TREATMENT OF SWINE WASTEWATER WITH BIOLOGICAL CONVERSION, FILTRATION, AND REVERSE OSMOSIS: A LABORATORY STUDY R. H. Zhang, P. Yang, Z. Pan, T. D. Wolf, J. H. Turnbull ABSTRACT. The performance of a bench-scale integrated swine wastewater treatment system was evaluated on the basis of energy recovery, fertilizer production, and water reclamation. The system consisted of one anaerobic sequencing batch reactor (ASBR), one or two aerobic sequencing batch reactors (SBR1 and SBR2), one sludge settling tank, one sand filter, and one reverse osmosis (RO) unit. The system was tested with swine wastewater (approximately 15,000 mg/L volatile solids). The chemical oxygen demand (COD) and solids in the wastewater were reduced by 89% to 97%, and total coliforms and E. coli were reduced by 1 log CFU after treatment with the ASBR and SBRs. The oxidized nitrogen (NO2 -N and NO3 -N) was 14% or 53% of total nitrogen in the wastewater after it passed through SBR1 or SBR1 and SBR2, respectively. The sand filter was used to further reduce the COD and solids, especially suspended solids, prior to RO treatment. Two types of spiral-wound RO membranes were tested and compared. The RO was found to be highly effective in separating nutrient and salt elements from water. After RO treatment, over 70% of NH3 -N, NO2 -N, and NO3 -N and over 90% of other elements, such as P, K, Cl, Ca, Mg, Na, Zn, Fe, and Cu, were concentrated in a liquid effluent with one-tenth the original volume. The reclaimed water needs to be further evaluated for its uses. Various operational cost and maintenance issues associated with individual processes and the overall system need to be addressed when the treatment system is scaled up and evaluated for farm applications. Keywords. Anaerobic digestion, Membrane separation, Reverse osmosis, Sequencing batch reactor, Swine manure. aste management is a major task for every ani- other valuable products from animal wastewater, such as fuel mal feeding operation. Nearly 40% of feed dry and fertilizer, along with reclamation of water, may help matter and up to 70% of nutrients fed to ani- improve the process economics. mals are excreted in manure (Van Horn et al., The overall goal of this research was to develop an 1994).W Liquid manure handling and storage systems are com- integrated wastewater treatment system capable of convert- monly used on livestock farms. Most of the water used on the ing animal wastewater into energy, fertilizer products, and farms enters the manure system. In areas where water re- clean water. The objective was to investigate the technical sources are limited or disposal of a large quantity of wastewa- feasibility of combining biological treatment processes ter is problematic, reclamation of clean water from animal (anaerobic and aerobic treatment) and physical treatment wastewater for recycling may become necessary. processes (sand filtration and reverse osmosis) in one system. Water reclamation requires removal of organic and Li and Zhang (2001) demonstrated the efficacy of using an inorganic compounds from wastewater. Due to high con- integrated anaerobic and aerobic treatment system for animal centrations of such compounds in animal wastewater, wastewater. The study reported in this article was an extensive treatment by means of a combination of different extension of the previous research to incorporate two treatment processes, such as solid/liquid separation, biologi- sequential separation processes, sand filtration and reverse cal degradation, and membrane separation, is necessary. The osmosis (RO), to provide further treatment of the liquid treatment costs can therefore be very high. Production of effluent of biological treatment processes to yield concen- trated nutrient liquid and clean water. Membrane separation technologies have been applied to Article was submitted for review in December 2002; approved for the separation of solids and recovery of materials from waste publication by the Structures & Environment Division of ASAE in streams, purification of polluted water, and desalination of September 2003. Presented at the 2002 ASAE Annual Meeting as Paper salt water (Duvel and Helfgott, 1975; Bilstad, 1995; Ozaki No. 024096. and Li, 2002). Reverse osmosis (RO) is a commonly used The authors are Ruihong Zhang, ASAE Member, Associate Professor, Peilin Yang, ASAE Student Member, Post-Graduate Researcher, and membrane separation process. It has been found to be capable Zhongli Pan, ASAE Member Engineer, Adjunct Assistant Professor, of removing a wide spectrum of impurities from contami- Department of Biological and Agricultural Engineering, University of nated water at high efficiencies (Bilstad, 1995). For domestic California, Davis, California; Thomas Wolf, Engineer, PerLorica, Inc., and industrial applications, solids sedimentation and