What does it take to renature cities? An expert-based analysis of barriers and strategies for the implementation of nature-based solutions.

This paper uses an expert-based methodology to survey the barriers and strategies related to the implementation of nature-based solutions (NBS). The ambition of the paper is to offer a bird's eye overview of the difficulties encountered by NBS deployment and ways to overcome them. With a wide participation of 80 experts from COST Action Circular City, we identify barriers specific to 35 pre-defined NBS of the following four categories: Vertical Greening Systems and Green Roofs; Food and Biomass Production; Rainwater Management; and Remediation, Treatment, and Recovery. The research sheds light on how a major interdisciplinary - yet predominantly technically-oriented - community of scientists and practitioners views this important topic. Overall, the most relevant barriers are related to technological complexity, lack of skilled staff and training programs and the lack of awareness that NBS is an option. Our results highlight concerns related to post implementation issues, especially operation and maintenance, which subsequently affect social acceptance. The paper identifies a "chain" effect across barriers, meaning that one barrier can affect the existence or the relevance of other barriers. In terms of strategies, most of them target governance, information, and education aspects, despite the predominantly technical expertise of the participants. The study innovates with respect to state-of-the-art research by showing a fine-grained connection between barriers, strategies and individual NBS and categories, a level of detail which is not encountered in any other study to date.

Competitive heavy metal adsorption on pinecone shells: Mathematical modelling of fixed-bed column and surface interaction insights.

Pinecone shells are assessed as a cost-effective biosorbent for the removal of metal ions Pb(II), Cu(II), Cd(II), Ni(II), and Cr(VI) in a fixed-bed column. Influent concentration, bed height, and flowrate are studied to improve efficiency. The breakthrough data is well fitted by the Sips adsorption model, suggesting a surface complexation mechanism, with maximum adsorption capacities of 11.1 mg/g for Cu(II) and 66 mg/g for Pb(II). In multimetal solutions, the uptake sequence at breakthrough and saturation is Pb(II) > Cu(II) > Cd(II). Characterization via FTIR and XRD reveals carboxyl and hydroxyl functional groups interacting with metal ions. Ca(II) does not compete with Pb(II), Cu(II), and Cd(II) adsorption, highlighting the ability of pinecone to adsorb heavy metals via surface complexation. Its application in the treatment of industrial effluents containing Cu(II), Ni(II), and Cr(VI) is explored. The study investigates bed media regeneration via eluting adsorbed metal ions with hydrochloric acid solutions. The potential of pinecone shells as an efficient biosorbent for removing toxic metal ions from industrial wastewater is emphasized. These findings enhance our understanding of the adsorption mechanism and underscore the fixed-bed column system's applicability in real-world scenarios, addressing environmental concerns related to heavy metal contamination of industrial effluents.

High-rate activated sludge at very short SRT: Key factors for process stability and performance of COD fractions removal.

In high-rate activated sludge (HRAS) processes, reducing the solid retention time (SRT) minimizes COD oxidation and allows to obtain the maximum energy recovery. The aim of this research was to operate a pilot plant with an automatic control strategy to assure the HRAS process stability and high COD fractions removal at very low SRT. This study combines simulation and experimental tools (pilot plant 35 m3·d - 1) operating at SRT (0.2 d), HRT (0.6 h) and DO (0.5 mg·L - 1) treating high-strength raw wastewater, at 18-26°C, at variable flow. The research includes the effects of temperature, influent concentration and MLSS reactor concentration over the sCOD, cCOD and pCOD removal. The study points out that the best parameter to control the HRAS at a low SRT is not strictly the SRT but rather the reactor MLSS concentration: operating at 2,000±200mg·L - 1 assured a stable process despite the large influents variation. Low SVI values of 50-70ml·g - 1 indicated the good settling properties of the biomass. With only a 6.9% COD oxidation, a high organic matter removal (57±9% for COD and 56±10% for BOD5), was reached. The high removal efficiencies for pCOD (74%) compared to the (29%) for sCOD and (12%) for cCOD also confirmed the importance of settling efficiency and stability in the HRAS. The direct correlation between COD influent and COD removal makes advisable to use the HRAS as a replacement of the primary clarifier. The HRAS acted efficiently as a filter for COD and pCOD peak loads and, in a lesser extent, for BOD5, while sCOD peaks were not buffered. The adopted model presented a good fit for COD fractions except for pCOD when the temperature exceeds 23 °C.

Increasing resilience through nudges in the urban water cycle: An integrative conceptual framework to support policy decision-making.

