Effect of thermal hydrolysis pretreatment on the stabilization of sludge with different solid contents during autothermal thermophilic aerobic digestion.

Sludge stabilization was affected by solid content during autothermal thermophilic aerobic digestion (ATAD). Thermal hydrolysis pretreatment (THP) could alleviate the issues of high viscosity, slow solubilization and low ATAD efficiency caused by increased solid content. The influence of THP on the stabilization of sludge with different solid contents (5.24%-17.14%) during ATAD was investigated in this study. The results demonstrated that stabilization was achieved with volatile solid (VS) removal of 39.0%-40.4% after 7-9 days of ATAD for sludge with solid content of 5.24%-17.14%. The solubilization of sludge with different solid contents reached 40.1%-45.0% after THP. The rheological analysis indicated that the apparent viscosity of sludge was obviously reduced after THP at different solid contents. The increase in fluorescence intensity of fulvic acid-like organics, soluble microbial by-products and humic acid-like organics in the supernatant after THP and the decrease in fluorescence intensity of soluble microbial by-products after ATAD were detected by excitation emission matrix (EEM). The molecular weight (MW) distribution in the supernatant elucidated that the proportion of 50 kDa < MW < 100 kDa increased to 16%-34% after THP and the proportion of 10 kDa < MW < 50 kDa decreased to 8%-24% after ATAD. High throughput sequencing showed that the dominant bacterial genera shifted from Acinetobacter, Defluviicoccus and Norank_f__norank_o__PeM15 to Sphaerobacter and Bacillus during ATAD. This work revealed that solid content of 13%-17% was appropriate for efficient ATAD and rapid stabilization under THP.

Successive choline addition enhancing the methanogenesis of waste activated sludge anaerobic digestion: Insight from hydrophilicity, electrochemical performance and microbial community.

Anaerobic digestion (AD) is a promising technology to treat waste-activated sludge, previous study proved that methane production could be enhanced with the addition of choline, this work aimed to solve the problem of rapid biodegradability of choline in the AD process by changing its dosing method. With 0.75 g/L as the optimal choline dosing concentration, experimental results showed that successive choline dosing during the first 3-6 days of AD (experimental groups, EGs) performed better than the single dosing. The accumulative biogas production in EGs was increased by 35.55-36.73%, which could be caused by the simultaneous promotion of hydrolysis-acidification and methanogenesis processes. Especially, the electron exchange capacity of digested sludge in EGs was increased by 16.71-34.58%. In addition, the surface Gibbs free energy (△GSL) of sludge in EGs was 105.51-172.21% higher (corresponding to stronger hydrophilicity and repulsion), which might help disperse sludge flocs and improve mass transfer efficiency, and the △GSL values were positively correlated with the accumulative methane production (R2 = 0.7029). Microbiological analysis showed that microbial communities in EGs were richer and Methanosaeta was regarded as the dominant species with 15.93-30.08% higher relative abundance with choline addition. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, EGs were found to be more active in metabolism clusters. Collectively, these findings demonstrated that successive choline dosing during the first 3-6 days is an effective and novel method to enhance methane production in AD process.

Factors affecting the durability of dimethyl dithiocarbamate-stabilized air pollution control (APC) residues derived from municipal solid waste incineration.

Sodium dimethyl dithiocarbamate (SDD) is widely used for stabilizing heavy metals to minimize pollution from air pollution control (APC) residues derived from municipal solid waste incineration. However, the effect of environmental conditions on heavy metal leaching from SDD-stabilized APC residues remains unknown. Therefore, this study aimed to evaluate the durability of SDD-stabilized APC residues and determine the relationship between heavy metal leaching and environmental factors, including pH, temperature, and oxygen. The results revealed that accelerated SDD decomposition and the decline in durability of SDD-stabilized APC residues were caused by acidic and aerated conditions and temperatures above 40 °C. A decrease in pH from 12.25 to 4.69 increased the Cd and Pb concentrations in SDD-stabilized APC residue leachate from below detection (0.002 mg/L) to 1.32 mg/L and 0.04 mg/L to 3.79 mg/L, respectively. Heating at 100 °C for 2 d increased the Cd and Pb concentrations from below detection (0.002 mg/L and 0.01 mg/L) to 2.96 mg/L and 0.47 mg/L, respectively. Aeration for 5 d increased the Cd and Pb concentrations from below detection to 0.09 mg/L and 0.49 mg/L, respectively. The decline in durability was attributed to acid hydrolysis, thermal decomposition, and oxidative damage of SDD, resulting in breakage of the chelated sulfur-metal bond, which was confirmed by the decrease in the oxidizable fraction of heavy metals and the SDD content. This study improves the understanding of the factors contributing to the decline in durability of heavy metals in SDD-stabilized APC residues, which is important for ensuring the long-term stabilization and environmental safety of these residues.

