Research Paper
Fish processing wastewater as a platform of the microalgal biorefineries

https://doi.org/10.1016/j.biosystemseng.2012.12.013Get rights and content

The aim was to develop a bioprocess for conversion of wastes of fish processing into single-cell oil and single-cell protein with parallel water reuse under the scope of a biorefinery. The wastes generated by the process were used to support the heterotrophic growth of microalgae simultaneously converting the organic matter, nitrogen, and phosphorus of the wastewater into biomass that is suitable for energy and nutrient production. Chemical treatment, based on coagulation–flocculation–sedimentation, was used to separate the biomass of the wastewater, and membrane microfiltration was used to reclaim water and permit reuse in industrial cooling systems.

Highlights

► Prototype microalgae biorefinery has been assessed. ► Wastes generated by the fish processing wastewater were used to microalgal growth. ► Production of energy and nutrients was considered.

Introduction

The biorefinery concept is similar to the scope of petroleum refineries, which produce multiple products from petroleum that are applicable to various industries. Industrial biorefineries have been identified as the most promising route to the generation of consumables, based on renewable biomass. A specific definition of the term is given by the IEA Bioenergy Task 42 document, which states, “the sustainable processing of biomass into a spectrum of marketable products and energy” (IEA, 2009). Through the production of multiple products, a biorefinery uses all of the biomass components and intermediates, thereby maximising the value derived from the biomass feedstock.

Cyanobacteria are a microorganism class with wide potential for use as a biocatalyst in biorefineries. They are robust, have simple nutritional requirements, and can use up to three metabolic pathways to obtain energy, i.e. photosynthesis, respiration, and nitrogen fixation (Tran et al., 2010).

The use of cyanobacteria for wastewater treatment may offer an inexpensive alternative to conventional forms of secondary and tertiary wastewater treatment, such as, activated sludge, nitrification–denitrification and chemical phosphorus precipitation. Heterotrophic microalgal bioreactors are a potential technology to treat wastewaters, where simple exogenous organic molecules and inorganic nutrients, in the dark, are simultaneously partially converted into biomass that has potential for the production of single-cell protein and single-cell oil that can be used as feedstock in the animal feed and bioenergy industry (Queiroz, Jacob-Lopes, Zepka, Bastos, & Goldbeck, 2007; Rawat, Kumar, & Bux, 2011; Zepka, Jacob-Lopes, Goldbeck, & Queiroz, 2008).

A key issue on the viable development of the industrial biorefineries is the general absence of low-cost processing technology (Rosenberg, Mathias, Korth, Betenbaugh, & Oyler, 2011). Fish processing is an important world economic activity. This process involves significant water consumption, on average equal to 11 m3 tonne−1 of fish processed, resulting in a significant volume of wastewater. This wastewater contains considerable quantities of carbon, nitrogen, phosphorus, metals, and solids that source from the raw material and are suitable for supporting microbial growth (Lim, Kim, & Hwang, 2003). The agro-industrial residues are potentially available on a large scale and can generate biomass that is cost-competitive versus low-cost petroleum.

Thus, the aim of this study was to develop a bioprocess for conversion of wastes of fish processing into single-cell oil and single-cell protein with parallel water reuse under the scope of a biorefinery.

Section snippets

Wastewater

Fish processing wastewater was used in the experiments as a culture medium. The wastewater was obtained from the fish processing industry (Rio Grande, RS, Brazil). It was collected from the discharge point of an equalisation tank over a period of 12 months, from January to December 2007, and analysed for pH, chemical oxygen demand (COD), total nitrogen (N-TKN), ammonium (NH4+1), total phosphorus (P-PO43), total solids (TS), suspended solids (SS), and volatile solids (VS) following the Standard

Results and discussion

Microalgal biorefineries has been proposed because of the ability of the microorganisms used to convert the organic substances and inorganic nutrients of wastewaters into commodity products, offering benefits in terms of sustainable resource supply and environmental quality. The composition of the fish processing wastewater is generally variable, as a function of the fish species, seasonal variability of the particular species, and the industrial processing type (González, 1995). Table 1 shows

Conclusion

Fish processing wastewater is a potential platform for microalgal biorefineries. The process proposed was effective in the water reclaim, creating the possibility of its reuse in cooling systems.

Substantial microalgal biomass (0.36 g l−1 d−1) was produced from wastes, resulting in lipid productivities of 0.05 g l−1 d−1. The microalgal lipid profile indicate proportions of 19.7, 29.9 and 49.6% of monounsaturated, saturated and polyunsaturated fatty acids, respectively, resulting in a biodiesel

Acknowledgements

Funding for this research was provided by National Council for Scientific and Technological Development – CNPq/Brazil.

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