Carboxymethyl cellulose biodegradation by activated sludge microbial communities

The biodegradability of water-soluble carboxymethyl cellulose (CMC) polymer, degree of substitution of 0.65, was evaluated in screening and simulation assays using activated sludge as the inoculum. In an OECD 301B, CMC 0.65 was slowly biodegraded, reaching 46.7 % and 41.0 % mineralization per replicate on day 28 and 63.7 % and 55.2 % mineralization per replicate on day 70. In a modified screening study, following dissolved organic carbon (DOC) removal as the analytical endpoint which provides an indication for biodegradation, an increase in rate and extent was observed with DOC removal reaching 82 ± 1 % after only 28 d. CMC 0.65 was radiolabeled with tritium (³H-CMC 0.65) and the mineralization potential was quantified in an OECD 301B study reaching 72.2 % and 65.5 % ³H₂O generation per replicate by day 70. In three different OECD 314B activated sludge simulation studies, ³H-CMC 0.65 biodegraded rapidly reaching >60 % in 6 h with ultimate biodegradation rates ranging from 0.8 to 1.6 h^-1. Gel permeation chromatography coupled with solid state scintillation counting of extracted sludge solids showed an immediate (10 min) shift from the starting ³H-CMC 0.65 polymer toward lower MW oligomers with a primary polymer biodegradation rate of 5.0 h^-1. This study quantified the significant impact of test design on biodegradation rate and extent and highlights the need to improve environmental realism in laboratory assays for more accurate assessments of polymer biodegradation if negative or inconclusive results are obtained in screening studies or if accurate predictions of biodegradation rates are needed.