LHMW are highly recalcitrant both in terms of mineralization and detoxification. However, photocatalytic oxidation may serve as an efficient processing tool, providing alternative or complementary solutions to this highly challenging issue. © 2021 Society of Chemical Industry (SCI).

Effect of vibration on the efficiency of ultrafiltration

Nowadays, several environmental challenges are present to cope with. One with outstanding importance is the protection of our water supplies, therefore examination of wastewater treatment technology is a priority, especially in the European Union. In this work, the effect of membrane module vibration amplitude on the efficiency of ultrafiltration (UF) was investigated in a vibratory shear enhanced membrane filtration system. Based on the results of model dairy effluent UF and statistical analysis, the maximum vibration level available resulted in the most efficient filtration process, due to the most significant reduction of membrane fouling. From our results it was observed that the permeate fluxes more than doubled, specific energy demand was roughly halved, with almost identical retentions for organic matter, and total filtration resistance was reduced to less than half. Results also showed that setting the optimal operating parameters, an advantageous, efficiency focused, and sustainable wastewater treatment technology can be established.

A Systematic Review of Drivers of Sustainable Wastewater Treatment Technology Adoption

In this systematic review we explore the forces that encourage or hinder the adoption of wastewater treatment and/or management technology. Our literature search uncovered 37 sources that discuss these issues. Retrieved sources were then subjected to qualitative synthesis. We adopted a systems-theory perspective in analyzing the qualitative data and provide insights into the interaction between the political environment and societal and organizational systems. Our findings indicate that sustainable change can best be achieved through understanding the interaction between systems and their actual capability to meet the needs of related systems. Societal-level systems emerge as having the possibility to influence the political environment as well as organizations.

Simultaneous enhancement of treatment performance and energy recovery using pyrite as anodic filling material in constructed wetland coupled with microbial fuel cells

Constructed wetland coupled with microbial fuel cells (CW-MFCs) are a promising technology for sustainable wastewater treatment. However, the performance of CW-MFCs has long been constrained by the limited size of its anode. In this study, we developed an alternative CW-MFC configuration that uses inexpensive natural conductive pyrite as an anodic filling material (PyAno) to extend the electroactive scope of the anode. As a result, the PyAno configuration significantly facilitated the removal of chemical oxygen demand, ammonium nitrogen, total nitrogen, and total phosphorus. Meanwhile, the PyAno increased the maximum power density by 52.7% as compared to that of the quartz sand control. Further, a typical exoelectrogen Geobacter was found enriched in the anodic zone of PyAno, indicating that the electroactive scope was extended by conductive pyrite. In addition, a substantial electron donating potential was observed for the anodic filling material of PyAno, which explained the higher electricity output. Meanwhile, a higher dissimilatory iron reducing potential was observed for the anodic sediment of PyAno, demonstrating the integrity of an iron redox cycling in the system and its promotive effect for the wastewater treatment. Together, these results implied that the PyAno CW-MFCs can be a competitive technology to enhance wastewater treatment and energy recovery simultaneously.

Designing a Sustainability Assessment Framework for Selecting Sustainable Wastewater Treatment Technologies in Corporate Asset Decisions

There is a growing demand for an integrated assessment to identify and select asset management options based on sustainability in the wastewater industry. However, water companies are often not equipped with a rigorous methodology and sufficient resources to perform sustainability assessments. Although many frameworks and tools for sustainability assessment have been developed in academia, practical challenges such as feasibility and usability remain when implementing sustainability assessment methods to support corporate decision-making. This study developed a Multi-Criteria Analysis based framework to evaluate wastewater treatment processes from a sustainability perspective. This study firstly explored the decision and organizational context of a water company with preliminary interviews and then applied the Analytical Hierarchy Process (AHP) with composite scores to evaluate wastewater technologies at a sewage treatment works. The preliminary interviews with stakeholders highlighted that the existing investment decisions were primarily driven by financial cost and compliance whilst calling for a wider consideration of other criteria. A selection of assessment criteria and indicators were then proposed to compare seven treatment technologies at a sewage treatment works. The results of composite scores indicated that the baseline activated sludge process (ASP) was the best option for this study. Experience from the development process highlighted usability, stakeholder engagement and the organizational context should all be considered as part of the design and implementation of the sustainability assessment. The insights from this study provide a valuable practical foundation for applying a multi-criteria approach to perform sustainability assessments and inform asset management decisions in the water company.

