Membrane fouling during the filtration of swine manure pretreated by flocculation using cationic polymer

Swine wastewater (SW) treatment by reverse osmosis (RO) filtration requires the application of efficient manure pretreatments. Flocculation using cationic polymers improves suspended solids (SS) removal, but residual polymer in the liquid fractio n may cause severe membrane fouling. This study investigated the effect of residual polymer in SW o n the fouling of an RO membrane. The effects of residual SS, polymer charge density (CD) were inves tigated. Permeate flux tended to be lower when the SW contained both residual polymer and SS. Wate r flux recovery of the fouled membrane was lower for tests with than without polymer, and foul ing tended to be higher with the low than the medium CD polymer. The fouling was reversible as ch emical cleaning gave complete recovery of water flux. The RO membrane could thus be used in c onjunction with a flocculation pretreatment without the polymer causing excessive fouling. Introduction The use of reverse osmosis (RO) filtration to conce ntrate manure nutrients in small volumes can improve the recycling of nutrients from livestock p roduction as it facilitates the transport of the nutrients to agricultural areas with low livestock density. However, efficient pretreatment of the raw manure to remove most of the suspended solids (SS) is required prior to membrane filtration [1]. Manure flocculation using cationic polymers signifi cantly increases the SS removal efficiency of solid-liquid separators, [2], making it a viable ch oice of pre-treatment for RO filtration. Polymer chains adhere to SS during flocculation and are rem ov d with the solid fraction during the separation step. However, some free polymer chains and small p articles coated with polymer may remain in the liquid fraction and cause excessive fouling of the m mbrane. Most membranes have a residual negative charge, which favours the attachment of ca tionic polymer to the membrane surface [3]. Masse et al. [4] reported a detrimental effect on n a o filtration (NF) and RO membrane performance when a cationic polymer was used as a pretreatment for liquid swine manure. Previous studies concluded that the presence of residual polymer cau sed membrane fouling and stressed the importance of optimising polymer dose to the requirement of th e effluent being treated as to minimize residual polymer in solution [4, 5]. The degree of membranepolymer interaction, and thereby the severity of fouling, is expected to depend on the concentration of residual polymer as well as the characteristics of the membrane, the polymer and the liquid being trea ted. This study investigated the effects of residua l SS and polymer concentration in solution as well as polymer charge density (CD) on the fouling of a RO membrane processing swine wastewater (SW). Materials and Methods Experimental procedures Swine manure was first pretreated by a mechanically based solid-liquid separator, which yielded a liquid fraction (LF) containing 669 mg L -1 SS on average. Part of the LF was passed through a n ultr filtration (UF) membrane to produce an UF permeate (UFP) without SS but with the same level of dissolved species and conductivity as the LF. Two p olymers were evaluated, Superfloc-C492 (CD10) and Superfloc-C496 (CD35) (Kemira, Québec, Canada). The polymers were both high molecular weight, linear, cationic polyacrylamide polymers wi th CD of 10% and 35% for the CD10 and CD35 polymer, respectively. Optimum doses to flocculate swine manure having SS concentrations ranging from 29 to 106 g L averaged 30 ±6.2 and 69 ±12 mg L -1 for CD10 and CD35, respectively [6]. In this study, CD10 and CD35 were added in doses of 0, 5, 1 0 and 20 mg L -1 to the LF effluent. The CD10 polymer was also added in doses of 0, 20 and 40 mg L to the UFP effluent. Polymer was added to 500 L of LF or UFP. Spiked effluents were processed using a low fouling, spiral-wound RO