Impact of different structures of biochar on decreasing methane emissions from sewage sludge composting.

Methane (CH4) emissions from sewage sludge composting can be reduced by using biochar more effectively. This study investigates the impact of different structure of biochar on CH4 emissions during sewage sludge composting. Corncob biochar (CB, pore size = 35.3990 nm), rice husk biochar (RB, pore size = 3.4242 nm) and wood biochar (WB, pore size = 1.6691 nm) were applied to the composting. The results showed that biochar decreased CH4 emissions, mainly through the indirect effect of improving the pile environment. Compared with the control group (CK), the biochars with smaller pore structures, WB and RB, reduced CH4 emissions by 41.83% and 33.59%, respectively, compared to only 8.20% for CB, which has a larger pore structure. In addition, RB and WB increased the free air space (FAS) by more than 10% and CB improved the microbial diversity. Methanothermobacter was reported in WB and RB, with an abundance of 45.45% in WB. Redundancy analysis (RDA) showed that pore size was positively correlated with the CH4 emission rate. The results of this study can provide a theoretical reference for CH4 reduction from biochar co-composting of sewage sludge.

Effect of organic concentration on biological activity and nitrogen removal performance in an anammox biofilm system.

The effects of different concentrations of organic matter on the biological activity and nitrogen removal performance of the anaerobic ammonium oxidation (anammox) system was studied. The results showed that under the conditions of low influent total organic carbon (TOC ≤ 100 mg/L), the activity rate of anammox bacteria was basically unaffected, the anammox bacteria and denitrifying bacteria formed a good synergistic effect, and the maximum total nitrogen (TN) removal efficiency reached 95.77%. However, when the influent TOC concentration was up to 200 mg/L, the activity of anammox bacteria was seriously inhibited. At this time, denitrification becomes the main pathway of nitrogen removal, the effluent ammonia nitrogen content increases, and the TN removal efficiency decreases to 64.17%. High-throughput sequencing analysis showed that with the increase in organic matter concentration, the relative abundance of Proteobacteria and Planctomycetes changed significantly. In particular, the relative abundance proportion of Proteobacteria increased from 21.06% to 25.57%, the Planctomycetes dropped from 10.01% to 3.03% and the Candidatus Brocadia genus had the largest decrease. In conclusion, the concentration range of organic matter for collaborative denitrification was proposed in this study, which provided theoretical reference for the practical application of anammox biofilm process.

Determination of water content in municipal sludge by multiple headspace extraction gas chromatography.

This paper reports a new method for the determination of sludge water content by a multiple headspace extraction gas chromatographic (MHE-GC) method. It is based on measuring the GC signals for the water vapor in a sample vial from the first five headspace extractions, from which the water content in the sludge sample can be extrapolated according to the established calculation equation. The results show that the method has a good repeatability (the relative standard deviation is less than 1%) and accuracy. The maximum relative difference is less than 16% compared to the reference method. The present method is very simple and efficient, and suitable for rapid sample testing in related applications.

Determination of activity of denitrifying enzyme in soil samples by a headspace gas chromatographic technique.

This paper reported a headspace gas chromatography (HS-GC) for the determination of denitrifying enzyme activity in soil samples. It was based on measuring the NO2 signal in a set of closed/air-free vials containing soil samples that incubated at the designated conditions. The results showed that the method has a good measurement precision (RSD < 5.0%) and reasonable accuracy for determining the denitrifying enzyme activity in soil samples. It is simple and efficient, and very suitable to be used in batch sample analysis.

Effect of emerging pollutant fluoxetine on the excess sludge anaerobic digestion.

Fluoxetine (FLX), an emerging pollutant, has been detected in the sewage and excess sludge (ES) at substantial levels. So far, however, the impacts of FLX on the ES anaerobic digestion and the related mechanisms have never been investigated. In this work, the effects of FLX on the ES anaerobic digestion were explored by the batch test under moderate temperature condition. The results indicated the effect of FLX on ES digestion was dose-dependent. When FLX was at a low dose (0.1 mg/kg), FLX had no significant impact on the methane generation from the ES digestion. However，when FLX was 2.0 mg/kg, the cumulative methane production was only 91.2 ± 4.3 mL/g volatile suspended solids (VSS), which was about 59.9 ± 3.4% of the blank (without FLX). Mechanisms revealed that the presence of FLX has inhibited hydrolysis, acidification and methanogenesis. Enzyme activity analysis showed that FLX inhibited the activities of key enzymes in the process of hydrolysis, acidification and methanogenesis. The results of this work are of great significance to explain the role of FLX in the process of ES fermentation, and provide some reference for the subsequent utilization of ES.

