Effect of coagulant and flocculant addition scheme on the treatment of dairy farm wastewater

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.