Abstract
The U.S. catfish industry is a major industry that has been declining over the years due to imports competition and growing operational costs. Catfish processing wastewater management and high energy requirement put a large financial burden on catfish processing facilities. Recovered protein-based solids have provided some value-added co-products, however, more co-products are needed to offset processing costs. Anaerobic digestion is a proven waste treatment method that produces methane, which is an energetic co-product that can be used within the processing facilities. This study was conducted to evaluate the potential of anaerobic digestion as an alternative to the currently used aerobic biotreatment of catfish processing wastewater. Initial assessments indicated the recalcitrance of the full-strength wastewater to anaerobic digestion, yielding only ~4 m3 per ton (U.S.) of input chemical oxygen demand (CODinput). Thus, several strategies were evaluated to improve the methane yield from the wastewater. These strategies include nutrient (nitrogen and sulfur) amendment, along with ozone, HCl, and NaOH pretreatment. The results showed that nutrient amendment was the most suitable strategy for improving the digestibility of the catfish processing wastewater. A methane yield of 121–236 m3/ton (U.S.) CODinput was obtained, with a purity of 67–80 vol.%. These results are similar to yields and purities of biogas from other feedstock, such as food waste, wastewater solids, and fish canning wastewater. This indicates that anaerobic digestion could be a viable alternative for simultaneous treatment and energetic co-product generation from catfish processing wastewater.
Highlights
Catfish is a major seafood industry in the U.S that produces over 300 million pounds of fish per year, with the majority of this production found in the Southeast U.S [1]
It can be seen that the wastewaters had a neutral pH which is optimal for supporting methane production using an anaerobic digester
Initial assessments of the full-strength wastewater indicated that its nitrogen and sulfur contents were below the level recommended for anaerobic digestion
Summary
Catfish is a major seafood industry in the U.S that produces over 300 million pounds of fish per year, with the majority of this production found in the Southeast U.S [1]. U.S farm-raised catfish ranks eighth on the top ten most eaten fish among U.S consumers [2], with a consumption of 0.56 pounds per capita each year. This valuable U.S industry ($358 million producer sales income in 2013) has decreased 50% in tonnage produced since its high of over 600 million pounds in 2003 [1,2]. During the processing (cleaning and filleting) of the harvested catfish, approximately 40% of the fish weight is wasted [5,6] The bulk of this solid waste includes heads, guts, bones, and skin [6]
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