Municipal solid waste incineration fly ash exposed to carbonation and acid rain corrosion scenarios: Release behavior, environmental risk, and dissolution mechanism of toxic metals.

This study investigated the leaching behavior, environmental risk, and dissolution mechanism of toxic metals (TMs) in solidified/stabilized municipal solid waste incineration fly ash (MSWI FA) exposed to alternative "carbonation + acid rain corrosion" disposal scenarios. The content of TMs (mg/kg) showed a trend of Zn (12,187.10 ± 168.60) > Pb (3374.43 ± 66.12) > Cu (1055.14 ± 32.52) > Cr (127.95 ± 8.12) > Cd (119.05 ± 6.26) > Ni (49.50 ± 3.20). Initial leaching of CO2-saturated water (CSW) and replacement of simulated acid rain (SAR) increased the environmental risk of leached TMs. The results of "average release rate" (mg/(kg·d)) of TMs indicated that Zn (0.8307)/Cu (0.0278)/Cd (0.0109) and Cu (0.0581)/Cr (0.001176)/Ni (0.004339) in phosphoric acid stabilized FA and Pb (0.0753)/Cr (0.001921)/Ni (0.00111) and Pb (0.0656)/Zn (1.0560)/Cd (0.0050) in Portland cement solidified FA were the key "problem TMs" during carbonation and acid rain corrosion, respectively. CSW leaching increased the independent environmental risk of most TMs in residual FA (especially Zn/Cd) due to the increased carbonate-bound fraction. Compared with independent carbonation, alternative "carbonation + acid rain corrosion" contributed to a higher comprehensive environmental risk for TMs in residual FA. CSW leaching system was an indirect carbonation based on CO2-water and FA matrix, in which "nucleation and dissolution" of carbonates and "immobilization and dissolution" of TMs coexisted. The dissolution mechanism of TMs was mainly controlled by reaction equilibrium of nucleation and dissolution of carbonates containing TMs. Dissolution and nucleation were the dominant mechanism in the early and later periods of CSW leaching, respectively. Carbonate layer dissolution, H+ corrosion/displacement, and counter-ion effect (SO42- > NO3- > Cl-) were the main mechanisms affecting TM dissolution during SAR leaching.

In-situ determination of the observed yield coefficient of aerobic activated sludge by headspace gas chromatography.

This paper describes a headspace gas chromatographic (HS-GC) method for the in-situ determination of the observed yield coefficient (Yobs) of aerobic activated sludge from domestic wastewater treatment plants. It is based on the measurement of oxygen and carbon dioxide in samples that have been incubated in headspace vials for relatively short periods of time. The method has good precision (the relative standard deviation < 5.46%) and accuracy (the relative differences < 9.23% when compared with the data from the reference method). The new method is much simpler and more efficient than the reference methods and should greatly facilitate the testing in aerobic activated sludge related applications, such as system design, operation and management.

Preparation of cotton-based fibrous adsorbents for the removal of heavy metal ions.

Cotton fiber functionalized with tetraethylenepentamine and chitosan (CTPC) was prepared and used as absorbents for the removal of Cu(II), Pb(II) and Cr(III) ions from aqueous solution. The functionalized materials (CTPC) were characterized by SEM/EDX, FTIR, BET and XRD to confirm the characterization and structural changes of fibers before and after the modifying process. The adsorption performance of CTPC was investigated with different pH, contact time and initial concentration of three kinds of metal ions. Results showed that the maximum adsorption capacity was 81.97 mg g-1 for Cu(II), 123.46 mg g-1 for Pb(II) and 72.99 mg g-1 for Cr(III) based on the Langmuir isotherm model at optimal pH (5.0). Adsorption kinetics of CTPC fibers for Cu(II), Pb(II), and Cr(III) ions followed the pseudo-second-order model. The adsorption-desorption experiments demonstrated that CTPC showed better stability, and CTPC would be an effective and practical material for the treatment and recycling of heavy metal ions in the wastewater.

