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A special issue of Processes (ISSN 2227-9717). This special issue belongs to the section "Environmental and Green Processes".

Deadline for manuscript submissions: closed (10 May 2022) | Viewed by 32272

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Special Issue Editor

Prof. Dr. Irina Ribarova

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Guest Editor

Department of Water Supply, Sewerage, Water and Wastewater Treatment, University of Architecture, Civil Engineering and Geodezy, 1046 Sofia, Bulgaria
Interests: circular economy in the water sector; eco-efficiency of urban water systems; nutrients removal and recovery in WWTPs; removal of hazardous compounds from wastewater and sludge; biological processes modeling; flood and drought management

Special Issue Information

Dear Colleagues,

Our society has reached a level of maturity that enables understanding that the “cradle to cradle‘‘ economic model provides many more opportunities for sustainable development than the current “cradle to grave” economic model. However, there are a number of challenges associated with this otherwise noble concept and there is still a long way to go from the conceptualization to its full practical implementation. Our main responsibility as researchers is to ensure that the transformation to more circular systems will be made in a sustainable way, encompassing human and environmental health, social prosperity and economic viability.

There are already a number of innovations and promising research results but the accumulated knowledge is still insufficient to guarantee safe transition to circular systems. This Special Issue on “Sustainable shift to circular solutions for water and waste management” aims to curate novel advances on how circular systems should be designed, adapted, operated and monitored to get closer to safe zero-waste economy. Topics include but are not limited to:

Safe shift from linear to circular urban water supply and sewerage systems: challenges and solutions;
Innovative technologies in water and waste management leading to usable and safe end-products and other co-benefits;
Biomass and waste conversion processes and technologies for energy or compost;
Sustainable and safe construction and demolition waste management;
Control and biocontrol of circular processes, resources and end-products in water and waste management.

Prof. Dr. Irina Ribarova
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Processes is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

biomass and waste conversion processes
circular urban water and sewerage systems
control and biocontrol
construction and demolition waste
design and operation
safe zero-waste economy

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Published Papers (11 papers)

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Research

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21 pages, 2548 KiB

Open AccessEditor’s ChoiceArticle

The Readiness of the Water Utilities in Bulgaria for Transition toward a Circular Economy

by Galina Dimova, Sonya Dimitrova, Irina Kostova, Svetlana Lazarova, Irina Ribarova, Dean Stoyanov, Radoslav Tonev, Emil Tsanov and Dobril Valchev

Processes 2022, 10(6), 1156; https://doi.org/10.3390/pr10061156 - 9 Jun 2022

Cited by 3 | Viewed by 2992

Abstract

Urban water systems are still in their infancy regarding the transition toward a circular economy, despite the sporadic successful examples worldwide. This paper was aimed at analyzing the preparedness of four water utilities in Bulgaria for the implementation of circular economy principles and solutions. These utilities provide water supply and sewerage services to about 30% of the population in Bulgaria. SWOT analysis was used as a core tool. Publicly available data such as nonrevenue water, pressure management, energy demand, network digitalization, and sludge utilization were used to explore the internal factors. The external environment was considered through the legislative and socioeconomic framework, climate change, etc. Finally, the credibility of the conclusions was verified in workshops with the water utilities. The key positive outcomes were that the external factors favor the shift to circular systems, while the major weakness, i.e., the aged infrastructure, is actually a good opportunity for the implementation of modern and circular solutions. The efficient collaboration of water utilities with other actors is a precondition for the development of a sustainable market for “circular” products. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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16 pages, 3357 KiB

Open AccessEditor’s ChoiceArticle

Modification of Quaternary Clays Using Recycled Fines from Construction and Demolition Waste

by Roumiana Zaharieva, Daniel Evlogiev, Nikolay Kerenchev and Tsveta Stanimirova

Processes 2022, 10(6), 1062; https://doi.org/10.3390/pr10061062 - 26 May 2022

Cited by 3 | Viewed by 2090

Abstract

Foundation of buildings in soft soil such as quaternary clay is often associated with difficult compaction, settlement, non-uniform and/or excessive deformation, and unsatisfactory shear resistance. The present study aims to assess the possibility of using recycled fines from construction and demolition waste, such as mechanically treated gypsum and waste concrete powder (WCP), instead of ordinary binders or industrial waste, in the stabilization of quaternary clay. A detailed characterization of soil components is presented. Seven mixes with various proportions of gypsum and WCP are prepared. Main geotechnical parameters of the modified soil are studied by applying standardized methods with a few deviations. XRD analysis and pH measurements are performed. It was found that the effect of 5% to 20% recycled di-hydrate gypsum is limited to improvement in moist soil compatibility. A gypsum content of 10% positively impacts soil cohesion and the oedometer modulus. WCP is an active component, containing non-hydrated cement, portlandite, calcite and calcium silicates hydrate. As a result, by adding 5% of WCP only, significant improvement can be achieved: greater soil cohesion, reduced deformability and higher UCS. When 5% of recycled gypsum is also added, soil cohesion is further improved because of ettringite formation. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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14 pages, 5318 KiB

