The effect of thermal hydrolysis pretreatment on the anaerobic degradation of nonylphenol and short-chain nonylphenol ethoxylates in digested biosolids

The presence of micropollutants can be a concern for land application of biosolids. Of particular interest are nonylphenol diethoxylate (NP₂EO), nonylphenol monoethoxylate (NP₁EO), and nonylphenol (NP), collectively referred to as NPE, which accumulate in anaerobically digested biosolids and are subject to regulation based on the environmental risks associated with them. Because biosolids are a valuable nutrient resource, it is essential that we understand how various treatment processes impact the fate of NPE in biosolids. Thermal hydrolysis (TH) coupled with mesophilic anaerobic digestion (MAD) is an advanced digestion process that destroys pathogens in biosolids and increases methane yields and volatile solids destruction. We investigated the impact of thermal hydrolysis pretreatment on the subsequent biodegradation of NPE in digested biosolids. Biosolids were treated with TH, anaerobic digestion, and aerobic digestion in laboratory-scale reactors, and NPE were analyzed in the influent and effluent of the digesters. NP₂EO and NP₁EO have been observed to degrade to the more estrogenic NP under anaerobic conditions; therefore, changes in the ratio of NP:NPE were of interest. The increase in NP:NPE following MAD was 56%; the average increase of this ratio in four sets of TH-MAD samples, however, was only 24.6 ± 3.1%. In addition, TH experiments performed in pure water verified that, during TH, the high temperature and pressure alone did not directly destroy NPE; TH experiments with NP added to sludge also showed that NP was not destroyed by the high temperature and pressure of TH when in a more complex sludge matrix. The post-aerobic digestion phases removed NPE, regardless of whether TH pretreatment occurred. This research indicates that changes in biosolids processing can have impacts beyond just gas production and solids destruction.     

Occurrence and behaviour of linear alkylbenzenesulphonates, nonylphenol, nonylphenol mono- and nonylphenol diethoxylates in sewage and sewage sludge treatment

The fluxes of linear alkylbenzenesulphonates (LAS), nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) through sewage and sludge treatment of 29 Swiss sewage treatment plants were investigated. Reversed-phase high-performance liquid chromatography (HPLC) was used to determine LAS. Normal-phase HPLC was employed to measure NP, NP1EO and NP2EO which are metabolites of the nonionic surfactants of the nonylphenol polyethoxylate type (NPnEO). Quantitative determinations were performed of raw sewage, primary and secondary effluents and of sewage sludge. Under normal conditions of sewage and sludge treatment, LAS were efficiently removed from the raw wastewater (> 99% w/w) and were partly transferred to the sewage sludge (15–20% w/w). About 50% (molar base) of NPnEO in the sewage were transformed to NP and accumulated in the digested sludge. Large variations existed among different sewage treatment plants. It was estimated that 1.0 g m⁻² y⁻¹ of LAS and 0.3 g m⁻² y⁻¹ of NP are applied with sewage sludge to Swiss soils.     

Bacterial community shifts in nonylphenol polyethoxylates-enriched activated sludge

A molecular approach was used to evaluate the effect of nonylphenol ethoxylate surfactants on the bacterial diversity in lab-scale activated sludge reactors. Separate bench-scale units were fed synthetic wastewater with and without addition of branched nonylphenol ethoxylates (NPnEO). The performance of the reactors, in terms of carbonaceous removal was largely unaffected by the presence of NP10EO in the feeding solution. However, addition of NP10EO exerted a pronounced shift in bacterial community composition. In situ hybridization analyzing larger phylogenetic groups of bacteria with ribosomal RNA-targeted oligonucleotide probes revealed the dominance of clusters composed of Betaproteobacteria, accounting for up to one-third of 4',6-diamidino-2-phenylindol-dihydrochloride (DAPI)-stained cells in NP10EO amended reactors and only 5% of DAPI-stained cells in the controls. These shifts in populations of larger phylogenetic groups were confirmed by dot-blot analysis of rRNA. Members of gamma subclass of Proteobacteria were present in low numbers in all activated sludge samples examined, suggesting that only bacteria affiliated with the beta subclass of Proteobacteria may have a specific role in NP10EO degradation.     

