Industrial wastewater treatment

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Fish Processing Wastewater Treatment

Brines recovery membrane UF & NF system for fish processing industry

Water resources protection from pollution and exhaustion is one of the most important environmental targets. Fish processing requires large amounts of water. Fish processing wastewater has a high organic content, and subsequently a high chemical oxygen demand (СOD), because of the presence of blood, tissue, and dissolved protein. It also typically has a high content of nitrogen and phosphorus. Techniques for treating industrial wastewater in this sector include different processes and equipment combination.

Industrial production of the salted fish products based on the fish pickling in concentrated NaCl brines. Waste brine generated after the fish pickling is a complex biochemical system consists of concentrated NaCl solution, salt-soluble protein, tissular and bacterial enzyme.

The presentation covers the application of the hybrid membrane technology of ultrafiltration under vacuum (UFV) and low-pressure nanofiltration (NF) for concentrated brines treatment as well as the wastewater treatment plants (WWTP) design features based on these technologies. Progressive development of the membrane and vacuum technologies makes it possible to create compact high-performance water and wastewater treatment equipment with low power consumption and zero operating costs for the removable elements. Moreover, when required, it is possible to increase WWTP capacity due to modular-type construction.

The technical and economic advantages of WWTP built according to the hybrid technology:

  • Ultrafiltration under vacuum system has relatively low power consumption. It has no disadvantages such as selectivity reduction due to concentration polarization effect that pressure-driven UF process. Application of ultrafiltration under vacuum makes it possible to wastewaters vacuum concentration without expensive pretreatment processes as far as suspended solids low effect on vacuum membrane filtration process;

  • High-performance construction materials, including polypropylene (until 50 years), polymeric UF and NF membranes (2 years at least);

  • High-efficiency waste brine regeneration process with concentrated NaCl solution reuse of 80% at least (Table 1.) and as result the increase the cost-efficiency of production;

  • Waste liquid volume reduction till to feasible minimum.

Fish processing waste brine treatment process flowsheet

Fish processing wastewater treatment

The pretreatment stage is represented only by rough mechanical waste brine filtration for the removal of particulate pollutants. The first main unit of WWTP is ultrafiltration under vacuum with the charged polymeric UF membranes with NMWCO from a 200 kDa to a 250 kDa. Ultrafiltration under vacuum is the most suitable choice for heavily polluted complex wastewaters from organic compounds such in the case of the fish processing waste brines. ultrafiltration under vacuum unit ensures treatment of wastewater with high salt concentration from organic compounds, oil products and suspended solids. In order to disinfect waste brines from bacteria, which can exist in concentrated salt solution, the NaClO disinfectant is dosed to UFV unit.

Ultrafiltration under vacuum

The ultrafiltration under vacuum unit consists of flat plate membrane module set plunged into the conical tank with wastewater. During the ultrafiltration under vacuum process wastewater level is automatically maintained under the membrane module set. For the continuous membranes surface treatment ultrafiltration under vacuum unit is equipped with agitating device and pressed air delivery system. Periodically, when the concentration of the pollutants achieved concentration design maximum, wastes are discharged into the sludge thickener. After the end of the thickening process solid wastes discard wastes are discarded to the off-site waste processing plants.

Table.1. The industrial WWTP working results:

Pollutants Units Concentration, mg/l
Waste brine After UFV After NF After SF Limits
pH pH 6-8 6-8 6-8 6-8 6-8
Total nitrogen mg/l 500 300-500 50-100 <30 <30
Oil and grease mg/l 120-50000 10-150 0,5-5 <0,1 <45
Total phosphorus mg/l 400 120 10 <10 <25
Sulphates, SO42- mg/l 200 200 <10 <10 <100
COD mgO2/l 1000-60000 420 <30 <10 250
Suspended solids mg/l 500 0,1 - - -
Chlorides, Cl- g/l 120-160 120-160 100-136 100-136 120-160

Represented hybrid membrane technology of ultrafiltration under vacuum, low-pressure nanofiltration (NF) and sorption on activated carbon for concentrated brines treatment is highly recommended for implementation in the WWTP of fish processing industry by interested investors. These WWTP ensure fine waste brine treatment from suspended solids and organic substances according the State standards. The implementation of the represented technology is increase the cost-effectiveness and economic feasibility of industrial enterprises and gives opportunity of establishment of water recycling with NaCl utilization.


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