Fate and effect of quaternary ammonium compounds on a mixed methanogenic culture

Influence of cetyltrimethyl ammonium bromide on nutrient uptake and cell responses of Chlorella vulgaris

The removal of nutrients by algae is regarded as a vital process in wastewater treatment, however algal cell activity can be inhibited by some toxic chemicals during the biological process. This study investigated the uptake of ammonia nitrogen (NH₄⁺) and total phosphorus (TP) by a green alga (Chlorella vulgaris) and algal cell responses under the stress of cetyltrimethyl ammonium bromide (CTAB), a representative for quaternary ammonium compounds (QACs, cationic surfactants). When the concentration of CTAB increased from 0 to 0.6 mg/L, the uptake efficiencies of NH₄⁺ and TP decreased from 88% to 18% and from 96% to 15%, respectively. Algal cell responses showed a decline in photosynthesis activity as indicated by the increase of chlorophyll autofluorescence from 2.9 a.u. to 25.3 a.u.; and a decrease of cell viability from 88% to 51%; and also a drop in esterase activity as indicated by the decrease in fluorescence of fluorescein diacetate stained cells from 71.5 a.u. to 4.7 a.u. Additionally, a transcription and translation response was confirmed by an enhancement of PO peak and amide II peak in algal cellular macromolecular composition stimulated by CTAB. The results suggest that QACs in wastewater may inhibit nutrient uptake by algae significantly through declining algal cell activities.

QSAR modeling of toxicity of acyclic quaternary ammonium compounds on Scenedesmus Quadricauda using 2D and 3D descriptors

Optimized calculation of typical acyclic quaternary ammonium compounds (QACs) was performed at B3LYP/6-311G** level using density functional theory (DFT) method. A two- dimensional quantitative structure-activity relationship (2D-QSAR) model was established with the obtained structure parameters as theoretical descriptors. And then three-dimensional quantitative structure-activity relationship (3D-QSAR) models were built using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) methods respectively. The 2D and 3D QSAR models exhibit optimum stability and predictive ability, revealing that steric and electronic effects influence the toxicity of acyclic QACs to Scenedesmus Quadricauda mostly.

Effects of Residual Hypochlorite Ion on Methane Production during the Initial Anaerobic Digestion Stage of Pig Slurry

The hypochlorite ion (OCl(-)) is a widely used disinfecting agent in pig rearing in Korea, but its residual effect on CH4 production from pig slurry is unclear. The objective of this study was to investigate the inhibition effects of residual OCl(-) on CH4 production during the initial anaerobic digestion stage of pig slurry. Three organic concentrations (9.9, 26.2 and 43.7 g/L) of volatile solids (VS) were tested with the addition of 52.3 mg/L OCl(-), ten times of the typical concentration used in Korea, or without OCl(-) (Control) in anaerobic batch culture. The culture was run under mesophilic (38°C) conditions for 20 d. At the lowest organic concentration with OCl(-), the VS degradation was 10.3% lower (p<0.05) than Control, while at the higher organic concentration with OCl(-), it did not differ from Control. CH4 yields were higher in the control treatments than their OCl(-) counterpart cultures, and CH4 yields of Control and OCl(-) treatments at the organic concentrations of 9.9, 26.2 and 43.7 g/L differed in the probability level (p) of 0.31, 0.04, and 0.06, respectively. Additionally, CH4 concentration increased steeply and reached 70.0% within 4 d in the absence OCl(-), but a gradual increase up to 60.0% was observed in 6 d in the OCl(-) treated cultures. The Rm (the maximum specific CH4 production rate) and λ (lag phase time) of 9.9 g/L with OCl(-) were 8.1 ml/d and 25.6 d, while the Rm was increased to 15.1 ml/d, and λ was reduced to 11.4 d in PS-III (higher organic concentration) with OCl(-). The results suggest that a prolonged fermentation time was necessary for the methanogens to overcome the initial OCl(-) inhibitory effect, and an anaerobic reactor operated with high organic loadings was more advantageous to mitigate the inhibitory effect of residual hypochlorite ion.

