Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Using vegetable tannin and polyaluminium chloride as coagulants for dairy wastewater treatment: A comparative study Marciel Dela Justina, Beatriz Rodrigues Bagnolin Muniz, Mariana Mattge Bröring, Valdeci José Costa, Everton Skoronski ⁎ Environmental and Sanitary Engineering Department, Santa Catarina State University, 2090 Luiz de Camões Avenue, Conta Dinheiro, Lages, Santa Catarina 88.520-000, Brazil ARTICLE INFO Keywords: Dairy wastewater Coagulation Flocculation Tannin PAC ABSTRACT The aim of this work was to compare the performance of tannin and polyaluminium chloride (PAC) in the coagulation process for dairy industry wastewater. The conditions of coagulation/flocculation with regards to the dosage, pH, velocity gradient and slow-mixing time were optimized and some parameters such as floc ag- gregation (K A ) and breakage (K B ) coefficients were computed. Additionally, it was carried out a thermogravi- metric analysis of the obtained sludge for both coagulants. The results showed no statistical differences between the performance of the two coagulants based on chemical oxygen demand, colour, turbidity and total solids removal. Particularly, the PAC showed higher alkalinity consumption and increased the electrical conductivity of the clarified wastewater, while tannin showed good performance within a wider pH, ranging from 5.0 to 10.0. Moreover, although the greatest K A values were observed for PAC usage, the tannin use presented higher re- sistance to floc breakage during the slow-mixing time. The obtained sludge from the experiments using tannin accounted for higher volatile solids and fixed carbon, and lower ash content when compared to PAC. In con- clusion, tannin is a promising alternative for dairy wastewater treatment regarding its process performance and wastewater treatment residuals management. 1. Introduction Coagulation is an essential process for surface water and industrial wastewater treatment [1]. It consists in a well-known process involving destabilization of colloids and other suspended substances so as to promote its aggregation as greater and weightier flocs [2,3]. Typically, inorganic coagulants derived from iron and aluminium salts as Al 2 (SO 4 ) 3 , FeCl 3 , and Polyaluminium Chloride (PAC), are employed in the coagulation processes [1,2]. Among these, the pre-hydrolyzed ones like PAC present some advantages, over the non-hydrolyzed, such as lower alkalinity consumption, and the generation of a smaller sludge amounts [4,5]. Alternatively to those inorganic metal-based coagulants, researchers have been looking for new and natural plant-based coagulants which have shown some advantages like the production of biodegradable sludge, lower alkalinity consumption and renewable sources origin [1]. On this way, tannin based coagulant has been being an effective coa- gulant in the treatment of numerous types of water and wastewater, presenting comparable or better performance than inorganic coagulants [6–9]. The tannins are macromolecular polyphenols, extracted from dif- ferent vegetable sources such as Schinopsis balansae Engler, Castanea sativa Miller and Acacia mearnsii De Wildemann. Due to the several natural sources extraction, tannin chemical structures are diverse, de- scribed as complex. Therefore, it is still a challenge to determine exactly the chemical structure of tannins [9]. Nevertheless, tannin is present in some plant barks and its presence is related to antimicrobial properties and thermal protection [10]. When naturally obtained, the vegetable tannin does not present cationic features, which is provided after a cationization procedure involving the Mannich reaction. In this process, a quaternary nitrogen is added to tannin poly- phenolic structure through a reaction with an aldehyde and an amine, producing a higher molecular weight compound [2]. Even though the cationization, which is essential for its application as a coagulant, the tannin preserves some original plant extract features like the water solubility. Moreover, tannin has an ampholytic behaviour caused by the presence of quaternary nitrogen and phenolic hydroxyls [9]. When tannin is extracted from Acacia mearnsii, the main monomeric units are gallocatechin and robinetinidol, but sometimes there are also catechin and fisetinidol units. Additionally, tannin from Acacia mearnsii https://doi.org/10.1016/j.jwpe.2018.08.001 Received 26 June 2018; Received in revised form 25 July 2018; Accepted 2 August 2018 ⁎ Corresponding author. E-mail address: skoronski@cav.udesc.br (E. Skoronski). Journal of Water Process Engineering 25 (2018) 173–181 2214-7144/ © 2018 Elsevier Ltd. All rights reserved. T