Valorization of fat balls and primary scum from wastewater treatment: a promising renewable lipid feedstock for biodiesel production

We investigated the potential of waste materials from wastewater treatment plants (WWTPs) to serve as an alternative lipid feedstock for biodiesel production. The average lipid recoveries from fat balls (46.4%) and primary scum (49.5-54.5%) were higher than the lipid recovery of primary sludge (15.8-16.4%). The yield of biodiesel produced from the extracted lipids ranged from 5.7 to 20.1%. There were considerable site- and season-dependent variations in the characteristics of the lipid waste materials. Radiocarbon analysis indicated the presence of fossil-derived carbon (26.0-42.0%) in the biodiesel obtained from wastewater lipids. Finally, we estimated the potential for biodiesel production from WWTP-derived lipids; about 333.0 metric tons of biodiesel per year could be produced from fat balls and primary scum in Japan. The results indicate that lipid-rich materials from WWTPs represent a valuable alternative feedstock for biodiesel production.

Model for projecting the generation of used disposable diapers in the era of depopulation and aging in Japan

Japan has entered a period of depopulation and aging ahead of any other country. One concern in an aging population is increases in the generation of used disposable diapers. The use of disposable diapers, which are largely composed of plastic, can be an important issue as we work towards building a carbon-free society and break away from using fossil-derived plastics. This study aimed to develop a model to project the future generation of used disposable diapers in each municipality in Japan through 2045 and to identify the effects on municipal solid waste (MSW) management. We revealed the per capita generation of used disposable diapers, distinguishing disposable diaper products, urine and faeces in an online survey of 2000 respondents. The generation of used disposable diapers was estimated to increase in general, but the amount was projected to decrease in rural areas where the population of elderly people would decline. The proportion of used disposable diapers in combustible waste was projected to increase by 2045 in almost all municipalities of Mie Prefecture. Based on the scenario in which disposable diaper products would become lighter in the future because of technical improvements, we concluded that the impact of the decrease in the lower heating value (LHV) of used disposable diapers on the incineration process cannot be ignored in the future.

Co-incineration effect of sewage sludge and municipal solid waste on the behavior of heavy metals by phosphorus

The effects of sewage sludge phosphorus (P) content on heavy metal behavior during co-incineration of sewage sludge and municipal solid waste (MSW) were evaluated. Thermogravimetric differential thermal analysis revealed that MSW incineration was mainly caused by organic matter and fixed carbon, while sewage sludge incineration was caused by volatile matter. During co-incineration, the peak weight loss at 460 °C shifted to slightly higher temperatures and the sludge ratio increased, indicating that interaction effects during co-incineration delayed pyrolysis and polymer/fixed carbon incineration. The residual heavy metal ratios after mono-incineration of sewage sludge were higher than those after MSW mono-incineration. The Cl content of MSW (0.757%) was much higher than that of sewage sludge (0.068%), which resulted in the conversion of heavy metals into metal chlorides and then volatilized during MSW mono-incineration. A synergistic effect of co-incineration was evident for Cu, but not for lead (Pb) or cadmium (Cd). X-ray absorption fine structure (XAFS) measurement revealed that Cu in MSW ash was in the form of CuO(s), but was Cu₃(PO₄)₂ in sewage sludge and co-incineration ashes. CuO(s) is relatively unstable and may be transformed to CuO(g) or CuCl(s) before volatilizing at high temperature or in the presence of Cl. Phosphorus has the effect of stabilizing Cu in sewage sludge during co-incineration.

In-situ biogas upgrading with H2 addition in an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge

Biological in-situ biogas upgrading is a promising approach for sustainable energy-powered technologies. This method increases the CH₄ content in biogas via hydrogenotrophic methanogenesis with an external H₂ supply. In this study, an anaerobic membrane bioreactor (AnMBR) was employed for in-situ biogas upgrading. The AnMBR was operated in semi-batch mode using waste activated sludge as the substrate. Pulsed H₂ addition into the reactor and biogas recirculation effectively increased the CH₄ content in the biogas. The addition of 4 equivalents of H₂ relative to CO₂ did not lead to appreciable biogas upgrading, although the acetate concentration increased significantly. When 11 equivalents of H₂ were introduced, the biogas was successfully upgraded, and the CH₄ content increased to 92%. The CH₄ yield and CH₄ production rate were 0.31 L/g-VS_input and 0.086 L/L/d, respectively. In this phase of the process, H₂ addition increased the acetate concentration and the pH because of CO₂ depletion. Compared with a continuously-stirred tank reactor, the AnMBR system attained higher CH₄ content, even without the addition of H₂. The longer solid retention time (100 d) in the AnMBR led to greater degradation of volatile solids. Severe membrane fouling was not observed, and the transmembrane pressure remained stable under 10 kPa for 117 d of continuous filtration without cleaning of the membrane. The AnMBR could be a promising reactor configuration to achieve in-situ biogas upgrading during sludge digestion.

Mercury emission profile for the torrefaction of sewage sludge at a full-scale plant and application of polymer sorbent

We evaluated mercury (Hg) behavior in a full-scale sewage sludge torrefaction plant with a capacity of 150 wet tons/day, which operates under a nitrogen atmosphere at a temperature range of 250-350 °C. Thermodynamic calculations and monitoring results show that elemental Hg (Hg⁰) was the dominant species in both the pyrolysis gas during the torrefaction stage and in the flue gas from downstream air pollution control devices. A wet scrubber (WS) effectively removed oxidized Hg from the flue gas and moved Hg to wastewater, and an electrostatic precipitator (ESP) removed significant particulate-bound Hg but showed a limited capacity for overall Hg removal. Hg bound to total suspended solids had a much higher concentration than that of dissolved Hg in wastewater. Total suspended solid removal from wastewater is therefore recommended to reduce Hg discharge. Existing air pollution control devices, which consist of a cyclone, WS, and ESP, are not sufficient for Hg removal due to the poor Hg⁰ removal performance of the WS and ESP; a further Hg⁰ removal unit is necessary. A commercial packed tower with sorbent polymer catalyst composite material was effective in removing Hg (83.3%) during sludge torrefaction.

