Reuse of California brine olive oil processing wastewater to meet zero discharge goal
Abstract
Reuse of low strength municipal wastewater is becoming quite common and many technologies are available for that purpose. However, treatment and reuse/recycling of high strength industrial wastewater is still a challenge. In this paper we present some case studies with implemented integrated systems to achieve zero discharge goal.
We will concentrate on the description of a wastewater recycling/reuse system that was implemented at an olive processor plant in California. Olive processing produces large amounts of high strength wastewater with significant amounts of suspended solids, oil and grease, dissolved organics and salts (brine and caustic). The integrated wastewater treatment system was installed to achieve a zero discharge goal. The integrated system included solid screens, chemical flocculation, centrifugal flotation, ultrafiltration, reverse osmosis, ozonization, carbon filters, chlorine dioxide disinfection and evaporation.
The integrated system achieved the zero discharge goal. However, concentration ratios of ultrafiltration and reverse osmosis devices and maximum flows were lower than predicted from pilot studies. The cost of treatment was high ($20 per 1000 gallons of treated water). The reverse osmosis system required cleaning with chemicals several times a day and energy costs of running the system were high.
In more recent installations, it is shown that more efficient integrated systems can be implemented to achieve zero discharge goals at similar food processing plants. A system that includes flocculation/flotation, anaerobic and aerobic bioreactors and, if needed, low pressure fouling resistant reverse osmosis for salt removal can achieve similar goals at much lower cost of treatment. However, initial installation costs of bioreactors are higher, particularly for high flow applications (100 gallons per minute or more).
Keywords: Industrial wastewater reuse, brine, zero discharge, integrated treatment system
Introduction
Wastewater treatment plants are designed to meet different challenges. Municipal wastewater treatment plants treat large amounts of low strength, diluted wastewater with relatively low amounts of suspended and dissolved contaminants. In recent years more emphasis has been placed at pretreatment of more concentrated high strength industrial or agricultural wastewater at the point of origin. Such an approach can significantly lower pressure at cash strapped municipal facilities everywhere.
Wastewater recycle/reuse is the ultimate goal of any treatment plant. Modern membrane treatment and membrane bioreactor technologies enable the reuse/recycle of wastewater at some municipal plants. In addition to more common irrigation reuse, replenishing of local groundwater or surface reservoirs is becoming a reality.
In an industrial wastewater plant the ultimate goal is a zero discharge facility with all water feeding back directly into the plant for reuse. Such an approach not only helps preserve the environment but also saves on potable water use. Needles to say, if water is to be reused in the plant processes, it has to be cleaned from almost all contaminants and microorganisms. This intended goal has to be achieved at an economically feasible cost of total treatment.
Integrated wastewater treatment systems have to be implemented to achieve zero discharge goals. Industrial high strength wastewater often contains high amounts of suspended solids, free and emulsified fats, oil and grease, dissolved organic materials and dissolved salts. It is particularly common to encounter wastewater that contains a mixture of suspended particles and stable oil emulsions. It is difficult to remove oily contaminants from wastewater and other natural and industrial systems containing oil. Oil can be present as a non - dispersed surface layer, usually floating at the air/water interface. Such layers can easily be removed. On the other hand, if oil is present as a dispersed phase in the form of fine droplets (oil in water emulsions), separation is much more difficult. Many emulsions are stabilized with surfactants or other emulsifying agents. Modern emulsions often contain droplets, which are very small (size range of less than 10 microns) and stabilized with powerful emulsifying agents. De-emulsification and oil extraction from such systems present huge challenges. Moreover, such processes have to be economically feasible to be accepted by industry.
Screens usually have to be used to remove large particles. Coagulation, flocculation and flotation are commonly used to remove suspended solids and fats oil and grease. Numerous options exist to remove fine colloidal solids, macromolecules and dissolved small organic molecules. Integrated membrane technologies such as ultrafiltration followed by reverse osmosis can be used to achieve this goal. Alternatively, biodegradation can be used to remove finely suspended and dissolved organic biodegradable materials. If salts are present, reverse osmosis or ion exchange are implemented at the end of process. Disinfection is commonly applied at the end of the treatment process. Careful analysis including pilot studies should be performed before designing and building any integrated wastewater treatment system.
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