Anaerobic nonylphenol ethoxylate degradation coupled to nitrate reduction in a modified biodegradability batch test

Co-metabolism of nonylphenol ethoxylate in sequencing batch reactor under aerobic conditions

The study evaluated the co-metabolism of nonylphenol polyethoxylate (NPEO) within a main substrate stream subjected to biodegradation in an activated sludge system. Peptone mixture simulating sewage was selected as the synthetic substrate. As a novel approach, the NPEO concentration was magnified to match the COD level of the peptone mixture, so that co-metabolism could be evaluated by respirometry and modeling. A sequencing batch reactor (SBR) set-up at high sludge age to also allow nitrification was operated for this purpose. A long acclimation phase was necessary to start NPEO biodegradation, which was completed with 15% residual by-products. Modeling of respirometric data could identify COD fractions of NPEO with corresponding process kinetics for the first time, where the biodegradation of by-products could be interpreted numerically as a hydrolysis mechanism. Nonylphenol diethoxylate (NP2EO) was observed as the major by-product affecting the biodegradation of NPEO, because NPEO and NP2EO accounted for 60 to 70% of the total soluble COD in the solution during the course of biological reactions. The co-metabolism characteristics basically defined NPEO as a substrate, with no appreciable inhibitory action on the microbial culture both in terms of heterotrophic and autotrophic activities.

Does electrolysis facilitate simultaneous nitrogen removal and toxicity reduction of low C/N dyeing wastewater by sulfur-based denitrification biofilter?

The concern about wastewater effluent toxicity has motivated the innovation of enhancement technologies on sulfur-based denitrification biofilter in recent years. Electrolysis is a common technology to reduce or remove toxic pollutants. However, the effect of electrolysis on simultaneous total nitrogen (TN) removal and toxicity reduction in sulfur-based denitrification biofilter has not been reported yet. Herein, for the first time, this study investigated the synergistic effects of electrolysis-induced TN removal and toxicity reduction of secondary effluent of dyeing wastewater containing 20 μg/L of nonylphenol (NP), at different carbon to nitrogen ratios (C/N) in several sulfur-based denitrification biofilters. All of the biofilters achieved the denitrification rate of 300.15 g∙N/m³∙d during the stabilization period at C/N = 5. The CSAHD (ceramisite and sulfur as filters) biofilter had highest TN removal rate to achieve the denitrification rate of 257.46 g∙N/m³·d at C/N = 2. Siderite and dolomite both facilitated TN removal efficiency by 9.3%-12.6% under low C/N ratio and acted as the buffer agent in biofilters. Toxicity characteristic leaching procedure (TCLP) test showed that the amount of leached heavy metals was lower than the concentration limit standard of USEPA. Electrolysis did not promote the removal of TN, however, it could reduce NP concentration and increase the biotoxicity relative inhibition rate of effluent by 12.5%-167%, and affect the functional microbial community structure. Our work clarified some misunderstandings about the application of electrolysis-based strengthening technology and enlightened the future development of simultaneous TN removal and toxicity reduction of dyeing wastewater.

Sorption and inhibitory effect of octylphenol ethoxylate Triton X-100 on methanogenic and denitrifying granular sludges

The aims of this work were to characterize the sorption and evaluate the inhibitory effect of octylphenol ethoxylate Triton X-100 (OPEOTx) on methanogenic and denitrifying sludges. According to Langmuir isotherm, maximums OPEOTx sorption values on methanogenic and denitrifying sludges were 60.70 mg (gVSS)^-1 and 87.47 mg (gVSS)^-1 respectively. The specific removal rate of chemical oxygen demand (r_COD) and the accumulated volume biogas (V_BG) were used to evaluate the OPEOTx inhibitory effect on sludges. Experimental inhibition data were fitted to the models of non-competitive inhibition and modified Gompertz. Methanogenic sludges reached higher levels inhibition in the r_COD and biogas production potential P_max (84.0 and 88.5%) comparing with denitrifying sludges (24.3 and 21.9%). Furthermore, in all OPEOTx concentrations, carbohydrates-proteins quotient value of the extracellular polymeric substances for the denitrifying sludges remained below respect to the same quotient in methanogenic sludges. The above contributes in part to explain the greater sorption capacity of the denitrifying sludges by OPEOTx and their granules resistance to be damaged by OPEOTx amphiphilic nature. The study gives insights to understand OPEOs interactions and their effects on methanogenic and denitrifying granular sludges.

Toxicity of nonylphenol diethoxylate in lab-scale anaerobic digesters

Nonylphenol compounds have high commercial, industrial and domestic uses owing to their surface active properties. In addition to their toxic, carcinogenic and persistent characteristics; they have drawn the attention of scientists lately due to their endocrine disrupting properties. Their widespread use and disposal cause them to enter wastewater treatment systems at high concentrations. Since they are highly persistent and hydrophobic, they accumulate mostly on sludge. In this study using Anaerobic Toxicity Assay (ATA) tests, the toxicity of a model nonylphenol compound, nonylphenol diethoxylate (NP2EO), for anaerobic digestion of sludge was determined. The test bottles were dosed with NP2EO in acetone, with concentrations ranging from 1 mg L(-1) to 30 mg L(-1). During the tests, gas productions and compositions in terms of methane and carbon dioxide were monitored. To be able to judge about the fate, the target compounds were extracted from water and sludge and analyzed using GC/MS. The sludge samples used for assembling the reactors were found to contain NP and NP1EO but no NP2EO. After the assay was completed, all the NP2EO spiked into the live reactors was found to disappear. The increase seen in NP1EO and NP and further accumulation of NP in the system, indicated the conversion of NP2EO to these metabolites. On the other hand, no conversion was observed in abiotic reactors. Inhibition of NP2EO for anaerobic microorganisms was not observed throughout the tests considering the biogas production of the test reactors in comparison to the control reactors.

Determination of nonylphenol and short-chained nonylphenol ethoxylates in drain water from an agricultural area

Water samples from agricultural drains were tested for the presence of nonylphenol and nonylphenol mono- and diethoxylates. The analytes belong to biodegradation products of long-chained nonylphenol ethoxylates, which are used as additives in pesticide formulations. Quantification of these analytes was performed by HPLC with fluorescence detection after isolation by using multi-capillary polytetrafluoroethylene (PTFE) trap extraction. This newly developed technique allowed obtaining about 90% recovery of these analytes in synthetic samples and several percent lower recovery in real samples. Also, no additional sample cleaning was needed before chromatographic analysis. The limit of quantitation for all the analytes was 0.1 microg L(-1). The nonylphenol, nonylphenol mono- and diethoxylates were detected at the concentrations ranging from 0.5 to 6.0 microg L(-1), from 0.2 to 0.7 microg L(-1) and from below 0.02 to 0.4 microg L(-1), respectively. Concentrations of nonylphenol and its derivatives were higher in samples taken in spring than in summer.