Open AccessArticle

Biodegradation of Naphthalene and Anthracene by Aspergillus glaucus Strain Isolated from Antarctic Soil

by Katya Stoyanova, Maria Gerginova, Ivayla Dincheva, Nadejda Peneva and Zlatka Alexieva

Processes 2022, 10(5), 873; https://doi.org/10.3390/pr10050873 - 28 Apr 2022

Cited by 14 | Viewed by 2683

Abstract

Biotechnologies based on microbial species capable of destroying harmful pollutants are a successful way to solve some of the most important problems associated with a clean environment. The subject of investigation is the Antarctic fungal strain Aspergillus glaucus AL1. The culturing of the examined strain was performed with 70 mg of wet mycelium being inoculated in a Czapek Dox liquid medium containing naphthalene, anthracene, or phenanthrene (0.3 g/L) as the sole carbon source. Progressively decreasing naphthalene and anthracene concentrations were monitored in the culture medium until the 15th day of the cultivation of A. glaucus AL1. The degradation was determined through gas chromatography–mass spectrometry. Both decreased by 66% and 44%, respectively, for this period. The GC-MS analyses were applied to identify salicylic acid, catechol, and ketoadipic acid as intermediates in the naphthalene degradation. The intermediates identified in anthracene catabolism are 2-hydroxy-1-naphthoic acid, o-phthalic acid, and protocatechuic acid. The enzyme activities for phenol 2-monooxygenase (1.14.13.7) and catechol 1,2-dioxygenase (1.13.11.1) were established. A gene encoding an enzyme with catechol 1,2-dioxygenase activity was identified and sequenced (GeneBank Ac. No KM360483). The recent study provides original data on the potential of an ascomycete’s fungal strain A. glaucus strain AL 1 to degrade naphthalene and anthracene. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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15 pages, 1433 KiB

Open AccessArticle

Challenges in Using Handheld XRFs for In Situ Estimation of Lead Contamination in Buildings

by Roumiana Zaharieva, Yana Kancheva, Kamen Kamenov, Vihren Tomov and Valentina Lyubomirova

Processes 2022, 10(5), 839; https://doi.org/10.3390/pr10050839 - 24 Apr 2022

Cited by 3 | Viewed by 1807

Abstract

Lead in buildings can be found in certain materials such as paints or can be a result of contamination during the use stage. In situ methods for lead identification can be vital for the proper treatment of hazardous CDW (from repair works or selective demolition). A conventional handheld XRF (HHXRF) spectrometer can be used for this purpose, and this study analysed its reliability. A laboratory experiment was conducted to test different calibrations, and to establish a procedure for the conversion of the HHXRF lead concentrations into lead loadings. Model latex paint with a constant lead content was used on two types of surfaces (plasterboard and concrete). A field study was performed to identify and quantify the lead in paint on masonry walls in a public building. ICP-MS analysis was performed in order to verify the lead content. The coefficients of proportionality in the proposed model depend on various parameters: the contamination type, the layer thickness, the substrate, and the built-in calibrations. Despite the limitations of the HHXRF and the discrepancy of the mean lead loadings from the HHXRF and ICP-MS analysis, the HHXRF can be useful for the identification of lead in paint layers up to 1 mm, with a low limit of detection of the order of 0.01 mg/cm² at worst. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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20 pages, 5954 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Application of Nanodiamonds in Modelled Bioremediation of Phenol Pollution in River Sediments

by Ivaylo Yotinov, Mihaela Belouhova, Anna Foteva, Nora Dinova, Yovana Todorova, Irina Schneider, Elmira Daskalova and Yana Topalova

Processes 2022, 10(3), 602; https://doi.org/10.3390/pr10030602 - 19 Mar 2022

Cited by 3 | Viewed by 2583

Abstract

The pollution of aquatic ecosystems is a big problem that has its impact on river sediments. In recent decades, an effective solution to this problem has been the application of bioremediation technologies. Nanoremediation is an innovative part of these technologies. We still know little about the efficiency of nanoparticles, especially nanodiamonds, in modelled conditions. The aim of the present study is to investigate the effect of nanodiamonds on the key parameters of modelled bioremediation of river sediments that are polluted with phenol, as well their effect on the structures and functions of microbial communities. An important indicative mechanism that was used is the application of fluorescent in situ hybridization for sediment microbial communities. The results of this study revealed the positive role of nanodiamonds that is associated with their intoxication with high concentrations of phenol. Readaptation was also found, in which the xenobiotic biodegradation potential evolved by increasing the relative proportions of non-culturable bacteria, namely Acinetobacter (at the 144th hour) and Pseudomonas (at the 214th hour). The results can help to find an effective solution to the question of how information from such precise molecular methods and the application of nanodiamonds can be translated into the accessible language of management and bioremediation technologies. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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10 pages, 9085 KiB

