Effect of temperature and organic nutrients on the biodegradation of linear alkylbenzene sulfonate (LAS) during the composting of anaerobically digested sludge from a wastewater treatment plant

Effect of individual or combined physical and chemical factors on the anaerobic biodegradation of linear alkylbenzene sulphonate

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.

PCDD/F determination in sewage sludge composting. Influence of aeration and the presence of PCP

Composting of sewage sludge is a common practice for sludge disposal. Some previous studies found high levels of polychorodibenzo-p-dioxins and polychorodibenzofurans (PCDD/Fs) after composting, especially octachlorodibenzo-p-dioxin (OCDD) but also 1234678-heptachlorodibenzo-p-dioxin (1234678-HpCDD) to a lesser extent. In this work, the concentrations of OCDD, 1234678-HpCDD and the rest of the 17 toxic congeners of PCDD/Fs were determined in compost obtained under different conditions. Although the toxicity of the two compounds mentioned above is small, their generation may reach undesirable levels. The PCDD/F content was analyzed in a composting plant and in a laboratory test. In both cases, the composted material was a mixture of sewage sludge, straw and sawdust. The composting plant was a tunnel with air turbine aeration and with a turner to homogenize and move the mixture upwards. The laboratory tests were carried out with Dewar vessels (with air dispersion at the bottom and controlled temperature) and with small vessels inside a controlled oven with non-forced aeration. The laboratory runs were also carried out with the addition of pentachlorophenol in some runs, as a dioxin precursor. The highest OCDD levels were found in three samples of the composting plant (30000-90000pg/g dry matter or dm), with toxicity values surpassing the limit level for soil amendment (17pgI-TEQ/gdm). Their formation was analyzed considering their concentration vs. that of octachorodibenzofuran (OCDF), which is not formed during composting. In the laboratory, in experiments carried out in a vessel with non-forced aeration conditions and with the addition of pentachlorophenol, the formation of OCDD was significant (e.g. from 80 to 1500pg/gdm). That means that these two factors, non-forced aeration and the presence of pentachlorophenol, can cause the OCDD formation.

Trace organic contaminants in biosolids: Impact of conventional wastewater and sludge processing technologies and emerging alternatives

This paper critically reviews the fate of trace organic contaminants (TrOCs) in biosolids, with emphasis on identifying operation conditions that impact the accumulation of TrOCs in sludge during conventional wastewater and sludge treatment and assessing the technologies available for TrOC removal from biosolids. The fate of TrOCs during sludge thickening, stabilisation (e.g. aerobic digestion, anaerobic digestion, alkaline stabilisation, and composting), conditioning, and dewatering is elucidated. Operation pH, sludge retention time (SRT), and temperature have significant impact on the sorption and biodegradation of TrOCs in activated sludge that ends up in the sludge treatment line. Anaerobic digestion may exacerbate the estrogenicity of sludge due to bioconversion to more potent metabolites. Application of advanced oxidation or thermal pre-treatment may minimise TrOCs in biosolids by increasing the bioavailability of TrOCs, converting TrOCs into more biodegradable products, or inducing complete mineralisation of TrOCs. Treatment of sludge by bioaugmentation using various bacteria, yeast, or fungus has the potential to reduce TrOC levels in biosolids.

Impact of compost process conditions on organic micro pollutant degradation during full scale composting

Knowledge about the effects of oxygen concentration, nutrient availability and moisture content on removal of organic micro-pollutants during aerobic composting is at present very limited. Impact of oxygen concentration, readily available nitrogen content (NH4(+), NO3(-)), and moisture content on biological transformation of 15 key organic micro-pollutants during composting, was therefore investigated using bench-scale degradation experiments based on non-sterile compost samples, collected at full-scale composting facilities. In addition, the adequacy of bench-scale composting experiments for representing full-scale composting conditions, was investigated using micro-pollutant concentration measurements from both bench- and full-scale composting experiments. Results showed that lack of oxygen generally prevented transformation of organic micro-pollutants. Increasing readily available nitrogen content from about 50 mg N per 100 g compost to about 140 mg N per 100 g compost actually reduced micro-pollutant transformation, while changes in compost moisture content from 50% to 20% by weight, only had minor influence on micro-pollutant transformation. First-order micro-pollutant degradation rates for 13 organic micro-pollutants were calculated using data from both full- and bench-scale experiments. First-order degradation coefficients for both types of experiments were similar and ranged from 0.02 to 0.03 d(-1) on average, indicating that if a proper sampling strategy is employed, bench-scale experiments can be used to represent full-scale composting conditions.