Nitrate/nitrite dependent anaerobic methane oxidation coupling with anammox in membrane biotrickling filter for nitrogen removal

Combining nitrate/nitrite dependent anaerobic methane oxidation (n-DAMO) and anaerobic ammonium oxidation (Anammox) is a promising sustainable wastewater treatment technology, which simultaneously achieve nitrogen removal and methane emission mitigation. However, the practical application of n-DAMO has been greatly limited by its extremely slow growth-rate and low reaction rate. This work proposes an innovative Membrane BioTrickling Filter (MBTF), which consist of hollow fiber membrane for effective methane supplementation and polyurethane sponge as support media for the attachment and growth of biofilm coupling n-DAMO with Anammox. When steady state with a hydraulic retention time (HRT) of 6.00 h was reached, above 99.9% of nitrogen was removed from synthetic sidestream wastewater at a rate of 3.99 g N L−1 d−1. This system presented robust capacity to withstand unstable partial nitritation effluent, achieving complete nitrogen removal at a varied nitrite to ammonium ratio in the range of 1.10–1.40. It is confirmed that n-DAMO and Anammox microorganisms jointly dominated the microbial community by pyrosequencing technology. The complete nitrogen removal potential at high-rate and efficient biomass retention (12.4 g VSS L−1) of MBTF offers promising alternative for sustainable wastewater treatment by the combination of n-DAMO and Anammox.

CFD Modeling of UV/H2O2 Process in Internal Airlift Circulating Photoreactor

UV chemical degradation is a low-cost and sustainable wastewater treatment technology that protects the environment. In this study, computational fluid dynamics (CFD), mass transfer, and photochemical kinetic models combined with the continuous flow mode of UV/H2O2 were applied for the photochemical reaction of internal airlift circulation photocatalytic reactor to improve the efficiency of the reaction. Results show that with the increase in gas flow rate, the turbulence intensity and internal circulation effect of liquid in the reactor can be enhanced under the condition of constant baffle spacing. The CFD simulation prediction results of the chemical components in the liquid flow show that H2O2 has a high correlation with the OH radical formation, which depends on the intensity of UV. Thus, the degradation rate of methylene blue (MB) has a high correlation with UV intensity. The degradation efficiency of MB is improved with the increase in gas velocity by comparing the experimental data with the numerical simulation data. The experimental data are generally lower than the numerical prediction data, and although a certain difference range is observed, the overall prediction results are better.

Novel sequential flow baffled microalgal-bacterial photobioreactor for enhancing nitrogen assimilation into microalgal biomass whilst bioremediating nutrient-rich wastewater simultaneously

A novel sequential flow baffled microalgal-bacterial (SFB-AlgalBac) photobioreactor was designed to cater for the synergistic interactions between microalgal and bacterial consortia to enhance nitrogen assimilation into microalgal biomass from nutrient-rich wastewater medium. The performance of the SFB-AlgalBac photobioreactor was found to be optimum at the influent flow rate of 5.0 L/d, equivalent to 20 days of hydraulic retention time (HRT). The highest microalgal nitrogen assimilation rate (0.0271 /d) and biomass productivity (1350 mg/d) were recorded amidst this flow rate. Further increase to the 10.0 L/d flow rate reduced the photobioreactor performance, as evidenced by a reduction in microalgal biomass productivity (>10%). The microalgal biomass per unit of nitrogen assimilated values were attained at 16.69 mg/mg for the 5.0 L/d flow rate as opposed to 7.73 mg/mg for the 10.0 L/d flow rate, despite both having comparable specific growth rates. Also, the prior influent treatment by activated sludge was found to exude extracellular polymeric substances which significantly improved the microalgal biomass settleability up to 37%. The employment of SFB-AlgalBac photobioreactor is anticipated could exploit the low-cost nitrogen sources from nutrient-rich wastewaters via bioconversion into valuable microalgal biomass while fulfilling the requirements of sustainable wastewater treatment technologies.

