Legacy and emerging poly- and perfluoroalkyl substances in wastewater treatment plant and receiving water: abundance, removal, and potential ecological risk

Poly- and perfluoroalkyl substances (PFASs) are toxic persistent organic pollutants and bioaccumulative chemicals, which affect the environment and ecology. PFASs in the wastewater treatment plant (WWTP) and receiving river downstream were investigated. Fourteen out of eighteen PFASs were detected, ranging from 197 to 0.14 ng L^-1. The main pollutants were 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3-heptafluoro-propoxy) propanoic acid (HFPO-DA), perfluorooctane sulfonate (PFOS), and perfluorooctanoic acid (PFOA). The concentration of HFPO-DA (181 ng L^-1) was the highest in influent, which indicated the use and emission of PFASs in the sewage collection region of WWTP changed from legacy to emerging ones. However, PFOS from catering wastewater as the main source was dominant PFASs in the reclaimed water. Biological treatment could be effective in the removal of PFASs, especially for HFPO-DA. HFPO-DA could directly bind to cytochrome P450 and bring potential ecotoxicity to the surrounding environment, and the ecological risk of degradation products should be under consideration. Coagulation might result in PFASs release from sludge. More attention should be paid to sewage treatment process decision of WWTP for the control of PFASs.

Non-invasive ultrasonic inspection of sludge accumulation in a pipe

Sludge accumulated inside a fluid-flowing pipe used in a chemical or semiconductor processing factory should be periodically removed to avoid flow blockage that increases undesirable pressure inside the pipe. Accordingly, it is common practice to periodically dismantle a pipe system, clean up the accumulate sludge, and reassemble. Therefore, an accurate estimation of sludge accumulation in the pipe is important to minimize the halting time of a chemical process using the system. Considering the lack of a practically efficient, non-invasive method to estimate the severity of sludge accumulation without interrupting the on-going chemical process, we propose an ultrasonic, non-invasive, real-time inspection method using a pair of ultrasonic wedge transducers installed circumferentially on the outer wall of a pipe at the same axial coordinate. To detect lowly accumulated sludge, an ultrasonic wave path from a transmitting transducer via a test pipe with accumulated sludge to a receiving transducer is carefully designed. The severity of sludge accumulation can then be determined by the amplitude of the longitudinal wave picked up by another transducer installed on the other side of the wall. We performed a series of experiments with steel and PVC pipes that are partially filled with water and sludge of different heights. The experimental results confirmed the effectiveness and practical viability of the proposed inspection method.