chemi- Grass Valley, California; and Jane Turnbull, Principal, Peninsula Energy cal precipitation are common pretreatment methods prior to Partners, Los Altos, California. Corresponding author: Ruihong Zhang, Department of Biological and Agricultural Engineering, University of membrane separation (Lopez-Ramirez et al., 2003). Reports California, One Shields Avenue, Davis, CA 95616; phone: 530-754-9530; describing the application of membrane separation to animal fax: 530-752-2640; e-mail: [email protected]. wastewater treatment are scarce. Bilstad et al. (1992) studied Transactions of the ASAE Vol. 47(1): 243-250 E 2004 American Society of Agricultural Engineers ISSN 0001-2351 243 the use of RO with raw and anaerobically digested pig EXPERIMENTAL SETUP AND OPERATION manure. An RO module consisting of 18 tubular polyamide A laboratory-scale wastewater treatment system, shown membranes was used to treat pig manure that had undergone in figure 1, was used for this study. The system consisted of anaerobic digestion, chemical treatment, and mechanical the following elements connected in series: one anaerobic solid/liquid separation. The pilot separation trials were sequencing batch reactor (ASBR), two aerobic sequencing performed in batches, i.e., the RO reject was returned to the batch reactors (SBR1 and SBR2), one solids settling tank, feed tank. After RO treatment, 95% of total nitrogen was one sand filter, and one reverse osmosis membrane unit (RO). removed from the liquid. RO proved to be an effective The ASBR and the two SBRs were made of clear acrylic process to separate nitrogen and salts from animal wastewa- tubes of 10 cm inside diameter. The ASBR had a 12 L ter. However, much more research is needed to investigate working volume and was heated using a hot water jacket the applications of membrane separation technologies in outside the reactor. The temperature of the ASBR was various animal wastewater treatment systems. controlled at 35°C ±1°C throughout the experiment. SBR1 and SBR2 had 4 L and 7.5 L working volumes, respectively. The SBRs, sand filter, and RO were operated at an ambient ° ° MATERIALS AND METHODS temperature of 20 C to 21 C. The ASBR was designed to treat swine manure of about SWINE MANURE COLLECTION AND PREPARATION 15,000 mg/L volatile solids (VS) at 3.0 g VS/L/d loading rate. Swine manure used in this study was collected on the This VS level was in the range encountered on swine farms. Swine Research Farm of the University of California, Davis The ASBR was initially seeded with 10 L of sludge from a (UC Davis). The pigs on the farm were 16 to 20 weeks old. mesophilic anaerobic digester at the UC Davis wastewater The manure was collected off a concrete floor and then treatment plant. The TS and VS of the seed sludge were slurried by adding tap water. The manure slurry was screened 53,000 mg/L and 31,000 mg/L, respectively. The ASBR was with two sieves with openings of 4 × 4 mm and 2 × 2 mm, first started with an influent of about 10,000 mg/L at 0.5 g respectively, to remove hairs and large particles. The VS/L/d loading rate (see table 3) and 20 d HRT. The loading screened manure was immediately stored in a freezer at rate was then increased to 1.0 g VS/L/d by decreasing the -20°C until use. When needed, the stored manure was HRT to 10 d. After the ASBR reached stable operation, as thawed, analyzed, and diluted with tap water to obtain indicated by steady daily biogas production, the influent VS desired volatile solids (VS) concentration. Due to loss of was increased to about 15,000 mg/L, and the loading rate was urine prior to manure collection, the collected manure increased to 1.5 g VS/L/d. Later, the loading rate was contained a relative low content of ammonia. Urea was added increased to 2.25 g/L/d and then to 3.0 g/L/d by decreasing to the manure to increase the NH3-N concentration to a level the HRT from 10 d to 6.7 d and then to 5 d. After the ASBR typically found in fresh manure on commercial swine farms. reached a steady state at 3.0 g VS/L/d, its effluent was The prepared manure was then stored in a refrigerator at 4°C discharged into SBR1 for aerobic treatment. The steady state and used as feed for the anaerobic sequencing batch reactor of the ASBR was defined by less than 5% variation of daily (ASBR). biogas production during a two-week (or greater) period. It normally took about two weeks for the ASBR to reach a steady operation after a new loading rate was applied. The Sand filter Gas SBR2 Mixer meter SBR1 ASBR Pump Sludge Feed tank Gas Solids circulation Settling Airflow meter tank Solenoid RO unit valve Liquid Gas Air Compressed air Humidifier Supply pump Permeate Concentrate Figure 1. Schematic of laboratory wastewater treatment system. 244 TRANSACTIONS OF THE ASAE ASBR was fed four times a day and mixed by gas recircula- Table 1.