Thermal behaviors and heavy metal vaporization of phosphatized tannery sludge in incineration process

The high concentration of heavy metal (Cu, Cr, Zn, Pb) in tannery sludge causes severe heavy metal emissions in the process of incineration. In the present investigation, the tannery sludge was treated with 85% phosphoric acid before the incineration process in the tube furnace to control the heavy metal emissions. The thermal behavior and heavy metal vaporization of pre-treated tannery sludge were investigated, and X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were also implemente...     

Thermal stabilization of chromium slag by sewage sludge: Effects of sludge quantity and temperature

To investigate the feasibility of detoxifying chromium slag by sewage sludge,synthetic chromium slag containing 3% of Cr(VI) was mixed with sewage sludge followed by thermal treatment in nitrogen gas for stabilizing chromium.The effects of slag to sludge ratio(0.5,1 and 2) and temperature(200,300,500,700 and 900°C) on treatment efficiency were investigated.During the mixing process before thermal treatment,59.8%-99.7% of Cr(VI) was reduced,but Cr could be easily leached from the reduction product.Increasing heating temperature and decreasing slag to sludge ratio strengthened the reduction and stabilization of Cr(VI).When the slag to sludge ratio was 0.5 and thermal treatment temperature was 300°C,the total leached Cr and Cr(VI) declined to 0.55 mg/L and 0.17 mg/L respectively,and 45.5% of Cr in the thermally treated residue existed as residual fraction.A two-stage mechanism was proposed for the reduction and stabilization of Cr.     

Removal of Cr from tannery sludge by bioleaching method

Bioleaching of Cr（Ⅲ） from tannery sludge using the mixture of ingenuous iron- and sulfur-oxidizing bacteria was investigated in batch flasks. Experiments involved the adaptation of indigenous iron-and sulfur-oxidizing bacteria, the pre-acidification the sludge to pH 6.0 and the addition of energy substrates. Results showed the inoculation of mixture of ingenuous iron- and sulfur-oxidizing bacteria and co-addition of Fe^2 and elemental sulfur accelerated acid production and increase of oxidation-reduction potential originating from the bio-oxidation of Fe2^＋ and elemental sulfur. Dissolved Cr concentration increased concomitant with pH decreased in the sludge and reached its maximum removal of 95.6%. The amelioration of the odor of bioleached sludge could be noted. However, 20.4%o of N, 24.5% of P and 14.3% of organic matter were lost in the bioleaching process. The residual Cr content in the leached tannery sludge was acceptable for use in agriculture. This study had shown the feasibility of applying the bioleaching process, developed for sewage sludge, to tannery sludge with high Cr.     

Nitrite pre-treatment of dewatered sludge for microbial fuel cell application

The effect of pre-treatment of dewatered sludge using different nitrite concentrations and pH for microbial fuel cell (MFC) application was investigated. The results show that the addition of nitrite was feasible to increase the solubilization rate of the sludge and may reduce mass transfer limitation at the anode. This helped the MFC to reach higher voltage and to generate more power. The higher free nitrous acid (FNA) concentration under the acidic condition helped to increase sludge solubilization. However, under an alkaline condition, during which the FNA concentration was relatively low, the solubilization of the sludge was higher. The highest voltage and power density produced was 390?mV and 153?mW/m², respectively, with the addition of nitrite at 100?mg-N/L and pH?9. Furthermore, it was found that elevated levels of FNA could inhibit electrogenic bacteria thus reducing power generation.     

Preliminary study on the electrocatalytic performance of an iron biochar catalyst prepared from iron-enriched plants

Eichhornia crassipes is a hyperaccumulator of metals and has been widely used to remove metal pollutants from water, but disposal of contaminated plants is problematic.Biochar prepared from plants is commonly used to remediate soils and sequester carbon.Here, the catalytic activity of biochar prepared from plants enriched with iron was investigated as a potentially beneficial use of metal-contaminated plants.In a 30-day hydroponic experiment, E.crassipes was exposed to different concentrations of Fe(Ⅲ)(0, 4, 8, 16, 32 and 64 mg/L), and Fe-biochar(Fe-BC) was prepared by pyrolysis of the plant roots.The biochar was characterized using X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectrometry(EDS), Brunauer–Emmett–Teller(BET) analysis, X-ray photoelectron spectroscopy(XPS) and atomic absorption spectrometry(AAS).The original root morphology was visible and iron was present as γ-Fe_2O_3 and Fe_3O_4.The biochar enriched with Fe(Ⅲ) at 8 mg/L(8-Fe-BC) had the smallest specific surface area(SSA, 13.54 m~2/g) and the highest Fe content(27.9 mg/g).Fe-BC catalytic activity was tested in the electrocatalytic reduction of H_2O_2 using cyclic voltammetry(CV).The largest reduction current(1.82 mA/cm~2) was displayed by 8-Fe-BC, indicating the highest potential catalytic activity.We report here, for the first time, on the catalytic activity of biochar made from iron-enriched plants and demonstrate the potential for reusing metalcontaminated plants to produce a biochar catalyst.     

