Impact of Algae on Sugar Mill Effluents: Water Treatment and Added Value Assessment

Installations similar to Louisiana sugar mills have been proposed as potential biorefineries for sugarcane, energy cane, and sweet sorghum. The nutrient-rich wastewater generated from the milling process can be used as an algal growth medium. Simultaneously, algae can serve as a water treatment strategy to deplete these effluents of excess nitrogen, phosphorus, and organic carbon. In this research the effluents of a sugar mill were characterized for water quality and nutrient characteristics; the effluents were determined to be suitable for growth of a native Louisiana co-culture of microalgae and cyanobacteria (Chlorella vulgaris/Leptolyngbya sp.); growth rate, biomass productivity and nutrient uptake capability of the co-culture was quantified; and a STELLA® water quality model was developed to simulate the degradation of a Louisiana sugar mill’s effluents over time. During the milling season, wash water effluents displayed poor overall water quality and contained high levels of total nitrogen, total phosphorus, and chemical oxygen demand ranging 24-75 mg-N/L, 30-48 mg-P/L, and 844-1148 mg/L, respectively. Evaporator water contained relatively minimal TN, TP, and COD ranging 0.7-1.4 mg-N/L, 0.2-0.5 mg-P/L, and 14-68 mg/L, respectively; and demonstrated an average discharge temperature of 39 ͦC during milling. Compared to Bold’s Basal medium control treatments, co-culture grown in at least 50% wash water exhibited significantly higher growth rate, biomass productivity, and nutrient uptake. These treatments removed total filtered phosphorus and total filtered nitrogen at efficiencies of 84-96% and 68-89%, respectively. Biomass productivity was highest in 100% unfiltered wash water treatments reaching 240 mg/L-day