Like in the oceans, the bulk of the pollution in rivers and lakes is not in the form of plastic bottles and other large pieces, but tiny pieces called microplastics that would be hard to spot. “Three quarters of what we take out of the Great Lakes are less than a millimeter in size,” she says. “It’s basically the size of a period of a sentence.” These plastics are concerning to scientists because they are being ingested by a variety of aquatic organisms. (…) (pbs.org, 11/05/2017)
Wastewater treatment plants (WWTPs) can offer a solution to reduce the point source input of microlitter and microplastics into the environment. To evaluate the contributing processes for microlitter removal, the removal of microlitter from wastewater during different treatment steps of mechanical, chemical and biological treatment (activated sludge) and biologically active filter (BAF) in a large (population equivalent 800 000) advanced WWTP was examined. Most of the microlitter was removed already during the pre-treatment and activated sludge treatment further decreased the microlitter concentration. The overall retention capacity of studied WWTP was over 99% and was achieved after secondary treatment. However, despite of the high removal performance, even an advanced WWTP may constitute a considerable source of microlitter and microplastics into the aquatic environment given the large volumes of effluent discharged constantly. The microlitter content of excess sludge, dried sludge and reject water were also examined. According to the balance analyses, approximately 20% of the microlitter removed from the process is recycled back with the reject water, whereas 80% of the microlitter is contained in the dried sludge. The study also looked at easy microlitter sampling protocol with automated composite samplers for possible future monitoring purposes.
Julia Talvitie, Anna Mikola, Outi Setälä, Mari Heinonen, Arto Koistinen, Water Research, Volume 109, 1 February 2017, Pages 164–172
Environmental contamination by plastic particles, also known as ‘microplastics’, brings synthetic materials that are non-degradable and biologically incompatible into contact with ecosystems. In this paper we present concentration data for this emerging contaminant in wastewater treatment plants (WWTPs) and freshwater and marine systems, reflecting the routes via which these particles can travel and the ecosystems they potentially impact along their path. Raw sewage influents, effluents and sewage sludge from seven municipal WWTPs in the Netherlands contained mean particle concentrations of 68–910 L− 1, 51–81 L− 1 and 510–760 kg− 1 wet weight (ww), respectively (particle sizes between 10 and 5000 μm). Even after treatment, wastewater constitutes a source of microplastic pollution of surface waters, and via biosolids applications in farming and forestry, plastic retained in sewage sludge can be transferred to terrestrial environments. The WWTPs investigated here had a mean microplastics retention efficiency of 72% (s.d. 61%) in the sewage sludge. In the receiving waters of treated and untreated wastewaters, we detected high microplastic levels in riverine suspended particulate matter (1400–4900 kg− 1 dry weight (dw)) from the Rhine and Meuse rivers. Amsterdam canal water sampled at different urban locations contained microplastic concentrations (48–187 L− 1), similar to those observed in wastewater that is emitted from sewage treatment facilities in the area. At least partial settling of the particles occurs in freshwater as well, as indicated by microplastics in urban canal sediments (< 68 to 10,500 particles kg− 1 dw). Microplastics in suspension in the water column have the potential to be discharged into the sea with other riverine suspended particulates. We report microplastic concentrations from 100 up to 3600 particles kg− 1 dry sediment collected at 15 locations along the Dutch North Sea coast. The high microplastic enrichment in marine sediments compared to most literature data for seawater at the surface supports the hypothesis of a seabed sink for these materials. Marine species are heavily exposed to plastic particles. Body residues between 10 and 100 particles g− 1 dw were measured in benthic macroinvertebrate species inhabiting the Dutch North Sea coast: filter-feeding mussels and oysters (species for human consumption) as well as other consumers in the marine food chain.
H.A. Leslie, S.H. Brandsma, M.J.M. van Velzen, A.D. Vethaak, Environment International, Available Environment International, Volume 101, April 2017, Pages 133–142
Wastewater treatment plant (WWTP) effluent has been identified as a potential source of microplastics in the aquatic environment. Microplastics have recently been detected in wastewater effluent in Western Europe, Russia and the USA. As there are only a handful of studies on microplastics in wastewater, it is difficult to accurately determine the contribution of wastewater effluent as a source of microplastics. However, even the small amounts of microplastics detected in wastewater effluent may be a remarkable source given the large volumes of wastewater treatment effluent discharged to the aquatic environment annually. Further, there is strong evidence that microplastics can interact with wastewater-associated contaminants, which has the potential to transport chemicals to aquatic organisms after exposure to contaminated microplastics. In this review we apply lessons learned from the literature on microplastics in the aquatic environment and knowledge on current wastewater treatment technologies, with the aim of identifying the research gaps in terms of (i) the fate of microplastics in WWTPs, (ii) the potential interaction of wastewater-based microplastics with trace organic contaminants and metals, and (iii) the risk for aquatic organisms.
The global presence of microplastic (MP) in aquatic ecosystems has been shown by various studies. However, neither MP concentrations nor their sources or sinks are completely known. Waste water treatment plants (WWTPs) are considered as significant point sources discharging MP to the environment.