Inhibition and biotransformation potential of naphthenic acids under different electron accepting conditions

Naphthenic acids (NAs) are a complex group of alkyl-substituted acyclic, monocyclic and polycyclic carboxylic acids present in crude oil, oil sands process water and tailings ponds, as well as in refinery wastewater. Bioassays were performed to investigate the biotransformation potential and inhibitory effect of a commercial NA mixture to nitrification, denitrification and fermentation/methanogenesis using mixed cultures not previously exposed to NAs. NAs inhibited nitrification in a mixed aerobic heterotrophic/nitrifying culture at concentrations as low as 80 mg NA/L, whereas, an enriched nitrifying culture was only affected at 400 mg NA/L. The lower nitrification inhibition in the latter assay is attributed to the higher population size of nitrosofying and nitrifying bacteria compared to the mixed heterotrophic/nitrifying culture. The NA mixture was not inhibitory to denitrifiers up to 400 mg/L. At higher NA concentrations, cell lysis was pronounced and lysis products were the main source of degradable carbon driving denitrification in culture series prepared without an external carbon source. In the presence of a degradable external carbon source, no difference was observed in nitrate reduction rates or nitrogen gas production at all NA concentrations tested. Methanogenesis was completely inhibited at NA concentrations equal to or higher than 200 mg/L. Methanogenic culture series amended with 80 mg NA/L were transiently inhibited and methane production in culture series prepared with NAs and an external carbon source or NAs only recovered in 136 and 41 days, respectively. Accumulation of volatile fatty acids was observed at inhibitory NA concentrations; however, carbon dioxide production was not affected by NAs, indicating that fermentation and acidogenesis were not affected by NAs. NAs were not degraded under nitrate-reducing or fermentative/methanogenic conditions used in the present study, regardless of the presence or not of another, degradable carbon/energy source.

Subcellular distribution of fluoranthene in Chlorella vulgaris with the presence of cetyltrimethylammonium chloride

This study explored the possible mechanism of the joint toxicity of binary mixtures of cetyltrimethylammonium chloride (CTAC) and fluoranthene (Flu) to the green alga Chlorella vulgaris by examining the subcellular distribution of Flu within the alga. The joint action of CTAC (100 μg L(-1)) and Flu (0-200 μg L(-1)) on the algae changed from a synergetic effect (0-50 μg L(-1)) to an antagonistic effect (50-200 μg L(-1)) with an increase of the Flu concentration. The Flu uptake was enhanced by the presence of CTAC through the intracellular detection of Flu. Furthermore, the highest amount of Flu bound to the cytosol, whereas the least amount bound to the cellular debris when synergistic effect was observed at 2.5 μg L(-1) Flu. However, the highest amount of Flu bound to the cellular debris, whereas the least amount bound to the organelles when antagonistic effect was displayed at 200 μg L(-1) Flu. The different subcellular distribution of Flu may affect the uptake of the highly toxic CTAC by the algae in the binary mixture, and consequently lead to a different level of CTAC toxicity. The abovementioned results indicate that the subcellular distribution of chemicals can be used to elucidate possible mechanisms for the joint toxicity of their binary mixtures to aquatic organisms.

Review on the fate of emerging contaminants during sludge anaerobic digestion

Several research papers have been published during the last years investigating the occurrence, fate and effects of emerging contaminants (ECs) on sludge anaerobic digestion (AD). Literature review revealed that research has been mainly focused on specific groups of compounds (linear alkylbenzene sulphonates, nonylphenol ethoxylates, some pharmaceuticals, estrogens, phthalates), while there are fewer or no data for others (personal care products, perfluorinated compounds, brominated flame retardants, organotins, benzotriazoles, benzothiazoles, nanoparticles). AD operational parameters (sludge residence time, temperature), sludge characteristics (type of sludge, adaptation on the compound), physicochemical properties of ECs and co-metabolic phenomena seem to affect compounds' biodegradation. The use of sludge pretreatment methods does not seem to enhance ECs removal; whereas encouraging results have been reported when AD was combined with other treatment methods. Future efforts should be focused on better understanding of biotransformation processes and sorption phenomena occurred in anaerobic digesters, as well as on identification of (bio)transformation products.

