Co-pyrolysis of sewage sludge and plastics have been utilized for producing biochars as a strategy to fix plastic pollution. However, comparative studies on the characteristics and environmental risk ...of heavy metals in biochars obtained by the co-pyrolysis of sludge and microplastic with/without metal additives are seldom. Here we demonstrated the effects of simulated co-pyrolysis (at 400 °C) of sewage sludge and metal-free or metal-loaded polyvinyl chloride (PVC) microplastics at different mass ratios (1:0, 19:1, 3:1, 1:3, sewage sludge: PVC (w/w)) respectively. Results revealed that co-pyrolysis of metal-loaded PVC and sewage sludge resulted in higher electrical conductivity, ash content, and an acidic pH of biochars as compared to the co-pyrolysis of metal-free PVC and sewage sludge. Addition of metal-loaded PVC increased total concentrations of calcium (Ca), magnesium (Mg), cadmium (Cd), and lead (Pb) in biochars, but reduced the bioavailability of Cd, chromium (Cr), nickel (Ni), and zinc (Zn) in biochars. Analysis of chemical speciation showed that heavy metals (except Pb) in biochars derived from co-pyrolysis of sewage sludge and metal-loaded PVC had higher percentage of more stable fraction (residual fraction) and lower potential ecological risk index (RI) value. S1AP3 (sludge: metal-loaded PVC = 1:3) biochar had the lowest environmental risk based on RI value (14.41). To sum up the present study suggests that the addition of metal-loaded PVC microplastic in sewage sludge had a positive impact on the immobilization of heavy metals during co-pyrolysis process.
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•Sewage sludge was co-pyrolyzed with metal-free/metal-loaded PVC to produce biochar.•Addition of metal-loaded PVC changed the acidic pH of sludge-PVC biochars to alkaline.•Addition of metal-loaded PVC increased total Ca, Mg, Cd, and Pb contents in biochars.•Addition of metal-loaded PVC reduced biochar bioavailable Cd, Cr, Ni, and Zn contents.•Co-pyrolysis of sewage sludge and metal-loaded PVC had a lower ecological risk index.
► Two sewage sludge ashes rich in Fe or Al are characterized and acid washed. ► Fe for P-precipitation during waste water treatment ease P recovery from the ash. ► Heavy metals are extracted ...simultaneous to P. ► Extraction in H2SO4 result in significant formation of gypsum crystals.
Ashes from mono-incineration of sewage sludge (ISSA) generally contain high concentrations of phosphorous (P) and can be regarded as secondary P resources. ISSA has no direct value as fertilizer as P is not plant available. The present paper experimentally compares P extraction in acid from two different ISSAs; one rich in Al (67g/kg) and the other in Fe (58g/kg). The difference related to P precipitation at the waste water treatment facilities. Another major difference between the ashes was that flue gas purification products were mixed into the first ash and it contained about 5% activated carbon. The Al rich ash had a significantly higher buffering capacity and required more acid for extraction of P. When acid extraction of P from ISSA is the method for recovery, it is thus beneficial to go back to the waste water treatment facility and e.g. choose Fe for P precipitation rather than Al.
Formation of a high amount of gypsum crystals in both ashes after extraction in H2SO4 was seen by SEM–EDX. H2SO4 is the cheapest mineral ash, but the gypsum formation must be taken into account when either finding possibility for using the remaining ash in e.g. construction materials or if the choice is deposition, as the gypsum increases the volume significantly.
The increasing use of silver (Ag) nanoparticles containing either elemental Ag (Ag-NPs) or AgCl (AgCl-NPs) in commercial products such as textiles will most likely result in these materials reaching ...wastewater treatment plants. Previous studies indicate that a conversion of Ag-NPs to Ag2S is to be expected during wastewater transport/treatment. However, the influence of surface functionality, the nature of the core structure and the effect of post-processing on Ag speciation in sewage sludge/biosolids has not been investigated. This study aims at closing these knowledge gaps using bench scale anaerobic digesters spiked with Ag nitrate, three different types of Ag-NPs, and AgCl-NPs at environmentally realistic concentrations. The results indicate that neither surface functionality nor the different compositions of the NP prevented the formation of Ag2S. Silver sulfides, unlike the sulfides of other metals present in sewage sludge, were stable over a six month period simulating composting/stockpiling.
► Surface functionality of Ag-NPs did not influence their transformation during WWT. ► AgCl-NPs degraded in waste water treatment similarly to metallic nanoparticles. ► In all cases silver sulfides were formed. ► Ag sulfides were stable over a six month period simulating composting/stockpiling.
Silver sulfides are the dominant and stable species of Ag present in sewage sludge irrespective of the characteristics of silver nanoparticles added to waste water.
