Sludge drying and dewatering processes influence the abundance and characteristics of microplastics in wastewater treatment plants

Integrating renewable energy in sewage sludge treatment through greenhouse solar drying: A review

Sewage sludge is the main by-product of wastewater treatment plants, requiring significant environmental and economic burdens for its management and disposal. Recently, solar drying processes, often performed through solar greenhouses, received interest due to their limited energy requirement and renewable energy exploitation. The dried sludge shows significant volume and mass reductions, reducing transportation and disposal costs. However, its physicochemical and microbiological characteristics must be properly assessed, especially if agricultural reuse is the final sludge destination, due to the possible accumulation of (micro)pollutants in the soil. This review depicts the state-of-the-art solar drying processes of sewage sludge, with a focus on the technological aspects and the sludge quality. The review discusses greenhouse-specific features, sludge composition (organic matter, pathogens, heavy metals and emerging pollutants) and drying conditions (seasonality, ventilation, sludge mixing and thickness, and drying speed). The economic aspects connected to sludge solar drying are presented. The limitations of this technology are discussed as well, including the limited applicability to wet sludge and the environmental issues connected to greenhouse structure degradation. A wider application of sludge solar drying is recommended to increase the sustainability of small and medium wastewater treatment plants, especially in areas with high amounts of solar radiation and dry weather conditions, while thermal drying still appears preferable for large plants. More agronomic studies must be conducted to assess the possible pollutant accumulation in crops, and alternative uses of the dried sludge (e.g., energy recovery through incineration, pyrolysis or gasification; utilization in construction materials) should be explored, also using life cycle assessment.

Microplastics in Morocco's most consumed fisheries: Chemical characterization, ecological traits, and implications for human health

The pervasive presence of microplastics (MPs) in the environment is well established, yet many critical questions remain about their distribution and potential impacts on both ecological and human health. To assess the risks that MPs pose, especially through marine ecosystems and human consumption, monitoring their ingestion by fish in natural environments is essential. This study investigated the contamination of 12 fish species, the most commonly consumed in Morocco, collected from the Atlantic Ocean off the Moroccan coast. Analysis of 240 fish (20 individuals per species) revealed that 100 % of the samples contained microplastics. MPs were detected in the gills, gonads, and gastrointestinal tracts of all 12 species. The average abundance of microplastics per fish ranged from 20.6 to 133.2 MPs, with the forms identified as fragments (60 %), fibers (30 %), films (8 %), and pellets and foams (1 %). Additionally, omnivorous and demersal species presented the highest levels of MP contamination. Infrared spectroscopy (ATR-FTIR) analysis identified seven polymers, with high-density polyethylene (34 %), polyethylene terephthalate (30 %), and polypropylene (17.5 %) being the most prevalent. The microplastics were predominantly dark or light in color, with a notable presence of red and blue particles. Fish ingest various sizes of microplastics, primarily particles smaller than 1 mm. Scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM/EDX) revealed that most MPs exhibited visible signs of weathering and contained inorganic components on their surfaces. The potential risk of MPs to fish, as assessed by the polymer hazard index (PHI), was categorized as level V, indicating that MPs may pose significant risks to human health. The highest estimated daily intake (EDI) of microplastics was found in children (1620 MPs/year), whereas the lowest intake was estimated in women (350 MPs/year) and men (337 MPs/year). Given the widespread presence of microplastics in commonly consumed fish species in Morocco, there is an urgent need for regulatory measures to ensure the safety of fisheries, both for domestic consumption and export. Policymakers should consider the development of guidelines for acceptable levels of microplastic contamination in fish to safeguard public health.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2-25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

Microplastic characterization and assessment of removal efficiency in an urban and industrial wastewater treatment plant with submarine emission discharge

