Evaluation of Electrolyzed Oxidizing Water Solutions as Alternatives for Milking System Cleaning-in-place and the Development of Mathematical Models

Open Access
Wang, Xinmiao
Graduate Program:
Agricultural and Biological Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
February 24, 2015
Committee Members:
  • Virendra Puri, Dissertation Advisor
  • Ali Demirci, Committee Chair
  • Paul Heinz Heinemann, Committee Member
  • Robert F Roberts, Committee Member
  • Robert Edwin Graves, Special Member
  • electrolyzed oxidizing (EO) water
  • milking system
  • cleaning-in-place (CIP)
  • blended EO water
  • one-step CIP
  • milk deposit removal
Cleaning and sanitizing of the food processing equipment are important and essential for the safety of food products. Specifically, the effective cleaning and sanitizing of milking system is essential to ensure the dairy product quality and safety. To achieve that, the cleaning and sanitizing of milking system on a dairy farm after the milking event are completed using a highly automated procedure referred as “cleaning-in-place (CIP)”. The chemicals used in the milking system CIP, however, are potentially hazardous to the farmers and the environment. Therefore, novel approaches are needed to solve this problem and further investigate the approaches to optimize the CIP process including investigation of the mechanism of milking system CIP. Electrolyzed oxidizing (EO) water is an emerging technology for cleaning processing systems in the food industry and as a cleaning and disinfecting agent. By electrolyzing dilute sodium hydroxide solution within an electrolytic chamber separated by a membrane, acidic EO water and alkaline EO water are generated simultaneously. Previous studies in our lab had already demonstrated the efficacy of using EO water as a potential alternative for the milking system CIP on a lab scale pilot milking system. Using EO water is cost effective once the EO water generator is purchased. Most importantly, it is environmentally benign as compared to the concentrated hazardous typical CIP chemicals. Building on past studies, this dissertation focused on further evaluating the application of EO water through a real world farm trial and conduct the operational cost comparison between using EO water and conventional chemicals for the milking system CIP. Additionally, another potential alternative to apply EO water was investigated, by combining alkaline and acidic EO water to formulate a blended EO water solution to conduct a one-step CIP on a lab scale pilot milking system. Moreover, a systematic study was carried out of the raw milk deposit removal mechanism during the alkaline and acidic EO water CIP and the optimized blended EO water one-step CIP process by mathematically developing deposit removal rate models for each CIP cycle. In this study, the real world validation of applying EO water on a commercial dairy farm was conducted and the operational cost was compared with that of using the conventional CIP. Results showed that using EO water CIP was performance wise comparable to using the conventional CIP but with a lower operational cost (25%). Additionally, an optimization process was performed to determine the optimal condition for the blended EO water one-step CIP on a lab scale pilot milking system. The optimal condition was found to be a cleaning time of 17 min, a starting temperature of 59°C and an acidic EO water percentage of 60% in the blended EO water solution to achieve a 100% CIP performance. When comparing the CIP performance of using the optimized blended EO water and the commercially available one-step CIP chemicals, results showed that using the optimal blended EO water solution was as good as the commercially available one-step chemicals and the operational cost of using the optimal blended EO water CIP was only about 20% as compared to the commercial one-step CIP. Moreover, the contribution of each CIP cycle to the entire milking system CIP process was studied on a stainless steel surface evaluation simulator by developing deposit weight based mathematical mechanistic models. A set of raw milk deposit removal kinetic models were developed and validated firstly for the alkaline and acid wash CIP process. Results showed a substantial amount (more than 90% of the initial deposited soil) of deposit removal occurrence during the initial warm water rinse cycle and a two-stage zeroth order deposit removal during the alkaline wash and acid wash cycles. Based on the proposed models, a 55% reduction of the original CIP operational time was achieved, and this is essentially important from an energy saving aspect. To further explore the raw milk deposit removal mechanisms under different CIP conditions, similar experiments were also conducted for the optimal blended EO water one-step CIP and the corresponding models were developed and validated. Moreover, scanning electron microscopy (SEM) was used to examine the remaining deposit morphology visually on the specimen inner surface. The SEM micrographs served to better understand and explain the deposit removal process during CIP. In conclusion, this study validated the potential application of alkaline and acidic EO water on commercial dairy farms and investigated another possible one-step CIP method on a lab scale pilot milking system with success. Additionally, from the developed raw milk deposit removal models for the CIP procedures, a shortened operational CIP time duration was achieved. It was found that the raw milk deposit removal behaved differently under differently CIP processes, and the contribution of the initial warm water rinse cycle is of great significance in the raw milk deposit removal. Therefore, it is concluded that EO water can be applied as alternative milking system CIP solutions. This project made an effort to answer some fundamental questions for dairy farmers and industries to make an informed decision.