Leaching of metals on stabilization of metal sludge using cement based materials

Toxicity characteristic leaching procedure(TCLP) of zinc plating sludge was carried out to assess the leaching potential of the sludge and the leachates were analyzed for heavy metals. The concentration of zinc, chromium, and lead in the leachate were 371.5 mg/L, 1.95 mg/L and 1.99 mg/L respectively. Solidification of zinc sludge was carried out using four different binder systems consisting of cement mortar, fly ash, clay and lime and cured for 28 d, The ratio of sludge added varied from 60% to 80% by volume. The solidified products were tested for metal fixing efficiency and physical strength. It was observed that the volume of sludge added that resulted in maximum metal stabilization was 60% for all the combinations, above which the metal fixation efficiency decreased resulting in high values of zinc in the leachate. Addition of 5% sodium silicate enhanced the chemical fixation of metals in all the binder systems. Among the four fixing agents studied, mixture of fly ash: lime, and cement mortar: lime stabilized zinc and other metals in the sludge effectively than other combinations. Addition of lime increased the stabilization of zinc whereas cement mortar increased the strength of the solidified product.     

Effect of biomass addition on the surface and adsorption characterization of carbon-based adsorbents from sewage sludge

Sewage sludge with the additive corn cob was used as prescusor to prepare sludge-based carbon adsorbents by pyrolysis method. And then, the carbonizated products were activated with potassium hydroxide. The mixing ratio of the corn cob to sewage sludge was investigated. The surface area and pore size distribution, elemental composition, surface chemistry structure and the surface physical morphology were determined and compared. The results demonstrated that the addition of corn cob into the sewage sludge sample could effectively improve the surface area (from 287 to 591 m 2 /g) and the microporosity (from 5% to 48%) of the carbon based adsorbent, thus enhancing the adsorption behavior. The sulfur dioxide adsorption capacity was measured according to breakthrough test. It was found that the sulfur dioxide adsorption capacity of the adsorbents was obviously enhanced after the addition of the corn cob. It is presumed that not only highly porous adsorbents, but also a high metallic content of these materials are required to achieve good performances.     

Effect of manganese oxide-modified biochar addition on methane production and heavy metal speciation during the anaerobic digestion of sewage sludge

Low organic matter content and high heavy metal levels severely inhibit the anaerobic digestion (AD) of sewage sludge. In this study, the effect of added manganese oxide-modified biochar composite (MBC) on methane production and heavy metal fractionation during sewage sludge AD was examined. The MBC could increase the buffering capacity, enhance the methane production and degradation of intermediate acids, buffer the pH of the culture, and stabilize the sewage sludge AD process. The application of MBC positively impacted methane production and the cumulative methane yield increased up to 121.97%, as compared with the control. The MBC addition can improve metal stabilization in the digestate. An optimum MBC dose of 2.36?g was recommended, which would produce up to 121.1?L/kg volatile solids of methane. After the AD process, even though most of the metals accumulated in the residual solids, they could be transformation from the bio-available fractions to a more stable fraction. The total organic- and sulfide-bound and residual fraction content at a 3?g dose of MBC that is 0.12?g/g dry matter were 51.06% and 35.11% higher than the control, respectively. The results indicated that the application of MBC could improve the performance of AD and promote stabilization of heavy metals in sewage sludge post the AD process.     

