Water. desalination + reuse

PROJECTS | 22 | Desalination & Water Reuse | November-December 2014 DivERSiOn Of flOwS Partial or complete diversion of flows without interruption of production processes or development of detailed schedules and steps during production downtime events are vital. They are vital since limited production will change the characteristics of the influent from the combined production processes. Reduced flows and product loss during production startups can be below or well above the design range for influent loadings and flows. An understanding of production characteristics is pivotal when bringing all or partial treatment components on-line during a production process startup, or diverting flows to allow more effective treatment and acclimatizaton of biological elements. ACClimATizATiOn AnD influEnT START uP COnDiTiOnS Activated sludge processes and anaerobic treatment startup are not rapid – this is an important consideration when adding these processes. The bacteria and microorganisms involved may take weeks even months to become established and acclimatized to the process wastewater streams. Factors that affect this time include: • water temperature, availability of nutrients and micro-nutrients; • pH variations; • food-to-mass ratios; • seeding with purchased or donated biomass from another wastewater treatment plant; • addition of enzymes; and • recirculation. During the acclimatization period, additional problems might include excessive foaming caused by young biomass in aeration systems, incomplete treatment with poor quality effluent, analytical testing to confirm dosages of nutrients, microscopic evaluation of biomass and other evaluations to determine how to tweak the startup protocol. It is important to note that production staff at food and beverage facilities often do not fully understand the biological startup time and the integrated factors affecting this schedule. Biological nutrient removal (BNR) such as nitrification and denitrification and phosphorus removal will add more time to start-up as the organisms involved are slower to grow. The startup of the snack foods process water treatment and return plant took about six weeks in a hot climate and with supplemented purchased seed, while the startup of the potato process treatment system took months to establish complete enhanced biological phosphorus removal. influEnT STARTuP COnDiTiOnS Treatment processes are designed typically with a range of influent conditions generally including average influent loadings in concentration and average flows. Design and startup should also consider lower influent loading conditions than those used for the overall plant design since almost all treatment systems are designed for anticipated growth. Startup under low loading conditions can be as problematic as startup under higher loads. Equipment such as blowers, return sludge pumping systems, chemical feed systems, and similar treatment processes may, for example, not have sufficient turn-down capacity to prevent overfeeding chemicals. During system design many conditions need to be considered including at least the following: • average flow at average concentrations; • peak flow at average concentrations; and • maximum concentrations at average flow. Sludge management can easily be under-estimated if the actual loadings into the treatment process peak higher than predicted, if production processes cause high volumes of concentrated product losses, or if dewatering efficiencies are not as predicted. unknOwn influEnT fOulAnTS During startup at the snack food facility's water recovery plant, unexpected and unknown constituents caused higher-than- expected pressures on the RO treatment membranes. The pressures exceeded those predicted in the off-site pilot scale treatment process studies by third parties. This created the need for immediate on-site testing of alternative treatment processes upstream of the RO membranes to remove the fouling. This was concurrent to: • evaluation of in-plant chemical use for potential fouling in clean-in-place chemicals; • assessment of ingredients and impacts downstream; and • rigorous testing to evaluate membrane fouling and the capability for chemical cleaning to remove foulant. Cleaning the membranes was partially successful but the concentration of fouling chemicals was high enough to require unacceptably frequent cleaning cycles. A secondary evaluation determined that using GAC would remove the foulants and some of the colour in the recovered water. The project involved a lot of analytical work, research and pilot studies that included full-scale temporary GAC units utilized for Figure 3. GE Zenon ultrafilter membranes in concrete tanks with an overhead removal hoist.

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