LAUSR

Kinetic parameters affecting effluent water quality including half saturation constant ( K s ), maximum specific growth rate ( μ max ), and specific affinity ( a A 0 $$ {a}_A^0 $$ , defined as μ max / K s ) were investigated using three types of anaerobic sludge (raw anaerobic digestion sludge referred to as unacclimated sludge, unacclimated sludge after endogenous decay, and sludge acclimated to low-strength wastewater in an anaerobic membrane bioreactor (AnMBR) for 360 days). Long-term acclimation to low-strength wastewater resulted in sludge with high specific affinity (1.6 × 10 −3 L/mg COD/day for acclimated sludge compared to 4.1 × 10 −4 L/mg COD/day for unacclimated sludge). The μ max values for unacclimated sludge and acclimated sludge were 0.08 and 0.07 day −1 , respectively. The K s values for unacclimated sludge and acclimated sludge were 194 ± 81 mg COD/L and 45 ± 13 mg COD/L, respectively. Although the K s of unacclimated sludge after endogenous decay increased to 772 ± 74 mg COD/L, μ max increased to 0.35 day −1 as well, resulting in no statistically significant difference of a A 0 $$ {a}_A^0 $$ between the two types of unacclimated sludge. Overall, a A 0 $$ {a}_A^0 $$ is a better indicator than μ max or K s alone for determining effluent water quality, as effluent substrate concentration is approximately inversely proportional to the specific affinity. 16S rRNA sequencing data analysis indicated a high abundance (85.8% of total archaea) of Methanosaeta in the microbial community after long-term acclimation. High a A 0 $$ {a}_A^0 $$ associated with the enrichment of Methanosaeta appears to ensure successful anaerobic treatment of low-strength wastewater.