Degradation of refractory organic matter in the effluent from a semi-aerobic aged refuse biofilter-treated landfill leachate by a nano-Fe3O4 enhanced ozonation process.

In this study, the transformation and degradation mechanisms of refractory organic matter in biologically treated leachate from a semi-aerobic aged refuse biofilter (SAARB) in a nano-Fe3O4 enhanced ozonation process (nFe3O4-O3) were investigated in batch experiments. A continuous experiment then confirmed the effectiveness of the process for SAARB effluent treatment. In a batch experiment, the effects of influencing factors, including nFe3O4 dosage, O3 dosage and initial pH on the treatment performance of nFe3O4-O3 process, were comprehensively investigated. The results showed that when the nFe3O4 dosage = 6 g L-1, O3 dosage = 0.15 L minute-1 and initial pH = 7, the total organic carbon, absorbance at 254 nm and colour number removal efficiencies were 40.58%, 62.55% and 89.80%, respectively. In addition, most of the humic- and fulvic-like substances in the SAARB effluent were removed, and the condensation degree, aromaticity and humification degree of the organics were substantially reduced. The morphology and elemental valence state analysis showed that the nFe3O4 in the process was relatively stable and could form an nFe3O4-organic complex. Therefore, the probability of organics reacting with hydroxyl radical increased and the oxidation efficiency was enhanced. In the continuous experiment, both the O3 dosage and hydraulic retention time (HRT) were the key influencing factors. The treatment efficiency of the nFe3O4-O3 process was enhanced at a higher O3 dosage and longer HRT. The electrical energy consumption of the continuous nFe3O3-O3 process was calculated to be 17.72 kW h m-3 in SAARB effluent treatment. This study proved the feasibility of biologically treated landfill leachate treatment by the nFe3O3-O3 process.

Effect of biochar addition on the removal of organic and nitrogen pollutants from leachate treated with a semi-aerobic aged refuse biofilter.

The effect of biochar on the removal of organic and nitrogen contaminants from leachate in a semi-aerobic aged refuse biofilter (SAARB) was investigated. A preset amount of biochar was mixed with the aged refuse to explore the enhancement ability of pollutant removal by characterizing the leachate effluent and gas. The results showed that biochar contributed to the removal of organic and nitrogen pollutants from the leachate and that increasing the amount of biochar added led to higher colour number, chemical oxygen demand, ammonia nitrogen, and total nitrogen removal efficiencies. Furthermore, the addition of biochar significantly increased the removal of large molecule organic pollutants from the leachate. The improved removal of organics was due to the considerable number of surface functional groups and the large surface area of the biochar, which effectively absorbed and removed a significant amount of the organic matter from the leachate. Biochar elevated the dissolved oxygen concentration in the semi-aerobic system, which facilitated the completion of the nitrification reaction. It also promoted denitrification by acting as a supplementary carbon source. The nitrous oxide (N2O) emissions decreased as the amount of biochar added increased. When the biochar proportion reached 3%, the N2O emission was only 1.11% of the original total nitrogen and the di-nitrogen emission was 19.61%. The findings of this study can be used to improve the treatment of leachate using biochar combined with a SAARB.

Stabilization of solid digestate and nitrogen removal from mature leachate in landfill simulation bioreactors packed with aged refuse.

Digestate from biogas plants managing municipal solid waste needs to be stabilized prior to final utilization or disposal. Based on the concept of urban mining, aged refuse from a closed landfill was used to treat landfill leachate, but nitrogen removal by biological denitrification was limited. The aim of this study was to use a digestate layer in bioreactors containing aged refuse to enhance the biological denitrification capacity of the aged refuse, stabilize digestate, and mitigate the ammonia emissions from digestate leaching with leachate recirculation. Six identical landfill columns filled with 0% (R0), 5% (R5), and 15% (R15) of solid digestate above aged refuse (ratios based on Total Solids) were setup and nitrified leachate was periodically fed and recirculated to the columns. The nitrate removal rate in R5 and R15 was 3.4 and 10 times higher relative to the control (no digestate added). A 31.5-35.9% increase of solid digestate biostability was confirmed by tests performed under both aerobic and anaerobic conditions. The results showed that instead of land use, the solid fraction of digestate could be utilized as an inexpensive functional layer embedded in an old landfill site to enhance the denitrification capacity and achieve digestate stabilization with minimal ammonia leaching from digestate.