Roles of catalytic ozonation by bimetallic Fe/Ce loading sludge-derived biochar in amelioration of sludge dewaterability: Performance and implementation mechanisms.

In this study, an environmentally friendly alternative was developed using catalytic ozonation by sludge-derived biochar loaded with bimetallic Fe/Ce (O3/SBC-FeCe) for enhanced sludge dewatering. The results indicated that the lowest capillary suction time (CST) of 20.9 s and water content of dewatered sludge cake (Wc) of 64.09% were achieved under the dosage of 40 mg O3/g dry solids (DS) and 0.4 g SBC-FeCe/g DS which were considered as the optimum condition. In view of excellent electron exchanging capacity of SBC-FeCe with rich Lewis acid sites and conversions of valence sates of Fe and Ce, more O3 were decomposed into reactive oxygen species under the catalytic action of SBC-FeCe, which strengthened oxidizing capacity. Enhanced oxidation rendered sludge cells inactivation and compact network structure rupture releasing intracellular water and organic substances. Subsequently, hydrophilic organic matters were attacked and eliminated lessening sludge viscosity and colloidal forces and intensifying hydrophobicity and flowability. In addition, changes of sludge morphology suggested that sludge roughness was alleviated, structural strength and compressibility were raised and porous and retiform structure was constructed providing channels for water outflow by adding skeleton builder of SBC-FeCe. Overall, the synergistic interaction of strengthened oxidation and skeleton construction improved sludge dewaterability.

Medium-Low Temperature Conditions Induce the Formation of Environmentally Persistent Free Radicals in Microplastics with Conjugated Aromatic-Ring Structures during Sewage Sludge Pyrolysis.

Medium-low temperature pyrolysis is an effective method of retaining active components in sludge char. However, we found that incomplete cracking reactions resulted in residues of microplastics (MPs) remaining in the char; moreover, high levels of environmentally persistent free radicals (EPFRs) were detected in these MPs. Here, we investigated the temperature-dependent variations in the char-volatile products derived from sludge and MPs under different pyrolysis scenarios using multiple in situ probe coupling techniques and electron paramagnetic resonance spectroscopy, thereby identifying the sources of EPFRs and elucidating the corresponding formation-conversion mechanisms. The temperature was the key factor in the formation of EPFRs; in particular, in the 350-450 °C range, the abundance of EPFRs increased exponentially. Reactive EPFR readily formed in MPs with conjugated aromatic-ring structures (polyethylene terephthalate and polystyrene) at a temperature above 350 °C; EPFR concentrations were 5-17 times higher than those found in other types of polymers, and these radicals exhibited half-lives of more than 90 days. The EPFR formation mechanism could be summarized as solid-solid/solid-gas interfacial interactions between the polymers and the intermediate products from sludge pyrolysis (at 160-350 °C) and the homolytic cleavage-proton transfer occurring in the polymers themselves under the dual action of thermal induction and acid sites (at 350-450 °C). Based on the understanding of the evolution of EPFRs, temperature regulation and sludge components conditioning may be effective approaches to inhibit the formation of EPFRs in MPs, constituting reliable strategies to diminish the environmental risk associated with the byproducts of sludge pyrolysis.

Coupling sludge-based biochar and electrolysis for conditioning and dewatering of sewage sludge: Effect of char properties.