Humification characterization of biochar and its potential as a composting amendment

Biochar has received increasing attention due to its applications as a soil amendment. Here, the chemical properties of solid and water-extractable fractions of four biochar samples were investigated. The results showed that wood biochar and bamboo biochar samples were 60%–80% more hydrophobic than those of rice husk biochar and rice husk ash. In addition, the acidity was 3.88 mmol/g from the total functional groups and 1.03 mmol/g from the carboxyl groups/lactones/phenols found in the wood biochar sample, which were about 1.5 times greater than those of the bamboo biochar sample. These functional groups could be used to determine the sorptive capacity of biochar for ionic solutes and water content and to increase the degradation of compost organics. The wood biochar sample was found to have the most humification materials(fulvic acid-like material + humic acid-like material) in the water-extractable fraction, which was 3–10 times higher than that in the rice husk biochar and rice husk ash; humified materials were not detected in the bamboo biochar sample. Humification materials in biochar may be involved in increasing the proportion of humic acid-like materials in humic-like substances within the compost product. Wood biochar had better hydrophobic, sorptive, aromatic, and humification properties compared to other biochars, suggesting that it may be used in composting in order to exert its effect as both a bulking agent and a composting amendment during the solid waste composting process.     

Impacts of produced water origin on bacterial community structures of activated sludge

The purpose of this study was to reveal how activated sludge communities respond to influent quality and indigenous communities by treating two produced waters from different origins in a batch reactor in succession. The community shift and compositions were investigated using Polymerase Chain Reaction–denaturing gradient gel electrophoresis(PCR–DGGE) and further16 S ribosomal DNA(r DNA) clone library analysis. The abundance of targeted genes for polycyclic aromatic hydrocarbon(PAH) degradation, nah Ac/phn Ac and C12O/C23 O, was tracked to define the metabolic ability of the in situ microbial community by Most Probable Number(MPN) PCR. The biosystem performed almost the same for treatment of both produced waters in terms of removals of chemical oxygen demand(COD) and PAHs. Sludge communities were closely associated with the respective influent bacterial communities(similarity 60%), while one sludge clone library was dominated by the Betaproteobacteria(38%) and Bacteriodetes(30%)and the other was dominated by Gammaproteobacteria(52%). This suggested that different influent and water quality have an effect on sludge community compositions. In addition, the existence of catabolic genes in sludge was consistent with the potential for degradation of PAHs in the treatment of both produced waters.     

Insights into sludge granulation during anaerobic treatment of high-strength leachate via a full-scale IC reactor with external circulation system

In this study, a full-scale internal circulation(IC) reactor coupled with an external circulation system was developed to treat high-strength leachate from a municipal solid waste(MSW)incineration plant, in which anaerobic sludge granulation was intensively investigated. Results showed that the IC reactor achieved excellent treatment performance under high organic loading rates(OLR) of 21.06–25.16 kg chemical oxygen demand(COD)/(m3? day). The COD removal efficiency and biogas yield respectively reached 89.4%–93.4% and 0.42–0.50 m3/kg COD.The formation of extracellular polymeric substances(EPS) was closely associated with sludge granulation. Protein was the dominant component in sludge EPS, and its content was remarkably increased from 21.6 to 99.7 mg/g Volatile Suspended Solid(VSS) during the reactor operation. The sludge Zeta potential and hydrophobicity positively correlated with the protein/polysaccharide ratio in EPS, and they were respectively increased from-26.2 m V and 30.35% to-10.6 m V and 78.67%, which was beneficial to microbial aggregation. Three-dimensional fluorescence spectroscopy(3 D-EEM) and Fourier transform infrared spectroscopy(FT-IR)analysis further indicated the importance of protein-like EPS substances in the sludge granulation. Moreover, it was also found that the secondary structures of EPS proteins varied during the reactor operation.     

Sewage sludge disintegration by high-pressure homogenization: A sludge disintegration model

High-pressure homogenization (HPH) technology was applied as a pretreatment to disintegrate sewage sludge. The effects of homogenization pressure, homogenization cycle number, and total solid content on sludge disintegration were investigated. The sludge disintegration degree (DDCOD), protein concentration, and polysaccharide concentration increased with the increase of homogenization pressure and homogenization cycle number, and decreased with the increase of sludge total solid (TS) content. The maximum DDCOD of 43.94% was achieved at 80 MPa with four homogenization cycles for a 9.58 g/L TS sludge sample. A HPH sludge disintegration model of DD_COD= kN^aP^b was established by multivariable linear regression to quantify the effects of homogenization parameters. The homogenization cycle exponent a and homogenization pressure exponent b were 0.4763 and 0.7324 respectively, showing that the effect of homogenization pressure (P) was more significant than that of homogenization cycle number (N). The value of the rate constant k decreased with the increase of sludge total solid content. The specific energy consumption increased with the increment of sludge disintegration efficiency. Lower specific energy consumption was required for higher total solid content sludge.     

