Strategies to evaluate biodegradability: application to chlorinated herbicides

Abstract

The biodegradability of nitrochlorinated (diuron and atrazine) and chlorophenoxy herbicides (2,4-D and MCPA) has been studied through several bioassays using different testing times and biomass/substrate ratios. A fast biodegradability test using unacclimated activated sludge yielded no biodegradation of the herbicides in 24 h. The inherent biodegradability test gave degradation percentages of around 20-30% for the nitrochlorinated herbicides and almost complete removal of the chlorophenoxy compounds. Long-term biodegradability assays were performed using sequencing batch reactor (SBR) and sequencing batch membrane bioreactor (SB-MBR). Fixed concentrations of each herbicide below the corresponding EC50 value for activated sludge were used (30 mg L(-1) for diuron and atrazine and 50 mg L(-1) for 2,4-D and MCPA). No signs of herbicide degradation appeared before 35 days in the case of diuron and atrazine and 21 days for 2,4-D, whereas MCPA was partially degraded since the early stages. Around 25-36% degradation of the nitrochlorinated herbicides and 53-77% of the chlorophenoxy ones was achieved after 180 and 135 days, respectively, in SBR, whereas complete disappearance of 2,4-D was reached after 80 days in SB-MBR.

Thiamethoxam removal by Fenton and biological oxidation

“…Because it is not influenced by the amount of organic matter present or its oxidative status, the BOD 5 :COD ratio is an accurate parameter for assessing biodegradability. Indeed, the ratio is commonly used to assess the biodegradability of pollutants in wastewater treatment effluents; thus, an increased BOD 5 :COD ratio is associated with a high removal efficiency . In general, effluents are deemed biodegradable if their BOD 5 :COD ratio exceeds a threshold value of 0.3–0.4 .…”

Assessment of toxicity and biodegradability on activated sludge of priority and emerging pollutants

“…[5,6] It is important to recognize that toxicity and biodegradability are not always mutually exclusive. Thus, substances which are regarded as toxic compounds can be removed efficiently in a bioreactor at concentrations below their EC50, [7] whereas other less toxic or inhibitory compounds poorly biodegradable would be released to the environment with the risk of accumulating and reaching concentrations over the NOAEL (No Observed Adverse Effect Level) for different environmental compartments.…”

Biological oxidation of choline‐based ionic liquids in sequencing batch reactors

“…Also, they promote adaptation of microbial populations to specific pollutants. SBRs have proved effective for degrading pollutants such as phenols and chlorophenols, herbicides, coke wastewater and pharmaceutical wastewater …”