Liquefied dimethyl ether based multi-stage extraction for high efficient oil recovery from spent bleaching clay

With the increasing production of spent bleaching clay (SBC), the recovery of the waste oil in SBC is becoming an important and urgent needs for our environment and economy. In this research, we have developed a new effective recovery technique to recover oil from SBC by use of liquefied dimethyl ether (DME). Over 65 wt% oil and 81% wt.% oil are efficiently recovered from SBC under equilibrium single-stage extraction conditions and multi-stage extraction conditions, respectively based on the systematically investigation to the effects of the DME/SBC ratio, extraction time, stirring speed and extraction stage number on oil recovery via a batch extractor. Compared with using other extraction solvents, the extraction solvent DME can be reused without heating and therefore significantly reduce the energy consumption during the oil recovery process. In addition, the quantitative oil extraction relationship is derived from the adsorption equilibrium model and is well verified by experimental results. The results show a great potential for using this oil recovery technique in SBC as well as in the large amount of oily sludge and oil sands.

Evaluation of a sludge-treatment process comprising lipid extraction and drying using liquefied dimethyl ether

Liquefied dimethyl ether (DME) was used to extract lipids from sewage sludge. Factorial experimental analyses were used to evaluate the influence of different variables on raw lipid extraction and sludge drying. The DME method was compared with the Bligh and Dyer (B&D) method for three undigested and two anaerobically digested dewatered sludges. The results indicate that although the raw lipid yield of the B&D method was 5% higher than that of the DME method, the proportion of fatty acid methyl esters (FAMEs) in raw lipids extracted by the DME method was 14.1-33.4%, almost twice that of the B&D method. The FAME composition varied according to sludge type, and the dewatered undigested sludges contained more unsaturated fatty acids (e.g. C18:1, C18:2). The lower heating value (LHV) of product by the DME method ranged from 3.74 to 5.70 MJ/kg compared with 1.21-0.39 MJ/kg for the B&D method. Also, DME could be reused at least five times without significantly reducing the lipid yield and drying efficiency. Finally, an economic analysis of the DME, the conventional solvent extraction, and the heat-drying methods was conducted.

Microalgae preparation and lipid extraction by subcritical dimethyl ether

Biodiesel produced from microalgae is a potential alternative due to the high growth rate of microalgae, the possibility of using nonarable land, and high lipid accumulation rate. Microalgae cultivation, cell harvesting and disruption are the important steps before lipid extraction for the biodiesel. In the co-submission article, the details of the whole process cannot be clearly explained. In this regard, we present the details of methods on parameter of photo-bioreactor for cultivating microalgae, flocculation tests to determine optimal flocculant dosage in harvesting, parameter of Dimethyl ether (DME) subcritical extraction device and full-factorial design for investigating the influence of extraction time, initial water content and DME dosage on the extraction performance. It will allow researchers to reproduce these experiments.

• The method shows a cell disruption assisted lipid extraction by subcritical dimethyl ether.

• Model is built from full-factorial design to investigate multi-factor influence.

• Differential scanning calorimetry can be applicable to measure free water content.

Influence of water content and cell disruption on lipid extraction using subcritical dimethyl ether in wet microalgae

Subcritical dimethyl ether, a green solvent, was used to extract lipids from microalgae. The effect of the water content on the process was firstly investigated. Secondly, microalgal samples were subjected to five cell disruptions, and the effects on raw lipid and fatty acid methyl ester, and its profile were evaluated. Among them, heating, microwave, and ultrasonic treatments greatly improved extraction. Mechanism analysis revealed the improvements by the three treatments were due to increased cell wall permeability rather than to complete cell disruption. After the extraction, microalgal cells with lipid being well-extracted were shriveled with extensive surface folds, indicating a loss of intracellular substances, but the cell structure was undamaged. As for dewatering performance, extraction process removed almost all of the free water but left bound water. Finally, the potential of the residues after lipid extraction to serve as solid fuel was evaluated by combustion characteristics and heating value calculation.

Effect of pH on the performance of an acidic biotrickling filter for simultaneous removal of H2S and siloxane from biogas

Acidic biotrickling filters (BTF) can be used for simultaneous removal of hydrogen sulfide (H₂S) and siloxane from biogas. In this study, the performance of a BTF under different acidic pH conditions was investigated. The removal profile of H₂S showed that 90% of H₂S removal was achieved during the first 0.4 m of BTF height with down-flow biogas. Decamethylcyclopentasiloxane (D5) removal decreased from 34.5% to 15.6% when the pH increased from 0.88 to 3.98. Furthermore, the high partition coefficient of D5 obtained in under higher pH condition was attributed to the higher total ionic strength resulting from the addition of sodium hydroxide solution and mineral medium. The linear increase in D5 removal with the mass transfer coefficient (k_L) indicated that the acidic recycling liquid accelerated the mass transfer of D5 in the BTF. Therefore, the lower partition coefficient and higher k_L under acidic pH conditions lead to the efficient removal of D5. However, the highly acidic pH 0.9 blocked mass transfer of H₂S and O₂ gases to the recycling liquid. Low sulfur oxidation activity and low Acidithiobacillus sp. content also deteriorated the biodegradation of H₂S. Operating the BTF at pH 1.2 was optimal for simultaneously removing H₂S and siloxane.

Survey of elemental composition in dewatered sludge in Japan

The elemental composition of 120 dewatered sludge samples from 32 wastewater treatment plants in Japan was analyzed, and the influential factors determining sludge elemental composition were clarified. Through Hayashi's quantification method I, the relationship and influence of each element to the dominant categories were confirmed, and the correlation between the elements was also analyzed. The Van Krevelen diagram was used to determine the similarity in organic contents between sludge and biomass/fossil fuels. Principal component and cluster analyses were used to verify the identification of influential factors. Finally, a standard composition of dewatered sludge in Japan was defined based on different sewage collection systems and digestion processes, shown to have the greatest influence on sludge composition. The potential of sludge for agricultural and cement industrial recycling was also assessed.

