Ultrasonic sludge pretreatment under pressure

The objective of this work was to optimize the ultrasound (US) pretreatment of sludge. Three types of sewage sludge were examined: mixed, secondary and secondary after partial methanisation (“digested” sludge). Thereby, several main process parameters were varied separately or simultaneously: stirrer speed, total solid content of sludge (TS), thermal operating conditions (adiabatic vs. isothermal), ultrasonic power input (P_US), specific energy input (ES), and for the first time external pressure. This parametric study was mainly performed for the mixed sludge. Five different TS concentrations of sludge (12–36 g/L) were tested for different values of ES (7000–75,000 kJ/kg_TS) and 28 g/L was found as the optimum value according to the solubilized chemical oxygen demand in the liquid phase (SCOD). P_US of 75–150 W was investigated under controlled temperature and the “high power input – short duration” procedure was the most effective at a given ES. The temperature increase in adiabatic US application significantly improved SCOD compared to isothermal conditions. With P_US of 150 W, the effect of external pressure was investigated in the range of 1–16 bar under isothermal and adiabatic conditions for two types of sludge: an optimum pressure of about 2 bar was found regardless of temperature conditions and ES values. Under isothermal conditions, the resulting improvement of sludge disintegration efficacy as compared to atmospheric pressure was by 22–67% and 26–37% for mixed and secondary sludge, respectively. Besides, mean particle diameter (D[4,3]) of the three sludge types decreased respectively from 408, 117, and 110 μm to about 94–97, 37–42, and 36–40 μm regardless of sonication conditions, and the size reduction process was much faster than COD extraction.     

Leaching of polycyclic aromatic hydrocarbons (PAHs) from industrial wastewater sludge by ultrasonic treatment

Ultrasonic treatment for sludge reduction in wastewater treatment plants (WWTPs) can substantially affect the fate of trace pollutants. However, their fates in the different phases of sludge and mass balances have rarely been reported. In this study, wastewater sludge samples were ultrasonicated at 600 W for 0–30 min. Then, the leaching of the 16 priority polycyclic aromatic hydrocarbons (PAHs) from the sludge solids (sediment) to the liquid phase (supernatant) was investigated. The total concentration of PAHs (∑₁₆ PAHs) in the sludge sediment (2.10 μg/g) was comparable with those of previous worldwide studies. Among the 16 PAHs, naphthalene and acenaphthylene were dominant. The total concentrations of PAHs in the supernatant generally increased with sonication time, indicating that PAHs associated with sludge materials, such as microorganisms, were released into the supernatant. Lighter and more water soluble PAHs were released preferentially into the supernatant in dissolved form, whereas heavier and more hydrophobic PAHs were strongly bound to particles. According to mass balance calculations, 21% of the PAHs in the sludge sediment moved to the supernatant without discernible sonodegradation. An additional experiment for degradation of PAHs supported this interpretation, and several reasons for the no significant sonodegradation were discussed. This result suggests that leaching trace pollutants may significantly contaminate the sludge filtrate after ultrasonic treatment, and therefore their fates should be investigated.     

The effects of waste-activated sludge pretreatment using hydrodynamic cavitation for methane production

Disintegration of waste-activated sludge (WAS) is regarded as a prerequisite of the anaerobic digestion (AD) process to reduce sludge volume and increase methane yield. Hydrodynamic cavitation (HC), which shares a similar underlying principle with ultrasonication but is energy-efficient, was employed as a physical means to break up WAS. Compared with ultrasonic (180–3600 kJ/kg TS) and thermal methods (72,000 kJ/kg TS), HC (60–1200 kJ/kg TS) found to consume significantly low power. A synergetic effect was observed when HC was combined with alkaline treatment in which NaOH, KOH, and Ca(OH)₂ were used as alkaline catalysts at pH ranging from 8 to 13. As expected, the production yield of CH₄ gas increased proportionally as WAS disintegration proceeded. HC, when combined with alkaline pretreatment, was found to be a cost-effective substitute to conventional methods for WAS pretreatment.     

