Aquaculture and processing present challenges in terms of water footprint and pollution

The seafood industry has been growing around the world, and attention to attendant water issues has been increasing as well. Seafood consumption has grown 3.6% annually since 1961, which is double the rate of population growth. At the same time, technological advances have transformed the seafood industry, with trade and production now more globalized.

Among many seafood-related water issues, two categories stand out: The industry’s water footprint, and pollution caused by aquaculture and processing.

Seafood’s Freshwater Footprint

Fresh water used by the seafood industry often is neglected in studies of the water-food nexus (WFN). This “seafood gap” is ever more conspicuous as demand for seafood increases around the world. More than 3 billion people now consume 20% or more of their animal protein from seafood, along with essential omega-3 fatty acids and micronutrients.

Currently, agriculture and livestock production are responsible for 60% of freshwater withdrawals globally, and more than 90% of consumptive use. With livestock production under fire for its excessive water and carbon footprints, the seafood industry may grow even faster, with many studies now recommending a shift away from meat-based diets. So, not only is demand increasing because of population and economic growth, the seafood industry’s share may also grow faster than the livestock industry’s.

Aquaculture

As aquaculture becomes more widespread, its water use is beginning to be quantified. Studies have shown that use of fresh water can be significant for some aquaculture systems, but consumption varies significantly by location, species, growing system (recirculating, semi-closed, or open water), and the amount of water used to produce feed.

Aquaculture has increased its market share to 50% of global seafood production, and species cultivated have changed, making its relationship with freshwater resources more significant. For instance, droughts and floods have closed aquaculture operations, causing many disputes. And, groundwater extraction for aquaculture in some parts of China has caused subsidence of as much as 25 cm annually. In Bangladesh and Thailand, it has been blamed for saltwater intrusion.

In 2015 in the United States, withdrawals of fresh water for aquaculture production were 7,550 million GPD, 79% of which was from surface water, although much of the water used was returned directly to its source via flow-through raceways. Aquaculture accounted for 2% of total 2015 withdrawals.

Seafood Processing

Seafood processing produces environmental impacts both in terms of water use, and the volume and type of wastewater generated. Impacts vary by the type of operation and which products are produced. Generally, effluent from seafood processing is heavily laden with nitrogen, proteins, and micronutrients. Data on the industry’s global water footprint is scarce, but its wastewater streams, when properly handled, provide significant opportunities for nutrient recovery, water reuse, and waste-to-energy systems.

Wastewater Nutrient Recovery

In 2018, the Nordic project Extracting Novel Values from Aqueous Seafood Side Streams (NoVAqua) demonstrated a system that can recover as much as 98% of proteins and 99% of omega 3 fatty acids from seafood plant process water. Shrimp boiling water yielded biomass for use in salmon feed, and leftover liquid was proved more effective than water as a frozen glaze for seafood. It also enhanced growth of two algae varieties in microalgae-cultivation, for use as proteins or pigments.

Water Reuse and Waste-to-Energy

In Ecuador, seafood-processing plants have been identified as posing a significant environmental threat. With stiffer regulations springing from constitutional changes, wastewater treatment is now a priority and companies have responded with new technology.

The following case studies illustrate how Fluence technology was able to benefit seafood processors. With water reuse technology, one plant that previously trucked in water for plant operations was able to produce a surplus of recycled water. Another processor was able to add an anaerobic digestion step to its existing wastewater treatment plant to produce energy for plant operations.

Reuse Turns Around Plant’s Water Supply

Tadel SA, a company that produces fish oil and flour, generates a stream of washing, boiler blowdown, and cooling tower wastewater, along with waste from broth concentration. The nitrogen content of the plant’s effluent was 600-800 mg/L, phosphorus was 30-80 mg/L, and COD was between 5,000 and 8,000 mg/L. Not only was the company facing tougher regulation, its location in Western Ecuador is prone to shortages of drinking and irrigation water, so Tadel was forced to buy expensive water from tanker trucks to make up for the water it couldn’t source from the public supply.

The challenges of salinity and rich nitrogen content were met with Fluence aerobic biological denitrification with a membrane bioreactor (MBR), followed by reverse osmosis (RO) ultrafiltration for demineralization. Demineralization lowered the salinity, which lowered boiler blowdown for fuel and water savings, and produced an effluent suitable for irrigation. The solution recovered $210,000 of demineralized water annually and reduced boiler purge fuel costs for savings of $140,000 annually. The plant zeroed its water footprint and now produces a surplus for irrigation, reuse, or clean discharge.

Waste-to-Energy Produces Biogas to Fuel Boiler

In Manta, Ecuador, Eurofish processes about 200 tons of tuna per day and has been expanding its line. The plant produces a difficult-to-treat effluent rich in organic biological compounds. Eurofish opted to keep and improve its existing dissolved air flotation (DAF) system, adding a waste-to-energy system that uses anaerobic digestion to treat sludge and simultaneously produce biogas, which is then used to fuel the plant’s boiler. Significantly, the wastewater treatment system was added without interrupting the plant’s operations.

The plant reduced its waste sludge by 75% and met the new wastewater standards, concurrently reducing treatment cost by 50% and energy consumption by 35-40% for a total of $120,000 in yearly savings.

Increasing Focus on Seafood

An increasing global focus on the seafood industry — both in terms of aquaculture and processing — means a continuing need for up-to-date wastewater processing. How can Fluence help your seafood business? Contact our experts for more information about our sustainable solutions.