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Fine screening is generally used as pretreatment ahead of more advanced physical, chemical and biological methods. Fish processing plants in which offal is flumed generally employ coarse screening prior to fine screening. In these facilities the flumes discharge onto wire mesh conveyors which allow process water to drain to a collection sump, but retain large offal pieces for transport to an offal hopper. 5.3.3 Flotation Flotation is a wastewater treatment process in which minute air bubbles are generated in a reactor vessel. As these bubbles rise to the surface they carry particulate matter and emulsified oil with them. A skimmer removes the resulting scum to a separate channel while the treated liquid moves on for further treatment or discharge. The most widely used flotation technique for food processing wastes is dissolved air flotation (DAF). In DAFs the liquid effluent is saturated with air inside a pressurized chamber and then released to a reactor vessel under atmospheric pressure. The resulting pressure drop causes the wastewater to become supersaturated with air, which consequently causes the formation of minute bubbles. The operation of a DAF unit usually requires pretreatment of the process water by screening. Generally, flotation is effective in removing fats and to a lesser extent suspended solids, but less effective in reducing BOD, especially soluble BOD. The addition of coagulant and flocculants is needed for improved BOD and TSS reduction. Graham and Yacob (1978) reported low protein and total solids removal with DAF without coagulant addition. Krofta et al. (1988) reported BOD removal of only 35 % and suspended solids removal of only 26 % for DAF without coagulant addition (on-site field testing). Existing DAF units located in Europe and operating without chemical addition also showed low efficiencies in removal of BOD (Table 5.6). < DAF is generally not suited for the treatment of fish processing plant effluents in B.C. due primarily to the large fluctuations in effluent flow and composition, both within and between seasons, generally experienced by these plants which would reduce the efficiency of this type of treatment. In addition, a substantial amount of time is generally required to optimize the operation of flotation plants, particularly when combined with chemical treatment (see Section 5.3.4). Flotation plants may, therefore, not be optimized during the relatively short processing seasons such as for herring and salmon. Use of 61
‘ DAF in fish year-round processing plants in Europe is generally restricted to plants operating on a basis (NovaTec, 1993a). 5.3.4 Chemical Treatment Chemical treatment generally refers to the addition of chemicals to screened effluent. This is required as emulsified oil and particulate matter suspended in wastewater are generally negatively charged. The resulting repulsion substantially impedes certain particle removal processes such as gravity settling, flotation and hydrocyclone separation. Consequently, coagulant which reduce or eliminate the repulsive forces between particles are often added to wastewaters prior to employing these processes. Coagulant are generally used in conjunction with flocculants which are long chain synthetic or natural polymers and cause the agglomeration of the now neutral particles. Both coagulant and flocculants require rapid mixing with the wastewater in order to be effective. Metal salts are the most common coagulant and flocculants in use at full scale facilities practicing chemical aided treatment. The most widely used coagulant and coagulant combinations are: ferric chloride and ferric sulphate, aluminum chloride and aluminum sulphate, sodium hexametaphosphate, anionic polyelectrolyte, and calcium chloride. Accurate pH control is generally required, as the efficiency of coagulant and . flocculants is pH dependent. A disadvantage of using iron or aluminum salts as coagulant is the increase in sludge volume, contamination of the resulting sludge with metals which may make the product unsuitable for reuse, reduce its value, or cause the sludge not to be accepted at landfills. Water soluble organic polyelectrolytes avoid these problems and have the added advantages of requiring concentrations of only a few milligrams per Iitre and not generating extra quantities of waste for disposal (Steiner and Gee, 1992). Nonetheless, there are very few full scale installations using only organic polyelectrolytes. The major detriment appears to be lower removal efficiencies (NovaTec, 1993a). Results of selected jar-test and bench scale studies are reported below. The economics, however, are unknown. Numerous processes using coagulation for treating fish processing wastewater have been reported. Ohhashi (1974) described a process involving heating effluent to 70-100 “C 62
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Environment Canada Industrial Progr
Page 4 and 5:
ACKNOWLEDGEMENTS This document was
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TABLE OF CONTENTS ACKNOWLEDGEM’EN
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5.4 5.5 BEST 6.1 6.2 6.3 5.3.4.2 Ot
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Figure 2.1 Figure 2.2 Figure 2.3 Fi
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Table 5.8 Table 5.9 Table 5.10 Tabl
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1 INTRODUCTION 1.1 Terms of Referen
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2 BACKGROUND INFORMATION 2.1 Genera
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1992a). In 1990, approximately 70 %
Page 20 and 21:
Development of aquiculture (husband
Page 22 and 23:
REDUCTION PLANT Q \ \ PRINCE RUPERT
Page 24 and 25: 2.4 Review of Current Regulations 2
Page 26 and 27: 2.4.3 Municipal and Regional Bylaws
Page 28 and 29: Table 3.1 Water Consumption Rates -
Page 30: 3.2 Wastewater Characteristics 3.2.