Wastewater treatment plants (WWTPs) are significant contributors to microplastic (MP) pollution in marine ecosystems when they are inefficient. This study aimed to evaluate the effectiveness of microplastic removal from the effluent of the Anza WWTP (Morocco), which processes industrial and urban wastewater using a lamellar decantation system combined with a submarine emissary for treated water discharge. Additionally, this study investigated the presence of microplastics in the Atlantic seawater where treatment plant effluent is released. Microplastics were collected and extracted from wastewater and seawater samples to assess their abundance, shape, size, polymer type, and removal rates in the treatment plant. The findings revealed an average MP concentration of 1114 ± 90 MPs/L in the influent and 607 ± 101 MPs/L in the effluent, indicating a removal efficiency of 46 %. Seasonal analysis revealed the highest MP concentrations during the summer, with 2181.33 MPs/L in the influent and 1209 MPs/L in the effluent. Seawater samples from the discharge zone of the submarine emissary had an average MP concentration of 1600 MPs/m3. Characterization of the MPs revealed that fibers were the most common form of MPs in all the samples. The 500-100 μm size fraction was predominant in the WWTP samples, while MPs smaller than 1 mm were more abundant in the seawater samples. Seven polymer types were identified using attenuated total reflection fourier transform infrared spectroscopy (ATR-FTIR), with PET, PE, PVC, PA, PS, PP, and EVA being the most prevalent. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDX) revealed various degrees of weathering and chemical elements adhering to the MP surfaces. The results of this study provide valuable insights into the effectiveness of conventional treatment systems in removing microplastics and offer a reference for developing management strategies to mitigate MP pollution in Morocco's marine ecosystems.

Metabolomic and biochemical disorders reveal the toxicity of environmental microplastics and benzo[a]pyrene in the marine polychaete Hediste diversicolor

Recently, the abundance of environmental microplastics (MPs) has become a global paramount concern. Besides the danger of MPs for biota due to their tiny size, these minute particles may act as vectors of other pollutants. This study focused on evaluating the toxicity of environmentally relevant concentrations of MPs (10 and 50 mg/kg sediment) and benzo[a]pyrene (B[a]P, 1 µg/kg sediment), alone and in mixture, for 3 and 7 days in marine polychaete Hediste diversicolor, selected as a benthic bioindicator model. The exposure period was sufficient to confirm the bioaccumulation of both contaminants in seaworms, as well as the potential capacity of plastic particles to adsorb and vehiculate the B[a]P. Interestingly, increase of acidic mucus production was observed in seaworm tissues, indicative of a defense response. The activation of oxidative system pathways was demonstrated as a strategy to prevent lipid peroxidation. Furthermore, the comprehensive Nuclear Magnetic Resonance (NMR)-based metabolomics revealed significant disorders in amino acids metabolism, osmoregulatory process, energetic components, and oxidative stress related elements. Overall, these findings proved the possible synergic harmful effect of MPs and B[a]P even in small concentrations, which increases the concern about their long-term presence in marine ecosystems, and consequently their transfer and repercussions on marine fauna.

Scenic degradation and visual pollution along the Agadir coastline (Morocco): Analysis and management

Visual pollution refers to the degradation of landscape aesthetics, manifesting as visible deterioration. On the Agadir coast in Morocco, factors such as urbanization, erosion, marine wracking, litter, sewage, beach driving, and animal waste contribute to this issue, which detracts from coastal scenery. This study employs the coastal scenery evaluation system (CSES) to conduct a scenic assessment of 40 coastal sites, aiming to describe the current state of visual pollution and inform management interventions. The CSES utilizes a checklist comprising 18 physical and 8 human parameters to calculate a scenic evaluation index (D value), which categorizes coastal sites into five classes. These range from Class I - typically undisturbed natural areas with pristine scenic qualities - to Class V - which are degraded natural areas significantly impacted by human activities. The scenic evaluation classified these sites into three classes. Four sites (10 %) were classified as Class III, fifteen (37.5 %) as Class IV, and twenty-one (52.5 %) as Class V. No sites were classified as Classes I or II. The assessments presented here offer a comprehensive overview of the Agadir coastal scenery and establish a baseline for developing strategies to address visual pollution.