Assessment and analysis of aged refuse as ammonium-removal media for the treatment of landfill leachate.

This is the first attempt to explore the sustainability of aged refuse as ammonium-removal media. Batch experiments combined with the aged-refuse-based reactor were performed to examine how the adsorption and desorption processes are involved in the ammonia removal via aged refuse media in this research. The results showed that the adsorption of ammonium by aged refuse occurred instantly and the adsorbed ammonium was stable and less exchangeable. The adsorption data fit the Freundlich isotherms well and the n value of 0.1-0.5 indicated that the adsorption of ammonium occurred easily. The maximum adsorbed ammonium occupied less than 10% of the cation exchange capacity in aged-refuse-based reactors owing to the high solid/liquid ratios (50:1-120:1). The synergistic transformations of ammonium within the aged-refuse-based reactor indicated that the cation exchange sites only provide temporary storage of ammonium, and the subsequent nitrification process can be considered the predominant restoration pathway of ammonium adsorption capacity of the reactor. It seems reasonable to assume that there is no expiry for the aged-refuse-based reactor in terms of ammonium removal owing to its bioregeneration via nitrification.

Characteristics of H2S emission from aged refuse after excavation exposure.

Hydrogen sulfide (H2S(g)) emission from landfills is a widespread problem, especially when aged refuse is excavated. H2S(g) emission from aged refuse exposed to air was investigated and the results showed that large amounts of H2S(g) can be released, especially in the first few hours after excavation, when H2S(g) concentrations in air near refuse could reach 2.00 mg m(-3). Initial exposure to air did not inhibit the emission of H2S(g), as is generally assumed, but actually promoted it. The amounts of H2S(g) emitted in the first 2 d after excavation can be very dangerous, and the risks associated with the emission of H2S(g) could decrease significantly with time. Unlike a large number of sulfide existed under anaerobic conditions, the sulfide in aged municipal solid waste can be oxidized chemically to elemental sulfur (but not sulfate) under aerobic conditions, and its conversion rate was higher than 80%. Only microorganisms can oxidize the reduced sulfur species to sulfate, and the conversion rate could reach about 50%. Using appropriate techniques to enhance these chemical and biological transformations could allow the potential health risks caused by H2S(g) after refuse excavation to be largely avoided.

Destabilization mechanisms of Semi-aerobic aged refuse biofilters under harsh treatment conditions: Evidence from fluorescence and microbial characteristics.

Semi-aerobic aged refuse biofilters (SAARB) are commonly-used biotechnologies for treating landfill leachate. In actual operation, SAARB often faces harsh conditions characterized by high concentrations of chemical oxygen demand (COD) and Cl-, as well as a low carbon-to-nitrogen ratio (C/N), which can disrupt the microbial community within SAARB, leading to operational instability. Maintaining the stable operation of SAARB is crucial for the efficient treatment of landfill leachate. However, the destabilization mechanism of SAARB under harsh conditions remains unclear. To address this, the study simulated the operation of SAARB under three harsh conditions, namely, high COD loading (H-COD), high chloride ion (Cl-) concentration environment (H-Cl-), and low C/N ratio environment (L-C/N). The aim is to reveal the destabilization mechanism of SAARB under harsh conditions by analyzing the fluorescence characteristics of effluent DOM and the microbial community in aged refuse. The results indicate that three harsh conditions have different effects on SAARB. H-COD leads to the accumulation of proteins; H-Cl- impedes the reduction of nitrite nitrogen; L-C/N inhibits the degradation of humic substances. These outcomes are attributed to the specific effects of different factors on the microbial communities in different zones of SAARB. H-COD and L-C/N mainly affect the degradation of organic matter in aerobic zone, while H-Cl- primarily impedes the denitrification process in the anaerobic zone. The abnormal enrichment of Corynebacterium, Castellaniella, and Sporosarcina can indicate the instability of SAARB under three harsh conditions, respectively. To maintain the steady operation of SAARB, targeted acclimation of the microbial community in SAARB should be carried out to cope with potentially harsh operating conditions. Besides, timely mitigation of loads should be implemented when instability characteristics emerge, and carbon sources and electron donors should be provided to restore treatment performance effectively.