Relevant challenges associated with the urban water cycle must be overcome to meet the United Nations Sustainable Development Goals (SDGs) and improve resilience. Unlike previous studies that focused only on the provision of drinking water, we propose a framework that extends the use of the theory of nudges to all stages of the overall urban water cycle (drinking water and wastewater services), and to agents of influence (citizens, organizations, and governments) at different levels of decision making. The framework integrates four main drivers (the fourth water revolution, digitalization, decentralization, and climate change), which influence how customers, water utilities and regulators approach the challenges posed by the urban water cycle. The proposed framework, based on the theory of nudges first advanced by the Nobel Prize in behavioral economics Richard H. Thaler and Cass R. Sunstein (Thaler and Sunstein, 2009), serves as a reference for policymakers to define medium- and long-term strategies and policies for improving the sustainability and resilience of the urban water cycle. Finally, we provide new insights for further research on resilience approaches to the management of the urban water cycle as an element to support the more efficient formulation of policies.

Landfill Leachate Treatment by Using Second-Hand Reverse Osmosis Membranes: Long-Term Case Study in a Full-Scale Operating Facility.

Landfill leachate (LFL) has a complex inorganic, organic and microbiological composition. Although pressure-driven membrane technology contributes to reaching the discharge limits, the need for frequent membrane replacement (typically every 1-3 years) is an economical and environmental limitation. The goal of this work is to evaluate the feasibility of using second-hand reverse osmosis (RO) membranes to treat LFL in an industrially relevant environment. End-of-life RO membranes discarded from a seawater desalination plant were first tested with brackish water and directly reused or regenerated to fit with requirements for LFL treatment. A laboratory scale test of second-hand membrane reuse was carried out using ultrafiltered LFL. Then, a long-term test in an LFL full-scale facility was performed, where half of the membranes of the facility were replaced. The industrial plant was operated for 27 months with second-hand membranes. The permeate water quality fit the required standards and the process showed a trend of lower energy requirement (up to 12 bar lower transmembrane pressure and up to 9% higher recovery than the average of the previous 4 years). Direct reuse and membrane regeneration were successfully proven to be an alternative management to landfill disposal, boosting membranes towards the circular economy.

Benchmarking empirical models for THMs formation in drinking water systems: An application for decision support in Barcelona, Spain.

Drinking water treatment plants (DWTPs) face changes in raw water quality, which affect the formation of disinfection by-products. Several empirical modelling approaches have been reported in the literature, but most of them have been developed with lab-scale data, which may not be representative of real water systems. Therefore, the application of these models for real-time operation of DWTPs might be limited. At the present study, multiple linear regression (MLR) and multi-layer perceptrons (MLP) were benchmarked using field-scale data for predicting the THMs formation in a case-study DWTP in Barcelona, Spain. After fitting the studied models, MLR exhibited good fit with the validation data set (R2 = 0.88 and MAE = 4.0 µg·L-1) and described the most plausible input-output relationships with field-scale data. The MLR predictive model was incorporated into an environmental decision support system (EDSS) for assessing the THMs formation at two critical points of the distribution network. A Monte Carlo scheme was applied for quantifying uncertainty of model predictions at these points, considering low and high water quality scenarios and different degrees of treatment by an electrodialysis reversal process. The results show that the use of the proposed EDSS can help in real operation of complex drinking water systems, which face important changes in water quality throughout the year.

When the fourth water and digital revolution encountered COVID-19.

The ongoing COVID-19 pandemic is, undeniably, a substantial shock to our civilization which has revealed the value of public services that relate to public health. Ensuring a safe and reliable water supply and maintaining water sanitation has become ever more critical during the pandemic. For this reason, researchers and practitioners have promptly investigated the impact associated with the spread of SARS-CoV-2 on water treatment processes, focusing specifically on water disinfection. However, the COVID-19 pandemic impacts multiple aspects of the urban water sector besides those related to the engineering processes, including sanitary, economic, and social consequences which can have significant effects in the near future. Furthermore, this outbreak appears at a time when the water sector was already experiencing a fourth revolution, transitioning toward the digitalisation of the sector, which redefines the Water-Human-Data Nexus. In this contribution, a product of collaboration between academics and practitioners from water utilities, we delve into the multiple impacts that the pandemic is currently causing and their possible consequences in the future. We show how the digitalisation of the water sector can provide useful approaches and tools to help address the impact of the pandemic. We expect this discussion to contribute not only to current challenges, but also to the conceptualization of new projects and the broader task of ameliorating climate change.

Implementation of an environmental decision support system for controlling the pre-oxidation step at a full-scale drinking water treatment plant.

Drinking water treatment plants (DWTPs) face changes in raw water quality, and treatment needs to be adjusted to produce the best water quality at the minimum environmental cost. An environmental decision support system (EDSS) was developed for aiding DWTP operators in choosing the adequate permanganate dosing rate in the pre-oxidation step. To this end, multiple linear regression (MLR) and multi-layer perceptron (MLP) models are compared for choosing the best predictive model. Besides, a case-based reasoning (CBR) model was approached to provide the user with a distribution of solutions given similar operating conditions in the past. The predictive model consisted of an MLP and has been validated against historical data with sufficient good accuracy for the utility needs (R2 = 0.76 and RSE = 0.13 mg·L-1). The integration of the predictive and the CBR models in an EDSS gives the user an augmented decision-making capacity of the process and has great potential for both assisting experienced users and for training new personnel in deciding the operational set-point of the process.

