Abstract

This article examines the potential benefits of using Data Envelopment Analysis (DEA) for conducting energy-efficiency assessment of wastewater treatment plants (WWTPs). WWTPs are characteristically heterogeneous (in size, technology, climate, function …) which limits the correct application of DEA. This paper proposes and describes the Robust Energy Efficiency DEA (REED) in its various stages, a systematic state-of-the-art methodology aimed at including exogenous variables in nonparametric frontier models and especially designed for WWTP operation. In particular, the methodology systematizes the modelling process by presenting an integrated framework for selecting the correct variables and appropriate models, possibly tackling the effect of exogenous factors. As a result, the application of REED improves the quality of the efficiency estimates and hence the significance of benchmarking. For the reader's convenience, this article is presented as a step-by-step guideline to guide the user in the determination of WWTPs energy efficiency from beginning to end. The application and benefits of the developed methodology are demonstrated by a case study related to the comparison of the energy efficiency of a set of 399 WWTPs operating in different countries and under heterogeneous environmental conditions.

Abstract

Anaerobic fermentation of organic wastes using microbial mixed cultures is a promising avenue to treat residues and obtain added-value products. However, the process has some important limitations that prevented so far any industrial application. One of the main issues is that we are not able to predict reliably the product spectrum (i.e. the stoichiometry of the process) because the complex microbial community behaviour is not completely understood. To address this issue, in this work we propose a new metabolic network of glucose fermentation by microbial mixed cultures that incorporates electron bifurcation and homoacetogenesis. Our methodology uses NADH balances to analyse published experimental data and evaluate the new stoichiometry proposed. Our results prove for the first time the inclusion of electron bifurcation in the metabolic network as a better description of the experimental results. Homoacetogenesis has been used to explain the discrepancies between observed and theoretically predicted yields of gaseous H2 and CO2 and it appears as the best solution among other options studied. Overall, this work supports the consideration of electron bifurcation as an important biochemical mechanism in microbial mixed cultures fermentations and underlines the importance of considering homoacetogenesis when analysing anaerobic fermentations.

Abstract The aim of this study was to compare the environmental performance and sustainability of different management options for livestock waste in Cyprus. The two most common practices in the country, i.e. the use of anaerobic lagoons and conventional biogas plants, were compared with the innovative scheme developed in the LiveWaste project (LIFE12 ENV/CY/000544), which aims not only to produce bioenergy, but also to treat the digestate for nutrient recovery and water reuse. The Life Cycle Assessment (LCA) methodology was combined with the Analytic Hierarchy Process (AHP) to compare the performance of these alternatives. Four relevant indicators were selected for each dimension of sustainability (environmental, social and economic). The results of the evaluations showed that anaerobic lagoons are not an appropriate option for the sustainable management of livestock waste due to environmental (e.g. climate change, acidification and eutrophication) and social impacts (e.g. noise exposure, visual impact and risk perception for human health). The most important strengths and weaknesses of anaerobic treatment with and without digestate treatment were identified. Compared to conventional anaerobic digestion where digestate is directly applied as an organic fertiliser, the technology proposed in the project entails higher technological complexity due to nitrogen removal and phosphorus recovery. The rise in chemical and electricity requirements increased the impacts on some indicators, such as climate change and operational cost (emissions of greenhouse gases and operation costs were around 50% higher), while reduced impacts in others due to proper nutrient management, as acidification and eutrophication impacts (which were 10 and almost two times lower, respectively). For the specific Cypriot conditions, where the overapplication of nutrients leads to pollution of water bodies, the innovative treatment scheme with higher technological development presents an interesting approach. Nevertheless, the treatment of the digestate should be analysed taking into account the specific characteristics of each scenario.