Aerobic biotransformation of n-tetradecylbenzyldimethylammonium chloride by an enriched Pseudomonas spp. community

The biotransformation of n-tetradecylbenzyldimethylammonium chloride (C(14)BDMA-Cl), a quaternary ammonium compound (QAC), under aerobic conditions by an enriched microbial community growing on benzalkonium chlorides (BACs) was investigated. Biotransformation of C(14)BDMA-Cl commenced with cleavage of the C(alkyl)-N bond and formation of benzyldimethylamine (BDMA). BDMA was further degraded, but in contrast to a previously reported BAC biotransformation pathway, neither benzylmethylamine (BMA) nor benzylamine (BA) was detected as a BDMA biotransformation product. Kinetic assays further confirmed that BMA and BA were not intermediates of C(14)BDMA-Cl transformation by the enriched community. Thus, BDMA is thought to be transformed to dimethylamine and benzoic acid via debenzylation. The biomass-normalized rate of C(14)BDMA-Cl biotransformation was 0.09 μmol/[mg of volatile suspended solids (VSS)·h]. The Microtox acute toxicity EC(50) value of BDMA was 500 times higher than that of C(14)BDMA-Cl. Thus, the aerobic biotransformation of C(14)BDMA-Cl to BDMA results in substantial toxicity reduction. Phylogenetic analysis of Bacteria diversity indicated that the majority of the sequenced clones (98% of the clone library) belonged to the genus Pseudomonas.

Fate and effect of benzalkonium chlorides in a continuous-flow biological nitrogen removal system treating poultry processing wastewater

Quaternary ammonium compounds (QACs) are used for sanitation in many poultry processing facilities. This work investigated the fate and effect of a mixture of benzalkonium chlorides (BACs), a class of QACs widely used in commercial antimicrobial formulations, on the biological nitrogen removal (BNR) processes. A laboratory-scale BNR system was operated continuously for 670 days, fed with poultry processing wastewater amended with a mixture of BACs. Initially, the nitrogen removal efficiency deteriorated at a BAC feed concentration of 5 mg/L due to the complete inhibition of nitrification. However, after 27 days of operation, the system recovered and achieved 100% ammonia removal. High nitrogen removal efficiency was achieved even after the feed BAC concentration was stepwise increased up to 120 mg/L. Batch nitrification assays performed before, during, and after BAC exposure, showed that rapid microbial acclimation and BAC biodegradation contributed to the recovery of nitrification achieving efficient and stable long-term BNR system operation.

Biotransformation of alkanoylcholines under methanogenic conditions

Ester quaternary ammonium compounds (esterquats), which are mainly used as active ingredients in fabric softeners and personal care products, are beginning to replace traditional quaternary ammonium compounds. As a result of hydrophobicity and increasing use, esterquats reach anaerobic treatment systems. However, little is known about the fate of esterquats under anaerobic conditions. In the present study, the potential inhibitory effect and biotransformation of two alkanoylcholines - acetylcholine chloride (ACh-Cl) and lauroylcholine chloride (LCh-Cl) - which are simple esterquats, under methanogenic conditions were investigated. ACh-Cl up to 300 mg/L was not inhibitory to a mixed methanogenic culture. In contrast, methanogenesis was inhibited by LCh-Cl above 50 mg/L, primarily caused by the accumulation of lauric acid which resulted from the abiotic hydrolysis of LCh. Below inhibitory concentrations, both ACh and LCh were transformed to methane by the mixed methanogenic culture. Mass spectrometric analysis confirmed that both alkanoylcholines were first abiotically hydrolyzed to choline and the corresponding alkanoic acid, which were then biotically transformed to methane, carbon dioxide, and ammonia. Thus, alkanoylcholine-containing waste streams can be bioprocessed to form methane, but hydrolysis products such as long-chain alkanoic acids may adversely impact the anaerobic bioconversion of alkanoylcholines.

Biotransformation of nitrosamines and precursor secondary amines under methanogenic conditions

The biotransformation potential of six nitrosamines and their precursor secondary amines by a mixed methanogenic culture was investigated. Among the six nitrosamines tested, N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), and N-nitrosopyrrolidine (NPYR) were almost completely degraded but only when degradable electron donors were available. On the contrary, N-nitrosodiethylamine (NDEA), N-nitrosodipropylamine (NDPA), and N-nitrosodibutylamine (NDBA) were not degraded. Three precursor secondary amines, corresponding to the three biodegradable nitrosamines, were also completely utilized even with very low levels of available electron donors. The secondary amine precursors of the three, nonbiodegradable nitrosamines were also recalcitrant. A bioassay conducted to elucidate the biotransformation pathway of NDMA in the mixed methanogenic culture using H(2) as the electron donor showed that NDMA was utilized as an electron acceptor and transformed to dimethylamine (DMA), which in turn was degraded to ammonia and methane. The H(2) threshold concentration for NDMA bioreduction ranged between 0.0017 and 0.031 atm. Such a high H(2) threshold concentration suggests that in mixed methanogenic cultures, NDMA reducers are weak competitors to other, H(2)-consuming microbial species, such as homoacetogens and methanogens. Thus, complete removal of nitrosamines in anaerobic digestion systems, where the H(2) partial pressure is typically below 10(-4) atm, is difficult to achieve.