Effective lipid extraction from undewatered microalgae liquid using subcritical dimethyl ether

BACKGROUND

Recent studies of lipid extraction from microalgae have focused primarily on dewatered or dried samples, and the processes are simple with high lipid yield. Yet, the dewatering with drying step is energy intensive, which makes the energy input during the lipid production more than energy output from obtained lipid. Thus, exploring an extraction technique for just a thickened sample without the dewatering, drying and auxiliary operation (such as cell disruption) is very significant. Whereas lipid extraction from the thickened microalgae is complicated by the high water content involved, and traditional solvent, hence, cannot work well. Dimethyl ether (DME), a green solvent, featuring a high affinity for both water and organic compounds with an ability to penetrate the cell walls has the potential to achieve this goal.

RESULTS

This study investigated an energy-saving method for lipid extraction using DME as the solvent with an entrainer solution (ethanol and acetone) for flocculation-thickened microalgae. Extraction efficiency was evaluated in terms of extraction time, DME dosage, entrainer dosage, and ethanol:acetone ratio. Optimal extraction occurred after 30 min using 4.2 mL DME per 1 mL microalgae, with an entrainer dosage of 8% at 1:2 ethanol:acetone. Raw lipid yields and its lipid component (represented by fatty acid methyl ester) contents were compared against those of common extraction methods (Bligh and Dryer, and Soxhlet). Thermal gravimetry/differential thermal analysis, Fourier-transform infrared spectroscopy, and C/H/N elemental analyses were used to examine differences in lipids extracted using each of the evaluated methods. Considering influence of trace metals on biodiesel utilization, inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectroscopy analyses were used to quantify trace metals in the extracted raw lipids, which revealed relatively high concentrations of Mg, Na, K, and Fe.

CONCLUSIONS

Our DME-based method recovered 26.4% of total raw lipids and 54.4% of total fatty acid methyl esters at first extraction with remnants being recovered by a 2nd extraction. In additional, the DME-based approach was more economical than other methods, because it enabled simultaneous dewatering with lipid extraction and no cell disruption was required. The trace metals of raw lipids indicated a purification demand in subsequent refining process.

Evaluation of flocculation performance of amphoteric flocculant when harvesting microalgae Coccomyxa sp. KJ by response surface methodology

A response surface methodology was used to investigate the flocculation performance of an amphoteric flocculant (acrylamide-methacrylic acid ester-acrylic acid copolymer [ACPAM]) for harvesting microalgae. After three potential influencing factors (pH, dosage, and the stirring speed of an intensive mixing step ω₁) passed screening in experiments using a Plackett-Burman design, steepest ascent experiments were conducted to identify the parameters for Box-Behnken assessments. In those assessments, ω₁, dosage, ω₁², dosage², and ω₁ ∙ dosage were identified as significant factors. This model was optimized by removing nonsignificant factors and applying Box-Cox transformation, both of which significantly improved the adequacy of the model. An optimized set of conditions (pH = 9.0, ω₁ = 339.3 rpm, and dosage = 28.54 mg/L) was obtained under which flocculation efficiency (FE) was predicted to be 95.85% and 98.00% for the nonsignificant factors removed and Box-Cox transformed models, respectively, compared to an experimentally determined value of 98.06%. Thermal stability analyses showed that the ACPAM was generally stable below 100 °C with some weight loss caused by moisture evaporation. However, crosslinking of its molecules by imidization and condensation started to occur at 120 °C, resulting in a lower flocculation performance. Finally, the applicability of the ACPAM was studied by comparing its FE to those of two other flocculants (AlCl₃ and chitosan) when harvesting three microalgal species. The results showed flocculation performance of ACPAM varied with microalgae species, for one species the ACPAM dosage needed was highest while for another species, the dosage was lowest.

Simultaneous removal of siloxanes and H2S from biogas using an aerobic biotrickling filter

The feasibility of simultaneous removal of siloxane and H₂S from biogas was investigated using an aerobic biotrickling filter (BTF). The biodegradation of H₂S in the BTF followed a first-order kinetic model and more than 95 % H₂S was eliminated within a residence time of 0.3 min. The removal of decamethylcyclopentasiloxane (D5) increased with longer empty bed residence time (EBRT). The partition test and microbial community analysis further reveals that up to 52 % removal of D5 was reached mainly by the chemical-absorption in acid recycling liquid. Finally, D5 was converted into mixtures of dimethylsilanediol (DMSD) and hexamethyldisiloxane (L2) via ring-opening hydrolysis in acid liquid and ring-shrinking polyreaction using CH₄ derived from biogas. These operational characteristics demonstrate that the abiotic removal of D5, in addition to biological removal of H₂S in an aerobic BTF can significantly decrease the siloxane loading to the downstream siloxane removing units.

Comparison of sewage sludge mono-incinerators: Mass balance and distribution of heavy metals in step grate and fluidized bed incinerators

We investigated the distribution of 18 elements including non-volatiles (Al, P, Ca, Fe, Mg, K, Mn, Cu, Na, Cr, and Ni), semi-volatiles (Zn, Pb, Ag, As, and Cd), and volatiles (Hg and S) and compared their behaviors in two types of full-scale sewage sludge mono-incinerators, namely, a step-grate stoker (GS) and two fluidized bed incinerators (F-types), with the same feed sludge. Most of the non-volatile elements were enriched five-fold in all incinerated sewage sludge ash (ISSA), while the volatile S and Hg were barely enriched in ash due to the combustion components generated in the gas phase. While the semi-volatile elements were also enriched five-fold in the F-types, a different enrichment behavior was observed in the GS. Boiler and multi-cyclone dust in the GS showed higher enrichments of Pb and Cd compared to ash due to the combined effects of lower temperature and smaller particle size. Compared to the F-types, the GS generated ashes with lower toxicity as the major component (99.7%) and hazardous dust as the minor component. In the future, more attention should be paid to grate stokers in terms of recycling ISSA.