Fate of nonylphenol polyethoxylates and their metabolites in four Beijing wastewater treatment plants

Four Beijing wastewater treatment plants (WWTPs) were selected to investigate behaviours of nonylphenol polyethoxylates and their metabolites in different wastewater treatment processes. The results showed that the total concentrations of nonylphenolic compounds in the influents of the four WWTPs ranged from 0.115 to 0.347 μmol/L, as well as their removal efficiencies ranging from 75.7% to 90.8%. Both influent concentrations and removal efficiencies of nonylphenol polyethoxylates were correlated to seasons as follows: higher in the summer than in the winter, and influent concentrations were lower during the rain weather. The analysis revealed that 21.8-47.6% of nonylphenol polyethoxylates and their metabolites entering WWTPs were released via effluents and excess sludge, leaving a great part of them for biodegradation. Nonylphenol and short-chain nonylphenol polyethoxylates were disposed to the environment mainly via sewage sludge, while carboxylated nonylphenol polyethoxylates were the most abundant group of nonylphenol polyethoxylates in effluents.     

Comparing steroid estrogen, and nonylphenol content across a range of European sewage plants with different treatment and management practices

The effluent of 17 sewage treatment works (STW) across Norway, Sweden, Finland, The Netherlands, Belgium, Germany, France and Switzerland was studied for the presence of estradiol (E2), estrone (E1), ethinylestradiol (EE2) and nonylphenol (NP). Treatment processes included primary and chemical treatment only, submerged aerated filter, oxidation ditch, activated sludge (AS) and combined trickling filter with activated sludge. The effluent strength ranged between 87 and 846 L/PE (population equivalent), the total hydraulic retention time (HRT) ranged between 4 and 120 h, sludge retention time (SRT) between 3 and 30 d, and water temperature ranged from 12 to 21 °C. The highest estrogen values were detected in the effluent of the STW which only used primary treatment (13 ng/L E2 and 35 ng/L E1) and on one occasion in one of the STW using the AS system (6.5 ng/L E2, 50.5 ng/L E1, but on three other occasions the concentrations in this STW were at least a factor of 6 lower). For the 16 STW employing secondary treatment E2 was only detected in the effluent of six works during the study period (average 0.7-5.7 ng/L). E1 was detected in the effluent of 13 of the same STW. The median value for E1 for the 16 STW with secondary treatment was 3.0 ng/L. EE2 was only detected in two STW (1.1, <0.8-2.8 ng/L). NP could be detected in the effluent of all 14 STW where this measurement was attempted, with a median of 0.31 μg/L and values ranging from 0.05 to 1.31 μg/L. A comparison of removal performance for E1 was carried out following prediction of the probable influent concentration. A weak but significant (α<5%) correlation between E1 removal and HRT or SRT was observed.     

UV-VIS and FTIR spectroscopic analyses of inclusion complexes of nonylphenol and nonylphenol ethoxylate with β-cyclodextrin

A study of inclusion complexation of liquid non-ionic surfactants, nonylphenol (NP) and nonylphenol 9 mole ethoxylate (NP9EO), with β-cyclodextrin (β-CD), was carried out by mass spectrometry, surface tension, and ultraviolet-visible (UV-VIS) and Fourier transform infrared (FTIR) spectroscopies. The inclusion complexation was effectuated by heating at 80 °C and filtration of aqueous NP + β-CD and NP9EO + β-CD suspensions. The mass spectrometry and surface tension measurements revealed that NP and NP9EO form inclusion complexes with β-CD and β-CD possesses a higher affinity for NP. These results are supported by the data from UV-VIS spectroscopic analyses that have indicated that a three times greater amount of NP is entrapped into β-CD than NP9EO. This phenomenon has been associated with the smaller size and a higher degree of hydrophobicity of NP that favours its entrapment into β-CD as compared to that of NP9EO. At the structural level, the data from FTIR spectroscopic study have indicated that alkyl chains of NP and NP9EO can form van der Waals interactions with the cavity of β-CD. Moreover, NP and NP9EO seem to cause a reorganization of the intramolecular hydrogen bonds and change of the hydration of β-CD, but did not appear to strongly interact with C-C, C-O-C, and OH groups of β-CD. Together these results suggest that the formation of inclusion complexes by NP and NP9EO with β-CD molecules could constitute an effective and advantageous technique to remove liquid non-ionic surfactants from wastewater due to the non-toxic character of β-CD to humans and the environment.     