Effect of temperature and benzalkonium chloride on nitrate reduction

The effect of temperature and benzalkonium chloride (BAC) on nitrate reduction was investigated in batch assays using a mixed nitrate reducing culture. Nitrate was transformed completely, mainly through denitrification, to dinitrogen at 5, 10, 15 and 22 °C. In the absence of BAC, reduction of individual nitrogen oxides had different susceptibility to temperature and transient nitrite accumulation was observed at low temperatures. When the effect of BAC was tested up to 100 mg/L from 5 to 22 °C, denitrification was inhibited at and above 50mg BAC/L with transient nitrite accumulation at all temperatures. The effect of BAC was described by a competitive inhibition model. Nitrite reduction was the denitrification step most susceptible to BAC, especially at low temperatures. BAC was not degraded during the batch incubation and was mostly biomass-adsorbed. Overall, this study shows that low temperatures exacerbate the BAC inhibitory effect, which in turn is controlled by adsorption to biomass.

Biosorption of tetradecyl benzyl dimethyl ammonium chloride on activated sludge: kinetic, thermodynamic and reaction mechanisms

The biosorption of tetradecyl benzyl dimethyl ammonium chloride (C(14)BDMA) onto activated sludge was examined in aqueous solution with respect to the contact time, temperature and particle size. Equilibrium reached in about 2h contact time. An decrease in the temperature increases of biosorption capacity of C(14)BDMA onto activated sludge, which also increases with decreasing particle size. The experimental data fit the pseudo-second-order kinetics model well. The Langmuir and Freundlich models were applied to describe equilibrium isotherms, and the equilibrium partitioning data was described well by both models. Thermodynamic data showed that C(14)BDMA biosorption onto activated sludge was feasible, spontaneous and exothermic. The Fourier transform infrared (FT-IR) spectrophotometry results show that both physisorption and chemisorption were involved. The measured zeta potential values and the enhanced cation concentration indicate the presence of electrostatic interactions, hydrophobic interactions and ion exchange.

Joint action of binary mixtures of cetyltrimethyl ammonium chloride and aromatic hydrocarbons on Chlorella vulgaris

The joint action of binary mixtures of cetyltrimethyl ammonium chloride (CTAC), a cationic surfactant, and six aromatic hydrocarbons (AHs) on green algae Chlorella vulgaris was investigated. In single systems, inhibition efficiency of CTAC on the growth of algae was much higher than that of AHs (benzene, toluene, phenol, nitrobenzene, phenanthrene and fluoranthene). In combined systems, the toxicity of CTAC was enhanced by low concentrations of AHs. 96 h EC(50) value of CTAC varied from 145±13.35-56±8.27 to 56±8.27-226±8.22 μg/L when exposed to 0-1.13 and 1.13-100.84 μg/L fluoranthene, respectively. Zeta potential of algae initially increased and then decreased with the increase of fluoranthene concentration, whereas residual CTAC concentration displayed an opposite trend in the combined system. These results of this investigation showed that fluoranthene influenced the sorption of CTAC by C. vulgaris. The above results indicated that cationic surfactants and AHs have synergetic toxic effects on aquatic biota.