The construction industry already recognises the strong business case for improving resource productivity. It is associated with circular economy system (CE), propagated by the European Union. ...Circular economy systems keep the added value in products for as long as possible and virtually eliminate waste. Transition to a more circular economy requires changes throughout value chains, from product design to new business and market models, from new ways of turning waste into a resource to new modes of consumer behaviour. These actions relate to all industries, including the construction industry. Nowdays, the increase in demand for construction materials as a result of development has called for an alternative way to develop or derive construction materials from different sources, including sewage sludge ash (SSA). SSA is produced after the firing process of sewage sludge, and it must be disposed by other means. Researches were already accomplished investigating the use of sewage sludge ash for the building materials manufacturing, such as produce bricks and tiles, as a raw materials for cement production, as aggregates for concrete and mortar, as a component of the synthesis of lightweight materials and as substitute for sand and/or cement in cement stabilized bases, subbases and embankments in road constuctions. A detailed description of each application as a way towards a circular economy is presented in this paper.
•Aqueous phase recycling of sewage sludge hydrothermal carbonization was investigated.•The O/C and H/C atomic ratios revealed that dehydration was the main reaction during hydrothermal ...carbonization.•The pH value step increased with increasing recycling number, indicating that aqueous phase acted as a catalyst.•The organic matter recovery from the aqueous phase influenced on the combustion property of hydrochar.
In this study, the aqueous phase produced from the hydrothermal carbonization (HTC) of sewage sludge (SS) with pure water was reused for the HTC of fresh SS, aiming to maximize energy recovery from the aqueous phase. The aqueous phase was recycled four times. The effects of aqueous phase recycling on the properties of the aqueous phase and hydrochar produced at temperatures of 200, 230, and 260 °C were studied. The hydrochar yield always decreased with increasing temperature regardless of whether the aqueous phase was recycled. The C and N contents and higher heating values of the hydrochars produced with aqueous phase recycling were all higher than that of the hydrochar produced with pure water and slightly increased as the number of recycling times increased. The O/C and H/C atomic ratios of the hydrochars revealed that dehydration was the main reaction pathway during HTC of SS. The pH value of the aqueous phase increased as the number of recycling times increased, indicating that the concentration of NH4+-N in the aqueous phase increased. The process of aqueous phase recycling affected the carbonization of the hydrochar. These results suggest that aqueous phase recycling was favorable for energy recovery from the aqueous phase produced from the HTC of SS and for improving the combustion properties of the hydrochar. Thus, we believe that aqueous phase recycling was a promising strategy for energy recovery, aqueous phase disposal, and the production of high-quality hydrochar with respect to the HTC of SS.
Due to the increasingly demanding legal regulations, regarding both sewage sludge (SS) and solid residues obtained during its thermal utilization processes, new solutions to limit their negative ...impact on the environment are sought. One approach that eliminates the risk of sewage sludge ash (SSA) is its use in cement building materials. The article contains a detailed literature review regarding the use of SSA in mortars and concretes, where it is defined as the addition or substitute of the main binder. The issues of the impact of SSA quality (CaO content, the share of pozzolanic oxides, their ratio) on cement products are discussed in details. In addition to the description of the mechanical properties of building materials, the SSA impact on parameters such as workability, shrinkage of products and setting time is also described. It can be stated that using SSA in building industry is one of the most ecological approaches of SSA managing. Due to the toxic nature of SSA, data on the leaching of heavy metals from hardened mortar or concrete samples are presented to emphasize the contaminants immobilization effectiveness by cement products. Based on the analysis of the data presented in the article, solutions that can reduce the negative consequences of including SSA in building materials have been identified. However, due to the significant differences in SS thermal utilization technologic and SS characteristics, every SSA should be thoroughly characterized before implementing the most suitable stabilization/solidification methods.
Over the past years, numerous technologies have been developed to recover phosphorus (P) from waste streams to repair currently broken nutrient cycles. These developments were largely triggered by ...environmental considerations (sustainability, resource efficiency), concerns regarding the finite and geopolitically concentrated deposits of raw phosphate ore, and phosphate price increases. Municipal wastewater is a promising and viable source to recover P in larger quantities, to re-establish a circular economy and therefore increase net use efficiency. This work compiles the latest knowledge on approaches to recover P from municipal wastewater and related waste flows with a specific focus on the existing well-developed wastewater management infrastructure, available in significant parts of Europe (e.g., secondary treated effluent, digester supernatant, sewage sludge, sewage sludge ash). About 50 technologies were identified at various levels of development (industrial-, full-, pilot- and laboratory scale). The current selection of P recovery processes is broad and ranges from simple precipitation of dissolved P to complex multi-step approaches, and only a few of these displayed potential for full-scale implementation. They are discussed with regard to their technical principles, process parameters, recovery efficiency, resource demand, possible effects on wastewater treatment, waste flows, and fate of pollutants. We also evaluated them with respect to their rates of P removal from wastewater and their access points of P recovery. For selected technologies, material flow models are presented to facilitate the understanding of even complex processes. This work serves as a basis for future integrated comparative assessments of selected recovery approaches according to technical, environmental and economic criteria.