Simple and efficient dual-wavelength spectroscopy for the determination of organic matter in sewage sludge from wastewater treatment.

In this study, a dual-wavelength spectroscopic method for rapid determination of organic matter in sludge was developed. The contents of the organic matter were calculated by determining the consumption of potassium dichromate (K2Cr2O7) based on the production of trivalent chromium ions (Cr3+). Cr3+ could be determined by subtracting the absorption at 800 nm (spectral interference) from the absorption at 650 nm (only contributed by Cr3+). The results showed that the relative standard deviation in the test was less than 5%. The same set of samples was used and when the content of organic matter was more than 150 g kg-1, the relative difference between the spectroscopic method and titration method was within 1%. Furthermore, the method does not require calibration based on the standard samples. In conclusion, the present method is simple, reliable, accurate and suitable for application in mass testing for sludge samples.

Determination of total phosphorus in soil and sludge by an effective headspace gas chromatographic method.

This paper reported a novel method for the determination of total phosphorus (TP) content in soil and sludge by a headspace gas chromatography (HS-GC) method. It was based on a reaction between the soluble phosphate in the digestion solution and calcium oxalate solid to form a calcium phosphate precipitate and release oxalate ions, which can react with permanganate to form carbon dioxide, which was then measured by HS-GC. The results showed the complete conversion of phosphate (meanwhile to free oxalate ions in calcium oxalate) in 15 min at 60 °C. The present method has good repeatability (RSD < 2.6%) and good accuracy (RD < 7.3%) compared to the reference method. Therefore, the present HS-GC method can become a more effective method for determining the TP content in soil and sludge samples.

[Mechanism of Action of Activated Sludge Properties in Nitrogen Removal by Endogenous Denitrification Through an Intelligent Aeration-controlled A/O Process].

In order to evaluate the mechanism of action of activated sludge properties in nitrogen removal by endogenous denitrification (henceforth EDNR), a new kind of automatic oxygen supply device(AOSD), was applied to the A/O process. The domestication effect of the aeration mode on the activated sludge properties and microbial communities was investigated under the intelligent aeration-controlled A/O process (I-A/O)and the continuous aeration A/O process (C-A/O). The results demonstrated that the effluent NH4+-N and NO2--N components showed obvious accumulation efficiencies and activated sludge generated conspicuous limited bulking in the I-A/O process. Domesticated sludge in the I-A/O process was able to enrich more SCOD to transfer into the polymeric substances as Gly, under a rich exogenous carbon supply state, and stimulated nitrogen removal by endogenous denitrifying under a scarce exogenous carbon supply state. The EDNR rate went up to 0.83 mg·(L·h)-1 in the I-A/O process, which was more than that achieved by the C-A/O process. The microbial communities in the two processes were evaluated by the Illumina HiSeq high-throughput sequencing technology. The results showed that there was no obvious difference in the sludge microbial community diversity between the two processes, but the Candidate division TM7 proliferated in the I-A/O process, and become the abundant taxa to prompt limited filamentous sludge bulking and Gly storage capability enhancement. The oxygen supply mode of AOSD made the activated sludge properties and microbial communities to be screened selectively in the new environment, aerobic heterotrophic bacterial activity to decline, and endogenous denitrifying action to strengthen, which made the I-A/O process implement a kind of dynamic balanced state that limited the DO demand.

Remediation of chromite ore processing residue by pyrolysis process with sewage sludge.

The present work developed a novel technique to treat chromite ore processing residue (COPR). The process involved mixing the COPR with sewage sludge followed by pyrolysis. The gaseous organic fraction generated during pyrolysis of sludge was beneficial to Cr(VI) reduction. Process variables, such as the amount of sludge added to COPR (sludge-to-COPR (S/C) ratio), heating temperature, reaction time and particle size, were systematically varied, and their influences on the Cr(VI) reduction in COPR were investigated. Cr(VI) content had decreased greatly, from 3384 mg kg(-1) for untreated COPR to less than 30 mg kg(-1) for COPR treated at 600 degrees C.

Factors affecting the sorption of trivalent chromium by zeolite synthesized from coal fly ash.