Analysis of fluorotelomer alcohols in soils: Optimization of extraction and chromatography

This article describes the development of an analytical method for the determination of fluorotelomer alcohols (FTOHs) in soil. The sensitive and selective determination of the telomer alcohols was performed by extraction with methyl tert-butyl ether (MTBE) and analysis of the extract using gas chromatography with detection and quantification by mass spectrometry operated in the positive chemical ionization mode. The protonated molecular ion, [M+H]⁺ and a fragment ion (loss of HF + H₂O) m/z 38 less than the molecular ion were monitored to identify tentatively FTOHs in MTBE extracts of contaminated soils. The FTOHs were confirmed by treatment of the extract with a silylation reagent and observing the disappearance of the FTOH response and the appearance of peaks attributable to the [M+H]⁺ ions of the trimethylsilyl derivatives. Mass-labeled FTOHs were used as recovery and matrix internal standards. Recovery experiments on soils shown to be free of endogenous FTOHs at instrument detection limits (IDL) of 16 fg/μL for 6:2 FTOH, 10 fg/μL for 8:2 FTOH and 14 fg/μL for 10:2 FTOH yielded a limit of quantitation (LOQ) of 190, 100, and 160 fg/μL for 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH, respectively when 3 g samples of soil were extracted with 1 mL MTBE. The levels of the 6:2 FTOH, 8:2 FTOH, and 10:2 FTOH in five soils contaminated with FTOHs by exposure to the laboratory atmosphere during air drying were determined. In these air-dried soils, concentrations of FTOHs ranged from non-detectable to 3600 fg/μL (0.6 ng/g) of the 6:2 FTOH in the extract of a commercial topsoil. This method was used to determine even and odd numbered FTOHs from 6:2 through 14:2 in soils from fields that had received applications of sewage sludge. Concentrations of FTOHs in these sludge-applied soils ranged as high as 820 ng/g of dry soil for the 10:2 FTOH.     

Effect of coagulation conditions on the dewatering properties of sludges produced in drinking water treatment

The coagulation and flocculation processes in conventional drinking water treatment generate aggregates which settle to form a sludge waste. This sludge can be dewatered further by thickening, centrifugation and filtration operations in order to recover water and minimise the volume of the waste stream.A range of water treatment sludges generated in the laboratory were characterised according to a phenomenological method that is valid from the dilute free-settling regime to the concentrated cake compression stages. These were compared with plant samples.Experimental results show that raw water natural organic matter (NOM), coagulant dose and coagulation pH affected both the rate and potential extent of dewatering. Similar effects were observed for both aluminium sulfate and ferric chloride. These results suggest that increasing dose or pH leads to an increase in the proportion of rapidly precipitated material in the sludge or flocs, which form looser aggregates and hence exhibit inferior dewatering properties.     

Degradation of chlortetracycline in wastewater sludge by ultrasonication,Fenton oxidation,and ferro-sonication

Residual emerging contaminants in wastewater sludge remain an obstacle for its wide and safe applications such as landfilling and bio-fertilizer. In this study, the feasibility of individual ultrasonication (UlS) and Fenton oxidation (FO) and combined, Ferro-sonication processes (FO) on the degradation of chlortetracycline (CTC) in wastewater sludge was investigated. UlS parameters such as amplitude and sonication time were optimized by response surface methodology (RSM) for further optimization of FS process. Generation of highly reactive hydroxyl radicals in FO and FS processes were compared to evaluate the degradation efficiency of CTC. Increasing in the ratio of hydrogen peroxide and iron concentration showed increased CTC degradation in FO process; whereas in FS, an increase in iron concentration did not show any significant effect (p > 0.05) on CTC degradation in sludge. The estimated iron concentration in sludge (115 mg/kg) was enough to degrade CTC without the addition of external iron. The only adjustment of sludge pH to 3 was enough to generate in-situ hydroxyl radicals by utilizing iron which is already present in the sludge. This observation was further supported by hydroxyl radical estimation with adjustment of water pH to 3 and with and without the addition of iron. The optimum operating UlS conditions were found to be 60% amplitude for 106 min by using RSM. Compared to standalone UlS and FO at 1:1 ratio, FS showed 15% and 8% increased CTC degradation respectively. In addition, UlS of sludge increased estrogenic activity 1.5 times higher compared to FO. FS treated samples did not show any estrogenic activity.     

