Water. desalination + reuse

PROJECTS November-December 2014 | Desalination & Water Reuse | 21 | REvERSE OSmOSiS mEmbRanES A pivotal process technology decision was the selection of the RO membranes in the context of high temperatures in both plants as well as their distinct influent chemical characteristics. The use of RO systems on constant or near constant influent conditions is well established. Examples include: groundwater treatment; polishing for water supply treatment systems; and in industrial beverage production. But additional attention is vital when selecting RO membranes for food process wastewater treatment because there are literally hundreds of products and flavours and multiple product changeovers occurring sometimes daily. For the snack foods facility, pilot testing at a similar production plant in a different state had showed water temperature to be much cooler than the actual site process water temperature. And there were differences in the process wastewater constituents between the pilot and actual sites. These included higher concentrations of arsenic and selenium at the actual site influent than at the pilot. No pilot testing was done on the potato wastewater stream since a complete new production process was also being built. Afterwards the wastewater was found to contain higher concentrations of aluminum than recommended for the RO membranes. Sources of the aluminum were removed in the production process so the selected RO membranes could continue to be used. These findings raise questions about the value of using a similar plant as a pilot. Just because a plant makes similar or even identical products, it does not mean the same membrane technology is applicable, or scale- up from pilot testing is prudent. It is best to pilot test at the actual treatment plant site. STaRT-uP and OPERaTiOn Planning for start-up of the process water and recycling facility has to be performed early in the design as there are critical steps in integrating the new treatment systems into existing treatment and production processes. Some startup issues that need to be addressed include: • training of operators and maintenance staff; • diversion of flows; • acclimatization of biological systems; • influent conditions at startup; and • unknown influent foulants for membrane processes. TRaining Operations and maintenance staff should be trained during the near-final construction period. And they should be involved in equipment vendor training as well as training on the overall plant integration. Equipment vendors know their systems and components well, but they often do not relate the performance of their systems to upstream or downstream treatment systems. A wise approach is to record on video – with the trainer's permission – some of this training because staff turnover can lead to loss of the original vendor training. For the potato processing facility, the design and build firm provided a full-time, on-site qualified operator to train and troubleshoot the processes during startup for the first six months of operation. Management planning Evaluating a proposal for developing a project to reuse production water is influenced by many considerations. Sustainability, costs as well as regulatory and operational considerations feature highly but ultimately decisions have to hinge on the capacity to overcome concerns about product reputation. Chief areas for questions Economics Do the projected capital and operational costs of the treatment systems indicate that water reuse is a viable proposition? Viability grows more likely as water-stressed areas and droughts grow more common under climate changing conditions, and as proven advances in treatment technology make it more generally accepted. design What does production discharge and how can this be identified? What water quality is achievable? Does the achievable quality meet the requirements of the selected reuse purposes? Selection of the design influent conditions is a critical step in a successful treatment and reuse project. Physical footprint How much area for treatment systems is needed? Generally, biological systems require more space than physical treatment systems. Security Can a treatment process be secured on the site to protect water quality and equipment? Reliability Can a treatment process be guaranteed to work all of the time? Continuous operation depends on predictable influent limits, available redundancy, operator knowledge and dedication, and the dependability of the power supply. Permitting What would be necessary to get a treatment plant permitted from regulatory agencies to reuse water in a food processing facility? Each reuse has separate regulatory considerations and review times vary from weeks to months in some cases. Legal Does the reuse of the process water constitute becoming a water utility and therefore require implementation of public utility regulations? If the water is to be used for human consumption, then the plant could constitute a water utility provider. Perception How would the employees and customers react to reuse of process water - would it cause customers to be concerned about quality? marketing strategy Does a water reuse project have strategic value to the company? Critical failure analyses What are the most critical factors to ensure treatment performance? Figure 2. Neuros blowers operating quietly at the potato processing facility.

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