Modeling organic micro pollutant degradation kinetics during sewage sludge composting

Degradation of 13 different organic micro-pollutants in sewage sludge during aerobic composting at 5 different temperatures over a 52 day period was investigated. Adequacy of two kinetic models: a single first order, and a dual first order expression (using an early (first 7 days) and a late-time (last 45 days) degradation coefficient), for describing micro-pollutant degradation, and kinetic constant dependency on composting temperature were evaluated. The results showed that both models provide relatively good descriptions of the degradation process, with the dual first order model being most accurate. The single first order degradation coefficient was 0.025 d(-1) on average across all compounds and temperatures. At early times, degradation was about three times faster than at later times. Average values of the early and late time degradation coefficients for the dual first order model were 0.066 d(-1) and 0.022 d(-1), respectively. On average 30% of the initial micro-pollutant mass present in the compost was degraded rapidly during the early stages of the composting process. Single first order and late time dual first order kinetic constants were strongly dependent on composting temperature with maximum values at temperatures of 35-65°C. In contrast the early time degradation coefficients were relatively independent of composting temperature.

Impact of compost process temperature on organic micro-pollutant degradation

Aerobic composting has gained considerable attention because of its ability to remove organic micro-pollutants. Compost process temperature is a key parameter controlling degradation rate. Impact of process temperature on removal of 15 key organic micro-pollutants often found in sewage sludge (including two metabolites) during sewage sludge composting was investigated at 18-70°C over 52 days. Removal rates generally depended strongly on temperature and for all compounds an optimal temperature for removal was observed. Optimal temperatures for the 13 parent compounds ranged from 25 to 70°C and relative removal of the 13 parent compounds was as high as 99% across all combinations of compound and temperature with an average removal of 66%. The two metabolites were both formed and removed during the course of composting and the data indicated that metabolites may very well have other optimal removal temperatures than their parent compounds.

Chemical and toxicological assessment of a full-scale biosolid compost

The impact of a full-scale biosolid composting plant on the fate of a broad range of priority organic pollutants was investigated. Chemical analysis was performed at different steps of the process during two seasons. Simultaneously, the toxicological quality was assessed using estrogen α-, dioxin-, and pregnane X-receptor reporter cell lines. Mass-balance calculation highlighted the removal of easily degradable pollutants during composting. The important variations observed for each compound and for the two seasons might be explained by pollutant-fate dependency on process parameters like temperature. The final compost displayed low pregnane X activity but high estrogenic activity. The dioxin-like activity stayed constant through the process. The chemical and toxicological results highlight the importance of combining both approaches to accurately assess the compost quality. Such compilation of data on full-scale processes may be also very helpful for the environmental risk assessment of new organic waste disposal practices.

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.

Genetic and chemical analyzes of transformations in compost compounds during biodegradation of oiled bleaching earth with waste sludge

Composting of oiled bleaching earth with waste sludge and corn straw was carried out to investigate the ability of microorganisms to synthesize biosurfactants that might decrease the surface tension of composts. Analytical results and changes in the surface tension suggest that biodegradation of fatty by-products was the consequence of emulsifying properties of higher fatty acids. The surface tension for isolates from all composting phases was between 37 and 43 mN m(-1). No substances synthesized by microorganisms that might be able to decrease the surface tension were detected in composts. Tensammetric, TLC and HPLC-MS results and changes in surface tension suggest that biodegradation of fatty by-products results from the emulsifying properties of higher fatty acids. A decrease in fatty content from 144 to 6 mg g(-1) dry matter was obtained.

Dissipation pathways of organic pollutants during the composting of organic wastes

The organic pollutants (OPs) present in compostable organic residues can be recovered in the final composts leading to environmental impacts related to their use in agriculture. However, the composting process may contribute to their partial dissipation that is classically evaluated through the concentration decrease in extractable OPs, without identification of the responsible mechanisms as mineralization or stabilization of OP as non-extractable residues (NER) or bound residues. The dissipation of four (14)C-labeled OPs (fluoranthene; 4-n-nonylphenol, NP; sodium linear dodecylbenzene sulfonate, LAS; glyphosate) was assessed during composting of sewage sludge and green waste. The dissipation of LAS largely resulted from its mineralization (51% of initial LAS), whereas mineralization was intermediate for NP (29%) and glyphosate (24%), and negligible for fluoranthene. The NER pathway mostly concerned NP and glyphosate, with 45% and 37% of the recovered (14)C being found as NER at the end of composting, respectively. In the final composts, the proportions of water soluble residues of OPs considered as readily available were <11% of recovered (14)C-OPs. However, most fluoranthene remained solvent extractable (72%) and potentially available, whereas only 18% of glyphosate and less than 7% of both NP and LAS remained solvent extractable in the final compost.

