Doctoral Dissertations

Date of Award

12-2000

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Biosystems Engineering

Major Professor

Raj Raman

Committee Members

Robert T. Burns, Tim L. Cross, Luther R. Wilhelm, Ronald E. Yoder

Abstract

This research examined the potential of reducing dairy waste lagoon organic loading with high-rate anaerobic digestion (HRAD) systems operating at hydraulic retention times (HRT) of less than one day. An in-line approach was examined as a means of pre-treating the wastestream to reduce the lagoon organic load. An off-line approach was examined as a means to reduce the organic load within the anaerobic lagoon through the removal of volatile fatty acids. Two types of HRADs were tested, an anaerobic sequencing batch reactor (ASBR) and a downflow anaerobic filter (DFAF), both of which operated at 25 and 35° C. Initial plans were to use the HRADs for removal of organics by operating upstream of anaerobic lagoons. However, initial results of this approach were unsatisfactory, and it was suspected that the reactors were removing organic materials through settling rather than biodegradation. This possibility was tested by performing a chemical oxygen demand (COD) mass balance to determine if suspended solids settling was the main method of wastewater treatment. The mass balance demonstrated that 100% of the COD removed in the ASBRs, and 72% of the COD removed in the DFAFs, could be attributed to settling instead of biodegradation. The second experiment demonstrated that volatile fatty acids (VFA), mainly acetic (HAc), could be removed from the anaerobic lagoon if an HRAD was used in an off-line mode. Off-line operation would involve pulling HRAD influent from below the lagoon surface with the effluent being returned to the lagoon. At low loading rates (1.0 and 3.0 kg HAc m-3 d-1), both reactor types had treatment efficiencies greater than 30%. At the lowest loading there was no difference among the reactor types at the same temperature (P > 0.33 for both temperatures). At the higher loading, there was a difference across reactor types at the same temperature (P < 0.0001 for both temperatures). At a loading of 6.0 kg HAc -3 d-1 the ASBRs proved to be ineffective; whereas, the DFAJFs had removal efficiencies > 70% for both temperatures. The DFAFs also provided > 40% removal of HAc at loading rates of 24 kg HAc -3 d-1; thereby, suggesting that DFAFs are superior to ASBRs for removing accumulated VFAs at high loading rates. The high removal rates at the low HRTs allow for a smaller volumetric reactor and thereby a more feasible system. An economic model was developed to explore the feasibility of installing a DFAF system compared to expanding an existing anaerobic lagoon. The model computed the equivalent annualized annuity (EAA) of the two alternatives with a DFAF reactor operating at 0.8 kg HAc -3 d-1 and 2.4 kg HAc -3 d-1. The model was run for herd sizes ranging from 100 to 800 cows and overloads ranging from 10 to 100%. The results of the model suggests that for facilities with small herd sizes (< 400 cows) and overloads less than 70%, expanding the lagoon is the preferred alternative. With large herd sizes (> 400 cows) and overloads greater than 70%, the DFAF was suggested to be the preferred alternative.

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