Open AccessArticle

Assessment of the Possibilities for Removal of Ni (II) from Contaminated Water by Activated Carbon foam Derived from Treatment Products of RDF

by Ivanka Stoycheva, Boyko Tsyntsarski, Angelina Kosateva, Bilyana Petrova and Pavlinka Dolashka

Processes 2022, 10(3), 570; https://doi.org/10.3390/pr10030570 - 15 Mar 2022

Viewed by 1760

Abstract

Carbon foam is a sophisticated porous material with wide applications that depend on its structure, low density, thermal conductivity and electrical characteristics. This study deals with the preparation of carbon foam by the thermo-oxidative modification with HNO₃ of mixtures containing different organic materials with appropriate chemical characteristics—furfural and tar pitch derived from RDF. Carbon foam is characterized by thermogravimetry, differential scanning calorimetry, elemental analysis, Raman spectroscopy, N₂ sorption, infrared spectroscopy and scanning electron spectroscopy. The investigation of adsorption activity of carbon foam towards nickel (II) in water solution is carried out. Experimental results fit very well with the Langmuir adsorption model. The carbon foam, obtained from tar pitch derived from RDF and furfural, shows a high adsorption capacity towards nickel ions (203.67 mg/g). The high adsorption capacity could be explained by the properties of the adsorbent—moderately high surface area, micro-mesoporous texture and presence of oxygen-containing surface groups. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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11 pages, 2236 KiB

Open AccessEditor’s ChoiceArticle

Potential Use of Microbial Fuel Cell Technology in Wastewater Treatment

by Ralitza Koleva, Gergana Peeva, Hyuseyin Yemendzhiev and Valentin Nenov

Processes 2022, 10(3), 486; https://doi.org/10.3390/pr10030486 - 28 Feb 2022

Cited by 4 | Viewed by 3015

Abstract

Two options, in regard to applying microbial fuel cells (MFCs) in water treatment, are under discussion, namely the conversion of the chemical energy of organic substrates to electricity, as well as the use their potential to reduce different species, such as the ionic form of copper (Cu²⁺ converted to metal copper) and iron (Fe³⁺ converted to Fe²⁺). The high reduction potential of Cu²⁺ and Fe³⁺ makes the processes of electricity production and metal reduction, to be performed simultaneously in MFC, achievable. The electrical yield measurement during the experiments of anodic organic matter degradation by MFC in treating an artificial wastewater with chemical oxygen demand (COD) 0.6 and 1.6 g O₂·dm⁻³, as initial COD, are given. It is demonstrated that the higher organic load is associated with better electrical yield. A comparison of MFC and conventional anaerobic digestion performance is discussed, as well. Experimental proofs of copper removal and phosphate mobilization, following the iron reduction of FePO₄, are also reported. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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21 pages, 4261 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Purposely Development of the Adaptive Potential of Activated Sludge from Municipal Wastewater Treatment Plant Focused on the Treatment of Landfill Leachate

by Mihaela Belouhova, Ivaylo Yotinov, Irina Schneider, Nora Dinova, Yovana Todorova, Valentina Lyubomirova, Veronika Mihaylova, Elmira Daskalova, Stilyana Lincheva and Yana Topalova

Processes 2022, 10(3), 460; https://doi.org/10.3390/pr10030460 - 24 Feb 2022

Cited by 4 | Viewed by 2800

Abstract

Biological treatment is a key technology in landfill leachate treatment However, often its efficiency is not high enough due to the pollutants in concentrations above the critical ones. The present study aimed to investigate the adaptive responses that occur in activated sludge (AS) during landfill leachate purification. A model process with AS from a municipal wastewater treatment plant and landfill leachate in increasing concentrations was constructed. The data showed that when dilutions 25 and 50 times had been applied the structure of the AS was preserved, but the COD cannot be reduced below 209 mg O₂/L. The feed of undiluted leachate destroyed the AS structure as SVI was reduced to 1 mL/g, biotic index to 1, floc size was greatly reduced and COD remained high (2526 mg O₂/L). The dominant group of protozoa was changed from attached to free-swimming ciliates. An increase of the bacterial groups responsible for the xenobiotics elimination (aerobic heterotrophs, genera Pseudomonas, Acinetobacter, Azoarcus, Thauera, Alcaligenes) was registered. This was accompanied by a significant increase in free bacteria. The obtained data showed that for optimal treatment of this type of water it is necessary to include a combination of biological treatment with another non-biological method (membrane filtration, reverse osmosis, etc.). Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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13 pages, 3712 KiB