Bioaccessibility and human health risk assessment of metal(loid)s in soil from an e-waste open burning site in Agbogbloshie, Accra, Ghana

Environmental pollution and human health issues due to unrestricted electronic waste (e-waste) recycling activities have been reported at a number of locations. Among different e-waste recycling techniques, open burning of e-waste releases diverse metal(loid)s into the environment, which has aroused concern worldwide. In human health risk assessments (HHRAs), oral ingestion of soil can be a major route of exposure to many immobile soil contaminants. In vitro assays are currently being developed and validated to avoid overestimation of pollutants absorbed by the human body when calculating total pollutant concentrations in HHRAs. In this study, Cu, As, Cd, Sb, and Pb bioaccessibility in polluted soils (n = 10) from e-waste open burning sites at Agbogbloshie in Accra, Ghana, was assessed using an in vitro assay, the physiologically based extraction test. A bioaccessibility-corrected HHRA was then conducted to estimate the potential health risks to local inhabitants. The in vitro results (%) varied greatly among the different metal(loid)s (Cu: 1.3-60, As: 1.3-40, Cd: 4.2-67, Sb: 0.7-85, Pb: 4.1-57), and also showed marked variance between the gastric phase and small intestinal phase. The particle sizes of soil samples and chemical forms of metal(loid)s also influenced bioaccessibility values. Using these bioaccessibility values, both the hazard index and carcinogenic risk were calculated. The hazard index was above the threshold value (>1) for 5/10 samples, indicating a potential health risk to local inhabitants.

The effect of gas emission on the strength of composite products derived using alkali-activated municipal solid waste incineration fly ash/pyrophyllite-based systems

We explored the effects of gas emission by mixtures undergoing alkali-activation of municipal solid waste incineration fly ash (MSWIFA) and pyrophyllite (the mixtures included dehydrated pyrophyllite, MSWIFA, 14 mol/L aqueous sodium hydroxide, and sodium silicate; curing proceed at 105 °C for 24 h). We measured the compressive strengths of the derived solid composites. The causes of gas emission, and the physical and chemical properties of products created under controlled gas emission, were investigated. Hydrogen was emitted after mixing MSWIFA and alkali. The compressive strength of products prepared when gas emission was complete was 2-3.4-fold greater than that of products prepared when gas emission was incomplete. X-ray micro-tomography and mercury intrusion porosimetry showed that products formed during complete gas emission tended to have smaller pores. X-ray diffraction and nuclear magnetic resonance (²⁷Al and ²⁹Si) indicated that the aluminum substitution levels in tectosilicate differed under such conditions, although the minerals were identical. Thus, complete gas emission after mixing improved ultimate products.

Distribution and characteristics of heavy metals in a first-generation monofill site for incinerator residue

This study investigated core samples from a landfill site for incinerator residue. The landfill site is one of the first monofill sites for municipal solid waste incinerator residue in the world. The concentrations of the heavy metals Cd, Cr, Cu, Pb, Zn, and Ni in the landfilled incinerator residues were 1-108, 41-926, 40-5498, 35-9806, 103-11453, and 25-719 mg/kg, respectively. Based on comparisons of heavy metal contents between raw incinerator fly ash and bottom ash reported in the literature, our samples comprised a mixture of incinerator fly ash and bottom ash. Rainfall had removed the dissolvable salts from the incinerator residues. The compositions of incinerator residues from different locations varied markedly. The vertical distribution showed a high heavy metal content in the waste layers, suggesting no vertical movement of heavy metals in this landfill site. A comparison between the experimental data and data calculated from historic records of the original metal compositions of the incinerator residues suggested high mobility of Zn, Cu, and Pb and low mobility of Cr and Cd. This trend was supported by a leaching test of waste layer samples. Zn and Cu were leached more readily at pH 9.0-10.0 and 10.5-11.5, respectively.

Quantitative cesium speciation and leaching properties in alkali-activated municipal solid waste incineration fly ash and pyrophyllite-based systems

There is an urgent need to dispose safely of the municipal solid waste incineration fly ash (MSWIFA) contaminated by cesium (Cs) released from the Fukushima Daiichi nuclear power plant accidents. This study investigated the relationship between quantitative Cs speciation and Cs immobilization in composite product from alkali-activated pyrophyllite and MSWIFA, with added stable cesium chloride and cesium carbonate. Cesium speciation was determined using X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS), while Cs immobilization was evaluated by a leaching method. Twenty-four composite products, with different Cs leaching properties, were prepared under various conditions. The XRD analysis of six composite products with different Cs leaching properties qualitatively identified a crystalline pollucite in the two products with the least Cs leaching. The quantitative speciation determined using XAFS revealed a strong negative correlation between the pollucite content in the 24 products and their Cs leaching ratio. Cesium species with a CsO bond were found in all products. These were at least two Cs species with different leaching properties. These results indicate that the change from a Cs species to pollucite in the product increased the Cs immobilization level in the system.

Mercury behaviour in flue gas from sewage sludge incinerators and melting furnace

Thermal conversion of sewage sludge can be a clean source of renewable energy if the emission of air pollutants from the source is controlled. In 2013, the Minamata Convention on Mercury was adopted, placing greater emphasis on the control of mercury emissions, including mercury emissions from sewage sludge incinerators. To characterise the behaviour of mercury in flue gas, particulate and gaseous mercury concentrations in two incinerators and a melting furnace were measured by manual sampling. In a third facility, continuous emission monitoring was used to characterise temporal trends in gaseous mercury concentrations. Wet scrubbers were determined to be effective air pollution control devices suitable for mercury removal. Stack mercury concentrations were found to be <10 μg/Nm³, which meets the mercury emission standard for existing plants (50 μg/Nm³).

Stabilization of cesium in alkali-activated municipal solid waste incineration fly ash and a pyrophyllite-based system

Environmentally sound treatments are required to dispose of municipal solid waste incineration fly ash (MSWIFA) contaminated with radioactive cesium (Cs) from the Fukushima Daiichi nuclear power plant accident in Japan. This study focuses on the stabilization of Cs using an alkali-activated MSWIFA and pyophyllite-based system. Three composite solid products were synthesized after mixtures of raw materials (dehydrated pyrophyllite, MSWIFA, 14 mol/L aqueous sodium hydroxide, and sodium silicate solution) were cured at 105 °C for 24 h. Three types of MSWIFAs were prepared as raw fly ash, raw fly ash with 0.1% CsCl, and raw fly ash with 40% CsCl to understand the stabilization mechanism of Cs. Cs stabilization in two solid products was successful, with less than 6.9% leaching observed from two types tests, and was partly successful for the solid product with the highest concentration of Cs. X-ray diffraction showed that all of the solid products produced several crystalline phases, and that pollucite was formed in the highest Cs concentration product. The X-ray absorption fine structure and scanning electron microscopy with X-ray analysis suggested that most Cs species formed pollucite in the two solid products from MSWIFA with added CsCl. This system provides a technique for the direct stabilization of Cs in MSWIFA.

