Membrane ﬁltration and sonication for industrial wastewater reuse C. Caretti, E. Coppini, E. Fatarella and C. Lubello ABSTRACT This paper presents an experimental study aimed at estimating the efﬁciency of the innovative process of ultraﬁltration (UF) combined with sonication (Son.) for the reﬁnement of treated efﬂuent to be reused in wet textile processes. Such a novel approach, which has not yet been employed on a full industrial scale, has been experienced at pilot scale on the secondary efﬂuent of the Baciacavallo wastewater treatment plant (WWTP), which treats part of the efﬂuent from one of the largest textile industry districts in Italy. The combined treatment efﬁciency was assessed both on ozonated and non-ozonated Baciacavallo secondary efﬂuent. The membrane ﬁltration process was optimized in terms of running time, backwash, chemical addition and cleaning procedures. The sonication treatment was optimized on laboratory-scale with synthetic solutions (demineralized water added with dyestuffs) in terms of hydroxyl radicals formation rate, frequency, acoustic power, hydrogen peroxide addition, contact time and pH. The optimal conditions have been applied on the pilot-scale sonicator which was used in combination with the UF treatment. According to the experimental results, the best conﬁguration within the Baciacavallo WWTP was the sonication of non-ozonated wastewater followed by the UF. The combined treatment guaranteed the compliance with the target values for wastewater reuse in wet textile industries. This study is part of the Research Project PURIFAST (Puriﬁcation of industrial and mixed wastewater by combined membrane ﬁltration and sonochemical technologies) LIFE þ ENV/IT/000439. C. Caretti (corresponding author) C. Lubello Department of Civil and Environmental Engineering, University of Florence, via Santa Marta 3, 50139 Firenze, Italy E-mail: cecilia@dicea.uniﬁ.it E. Coppini GIDA S.p.A., via Baciacavallo 54, 59100 Prato, Italy E. Fatarella Next Technology Tecnotessile, Via del Gelso 13, 59100 Prato, Italy Key words | ﬁltration, membrane, reuse, sonication, textile, wastewater INTRODUCTION The district of Prato (Central Italy) is one of the main textile areas in Europe. The wet textile industry in Prato takes up to 97% of the total amount of water resources required for the entire industrial sector (about 14 Mm 3 /year). Industrial and municipal wastewaters discharged from the area of Prato are both treated in two centralized activated sludge wastewater treatment plants (WWTP), managed by GIDA SpA. The most important one is Baciacavallo WWTP, a conventional activated sludge plant, which treats about 120,000 m 3 /year of domestic (30%) and textile (70%) wastewaters. Since tex- tile industry is likely to be one of the industrial activities with the highest water demand, most of the industries are facing increasing pressures to avoid using high-quality water supplies for non-potable purposes. A highly innovative solution has been applied in the district of Prato: an indus- trial aqueduct provides about 1,500,000 m 3 /year of reﬁned wastewater to 90 textile industries in the area. The reﬁnery treatment plant (clariﬂocculation–ﬁltration–ozonation) is located at the Baciacavallo WWTP site. Before recycling, the reﬁned efﬂuent is mixed with freshwater from the Bisen- zio river (about 30% of the total) to control the salinity in the recycling system; wastewater from the Baciacavallo WWTP is partially discharged into the Bisenzio river in order to keep the river hydro balance unchanged. The aim of this study was to compare the efﬁciency of the present reﬁnery treatment (clariﬂocculation–ﬁltration– ozonation) and the innovative process of ultraﬁltration (UF) combined with ultrasound treatment (Son.). This study is part of the Research Project PURIFAST (Puriﬁ- cation of industrial and mixed wastewater by combined membrane ﬁltration and sonochemical technologies) LIFE þ ENV/IT/000439. Industrial wastewaters contain pollutants recalcitrant to conventional oxidation and biological treatments, which 2500 © IWA Publishing 2011 Water Science & Technology | 64.12 | 2011 doi: 10.2166/wst.2011.800 Downloaded from https://iwaponline.com/wst/article-pdf/64/12/2500/443447/2500.pdf by guest on 14 June 2020