Composting in small laboratory pilots: performance and reproducibility

Small-scale reactors (<10 l) have been employed in composting research, but few attempts have assessed the performance of composting considering the transformations of organic matter. Moreover, composting at small scales is often performed by imposing a fixed temperature, thus creating artificial conditions, and the reproducibility of composting has rarely been reported. The objectives of this study are to design an innovative small-scale composting device safeguarding self-heating to drive the composting process and to assess the performance and reproducibility of composting in small-scale pilots. The experimental setup included six 4-l reactors used for composting a mixture of sewage sludge and green wastes. The performance of the process was assessed by monitoring the temperature, O(2) consumption and CO(2) emissions, and characterising the biochemical evolution of organic matter. A good reproducibility was found for the six replicates with coefficients of variation for all parameters generally lower than 19%. An intense self-heating ensured the existence of a spontaneous thermophilic phase in all reactors. The average loss of total organic matter (TOM) was 46% of the initial content. Compared to the initial mixture, the hot water soluble fraction decreased by 62%, the hemicellulose-like fraction by 68%, the cellulose-like fraction by 50% and the lignin-like fractions by 12% in the final compost. The TOM losses, compost stabilisation and evolution of the biochemical fractions were similar to observed in large reactors or on-site experiments, excluding the lignin degradation, which was less important than in full-scale systems. The reproducibility of the process and the quality of the final compost make it possible to propose the use of this experimental device for research requiring a mass reduction of the initial composted waste mixtures.

Soil bioassays as tools for sludge compost quality assessment

Composting is a waste management technology that is becoming more widespread as a response to the increasing production of sewage sludge and the pressure for its reuse in soil. In this study, different bioassays (plant germination, earthworm survival, biomass and reproduction, and collembolan survival and reproduction) were assessed for their usefulness in the compost quality assessment. Compost samples, from two different composting plants, were taken along the composting process, which were characterized and submitted to bioassays (plant germination and collembolan and earthworm performance). Results from our study indicate that the noxious effects of some of the compost samples observed in bioassays are related to the low organic matter stability of composts and the enhanced release of decomposition endproducts, with the exception of earthworms, which are favored. Plant germination and collembolan reproduction inhibition was generally associated with uncomposted sludge, while earthworm total biomass and reproduction were enhanced by these materials. On the other hand, earthworm and collembolan survival were unaffected by the degree of composting of the wastes. However, this pattern was clear in one of the composting procedures assessed, but less in the other, where the release of decomposition endproducts was lower due to its higher stability, indicating the sensitivity and usefulness of bioassays for the quality assessment of composts.

Environmental monitoring study of linear alkylbenzene sulfonates and insoluble soap in Spanish sewage sludge samples

In this work we present a monitoring study of linear alkylbenzene sulfonates (LAS) and insoluble soap performed on Spanish sewage sludge samples. This work focuses on finding statistical relations between LAS concentrations and insoluble soap in sewage sludge samples and variables related to wastewater treatment plants such as water hardness, population and treatment type. It is worth to mention that 38 samples, collected from different Spanish regions, were studied. The statistical tool we used was Principal Component Analysis (PC), in order to reduce the number of response variables. The analysis of variance (ANOVA) test and a non-parametric test such as the Kruskal-Wallis test were also studied through the estimation of the p-value (probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true) in order to study possible relations between the concentration of both analytes and the rest of variables. We also compared LAS and insoluble soap behaviors. In addition, the results obtained for LAS (mean value) were compared with the limit value proposed by the future Directive entitled "Working Document on Sludge". According to the results, the mean obtained for soap and LAS was 26.49 g kg(-1) and 6.15 g kg(-1) respectively. It is worth noting that LAS mean was significantly higher than the limit value (2.6 g kg(-1)). In addition, LAS and soap concentrations depend largely on water hardness. However, only LAS concentration depends on treatment type.

