Determination of The Best Available Coagulation/Flocculation Technology with Novel Pre-hydrolysed Coagulants for Colour Removal from Biologically Treated Textile Wastewater

Abstract

Chemical coagulation/flocculation technology  has a complex structure involving various inter-related parameters, since it is very critical to define that how well coagulant will function under given conditions. The literature studies have reported that novel pre-hydrolysed coagulants such as Polyaluminium chloride (PACl), Polyaluminium ferric chloride (PAFCl), Polyferrous sulphate (PFS) and Polyferric chloride (PFCl) seem to give better colour removal even at low temperature and may also produce lower volume of sludge. In this connection, the effectiveness of various novel pre-hydrolysing coagulants for the treatment of textile wastewater have been studied in the literature recently and these studies mostly reported that both they don’t need pH correction, additional coagulant aid exct. and they seem to give better colour removal even at low temperature and may also produce lower volume of sludge compared to conventional coagulants. By the way, there are very limited studies carried out on the decolourisation of textile wastewater containing multiple dyes of different classes along with the various chemical additives which are used during textile processing (especially denim washing and reactive dyeing), in the literature. So, the aim of this study is to determine the best available coagulation/flocculation technology with PACl and PAFCl as a novel pre-hydrolysed coagulants for colour removal from an aerobic treated textile wastewater including multiple dyes consists of mostly indigo dye together with reactive dye. According to the results, the colour value of  biologically treated textile wastewater was measured as 26,2 m^-1/ 23,3 m^-1/ 23,7 m^-1 for 436 nm, 525nm 620 nm. The best colour removal efficiency obtained from 80 mg/L PACl with 2 mg/L Anionic Polyelectrolyte at  pH 6,98 was calculated as 74% while sludge prduction rate calculated as 79 kg/day for 1500 m3/day wasteawter. Besides, 10 mg/L PAFCl and 2 mg/L anionic polyelectrolyte at pH 6,98, which is the real pH of the investigated Wastewater Treatment Plant (WWTP) effluent, showed the cost effective result as a coagulant in terms of both colour removal efficiency and sludge production rate with the values 75% and 60 kg sludge/day, respectively,as compared to PACl.