The addition of sludge-based biochar during electrochemical pretreatment of sewage sludge, as an efficient hybrid technology, is potentially to be applied in sludge deep-dewatering. The chars functioned as conductors, catalysts and skeleton particles could enhance the sludge dewaterability and increase the calorific value of the dewatered sludge cake. However, the effect of synthesis conditions on the char properties and further on the dewatering performance is still unknown. Herein, the sludge-based particle electrodes (SPEs) under three main synthesis conditions, including liquid-solid ratio, pyrolysis temperature and time, were prepared. The sludge-based biochars (i.e., SPE-400, SPE-600, and SPE-800 pyrolyzed under 400, 600 and 800 °C, respectively) were characterized and utilized as three-dimensional electrodes during sludge electrolysis. The increased pyrolysis temperature (within 400-800 °C) resulted in the enrichment of metallic ions and increment of specific surface area and pore volume of SPE, which led to the increased catalysis and adsorption sites for viscous proteins (PNs). Particularly, the pores of SPE-800 provided more drainage channels as skeleton builders. Compared with raw sludge, the capillary suction time (CST) and the specific resistance of filtration (SRF) of the treated sludge with 3D-SPE-800 were reduced by 58.12% and 81.01%, respectively, but the net sludge solids yield (YN) was increased by 87.05%. The highest decrease of hydrophilic α-Helix content in PNs (from 9.93% to 7.30%) was observed when using SPE-800 as particle electrode, revealing the crucial role of char characteristics on protein reduction and subsequent dewatering enhancement. The synergistic effects of electrolysis and sludge-based biochar provided a new insight for a closed-loop pretreatment of sewage sludge in the wastewater treatment plant.

Accelerated stabilization of high solid sludge by thermal hydrolysis pretreatment in autothermal thermophilic aerobic digestion (ATAD) process.

Autothermal thermophilic aerobic digestion (ATAD) is a rapid biological treatment technology for sludge stabilization. To improve digestion efficiency and shorten stabilization time, thermal hydrolysis pretreatment was employed before ATAD of high solid sludge. The results showed that accelerated stabilization of high solid sludge (total solid = 10.1%) was achieved by thermal hydrolysis pretreatment with volatile solid removal efficiency of 40.3% after 8 days of ATAD, 11 days earlier than unpretreated sludge. The enhanced release and hydrolysis of intracellular organics resulted in a solubilization degree of 45.3%. The reduced sludge viscosity and improved fluidity after thermal hydrolysis facilitated mixing, aeration and organics degradation during ATAD. Excitation emission matrix analysis indicated that the fluorescence intensity of soluble microbial byproduct and tyrosine-like protein increased markedly after thermal hydrolysis and decreased after ATAD. The proportion of high molecular weight (MW > 10 kDa) substances in the supernatant increased significantly after thermal hydrolysis, while the low MW (MW < 1 kDa) substances decreased after ATAD. The significant difference in microbial composition between the pretreatment and control groups elucidated the accelerated sludge stabilization under thermal hydrolysis. This work provides an efficient and practical strategy to achieve rapid stabilization of high solid sludge.

Low-molecular-weight dissolved organic nitrogen transformation behavior in concentrated leachate by O3 and •OH: Partition, molecular insight, and potential precursor-product relationship.

Low-molecular-weight dissolved organic nitrogen (LMW-DON) is an emerging issue in concentrated leachate (CL). Ozonation is crucial to remove LMW-DON, but selectivity mechanisms of different reactive oxygen species were unknown. Here, reactions of O3 and •OH with LMW-DON at different dosages were determined from composition, unsaturation/redox potential, and precursor-product relationship. The molecular weight of LMW-DON in CL presented a normal distribution and 76.5% was below 450 Da. LMW-DON with 400-1000 Da increased to 55.6%-66.7% and O/Cwa increased by over 40.0% due to electrophilic substitution of O3. LMW-DON with <400 Da and 550-1000 Da were preferentially degraded by •OH at the low and high O3 dosage, respectively. O3 preferred to remove lipid-like (69.1%), protein-like (58.2%), and amino sugars-like (72.8%) LMW-DON, whereas •OH preferred to the refractory LMW-DON, such as carbohydrates-like (71.1%), lignin-like (49.6%), and tannins-like (72.5%) LMW-DON. Forty-three transformation reactions were quantified using mass difference analysis, and O3 preferred to oxygen addition (e.g., +2O) and conversed amino to nitro groups, and saturated LMW-DON increased via unsaturated bonds rupture. •OH attacked the carbon groups (e.g., -CH2) and nitrogen groups (e.g., -NH3+O, -NO2+H). These findings provide molecular evidence for the selectivity of oxidants with LMW-DON and improve the ozonation application in wastewater treatment.

