Use of Spirulina platensis in treatment of fish farming wastewater

ABSTRACT Each year, the amount of fish produced around the world increases, which contributes to several environmental impacts such as the disposal of effluents without treatment in the environment. This scientific work had as main objective the development of Spirulina platensis in fish effluents, a low cost medium for the production of biomass, in order to reduce the levels of some inorganic nutrients to reach the allowed parameters by the Brazilian environmental standards for effluent disposal and to enable reuse of the water. Nile tilapia (Oreochromis niloticus) fingerlings were produced in fresh water. The effluent generated by the culture was transferred to a pool where seawater was added until the salinity of 10 ‰ was reached. A strain of cyanobacteria, Spirulina platensis, was inserted into the mixture in order to remove the nutrients dissolved on the fish culture effluent. The abiotic parameters analyzed were: absorbance, pH, dissolved oxygen, temperature, salinity and concentrations of ammonia, nitrite, nitrate and phosphate. The results revealed that the maximum cellular density of S. platensis resulted in the production of 0.22 g L-1 of dry biomass and maximum productivity of 0.03 g L-1 day-1. The concentration of ammonia, nitrite, nitrate and phosphate got lowered by more than 94.8%, maintaining the nutrient levels within the standards those required by Brazilian environmental standards. Hence, this effluent has become adequate for reuse in fish production or could be safely disposed in nature.

摘要 全球鱼类年产量逐年攀升，由此引发诸多环境负面影响，例如未经处理的养殖废水直接排入自然环境。本研究的核心目标为以鱼类养殖废水为培养基培养钝顶螺旋藻（Spirulina platensis）——一种低成本的生物质生产体系，以期降低废水中部分无机营养盐的浓度，使其符合巴西环保部门规定的废水排放限值标准，并实现养殖废水的循环回用。本研究以淡水培育尼罗罗非鱼（Oreochromis niloticus）鱼苗，将养殖过程中产生的废水导入池中，添加海水直至盐度达到10‰。随后向该混合体系中接入一株蓝细菌，即钝顶螺旋藻（Spirulina platensis），以去除养殖废水中溶解的营养盐。本次实验检测的非生物参数包括：吸光度、pH值、溶解氧、水温、盐度，以及氨氮、亚硝酸盐、硝酸盐和磷酸盐的浓度。实验结果显示，钝顶螺旋藻的最大细胞密度可实现0.22 g·L⁻¹的干生物质产量，最大生产力达0.03 g·L⁻¹·d⁻¹。氨氮、亚硝酸盐、硝酸盐与磷酸盐的浓度降幅均超过94.8%，营养盐水平维持在巴西环保排放标准规定的限值范围内。综上，该养殖废水已满足鱼类再生产的回用要求，亦可安全排放至自然环境中。