Occurrence and fate of endocrine disrupters in Greek sewage treatment plants

The occurrence of five endocrine-disrupting compounds (EDCs), namely 4-n-nonylphenol (4-n-NP), nonylphenol monoethoxylate (NP1EO), nonylphenol diethoxylate (NP2EO), triclosan (TCS) and bisphenol A (BPA), was assessed in the raw, treated wastewater and sewage sludge of eight sewage treatment plants (STPs) in Greece. The analytes were extracted by solid-phase extraction (dissolved phase) or sonication (solid phase). Qualitative and quantitative analyses were performed by gas chromatography-mass spectrometry (GC-MS). The average concentrations in the raw and treated wastewater ranged from 0.23 (4-n-NP) to 5.76microgL(-1) (NP1EO) and from 0.15 (BPA) to 1.84microgL(-1) (NP2EO), respectively. A great part of the detected EDCs was sorbed on suspended solids. In sewage sludge, the average concentrations ranged between 0.17 (4-n-NP) and 12.3microgg(-1)dw (NP1EO). Analysis of daily mass flows in STP of Athens showed that, with the exception of 4-n-NP, all other EDCs were significantly removed (>85%) during wastewater treatment. Regarding the fate of these compounds, a significant part ranging from 45% (for TCS) to more than 70% (for NP1EO, NP2EO and BPA) was transformed by abiotic or biotic mechanisms, while the rest was accumulated in sewage sludge or disposed to the environment via the effluents. Calculation of risk quotients showed the existence of possible threat due to the presence of certain EDCs in treated wastewater and sludge.     

Correlations of nonylphenol-ethoxylates and nonylphenol with biomarkers of reproductive function in carp (Cyprinus carpio) from the Cuyahoga River

Various chemical and biological measures were determined in carp (Cyprinus carpio) sampled from seven sites along the Cuyahoga River, Ohio; from the relatively pristine headwaters to the lower portion heavily polluted from various industrial, urban and wastewater treatment plants (WWTP). Levels of nonylphenol (NP), nonylphenol ethoxylates (NPEs; NP1EO, NP2EO) and total NPEs (NP plus the NPEs) in fish increased in a downstream direction, with maximal values observed below the discharge of the Akron WWTP. In female fish there were no significant differences between sites in GSI or levels of vitellogenin (VTG) and 17beta-estradiol (E2). However, differences were observed between sites using measures of 11-ketotestosterone (11-KT) and the ratio E2/11-KT. In male fish the highest levels of VTG were observed downstream of the Akron WWTP and a significant correlation (r=85%) between levels of NP and VTG was demonstrated. No site differences were observed in the measures of GSI, E2, 11-KT or the E2/11-KT ratio in male fish. These data suggest that endocrine active chemicals, such as, NP and NPEs are impacting fish downstream of the Akron WWTP; however, further work is warranted to separate linkages to other possible chemical factors in the water.     

Selected personal care products and endocrine disruptors in biosolids: an Australia-wide survey

Personal care products (PCPs) and endocrine disrupting compounds (EDCs) are groups of organic contaminants that have been detected in biosolids around the world. There is a shortage of data on these types on compounds in Australian biosolids, making it difficult to gain an understanding of their potential risks in the environment following land application. In this study, 14 biosolids samples were collected from 13 Australian wastewater treatment plants (WWTPs) to determine concentrations of eight compounds that are PCPs and/or EDCs: 4-t-octylphenol (4tOP), 4-nonylphenol (4NP), triclosan (TCS), bisphenol A (BPA), estrone (E1), 17β-estradiol (E2), estriol (E3) and 17α-ethinylestradiol (EE2). Concentration data were evaluated to determine if there were any differences between samples that had undergone anaerobic or aerobic treatment. The concentration data were also compared to other Australian and international data. Only 4tOP, 4NP, TCS, and BPA were detected in all samples and E1 was detected in four of the 14 samples. Their concentrations ranged from 0.05 to 3.08 mg/kg, 0.35 to 513 mg/kg, < 0.01 to 11.2 mg/kg, < 0.01 to 1.47 mg/kg and < 45 to 370 μg/kg, respectively. The samples that were obtained from WWTPs that used predominantly anaerobic treatment showed significantly higher concentrations of the compounds than those obtained from WWTPs that used aerobic treatment. Overall, 4NP, TCS and BPA concentrations in Australian biosolids were lower than global averages (by 42%, 12% and 62%, respectively) and 4tOP concentrations were higher (by 25%), however, of these differences only that for BPA was statistically significant. The European Union limit value for NP in biosolids is 50 mg/kg, which 4 of the 14 samples in this study exceeded.     

