Revolutionizing Effluent Management in Fishing Vessels Through Enhanced the Anaerobic Anoxic Oxic Technology

This study investigated an anaerobic-anoxic-oxic (AAO) technology, enhanced with stripping and advanced oxidation processes, for treating effluent from fishing vessels at Tho Quang Harbor in Danang City, Vietnam. The acclimatization period for the treatment system was 93 days, significantly longer than the typical 30-45 days. Following the anaerobic process, initial chemical oxygen demand (COD) decreased from <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2380 \text{mg} / \mathrm{L}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$947 \text{mg} / \mathrm{L}$</tex>. However, the subsequent anoxic and oxic stages exhibited limited COD and nitrogen removal efficiencies. To address this, a pre-treatment step, incorporating calcium hypochlorite and stripping, was introduced after the anaerobic tank. These modifications resulted in a substantial reduction of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 4. 5 \%}$</tex> in COD and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{8 8. 1 \%}$</tex> in total nitrogen (TN). Notably, particulate organic matter, a major COD contributor, was chemically decomposed within hours, a process that typically months biologically. The limited space available for the treatment system necessitated this rapid decomposition, as slower biological processes would demand a larger area for extended hydraulic retention times. It is crucial, however, to manage the residual chlorine levels after pretreatment to prevent any adverse effects on biological activities during the anoxic and oxic stages.