A Polydimethylsiloxane Rod Extraction-Based Method for the Determination of Pharmaceuticals and Triclosan by Liquid Chromatography in Water Samples.

A new analytical method for the determination of naproxen, ketoprofen, diclofenac, carbamazepine, and triclosan (TCS) in water samples by liquid chromatography is developed and validated. The method is based on the extraction of the analytes by a polydimethylsiloxane (PDMS) rod. The different parameters affecting extraction, such as the addition of salt, pH, initial volume, extraction and elution times and elution solvent, as well as the application of sonication, are studied. The results showed that the detection limits are all in the 0.1-0.3 µg L-1 range except for carbamazepine (6 µg L-1) with relative standard deviations in the range of 0.4%-9.7%. The method developed, which was validated by analysing spiked surface water samples at 10, 25 and 75 µg L-1 gave recoveries of between 84.8% and 111.2%. In the case of carbamazepine, a recovery of 99.1% was obtained at 75 µg L-1. The main advantage of the developed method is that allows high performance liquid chromatography-diode array detection, which is widely available in non-specialised laboratories, to be applied for pharmaceuticals and TCS determination in surface waters after performing a preconcentration/clean-up step with PDMS rods as it has been shown by analysing real water samples.

Granulated cork as biosorbent for the removal of phenol derivatives and emerging contaminants.

This study evaluated the ability of cork to adsorb a broad range of phenolic, pharmaceutical and cosmetic compounds: phenol, 2-chlorophenol, 2-nitrophenol, 2,4-dichlorophenol, pentachlorophenol carbamazepine, naproxen, ketoprofen, diclofenac, triclosan, and methyl paraben. The effect of variables such as the compound concentrations and the amount of cork were studied resulting in a highly pH dependence in the case of phenolic compounds. Maximum removal percentages and uptake values of 75% (1.61 mg/g) for 2,4-dichlorophenol, 55% (1.25 mg/g) for 2-nitrophenol, 45% (1.47 mg/g) for 2-chlorophenol, 20% (0.63 mg/g) for phenol, and 100% for pentachlorophenol, were obtained for a 30 mg L-1 solution at pH 6, showing that the adsorption process increased with greater electronegativity of the phenolic substituting group. Removal percentages and uptakes of 82% (3.56 mg/g) for naproxen, 57% (2.31 mg/g) for ketoprofen, 50% (1.84 mg/g) for carbamazepine, 50% (1.78 mg/g) for methyl paraben, 100% for sodium diclofenac, and 100% for triclosan, were obtained using 5 mg of cork and a 1 mg L-1 solution of each compound. The adsorption process was almost complete after 30 min for all the micropollutants. Experimental equilibrium data were analysed by Freundlich and Langmuir adsorption models. Cork has proved to be an effective sorbent for the removal of phenols and emerging contaminants from contaminated waters and is a readily available material that can be acquired at minimal or no cost in cork-producing areas.

Fate of NDMA precursors through an MBR-NF pilot plant for urban wastewater reclamation and the effect of changing aeration conditions.

The removal of N-nitrosodimethylamine (NDMA) formation potential through a membrane bioreactor (MBR) coupled to a nanofiltration (NF) pilot plant that treats urban wastewater is investigated. The results are compared to the fate of the individual NDMA precursors detected: azithromycin, citalopram, erythromycin, clarithromycin, ranitidine, venlafaxine and its metabolite o-desmethylvenlafaxine. Specifically, the effect of dissolved oxygen in the aerobic chamber of the MBR pilot plant on the removal of NDMA formation potential (FP) and individual precursors is studied. During normal aerobic operation, implying a fully nitrifying system, the MBR was able to reduce NDMA precursors above 94%, however this removal percentage was reduced to values as low as 72% when changing the conditions to minimize nitrification. Removal decreased also for azithromycin (68-59%), citalopram (31-17%), venlafaxine (35-15%) and erythromycin (61-16%) on average during nitrifying versus non-nitrifying conditions. The removal of clarithromycin, o-desmethylvenlafaxine and ranitidine could not be correlated with the nitrification inhibition, as it varied greatly during the experiment time. The MBR pilot plant is coupled to a nanofiltration (NF) system and the results on the rejection of both, NDMA FP and individual precursors, through this system was above 90%. Finally, results obtained for the MBR pilot plant are compared to the percentage of removal by a conventional full scale biological wastewater treatment plant (WWTP) fed with the same influent. During aerobic operation, the removal of NDMA FP by the MBR pilot plant was similar to the full scale WWTP.