Stabilization of lead in an alkali-activated municipal solid waste incineration fly ash-Pyrophyllite-based system

This work focuses on the stabilization and speciation of lead (Pb) in a composite solid produced from an alkali-activated municipal solid waste incineration fly ash (MSWIFA)-pyophyllite-based system. The solid product was synthesized after mixtures of raw materials (dehydrated pyrophyllite, MSWIFA, 14 mol/L aqueous sodium hydroxide, and sodium silicate solution) were cured at 105 °C for 24 h. The product could reduce the leaching of Pb and the Pb concentration in the leachate was 7.0 × 10^-3 using the Japanese leaching test and 9.7 × 10^-4 mg/L using toxicity characteristics leaching procedure method, which satisfied the respective test criteria and successfully stabilized Pb in this system. The solid product had a compressive strength of 2 MPa and consisted mainly of crystalline phases. Scanning electron microscopy with X-ray analysis and X-ray absorption fine structure suggested that Pb was present along with Al, Si, and O, and that the atomic environment around the Pb was similar to that of PbSiO₃. These results suggest that the alkali-activated MSWIFA-pyrophyllite-based system could be used to stabilize Pb in MSWIFA.

Influence of activated-carbon-supported transition metals on the decomposition of polychlorobiphenyls. Part II: Chemical and physical characterization and mechanistic study

This paper studies the synergism between transition metals (TMs) and activated carbon (AC) as a catalyst support used in the catalytic decomposition of PCBs. A series of AC-supported TM catalysts was prepared according to two distinct methods: impregnation and ion exchange which were defined as LaTM-C and IRTM-C, respectively. The catalytic reactions between 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153) and AC-supported Fe, Ni, Cu and Zn catalysts were conducted under N2 atmosphere. Changes in the nature of the catalysts as well as the decomposition mechanism of PCB-153 are discussed. Important findings include: (i) a higher metal concentration and a better metal distribution on AC is realized using ion-exchange, despite a lower AC specific surface area, (ii) IRTM-C had better effects on the decomposition of PCB-153 than LaTM-C, (iii) the role of Ni, Cu, and Fe as electron donors in PCB dechlorination was evaluated vs. the stability of Zn, and (iv) both temperature and chemical composition of TM catalysts influenced the decomposition efficiency of PCBs.

Emission and control of N2O and composition of ash derived from cattle manure combustion using a pilot-scale fluidized bed incinerator

This study investigates the emission of nitrous oxide (N₂O) and discusses the reduction of N₂O emissions during the 24-h combustion of cattle manure using a pilot-scale fluidized bed incinerator under various experimental conditions. The results of these experiments were then validated against previously reported data. In addition, the characteristics of cattle manure incineration ash and their changes under different combustion conditions were estimated. In incineration experiments with composted cattle manure, N₂O concentrations using multi-stage combustion were 75% lower than the concentrations resulting from normal combustion without additional auxiliary fuel, since N₂O could be decomposed in the high-temperature zone formed by the inlet of the secondary combustion air. The N₂O emission factor under normal combustion conditions (800°C) was 6.0% g-N₂O-N/g-N. This result is similar to the values found in previous studies at the same temperature. The N₂O emission factor was decreased to 1.6% g-N₂O-N/g-N using a multi-stage combustion procedure. The current Japanese N₂O emission factor of 0.1% g-N₂O-N/g-N is an underestimate for some conditions and should be uniquely specified for each condition. Finally, cattle manure ash contains ample fertilizer elements, little Fe, Al and Zn, but abundant Cl. Therefore if Cl could be removed by some kind of pretreatment, cattle manure ash could be used as a favourable fertilizer.

Behavior of cesium in municipal solid waste incineration

As a result of the Fukushima Daiichi Nuclear Power Plant accident on March 11, 2011 in Japan radioactive nuclides, primarily (134)Cs and (137)Cs were released, contaminating municipal solid waste and sewage sludge in the area. Although stabilizing the waste and reducing its volume is an important issue differing from Chernobyl nuclear power plant accident, secondary emission of radioactive nuclides as a result of any intermediate remediation process is of concern. Unfortunately, there is little research on the behavior of radioactive nuclides during waste treatment. This study focuses on waste incineration in an effort to clarify the behavior of radioactive nuclides, specifically, refuse-derived fuel (RDF) with added (133)Cs (stable nuclide) or (134)Cs (radioactive nuclide) was incinerated in laboratory- and pilot-scale experiments. Next, thermogravimetric (TG) and differential thermal analysis (DTA) of stable Cs compounds, as well as an X-ray absorption fine structure (XAFS) analysis of Cs concentrated in the ashes were performed to validate the behavior and chemical forms of Cs during the combustion. Our results showed that at higher temperatures and at larger equivalence ratios, (133)Cs was distributed to the bottom ash at lower concentration, and the influence of the equivalence ratio was more significant at lower temperatures. (134)Cs behaved in a similar fashion as (133)Cs. We found through TG-DTA and XAFS analysis that a portion of Cs in RDF vaporizes and is transferred to fly ash where it exists as CsCl in the MSW incinerator. We conclude that Cs-contaminated municipal solid wastes could be incinerated at high temperatures resulting in a small amount of fly ash with a high concentration of radioactive Cs, and a bottom ash with low concentrations.

Methane and nitrous oxide emissions following anaerobic digestion of sludge in Japanese sewage treatment facilities

Methane (CH4) and nitrous oxide (N2O) are potent greenhouse gases with global warming potentials (expressed in terms of CO2-equivalents) of 28 and 265, respectively. When emitted to the atmosphere, they significantly contribute to climate change. It was previously suggested that in wastewater treatment facilities that apply anaerobic sludge digestion, CH4 continues to be emitted from digested sludge after leaving the anaerobic digester. This paper studies the CH4 and N2O emissions from anaerobically digested sludge in the subsequent sludge treatment steps. Two full-scale treatment plants were monitored over a 1-year period. Average emissions of CH4 and N2O were 509±72 mg/m(3)-influent (wastewater) and 7.1±2.6 mg/m(3)-influent, respectively. These values accounted for 22.4±3.8% of the indirect reduction in CO2-emissions when electricity was generated using biogas. They are considered to be significant.