Novel insights into sludge dewaterability by fluorescence excitation-emission matrix combined with parallel factor analysis

Sludge dewatering is of major interest in sludge volume reduction and handling properties improvement. Here we report an approach of fluorescence excitation-emission matrix (EEM) combined with parallel factor (PARAFAC) analysis to elucidate the factors that influence sludge dewaterability. Sludge flocs from 11 full-scale wastewater treatment plants were collected to stratify into different extracellular polymeric substances (EPS) fractions and then to characterize their fluorescence EEMs. Both the normalized capillary suction time (CST) and specific resistance to filtration (SRF) were applied to determine sludge dewaterability. The results showed that fluorescence EEMs of tightly bound fractions were not affected by the wastewater sources. In contrast, fluorescence EEMs of loosely bound fractions were affected by the wastewater sources. All the fluorescence EEMs could be successfully decomposed into a six-component model by PARAFAC analysis. Both normalized CST and SRF were significantly correlated with component 1 [excitation/emission (Ex/Em) = (220, 275)/350] in the supernatant fraction, with components 5 [Ex/Em = (230, 280)/430] and 6 [Ex/Em = (250, 360)/460] in the slime and LB-EPS fraction. These results reveal that except for proteins-like substances (component 1), sludge dewaterability is also affected by humic acid-like and fulvic acid-like substances (components 5 and 6) in the slime and LB-EPS fractions. Furthermore, this paper presents a promising and facile approach (i.e., EEM-PARAFAC) for investigating sludge dewaterability.     

Occurrence of selected surfactants in untreated and treated sewage

Several surfactants were monitored in treated and untreated sewage in nine municipal wastewater treatment plants (WWTPs) in western Austria. The nine sampled WWTPs cover a wide variety referring to size and applied treatment technology. The investigation focused on linear alkylbenzene sulphonate (LAS), quaternary ammonia compounds (QAC), nonylphenol (NP), octylphenol (OP), nonylphenolmono- (NP(1)EO) and -diethoxylates (NP(2)EO). Whereas LAS, NP, OP and NP(1,2)EO were analysed separately in the liquid phase and in the solid phase, the QACs were measured in the total sample. Total influent concentrations of LAS varied between 2.4 mg l(-1) up to 6.7 mg l(-1) whereas total effluent concentrations were in the lower microg l(-1) range (11-50 microg l(-1)). Whichever the type of treatment, a clear removal during treatment was observed. Solid liquid distribution coefficients K(d) were calculated for untreated sewage. The calculated K(d) values varied between 1300 and 3900 l kg(-1). OP was of minor importance with total influent concentrations below 1microg l(-1). NP and NP(1,2)EO were present in all analysed influents in concentrations between 1 and 35microg l(-1). Effluent concentrations were notably lower than the measured influent concentrations. K(d) values for NP varied between 500 and 6600 l kg(-1), for NP(1)EO between 800 and 2700 l kg(-1) and for NP(2)EO between 100 and 1800 l kg(-1). From the QACs several alkyl benzyl (BAC), dialkyl (DDAC) and trialkyl (ATAC) ammonium chlorides with varying alkyl chain lengths were analysed. Highest total concentrations in the influents to the WWTPs were observed for the BAC-C12 and the ATAC-C16 homologues. Effluent concentrations were notably lower compared to influent concentrations, indicating removal by adsorption and/or biodegradation. The influence of the removal by adsorption increased with increasing alkyl chain length.     

