GLRPPR Sector Resource: Inhibitory Effect of Decomposing Barley Straw on Algal Growth in Water and Wastewater
Inhibitory Effect of Decomposing Barley Straw on Algal Growth in Water and Wastewater
Wastewater lagoons and industrial ash ponds are engineered earthen basins for municipal or industrial wastewater treatment and ash solids removal. Many lagoons and ponds experience algal overgrowth in summer, resulting in the violation of discharge criteria, because algae form a major fraction of suspended solids. The use of chemicals such as copper sulfate to control algae increases the toxicity of the receiving water. Earlier studies have shown that decomposing barley straw appears to be a promising and inexpensive method of algal control in surface water bodies. However, there is little information on the effects of decomposing barley straw on algal growth.
The purpose of this seed project was to identify key variables to guide further investigation of this subject. This project studied how water temperature, water characteristics (dechlorinated tap water vs. wastewater), barley straw loading rate, and the duration of barley straw application affect algal growth and water quality parameters. The study also identified chemical compounds from decomposed barley straw in water. Several batch reactors were used in the laboratory work. They were operated at 22oC or 27oC. Barley straw loading rates of 0.5, 1, 2, and 4 g/L were
studied. Chlorophyll a concentration was measured to quantify the amount of algae. Microscopic examination characterized algal species in several selected samples.
This study found that decomposing barley straw at a loading rate of 4 g/L was effective in inhibiting the growth of Anabaena and Oscillatoria in dechlorinated tap water at 22oC. Loading rates of 2 g/L and 4 g/L were both effective (no significant differences at a 90% confidence level) in inhibiting the growth of Anabaena in water at 27oC. Each gram of barley straw
produced 5.2 to 7 mg PO4 3- and 1.4 mg NO3 --N in nine weeks of decomposition in water at 22oC. For wastewater with existing algal populations at 22oC, a paired t-test revealed that, at a 90% confidence level, each of the tested loading rates (0.5, 1, 2 g/L) lowered algal growth. A loading rate of 2 g/L of barley straw resulted in a statistically more significant effect on algal growth than 0.5 g/L or 1 g/L of barley straw. However, the difference in the effect between 0.5 g/L and 1 g/L was not significant. For wastewater at 27oC, changes in algal species and variability in the values
of chlorophyll a caused difficulty in determining the effects of barley straw on algal growth. The chemical compounds of 2,6-Dimethoxy-4-(2-propenyl)phenol and octanoic acid were below detection limit in the water samples in which 0.83 g/L of barley straw decomposed. Three other compounds were detected: 1,2,4-trimethyl benzene; 1,3,5-trymethyl benzene; and 1-ethyl-4-
methyl benzene. These and several additional chemical compounds, including butylated hydroxytouluene and 2-methoxy-4-vinylphenol that were frequently found in the water samples in which 5.4 g/L of barley straw had decomposed, are good candidates for further investigation of their specific effects on algal growth.
Keywords: Wastewater treatment lagoon, algae, barley straw, chlorophyll a
Illinois Sustainable Technology Center
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