Biogas potential of municipal sludge, industrial waste, livestock manure, and preliminary study of Røysland farm biogas plant

Abstract

Anaerobic digestion involves a series of metabolic reactions in which complex substrates in the feed are reduced to a mixture having as main products methane and carbon dioxide. Biochemical methane potential (BMP) of wastewater sludge, manure, food waste and industrial waste samples have been tested by using an automated methane potential test system II, in batch system, at 35°C. In addition, the effectiveness of the farm scale Røysland biogas plant has been investigated by analysing the COD and VS removal, the VFA, pH and alkalinity variations for a period of 3 months (January to April 2017). The farm itself is equipped with one up-flow anaerobic sludge blanket reactor (UASB, R1) and one anaerobic baffled reactor (ABR, R2). High BMP was found in mixed food waste (0.672 m3 CH4/kg VS), Grødaland primary sludge (0.756 m3 CH4/kg VS) and in influent R1 (0.614 m3 CH4/kg VS). The specific methanogenic activity of the granules/inoculum, the extent of fat fraction (thus COD/VS ratio), the environmental conditions, as well as the availability of substrates are the main parameters influencing the methane potential. Analysis of the manure percolate of R1 has shown a low VFA concentration and higher pH in post-starting of the reactor (period 1, from 1 to 69 days) compared to a high VFA and a lower pH found in period 2 (from 85 to 139 days). Period 3 (from 161 and further) where restarting of the reactor occurred has shown a low VFA and high pH, which is similar as found in period 1. Also, a significant increase in COD and VS was found from period 1 to period 2, which led to an increase in the organic loading rate (OLR). The change in the type of feed manure might be the reason behind the COD increase. Performance issue was observed concerning the COD/VS removal in R1, which upset the process. Bad hydraulics leading to a channelling of substrate distribution), and/or bad quality granule might have caused the low biogas production, far from the total estimated potential. While a high alkalinity prevented reactor souring due to high VFA observed in the sample. The methane potential results were within expectation. Feedstock manures are full of potential compared to other organic materials, in addition to the potential of phosphorous and nitrogen recovery.