https://doi.org/10.1016/j.scitotenv.2018.03.299

Abstract

Organic micropollutants (OMPs) comprise a wide group of substances highly consumed in modern societies. There has been a growing social and scientific interest on OMPs in wastewaters in the twentyfirst century. This research paper has identified the evolution of the research trends in the period 2001–2017 on OMPs fate during secondary wastewater treatment. These trends have moved from a global perspective on the occurrence of OMPs in wastewaters to more specific research focussed on understanding their behaviour during advanced treatment processes. Based on a bibliometric analysis carried out using one of the leading scientific databases, pharmaceuticals have been identified as the main group of OMPs. An increasing number of publications have been released on the fate of pharmaceuticals in wastewater with a growing number of countries involved: from 38 publications belonging to 14 countries in first 5-year period analysed (2001–2005) up to 138 from 42 countries only in the last 2 years (2016–2017). The main operational conditions in wastewater treatment plants influencing the removal of OMPs, as well as the mechanisms involved depending on the physico-chemical characteristics of the substances are reviewed. The paper also considers the role of microbial populations, as well as technological and operational features in OMPs abatement. Finally, a specific section is dedicated to the metabolic and cometabolic biotransformations of some OMPs taking place under heterotrophic, nitrifying and anaerobic conditions, a more novel research trend explored more recently.

Abstract

Granular activated carbon (GAC) is applied as post-treatment technology in wastewater treatment plants (WWTPs) in order to increase the elimination of organic micropollutants (OMPs). However, the efficiency and life-time of GAC depend on several parameters, such as the quality of the effluent to be treated or the type of GAC. In the present paper, two types of GAC, based on bituminous carbon (BC-GAC) and coconut shell (CS-GAC), were assessed from a technical, economic and environmental point of view to further remove OMPs present in two secondary effluents, coming from integrated biological systems with a membrane or a settler, respectively. Although all GAC filters were efficient in removing selected OMPs, the quality of the secondary effluent had a strong influence on the lifespan of adsorbent material and the technical operability of the filtration systems. While GAC filters treating membrane effluent were highly effective to remove recalcitrant compounds, such as carbamazepine and diazepam (>80%), even after 430 d of operation (>30,800 BV), the efficiency of GAC filters treating settler effluent quickly lowered to 50% after 100 d of operation (<7200 BV). Both types of GAC showed similar adsorption capacities and only slight differences were found in terms of costs (2.4 €/kg vs 2.7 €/kg). However, CS-GAC has a lower carbon footprint than BC-GAC, mainly due to the more environmentally friendly production process of CS-GAC.

Abstract

Humic acid has a controversial effect on the biological treatment processes. Here, we have investigated humic acid effects on the Anammox activity by studying the nitrogen removal efficiencies in batch and continuous conditions and analyzing the microbial community using Fluorescence in situ hybridization (FISH) technique. The results showed that the Anammox activity was affected by the presence of humic acid at a concentration higher than 70 mg/L. In fact, in the presence of humic acid concentration of 200 mg/L, the Anammox activity decreased to 57% in batch and under continuous condition, the ammonium removal efficiencies of the reactor decreased from 78 to 41%. This reduction of Anammox activity after humic acid addition was highlighted by FISH analysis which revealed a considerable reduction of the abundance of Anammox bacteria and the bacteria living in symbiosis with them. Furthermore, a total inhibition of Candidatus Brocadia fulgida was observed. However, humic acid has promoted heterotrophic denitrifying bacteria which became dominant in the reactor. In fact, the evolution of the organic matter in the reactor showed that the added humic acid was used as carbon source by heterotrophic bacteria which explained the shift of metabolism to the favor of heterotrophic denitrifying bacteria. Accordingly, humic acid should be controlled in the influent to avoid Anammox activity inhibition.