Enhanced performance and mechanism of the combined process of ozonation and a semiaerobic aged refuse biofilter for mature landfill leachate treatment.

A semiaerobic aged refuse biofilter (SAARB) can effectively treat mature landfill leachate (ML), but prolonged operation can lead to the enrichment of pollutants in the biofilter, resulting in severely degraded treatment performance. In this study, we constructed a combination process of ozonation and a SAARB to treat ML based on the principles of selective oxidation of aromatic organics by ozone and the preference of microorganisms for ozonation products. The results showed that the removal of organic and nitrogen pollutants became extremely poor after long-term treatment of ML using the SAARB alone. The decrease of chemical oxygen demand (COD), light absorbance at 254 nm (UV254), NH4+, and total nitrogen (TN) improved significantly after recirculating the ozonated ML effluent (OLE) into the SAARB, and the removal extents increased significantly to 63.59% (COD), 26.14% (UV254), 92.85% (NH4+), and 52.04% (TN), respectively. In addition, the recirculation of OLE enhanced the complete denitrification and tolerance to high NH4+ loading by the SAARB. An analysis of the community composition of 16S_bacteria and ammonia oxidation bacteria (AOB) showed that long-term treatment of ML using the SAARB alone had difficulty enriching the dominant functional bacteria. In the OLE recirculation stage, environmental factors-such as influent organic matter species and concentration, nitrogen pollutant concentration, and pH-were changed to influence the community composition of 16S_bacteria and AOB and enrich functional bacteria (e.g., Truepera, Luteibacter, and Nitrosospira). Therefore, ozonation combined with a SAARB can remove organic and nitrogen pollutants more effectively. In particular, this can be used to solve the problem of inefficient total nitrogen removal using the SAARB alone. This study provides a theoretical reference for the efficient and stable operation of biological processes when treating ML.

Combination of coagulation, Fe0/H2O2 and ultra-high lime aluminium processes for the treatment of residual pollutants in biologically-treated landfill leachate.

Refractory substances (humus) and salts (chloride (Cl-) and sulphate (SO42-) ions) remain in the biotreated landfill leachate treatment, and it is necessary to carry out further treatments by a suitable method before discharge. In this study, the effect and operational mechanism of a combination of the coagulation Fe0/H2O2 and ultra-high lime aluminium (UHLA) processes for the treatment of refractory organic substances and salts in the leachate effluent of a semi-aerobic aged refuse biofilter (SAARB) were investigated. The results showed that polyferric sulphate is a relatively efficient coagulant comparing to FeCl3, Al2(SO)4, and polyaluminium chloride. The Fe0/H2O2 process further removed refractory organics from wastewater, achieving 49.8% of total organic carbon removed. Further treatment by the UHLA process was carried. The results demonstrated that the amount of precipitant, reaction duration, and temperature had a significant impact on the Cl- and SO42- removals. After three treatments, the cumulative SO42- and Cl- removal efficiencies were 98% and 80%, respectively. The SO42- and Cl- were removed in the form of precipitates such as UHLA, specific components of which included calcium alumina, Fremy's salt of calcium, aluminium chloride, and calcium hydroxide. Overall, the UV254, CN, Cl-, and SO42- removal efficiencies from the SAARB effluent were 94.08%, 98.73%, 79.96%, and 98.44%, respectively, for the combined coagulation Fe0/H2O2 and UHLA processes. Therefore, the combined processes could effectively remove residual pollutants in the biologically-treated landfill leachate, and the study provides a useful reference for the removal of refractory organic matter and salts in landfill leachate.

Advanced treatment of aged landfill leachate through the combination of aged-refuse bioreactor and three-dimensional electrode electro-Fenton process.