Polyhexamethylene biguanidine used as a new type sewage sludge conditioning agent: Effect on sludge dewaterability and mechanism.

Dewatering is the basic procedure of sludge treatment and disposal, and environmentally friendly and efficient sludge conditioning methods are urgently needed. Polyhexamethylene biguanide (PHMB), a broad-spectrum germicide used in daily life and medicine, was proposed as a sludge conditioning reagent in this paper, and its effect on waste activated sludge (WAS) dewaterability was studied for the first time. Results showed that PHMB can improve sludge dewatering performance, and capillary suction time (CST) and water content (Wc) of dewatered sludge cake was reduced by 78.11% and 13.37% with 100 mg PHMB/g dry sludge (DS). Further investigation revealed that the sludge properties changed pronouncedly after PHMB conditioning, the bound water content decreased from 1.58 g/g DS to 1.29 g/g DS, the particle size (D50) increased from 34.3 µm to 39.2 µm, the zeta potential increased from -20.96 mV to -3.36 mV, and the flowability increased whilst the viscosity decreased. When the dose of PHMB was lower than 50 mg/g DS, it mainly reacted with extracellular polymeric substance (EPS), resulting in a decrease in its content, which was also manifested by the decrease of molecular weights. However, when the dose reached 100 mg/g DS, PHMB would disrupt the cytomembranes of microorganisms and release cellular contents, reflected by a corresponding growth of EPS contents and the intensity of Fourier transform infrared (FTIR) spectrum. And the scanning electron microscope (SEM) images showed that PHMB conditioning made cracks and holes on sludge microstructures. The key mechanism of PHMB improving sludge dewaterability was inferred as "organic molecules disrupting" and "sludge particles flocculating". These findings demonstrate that PHMB is promising to be a novel, effective, and environmentally friendly sludge conditioning reagent.

Towards efficient elimination of polycyclic aromatic hydrocarbons (PAHs) from waste activated sludge by ozonation.

Sewage sludge is one of the sinks for PAHs accumulation and concerns are growing regarding the environmental risk of the discharge of PAHs in waste activated sludge (WAS) as a major byproduct of sewage treatment. Here, we evaluated the effectiveness of ozone treatment to eliminate the 16 priority PAHs in WAS. The PAHs removal efficiency increased with ozone dosage and was strongly pH dependent. Even at ozone dosage of 40 mg O3·g-1, the PAHs removal efficiency at pH 9.0 (44.5%) was significantly higher than that observed at pH 5.0 and 200 mg O3·g-1 (41.7%). The pH-dependent elimination behavior of PAHs was attributed to the varying yield of hydroxyl radicals (OH) and degree of sludge disintegration (R2 = 0.88-0.92). Over 96% of the PAHs were in the particulate flocs (PF) phase, while the fraction bound to the freely dissolved (FS) and dissolved and colloidal (DC) matters was negligible, indicating the need of WAS disintegration during ozonation to make PAHs more accessible to O3 molecules and OH to initiate oxidation reactions. Failure of the three-compartment model to describe the PAHs sorption behavior in sludge matrix during ozonation implied that oxidation reaction occurred simultaneously with the partitioning of PAHs from PS to DC/FS fraction. Lastly, the results of the intermittent ozonation experiment demonstrated the interference of soluble organic compounds during PAHs degradation, particularly proteins and humic substances, as O3 and OH scavengers. At ozone dosage of 120 mg O3·g-1 (pH 9.0), the PAHs removal efficiency was improved by 19.5% by intermittent ozonation, as compared to continuous ozonation under the same conditions.

Recovery of cathode materials from spent lithium-ion batteries and their application in preparing multi-metal oxides for the removal of oxygenated VOCs: Effect of synthetic methods.