Interaction between temperature and ammonia in mesophilic digesters for animal waste treatment

Four anaerobic sequencing batch reactors (ASBRs) were operated during a period of 988 days to evaluate the effect of temperature, ammonia, and their interconnectivity on the methane yield of anaerobic processes for animal waste treatment. During period 1 (day 0-378), the methane yield was 0.31 L CH(4)/g volatile solids (VS) for all digesters (with no statistical differences among them) at a temperature and total ammonium-N levels of 25 degrees C and approximately 1200 mg NH(4)(+)-N/L, respectively. During period 2 (day 379-745), the methane yield at 25 degrees C decreased by 45% when total ammonium-N and ammonia-N were increased in two of the four ASBRs to levels >4000 mg NH(4)(+)-N/L and >80 mg NH(3)-N/L, respectively. During period 3 (day 746-988), this relative inhibition was reduced from 45% to 13% compared to the low-ammonia control reactors when the operating temperature was increased from 25 degrees C to 35 degrees C (while the free ammonia levels increased from approximately 100 to approximately 250 mg NH(3)-N/L). The 10 degrees C increase in temperature doubled the rate constant for methanogenesis, which overwhelmed the elevated toxicity effects caused by the increasing concentration of free ammonia. Thus, the farmer/operator may alleviate ammonia toxicity by increasing the operating temperature within the mesophilic range. We extrapolated our data to correlate temperature, ammonia, and methane yield and to hypothesize that the difference between high- and low-ammonia reactors is negligible at the optimum mesophilic temperature of 38 degrees C.

Anaerobic Biodegradation of Detergent Surfactants

Detergent surfactants can be found in wastewater in relevant concentrations. Most of them are known as ready degradable under aerobic conditions, as required by European legislation. Far fewer surfactants have been tested so far for biodegradability under anaerobic conditions. The natural environment is predominantly aerobic, but there are some environmental compartments such as river sediments, sub-surface soil layer and anaerobic sludge digesters of wastewater treatment plants which have strictly anaerobic conditions. This review gives an overview on anaerobic biodegradation processes, the methods for testing anaerobic biodegradability, and the anaerobic biodegradability of different detergent surfactant types (anionic, nonionic, cationic, amphoteric surfactants).

Transformation of benzalkonium chloride under nitrate reducing conditions

The effect and transformation potential of benzalkonium chlorides (BAC) under nitrate reducing conditions were investigated at concentrations up to 100 mg/L in batch assays using a mixed, mesophilic (35 degrees C) methanogenic culture. Glucose was used as the carbon and energy source and the initial nitrate concentration was 70 mg N/L Dissimilatory nitrate reduction to ammonia (DNRA) and to dinitrogen (DNRN) were observed at BAC concentrations up to 25 mg/L At and above 50 mg BAC/L, DNRA was inhibited and DNRN was incomplete resulting in accumulation of nitrous oxide. Long-term inhibition of methanogenesis and accumulation of volatile fatty acids were observed at and above 50 mg BAC/L Over 99% of the added BAC was recovered from all cultures except the one amended with 100 mg BAC/L where 37% of the initially added BAC was transformed during the 100 day incubation period. Abiotic and biotic assays performed with 100 mg/L of BAC and 5 mM (in the liquid phase) of either nitrate, nitrite, or nitric oxide demonstrated that BAC transformation was abiotic and followed the modified Hofmann degradation pathway, i.e., bimolecular nucleophilic substitution with nitrite. Alkyl dimethyl amines (tertiary amines) were produced at equamolar levels to BAC transformed, but were not further degraded. This is the first report demonstrating the transformation of BAC under nitrate reducing conditions and elucidating the BAC transformation pathway.

Effect of polyelectrolytes and quaternary ammonium compounds on the anaerobic biological treatment of poultry processing wastewater

Quaternary ammonium compounds (QACs) and polyelectrolytes are extensively used in poultry processing facilities as sanitizing agents and flocculants, respectively. These chemicals may affect the performance of biological treatment systems resulting in low effluent quality. The impact of these chemicals on the anaerobic treatment of poultry processing wastewater (PPWW) samples, collected before and after a solids separation process, was tested in batch assays using a mixed, mesophilic (35 degrees C) methanogenic culture. The results of this study showed that Vigilquat (VQ), a commercial mixture of four QACs, has a high affinity for the organic solids in the PPWW. Cationic and anionic polyelectrolytes, alone or in combination, did not have any adverse effect on the anaerobic biodegradation of PPWW at concentrations typically used in poultry processing facilities (20 and 5 mg/L, respectively). In spite of the high affinity of VQ for the PPWW solids, VQ at a concentration of 50mg/L and above adversely affected the anaerobic degradation of the PPWW, which resulted in a significantly reduced methane production and accumulation of volatile fatty acids. In the absence of any inhibition, the methane yield varied from 0.76 to 0.98 L methane at STP per g volatile solids added. VQ was not biodegraded under the batch, methanogenic conditions used in this study.