A combined process of the aged-refuse bioreactor (ARB)/three-dimensional electrode electro-Fenton (3D-EF) system was developed at lab-scale to treat aged landfill leachate. The optimum operating conditions were found to be 15 L/m3•d hydraulic loading rate for ARB; Fe2+ concentration 1.0 mM, initial pH 3.0, current density 30 mA/cm2 and electrode distance 6 cm for 3D-EF. Under these conditions, the total removal ratios of chemical oxygen demand, NH3-N, total phosphorus and colour were 96.2%, 94.3%, 99.2% and 93.6%, respectively. The microtoxicity of the leachate was substantially reduced after undergoing the hybrid treatment. The ARB process removed a considerable proportion of organic matter, while the 3D-EF system played an important role in removing the residue of recalcitrant substances and post-polish of final effluent. The combined process showed a promising potential for treatment of aged landfill leachate.

Microbial response during treatment of different types of landfill leachate in a semi-aerobic aged refuse biofilter.

In this research, for the first time, three kinds of landfill leachate (young (YL), mature (ML) and mixed (MYL) leachate) were treated in a semi-aerobic aged refuse biofilter (SAARB) to compare the effectiveness of, and microbial changes in, this biofilter when treating leachates that have significantly different characteristics. The SAARB achieved stable removal of organic matter from all three leachates and reduced the concentrations of aromatic substances. The best treatment was achieved with YL, followed in order by MYL and ML. The removal of nitrogen from all three leachates by the SAARB was particularly significant. The microbial abundance and diversity in the media of the SAARB changed after treatment of the three leachates, and the order of change from small to large was ML# < MYL# < YL#. The microbial communities were mainly affected by (and negatively correlated to) the relative content of refractory organics in leachate. Proteobacteria was the dominant microorganism. Deinococcus-thermus responded most to the quality of leachate being treated, increasing in relative abundance as the content of refractory organics increased. This was opposite to the response of Chloroflexi. In YL# the dominant species at the genus level was Thauera, and in ML# the dominant species were Truepera and Iodidimonas. The microbial activity and metabolic intensity were enhanced after treatment of the different leachates. The expression of nitrification-related genes was the strongest and the total abundance was the highest when YL was treated. This study promotes the optimization and application of SAARB.

Transformation mechanisms of refractory organic matter in mature landfill leachate treated using an Fe0-participated O3/H2O2 process.

An Fe0-participated O3/H2O2 (Fe0-O3/H2O2) process was applied to remove refractory organic matter (OM) in semi-aerobic aged refuse biofilter (SAARB) leachate arising from treating mature landfill leachate. The degradation and transformation characteristics of refractory OM were revealed at molecular level. Removal efficiencies of aromatic substances were 63.55% by the Fe0-O3/H2O2 process (much higher than in other single or binary processes), and fulvic- and humic-like substances were more effectively degraded by this process than by other treatments. According to Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS), 6645 categories of OM in SAARB leachate were identified. Although there was little difference in number of OM categories after treatment using the single-O3 and Fe0-O3/H2O2 processes, Fe0-O3/H2O2 process can better reduce OM relative abundance. It is noteworthy that the Fe0-O3/H2O2 process more effectively degraded CHONS compounds than the single-O3 process, while also producing more CHO compounds having higher bio-availability. The enhanced degradation efficiency of the Fe0-O3/H2O2 process were attributed to the formation of the Fenton process initiated by leached Fe2+ and H2O2. The heterogeneous catalytic effect from iron (hydro) oxides for O3/H2O2 also increased the treatment capacity of the Fe0-O3/H2O2 process, resulting in better total organic carbon removal. The Fe0-O3/H2O2 process is an efficient method for removing refractory OM in SAARB leachate.

Degradation of recalcitrant organic matter in SAARB leachate by a combined process of coagulation and catalytic ozonation.

A combined coagulation and γ-Al2O3 catalytic ozonation process was used to treat semi-aerobic aged refuse biofilter (SAARB) effluent from treating mature landfill leachate. First, the coagulant providing the best pretreatment performance was selected. Then, the coagulated SAARB leachate was further treated in an optimized γ-Al2O3-catalyzed ozonation process. Characteristics of the γ-Al2O3-catalyzed ozonation process were determined, and a reaction mechanism was proposed. FeCl3 provided the best treatment efficiency (chemical oxygen demand (COD) removal of 65.8%, absorbance at 254 nm (UV254) removal of 68.55%, and color number (CN) removal of 79.4%). Under optimized O3 dosage (18.92 mg/min) and γ-Al2O3 dosage (10 g/L), efficiencies of removing COD, UV254, and CN were 54.3%, 82.9%, and 95.9%, respectively, at 30 min. In addition, spectral analysis indicated that fulvic-like substances in ultraviolet and visible regions were effectively degraded in the γ-Al2O3-O3 process and some smaller organic products were produced. Characterization of γ-Al2O3 showed that γ-Al2O3 was relative stable; its morphology and constituent elements did not change much after reaction. In addition, ozonation capacity was enhanced by heterogeneous catalytic effects of γ-Al2O3. The combined coagulation and γ-Al2O3 catalytic ozonation process was proven to be an efficient treatment method for removing bio-refractory organic matter contained in SAARB leachate.

