Mass Loading and Fate of Linear and Cyclic Siloxanes in a Wastewater Treatment Plant in Greece

Abstract

The occurrence and fate of 5 cyclic (D3 to D7) and 12 linear (L3 to L14) siloxanes were investigated in raw and treated wastewater (both particulate and dissolved phases) as well as in sludge from a wastewater treatment plant (WWTP) in Athens, Greece. Cyclic and linear siloxanes (except for L3) were detected in all influent wastewater and sludge samples at mean concentrations of (sum of 17 siloxanes) 20 μg L(-1) and 75 mg kg(-1), respectively. The predominant compounds in wastewater were L11 (24% of the total siloxane concentration), L10 (16%), and D5 (13%), and in sludge were D5 (20%) and L10 (15%). The distribution of siloxanes between particulate and dissolved phases in influents differed significantly for linear and cyclic siloxanes. Linear siloxanes showed higher solid-liquid distribution coefficients (log K(d)) than did cyclic compounds. For 10 of the 16 compounds detected in influents, the removal efficiency was higher than 80%. Sorption to sludge and biodegradation and/or volatilization losses are important factors that affect the fate of siloxanes in WWTPs. The mean total mass of siloxanes that enter into the WWTP via influent was 15.1 kg per day(-1), and the mean total mass released into the environment via effluent was 2.67 kg per day(-1).

Techniques for Siloxanes Removal from Biogas Produced by Sewage Sludge Digestion

“…Otherwise, the siloxane could also be classified into low-molecular volatile methyl siloxane (VMS) and high-molecular polymer polydimethylsiloxane (PDMS). With high vapor pressure, the VMS is the main siloxane in biogas, and the common VMS in biogas was D3-D5 and L2-L5 [3]. In contrast, PDMS is non-volatile and indissoluble, so it is generally adsorbed on sediment or sludge [3].…”

“…With high vapor pressure, the VMS is the main siloxane in biogas, and the common VMS in biogas was D3-D5 and L2-L5 [3]. In contrast, PDMS is non-volatile and indissoluble, so it is generally adsorbed on sediment or sludge [3]. The siloxanes is reported to have a stable chemical and biological properties like low flammability and water repelling properties, high thermal stability and low toxicity, and it will stay 10 d-30 d in the atmosphere for VMS [5].…”

“…The siloxanes is a widely-used and greatlyproduced chemical in many industries, and it has an high level in environment [3,4,5]. The wastewater network is one of the most important destinations of siloxanes.…”

Problemas en el análisis de metilsiloxanos volátiles (VMS): origen y soluciones

“…Además, no siempre es posible preparar una muestra blanca artificial que simule bien la matriz analizada. Por estas razones se ha reportado el uso de muestras blancas muy variadas, como es el caso de Bletsou y col. 47 que emplearon muestras de suelos que no contenían niveles detectables de VMS, como matriz blanca en el análisis de fangos de depuradora. Como otro ejemplo podemos citar a Kaj y col. 11,12 que utilizan sílice como matriz blanca para el control de la toma de muestra en análisis de suelos, fangos y sedimentos.…”

“…Por último, se debe mencionar que también se ha aplicado la extracción líquido-líquido convencional en el análisis de VMS en agua residual. 47,59 Sin embargo, esta opción no se recomienda ya que puede ocasionar pérdidas significativas de los compuestos más volátiles, y en su lugar es preferible aplicar las técnicas de microextracción ya citadas. Como hemos mencionado anteriormente, para minimizar las pér-didas por volatilización durante el análisis de VMS se suele evitar el uso de etapas de pre-concentración de los extractos, sin embargo, esto conlleva una pérdida de sensibilidad importante en la determinación.…”