Due to the sustainable use of wastes, cathode materials of spent lithium-ion batteries are recovered and used as transition metal precursors to prepare metal oxides catalysts for the oxidation of VOCs. In this work, a series of manganese-based and cobalt-based metal oxides are synthesized via different preparation methods. Catalytic activities of the catalysts prepared are investigated through complete oxidation of oxygenated VOCs and the physicochemical properties of optimum samples are characterized. Evaluation results indicate that MnOx (SY) (HT) sample prepared via hydrothermal method and CoOx (GS) (CP) synthesized via co-precipitation method had better performance, because they have higher specific surface area, higher concentration of active oxygen species and high-valence metal ion, as well as better low-temperature reducibility compared to the other multi-metal oxides used in the study. In addition, TD/GC-MS results imply that further oxidation of by-products requires high reaction temperature during VOCs oxidation.

A sodium dichloroisocyanurate-based conditioning process for the improvement of sludge dewaterability and mechanism studies.

Sludge dewatering is necessary to reduce the volume of sludge for cost-effective transport and ultimate disposal. In this study, a novel combined chemical conditioning process was proposed to improve sludge dewatering performance in which sludge flocs were destructed by sodium dichloroisocyanurate (DCCNa) and re-flocculated by Al2(SO4)3 and the mechanism was elucidated. The results showed that sludge capillary suction time (CST) dropped to 15.4 s and moisture content of dewatered sludge cake (Mc) deceased to 71.01% respectively, after the application of combined conditioning with the optimal dosage of 200 mg DCCNa/g dry solids (DS) and 80 mg Al2(SO4)3/g DS. With chemical conditioning, sludge physicochemical properties were greatly changed. With the DCCNa application, the percentage of low-molecular-weight substances in soluble extracellular polymeric substances (S-EPS) increased. Also, the sludge zeta potential dropped from -16.85 mV to -25.45 mV and the median particle size (D50) decreased from 54.1 µm to 51.6 µm. However, the subsequent conditioning by Al2(SO4)3 dosing not only led to an increment of 18% in the portion of macromolecules in S-EPS, but also increased the zeta potential and D50 to -10.74 mV and 53.2 µm, respectively. The bound water content in sludge declined from 2.92 g/g DS to 1.98 g/g DS after combined conditioning. We concluded that DCCNa disintegrated the sludge flocs and microbial cells leading to the release of bound water, fine particles and organic substances with negative charge, and the fine colloidal particles can be flocculated into large dense aggregations with the dosing of Al2(SO4)3. In summary, the proposed combined conditioning provided a highly effective and environmental friendly approach to improve the sludge dewatering performance.

Identifying the key sludge properties characteristics in Fe2+-activated persulfate conditioning for dewaterability amelioration and engineering implementation.

Fe2+-activated persulfate process has been introduced into sludge conditioning currently, however the key sludge properties characteristics are worthwhile comprehensively considering for the engineering implementation and management. The results indicated that both the optimal dosages of persulfate and Fe2+ were 0.6 mmol/gTS for sludge dewaterability amelioration, and the reduction efficiencies of capillary suction time (CST), specific resistance of filtration (SRF), and water content (Wc) of dewatered sludge cake reached to 90.5%, 97.2%, and 22.4%, respectively. Significantly, the persulfate and Fe2+ exerted distinctive roles in the conditioning process. The increased persulfate could promote the oxidatively disintegrated effect on sludge flocs, rendering the decrease of particle size. With the oxidative decomposition of the negatively charged biopolymers, sludge zeta potential rose gradually. However, Fe2+ contributed to more persulfate activation to generate free radicals, and the produced Fe3+ could further electrically neutralize the broken sludge fragments. The core mechanism of Fe2+-activated persulfate conditioning is "destroying and re-building" of sludge flocs. Noteworthily, EPS protein was oxidatively degraded more preferentially than EPS polysaccharide, and the decrease of the α-helix content of EPS protein was conducive to the enhancement of sludge dewaterability. Furthermore, the hydrophilic functional groups reduced clearly and element chemical states on sludge flocs altered pronouncedly, also the destroyed structure and microchannel facilitated the flowability of water. These findings provide theoretical and technical support for the practical engineering implementation of the Fe2+-activated persulfate conditioning process.

Insight into the roles of electrolysis-activated persulfate oxidation in the waste activated sludge dewaterability: Effects and mechanism.