Full-scale validation of an air scour control system for energy savings in membrane bioreactors.

Membrane aeration represents between 35 and 50% of the operational cost of membrane bioreactors (MBR). New automatic control systems and/or module configurations have been developed for aeration optimization. In this paper, we briefly describe an innovative MBR air scour control system based on permeability evolution and present the results of a full-scale validation that lasted over a 1-year period. An average reduction in the air scour flow rate of 13% was achieved, limiting the maximum reduction to 20%. This averaged reduction corresponded to a decrease in energy consumption for membrane aeration of 14% (0.025 kWh m(-3)) with maximum saving rates of 22% (0.04 kWh m(-3)). Permeability and fouling rate evolution were not affected by the air scour control system, as very similar behavior was observed for these variables for both filtration lines throughout the entire experimental evaluation period of 1 year.

Optimizing chemical conditioning for odour removal of undigested sewage sludge in drying processes.

Emission of odours during the thermal drying in sludge handling processes is one of the main sources of odour problems in wastewater treatment plants. The objective of this work was to assess the use of the response surface methodology as a technique to optimize the chemical conditioning process of undigested sewage sludges, in order to improve the dewaterability, and to reduce the odour emissions during the thermal drying of the sludge. Synergistic effects between inorganic conditioners (iron chloride and calcium oxide) were observed in terms of sulphur emissions and odour reduction. The developed quadratic models indicated that optimizing the conditioners dosage is possible to increase a 70% the dewaterability, reducing a 50% and 54% the emission of odour and volatile sulphur compounds respectively. The optimization of the conditioning process was validated experimentally.

Knowledge-based control module for start-up of flat sheet MBRs.

In start-up periods low MLSS concentration may lead to fouling phenomena and uncommon frequency of chemical cleanings using membrane bioreactors. A knowledge-based control module for the optimisation of start-up procedures in membrane bioreactors is presented and validated in this paper. The main objective of the control module is to accelerate the growth of MLSS and the achievement of the design flux while minimising the fouling phenomenon during start-up periods. The module was validated in a pilot-scale membrane bioreactor with the University of Cape Town configuration and submerged flat sheet microfiltration membranes. The knowledge of the control system was represented as a decision tree before being implemented. A fully satisfactory start-up, both for the filtration and the biological phase, was obtained in 20 days, saving time and preserving the membrane integrity.

Removal of microbial indicators from municipal wastewater by a membrane bioreactor (MBR).

The impact of removable and irremovable fouling on the retention of viral and bacterial indicators by the submerged microfiltration membrane in an MBR pilot plant was evaluated. Escherichia coli, sulphite-reducing Clostridium spores, somatic coliphages and F-specific RNA bacteriophages were used as indicators. The membrane demonstrated almost complete removal of E. coli and sulphite-reducing Clostridium spores. However, there was no correlation with membrane fouling. The phage removal varied in accordance with the irremovable fouling, rising from 2.6 to 5.6 log(10) units as the irremovable fouling increased (measured by the change in the transmembrane pressure). In contrast, removable fouling did not have any effect on the retention of viruses by the membrane. These results indicate that irremovable membrane fouling may affect the removal efficiency of MBRs and, therefore, their capacity to ensure the required microbiological standards for the permeate achieved.

Biological nutrient removal in an MBR treating municipal wastewater with special focus on biological phosphorus removal.

The performance of an MBR pilot plant for biological nutrient removal was evaluated during 210days of operation. The set point values for the internal recycles were determined in advance with the use of an optimisation spreadsheet based on the ASM2d model to optimise the simultaneous removal of C, N and P. The biological nutrient removal (BNR) efficiencies were high from the start of operation with COD and N removal efficiencies of 92+/-6% and 89+/-7, respectively. During the course of the experiment P removal efficiencies increased and finally a P-removal efficiency of 92% was achieved. The activity of poly-phosphate accumulating organisms (PAOs) and denitrifying poly-phosphate accumulating organisms (DPAOs) increased and the specific phosphate accumulation rates after 150days of operation amounted to 13.6mgPg(-1)VSSh(-1) and 5.6mgPg(-1)VSSh(-1), for PAOs and DPAOs, respectively.

Nitrogen removal from landfill leachate using the SBR technology.

Landfill leachate is a concern in the wastewater field due to its toxicity, high ammonium and low biodegradable organic matter concentrations. The aim of this paper is to study the reliability of landfill leachate treatment using Sequencing Batch Reactor (SBR) technology for biological nitrogen removal. During the study the SBR pilot plant treated successfully 0.48 kg N x m(-3) d(-1) of urban landfill leachate. Furthermore, high nitrogen removal efficiencies (80%, on average) have been achieved by the operational conditions applied (step-feed strategy and alternating anoxic-aerobic conditions).