Open AccessArticle

Microbiological Control in Decontamination of Sludge from Wastewater Treatment Plant

by Boyka Z. Malcheva, Petar G. Petrov and Veneta V. Stefanova

Processes 2022, 10(2), 406; https://doi.org/10.3390/pr10020406 - 18 Feb 2022

Cited by 11 | Viewed by 2845

Abstract

Dynamics of the microbiological indicators of fresh sludge from wastewater treatment plants with a concentration of CaO, 10% and 20%, and ash, −30% and 50%, and treated with quicklime, ash, and microbial fertilizer for a 50-day period of composting were studied. The influence of temperature, water content, and oxygen on the development of microbes was established in laboratory conditions. Microbiological analysis included the determination of non-pathogenic (non-spore-forming bacteria, bacilli, actinomycetes, micromycetes, bacteria digesting mineral nitrogen), and pathogenic (Salmonella, Listeria, Escherichia coli, Enterococcus, Clostridium perfringens) microorganisms. Of the beneficial microflora in the sludge before treating, the amount of non-spore-forming bacteria was the highest, followed by bacilli and micromycetes. It was found that actinomycetes were absent in the untreated sludge. Clostridium perfringens occupied a major share in the composition of the pathogenic microflora, followed by Escherichia coli, Enterococcus, and Listeria. The best results for decontamination of the sludge were obtained by adding 20% quicklime and 50% ash. Alkalization of the sludge after treatment led to the destruction of pathogenic microflora but also reduced the number of beneficial microorganisms. The decrease in pH during the study period determined the redevelopment of pathogenic microflora. Combined variants with lime or ash and microbial fertilizer showed better results for the development of non-pathogenic microflora and the destruction of pathogens. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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15 pages, 9236 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Non-Thermal Atmospheric Plasma for Microbial Decontamination and Removal of Hazardous Chemicals: An Overview in the Circular Economy Context with Data for Test Applications of Microwave Plasma Torch

by Yovana Todorova, Evgenia Benova, Plamena Marinova, Ivaylo Yotinov, Todor Bogdanov and Yana Topalova

Processes 2022, 10(3), 554; https://doi.org/10.3390/pr10030554 - 11 Mar 2022

Cited by 14 | Viewed by 3467

Abstract

The transformation of our linear “take-make-waste” system to a cyclic flow of materials and energy is a priority task for society, but the circular use of waste streams from one industry/sector as a material input for another must be completely safe. The need for new advanced technologies and methods ensuring both microbiological safety and the removal of potential chemical residues in used materials and products is urgent. Non-thermal atmospheric plasma (cold atmospheric plasma—CAP) has recently attracted great research interest as an alternative for operative solutions of problems related to safety and quality control. CAP is a powerful tool for the inactivation of different hazardous microorganisms and viruses, and the effective decontamination of surfaces and liquids has been demonstrated. Additionally, the plasma’s active components are strong oxidizers and their synergetic effect can lead to the degradation of toxic chemical compounds such as phenols and azo-dyes. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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28 pages, 29241 KiB

Open AccessFeature PaperReview

A Review on the Reliability and the Readiness Level of Microalgae-Based Nutrient Recovery Technologies for Secondary Treated Effluent in Municipal Wastewater Treatment Plants

by Dobril Valchev and Irina Ribarova

Processes 2022, 10(2), 399; https://doi.org/10.3390/pr10020399 - 18 Feb 2022

Cited by 20 | Viewed by 4532

Abstract

Algae-based wastewater treatment technologies are promising green technologies with huge economical potential and environmental co-benefits. However, despite the immense research, work, and achievement, no publications were found wherein these technologies have been successfully applied in an operational environment for nitrogen and phosphorus removal of secondary treated effluent in municipal wastewater treatment plants. Based on a literature review and targeted comprehensive analysis, the paper seeks to identify the main reasons for this. The reliability (considering inlet wastewater quality variations, operating conditions and process control, algae harvesting method, and produced biomass) as well as the technology readiness level for five types of reactors are discussed. The review shows that the reactors with a higher level of control over the technological parameters are more reliable but algal post-treatment harvesting and additional costs are barriers for their deployment. The least reliable systems continue to be attractive for research due to the non-complex operation and relieved expenditure costs. The rotating biofilm systems are currently undertaking serious development due to their promising features. Among the remaining research gaps and challenges for all the reactor types are the identification of the optimal algal strains, establishment of technological parameters, overcoming seasonal variations in the effluent’s quality, and biomass harvesting. Full article

(This article belongs to the Special Issue Sustainable Shift to Circular Solutions for Water and Waste Management)

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