From toilet to agriculture: Fertilization with microalgal biomass from wastewater impacts the soil and rhizosphere active microbiomes, greenhouse gas emissions and plant growth

Human activities are pushing earth beyond its natural limits, so recycling nutrients is mandatory. Microalgae are highly effective in nutrient recovery and have strong potential as a sustainable wastewater treatment technology. Here, nutrients from black water (toilet wastewater) were recovered as microalgal biomass, which was dried and assessed as a fertilizer in pot experiments compared with inorganic fertilizer. We deciphered the effects of microalgal biomass as a biofertilizer on plant growth and quality and the biological processes linked to greenhouse gas (GHG) emissions. In addition, we elucidated the assembly of the active microbiome in bulk soil and rhizosphere during barley development. Microalgal biomass application and inorganic fertilizer (NPK) resulted in similar plant productivity (16.6 g pot−1). Cumulative nitrous oxide (N2O) emissions were 4.6-fold higher in the treatment amended with microalgal fertilizer (3.1% of applied N) than that with inorganic fertilizer (0.5% of applied N). Nitrification by bacteria was likely the main pathway responsible for N2O emissions (R2 = 0.7, p ≤ 0.001). The application of nitrogen fertilizers affected the structures of both the active bacterial and protozoan communities, but these effects were less obvious than the strong plant effect, as the recruited microbiota varied among different plant developmental stages. Both treatments enriched similar bacterial and protozoan taxonomic orders but with different distributions through time across the plant developmental stages. Furthermore, the bacterial community showed a clear trend of resilience from the beginning of the experiment until harvest, which was not observed for protozoa. Our results indicate that the use of microalgal biomass as a fertilizer is a viable option for recycling nutrients from wastewater into plant production.

Assessment of wastewater reuse potential for irrigation in rural semi-arid areas: the case study of Punitaqui, Chile

Wastewater reuse in agriculture has been identified as an adaptive solution to climate change. This practice copes with two of the most limiting factors that are affecting sustainable development in rural areas: the lack of sanitation services and water shortages. This paper proposes a multi-criteria methodological approach to evaluate wastewater reuse potential for irrigation in rural areas and to select the most sustainable and context-aware wastewater treatment technology. In order to validate the procedure, an empirical application for the Coquimbo region (Chile) was developed. The water balance conducted illustrated that the potential wastewater source can only partially substitute for the water canonical sources. According to local citizen preferences, among the three evaluated, the most sustainable wastewater treatment technology option consists of septic tank and constructed wetland. This study provides evidence for the relevance of integrating social and environmental criteria, in addition to technical and economic ones, for supporting decision-making processes related to wastewater reuse.

How does electron transfer occur in microbial fuel cells?

Microbial fuel cells (MFCs) have emerged as a promising technology for sustainable wastewater treatment coupled with electricity generation. A MFC is a device that uses microbes as catalysts to convert chemical energy present in biomass into electrical energy. Among the various mechanisms that drive the operation of a MFC, extracellular electron transfer (EET) to the anode is one of the most important. Exoelectrogenic bacteria can natively transfer electrons to a conducting surface like the anode. The mechanisms employed for electron transfer can either be direct transfer via conductive pili or nanowires, or mediated transfer that involves either naturally secreted redox mediators like flavins and pyocyanins or artificially added mediators like methylene blue and neutral red. EET is a mechanism wherein microorganisms extract energy for growth and maintenance from their surroundings and transfer the resulting electrons to the anode to generate current. The efficiency of these electron transfer mechanisms is dependent not only on the redox potentials of the species involved, but also on microbial oxidative metabolism that liberates electrons. Attempts at understanding the electron transfer mechanisms will boost efforts in giving rise to practical applications. This article covers the various electron transfer mechanisms involved between microbes and electrodes in microbial fuel cells and their applications.