Evaluation of fungal potentiality for bioconversion of domestic wastewater sludge

This study was undertaken to screen the filamentous fungi isolated from its relevant habitats (wastewater, sewage sludge and sludge cake) for the bioconversion of domestic wastewater sludge. A total of 35 fungal strains were tested against wastewater sludge (total suspended solids, TSS 1%-5% w/w) to evaluate its potentiality for enhancing the biodegradability and dewaterability using liquid state bioconversion(LSB) process. The strains were divided into five groups i. e. Penicillium, Aspergillus, Trichoderma, Basidiomycete and Miscellaneous, respectively. The strains WWZP1003, SCahmA103, SCahmT105 and PC-9 among their respective groups of Penicillium,Aspergillus, Trichoderma and Basidiomycete played potential roles in terms of separation (formation of pellets/flocs/filaments),biodegradation(removal of COD) and filtration(filterability) of treated domestic wastewater sludge. The Miscellaneous group was not considered due to its unsatisfactory results as compared to the other groups. The pH value was also influenced by the microbial treatment during fermentation process. The filterability of treated sludge was improved by fungal treatment, and lowest filtration time was recorded for the strain WWZP1003 and SCahmA103 of Penicillium and Aspergillus groups respectively compared with other strains.     

The key role of inoculated sludge in fast start-up of sequencing batch reactor for the domestication of aerobic granular sludge

Two types of inoculated sludges, granular sludge that had been stored at-20°C and activated sludge, were investigated for the domestication of aerobic granular sludges(AGSs in sequencing batch reactors(SBRs). The results showed that using the stored granular sludge as inoculation sludge could effectively shorten the domestication time of AGS and yielded mature granular sludge after 22 days of operation. The AGS domesticated by stored granular sludge had better biomass and sedimentation properties; its MLSS and SVI reached8.55 g/L and 35.27 mL/g, respectively. The removal efficiencies for chemical oxygen demand(COD), ammonium nitrogen(NH_4~+-N) and total phosphorus(TP) reached 90.76%, 97.39% and 96.40%, respectively. By contrast, 54 days were needed to obtain mature granules using activated sludge. The microbial community structure was probed by using scanning electron microscopy(SEM) and high-throughput sequencing. The results showed that the diversity of the microbial community in mature granules was reduced when stored granular sludge rather than activated sludge was employed as inoculation sludge, and the dominant microbes were changed. The dominant species in mature granules domesticated using stored granular sludge were Zoogloea, Acidovorax and Tolumonas at the genus classification level, while the dominant species were Zoogloea and TM7-genera in granules developed from activated sludge.     

Influence of sodium dodecyl sulfate coating on adsorption of methylene blue by biochar from aqueous solution

Biochar is regarded as a promising new class of materials due to its multifunctional character and the possibility of effectively coupling different properties. With increasing introduction into the environment, environmental chemicals such as surfactants will load onto the released biochar and change its physicochemical characteristics and adsorption behavior toward pollutants. In this study, sodium dodecyl sulfate(SDS), as one type of anionic surfactant, was coated onto biochar with different loading amounts. The influence of SDS loading onto biochar's physicochemical properties were investigated by Fourier transform infrared(FT-IR) spectroscopy, elemental analysis, zeta potential and Brunauer–Emmett–Teller(BET) surface area and pore size distribution analysis. Results showed that the pore size of the biochar decreased gradually with the increase of SDS loading because of the surface-adsorption and pore-blocking processes; the p H of the point of zero charge(pHPZC) decreased with increasing SDS loading. Although surface-coating with SDS decreased the pore size of the biochar, its adsorption capacity toward Methylene Blue(MB) significantly increased. The biochar-bound SDS introduced functional groups and negative charges to the biochar surface, which could thus enhance the adsorption of MB via hydrogen bonding and electrostatic interaction. The results can shed light on the underlying mechanism of the influence of anionic surfactants on the adsorption of MB by biochar.     