Removal of the endocrine disrupter nonylphenol and its estrogenic activity in sludge treatment processes

The estrogenic compound nonylphenol (NP) is frequently found in sludge from sewage treatment works. Hence, when sewage sludge is spread on the land, endocrine-disrupting compounds may get into the soil. The goal of this study was to investigate the extent to which aerobic mesophilic treatment in continuous reactors permits the removal of NP from sludge and how this process may be useful for treating anaerobically stabilised sludge. We also report on the behaviour of NP during the anaerobic treatment of sludge. The reduction in sludge estrogenic activity observed in the different types of treatment, as measured using estrogen-responsive reporter cells lines (MELN bioassay), was compared with NP removal rates. Under anaerobic conditions, no degradation of NP and its estrogenic activity was observed. Indeed, an accumulation of the compound occurred. In contrast, high removal of NP was achieved in aerobic conditions as well as in aerobic Post-treatment of anaerobically pre-digested sludge, with a concomitant reduction of the sludge's estrogenic potency.     

Occurrence and implications of estrogens and xenoestrogens in sewage effluents and receiving waters from South East Queensland

We report a survey on the occurrence of estrogens (estrone, E1; 17β-estradiol, E2; 17α-ethynylestradiol, EE2) and xenoestrogens (bisphenol-A, BPA; 4-t-octylphenol, 4-t-OP; 4-nonylphenols, 4-NP; and nonylphenol mono- and di-ethoxylates, NPE1 and NPE2) in effluents from five wastewater treatment plants and their receiving waters in South East Queensland. The total xenoestrogen concentrations in effluent ranged between 2446 ng/L and 6579 ng/L, with 4-NP and NPE1-2 having much higher concentration levels than BPA and 4-t-OP. The estrogen levels in effluent varied from 9.12 to 32.22 ng/L for E1, from 1.37 ng/L to 6.35 ng/L for E2 and from 0.11 ng/L to 1.20 ng/L for EE2. No significant differences (p < 0.05) in the concentrations of the selected estrogenic compounds were found for the effluents from the five sewage treatment plants. The estrogens and xenoestrogens were also found in the receiving waters at relatively lower concentration levels due to dilution of effluents in the rivers. Based on the chemical analysis data and relative potency of the compound from in vitro and in vivo bioassays from the literature, the calculated in vitro EEQ values (estrogen equivalents) in the receiving river waters downstream of the effluent discharge points ranged from 1.32 to 11.79 ng/L, while the in vivo EEQ values (vitellogenin response in rainbow trout) ranged from 2.48 to 21.18 ng/L. The three estrogens accounted for the majority of the EEQ in the water samples. This study indicates that the rivers of South East Queensland are at potential risk.     

Degradation of polyethoxylated nonylphenols in a sewage treatment plant. Quantitative analysis by isotopic dilution-HRGC/MS

Polyethoxylated alkylphenols (APnEO, where n is the number of ethylene oxide molecules), are non-ionic surfactants widely used for domestic and industrial purposes. Most of APnEO are polyethoxylated nonylphenols (NPnEO). NPnEO are widespread environmental pollutants with relatively low toxicity for mammals and higher toxicity for aquatic organisms. In addition, they have been described as endocrine disrupters in recent publications. One of the main problems related to these surfactants is their uncomplete degradation, even in the most effective sewage treatment plants. Usually, the final products, more toxic and resistant to biological degradation than NPnEO, are nonylphenol (NP), monoethoxylated nonylphenol (NP1EO), diethoxylated nonylphenol (NP2EO), nonylphenoxy acetic acid (NP1EC), and nonylphenoxyethoxy acetic acid (NP2EC). In this paper, the degradation of NPnEO was studied in the different processes of a sewage treatment plant. For this purpose, NP, NP1EO and NP2EO were analysed in composite samples collected at different points along the plant (influent, pre-treatment effluent, primary effluent, plant effluent). Analyses were carried out by isotopic dilution-HRGC/MS, using available labelled nonylphenols (13C6-NP, 13C6-NP1EO, 13C6-NP2EO) as internal standards. Extraction of NPnEO from aqueous samples, previous to analysis, was performed by the Likens-Nickerson method (simultaneous steam distillation/solvent extraction, SDE).     

