Occurrence, identification and removal of microplastic particles and fibers in conventional activated sludge process and advanced MBR technology

Abstract

Wastewater treatment plants (WWTPs) are acting as routes of microplastics (MPs) to the environment, hence the urgent need to examine MPs in wastewaters and different types of sludge through sampling campaigns covering extended periods of time. In this study, the efficiency of a municipal WWTP to remove MPs from wastewater was studied by collecting wastewater and sludge samples once in every two weeks during a 3-month sampling campaign. The WWTP was operated based on the conventional activated sludge (CAS) process and a pilot-scale membrane bioreactor (MBR). The microplastic particles and fibers from both water and sludge samples were identified by using an optical microscope, Fourier Transform Infrared (FTIR) microscope and Raman microscope. Overall, the retention capacity of microplastics in the studied WWTP was found to be 98.3%. Most of the MP fraction was removed before the activated sludge process. The efficiency of an advanced membrane bioreactor (MBR) technology was also examined. The main related finding is that MBR permeate contained 0.4 MP/L in comparison with the final effluent of the CAS process (1.0 MP/L). According to this study, both microplastic fibers and particles are discharged from the WWTP to the aquatic environment.

Microplastics and Wastewater Treatment Plants—A Review

“…So far, all tertiary treatment methods such as ultrafiltration and reverse osmosis lead to the discharge of MPs in the effluent so that there is effectively no commercial separation method put into place that leads to zero emission of microplastics from WWTPs. Moreover, while by far the most MPs are already retained in the primary stage, the fate of the remaining MPs through subsequent treatment stages is not always easy to predict [143] as diverse feedback cycles exist.…”

“…Water from dewatering sludge and water from rinsing removed solids and grease, which are mixed back into the influent, may carry appreciable amounts of MPs [109] [143]. Much of the microplastics end up in the sludge.…”

“…value in 1.060,000 m 3 of treated water, [111]]. Another study comes from Finland, where wastewater and sludge samples were collected from the Kenkäveronniemi WWTP, situated near the city of Mikkeli [143]. The treatment plant purifies 10,000 m 3 wastewater per day and features screening, grit separation, primary separation, biological treatment with activated sludge, final sedimentation and disinfection [143].…”

Removal of >10 µm Microplastic Particles from Treated Wastewater by a Disc Filter

“…That is because WWTPs collect vast volumes of wastewater of various origin such as industrial plants and households, along with stormwater runoff, which potentially contains considerable amounts of MPs [13,14]. Although research has shown that WWTPs remove 96-98% of the inflowing MPs [17][18][19], the limited percentage of MP particles discharged to receiving water bodies adds up to a substantial amount, owing to the large flux of wastewater [14,15]. For instance, annual wastewater production in Denmark alone is approximately 700 million m 3 year −1 [20].…”

Consumers’ Perceptions and Attitudes toward Products Preventing Microfiber Pollution in Aquatic Environments as a Result of the Domestic Washing of Synthetic Clothes

“…In developing countries, with less infrastructure, it is common that wastewater is not collected and treated [18]. Even if the WWTP were completely effective in removing all microfibers from the wastewater, the extracted microplastics often still enter the environment through the sludge being employed as soil fertilizer [5,11,19,20]. Concentrations of microplastics in the seabed where sewage sludge was dumped until 1998 in the UK were three times higher than at other reference sites [3].…”