Nutrient removal and algal succession during the growth of Spirulina platensis and Scenedesmus quadricauda on swine wastewater

Abstract

The efficiency of pig wastewater treatment by the green alga Scenedesmus quadricauda and blue-green alga Spirulina platensis was investigated. Algal succession in batch cultures and their replacement by autochtonous algae was also studied. The liquid phase of swine waste was diluted to 10%, 20%, 30%, 40% and 50% of the original. In the case of S. platensis, 1% of NaHCO 3 was added to diluted waste: the undiluted wastewater contained 4745 mg/l total nitrogen, 4650 mg/l NH 3N, 17·0 mg/l PPO 4 and 2·1 g/l of total solids. Microscopic examination revealed the occurrence of algal succession in all cases. The abundance of the introduced alga depended upon time of cultivation and dilution of waste. At lower concentrations of waste, the nutrient uptake was efficient and the introduced algae were able to compete with autochtonous algae. At higher manure concentrations the efficiency of nutrient uptake was lower, and the introduced algae were outcompeted by autochtonous algae. At 50% dilution of swine waste, the introduced alga S. platensis was eliminated by the autochtonous algae by the 11th day of cultivation. Delayed replacement of cyanobacterium in comparison with the green alga, can be explained by addition of NaHCO 3, which provided a substrate which was favorable only for the introduced alga. The dominant autochtonous alga was an unidentified unicellular alga resembling Chlorella.