Phosphorus recovery from biogas fermentation liquid by Ca-Mg loaded biochar

Shortage in phosphorus (P) resources and P wastewater pollution is considered as a serious problem worldwide. The application of modified biochar for P recovery from wastewater and reuse of recovered P as agricultural fertilizer is a preferred process. This work aims to develop a calcium and magnesium loaded biochar (Ca-Mg/biochar) application for P recovery from biogas fermentation liquid. The physico-chemical characterization, adsorption efficiency, adsorption selectivity, and postsorption availability of Ca-Mg/biochar were investigated. The synthesized Ca-Mg/biochar was rich in organic functional groups and in CaO and MgO nanoparticles. With the increase in synthesis temperature, the yield decreased, C content increased, H content decreased, N content remained the same basically, and BET surface area increased. The P adsorption of Ca-Mg/biochar could be accelerated by nano-CaO and nano-MgO particles and reached equilibrium after 360 min. The process was endothermic, spontaneous, and showed an increase in the disorder of the solid-liquid interface. Moreover, it could be fitted by the Freundlich model. The maximum P adsorption amounts were 294.22, 315.33, and 326.63 mg/g. The P adsorption selectivity of Ca-Mg/biochar could not be significantly influenced by the typical pH level of biogas fermentation liquid. The nano-CaO and nano-MgO particles of Ca-Mg/biochar could reduce the negative interaction effects of coexisting ions. The P releasing amounts of postsorption Ca-Mg/biochar were in the order of Ca-Mg/B600 > Ca-Mg/B450 > Ca-Mg/B300. Results revealed that postsorption Ca-Mg/biochar can continually release P and is more suitable for an acid environment.     

Adsorption behavior of sulfamethazine in an activated sludge process treating swine wastewater

Swine wastewater is an important pollution source of antibiotics entering the aquatic environment. In this work,the adsorption behavior of sulfamethazine(SMN),a commonlyused sulfonamide antibiotic,on activated sludge from a sequencing batch reactor treating swine wastewater was investigated. The results show that the adsorption of SMN on activated sludge was an initially rapid process and reached equilibrium after 6 hr. The removal efficiency of SMN from the water phase increased with an increasing concentration of mixed liquor suspended solids,while the adsorbed concentration of SMN decreased. Solution pH influenced both the speciation of SMN and the surface properties of activated sludge,thus significantly impacting the adsorption process. A linear partition model could give a good fit for the equilibrium concentrations of SMN at the test temperatures(i.e.,10,20 and 30°C). The partition coefficient(Kd) was determined to be 100.5 L/kg at 20°C,indicating a quite high adsorption capacity for SMN. Thermodynamic analysis revealed that SMN adsorption on activated sludge was an exothermic process. This study could help to clarify the fate and behavior of sulfonamide antibiotics in the activated sludge process and assess consequent environmental risks arising from sludge disposal as well.     

Effect of biochar on fate and transport of manure-borne estrogens in sandy soil

The feasibility of using two types of biochars to reduce steroid hormone pollution from poultry and swine manure application on agricultural land was evaluated.The sorption affinity and desorption resistance of softwood and hardwood biochars were also determined for two estrogen hormones,17β-estradiol(E2) and its primary metabolite estrone(E1).The softwood and hardwood biochars demonstrated high retention capacity for both estrogens.The effective distribution coefficient(K_d~(eff)) of soil-softwood-derived biochar(SBS_(450)) was significantly higher than soil-hardwood-derived biochar(SBH750),indicating the stronger sorption affinity of SBS450 for estrogens.To validate the laboratory results,a field lysimeter experiment was conducted to study the fate and transport of E2 and E1 in soil and leachate in the presence of 1% softwood-biochar(BS450) in topsoil and to compare it with soil without any amendments.The spatio-temporal distribution of both estrogens was monitored at four depths over a 46-day period.The lysimeters,in which the surface layer of soil was amended with biochar,retained significantly higher concentrations of both estrogen hormones.Although they leached through the soil and were detected in leachates,collected at 1.0 m depth,the concentrations were significantly lower in the leachate collected from biochar-amended lysimeters.The result confirmed the efficacy of biochar amendment as a remediation technique to alleviate the manure-borne hormonal pollution of groundwater.     

Municipal sludge as landfill barrier material

The aim of this research is to find substitute barrier materials for natural clay from two kinds of municipal sludge: waterworks sludge( Sw ) and dredging sludge( Sd ). Laboratory tests were performed firstly to determine their Atterberg limits and hydraulic conductivity.Based on the results, the use of waterworks sludge was recommended. Then, shear strength tests were performed and it was found the shear resistance property of waterworks sludge is strong enough to maintain slope stability. In order to evaluate the possibility of secondary pollution, the heavy metal contents of waterworks sludge was determined and the results indicated that secondary pollution is unlikely happened. Finally, economic analysis proves that reusing waterworks sludge as barrier will reduce the lost a great for both landfill and waterworks. Based on the results, waterworks sludge was proposed to use and a further long-term simulated landfill test was suggested.