This research was initiated to determine the effects of different constituents and properties of zeolite synthesized from fly ash (ZFA) on Cr(III) sorption. The uptake of Cr(III) by ZFA was influenced greatly by pH, increasing with the increase in pH. The pH was controlled mainly by calcium-related components (especially CaCO3 and free CaO) and zeolite components in ZFAs. Sorption maximum of Cr(III) (Qm), determined by a repeated batch equilibration method, ranged from 22.29 to 99.91 mg/g for the 14 ZFAs. The Q(m) value correlated significantly with Ca-related components. The correlation coefficients were 0.9467, 0.5469, 0.7521, and 0.9195 for total Ca, CaCO3, CaSO4, and f.CaO, respectively. The Qm value was also closely related to cation-exchange capacity (r=0.6872) and specific surface area (r=0.7249). Correlation coefficients of Qm with dissociated Fe2O3 and Al2O3 were much higher than those of total Fe and total Al contents, respectively. It was suggested that, in ZFAs, zeolite and iron oxide acted as ion exchanger and adsorbent for Cr(III), respectively, while Ca components elevated the pH of the reaction system and consequently promoted ion exchange and adsorption and caused the surface precipitation of chromium hydroxide.

Changes in chlorinated organic pollutants and heavy metal content of sediments during pyrolysis.

BACKGROUND: There has been an increasing concern about the treatment and disposal of contaminated sediment from dredged rivers, harbors or estuaries due to the accumulated toxic organics such as dioxins and inorganics, particularly heavy metals like Cr, Pb, Zn, Cu, Hg and Cd. However, considering the huge amount of materials and financial costs involved, any candidate technology must ultimately result in reusable, residual by-products. This can only be made possible if the toxic pollutants are removed or stabilized in the raw sediment and then fed back into the materials cycle. Currently, we are developing a pyrolysis process for the commercial-scale cleanup of dioxins and heavy metal-contaminated river sediment to yield reusable char for various economical applications. In this connection, this paper describes our preliminary investigation into the extent of dioxins and heavy metal volatilization from actual contaminated sediment. The stabilization of certain metallic species, particularly Cr ions, was studied. METHODS: Laboratory scale pyrolysis experiments were conducted using a special, horizontal lab-scale pyrolyzer. Sediment samples from Shanghai Suzhou Creek and Tagonoura harbor were pyrolyzed in the reactor under nitrogen gas at 800 degrees C and different retention times of 30, 60 and 90 min. A constant heating rate of 10 degrees C min(-1) was employed. The pyrolysis gas was first allowed to pass through a cold trap to condense the tar. Uncondensed gases were then channeled through a column containing an adsorbent (XAD-2 Resin) for dioxins. Heavy metal concentrations in the initial and final sediment residues were analyzed by ICP (Nippon Jarrel-Ash) following their acid and alkali (for Cr6+) digestion. Dioxin contents of the pyrolysis char, tar, and exhaust gases in the dioxin adsorbent were also determined. For comparative purpose, thermal treatment under air flow was conducted. RESULTS: The data for the removal of heavy metals from Suzhou Creek sediment showed very significant reductions in Pb, Zn and Cr6+ content of the sediment at this condition. Percentage removals were 42.4%, 60.8% and 42.2%, respectively. The disappearance of Cr6+ was due to reduction reactions rather than volatilization, since the total Cr content remained almost unchanged. Other heavy metals such as Cu, Fe and Ni showed very minimal reductions. Nonetheless, Toxicity Characteristics Leaching Procedure (TCLP) tests confirmed that these residual heavy metals were rather stable in the pyrolysis char. Reduction of toxic Cr6+ at 42.2% has also been achieved by pyrolysis (with N2) as opposed to the more than 580% increase in Cr6+ observed during thermal oxidation (with air). DISCUSSION: Pyrolysis also removes toxic organics, particularly dioxins, from the sediment. For the total dioxins, removal percentage of 99.9999% was achieved even at the lowest retention time of 30 min. Almost all polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) were removed at any retention time. The TEQs detected from the solid residues were mainly contributed by dioxin-like PCBs, yet these were present in relatively trace quantities. At the shortest retention time of 30 min, only 0.000085 pg-TEQ g(-1) of polychlorinated biphenyls (PCBs) was detected in the pyrolysis char. Furthermore, the residual PCBs have very low toxicity ratings and none of the highly toxic PCBs, which were initially present in the sediment such as 3,3',4,4',5-PeCB and 3,3',4,4'5,5'-HxCB, were detected in the char. Results further confirmed that most of the dioxins that were removed were transferred to the gas phase so that volatilization may be considered as the main mechanism for their removal. CONCLUSION: Some heavy metals, particularly Pb and Zn, can be volatilized under N2 pyrolysis at 800 degrees C. Pyrolysis also prevented the formation of more toxic Cr6+ ions and, at the same time, resulted in its reduction by around 42.2%, in contrast to the 580% increase during thermal oxidation. PCDDs and PCDFs have been removed and were not formed in the solid products over the retention time range of 30-90 min at 800 degrees C. Dioxin-like PCBs mostly remained and a retention time of 30 min was found to be sufficient for its maximum removal. Recommendations and Perspectives. With the above results, a temperature of 800 degrees C at a retention time of 30 min is sufficient for the removal of total dioxins and of some heavy metals by volatilization. It is, however, necessary to destroy the dioxins as well as recover heavy metals in the gas phase. Stability of remaining heavy metals in the char also needs to be confirmed by leaching tests. These are the major concerns, which we are currently evaluating in order to establish the feasibility of our proposed, large scale pyrolysis system for sediment treatment.