Abstract

A single stage partial nitritation and anammox granular pilot scale reactor (600 L) was operated to treat primary settled sewage in an urban wastewater treatment plant. The fed wastewater contained low total nitrogen concentrations of 6–25 mg TN/L and the system operated without temperature control ranging from 18 to 12 °C. A control strategy, based on the pH value, was applied to stop the aeration supply. The pH set-point was fixed at 6.0 and allowed obtaining a total nitrogen removal efficiency approximately of 50% treating a load of 67 mg TN/(L·d) without the addition of any chemicals. Although nitrite oxidizing bacteria were present in the inoculated sludge, when the pH-based control was implemented (day 30) the ammonium oxidation was favored compared to the nitrite oxidation activity. Then, the system operated stable the rest of the operational period (days 30–94) despite the presence of organic matter in the wastewater and the high variability of nitrogen load and temperature during the operation. Nitrogen was autotrophically removed accomplishing the stringent discharge limits (10 mg TN/L) and nitrate concentrations in the effluent lower than 3 mg NO3−-N/L. Both biomass concentration and granules size increased during the operational period indicating the growth of the biomass inside the reactor and therefore the potential treatment capacity.

Abstract

The general framework of the Chemical Engineering studies in Spain includes the Bachelor's Degree (4 years), Master's Degree (the most common duration is 1.5 years) and Doctorate (3-4 years). In 2008, the Conference of Directors and Deans of Chemical Engineering (CODDIQ) was constituted with the main objective of promoting and improving the quality of Chemical Engineering studies in Spain. Currently, Faculties and Schools of 29 Spanish universities are members of CODDIQ. An analysis of the most characteristic indicators provides a representative radiography of the Chemical Engineering Studies in Spain, whose most outstanding data are: (i) 7,396 undergraduate students, 1,014 Master students and 556 PhD students, (ii) according to the gender profile of undergraduates and graduates, the percentage of women is similar to that of men, while for faculty staff, the percentage of women is 43% and 46% for Associate and Assistant Professor (respectively) and 23% for the category of Full Professor category; (iii) after completing the Bachelor studies, most of them continue their training in the MSc in Chemical Engineering, (iv) the employability after obtaining the Master's degree is very high (>75%), which in the case of PhDs is close to 100%. The studies of Chemical Engineering in Spain have a very direct relationship with society, especially in the chemical, environmental, biotechnological and energy fields. The companies that collaborate in the training of future professionals are distributed throughout the national territory, which allows a strong connection with the socioeconomic environment.

Normalisation is an optional step in Life Cycle Assessment (LCA), often used in decision making since it helps interpreting the results of LCA studies with regard to some reference information. The applicable ISO standard recommends considering different reference systems to guarantee the robustness of the normalisation step, and so the availability of different normalisation datasets becomes of high relevance. Life Cycle Impact Assessment (LCIA) methods provide normalisation factors (NFs) for global and regional areas, but no NFs are proposed for smaller areas such as local or subnational scales. The aim of this paper is to evaluate the feasibility of using territorial LCA approach to determine subnational NFs. Normalisation datasets for both Galician (NW Spain) production and consumption activities have been calculated considering a life cycle perspective. In addition to this, the normalisation datasets calculated for Galicia have been used to evaluate two food products produced and/or consumed in the region as case studies. Then, the normalised results have been compared to those obtained using different reference systems (Europe and the World), calculated following the same methodology (ReCiPe). A qualitative uncertainty analysis of the NFs has been carried out, and the usefulness of territorial LCA to determine them has been discussed. It was concluded that territorial LCA is a promising way to determine NFs but that some improvements could be made, which have also been pointed out here.