Modelling of methylene blue adsorption using peroxidase immobilized functionalized Buckypaper/polyvinyl alcohol membrane via ant colony optimization

Jicama peroxidase (JP) was covalently immobilized onto functionalized multi-walled carbon nanotube (MWCNT) Buckypaper/Polyvinyl alcohol (BP/PVA) membrane and employed for degradation of methylene blue dye. The parameters of the isotherm and kinetic models are estimating using ant colony optimization (ACO), which do not meddle the non-linearity form of the respective models. The proposed inverse modelling through ACO optimization was implemented, and the parameters were evaluated to minimize the non-linear error functions. The adsorption of MB dye onto JP-immobilized BP/PVA membrane follows Freundlich isotherm model (R2 = 0.99) and the pseudo 1st order or 2nd kinetic model (R2 = 0.980 & 0.968 respectively). The model predictions from the parameters estimated by ACO resulted values close the experimental values, thus inferring that this approach captured the inherent characteristics of MB adsorption. Moreover, the thermodynamic studies indicated that the adsorption was favourable, spontaneous, and exothermic in nature. The comprehensive structural analyses have confirmed the successful binding of peroxidase onto BP/PVA membrane, as well as the effective MB dye removal using immobilized JP membrane. Compared to BP/PVA membrane, the reusability test revealed that JP-immobilized BP/PVA membrane has better dye removal performances as it can retain 64% of its dye removal efficiency even after eight consecutive cycles. Therefore, the experimental results along with modelling results demonstrated that JP-immobilized BP/PVA membrane is expected to bring notable impacts for the development of effective green and sustainable wastewater treatment technologies.

Deciphering the effects of temperature on bio-methane generation through anaerobic digestion.

Anaerobic digestion (AD) is a sustainable wastewater treatment technology which facilitates energy, nutrient, and water recovery from organic wastes. The agricultural and industrial wastes are suitable substrates for the AD, as they contain a high level of biodegradable compounds. The aim of this study was to examine the AD of three different concentrations of phenol (100, 200, and 300mg/L) containing wastewater with and without co-substrate (acetate) at four different temperatures (25, 35, 45, and 55°C) to produce methane (CH4)-enriched biogas. It was observed that the chemical oxygen demand (COD) and phenol removal efficiencies of up to 76% and 72%, respectively, were achieved. The CH4 generation was found higher in anaerobic batch reactors (ABRs) using acetate as co-substrate, with the highest yield of 189.1μL CH4 from 500μL sample injected, obtained using 200mg/L of phenol at 35°C. The results revealed that the performance of ABR in terms of degradation efficiency, COD removal, and biogas generation was highest at 35°C followed by 55, 45, and 25°C indicating 35°C to be the optimum temperature for AD of phenolic wastewater with maximum energy recovery. Scanning electron microscopy (SEM) revealed that the morphology of the anaerobic sludge depends greatly on the temperature at which the system is maintained which in turn affects the performance and degradation of toxic contaminants like phenol. It was observed that the anaerobic sludge maintained at 35°C showed uniform channels leading to higher permeability through enhanced mass transfer to achieve higher degradation rates. However, the denser sludge as in the case of 55°C showed lesser permeability leading to limited transfer and thus reduced treatment. Quantitative real-time PCR (qPCR) analysis revealed a more noteworthy change in the population of the microbial communities due to temperature than the presence of phenol with the methanogens being the dominating species at 35°C. The findings suggest that the planned operation of the ABR could be a promising choice for CH4-enriched biogas and COD removal from phenolic wastewater.

A comprehensive evaluation method for sludge pyrolysis and adsorption process in the treatment of coking wastewater

This study proposes a new evaluation method based on expert scoring and data normalization to optimize operational conditions of sludge pyrolysis and assess the comprehensive benefits of the adsorption process in coking wastewater treatment. Pyrolysis temperature, holding time and heating rate were considered as the experimental parameters in sludge pyrolysis. They were optimized by the proposed method, considering raw material cost, net energy consumption, carbon emission and adsorption capacity of sludge-derived bio-char (SB). Two operational modes (cyclic centralized and traditional distributed) were compared to identify a better solution for coking wastewater treatment. The results showed that the optimized operational conditions of coking sludge pyrolysis were that temperature of 550 °C, holding time of 60 min and heating rate of 20 °C/min, using the proposed method. Cyclic centralized mode has been demonstrated as the better mode for wastewater treatment by the proposed method, due to the higher comprehensive score of −0.296. It is a promising technology for sustainable wastewater treatment in terms of sludge recycling, energy saving and carbon emission reduction.