Recovery of efficient treatment performance in a semi-aerobic aged refuse biofilter when treating landfill leachate: Washing action using domestic sewage.

Semi-aerobic aged refuse biofilters (SAARB) are known to efficiently remove organic matter, nitrogenous substances, and anions from landfill leachate. However, long-term recirculation of mature landfill leachate inevitably leads to accumulation of pollutants and decreases treatment capacity. In this study, the washing action provided by domestic sewage was used to recover and even enhance the treatment performance of SAARBs treating mature landfill leachate. Three SAARB columns were operated for 300 d after which a "Recirculation-Washing-Recirculation" sequence was followed. In the first recirculation period (22 d), removal of chemical oxygen demand (COD) and total nitrogen (TN) decreased from ca. 90% and 60%, respectively, initially to about 75% and less than 20%, respectively. Thereafter, washing (20 d) of the SAARBs was accomplished by applying domestic sewage. In the subsequent second recirculation period (30 d), the SAARBs were operated at the same hydraulic loading as used initially, but achieved high (ca. 90%) COD and relatively high (ca. 59%-76%) TN removal, including degradation of refractory organic matter such as humic- and fulvic-like substances. Overall, the mechanisms of the treatment performance recovery (including organics degradation and nitrification-denitrification) using domestic sewage can be attributed to three main effects: (1) some accumulated pollutants were washed out, thereby leading to recovery of the adsorption ability of aged refuse; (2) the inhibition of bio-refractory organics stress on microbial activities was mitigated by domestic sewage washing; and (3) the wash out of some accumulated salts (e.g., chloride and sulfate ions) probably helped the microbial activity recover.

Elimination of UV-quenching substances from MBR- and SAARB-treated mature landfill leachates in an ozonation process: A comparative study.

Ultraviolet-quenching substances (UVQS), recently identified pollutants in landfill leachate, can interfere with ultraviolet disinfection when landfill leachate is co-treated with municipal sewage. This study investigated the elimination of UVQS in mature landfill leachates through a membrane bioreactor (MBR) and a semi-aerobic aged refuse biofilter (SAARB). Humus (i.e., fulvic and humic acids) was the main component of organic matter in both MBR- and SAARB-treated landfill leachates, while there was a more stable chemical structure of humus in the MBR-treated leachate. The concentration of UVQS in MBR-treated mature landfill leachate was higher than that of SAARB-treated leachate. Ozonation can degrade UVQS effectively, especially for landfill leachate containing a high concentration UVQS (i.e., MBR-treated landfill leachate). However, a large accumulation of small molecule acid might be caused by ozonation for highly concentrated UVQS in landfill leachate, leading to the delayed degradation of total organic carbon. Moreover, ozonation degraded both fulvic acid and humic acid; and degraded humic acid more effectively. For instance, 88.0% removal (MBR-CP2) and 96.0% removal (SAARB-CP2) of humic acid was higher than those (83.3% for MBR-CP1 and 92.3% for SAARB-CP1) of fulvic acid. The destruction of UV-quenching functional groups of organics (such as CC) by ozone was the main UVQS degradation mechanism of ozonation applied to MBR- and SAARB-treated landfill leachates. Therefore, the ozonation process can efficiently decrease UV absorption intensity in both MBR- and SAARB-treated landfill leachates.

Sequential coagulation and Fe0-O3/H2O2 process for removing recalcitrant organics from semi-aerobic aged refuse biofilter leachate: Treatment efficiency and degradation mechanism.