Sorption and mineralization of organic pollutants during different stages of composting

The organic pollutant (OP) content is a key factor when determining compost quality. The OPs present in feedstock materials may either be degraded during composting or stabilized in the compost by sorption interactions with organic matter (OM), which may reduce the availability of OP to microorganism degradation. It is particularly important to identify the key stages during composting that are involved in OP mineralization so as to be able to optimize the composting process and determine whether OP sorption on OM is a limiting factor to OP mineralization. Four (14)C-labeled OPs were used during the study: a polycyclic aromatic hydrocarbon (fluoranthene), two surfactants (4-n-nonylphenol - NP and sodium linear dodecylbenzene sulfonate - LAS) and a herbicide (glyphosate). The potential for compost microflora to degrade OP, and compost sorption properties, were characterized at different stages of composting. The highest levels of LAS and glyphosate mineralization were found during the thermophilic stage, at the beginning of maturation for NP and at the end of maturation for fluoranthene. A specific microflora was probably involved in the biodegradation of fluoranthene while NP, LAS and glyphosate mineralization were linked to total microbial activity. OP sorption on compost was linked to their hydrophobicity, decreasing in the order: fluoranthene>NP>LAS>glyphosate. Moreover, sorption decreased as compost maturity increased, except for glyphosate. The sorption coefficients were positively correlated to mineralization kinetics parameters for NP, LAS and glyphosate, suggesting a positive effect of sorption on increasing mineralization rates.

On the fate of LAS, NPEOs and DEHP in municipal sewage sludge during composting

The fate of hydrophobic xenobiotic pollutants such as linear alkylbenzene sulfonates (LAS), nonylphenol ethoxylates (NPEO) and di-ethyl-hexyl phthalate (DEHP) during sewage sludge composting was addressed in this work. The experiments were conducted in a fully automated in-vessel autothermal composting system which was fed with a mixture of primary and secondary sludge and manure. The mixture composition was determined to achieve satisfactory humidity, C/N ratio and free air space (FAS). The effect of various parameters, such as the initial xenobiotic concentration, the presence of multiple xenobiotic compounds and the temperature of composting material sustained during the process on the xenobiotics biodegradation kinetics was investigated. It was generally established that significant xenobiotic reduction is achievable through composting under all conditions tested. According to the obtained results, the presence of LAS, NPEO and DEHP even at higher concentrations was not inhibitory to the bioprocess. However, the presence of multiple xenobiotic compounds such as NPEO, NP and DEHP in the sludge can influence LAS removal during LAS composting.

Comparison of solid-phase and eluate assays to gauge the ecotoxicological risk of organic wastes on soil organisms

Development of methodologies to assess the safety of reusing polluted organic wastes in soil is a priority in Europe. In this study, and coupled with chemical analysis, seven organic wastes were subjected to different aquatic and soil bioassays. Tests were carried out with solid-phase waste and three different waste eluates (water, methanol, and dichloromethane). Solid-phase assays were indicated as the most suitable for waste testing not only in terms of relevance for real situations, but also because toxicity in eluates was generally not representative of the chronic effects in solid-phase. No general correlations were found between toxicity and waste pollutant burden, neither in solid-phase nor in eluate assays, showing the inability of chemical methods to predict the ecotoxicological risks of wastes. On the contrary, several physicochemical parameters reflecting the degree of low organic matter stability in wastes were the main contributors to the acute toxicity seen in collembolans and daphnids.

Optimization and validation of a new method for analysis of linear alkylbenzene sulfonates in sewage sludge by liquid chromatography after microwave-assisted extraction

A new approach has been developed for the monitoring of linear alkylbenzene sulfonates (LAS) (C10-C13) in sewage sludge. It is based on microwave-assisted extraction (MAE) prior to high performance liquid chromatography coupled with diode array (HPLC-DAD) and fluorescence (HPLC-FL) detectors. Column Zorbax XDB-C8, 150 mm x 4.6 mm i.d., 5 microm particle size was used as well as acetonitrile-water containing 0.1 M NaClO4 (65:35) and isocratic elution. Compounds were isocratically eluted over 6 min runtime at a flow rate of 1 mL min(-1). Since polar interferences are eluted between 0 and 2 min, they do not interfere in the analysis. The column was thermostated at a temperature of 25 degrees C. For the determination of LAS, DAD-UV (lambda(ex) = 225 nm) and fluorescence (lambda(ex) = 225 nm, lambda(em) = 295 nm) detectors were employed. The main factors affecting the extraction efficiency (extractant volume, microwave power and irradiation time) were optimized using a compost sludge. The detection limit for total LAS in the sludge was < 5 mg kg(-1). The extraction of C10-C13 homologues is carried out by using an extraction time of 10 min and 5 mL of methanol; whereas Soxhlet needs a 12 h extraction. The method did not require clean-up or preconcentration steps. Concentration levels of LAS were between 13,037 mg kg(-1) for digested sludge and 2492 mg kg(-1) for compost sludge.