Case study: fish processing plant wastewater treatment

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Abstract

This presentation describes the full scale installation of a wastewater treatment system at the Ocean Gold Seafood ('OCS') plant in Westport, Washington, USA. Local Government requires that fish processors remove total suspended solids (TSS), fats, oil and grease (FOGs) and colloidal materials almost completely in order to allow for efficient disinfection. The OCS plant had only a limited amount of space. Clean Water Technology, Inc. ('CWT') and OCS teams designed the system with an underground equalization tank, 1/8 inch rotating drum screcas, flocculation - flotation ('GEM System') and chlorination - dechlorination.

Hybrid centrifugal - dissolved air flocculation- flotation (the GEM System), is the key component of the wastewater treatment plant. The GEM System built to treat 500 GPM of wastewater required only an 8' - 16' area. The System has operated since 2004. TSS and FOGs are almost completely removed to less than 20 mg/1 and 1 mg/l, respectively. This allowed for successful breakpoint chlorination - dechlorination and fecal coliform removal (99.995%). The produced sludge after overnight drainage contains over 15% of solids. Novel ultrahigh molecular weight polyacrylamide flocculants used in the process enabled TSS and FOG removal even at high salinity. The GEM System variable mixing energy inside hydrocylone heads and columns enabled activation of flocculant long polymeric chains without chain or floe breakage that occurs with classical impeller high energy mixing.

Keywords: Fish processing wastewater treatment, flocculation - flotation, TSS, FOG and fecal coliforms removal

Introduction
The seafood industry consists primarily of many small processing plants, with a number of larger plants located near industry and population centers. Numerous types of seafood are processed, often at the same plant. Saltwater fish (tuna, sardines, pacific whiting, swordfish), mollusks (oysters, clams, scallops), crustaceans (crabs and lobster) and others such as shrimp, octopus etc. are often processed concurrently or seasonally.

As in most processing industries, seafood ñ processing operations produce wastewater containing a substantial amount of contaminants in soluble, colloidal and particulate forms. The degree of contamination depends on the process. It may be small (washing operations), mild (fish filleting), or heavy (boat storage tanks unloading, blood water from facilities storage tanks, stick water from fishmeal processing).

Wastewater from seafood processing operations can be very high in dissolved and suspended organic materials. This results in high biological oxygen demand (BOD) and chemical oxygen demand (COD). Fats, oil and grease are also present in high amounts. Often suspended solids and nutrients such as nitrogen and phosphate can be high. Unpleasant odor and high temperature are also issues. Seafood processing wastewater was noted to sometimes contain a high concentration of sodium chloride from boat unloading, processing water and brine solutions.

The major types of waste found in seafood processing wastewater are blood, offal products, viscera, fins, fish heads, shells, skins, and meat. The major process operations include product receiving, boat unloading, sorting and weighing, preparation (butchering, scaling, filleting, skinning, evisceration), inspection and trimming, product processing such as pickling brining etc, further processing (canning, bottling), packaging and dispatch. Organic materials in the wastewater are produced in the majority of these processes. However, most of it originates from the butchering process, which generally produces organic materials such as blood and gut materials.

Wastewater from seafood processing industries generally can be divided into two categories: high volume ñ low strength wastes and low volume ñ high strength wastes. High volume low strength wastes consist of the water used for unloading, fluming, transporting, and handling the fish plus the washdown water. The boat bilge water, fish preparation water and stick water from fish meal processing are examples of low volume ñ high strength water.

The degree of pollution of wastewater depends on several parameters. The type of operation involved and type and amount of seafood processed are the most important factors involved. Good manufacturing practices, including water savings and segregation of high strength wastes also influence the strength and volume of wastewater produced. Tuna canning plants commonly produce light, easy to treat wastewater, with low BODs and CODs (700 and 1,600 mg/l average was reported), low TSS (up to 500 mg/l) and moderate FOGs (up to 500 mg/l). Fishmeal plants were reported to produce some of the most contaminated and challenging to treat wastewater with BODs and CODs as high as 30,000 and 50,000 mg/l, TSS 30,000 mg/l and FO’s over 10,000 mg/l. All herring processing also produces heavy load wastewater. Salmon, cod, mahimahi, and pacific whiting processing produce moderately contaminated wastewaters with BODs and CODs up to 6,000 and 15,000 mg/l, TSS up to 12,000 mg/l and FOGs up to 2,000 mg/l. Crab and shrimp processing also produce moderately contaminated wastewater.

Fats, oil and grease are among the most objectionable components from the seafood processing wastewater. The presence of FOG in an effluent is mainly due to processing operations such as canning. Fish oil, unless removed in a fishmeal plant, often ends up in the processing wastewater. The FOG should be removed from wastewater for numerous reasons: it usually floats on top of water surface and affects the oxygen transfer to the water; it is objectionable from an aesthetic point of view, and its decomposition generates unpleasant odors. FOGs also cling to tanks as well as pumps, ducts and pipes reducing their capacity in the long term. The FOGs of a seafood processing wastewater varies from 10 to 20,000 mg/l, depending on the seafood being processed and the operation being carried out. Suspended solids (TSS) present similar problems. Heavy solids also sediment and over time can clog pumps, pipes, tanks or accumulate at waterways floors. Solids and FOGs should be removed as soon as possible in the wastewater treatment process with as low shear ñ mixing energy as possible. Time and shear energy often dissolve solid and colloidal components. Dissolved organic materials are much more expensive to remove.

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