Investigation of microplastics in advanced biological wastewater treatment plant effluent

In recent years, plastic pollution in the environment has also increased due to the increasing production and consumption of plastics worldwide. The presence of microplastics (MPs) in the environment from different sources is observed almost everywhere, especially in aquatic environments. A standard method for sampling, identification, and quantification of MPs in wastewater has not yet been established. In this study, it was aimed to determine the MPs and their characteristics in the effluent of an advanced biological domestic wastewater treatment plant. The seasonal changes of MPs in a year were revealed. Pre-treatments suitable for the studied wastewater were developed for visual determination of MPs. Fibers are the dominant type of MPs, with numbers ranging between 32.0 and 95.5 particle/L. MPs in five different polymer structures were determined by FTIR analysis. These are Polyethylene, Polypropylene, Polyester, Polyurethane and Polyethylene terephthalate. The results were evaluated according to QA/QC and determined to meet the standards.

Influence of the geographic location and house characteristics on the concentration of microplastics in indoor dust

Microplastics (MPs) are known for their ubiquity, having been detected in virtually any environmental compartment. However, indoor MPs concentrations are poorly studied despite being closely related to human exposure. The present study aims to evaluate the presence of MPs in settled atmospheric dust in 60 houses distributed in 12 districts of the metropolitan city of Lima, Peru, and investigate the influence of their geographical location and house characteristics. MPs concentration ranged from 0.01 to 33.9 MPs per mg of dust. Fibers and blue were the most frequent shape and color (98 % and 69 %, respectively). Also, 82 % of the particles were between 500 μm - 5 mm in size. A higher concentration of MPs was identified in the center-south of the city. The houses located on the highest floors (levels 4 to 13 to ground) displayed higher concentrations. MPs were primarily composed of polyester (PET), polypropylene (PP), and ethylene-vinyl acetate (EVA), among others. The polymers identified suggest that MPs derived from the fragmentation of components frequently found in houses, such as synthetic clothing, food storage containers, toys, carpets, floors, and curtains. The incorporation of MPs from the outside into dwellings is not ruled out. Future studies should evaluate the influence of consumption habits and housing characteristics on the abundance of MPs.

Exploring marine biofouling on anthropogenic litter in the Atlantic coastline of Morocco

Today, the world is increasingly concerned about marine litter and its interaction with marine biodiversity. However, knowledge concerning the fouling organisms associated with marine litter is very limited in many of the world's marine environments. In this survey, we investigated biofouling on different types of marine litter washed up on all the coasts of the central Atlantic of Morocco. The findings revealed 21 fouling species belonging to 9 phyla (Arthropoda, Mollusca, Echinodermata, Annelida, Bryozoa, Porifera, Chlorophyta, Ochrophyta, and Ascomycota). More specifically, frequently observed fouling species include Mytilus galloprovincialis, Balanus laevis, Megabalanus coccopoma, and Pollicipes pollicipes species. Large marine litter items recorded the highest colonization of marine organisms in comparison to small ones. The frequency of occurrence (FO) of the species most commonly fouled on all coasts was Perforatus perforatus (FO = 48.60), followed by Mytilus galloprovincialis (FO = 45.80), Balanus trigonus (FO = 32.05), Balanus laevis (FO = 30.25), Megabalanus coccopoma (FO = 25.25), Bryozoa species (FO = 19.40), Spirobranchus triqueter (FO = 18.18), Lepas pectinata (FO = 14.45), and Pollicipes pollicipes (FO = 13.05). The majority of the species registered in this study are sessile. Substrate coverage by fouling taxa was significantly different between plastic substrate and other types of marine litter. Likewise, this study revealed that the proportion of fouling organisms is higher on rough surfaces. Overall, this research could be crucial to understanding the little-known subject of marine litter and its colonization by marine biota. Given that these marine litters can act as vectors and cause ecological, biogeographical, and conservation issues in the marine environment, minimizing the quantity of anthropogenic litter reaching the Moroccan Atlantic could significantly reduce its accumulation on the sea surface and seabed, thereby reducing the risk of invasion by non-indigenous species.