Textiles release fibres to the environment during production, use, and at end-of-life disposal. Approximately two-thirds of all textile items are now synthetic, dominated by petroleum-based organic ...polymers such as polyester, polyamide and acrylic. Plastic microfibres (<5 mm) and nanofibres (<100 nm) have been identified in ecosystems in all regions of the globe and have been estimated to comprise up to 35% of primary microplastics in marine environments, a major proportion of microplastics on coastal shorelines and to persist for decades in soils treated with sludge from waste water treatment plants. In this paper we present a critical review of factors affecting the release from fabrics of microfibres, and of the risks for impacts on ecological systems and potentially on human health. This review is used as a basis for exploring the potential to include a metric for microplastic pollution in tools that have been developed to quantify the environmental performance of apparel and home textiles. We conclude that the simple metric of mass or number of microfibres released combined with data on their persistence in the environment, could provide a useful interim mid-point indicator in sustainability assessment tools to support monitoring and mitigation strategies for microplastic pollution. Identified priority research areas include: (1) Standardised analytical methods for textile microfibres and nanofibres; (2) Ecotoxicological studies using environmentally realistic concentrations; (3) Studies tracking the fate of microplastics in complex food webs; and (4) Refined indicators for microfibre impacts in apparel and home textile sustainability assessment tools.
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•Accumulation of microplastic waste in ecosystems is a key global concern.•A significant proportion of plastic pollution is microfibres from textiles.•Environmental impacts of apparel and home textile microfibres are reviewed.•Including loss of synthetic microfibres in sustainability assessment is recommended.•Research priorities to improve microfibre monitoring and mitigation are identified.
Waste activated sludge is slower to biodegrade under anaerobic conditions than is primary sludge due to the glycan strands present in microbial cell walls. The use of pre-treatments may help to ...disrupt cell membranes and improve waste activated sludge biodegradability. In the present study, the effect of ultrasound, low-temperature thermal and alkali pre-treatments on the rheology, hygienization and biodegradability of waste activated sludge was evaluated. The optimum condition of each pre-treatment was selected based on rheological criteria (reduction of steady state viscosity) and hygienization levels (reduction of Escherichia coli, somatic coliphages and spores of sulfite-reducing clostridia). The three pre-treatments were able to reduce the viscosity of the sludge, and this reduction was greater with increasing treatment intensity. However, only the alkali and thermal conditioning allowed the hygienization of the sludge, whereas the ultrasonication did not exhibit any notorious effect on microbial indicators populations. The selected optimum conditions were as follows: 27,000 kJ/kg TS for the ultrasound, 80 °C during 15 min for the thermal and 157 g NaOH/kg TS for the alkali. Afterward, the specific methane production was evaluated through biomethane potential tests at the specified optimum conditions. The alkali pre-treatment exhibited the greatest methane production increase (34%) followed by the ultrasonication (13%), whereas the thermal pre-treatment presented a methane potential similar to the untreated sludge. Finally, an assessment of the different treatment scenarios was conducted considering the results together with an energy balance, which revealed that the ultrasound and alkali treatments entailed higher costs.
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•Thermal and alkali conditioning but not ultrasonication allowed WAS hygienization.•The three pre-treatments were able to reduce the viscosity of WAS.•Alkali and ultrasound pre-treatments increased WAS biodegradability.•Thermal pre-treatment barely increased WAS biodegradability.•Under tested conditions, ultrasound and alkali treatment entailed high costs.
The methods of sewage sludge management in Poland have largely been determined by the legal requirements related to the Poland’s membership in the European Union. Since 1st January 2016, sewage ...sludge landfilling is prohibited. It must be emphasised that legal changes regarding wastewater management, along with the systematic increase in the volume of produced sludge, entail the necessity to change the existing method of sewage sludge management. This paper contains an analysis of solutions for management of sewage sludge produced in Poland over the period of 8 years. The goal of the work was an assessment of comprehensive management of sewage sludge produced in Poland from 2009 to 2016. Despite the decrease in the agricultural use of sewage sludge, their average share of 32% was the highest among other forms of sewage sludge management in Poland. Another form, related with the final stage of sewage sludge management, concerned its thermal processing. It was treated as a promising method, with a 19% increase over the analysed period. An optimal solution should be found to ensure safe management of sewage sludge.
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