The removal of pharmaceuticals, personal care products, endocrine disruptors and illicit drugs during wastewater treatment and its impact on the quality of receiving waters

A 5-month monitoring program was undertaken in South Wales in the UK to determine the fate of 55 pharmaceuticals, personal care products, endocrine disruptors and illicit drugs (PPCPs) in two contrasting wastewater plants utilising two different wastewater treatment technologies: activated sludge and trickling filter beds. The impact of treated wastewater effluent on the quality of receiving waters was also assessed.PPCPs were found to be present at high loads reaching 10 kg day⁻¹ in the raw sewage. Concentrations of PPCPs in raw sewage were found to correlate with their usage/consumption patterns in Wales and their metabolism. The efficiency of the removal of PPCPs was found to be strongly dependent on the technology implemented in the wastewater treatment plant (WWTP). In general, the WWTP utilising trickling filter beds resulted in, on average, less than 70% removal of all 55 PPCPs studied, while the WWTP utilising activated sludge treatment gave a much higher removal efficiency of over 85%. The monitoring programme revealed that treated wastewater effluents were the main contributors to PPCPs concentrations (up to 3 kg of PPCPs day⁻¹) in the rivers studied. Bearing in mind that in the cases examined here the WWTP effluents were also major contributors to rivers' flows (dilution factor for the studied rivers did not exceed 23 times) the effect of WWTP effluent on the quality of river water is significant and cannot be underestimated.     

Occurrence of synthetic musks in Korean sewage sludges

Six polycyclic musks (PCMs) and five nitro musks (NMs) were analyzed in dewatered sludge samples from 13 municipal, 4 livestock and 1 pharmaceutical wastewater treatment plants (WWTPs) in South Korea. 1,3,4,6,7,8-Hexahydro-4,6,6,7,8,8-hexamethylcyclopenta-(g)-2-benzopyran (HHCB; Galaxolide^®, Abbalide^®), and 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN; Tonalide^®, Fixolide^®) were the two predominant PCMs in the sludge samples, at concentrations ranging from 0.52 to 82.0 mg/kg dry weight (dw) and 0.12 to 28.8 mg/kg (dw), respectively, suggesting the extensive use of these two PCMs in South Korea. Hierarchical cluster analysis (HCA) revealed the different usage patterns of PCMs between livestock cultivating farm and household. The levels of HHCB and AHTN in the effluent discharged from the WWTPs were lower than the threshold effect levels derived for fish, suggesting low potential risks to aquatic organisms. Nevertheless, the calculated discharge of synthetic musks (SMs) from sludge in each target WWTP ranged from 36 to 10,961 g/d. These results indicate the necessity of conducting monitoring studies in marine ecosystems due to ocean disposal of sludge, particularly focused on the two prevailing PCMs.     

Occurrence and removal of N-nitrosamines in wastewater treatment plants

The presence of nitrosamines in wastewater might pose a risk to water resources even in countries where chlorination or chloramination are hardly used for water disinfection. We studied the variation of concentrations and removal efficiencies of eight N-nitrosamines among 21 full-scale sewage treatment plants (STPs) in Switzerland and temporal variations at one of these plants. N-nitrosodimethylamine (NDMA) was the predominant compound in STP primary effluents with median concentrations in the range of 5-20 ng/L, but peak concentrations up to 1 μg/L. N-nitrosomorpholine (NMOR) was abundant in all plants at concentrations of 5-30 ng/L, other nitrosamines occurred at a lower number of plants at similar levels. From concentrations in urine samples and domestic wastewater we estimated that human excretion accounted for levels of <5 ng/L of NDMA and <1 ng/L of the other nitrosamines in municipal wastewater, additional domestic sources for <5 ng/L of NMOR. Levels above this domestic background are probably caused by industrial or commercial discharges, which results in highly variable concentrations in sewage. Aqueous removal efficiencies in activated sludge treatment were in general above 40% for NMOR and above 60% for the other nitrosamines, but could be lower if concentrations were below 8-15 ng/L in primary effluent. We hypothesize that substrate competition in the cometabolic degradation explains the occurrence of such threshold concentrations. An additional sand filtration step resulted in a further removal of nitrosamines from secondary effluents even at low concentrations. Concentrations released to surface waters were largely below 10 ng/L, suggesting a low impact on Swiss water resources and drinking water generation considering the generally high environmental dilution and possible degradation. However, local impacts in case a larger fraction of wastewater is present cannot be ruled out.     