Landfill leachate effluent obtained after semi-aerobic aged refuse biofilter (SAARB) treatment still contains various recalcitrant organics. In this study, a sequential coagulation and Fe0-O3/H2O2 process was developed for treating SAARB leachate. The effects in terms of degradation of recalcitrant organics and the related mechanisms due to the coagulation and Fe0-O3/H2O2 processes were systematically explored and discussed. The results indicated that polymerized ferric sulfate was the most efficient coagulant for treating SAARB leachate where the chemical oxygen demand (COD), UV254, and CN removal efficiencies were 59.60%, 63.22%, and 70.32%, respectively. In the Fe0-O3/H2O2 process under the optimized conditions comprising Fe0 dose = 0.6 g/L, O3 dose = 26.80 mg/min, H2O2 dose = 1.0 mL/L, and reaction time = 20 min, the COD, UV254, and CN removal efficiencies with the coagulated supernatant were 43.39%, 59.47%, and 93.20%, respectively, and the biodegradability (biochemical oxygen demand/COD) improved greatly from 0.06 to 0.34. Analysis of UV-Vis and 3D-EEM spectra indicated that coagulation-resistant substances in the SAARB leachate could be effectively degraded and destroyed by the Fe0-O3/H2O2 process. In the O3/H2O2 environment, Fe0 generated Fe2+ and iron oxides (Fe2O3, Fe3O4, and FeOOH) with homogeneous and heterogeneous catalytic roles against O3/H2O2 to produce reactive oxygen species. Furthermore, Fe(OH)2 and Fe(OH)3 colloids contributed to the removal of organics to some extent via adsorption and precipitation effects. In conclusion, the proposed sequential coagulation and Fe0-O3/H2O2 process is an efficient method for treating recalcitrant organics in SAARB leachates.

Molecular-level insights into the transformation mechanism for refractory organics in landfill leachate when using a combined semi-aerobic aged refuse biofilter and chemical oxidation process.

Landfill leachate contains high concentrations of complex organic matter (OM) that can severely impact the ecological environment. If landfill leachate is to be treated using a combined "biological + advanced treatment" process, the molecular information of OM must be investigated to optimize the operation parameters of the combined process and maximize the removal of organic pollutants. This study applied ultra-high resolution mass spectroscopy to investigate the degradation and transformation characteristics of refractory OM in mature landfill leachate at the molecular level (m/z = 150-800) during biological treatment (i.e., semi-aerobic aged refuse biofilter, SAARB) and subsequent chemical oxidation (i.e., the Fenton process and ozonation). After SAARB treatment, the polycyclic aromatics (aromatic index, AI > 0.66) and polyphenol (0.66 ≥ AI > 0.50) contents increased, and the highly unsaturated phenolic compounds (AI ≤ 0.50 and H/C < 1.5), which have a high bioavailability, were mostly removed. Compared with raw leachate, SAARB effluent (i.e., SAARB leachate) contained fewer organics with short carbon chains, more organics with long carbon chains, an elevated condensation degree for organics and, thus, a considerably reduced biodegradability. Although both the Fenton and ozonation processes could remove many of the polycyclic aromatics and polyphenols, ozone produced considerable amounts of aliphatic compounds with high bioavailability. Compared to ozonation, the Fenton process utilized the hydroxyl radical to non-selectively react with OM and produced better mineralization results.

Hydroxyl radical-based and sulfate radical-based photocatalytic advanced oxidation processes for treatment of refractory organic matter in semi-aerobic aged refuse biofilter effluent arising from treating landfill leachate.