Electrically enhanced dewatering (EED) of particulate suspensions

Electrically enhanced dewatering has been characterised from first principles using model kaolinite suspensions in both the coagulated and dispersed state and sludge from a potable water treatment plant. The dewatering properties, namely the compressive yield stress or extent of dewatering (quantified as the applied pressure at an equilibrium solids concentration) and the hindered settling function or the resistance of fluid flow (quantified as the rate of fluid expression at an equilibrium solids concentration), have been measured as a function of electric field strength. For both the dispersed and coagulated kaolinite suspensions, the rate of dewatering was found to improve at all applied pressures and with increasing applied electrical field strength, up to 1250 V m⁻¹. Improvements in the extent of dewatering were also observed but only for the coagulated suspension. The greatest improvements in dewatering were observed at the lowest applied pressures. Improvement in suspension compressibility is only predicted for the specific case where the feed to the process is both coagulated and at a neutral or low pH. For the potable water sludge, improvements in the rate of dewatering were observed at all pressures above 10 kPa. At lower pressures, the low particle surface charge caused a slow onset of electro-osmotic effects. In general, the results indicate that the application of an electric field in situ during dewatering primarily helps to increase the rate of dewatering and the benefit of this methodology is predicted to be for suspensions that exhibit low permeability at low solids concentrations in applications where the pressure is low or the process is gravity driven.     

氢化物发生-原子荧光法测定污泥中的痕量汞

针对污泥中复杂基质的特点,进行了三种样品湿法消解体系、还原剂、载流等实验条件的研究,确定了HNO₃-HClO₄湿法消解体系、5%硝酸载流和0.1%硼氢化钠还原剂、以及标准和样品中5％硝酸+0.05%重铬酸钾混合溶液的酸度介质等,用以测试污泥中痕量Hg的实验条件。该方法快速、准确,易操作,检出限为0.06 μg·L-1,连续11次测定4.0 μg·L-1Hg标准溶液相对标准偏差为2.0%,实验建立的氢化物原子荧光(HG-AFS)测定污泥中痕量Hg的测试方法具有较好的应用前景。     

微波消解-石墨炉原子吸收法测定活性污泥中的钴

建立了一种微波消解样品 ,石墨炉原子吸收法测定活性污泥中钴含量的方法。实验选用不同的消解体系及不同基体改进剂 ,进行了对比实验 ,在优化实验条件下 ,测定了 3个经中温 (33— 35℃ )厌氧微生物消化后的剩余活性污泥样品 ,并做了常压消解对比实验 ,空白和加标回收率实验。样品中钴加标回收率>90 % ,相对标准偏差 <6 % ,检出限为 (3s) 0 .0 5 31ng· g-1,该法具有简便、快速、准确、空白值低、重现性好等优点     

Determination of organochlorine pesticides in sewage sludge by matrix solid-phase dispersion and gas chromatography-mass spectrometry

A method based on matrix solid-phase dispersion (MSPD) has been developed for the determination of 16 organochlorine pesticides (OCs) in sludge from municipal sewage plants. Samples of lyophilized sludge were blended with alumina, placed in small columns and OCs extracted with dichloromethane assisted by sonication. Purification of the extracts was accomplished by solid-phase extraction on C₁₈ columns and OCs were eluted with acetonitrile. Analyses were performed by gas chromatography with electron impact mass spectrometric detection in the selected ion monitoring mode (GC–MS-SIM) using deuterated OCs as internal standards. The limits of detection were between 0.03 ng/g for 4,4′-DDE and 0.7 ng/g for endrin aldehyde.

Levels of OCs were determined in sewage sludge collected from 19 water treatment plants located in the province of Madrid (Spain). In all of the analyzed samples, aldrin was the compound most often found with a mean concentration of 76 ng/g. Endosulfan-I, -BHC, 4,4′-DDE and 4,4′-DDT were also present at high concentrations, with average values ranging from 32.3 to 74.3 ng/g. OCs were detected in all of the samples, with a total concentration ranging from 52 to 528 ng/g dry weight.