Potential nanosilver impact on anaerobic digestion at moderate silver concentrations

Silver nanoparticles (AgNPs, nanosilver) entering the sewers and wastewater treatment plants (WWTPs) are mostly accumulated in the sludge. In this study, we determined the impact of AgNPs on anaerobic glucose degradation, sludge digestion and methanogenic assemblages. At ambient (22 °C) and mesophilic temperatures (37 °C), there was no significant difference in biogas and methane production between the sludge treated with AgNPs at the concentrations up to 40 mg Ag/L (13.2 g silver/Kg biomass COD) and the control. In these anaerobic digestion samples, acetate and propionic acid were the only detectable volatile fatty acids (VFAs) and they were depleted in 3 days. On the other hand, more than 90% of AgNPs was removed from the liquid phase and associated with the sludge while almost no silver ions were released from AgNPs under anaerobic conditions. Quantitative PCR results indicated that Methanosaeta and Methanomicrobiales were the dominant methanogens, and the methanogenic diversity and population remained largely unchanged after nanosilver exposure and anaerobic digestion. The results suggest that AgNPs at moderate concentrations (e.g., ≤40 mg/L) have negligible impact on anaerobic digestion and methanogenic assemblages because of little to no silver ion release.     

Biodegradation of nonylphenol polyethoxylates under sulfate-reducing conditions

Biodegradation behavior of nonylphenol polyethoxylates (NPEOs) under sulfate-reducing conditions was investigated. The results showed that NPEOs were readily degraded under sulfate-reducing conditions. These compounds were degraded via sequential removal of ethoxyl units to nonylphenol (NP) without forming carboxylated intermediates under sulfate-reducing conditions. The biodegradation of NPEOs under sulfate-reducing conditions was not inhibited even at very high initial concentrations of NPEOs. The maximum removal rate increased about 1.3 microM d(-1) for each 10 micromol increase in initial concentration. The decrease in temperature caused a sharp decrease in the removal efficiency of NPEOs. The temperature coefficient (Phi) for the biodegradation of NPEOs under sulfate-reducing conditions was 0.008. Severe accumulation of NP and short-chain NPEOs occurred when most NPEOs were removed and this accumulation led to an increase in the estrogenic activity. The highest estrogenic activity appeared on day 21 when the total concentration of these metabolites reached its top (18.03+/-4.73 microM). NP could inhibit the biodegradation of NPEOs under sulfate-reducing conditions only at relatively high concentration. These findings are of major environmental importance in terms of the environmental behavior of NPEO contaminants in natural environment.     

Strategies for lipids and phenolics degradation in the anaerobic treatment of olive mill wastewater

Strategies are proposed for the anaerobic treatment of lipid and phenolic-rich effluents, specifically the raw olive mill wastewater (OMW). Two reactors were operated under OMW influent concentrations from 5 to 48 g COD L⁻¹ and Hydraulic Retention Time between 10 and 5 days. An intermittent feeding was applied whenever the reactors showed a severe decay in the methane yield. This strategy improved the mineralization of oleate and palmitate, which were the main accumulated Long-Chain Fatty Acids (LCFA), and also promoted the removal of resilient phenolic compounds, reaching remarkable removal efficiencies of 60% and 81% for two parallel reactors at the end of a feed-less period. A maximum biogas production of 1.4 m³ m⁻³ d⁻¹ at an Organic Loading Rate of 4.8 kg COD m⁻³ d⁻¹ was obtained. Patterns of individual LCFA oxidation during the OMW anaerobic digestion are presented and discussed for the first time. The supplementation of a nitrogen source boosted immediately the methane yield from 21 and 18 to 76 and 93% in both reactors. The typical problems of sludge flotation and washout during the anaerobic treatment of this oily wastewater were overcome by biomass retention, according to the Inverted Anaerobic Sludge Blanket (IASB) reactor concepts. This work demonstrates that it is possible to avoid a previous detoxification step by implementing adequate operational strategies to the anaerobic treatment of OMW.