Fish industry wastewater is polluted with various contaminants: It typically contains a very high concentration of organic compounds. These include first and fish waste, nutrients such as nitrogen and phosphorus, blood, but also oils and fats. In much smaller quantities, fish industry wastewater contains microorganisms, heavy metals, and cleaning chemicals. This results in a high COD and BOD5 content as well as an elevated concentration of TSS.
Fish industry wastewater
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Characteristics of fish industry wastewater
Overview of the fish processing industry
The fish processing industry includes companies that harvest fish from seas, lakes or aquaculture, and that then process, package and distribute it. The focus is on fresh fish, frozen fish, canned fish, smoked fish and fish meal. This page gives you an overview of the different products from the fish industry and shows you the characteristics of the wastewater produced. The aim is to help you better understand your wastewater and then choose the appropriate treatment technology.
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The demand for fish products is increasing by about one percent per year. The amount of naturally caught fish remains constant. Aquaculture, on the other hand, is expanding rapidly. However, while wastewater is produced during fish farming, the majority is mainly produced during its processing. Due to the steadily increasing demand, the amount of wastewater produced is also growing and with it the need for wastewater treatment.
Wastewater generation in the fish industry
On average, around four litres of wastewater are produced during the processing of one fish, with large fish factories processing around 1500 tonnes of fish every day. Since impeccable hygiene must be ensured, water is necessary in almost every process step in the fish processing industry. For example, in dehydrating the fish, washing, and cleaning the processing machines, cooling, storage and transport. Water consumption depends on the size of the fish, the fish processing company, and the processing method.
Most of the fish industry wastewater is produced during the cleaning of tools, work surfaces and machines. The CIP process (Clean in Place) plays an important role here. This is an automated cleaning process in which cleaning water with chemicals is kept in tanks. At fixed intervals, the water is applied to the machines under precisely defined pressure and for a specific duration to clean them.
Categories of fish industry wastewater
Fish industry wastewater can be divided into three main categories: Slaughter and cutting processes, cleaning and disinfection, and packaging and transport.
Slaughter and cutting
Upon delivery, the fish, along with water, is pumped from the catching vessel to the processing plant. Once there, fish are sorted according to size. This produces drag water, which the company collects. A machine then automatically separates the head and tail fin from the fish and removes the innards, bones and – if desired – scales and skin. The resulting waste is collected separately and disposed of or processed into fish meal. During the cutting process, mainly blood is mixed into the wastewater. Specific fish have slightly different process. For example, with modern salmon aquaculture live fish are stunned and then put into water tanks to bleed out prior to processing.
Cleaning and disinfection
The cleaning of equipment and surfaces takes place by CIP procedures, and also by high-pressure cleaning. One example is the cutting of the head and tail fin. This is done by circular knives which are permanently sprayed with cleaning water to remove the residues of the cutting. High-pressure cleaning focuses on the disinfection of surfaces such as floors or work surfaces.
Packaging and transport
Fish products come in numerous varieties. For canned fish or fish salads, it is important that the fish has a particularly long shelf life. For this reason, the respective ingredients – usually fillets – are pickled for several days in brine, which is sometimes mixed with vinegar. Large fish processing companies consume several tonnes of salt and up to 3000 litres of vinegar daily.
Types of fish products
The variety of fish products ranges from raw fresh fish to frozen fish and canned fish to delicatessen fish such as fish salads. Below you will find an overview of the different types of fish products and their characteristics. We also shed light on the composition of the wastewater produced in the process
Fresh and frozen fish
Fresh fish has the highest nutrient content of all fish products because it is processed as soon as possible after harvest. This means that it often contains more moisture and less salt than frozen fish. This also makes the taste a little more intense. Frozen fish, on the other hand, is frozen quickly after processing to preserve nutrients and flavour as much as possible.
The processing of fresh and frozen fish is limited to heading, bleeding, gutting, boning, and filleting. Therefore, the wastewater contains increased COD and BOD5 as well as suspended solids and cleaning chemicals.
Canned fish is characterised by a significantly longer shelf life than fresh or frozen fish, as it is protected from spoilage in the can. A preservation process takes place beforehand by pasteurising the fish and then placing it in brine, vinegar, oils, or sauces. Canned fish is a very good alternative to include in the diet, as it does not need to be prepared immediately and can be stored easily.
Since salts, vinegar and in some cases, sugar are needed to preserve the fish, these are also a component of the wastewater. This increases the COD as well as the BOD5, which, however, also leads to a very good biodegradability of the contaminant load.
Delicatessen fish is either smoked fish, fish terrines or fish salads. These are often of higher quality, as they are partly processed by hand. In addition, spices or herbs can be used to flavour the fish.
While smoked fish has a particularly long shelf life, raw, fresh fish is usually used in fish salads. This is rarely preserved and therefore has a shorter shelf life, but usually contains more nutrients.
Due to the cleaning of the smokehouses and the addition of salad dressings, the wastewater has a high content of COD and BOD5.
As you can see, the wastewater from the different production areas differs greatly. However, in companies that process fish, all products are usually produced in one plant. This is because fish has to be processed quickly. Therefore, the wastewater produced usually flows together as mixed wastewater.
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Wastewater treatment is particularly important in fish processing companies. Depending on whether you want to reuse the wastewater, discharge it directly into the environment or into the public sewer system, the right treatment process is particularly important. Therefore, it is crucial that you know the exact composition of your wastewater to select the perfect treatment process.
The next step is to plan your individual wastewater treatment plant. Read on to learn about the process technologies that are best suited for treating fish industry wastewater.
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