Stabilizing conditions of metal mercury in mercury sulfurization using a planetary ball mill

This study used a non-heating process to stabilize mercury by mercury sulfurization. Elemental mercury and sulfur were mixed using planetary ball milling under various experimental conditions and the optimal conditions were determined. The labile intermediate, mercury sulfide, was observed in the early stages of milling, and the intermediates were then pulverized into mercury sulfide powder. These phenomena were significantly influenced by the diameter of the planetary ball. A larger diameter enhanced mercury stabilization. For a ball with a 19.04-mm diameter, the toxicity characteristic leaching procedure (TCLP) and the Japanese leaching test (JLT) values were 0.263μg/L and 0.0586μg/L, respectively, suggesting that mercury leachability was strictly controlled. When the molar ratio of sulfur to mercury was 1.05, the mercury concentration in the headspace was <1μg/Nm(3) at 20°C, which was equivalent to the level in pure reagent. The stability of the planetary ball milling product at optimum conditions was either comparable or superior to that in other stabilization techniques. The running cost of this technology was estimated to be 15,360Yen (154USD)/ton-Hg. This stabilization technology is cost-effective and environmentally sound for the long-term and safe management of mercury.

PCDD/DF and co-planar PCB emissions from crematories in Japan

Japan implemented dioxin emission guidelines for crematories in 2000, but the effects of the new guidelines have not been fully evaluated. In this study, concentrations of polychlorinated dibenzodioxins/dibenzofurans (PCDDs/DFs) and co-planar polychlorinated biphenyls (co-PCBs) were measured in flue gas, fly ash, and bottom ash (mainly bone) from several crematories as a follow-up investigation. Total concentrations (O2 12% normalized) of PCDDs/DFs and co-PCBs in flue gas ranged from 4.2 to 540 ng/mN(3), and toxic equivalent concentrations ranged from 0.000053 to 11 ng-TEQ/mN(3). Based on these measurements, the average emission factor was estimated to be 1400 ng-TEQ/body. This is approximately one-third the emission factor recorded in 1999. The emission factor distributions from 1999 and our study in 2007 were log-normally distributed. Emission factors were significantly lower in 2007 than in 1999, which suggests that the guidelines have been effective in reducing dioxin emissions. Meanwhile, toxic equivalent concentrations in fly ash ranged from 0.014 to 13 ng-TEQ g(-1). Higher dioxin concentrations in fly ash were observed in facilities that used a heat exchanger as a flue-gas cooling device. Because the concentrations of PCDDs/DFs and co-PCBs in flue gas were also elevated after heat exchangers during the investigation of PCDD/DF- and co-PCB-removal behaviors, secondary formation of PCDDs/DFs and co-PCBs on heat exchanger surfaces unambiguously occurred.

Effect of co-managing organic waste using municipal wastewater and solid waste treatment systems in megacities

A model was developed to calculate the mass and heat balances of wastewater and municipal solid waste treatment plants when these plants operate either separately or together with a mutual dependence on mass and energy. Then the energy consumption, life cycle costs (LCCs), greenhouse gas (GHG) emissions and effluent quality were evaluated under various scenarios to identify the most effective co-management and treatment system. The results indicated that co-digestion of kitchen waste and sewage sludge, and their co-combustion reduced LCCs by 30%, energy consumption by 54% and GHG emissions by 41% compared to the base case. However, co-digestion increased the total nitrogen load in the wastewater treatment plant effluent. Even if an advanced wastewater treatment system was applied to improve total nitrogen concentration, the above indicators were affected but still reduced compared to the base case. Therefore, it was confirmed that the integrated system was beneficial for megacities.

[Pretreatment technology for fly ash from MSWI and the corresponding study of chloride behavior]

The introduced pretreatment technology, WCCB (Washing + Calcination), was effective to reduce chlorides in fly ash by consuming relatively low energy for recycling fly ash as the raw material for cement industry. The washing conditions are: twice-washing, liquid/solid = 3, mixing speed = 150 r x min(-1), 1st mixing time = 5 min, and 2nd mixing time = 10 min. The original incinerator was used for the calcination process, 1 000 degrees C, 10% O2 and dwelling time of 1 hour were adopted. By adopting X-ray absorption near edge structure and X-ray diffraction, the behavior of chlorides was explained and NaCl, KCl and CaCl2 are the main form of chlorides existing in fly ash. The reagent used in the air pollution control system to neutralize the acid component in the discharged gas surely acted a very important role in the formation of chlorides. The insoluble chlorides in fly ash had a very similar structure as that of Friedel's salt, which was related with CaCl2.

Environmental and economic assessment of municipal sewage sludge management - a case study in Beijing, China

A case study was conducted in Beijing to identify municipal sewage sludge (SS) management systems appropriate for a sound material-cycle society. The environmental and economic impacts of four realistic SS-handling scenarios were investigated: stabilization by thermal drying, increased inclusion of SS in cement manufacture, and using either dried or carbonized SS as substitute fuel for coal-fired power generation plants. The results showed that the current sludge management system had the lowest operating cost but higher greenhouse gas (GHG) emissions and a low recycling rate. The case with the use of carbonized SS reused in coal-fired power plants had higher energy consumption and almost the same GHG emissions as the current system. On the other hand, the case including more SS in cement manufacture had the same level of energy consumption with much lower GHG emissions. The case with the use of dried SS in coal-fired power plants also resulted in lower energy consumption and lower GHG emissions than at present. Furthermore, sensitivity analysis showed that drying SS with surplus heat from cement plants used less energy and emitted less GHG compared to the other two drying methods.