The conception of urban metabolism has considered the perspective of environmental sustainability in the framework of cities. In this context, cities can be regarded complex entities driven by material and energy flows that entail consumption of resources and production of waste materials in the pursuit of economic welfare and social progress. According to a sustainability perspective, environmental, social and economic indicators must also be integrated into urban planning processes. However, methodological advances regarding the definition and development of sustainable cities are required since a consensus of indicators, weighting and data management is still lacking. In this paper, a multi-criteria approach that combines three methodologies: Material Flow Analysis (MFA), Life Cycle Assessment (LCA) and Data Envelopment Analysis (DEA) has been developed and applied to a sample of 26 representative Spanish cities with different characteristics (i.e., population, location, demands, economy, topography and culture). The combined approach allows identifying the non-sustainable cities considering an offset of indicators from the three pillars of sustainability. With this purpose, the mentioned items are implemented in a DEA model of efficiency, being the inefficient cities with an efficiency score lower than 100% defined as non-sustainable ones. Finally, this multi-criteria method allows setting the target values for the assessed indicators (benchmarked values), which become objectives for the non-sustainable cities to evolve toward a more sustainable performance. The outcomes from the analysis have identified six cities that ranked worse, with efficiency scores ranging from 57.9% to 85.8%. According to the targets of socio-economic indicators, attention should be paid to AROPE rate (people at risk of poverty and social exclusion), unemployment rate and number of crimes, meanwhile lower levels of electricity consumption, municipal solid waste and on-site greenhouse gases emissions are desirable from an environmental perspective. These outcomes are of potential interest for politicians, governments and inhabitants to aid in the identification of the metabolic flows and social/economic indicators to be optimized in search of sustainability.

Abstract

Use and production of industrialized wood based panels is increasing in Brazil and one of the outstanding products is the Oriented Strand Boards (OSB). At the same time, environmental concerns by companies and society about products and production systems are also growing, and the current study aims to assess the environmental impacts associated to the Brazilian OSB production in order to propose improvement alternatives focused on their profile's enhancement. Thus, a Life Cycle Assessment (LCA) study was performed according to ISO14040 and 14044 frameworks. The study covers the life cycle of OSB production from a cradle-to-gate perspective and considering real practices carried out in a representative Brazilian company. The production system has been divided in two main subsystems: Forest operations (SS1) and Panel factory (SS2). The environmental profiles have been reported considering characterization factors from the ReCiPe method, in terms of nine impact categories: climate change (CC), ozone depletion (OD), terrestrial acidification (TA), freshwater eutrophication (FE), marine eutrophication (ME), human toxicity (HT), photochemical oxidant formation (POF), terrestrial ecotoxicity (TET), freshwater ecotoxicity (FET), fossil depletion (FD). According to the results, the industrial activities carried out within SS2 have been identified as the largest responsible of contributions to all impact categories under assessment. The production of pyrethroid termiticide, which is applied in the panels to improve their resistance to attack by wood decay organisms, was the largest contributor to OD, FE, HT and FET. Scenarios based on the substitution of pyrethroid termiticide were proposed and results showed that substituting the pyrethroid termiticide by different types of boron based termiticides could lead to reduce environmental impacts up to 35%. The identification of the main environmental hotspots in the OSB cradle-to-gate life cycle can assist the Brazilian industry to improve its environmental profile by adopting the proposed scenarios for SS2. Finally, further research should be focused on exploring more types of termiticides that can be applied in the OSB panel.

Abstract

Several studies showed that some organic micropollutants (OMPs) are biotransformed during anaerobic digestion (AD). Yet, most of them aim at reporting removal efficiencies instead of understanding the biotransformation process. Indeed, how each of the main AD stages (i.e., hydrolysis, acidogenesis, and methanogenesis) contribute to OMP biotransformation remains unknown. This study focuses on investigating the role of methanogenesis, the most characteristic step of AD, to OMP removal. More specifically, the sorption and the biotransformation of 20 OMPs by methanogenic biomass were analyzed determining their concentrations in both liquid and solid phases. Sorption onto methanogenic biomass displayed a similar behavior as reported for digested sludge. Most of the OMPs were biotransformed to a medium extent (35–70%) and only sulfamethoxazole was completely removed. Comparing these results with those reported for the complete AD process, methanogenesis was proven to play a key role, accounting for more than 50% of the OMP biotransformation (except for roxithromycin) during AD. An increase in the organic loading rate from 1 to 2 g COD/L d, typical loads employed in sewage sludge anaerobic digesters, did not exert a clear cometabolic effect on the OMPs biotransformation. It is hypothesized that biotransformation occurs in both liquid and solid phases because no link between the partition coefficient (Kd) and the overall biotransformation efficiency was found. These findings allow a better understanding of the OMPs fate under anaerobic conditions, which is necessary to design efficient biological mitigation strategies.

