The application of Marinobacter hydrocarbonoclasticus as a bioaugmentation agent for the enhanced treatment of non-sterile fish wastewater.

Wastewaters generated by fish processing are characterised by salt concentrations similar to or greater than that of seawater together with high nutrient concentrations (e.g. organic carbon and total nitrogen) due to the presence of blood, oil, and fish tissues. Fish processing wastewater entering rivers and oceans have become a key factor leading to the pollution of receiving waters; the adequate treatment of this wastewater is, therefore, crucial to a sustainable fish industry. The present study aimed to determine whether augmentation of fish wastewater with either Marinirhabdus sp., Marinobacter hydrocarbonoclasticus or a consortium of the two halobacteria, could successfully enhance the removal of both chemical oxygen demand (COD) and total nitrogen (TN) from fish wastewater. Following 9 days of incubation, the bioaugmentation treatment resulted in a significant reduction in COD, 88%, 91%, and 92% in fish wastewater augmented with either Marinirhabdus sp., Marinobacter hydrocarbonoclasticus respectively, or a consortium of the two halobacteria compared with the control (non-bioaugmented) treatment (77% removal). In tall bioaugmentation treatments (79-88%) TN removal was also significantly greater than the control treatment (57%). After 9 days of incubation, the COD and TN in bioaugmentation reached the European Union's (EU) wastewater discharge standard (Level B, COD < 120 mg L, TN < 70 mg L). The addition of monoculture was effective in enhancing the removal of COD, while co-culture significantly improved TN removal. Results of 16S rDNA sequence analysis investigating the survival of these introduced bacteria showed that only Marinobacter hydrocarbonoclasticus was detected at the end of the treatment, constituting 36% of the total bacterial population when added alone to the wastewater. This study confirms the effectiveness of bioaugmentation in removing COD and TN in saline fish wastewater. The ability of Marinobacter hydrocarbonclasticus to enhance the treatment and dominate the bacterial community suggests the commercial potential of this organism for bioaugmentation of aquaculture wastewater without the need for further bioaugmentation.