The microbiological investigation on crude and treated wastewaters showed a sharp decrease in indicator organisms after heat treatment (Table 1).

Aeromonas spp are spread in aquatic environments, what may explain the presence of such organism in the crude effluent. Nevertheless, some species such as A. hydropila and A. salmonicida may be responsible for lethal infections in fish, bringing considerable economic losses to aquaculture (Maluping et al., 2005; Vieira, 2003) and some others have been described as emergent pathogens for humans (Vieira, 2003). So, the presence of this microorganism in the crude wastewater claims for periodic control in aquaculture, slaughter and processing of tilapia fish, as a way of avoiding financial injury to the fish industry and to consumers.

The presence of Salmonella enterica subsp. enterica serotype Typhi was detected in the wastewater, which represents a potential risk to public health and reveals deficient sanitary conditions during manipulation in the industry, since man is the natural reservoir of this serotype. This bacterium may be transmitted by water and foods contaminated with human feces, causing a serious infectious disease (Franco & Landgraf, 1996).

detergents used during cleaning operations or from protein degradation. Although this element may be essential to most living organisms, in high concentrations it may cause the proliferation of aquatic plants in water bodies and effluents. Oils and greases in wastewaters may originate from industrial kitchens, mechanic repairs garages, boilers and other equipments, as well as from raw material. They can easily be oxidized and so exhale bad odors in the environment. COD is an indirect measure of organic compounds concentration in wastewaters and so, reflects its pollutant load (Giordano, 2004; Liu, 2007).

The physicochemical data found for crude tilapia fish processing wastewater (Table 2) indicate the need for previous treatments for a safe discharge, according to Brazilian legislation. On the other hand, the presence of such organic matter in the wastewater was important to ensure the growth of R. gelatinosus with the resulting production of cells and oxycarotenoids.

The physicochemical characteristics of wastewaters presented herein differ from others previously reported. This happens because the particular characteristics of each industrial effluent derive from crude matter composition, season of the year, water supply, reuse procedures, factory installations and industrial processing techniques, among others (Liu, 2007). For settled and unsettled wastewater from sardine processing industry, for example, pH values from 6.2 to 6.3; 63,000 mg L-1 COD and 10.88 mg L-1 TN were described (Azad et al., 2001; 2003). For white fish filleting plants, Arvanitoyannis & Kassaveti (2008) reported the generation of wastewater with 50 kg COD and Prasertsan et al. (1993) reported 5.3 to 8.3 pH; 5,950 to 157,080 mg L-1 COD; 19.30 to 82.22 g L-1 TS and 666 to 32,182 mg L-1 OG for effluents from different seafood processing plants. Concentrations around 4,300 mg L-1 COD, 800 mg L-1 OG and 6.2 to 7.0 pH also were reported for wastewater from fish processing operations by Giordano (2004).

Changes in tilapia fish wastewater physicochemical parameters after biomass recuperation comprised removals of 82% in COD, 48% in OG and 22% in TN and a decrease in pH to 7.9, rendering it suitable for discharge in the environment, according to Brazilian laws. So, the biomass production process itself worked as a biological treatment for the reduction of pollution in tilapia fish industry wastewater.

Mean cell mass production and productivity achieved with the biological treatment were 0.18 g L-1 and 0.0634 g L-1 day-1, respectively. Prasertsan et al. (1993) credit the low cell production to the anaerobiosis/light cultivation conditions, in which the synthesis of oxycarotenoids is intensified. Other authors found higher cell mass concentrations when growing phototrophic organisms in industry wastewaters but, in those cases, initial organic matter and inoculum levels were higher than the ones used in this study and/or nutritional supplementation was adopted (Azad et a!., 2001, 2003; Prasertsan et al., 1997). In this study, we opted to maintain the original wastewater composition and to use a low inoculum level in an attempt to minimize costs and render the biomass production process feasible for the industry.

The microbiological investigation on Rubrivivax gelatinosus biomass indicated low counts on total coliforms (20.27 NMP g-1), fecal coliforms (< 1.0 NMP g-1) and molds and yeasts (1.2 x 103 UFC g-1) and the absence of pathogenic organisms. This way, the product showed to be in agreement with Brazilian microbiological standards required for feed ingredients, which ensures its safe utilization.

