Removal of formate from wastewater by anaerobic process

Formate in wastewater was effectively removed at 37°C by the upflow anaerobic sludge blanket (UASB) process. This was accomplished by keeping the recycle ratio at 3.0 and by lowering the pH of incoming wastewater to pH 3.8. The COD removal efficiencies were 97-98% at loading rates of 10-20 g-COD. L^-1. day^-1 but were reduced to 86-90% at 29-65 g-COD.L^-1.day^-1. When the loading was further increased to 77 g-COD.L^-1.day^-1, the reactor abruptly failed due to the sudden decrease of the pH. About 94% of COD of the formate removed was converted to methane with a sludge yield of 0.05 g-VSS.g-COD^-1. The small sludge granules settled satisfactorily and had a maximum specific methane production rate (SMPR) of 2.06 g-COD.VSS^-1day^-1. The specific methane activity (SMA) of granules using formate as substrate was 2.90 g-COD.g-VSS^-1.day^-1; but the granules were unable to degrade other fatty acids. Microscopic examinations indicated that the granules mainly comprised Methanobacterium formicicum-like bacteria, plus a small amount of Methanococcus vannielii-like bacteria, and an unknown species of bacterium.