Performance characteristic and microbial activity of anaerobic swine lagoons

Anaerobic lagoons are routinely used to effectively treat swine waste. However such lagoons can fail and often generate offensive odors.To function properly, anaerobic lagoons rely upon system management such as proper organic loading, and solids removal, and balanced anaerobic microbial activity from fermentation to methanogenesis. Disturbances to this balance may result in elevated hydrogen and a buildup of volatile fatty acids that can inhibit methanogens, ultimately disrupting treatment. Excessive volatile fatty acids cause problematic odors, as does H2S produced by sulfate-reducing bacteria (SRB). Performance characteristics and microbial activity in a functional (actively methanogenic, non-odoriferous) and non-functional lagoon (lacking gas production, malodorous) was studied to determine organic carbon removal efficiency as methane production and levels of hydrogen concentrations as possible indicators of metabolic health. Factors that might negatively impact methane production were also investigated. In addition, a microcosm study conducted at four different temperatures: 4, 10, 25 and 35 C o was performed to determine the impact that temperature had on methane production and hydrogen concentrations. The methane production rates were positively correlated to temperature for both lagoons. Surprisingly, the number of methanogens was higher in the non-functional lagoon. Both lagoons established apparent low steady state concentrations of hydrogen as well as near neutral pH values. Organic overloading that might negatively impact the methane production was apparent in the non-functional lagoon; albeit, the ratio of methane/SCOD for both lagoons was not significantly different. However, high sulfate concentration in the waste resulted in high SRB numbers in the non-functional lagoon, suggesting that excessive production of H 2S by SRB might create an odor problem in the non-functional lagoon. Purple sulfur bacteria, as indicated by a purple colored layer in anaerobic lagoons, can reduce odor by consuming H2S. Moreover, the non-functional lagoon displayed no signs that purple sulfur bacteria were present, suggesting that purple sulfur bacteria may have an important role in odor reduction.