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Chemical Speciation in the Effluent of an Anaerobic Digester Treating Dairy Waste: Implications for Nutrient Recovery and Reuse

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 53(5): 1727-1732. (doi: 10.13031/2013.34883) @2010
Authors:   S. Wahal, S. Viamajala, C. L. Hansen
Keywords:   Anaerobic digestion, Chemical speciation, Nutrients

In this study, effluent from an induced blanket reactor (IBR) anaerobic digester treating dairy manure was comprehensively characterized to determine the speciation and availability of nutrients (N and P). The study involved performing mass balances on the major elements in solid and liquid phases and determining the relative distribution of organic and inorganic C, N, and P. The chemical equilibrium model Visual MINTEQ 2.53 (VM) was then used to describe the speciation of the nutrients (especially PO4-3) in IBR effluents and predict P dissolution upon dilution of the medium. Experimentally determined PO4-3 solubilization data accurately matched model estimates. These results confirmed the VM prediction that Ca+2 and Mg+2 were responsible for most of the PO4-3 interactions in digested dairy waste. In addition, Ca+2 and Mg+2 also interacted with CO3-2, and the model calculations showed that relative magnitude of PO4-3 or CO3-2 precipitates was largely governed by the pH and alkalinity of the effluent. Thus, with as few as five input parameters (concentrations of Ca+2, Mg+2, and PO4-3 along with pH and total alkalinity), the behavior of inorganic P in chemically complex effluents from anaerobic digesters treating dairy wastes could be predicted.

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