Effect of coagulant and flocculant addition scheme on the treatment of dairy farm wastewater Maen M. Husein and Ahmad Al-As’ad ABSTRACT Our group was approached by a manufacturer of treatment trains to recycle wastewater from dairy farm manure. Company X treatment trains consist of microscreening, sedimentation and filtration units attached to a reverse osmosis (RO) membrane. To enhance screening, a coagulant and a flocculant are added to the stream feeding the microscreen. However, their customers experience foaming on the microscreen as well as frequent fouling of the RO membranes. This study aimed to identify the source of foaming and to optimize the performance of the treatment train. Results show that interactions between the alum coagulant, the polymer flocculant and the contaminants are the cause of foaming. Addition of silicon polymer antifoam A effectively reduced foaming, while maintaining the same removal of total suspended solids (TSS) and total organic carbon (TOC). Alternatively, we proposed a new reagent addition scheme which circumvents back-to-back addition of the polymer flocculant and the alum coagulant. The proposed scheme resulted in significant reduction in foaming and ∼50% increase in TSS and TOC removal, even at the 40% lower dose of the cationic polymer. In addition to the economic benefit, a low concentration of left-over polymer should alleviate the fouling of the RO membrane. Maen M. Husein (corresponding author) Ahmad Al-As’ad Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada E-mail: maen.husein@ucalgary.ca Key words | antifoam, coagulation, flocculation, membrane, total organic carbon, total suspended solids INTRODUCTION Description of the problem Company X builds trains targeting the treatment of waste- water from livestock farming. The treated water may be reused in the barn, while recovering raw manure and a con- centrated fertilizer stream for land spreading. Their train removes coarse and fine suspended solids, dissolved solids and soluble organics. The treatment process consists of the following major units: bulk solids removal, fine solids removal, polishing filter, reverse osmosis (RO), final water polishing and a reject water concentrator. Figure 1 is a flow diagram showing the major units of the company X treatment train. The coarse and fine solids removal units include a microscreen followed by a sedimentation tank. The wastewater stream feeding the microscreen from an equalization tank is almost simultaneously impregnated with alum as a coagulant and cationic polymer flocculants, in order to promote large floc formation and separation on the screens. The same chemicals also promote separation of the fine solids in the clarifier. Of course, part of the added flocculant will travel with the water stream as a water-soluble polymer and will likely make it to the RO unit. However, RO manufacturers warn against the use of cationic polymer flocculants, since they interact with the membrane material leading to low recovery ratios. In addition, customers complain about frequent foam buildup on the microscreen. Foam adversely impacts the performance of the micro- screen and the clarifier. Foam blocks screen openings and, hence, hinders the flow of solid-free water and leads to messy spills. Furthermore, foam traps air which causes fine solids to float rather than settle in the clarifier unit. 271 © IWA Publishing 2015 Journal of Water Reuse and Desalination | 05.3 | 2015 doi: 10.2166/wrd.2015.070 Downloaded from https://iwaponline.com/jwrd/article-pdf/5/3/271/377460/jwrd0050271.pdf by guest on 30 December 2018