Effect of linear alkylbenzene sulphonates (LAS) on the anaerobic digestion of sewage sludge (original) (raw)
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Bioresource Technology, 2010
The study presents a conceptual approach for the identification of the inhibition mechanisms of biodegradable inhibitors. Synthetic sewage was selected as the model degradable substrate to simulate domestic wastewaters. LAS, known to be a biodegradable but inhibitory compound, was selected as a model substrate for the determination of the inhibition mechanisms. Biodegradation of synthetic sewage and LAS were monitored through oxygen uptake rate (OUR) tests conducted to observe the dynamic response of the system when fed with synthetic sewage and synthetic sewage-LAS mixtures. The approach uses respirometry to calibrate the kinetic and stoichiometric coefficients of the proposed biochemical model. Model simulation results confirmed that presence of LAS has inhibitory effects on the biodegradation mechanisms of synthetic sewage. LAS imposed non-competitive inhibition on the hydrolysis process with an inhibition coefficient of 500 mg COD/L and effected heterotrophic growth through a competitive inhibition mechanism with an inhibition coefficient of 150 mg COD/L.
Inhibition of the anaerobic digestion process by linear alkylbenzene sulfonates
Biodegradation
Linear Alkylbenzene Sulfonates (LAS) are the most widely used synthetic anionic surfactants. They are anthropogenic, toxic compounds and are found in the primary sludge generated in municipal wastewater treatment plants. Primary sludge is usually stabilized anaerobically and therefore it is important to investigate the effect of these xenobiotic compounds on an anaerobic environment. The inhibitory effect of Linear Alkylbenzene Sulfonates (LAS) on the acetogenic and methanogenic step of the anaerobic digestion process was studied. LAS inhibit both acetogenesis from propionate and methanogenesis from acetate and hydrogen and it is shown that the propionateutilising bacteria are more sensitive to the presence of LAS than the acetoclastic methanogens. It has been proven that the inhibition intensity depends on the solids concentration and thus the term "biomass specific LAS concentration" has been introduced in order to describe the phenomenon better. Conclusively, it is beli...
2003
The anaerobic biodegradation of Linear Alkylbenzene Sulfonate (LAS) was studied in Upflow Anaerobic Sludge Blanket Reactors (UASB). One reactor was fed with easily degradable substrates and commercial LAS solution during a period of 3 months (Reactor 1), meanwhile a second reactor was fed with a commercial LAS solution without co-substrate (Reactor 2) during 4 months. Both reactors were operated with an organic loading rate of 4-5 mg-LAS/l * day and a hydraulic retention time of one day. The LAS biodegradation was determined by full mass balance. LAS was analysed by HPLC in the liquid phase (influent and effluent streams of the reactors) as well as in the solid phase (granular sludge used as biomass). The results indicate a high level of removal (primary biodegradation: 64-85%). Biodegradation was higher in the absence of external co-substrates than in the presence of additional sources of carbon. This indicates that the surfactant can be partially used as carbon and energy source by anaerobic bacteria. Under the operating conditions used, inhibition of the methanogenic activity or any other negative effects on the biomass due to the presence of LAS were not observed. The methanogenic activity remained high and stable throughout the experiment.
Journal of Environmental Management, 2022
The effect of six important factors on the anaerobic biodegradation of linear alkylbenzene sulphonate (LAS) was evaluated using a response surface methodology. The factors were: (i) co-substrate concentration (CC), (ii) contact time between LAS and microorganisms, (iii) temperature, (iv) hardness, (v) pH, and (vi) LAS source. The results showed that individually or combined, CC with chemical oxygen demand (COD) ≤50 mg L− 1 was the factor that mostly favoured LAS biodegradation; whereas at COD >50 mg L− 1 , adsorption to sludge and solubilisation in the aqueous medium were favoured. Two-factor interactions promoted the highest percentages of biodegradation (45–52%), adsorption (43–45%), and solubilisation (18–25%). The three-factor interactions resulted in small percentage increases of up to 11%, 5%, and 13% for biodegradation, adsorption, and solubilisation, respectively, compared to those of two-factor interactions. The interactions of four, five, and six factors resulted in a non-significant effect on LAS biodegradation, adsorption, and solubilisation, with percentages close to those quantified for the two- and three-factor interactions. Concentrations of up to 30 mg LAS L− 1 did not significantly affect the COD removal efficiency (74–88%) from the medium. These values are commonly obtained in full-scale anaerobic systems used to treat domestic sewage.
Waste Management, 2006
Limits on the application of biosolids (anaerobically processed sludges from wastewater treatment plants) as fertilizers for the amendment of soil are becoming greater because of the accumulation of recalcitrant substances, making necessary the use of techniques that bring the concentration of xenobiotics to lower concentrations than those permitted. In general, the biosolids composting process is sufficient to reduce the usual concentration of linear alkylbenzene sulfonates (LAS) to low levels. In this work, an assessment is made on the effect of temperature in the capacity of enriched bacterial populations to biodegrade LAS, together with the influence that the available nutrients may have in the biodegradation of these compounds. The results show that the microbial metabolism of LAS was not observed in the thermophilic range. The optimum temperature for the biodegradation of LAS appears to be around 40°C, this is, the lowest assayed here, and at this temperature the differences in the biodegradation of LAS among the nutritionally supplemented cultures are small.
