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The use of animal manure as fertilizer is an established method for reducing biosolids for landfill disposal. Manure contains necessary nutrients such as nitrogen (N), phosphorus (P), potassium (K), and micronutrients for crop growth. This study focuses on dairy manure in particular. There are two methods for manure application from the standpoint of nutrient loading: N-based or P-based. The P-based manure application strategy simply does not provide enough N for plant growth and thus farmers end up purchasing costly artificial fertilizers to make up for the additional N needed. N in manure is susceptible to losses via volatilization from time of excretion to surface application. Therefore, N-based manure application causes P accumulation on soil surfaces due to the N loss and already low N:P ratio of manure for optimal crop uptake. The accumulated P can reach surface waters through runoff and cause eutrophication, which may result in fish kills due to dissolved oxygen depletion, harmful algal blooms, taste and odor problems, and clogged filters at water intake locations for irrigation and drinking water treatment. It would be ideal to treat manure prior to land application so that the N:P ratio is more in line with the needs of the crops. For dairy manure, this ratio needs to increase, which can be achieved by reducing the amount of P relative to the amount of N in the manure.

There are multiple ways to address phosphorus removal in dairy manure. Phosphorus can be treated via chemical precipitation; however, the resulting sludge cannot be applied as fertilizer and must be disposed of accordingly due to its metal content. Alternatively, phosphorus can be removed biologically using a process called enhanced biological phosphorus removal (EBPR). Because EBPR is a biological process, the nitrogen-rich liquid effluent that is produced can be applied as a fertilizer and is the process considered in this project. The objective is to evaluate EBPR potential of solids-separated, pre-fermented dairy waste by estimating six selected key kinetic and stoichiometric parameters, simulating an ideal reactor configuration using the International Water Association Activated Sludge Model (ASM) No. 2, and pilot testing that configuration with real dairy waste. A 3.5 L lab-scale sequencing batch reactor (SBR) was fed solids-separated, pre-fermented dairy manure, and operated with repeated anaerobic and aerobic phases within each cycle to achieve effective EBPR. The biomass from this reactor was used to estimate the kinetic and stoichiometric parameters. The parameters estimated are currently being used with a computer simulation to identify the ideal reactor configuration for pilot testing. In the mean time, a 90 liter, pilot-scale SBR has been seeded with EBPR biomass from a domestic treatment plant and is operating at the Virginia Tech Dairy Center, which uses flushing to clean the barn and solids separation as a pretreatment process. The pilot plant configuration will be modified in response to the simulation results and evaluated for its effectiveness to achieve effective EBPR at a full-scale dairy operation.
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Document Type: Research Article

Publication date: 2005-01-01

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