Emission of greenhouse gases from controlled incineration of cattle manure

Greenhouse gas emission is a potential limiting factor in livestock farming development. While incineration is one approach to minimize livestock manure, there are concerns about significant levels of nitrogen and organic compounds in manure as potential sources of greenhouse gas emissions (N2O and CH4). In this study, the effects of various incineration conditions, such as the furnace temperature and air ratio on N2O and CH4 formation behaviour, of cattle manure (as a representative livestock manure) were investigated in a pilot rotary kiln furnace. The results revealed that N2O emissions decreased with increasing temperature and decreasing air ratio. In addition, CH4 emissions tended to be high above 800 degrees C at a low air ratio. The emission factors for N2O and CH4 under the general conditions (combustion temperature of 800-850 degrees C and air ratio of 1.4) were determined to be 1.9-6.0% g-N2O-N/g-N and 0.0046-0.26% g-CH4/g-burning object, respectively. The emission factor for CH4 differed slightly from the published values between 0.16 and 0.38% g-CH4/g-burning object. However, the emission factor for N2O was much higher than the currently accepted value of 0.7% g-N2O-N/g-N and, therefore, it is necessary to revise the N2O emission factor for the incineration of livestock manure.

Characteristics of biosolids in dimethyl ether dewatering method

In this study, a method for removing water from biosolids that uses dimethyl ether (DME) as an extractant was considered. This study evaluates the applicability of the DME dewatering method to biosolid cakes by using a DME flow-type experimental apparatus. It was found that a high dewatering ratio is clearly achieved by increasing the liquefied DME/biosolid ratio and lowering the liquefied DME linear velocity. As the liquefied DME/biosolid ratio was increased, the carbon content in dewatered biosolid showed a slight decrease and the TOC concentration in separated liquid increased significantly. Finally, the input energy Es to remove 1 kg of water from the biosolid cake, using both the DME dewatering method and the conventional drying method was estimated. The calculation shows that Es for the DME dewatering process is approximately a third of Es for the conventional thermal drying process.

Nutrient recovery from biomass cultivated as catch crop for removing accumulated fertilizer in farm soil

As a result of long-term continuous use of fertilizers in farm land, a large amount of nutrients accumulate in the soil, increasing the risk of eutrophication or nitrate pollution of groundwater. For rehabilitating the farm soil and recovering nutrients such as nitrogen, phosphorus and potassium, a new system has been developed by our research group. This paper discusses the methodology of extracting nutrients from biomass in order to recover phosphorus and other nutrients in crystal form. Around 80% or higher extraction rates were achieved for phosphorus and potassium by soaking the powdered tissue in distilled water or 1% NaOH solution for 24 h. The extracted phosphorus and potassium act as a potential resource for recycled fertilizer or other industrial materials.

The calcination process in a system for washing, calcinating, and converting treated municipal solid waste incinerator fly ash into raw material for the cement industry

Calcination is the second step in a washing-calcination-conversion system in which treated municipal solid waste incinerator fly ash and bottom ash can be reused as raw material in the cement industry and can decompose or stabilize hazardous compounds, reduce residue amounts, and alter residue characteristics. In this research, only fly ash is discussed. Chloride reduction is important if treated fly ash is to be reused in cement; however, the relationship between washed fly ash properties and chloride reduction by calcination is not well understood. This study used washed residues of three types of fly ash-raw fly ash (RFA) from the boiler or economizer of an incineration system, fly ash collected in a bag filter injected with calcium hydroxide (Ca(OH)2) for acid removal (CaFA), and fly ash collected in a bag filter injected with sodium bicarbonate (NaHCO3) for acid removal (NaFA)-in calcination experiments with varying temperature (400-1100 degrees C) and atmosphere (100% nitrogen [N2] at 25 mL/min or 10% oxygen [O2] [90% N2] at fluxes of 25, 50, and 75 mL/min). From the perspective of chloride reduction, heating to 1000 degrees C with 1-hr heating time, 1-hr holding time, and an atmosphere of 10% O2/90% N2 was most suitable for calcination. Under these conditions, chloride levels were reduced by 91, 52, and 96% in washed residues of RFA, CaFA, and NaFA, respectively. Among the washed residues, the weight of the washed residue of NaFA decreased the most.

Deodorization and dewatering of biosolids by using dimethyl ether

We proposed a method for the deodorising and dewatering of biosolids. In the proposed method, liquefied dimethyl ether (DME) was used as an extractant for odorous components and water. We developed a bench-scale experiment to almost completely deodorize and dewater biosolids by using liquefied DME at room temperature. The deodorized and dewatered biosolids have sufficient caloric density and can be used as a carbon neutral fuel.

Real-time gas-phase analysis of mono- to tri-chlorobenzenes generated from heated MSWI fly ashes containing various metal compounds: application of VUV-SPI-IT-TOFMS

We measured sensitive real-time change of low-chlorinated (Cl(1)-Cl(3)) benzenes in gas phase from heated model and real solid samples using the recently developed vacuum ultraviolet (VUV) single-photon ionization (SPI) ion trap time-of-flight mass spectrometer (VUV-SPI-IT-TOFMS). Model solid samples that contained activated carbon, potassium chloride, silicon dioxide, and trace metallic compounds (copper, iron, lead, and zinc) were used to simulate fly ash at a municipal solid waste incinerator (MSWI). The concentrations of chlorobenzenes determined by integrating the area for 30 min using VUV-SPI-IT-TOFMS were correlated with gas-phase concentrations analyzed by GC/MS. Real-time changes had characteristic patterns dependent on metal species and compounds. Comparing gas-phase real-time patterns of low-chlorinated benzenes between real and model fly ashes, copper chloride- and oxide-like compounds in real fly ash at the postcombustion zone in a MSWI may play key factors in the formation of low-chlorinated benzenes. Lead and zinc compounds and iron oxide in solid phase did not affect the formation of low-chlorinated benzenes in gas phase. VUV-SPI-IT-TOFMS can be applied to the time-dependent characterization of volatile low-chlorinated benzenes in gas phase in various artificial and environmental processes.