Abstract

The development of a cost‐effective process of struvite crystallization requires the selection of appropriate sources of alkali and magnesium. In this study, the effectiveness of two industrial grade products, MgO and Mg(OH)2, as magnesium and alkali sources to recover phosphorus as struvite were investigated and compared in a first set of experiments. Subsequently, the use of industrial Mg(OH)2 was compared in two different struvite crystallization systems, an upflow fluidized bed reactor (FBR) and a continuous stirred tank reactor (CSTR) coupled to a settler tank

Abstract

The infusion of yerba mate (Ilex paraguariensis St. Hil.) is the most popular tea-like beverage of southern Latin American countries, and its health benefits such as stimulating effect and antioxidant activity are well known. The exhausted mate leaves are managed as waste and are not currently exploited or valorized as a bio-resource. In this work, a cost-effective alternative for extracting antioxidant compounds from this type of residue as a possible valorization route was investigated. Accordingly, different liquid/solid ratios, solvents and extraction times were evaluated with the aim of maximizing extraction performance, total phenolic (TPC) and flavonoid (TFC) content and antioxidant activity (AA) of the extracts. The optimal conditions allowed the recovery of high level of phenolics (TPC 63.13 mg gallic acid equivalents/g) and flavonoids (TFC 148.45 mg rutin equivalents/g) in the extract, with remarkable content in AA (111.18 mg Trolox equivalents/g). Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analysis identified that the main compounds in the extract were terpenes (phenol, guaiacol, 4-vinylguaicol and eugenol), caffeine, 4-ethyl-resorcinol, hydroquinone, palmitic acid, and stearic acid. Fourier transform infrared (FTIR) and thermogravimetric analysis (TGA) analyses provided the functional characteristics and thermal stability of the extract. From the results obtained, it can be concluded that the residue of yerba mate after the infusion of the original yerba mate still possesses high antioxidant potential, mainly associated with its phenolic and flavonoid composition. Furthermore, the content of antioxidant phenolic compounds reported here was higher than most of those reported for agro-industrial residues. Therefore, this type of waste, that is generally discarded, can be valorized as a source of high added-value compounds.

Abstract

The development of nanotechnology has provided a range of diverse nanoscale carriers that can be potentially applied for enzyme immobilization. Among the different types of support, magnetic nanoparticles (mNPs) have received increasing attention because they can be easily recovered from the reaction medium by applying an external magnetic field. In the present study, silica-coated magnetic nanoparticles (Fe3O4@SiO2) were prepared, characterized, and used for covalent immobilization of laccase from Trametes versicolor. Different concentrations of the functionalization agent (3-aminopropyltriethoxysilane), cross-linker (glutaraldehyde), and laccase allowed a maximum enzyme loading of 2.68±0.08  U mg−1 mNP. Several factors, including pH, T, presence of inactivating compounds, enzyme stability, and reusability of the support, were evaluated. The oxidative action of the enzyme toward xenobiotics was proven in the formation of the chromogenic radical of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and the biotransformation of the endocrine-disrupting compound Bisphenol A (BPA). The enhancement of catalytic activity and stability of the nanobiocatalyst was evidenced by the increase of ABTS oxidation. Moreover, the superparamagnetic characteristic of the support allowed simple and fast recovery of the nanobiocatalyst. With the development of nanobiocatalyst-driven applications in mind, the development of magnetic nanoparticle synthesis at large scale as well as the design of bioreactors that assure the retention and recovery of the nanobiocatalyst need to addressed.