|Boykin jr, James|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/22/2005
Publication Date: 7/27/2005
Citation: Boykin Jr, J.C., Soerens, T.S., Siebenmorgen, T.J. 2005. Treatment of rice cooker wastewater and recovery of byproducts by membrane microfiltration. Applied Engineering in Agriculture. Vol. 21(4): 689-694. Interpretive Summary: Rice consumption in the U.S. is over 20 pounds per capita yearly. Twenty five percent of this rice goes into processed foods such as convenience cook rice, which is fully cooked and packaged for human consumption. Convenience cook rice operations produce an effluent that is extremely high in organic content, mostly starches, and requires large amounts of oxygen for biological treatment. Membrane microfiltration has been used in several other industrial food applications and could be used to recover starches from rice cooker effluents. This study evaluated the performance of a tubular, stainless steel membrane microfiltration system in removing starches from a rice cooker waste stream. The system was successful in removing most solids and biological oxygen demand from the waste stream. A concentrated starch solution, which has several potential uses as an animal feed or human consumption, was recovered as a byproduct. The system designed and tested in this study will likely be too expensive for starch recovery from rice cooker effluent; however, the concept was proven successful. Further studies with less expensive filtration methods should be considered. An inexpensive method of starch recovery would eliminate disposal charges, while creating a potentially valuable byproduct.
Technical Abstract: A pilot scale system was used to evaluate the performance of a membrane microfiltration system, rated at 0.1 micron, for the recovery of starches and other solids from rice cooker wastewater produced by a rice processing facility. Results of three experiments showed that a cross-flow velocity of 5.18 m/s (17 ft/s) and a trans-membrane pressure of 276 kPa (40 psi) were required for best filtration. In two experiments, a concentration of almost 9% total solids was achieved. Permeate flux rates decreased from over 2 m/d (50 gal./ft2/day, gfd) for unconcentrated samples to under 0.4 m/d (10 gfd) for the most concentrated samples. The treated and untreated streams were characterized to evaluate the performance of the system. The feed flow contained an average of 0.71% total solids and 4395 mg/L BOD. The permeate contained under 0.12% total solids and under 400 mg/L BOD. A membrane system was sized for the test site based on data from these experiments. A system capable of concentrating 68 L/min (18 gpm) of cook water to 5, 8, and 10 % total solids required a total membrane surface area of 77, 113, and 155 m2 (831, 1215, and 1665 ft2), respectively. Savings in sewage costs were calculated to be $10.90/hr (average cost savings per hour of filter operation).