Comparison of Methods for Assessing Reverse Osmosis Membrane Treatment of Shrimp Process Water

Abstract

Interest in reuse of process water from the food industry has reinforced the importance of controlling and monitoring the effectiveness and reliability of treatment systems regarding removal of organic matter and microorganisms. The ability of adenosine triphosphate bioluminescence, conductivity, turbidometry, absorbance, and multichannel fluorescence spectroscopy for indirectly monitoring the integrity of a reverse osmosis membrane when treating process water recovered from peeling in a shrimp processing line was evaluated. This study demonstrated that reverse osmosis was capable of removing bacteria (ca. 7 log CFU ml(-1)) to the levels required by the regulatory authorities for water recycling within the same food unit operation. Adenosine triphosphate and turbidometry showed a higher sensitivity for detecting compromising conditions at the treatment system (0.1% concentration of feed in permeate) and a better correlation with the aerobic count at lower levels than the other methods investigated. The sensitivity for assessing membrane integrity of conductivity and multichannel fluorescence was 1% of feed in permeate. Impact of feed variations was best leveled out in the permeates for turbidity measurements. Multichannel fluorescence spectroscopy may require laborious calibration procedures and expertise regarding data analysis and interpretation of results, which are not always available in food industries. Absorbance did not respond to changes in membrane integrity and was not well correlated to the aerobic count because of the poor sensitivity of this method for these purposes.

Current and Emerging Techniques for High-Pressure Membrane Integrity Testing

“…However, some reports suggest that VDT results correlate well with virus and total organic carbon (TOC) rejection by RO membranes and it is therefore a potentially useful integrity screening procedure for RO membrane elements [ 6 ]. Since the test is applied directly to membrane elements, the VDT cannot be performed when filtration is taking place [ 16 ] and thus does not enable real-time membrane integrity monitoring in the strictest sense but could allow frequent monitoring to identify slow degradation of system integrity.…”

“…Several integrity monitoring techniques have been developed for these systems and they are broadly classified into direct and indirect techniques [ 6 , 15 ]. In general, direct methods assess the integrity of membrane elements by the application of a pressure-based test whereas indirect methods use a surrogate parameter measured in the permeate for assessing the integrity of the whole membrane system [ 6 , 16 , 17 ]. Direct tests are usually performed offline on individual elements but indirect tests can be performed on membranes during service and have a wider scope for online continuous monitoring.…”

“…Direct tests are usually performed offline on individual elements but indirect tests can be performed on membranes during service and have a wider scope for online continuous monitoring. Challenge tests are a type of indirect technique where a surrogate species is introduced into the feed water and the removal efficiency is determined by the measurements of the surrogate species in the permeate [ 16 , 17 ].…”

Water reuse in a shrimp processing line: Safety considerations using a HACCP approach

“…Minimisation of the microbial risks associated with food process water treatment and reuse is ensured by guaranteeing an optimal performance of the treatment process and verifying filter or systems failures (Alspach, 2002). On-line monitoring of the microbiological quality of the treated water is not feasible, and the use of indirect methods is, therefore, recommended (Casani & Knøchel, 2002) The potential of various methods, i.e., Adenosine Triphosphate bioluminescence (ATP), conductivity, turbidometry, absorbance and multichannel fluorescence spectroscopy, for assessing at-line the integrity of the RO system was investigated (Casani, Hansen, Christensen, & Knøchel, 2005). ATP content showed a better correlation with aerobic count at levels close to those required for recycling and a higher sensitivity for detecting compromising conditions at the treatment system than the other methods investigated.…”

Treatment of Food Industry Foods and Wastes by Membrane Filtration

“…With the continuous RO system (34)(35)(36), the centrifuge effluent is divided into two streams: (a) the RO permeate amounting to about 90 m 3 of water; and (b) the RO retentate having 8% TS and about 90 m 3 of water. The RO permeate is recycled to the grinding operation for reuse, while the RO retentate is treated by steam heat, coagulation, and mechanical separation, which is then dried as a high grade protein concentrate (protomyl PF) that can be used as animal feed for small animals, such as piglets, poultry, dogs, cats, minks, etc.…”