Fate of linear alkylbenzene sulfonate (LAS) in activated sludge plants
Water Research, 2004
Monitoring data were collected in a pilot-scale municipal activated sludge plant to assess the fate of the C 12homologue of linear alkyl benzene sulfonate (LAS-C 12 ). The pilot-plant was operated at influent LAS-C 12 concentrations between 2 and 12 mg l À1 and at sludge retention times of 10 and 27 days. Effluent and waste sludge concentrations varied between 5 and 10 mg l À1 and between 37 and 69 mg g À1 VSS, respectively. In the sludge samples only 2-8% was present as dissolved LAS-C 12 , whereas the remaining 92-98% was found to be adsorbed to the sludge. In spite of this high degree of sorption, more than 99% of the LAS-C 12 load was removed by biodegradation, showing that not only the soluble fraction but also the adsorbed fraction of LAS-C 12 is readily available for biodegradation. Sorption and biodegradation of LAS-C 12 were also investigated separately. Sorption was an extremely fast and reversible process and could be described by a linear isotherm with a partition coefficient of 3.2 l g À1 volatile suspended solids. From the results of biodegradation kinetic tests it was concluded that primary biodegradation of LAS-C 12 cannot be described by a (growth) Monod model, but a secondary utilisation model should be used instead. The apparent affinity of the sludge to biodegrade LAS-C 12 increased when the sludge was loaded with higher influent concentrations of LAS-C 12 .
DESALINATION AND WATER TREATMENT, 2017
Linear alkylbenzene sulphonate (LAS) is widely used for household and industrial purposes while influencing negatively on the environment. Present paper aimed to study LAS biodegradation among different loading rates and fate of LAS in integrated fixed-film activated sludge (IFAS) using synthetic media. A synthetic wastewater among three LAS loading rates with LAS concentrations of 5, 12 and 20 mg/L was investigated within an operative period of 111 d. In doing so, a kinetic model was developed to explain the biodegradation rate of LAS. Finally, the obtained data were analyzed by analysis of variance statistical test. The mean removal efficiency of LAS among three LAS loading rates were 92.32% ± 2.81%, 95.55% ± 2.74% and 96.22% ± 2.74%, respectively. Nevertheless, in terms of total removal efficiency of LAS, the contributions of LAS biosorption in sludge among the three LAS loading rates were 21.3%, 34.2% and 48.5%. The mean removal efficiency of chemical oxygen demand (COD) in among three LAS loading rates were 92.17% ± 4.32%, 91.53% ± 3.34% and 90.91% ± 2.98%, respectively. Moreover, the higher LAS loading rate, the higher removal efficiency of LAS (p ≤ 0.001) and the lower COD removal efficiency (p ≤ 0.001). The results of Michaelis-Menten model for biodegradation kinetics showed that the LAS biodegradation follows the first-order reaction kinetics (R 2 = 0.9949). In addition, biodegradation kinetic and removal efficiency of LAS showed that following the increased concentration of LAS among different loading rates, the LAS biodegradation rate was increased. Therefore, IFAS system is argued to be applicable for wastewater treatment in low and high concentrations of LAS up to 20 mg/L.
Chemosphere, 2006
The degradation of linear alkylbenzene sulfonates and their degradation intermediates (sulfophenylcarboxylic acids) has been characterized at 9°C in an activated sludge pilot plant. After an adequate adaptation period (20 days), LAS primary degradation exceeds 99% and takes place preferentially for long alkyl chain homologues and external isomers. LAS homologues in the reactor are preferentially sorbed onto particulate matter, while sulfophenylcarboxylic acids (SPCs) are present predominantly in solution, due to their lower hydrophobicity. During the adaptation period the most abundant LAS biodegradation intermediates were long chain sulfophenylcarboxylic acids (SPCs) (C 9 -C 13 SPC). However once this system is fully adapted, the microorganisms are capable of degrading SPCs efficiently. SPCs with 7-9 carbon atoms in the carboxylic chain predominate due to their degradation being slower than for the rest of the SPCs. The presence of C 13 SPC confirms that LAS degradation in wastewater starts with a x-oxidation on the alkylic chain. A preferential degradation of SPC isomers of the types 2/C n SPC to 6/C n SPC was also detected, as shown by the relatively higher SPC concentrations of the remaining ones.
Environmental Technology Letters, 1989
Treatment of a wastewater containing high concentration of branced alkylbenzene sulphonates (123 to 250 mgL-1 MBAS) was achieved by means of an activated sludge system with recycle. The BOD, COD and MBAS levels of the recalcitrant wastewater were reduced by 87, 68 and 69 per cent, respectively. The high value of K(s) (111 mgL-a1) found for this recalcitrant wastewater indicates a lack of affinity by the enzymes to the substrate present. As such, biodegradation can be said to occur through a non-specific enzymatic action. http://www.tandfonline.com/doi/abs/10.1080/09593338909384781#.U7-OkEC9gtE
Journal of Environmental Management, 2013
Linear alkylbenzene sulfonate (LAS) is an anionic surfactant used in cleaning products, which is usually found in wastewaters. Despite the greater LAS removal rate related to a lower concentrations of volatile fatty acids (VFA), the influence of different ranges of VFA on LAS degradation is not known. LAS degradation was evaluated in upflow anaerobic sludge blanket (UASB) and expanded granular sludge bed (EGSB) reactors at different ranges of VFA concentrations. The reactors were fed with a synthetic wastewater containing LAS (14 mg/L). A greater LAS removal rate (40e80%) was related to the lower and narrower range of acetic acid concentration (1e22 mg/L) in the EGSB reactor. In the UASB reactor, the acetic acid concentrations presented a wider range (2e45 mg/L), and some low LAS removal rates (around 20e25%) were observed even at low acetic acid concentrations (<10 mg/L). The high recirculation rate in the EGSB reactor improved substrate-biomass contact, which resulted in a narrower range of VFA and greater LAS removal rate.