Effects of substrate COD/NO2−-N ratio on simultaneous methanogenesis and short-cut denitrification in the treatment of blue mussel using acclimated sludge

• Studied the combined methanogenesis and short-cut denitrification in batch reactors.
• Employed blue mussels, discharged worldwide in vast quantities, as solid substrate.
• Discussed the effects of COD/NO2−-N ratio in substrate and NO2−-acclimated sludge.
• Observed comparable methanogenic performance to other studies of liquid substrates.
• Using NO2− acclimated sludge promoted both denitrifying and methanogenic activities.

Simultaneous methanogenesis and short-cut denitrification processes have attracted attention because it enables the removal of organic matter and nitrogen in a same reactor. In this study, these processes were applied to the treatment of blue mussels, which are discharged worldwide intermittently and in vast quantities as organic solid waste. The effects of substrate COD/NO2−-N ratios on denitrifying and methanogenic performances were evaluated in batch experiments. NO2− acclimated sludge was used as a part of seed sludge to enhance the tolerance to NO2−. Two acclimated sludges were obtained by two-different acclimating conditions which exposed to influent COD/NO2−-N ratios of 25 with high COD loading rate and 5 with low COD loading rate during acclimation periods (referred to as AS25 and AS5). AS25 added reactors showed the relatively high methanogenic and denitrifying performances compared to AS5 added reactors. The results obtained in AS25 added reactors showed comparable results to different studies which used liquid substrates. High COD and NO2− removal efficiencies were achieved under substrate COD/NO2−-N ratio ranging from 8.6 to 123, representing the successful performance for the treatment of blue mussels which contains COD/N ratio of 16.3 in their tissue.