Decision making tools for selecting sustainable wastewater treatment technologies in Thailand

Wastewater consists of valuable resources that could be recovered or reused. Still it is under threat because of ineffective wastewater management and systems. In Thailand, less than 25% of wastewater generated may be treated while then rest is inadequately treated and sent back directly into waterbodies or the environment. Furthermore, the technologies that have been applied may be inefficient and unsustainable. Efficiency, sustainability, and simplicity are important concepts when designing an appropriate wastewater treatment system in developing countries. The objectives of this study were to review and evaluate wastewater treatment technologies and propose a method to improve or select an appropriate technology. An expert system in Excel® program was developed to determine the best solution. Sensitivity analysis was applied to compare and assess uncertainty factors. Due to the different conditions of each area, the key factor of interest was varied. Furthermore, Robust Decision Making tool was applied to determine the best way to improve existing wastewater treatment facility and to choose the most appropriate wastewater treatment technology.

Selecting appropriate wastewater treatment technologies using a choosing-by-advantages approach

Selecting the most sustainable wastewater treatment (WWT) technology among possible alternatives is a very complex task because the choice must integrate economic, environmental, and social criteria. Traditionally, several multi-criteria decision-making approaches have been applied, with the most often used being the analytical hierarchical process (AHP). However, AHP allows users to offset poor environmental and/or social performance with low cost. To overcome this limitation, our study examines a choosing-by-advantages (CBA) approach to rank seven WWT technologies for secondary WWT. CBA results were compared with results obtained by using the AHP approach. The rankings of WWT alternatives differed, depending on whether the CBA or AHP approach was used, which highlights the importance of the method used to support decision-making processes, particularly ones that rely on subjective interpretations by experts. This paper uses a holistic perspective to demonstrate the benefits of using the CBA approach to support a decision-making process when a group of experts must come to a consensus in selecting the most suitable WWT technology among several available.

Effects of electrolyte conductivity on power generation in bio-electrochemical systems

Bio-electrochemical systems (BESs) have recently attracted considerable attention as a promising technology for sustainable wastewater treatment. However, the practical applications of BESs remain limited partly because the conductivity of actual wastewater can vary from 0.2 to 40 ms/cm which is out of the appropriate range for power generation. Herein, we investigated the effect of anolyte and catholyte conductivities on power generation. The maximum current density (0.73 mA/cm2) was achieved by reactors using an anolyte solution with a conductivity of 14.93 ± 0.02 ms/cm; this was four times higher than the minimum current density (0.13 mA/cm2), obtained using a solution with a conductivity of 2.61 ± 0.04 ms/cm. Anolyte conductivity was found to be the primary rate-limiting factor for power generation and had a greater effect than the conductivity of the catholyte. Furthermore, an anolyte conductivity range of 6.45–14.93 ms/cm was found to be most appropriate for superior BES performance.

Development of a novel anaerobic membrane bioreactor simultaneously integrating microfiltration and forward osmosis membranes for low-strength wastewater treatment

Anaerobic osmotic membrane bioreactor (AnOMBR) has aroused growing interests for its low energy demand, ability to efficiently process low ionic strength wastewater and high effluent quality. However, salt accumulation remains a main obstacle for causing severe water flux decline, fouling aggravation and inhibitory on the microbial activity. Here, we report a novel microfiltration (MF) assisted AnOMBR (AnMF-OMBR) for mitigating salt accumulation. The results indicated that the MF membrane effectively prevented salt accumulation in the bioreactor. The stable salinity level (within the range of 2.5–4.0mS/cm) enabled the AnMF-OMBR to achieve a long-term continuous operation together with a higher methane production in comparison with a conventional AnOMBR. The forward osmosis (FO) permeate from the AnMF-OMBR had excellent water quality, while the MF permeate required further treatment (e.g., phosphorus precipitation and activated carbon adsorption) before its beneficial reuse. A thick fouling layer combining biofouling and inorganic scaling was existed on the FO membrane. Further confocal laser scanning microscopy (CLSM) revealed the dominance of polysaccharides and microorganisms over proteins. The current study demonstrated that the AnMF-OMBR can be a promising and sustainable wastewater treatment technology for its simultaneous energy recovery (in the form of biogas) and water reuse (from both FO and MF membranes).