Pilot-Scale Sludge Treatment by a Force-Fed Serpentine Plug-flow Reactor (SPFR)

Anaerobic digestion is among the oldest and most commonly used biological forms for both wastewater treatment and sludge treatment. With the relatively long retention time (15–30 days generally), there is interest in developing a high-rate and more economic anaerobic digester. Development of such a digester has applications in coastal communities, municipal wastewater treatment plants and coastal-based industries that are the essential economic fabric of the coastal Gulf Coast.The objective of this study is to develop and evaluate the operation and viability of an economic and high efficiency small-scale anaerobic digester that utilizes a force-fed fast rate digestion process for treatment of wastewater and sludge with gas production under a range of flow conditions. The warm climate in Louisiana allows the potential that the digester does not require heating. The flow pattern achieved by the specific configuration and gas production provides enough mixing for the digestion process, and consequently, no need for further costly mixing facilities. And the most important is that the plug flow automatically partially separates the whole anaerobic digestion, resulting in a multiple phase process. This design also has an advantage of relatively low hydraulic retention time, leading to substantial savings in digester capacity.A 935-gallon digester has been loaded at a steady state rate of 500-gallons per day of primary wastewater sludge at Center Wastewater Treatment Plant, Baton Rouge, Louisiana. The results indicated that COD, TSS and VSS reductions were significant for a 48-hour residence time without any heating, temperature control or pH control. The mean removal efficiency of total COD, TSS and VSS were 67%, 84%, and 80%, respectively. Data showed that temperatures of about 70% of the study period were in the optimal range of mesophilic digestion, while even during in the other days, the effluent quality was still tolerable to the primary clarifiers. Although literature suggests that the supplement of a carbon source would substantially improve the anaerobic digestion, the presence of sugar in this study, on the contrary, deteriorated the bioprocess.The high price of natural gas makes the digester's ability to produce methane as valuable of a by-product as its primary design objectives of wastewater/sludge treatment. The digester design can also be modified to treat a variety of organic-rich waste streams from coastal industries and communities for its simplicity and robust behavior.