Mean proximate composition of biomass and amino acid profile in the product are presented in Tables 3 and 4, respectively. As a typical feature of single cell proteins, the values indicate the high level of proteins in the biomass, which denotes its use in animal diets as a nutritional ingredient. Moreover, it also contained considerable amounts of all amino acids considered essential for animals, what reinforces the suggestion of its use in the supplementation of animal feeds in order to supply deficiencies that may cause, for instance, delay in protein utilization and reduction of growth, weight gain, feed conversion and immunity (Cyrino et al., 2004). In view of these findings, the bacterial biomass presents a potential for use as a nutritional ingredient for feeds.

Oxycarotenoids content in the biomass was found to be 3.03 mg g-1 dry biomass, which conferred a dark red color to the power product (L = 22.42; C = 14.22; h = 25.48). This is in agreement with Prasertsan et al. (1997), who found concentrations of 2.13 to 3.90 mg of carotenoids per gram of dry biomass of Rhodocyclus gelatinosus produced in tuna processing wastewater.

The main photosynthetic pigments produced by Rubrivivax gelatinosus are bacteriochlorophyll a and carotenoids from alternative spirilloxanthin series, which contains spheroidene, hydroxyspheroidene and spirilloxanthin as the major representants (Holt et al.,

2000) . The blend among these pigments gives the bacterial cultures a reddish color (Ponsano et al., 2002a, 2003a, 2008) that remains in the dry biomass, since sensorial and nutritional properties of lyophilized products remain intact after drying process (Pereda et al., 2005). Considering that these pigments are oxycarotenoids and so have the ability to deposit in animal tissues, this feature of the biomass suggests its application as a pigmenting ingredient for the rearing of different animals.

The use of natural or synthetic oxycarotenoids for the rearing of animals is reported by many authors. Salmonids, for instance, are noble fish natural from cold waters in North Hemisphere, but that are being commercially farmed in many parts of the world. According to Baker & Gunther (2004), in wild salmon, the natural carotenoid astaxanthin provides a majority of the color expected from this flesh. Nevertheless, for farmed salmonids, the same effect may be achieved by the use of pigmenting additives in rations. They may also be used for the raising of ornamental fish to increase skin color and beauty. For the raising of red Cyprinus carpio (Kawari), for instance, Gouveia et al. (2003) relate the utilization of carotenoids produced by micro algae Chlorella vulgaris.

For poultry products, the pigmentation varies according to market demand. In Mexico, Belgium, Italy, Peru and some regions in Brazil, for instance, the use of pigmenting ingredients in poultry production is a common practice since people prefer strong colors for broilers carcasses and egg yolks (Gouveia et al., 1996; Toyomizu et al., 2001). People often associate strong colors of a food item to safety and health and so look for strongly pigmented products. Taking it into account, Ponsano et al. (2002b, 2004a, b) added Rhodocyclus gelatinosus biomass produced in poultry slaughterhouse wastewater in broilers rations and found an increase in the color of breast meat. Polonio et al. (2010) used different concentrations of the same product in hens rations and found an improvement in yolks color, with no deleterious effects on birds performance. In the sensorial test, these authors identified the concentration of the biomass that, when used together with corn xanthophylls, provides a desired golden orange color to the yolks. Yet, Garcia et al. (2002) found an increase in yolks color, with no influence in the performance and eggs characteristics, when canthaxantin was used in hens diets.

Besides the pigmenting feature of oxycarotenoids, they are also known to exert benefits on animal health and welfare due to antioxidant properties. According to Baker & Gunther (2004), evidences suggest that the carry-over of these pigments into the human food chain could be beneficial to human health too. In humans, the consumption of oxycarotenoids is associated to aging prevention and to the decrease of the risk of diseases related to the accumulation of free radicals (Bhosale, 2004; Bhosale; Bernstein, 2005). So, for further studies on the properties of Rubrivivax gelatinosus biomass, the antioxidant ability of its carotenoids will be considered.

2. Conclusion

pigments but also for having an elevated nutritional value. Moreover, we showed that the biomass production process worked as a biological treatment for the reduction of pollution in the industrial wastewater, requiring simple and feasible methods that can be operated in the industry, so minimizing byproducts and still rendering profits from the biomass commercialization.