Chlorides behavior in raw fly ash washing experiments

Chloride in fly ash from municipal solid waste incinerators (MSWIs) is one of the obstructive substances in recycling fly ash as building materials. As a result, we have to understand the behavior of chlorides in recycling process, such as washing. In this study, we used X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) to study the chloride behavior in washed residue of raw fly ash (RFA). We found that a combination of XRD and XANES, which is to use XRD to identify the situation of some compounds first and then process XANES data, was an effective way to explain the chlorides behavior in washing process. Approximately 15% of the chlorine in RFA was in the form of NaCl, 10% was in the form of KCl, 51% was CaCl(2), and the remainder was in the form of Friedel's salt. In washing experiments not only the mole percentage but also the amount of soluble chlorides including NaCl, KCl and CaCl(2) decreases quickly with the increase of liquid to solid (L/S) ratio or washing frequency. However, those of insoluble chlorides decrease slower. Moreover, Friedel's salt and its related compound (11CaO.7Al(2)O(3).CaCl(2)) were reliable standards for the insoluble chlorides in RFA, which are strongly related to CaCl(2). Washing of RFA promoted the release of insoluble chlorides, most of which were in the form of CaCl(2).

Formation of chlorinated aromatics in model fly ashes using various copper compounds

Various copper compounds found in fly ash are related to the formation of chlorinated aromatics. The formation potentials of chlorinated aromatics in different model fly ashes containing various copper compounds and the chemical behavior of such copper compounds were investigated. In model fly ash with copper metal, hydroxide, carbonate, or oxides, the generated amounts of chlorobenzene (CBz) and polychlorinated biphenyls (PCBs) and the average chlorination numbers were low and at the same level, respectively. The maximum generated amounts of chlorinated aromatics were observed at 300 degrees C. Although X-ray absorption near edge structure (XANES) spectra indicated that the chemical form of copper compounds changed little, they were found to promote the formation of chlorinated aromatics. Therefore, these copper compounds play the same role as CuO. On the other hand, in model fly ash with copper chloride, the generated amounts of CBz and PCBs were quite high and the average chlorination numbers was high. Dynamic changes were observed in XANES spectra, and the pre-edge peak attributed to monovalent copper compounds appeared at around 300 degrees C. A large difference was observed between these two groups in the amount of CuCl generated and the homologs of chlorinated aromatics present, indicating that CuCl played an important role in the formation of chlorinated aromatics.

Extraction of PCBs and water from river sediment using liquefied dimethyl ether as an extractant

We investigated whether polychlorinated biphenyls (PCBs) and water could be simultaneously removed from river sediment by solvent extraction using liquefied dimethyl ether (DME) as the extractant. DME exists in a gaseous state at normal temperature and pressure and can dissolve organic substances and some amount of water; therefore, liquefied DME under moderate pressure (0.6-0.8 MPa) at room temperature can be effectively used to extract PCBs and water from contaminated sediment, and it can be recovered from the extract and reused easily. First, we evaluated the PCB and water extraction characteristics of DME from contaminated sediment. We found that 99% of PCBs and 97% of water were simultaneously extracted from the sediment using liquefied DME at an extraction time of 4320 s and a liquefied DME/sediment ratio of 60 mL g(-1). The extraction rate of PCBs and water was expressed in terms of a pseudo-first-order reaction rate. Second, we estimated the amount of DME that was recovered after extraction. We found that 91-92% of DME could be recovered. In other words, approximately 5-10% of DME was lost during extraction and recovery. It is necessary to optimize this process in order to recover DME efficiently. The extraction efficiency of the recovered DME is similar to that of the pure DME. From the results, we conclude that solvent extraction using liquefied DME is suitable for extracting PCBs and water from contaminated sediment.

Behaviour and adsorptive removal of siloxanes in sewage sludge biogas

We investigated the behaviour of siloxanes, which adversely affect biogas engines, as well as their concentration levels in sewage sludge biogas in Japan. We also performed experiments on the absorptive removal of siloxanes using various adsorbents and determined the main adsorbent characteristics required for the removal of siloxanes. The results of our study on the concentration and composition of siloxanes in biogas were similar to previous reports. Moreover, we found that the concentration of siloxanes changes in relation to the outside air temperature based on real-time measurements of siloxanes using a continuous analyser. We further speculated that the continuous analyser would accurately indicate the siloxane concentration in model biogas but overestimate the siloxane concentration in actual biogas because of positive interference by VOCs and other biogas components. In the siloxane adsorption experiment, the equilibrium uptake of both cyclic siloxanes, D4 and D5, was positively related to the BET-specific surface area of the adsorbents and the fraction of the external surface area taken up by relatively large diameter pores. We attributed the adsorption results to the fact that the siloxane molecules are generally larger than micropores; therefore, they are less susceptible to adsorption to micropores. Based on these results, we concluded that adsorbents with large BET-specific surface areas, especially those with a high external specific surface area and pores of relatively large diameters, are desired for the removal of siloxanes.

Incomplete transformations of Pb to pyromorphite by phosphate-induced immobilization investigated by X-ray absorption fine structure (XAFS) spectroscopy

For an accurate assessment of immobilization technologies, it is necessary to illustrate the transformation of target metal species into their final products. The present study employed extended X-ray absorption fine structure (EXAFS) spectroscopy combined with linear combination fitting (LCF) to determine Pb species and their proportions in contaminated soils treated with phosphate amendments. Lead contaminated soils collected from a shooting range were separately treated with calcium phosphate (CP), hydroxyapatite synthesized from ceramic waste (CHA), and incinerated poultry litter (PW). Soils were incubated at 32% water content for 7 and 380 d. The EXAFS-LCF analysis illustrated that Pb speciation in the control soil included organically-complexed phases (Pb(org), 32%), PbO (22%), PbCO(3) (28%), and Pb(3)(CO(3))(2)(OH)(2) (8%). As the incubation period increased, the proportion of chloropyromorphite [Pb(5)(PO(4))(3)Cl] increased from 20% to 27% in CHA and from 19% to 31% in CP soils. The spectra of PW-amended soils were reproduced adequately with a combination of Pb(org), PbO, and chloropyromorphite in the proportion of about 20%, 45%, and 23%, respectively. The effectiveness of amendments on Pb immobilization as indicated by the chloropyromorphite proportion was in the order of CP (31%)>CHA (27%)>PW (23%) after 380 d of incubation. Our study indicates that about 70% of Pb species was not immobilized as a form of chloropyromorphite, and the additional supply of phosphate amendment scarcely promoted chloropyromorphite formation. The EXAFS-LCF approach illustrated that organically-complexed Pb was persistent in all amended soils, suggesting that an enriched soil organic carbon may be an inhibitory factor for pyromorphite transformations.