Sludge dewatering, as one of the most important steps of sludge treatment, can facilitate transportation and improve disposal efficiency by reducing the volume of sludge. This study investigated the effects of electrolysis-activated persulfate oxidation on improving sludge dewaterability. The results indicated that the sludge capillary suction time (CST) and water content of dewatered sludge cake (Wc) reduced from 93.7 s and 87.8% to 9.7 s and 68.3% respectively at the optimized process parameters: electrolysis voltage of 40 V, electrolysis time of 20 min, and 1.2 mmol/g TS S2O82-. Correlation analysis revealed that the enhancement of sludge dewaterability was closely associated with the increased floc size and zeta potential, decreased protein content in three-layers extracellular polymeric substances (EPS) and viscosity (R = -0.868, p = 0.002; R = -0.703, p = 0.035; R ≥ 0.961, p < 0.001; R = 0.949, p < 0.001). Four protein fluorescence regions in EPS were analyzed by three-dimensional excitation-emission matrix parallel factor (3D-EEM-PARAFAC). The protein secondary structure was changed after the treatment, and the reduction of α-helix/(ß-sheet + random coil) indicated that more hydrophobic sites were exposed. Analysis by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) and rheological test demonstrated that the hydrophilic functional groups of the sludge were decreased and the sludge mobility was significantly enhanced after the treatment with electrolysis-activated persulfate oxidation. Moreover, bound water was converted to free water during SO4·- and ·OH generated by electrolysis-activated persulfate degraded EPS and attacked sludge cells. Meanwhile, scanning electron microscopy (SEM) images revealed that the treated sludge formed porous channel structures, which promoted the flowability of the water. These findings provide a new insight based on electrolysis-activated persulfate oxidation in sludge treatment for enhancing sludge dewaterability.

Enhancing the Stability of CH3NH3PbBr3 Quantum Dots by Embedding in Silica Spheres Derived from Tetramethyl Orthosilicate in "Waterless" Toluene.

Methylammonium lead halide perovskites suffer from poor stability because of their high sensitivity to moisture. Inorganic material coatings of SiO2 are preferred for coupling with perovskites to improve their stability, whereas the conventional SiO2 formation method is unsuitable because it requires water. Here, a simple SiO2 generation method based on the high hydrolysis rate of tetramethyl orthosilicate in analytical-grade toluene was developed to avoid the addition of water and catalyst. As a result, SiO2-encapsulated CH3NH3PbBr3 quantum dots (MAPB-QDs/SiO2) were fabricated without decreasing the quantum yield. Photostability tests indicated that the MAPB-QDs/SiO2 samples were markedly more stable than the unencapsulated MAPB-QDs. The photoluminescence (PL) of the MAPB-QDs/SiO2 powders was maintained at 94.10% after 470 nm LED illumination for 7 h, which was much higher than the remnant PL (38.36%) of the pure MAPB-QD sample under a relative humidity of 60%. Similar test results were observed when the MAPB-QDs/SiO2 powders were incorporated into the poly(methyl methacrylate) films. The enhanced photostability is ascribed to the SiO2 barriers protecting the MAPB-QDs from degradation.

Derivation of ecological criteria for copper in land-applied biosolids and biosolid-amended agricultural soils.

The difference in availability between soil metals added via biosolids and soluble salts was not taken into account in deriving the current land-applied biosolids standards. In the present study, a biosolids availability factor (BAF) approach was adopted to investigate the ecological thresholds for copper (Cu) in land-applied biosolids and biosolid-amended agricultural soils. First, the soil property-specific values of HC5add (the added hazardous concentration for 5% of species) for Cu2+ salt amended were collected with due attention to data for organisms and soils relevant to China. Second, a BAF representing the difference in availability between soil Cu added via biosolids and soluble salts was estimated based on long-term biosolid-amended soils, including soils from China. Third, biosolids Cu HC5input values (the input hazardous concentration for 5% of species of Cu from biosolids to soil) as a function of soil properties were derived using the BAF approach. The average potential availability of Cu in agricultural soils amended with biosolids accounted for 53% of that for the same soils spiked with same amount of soluble Cu salts and with a similar aging time. The cation exchange capacity was the main factor affecting the biosolids Cu HC5input values, while soil pH and organic carbon only explained 24.2 and 1.5% of the variation, respectively. The biosolids Cu HC5input values can be accurately predicted by regression models developed based on 2-3 soil properties with coefficients of determination (R2) of 0.889 and 0.945. Compared with model predicted biosolids Cu HC5input values, current standards (GB4284-84) are most likely to be less protective in acidic and neutral soil, but conservative in alkaline non-calcareous soil. Recommendations on ecological criteria for Cu in land-applied biosolids and biosolid-amended agriculture soils may be helpful to fill the gaps existing between science and regulations, and can be useful for Cu risk assessments in soils amended with biosolids.