Page 33 and 34: Table 3.4 Contaminant Concentration
Page 35 and 36: 3.2.2 Fish Processing Facilities in
Page 37 and 38: Table 3.7 Production-based Contamin
Page 39 and 40: which are permitted to grind and di
Page 41 and 42: 4 PROCESSING TECHNOLOGY The five ma
Page 43 and 44: ---- ,,, ,,, > “\ - Y’ I r ----
Page 45 and 46: VESSEL-HOLD WATER PACKERS AND RECIR
Page 47 and 48: && a- * I ---- ————-— --
Page 49 and 50: 4.4 Herring Processing 4.4.1 Genera
Page 51 and 52: Raw shrimp are held on ice for abou
Page 53 and 54: ~ PRODUCT — WASTEWATER ----- WATE
Page 55 and 56: -+ \ /’WATER’l \~uPPLY/ ‘T-
Page 57 and 58: 5 WATER AND WASTE MANAGEMENT 5.1 Cu
Page 59 and 60: Information Grind and Discha Coarse
Page 61: Table 5.1 Permit Summary ———-
Page 64 and 65: offal with wastewater, which is the
Page 66 and 67: equipment clean and to flush offal
Page 68 and 69: Table 5.4 Solid Waste Generation at
Page 70 and 71: process water. However, different r
Page 72 and 73: 5.2.4 Contaminant Reduction Several
Page 76 and 77: to coagulate proteins, cooling and
Page 78 and 79: Table 5.6 Summary of FM Proceeding
Page 80 and 81: 5.3.4.3 Enhanced Gravity Settling T
Page 82 and 83: To the knowledge of the authors, on
Page 84 and 85: To the knowledge of the authors, no
Page 86 and 87: 5.3.6.2 Hydrocyclones Hydrocyclones
Page 88 and 89: Solid wastes generated by seafood p
Page 90 and 91: Table 5.10 Results of Applications
Page 92 and 93: 5.4.9 Bone Meal Experiment conducte
Page 94 and 95: The comporting operation consists o
Page 96 and 97: ● ● ● ● ● ● ● ● ●
Page 98 and 99: ● / use of finer mesh screens (do
Page 100 and 101: 7 ECONOMIC ANALYSIS 7.1 Review of t
Page 102 and 103: wholesale and landed values as a me
Page 104 and 105: 7.2 Processing Technology Treatment
Page 106 and 107: (~nuJ!WU Jo %) SONICINVl u) (9 I <
Page 108 and 109: conservation and the implementation
Page 110 and 111: In-house modifications can result i
Page 112 and 113: Table 7.3 Expected Efficiency of Wa
Page 114 and 115: Table 7.4 Assumptions used for Econ
Page 116 and 117: quo had been maintained. For each t
Page 118 and 119: All cost estimates involving DAF un
Page 120 and 121: meet toxicity limits. However, biol
Page 122 and 123: BIBLIOGRAPHY Aegis Management Servi
Page 124 and 125:
Fukuda H. and H. Nakatani. Treatmen
Page 126 and 127:
Johnson R.A. and S.M. Gallanger. Us
Page 128 and 129:
NovaTec Consultants Inc.. Village o
Page 130:
( Takei M.. Treatment of Waste Wate
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