In this study, three photolytic advanced oxidation processes (AOPs) were applied to the treatment of refractory organic matter in semi-aerobic aged refuse biofilter (SAARB) effluent, and the treatment efficiencies of the three AOPs were systematically compared. The AOPs combined ultraviolet (UV) radiation with either hydrogen peroxide (UV-H2O2), peroxymonosulfate (UV-PMS) or both oxidants (UV-PMS/H2O2). The effects of key parameters on degradation characteristics of refractory organics, and the contribution of reactive oxygen species were systematically studied. Results indicated that UV radiation can greatly enhance treatment efficiencies of both PMS and H2O2. Furthermore, decreasing n(H2O2)/n(PMS) ratio and decreasing the reaction pH can increase treatment efficiency for refractory organics. Compared on the basis of chemical oxygen demand (COD), treatment efficiency followed the order UV-PMS (COD removal 37.39%) > UV-PMS/H2O2 (30.51%) > UV-H2O2 (28.59%) which is consistent with results from ultraviolet-visible spectra analysis. HO• and SO4•- were both identified in the UV-PMS/H2O2 and UV-PMS processes. In the UV-PMS process, SO4•- was the dominant ROS, which suggested that SO4•--based AOPs are better than HO•-based AOPs for degrading refractory organics contained in SAARB effluent. Parallel factor (PARAFAC) analysis indicated that UV-based AOPs were effective in degrading humic- and fulvic-like substances in the SAARB leachate, and the UV-PMS process achieved a much better degradation efficiency of refractory organics in the leachate than did the UV-PMS/H2O2 and the UV-H2O2 processes. Furthermore, the best treatment efficiency was achieved by the UV-PMS process and this process also consumed the least electrical energy. This study provides a theoretical reference for refractory organics degradation in SAARB effluent by UV-catalyzed AOPs.

Effects of char from biomass gasification on carbon retention and nitrogen conversion in landfill simulation bioreactors.

The application of char from biomass gasification as a filling material in landfill simulation reactors was investigated to evaluate the effect of char on carbon retention and nitrogen leaching, nitrogen denitrification, and waste stabilization. Landfill simulation columns filled with fine fraction of aged refuse (AR) and solid fraction of digestate (SFD) were used, with two char application methods: embedding a char layer between AR and SFD layers and mixing char with the SFD. The experimental results show that char application increased the biodegradable organic matter content as the respiration index (RI4) of the mixture char-SFD increased up to 37.7%, which could enhance the heterotrophic denitrification. Moreover, 12.3% of ammonia leaching was avoid by applying the SFD mixed with char. These results indicate that char from biomass gasification poses a significant enhancement on nitrogen and carbon retention which might increase the denitrification capacity of the SFD in the long run. Although high nitrogen removal rates were achieved (up to 23.1 mg N/kg-TS day), the addition of char from biomass gasification has little effect on the nitrate removal.

Bioremediation of petroleum-contaminated soil enhanced by aged refuse.

In this study, the effect of aged refuse on biodegradation of total petroleum hydrocarbons (TPH), microbial counts, soil ecotoxicity, dehydrogenase activity and microbial community compositions were investigated in solid phase reactors during a 30-week period. The results demonstrate that the removal efficiency of TPH was significantly higher in the soil supplemented with aged refuse than in the soil without aged refuse. After 30 weeks, the removal efficiencies of TPH in soils were 29.3%, 82.1%, 63.7% and 90.2% in the cases of natural attenuation, nutrient addition (with NH4NO3 and K2HPO4), supplement with 20% (w/w, dry weight basis) of aged refuse and the combination of nutrient and aged refuse. Nutrient plus aged refuse made the TPH concentration decrease to below the threshold level of commercial use required for Chinese soil quality for TPH (<3000 mg/kg) in 30 weeks. It was also found that dehydrogenase activity, bacterial counts and degrader abundance in the soil were remarkably enhanced by the addition of aged refuse (20%,w/w). Total organic carbon analysis demonstrates that large amounts of hydrocarbon intermediates occurred in the soil after bioremediation.

Aged refuse enhances anaerobic fermentation of food waste to produce short-chain fatty acids.

In this work, a new technology of intensifying anaerobic fermentation of food waste to accumulate SCFA by using landfill degradation product aged refuse (AR) was reported. The experimental results showed that AR enhanced the accumulation of SCFA, and when the optimal dosage of AR was 300 mg/g, the maximum accumulation of SCFA was 32.5 g/L, which was around 1.9 times that of the blank group. Mechanism investigations had shown that AR accelerated the disintegration of food waste to release soluble carbohydrates and proteins. The model experiment of synthetic wastewater revealed that AR improved both hydrolysis and acidification efficiencies but inhibited the methanogenesis process, thereby accumulating SCFA. 454 high-throughput sequencing showed that AR increased the relative abundance of Clostridium and Sporanaerobacter, which benefited anaerobic hydrolysis of food waste.