Environmental impacts of a large-scale incinerator with mixed MSW of high water content from a LCA perspective.

Large-scale incinerators are applied widely as a result of the heavy burden of municipal solid waste (MSW) generated, while strong opposition is arising from the public living nearby. A large-scale working incineration plant of 1500 ton/day was chosen for evaluation using life cycle assessment. It was found that the corresponding human toxicity impacts via soil (HTs), human toxicity impacts via water (HTw) and human toxicity impacts via air (HTa) categories are 0.213, 2.171, and 0.012 personal equivalents (PE), and global warming (GW100) and nutrient enrichment (NE) impacts are 0.002 and 0.001 PE per ton of waste burned for this plant. Heavy metals in flue gas, such as Hg and Pb, are the two dominant contributors to the toxicity impact categories, and energy recovery could reduce the GW100 and NE greatly. The corresponding HTs, HTw and HTa decrease to 0.087, 0.911 and 0.008 PE, and GW100 turns into savings of -0.007 PE due to the increase of the heating value from 3935 to 5811 kJ/kg, if a trommel screener of 40 mm mesh size is used to pre-separate MSW. MSW sorting and the reduction of water content by physical pressure might be two promising pre-treatment methods to improve the combustion performance, and the application of stricter standards for leachate discharge and the flue gas purification process are two critical factors for improvement of the environmental profile identified in this work.

Greenhouse gas emission and its potential mitigation process from the waste sector in a large-scale exhibition.

As one of the largest human activities, World Expo is an important source of anthropogenic Greenhouse Gas emission (GHG), and the GHG emission and other environmental impacts of the Expo Shanghai 2010, where around 59,397 tons of waste was generated during 184 Expo running days, were assessed by life cycle assessment (LCA). Two scenarios, i.e., the actual and expected figures of the waste sector, were assessed and compared, and 124.01 kg CO2-equivalent (CO2-eq.), 4.43 kg SO2-eq., 4.88 kg NO3--eq., and 3509 m3 water per ton tourist waste were found to be released in terms of global warming (GW), acidification (AC), nutrient enrichment (NE) and spoiled groundwater resources (SGWR), respectively. The total GHG emission was around 3499 ton CO2-eq. from the waste sector in Expo Park, among which 86.47% was generated during the waste landfilling at the rate of 107.24 kg CO2-eq., and CH4, CO and other hydrocarbons (HC) were the main contributors. If the waste sorting process had been implemented according to the plan scenario, around 497 ton CO2-eq. savings could have been attained. Unlike municipal solid waste, with more organic matter content, an incineration plant is more suitable for tourist waste disposal due to its high heating value, from the GHG reduction perspective.

The influence of factors on dewaterability of one-stage autothermal thermophilic aerobically digested sludges.

One-stage auto thermophilic aerobic digestion (ATAD) could achieve the same sludge stabilization efficiency as two- or multi-stage ATAD process does. However, the dewaterability of sludge might be affected through thermophilic digestion because of the release of intracellular substances under the thermophilic temperatures. This paper investigated which operation factors affect intracellular substances released in the liquid phase of sludge that lead to different extent of dewaterability. The results showed that optimal digestion time needs to be prolonged up to 480 h to avoid a deteriorated dewaterability phase. The deterioration in dewaterability of the sludge could be minimized at a retention time of 360 h (i.e., 15 days) under a digestion temperature of 65 °C. Specific capillary suction time (SCST) had quadratic correlations with SCOD, protein (PN) and polysaccharides (PS) in the liquid phase. The coefficient between SCST and the ratio of PN/PS had a value of 0.9764, indicating that the sludge dewaterability was significantly deteriorated by biopolymer of protein and polysaccharides in supernatant.