Transport Water Treatment in Fish Meal Installations with Decanters

Protection of the world‘s oceans

In Peru, a country with an important fish industry, the government has introduced environmental legislation, including a requirement for all companies in the fish meal industry to employ better treatment for effluent which is generated. This has been practiced very successfully by the largest fish meal manufacturer in the world, namely Technología de Alimentos S.A. (TASA), using a special decanter from GEA.

Processing transport water

Fishing vessels discharge their haul directly into the factory from the vessel via large pipelines. Sea water is used as the transport medium. When it is pumped through the pipelines, this transport water becomes contaminated with fish particles and fish oils. In its 17 fish meal factories in Peru with a total capacity of around 250,000 tons of fish p. a., TASA produces between 80 and 150 tons fish/h.

Approximately three times this quantity of water is required for conveying the fish from the fishing vessel to the factory. This is equivalent to a pump water quantity of around 250 to 450 m³/h in the various production facilities. Until several years ago, this pump water which contained oils, fats and solids, was discharged untreated into the sea. At the end of 2007, TASA then installed a processing stage at its location in Pisco-Ica with a capacity of 140 tons fish/day; the main aim of this installation was to recover the oils, fats as well as the solids contained in the water so that they could be further processed in the production process. 

For this purpose, the pump water is initially floated in a DAF unit (dissolved air flotation), and is then processed via two three­phase decanters. These machines separate the transport water into oils and solids, which can be further processed, as well as effluent.

Second treatment stage

However, the water remaining from this initial flotation process still contains excessive levels of oils and fats (3000 to 5000 ppm) and solids (8000 to 10,000 ppm). However, in its new legislation, the Peruvian government has specified values of 1500 ppm oils and fats and 2500 ppm solids specifically for the fish meal industry. But this is not enough: in four years, these figures will be reduced further to 350 ppm (oils and fats) and 700 ppm (solids).

Further effluent treatment using a second flotation unit was necessary for this purpose, with subsequent effluent clarification using a two-­phase decanter. The focus is not on recovering the oils and fats; instead, the overriding objective is to ensure that the clarified phase has to be as clean as possible before being returned to the sea. For this purpose, TASA employs decanters with new technology using polymer flocculants.

New technology

Only with the introduction of the new technology was it possible for the two-­phase decanter to be used for this application. With this technology, separation was increased from between 50 and 60 percent to between 95 and 98 percent. The solution functions as follows: the level of liquid in the decanter has an effect on the clarification performance. This so-called pond depth can be regulated by means of regulating rings in the discharge of the clarified liquid. If the aim is to achieve a high degree of clarification, the pond depth has to be changed. If an optimum pond depth is achieved, the turbulence in the settled solids is reduced, and there is an improvement in the caking of the oil which is still contained in the effluent to the solids as well as the settling behavior of these solids.

Legal requirements have been more than met

With the installed decanter, TASA is able to recycle a very clean centrate back into the second DAF unit. In practice, the legal requirements are more than met. This extensive processing of the pump water in the Peruvian fish meal factory can be transferred to the world-wide fish meal industry, specifically in South America and Asia in order to minimize effluent discharge values and to protect the ocean, which is the basis for fishing and fish processing. In the next fishing season, there are plans for even more extensive trials with decanters in order to improve clarification even further. For a clean ocean.