This study investigated MP in the effluents of 12 WWTPs in Lower Saxony, Germany. Samples were purified by a plastic-preserving enzymatic-oxidative procedure and subsequent density separation using a zinc chloride solution. For analysis, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FT-IR) and focal plane array (FPA)-based transmission micro-FT-IR imaging were applied. This allowed the identification of polymers of all MP down to a size of 20 μm. In all effluents MP was found with quantities ranging from 0 to 5 × 101 m−3 MP > 500 μm and 1 × 101 to 9 × 103 m−3 MP < 500 μm. By far, polyethylene was the most frequent polymer type in both size classes. Quantities of synthetic fibres ranged from 9 × 101 to 1 × 103 m−3 and were predominantly made of polyester. Considering the annual effluxes of tested WWTPs, total discharges of 9 × 107 to 4 × 109 MP particles and fibres per WWTP could be expected. Interestingly, one tertiary WWTP had an additionally installed post-filtration that reduced the total MP discharge by 97%. Furthermore, the sewage sludge of six WWTPs was examined and the existence of MP, predominantly polyethylene, revealed. Our findings suggest that WWTPs could be a sink but also a source of MP and thus can be considered to play an important role for environmental MP pollution.
S.M. Mintenig, I. Int-Veen, M.G.J. Löder, S. Primpke, G. Gerdts, Water Research, Volume 108, 1 January 2017, Pages 365–372
The accumulation of microplastics (plastic particles less than 5 mm) and similarly sized small anthropogenic litter (SAL; e.g., cellulosic products manufactured from natural material) in aquatic ecosystems is a growing concern. These particles can serve as vectors of chemical toxins and microbial pathogens and thus, as organisms consume them, may lead to biomagnification of these contaminants. As collection points in managed water systems, wastewater treatment plants (WWTPs) provide an opportunity to develop and implement novel technologies to manage SAL pollution. Here, we assessed the efficiency of different unit processes at three WWTPs in removing SAL. Samples were collected from WWTPs that employ either secondary treatment (activated sludge) or tertiary treatment (granular sand filtration) as a final step, as well as a pilot membrane bioreactor system that finishes treatment with microfiltration. SAL from 20 μm to 4.75 mm was quantified and categorized by shape. The WWTP with secondary treatment removed 95.6% of SAL, discharging 5.9 SAL per L in the final effluent; the plant with tertiary treatment removed 97.2% of SAL, discharging 2.6 SAL per L; the membrane bioreactor plant removed 99.4% of SAL, discharging 0.5 SAL per L. The majority of SAL in effluent from all plants was comprised of thin fibers (e.g., textile fibers). While the WWTP with tertiary granular sand filtration and the membrane bioreactor exhibited greater overall removal of SAL, fibers represented a larger percentage of SAL in effluent from these plants (79 and 83%, respectively) than the plant with activated sludge as a final step (44% fibers). This study suggests that retrofitting existing secondary WWTPs with granular sand filtration or membrane filtration would result in the highest possible removal of SAL—though treatment facilities would continue to serve as pathways of SAL pollution to the environment. Further, the fate of the 95–99% of SAL that is retained or leaves WWTPs through means other than effluent (e.g., sludge) must be resolved to effectively address this problem.
Environ. Sci.: Water Res. Technol., 2016, 2, 1064-1073
Municipal wastewater effluent has been proposed as one pathway for microplastics to enter the aquatic environment. Here we present a broad study of municipal wastewater treatment plant effluent as a pathway for microplastic pollution to enter receiving waters. A total of 90 samples were analyzed from 17 different facilities across the United States. Averaging all facilities and sampling dates, 0.05 ± 0.024 microparticles were found per liter of effluent. Though a small value on a per liter basis, even minor municipal wastewater treatment facilities process millions of liters of wastewater each day, yielding daily discharges that ranged from ∼50,000 up to nearly 15 million particles. Averaging across the 17 facilities tested, our results indicate that wastewater treatment facilities are releasing over 4 million microparticles per facility per day. Fibers and fragments were found to be the most common type of particle within the effluent; however, some fibers may be derived from non-plastic sources. Considerable inter- and intra-facility variation in discharge concentrations, as well as the relative proportions of particle types, was observed. Statistical analysis suggested facilities serving larger populations discharged more particles. Results did not suggest tertiary filtration treatments were an effective means of reducing discharge. Assuming that fragments and pellets found in the effluent arise from the ‘microbeads’ found in many cosmetics and personal care products, it is estimated that between 3 and 23 billion (with an average of 13 billion) of these microplastic particles are being released into US waterways every day via municipal wastewater. This estimate can be used to evaluate the contribution of microbeads to microplastic pollution relative to other sources (e.g., plastic litter and debris) and pathways (e.g., stormwater) of discharge.
Sherri A. Mason, Danielle Garneau, Rebecca Sutton, Yvonne Chu, Karyn Ehmann, Jason Barnes, Parker Fink, Daniel Papazissimos, Darrin L. Rogers, Environmental Pollution, Volume 218, November 2016, Pages 1045–1054