Characterization of sugar mill effluents for cultivation of microalgae/cyanobacteria co-culture

3/11/2015 8:18:54 PM

Factors affecting the water quality in the retention ponds. (Click on image to download)

Table 1. Parameters measured in effluent ponds during the milling season. (Click on image to download)

A) Growth rate of experiments using water collected after milling season. BBM is Bold's Basal Medium, the horizontal axis represents the percentage of rinse water in the culture media. B) Final biomass of co-culture grown in higher percentages of rinse water was significantly higher than BBM control. C) Initial and final filtered total phosphorus and filtered total nitrogen. D) Initial and filtered COD. 100% rinse water showed a decrease. (Click on image to download)

Microalgae have a variety of applications including biofuels, cosmetics, pharmaceuticals, natural dyes and animal feed. A commercially viable production plan for microalgae is still heavily debated, but Louisiana sugar mills have significant potential in supplying nutrient-rich algal culture medium via milling effluents. The objective of this study is to determine the suitability of sugar mill effluents from a Louisiana sugar mill for biomass production of a Louisiana native co-culture (Chlorella vulgaris/Leptolyngbya sp.) This study shows the effect of effluents in biomass productivity and nutrient uptake on water quality.

Water effluents from two sources in the Alma Plantation sugar mill in the Alma Plantation sugar mill were collected from five sequential rinse water retention ponds and the evaporation water outlet from the mill during and after the milling season. The water pH, temperature, dissolved oxygen (DO), redox potential (ORP) and conductivity were measured in-situ. Additionally, ammonium (NH4), total nitrogen (TN), orthophosphate (OP), total phosphorus (TP), chemical oxygen demand (COD) and carbonaceous biological oxygen demand (CBOD5) were determined in the laboratory.

Water held in the retention ponds is subject to a variety of environmental processes, which affect water quality and characteristics.

Water from the evaporator pond and rinse water retention pond were collected and used in a series of microalgal growth experiments. During late spring months, increased temperatures cause algal blooms in the retention ponds -- depleting the water of excess nutrients and COD. The experiment involved using media with rinse water in a proportion of 0 percent, 25 percent, 50 percent, 75 percent and 100 percent with the remainder coming from evaporator water. Bold's Basil Medium was used as a control. Water was obtained at the end of the milling season and preserved for five months by freezing. The temperature was held at 25 C, plus or minus 1 degree C. The average scalar irradiance was 400 µmol m-2s-1. This experiment determined nutrient removal capabilities.

Water quality characteristics, inorganic and organic nutrients of the retention ponds and evaporator water pond during the milling season are shown in Table 1.

The growth rate of treatments using sugar mill effluents were substantially higher than that of treatments using Bold's Basal Medium The lowest growth was obtained with evaporator water only. A positive effect on growth was obtained in the 100 percent, 75 percent and 50 percent rinse water treatments.

It was concluded sugar mill effluents can support the biomass production of microalgae/cyanobacteria co-culture, while simultaneously improving overall water quality. It also was determined high biomass yields show potential for lipid and pigment production using these effluents to culture microalgae and cyanobacteria.

Contact:

Jacob Foy
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