Removal of phosphate from aqueous solution by zeolite synthesized from fly ash.

Fifteen Chinese fly ashes were converted hydrothermally into zeolites, and phosphate immobilization capacity (PIC) of the synthesized zeolites and the corresponding raw fly ashes were determined using an initial phosphate concentration of 1000 mg/L. Results showed that there was a remarkable increase in PIC (from 1.2 to 7.6 times) following the synthesis process. Fractionation of immobilized phosphorus indicated that Fe+Al-P increased most significantly and consistently among all the phosphorus fractions following the conversion of fly ash to zeolite. The PIC and Ca+Mg-P were closely related to Ca content (with r values of 0.9683 and 0.9651, respectively) rather than Mg content (with r values of 0.3920 and 0.3212, respectively). The r values of PIC and Fe+Al-P with Fe content (with r values of 0.4686 and 0.6385, respectively) were higher than those with Al content (with r values of -0.7857 and -0.3770, respectively). Although calcium and iron components were mainly involved in phosphate immobilization, there was no significant change of Ca and Fe content following the conversion of fly ash to zeolite. Increase in dissociated Fe(2)O(3) and specific surface area probably accounted for the enhancement in PIC of synthesized zeolites compared with corresponding fly ashes. The PIC value of zeolites showed a significant correlation with dissociated Fe(2)O(3) (r=0.6186). The specific surface area increased 26.0-89.4 times as a result of the conversion of fly ash to zeolite. The maximum removal of phosphate occurred within different pH ranges for zeolites which were synthesized from high, medium and low calcium fly ashes and this behavior was explained by the reaction of phosphate with calcium and iron components.

Removal of PCDD/Fs and PCBS from sediment by oxygen free pyrolysis.

Abstract: Few studies have dealt on the evaluation of volatilization and decomposition reactions of dioxins from sediment by oxygen free pyrolysis. In this study, the performance of pyrolysis on the removal of dioxins from sediment was investigated. Dioxin concentrations of the raw sediment and the solid residues after pyrolysis were analyzed at different conditions. Results showed a removal efficiency of 99.9999% for total dioxins at 800 degrees C and retention time of 30 min. All the polychlorinated dibenzo-furans (PCDFs) have been removed and were not formed in the solid residues at the retention time range of 30-90 min at 800 degrees C. Close to 100% removal of polychlorinated dibenzo-p-dioxins (PCDDs) was also achieved. Only trace PCDDs were detected in the solid yields at a retention time of 60 min. The highest removal efficiency of polychlorinated biphenyls (PCBs) was more than 99.9994% at a retention time of 30 min. During cooling period following pyrolysis, however, the concentration of total dioxins in solid residues increased 130 times as compared to that of the raw sediment under air atmosphere. This confirmed that some complex reactions do occur to form PCDD/Fs and PCBs from 800 to 400 degrees C in the presence of oxygen. Oxygen-free atmosphere therefore can prevent formation of dioxin during thermal process thus generating clean solid residues.