Semi-aerobic Aged Refuse Biofilter Research Articles

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

ABSTRACT Refractory substances (humus) and salts (chloride (Cl−) and sulphate (SO4 2−) 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 SO4 2− removals. After three treatments, the cumulative SO4 2− and Cl− removal efficiencies were 98% and 80%, respectively. The SO4 2− 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 SO4 2− 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. Highlights Coagulation-Fe0/H2O2-UHLA process is effective to SAARB effluent treatment. Refractory organics are substantially degraded by the coagulation-Fenton-like stage. Both Cl− and SO4 2− in SAARB effluent are greatly removed by UHLA process.

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.

Microwave-enhanced iron–carbon-activated hydrogen peroxide process for the advanced treatment of semi-aerobic aged refuse biofilter effluent

The microwave-enhanced iron–carbon-activated hydrogen peroxide process is efficient for organics and humus removal in the treatment of biologically treated landfill leachate.

Bioremediation of petroleum-contaminated soil by semi-aerobic aged refuse biofilter: Optimization and mechanism

Petroleum-contaminated soil (PCS) is a global environmental issue. An effective remediation technique is urgently needed to address this problem. This study applied a semi-aerobic aged refuse biofilter (SAARB) to the decontamination and remediation of PCS. The effects of petroleum content, surfactant content, and water content on oil removal efficiency were studied, and the operation conditions were optimized using the response surface method. Results showed that contents of petroleum and water that were too high or too low depressed total petroleum hydrocarbon (TPH) removal. The presence of surfactant markedly reduced the TPH removal efficiency. The optimal operation conditions were the ratio of aged refuse to PCS = 1.6; water content = 41%; and petroleum content = 3.8%. The TPH removal efficiencies under optimized conditions and during a confirmatory experiment were 59.89% and 51.38%, respectively. PCS contained an abundance of polycyclic aromatic hydrocarbons and macro molecular alkanes, and these organic compounds were considerably removed by SAARB treatment. The microbial community exhibited a marked change at both phylum level and genus level after 3 months of remediation in the PCS. At the genus level, norank_f_SS1–B-06-26 became the most dominant; further isolation and verification experiments for its ability to degrade petroleum are needed. In addition, the abundance of norank_o_Saccharimonadales, Aquabacterium, Hydrogenophaga, and norank_f_Saccharimonadaceae, which can degrade hydrocarbons, also increased. This study provides a theoretical reference for SAARB application in the remediation of PCS.

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.

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.

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.

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 254nm (UV254) removal of 68.55%, and color number (CN) removal of 79.4%). Under optimized O3 dosage (18.92mg/min) and γ-Al2O3 dosage (10g/L), efficiencies of removing COD, UV254, and CN were 54.3%, 82.9%, and 95.9%, respectively, at 30min. 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.

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.

Degradation of organics from landfill leachate by combined process of semi-aerobic aged refuse biofilter and ozone oxidation

Degradation of organics from landfill leachate by combined process of semi-aerobic aged refuse biofilter and ozone oxidation

Sequential ozonation and Fenton process for the removal of refractory organics from semi-aerobic aged refuse biofilter leachate effluent

Sequential ozonation and Fenton process for the removal of refractory organics from semi-aerobic aged refuse biofilter leachate effluent

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 300d after which a "Recirculation-Washing-Recirculation" sequence was followed. In the first recirculation period (22d), 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 (20d) of the SAARBs was accomplished by applying domestic sewage. In the subsequent second recirculation period (30d), 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.

Treatment of semi-aerobic aged-refuse biofilter effluent from treating landfill leachate with the Fenton method

Semi-aerobic aged-refuse biofilter (SAARB) can achieve good treatment efficiency for organics and nitrogen ammonia, but the effluent of SAARB from treating landfill leachate (SAARB leachate) has high chemical oxygen demand (COD), compared to the discharge standard (100 mg/L), and high humification degree. In this study, the conventional Fenton method was used in the advanced treatment of SAARB leachate. Fluorescent components in SAARB leachate were identified and tracked with parallel factor (PARAFAC) analysis, and the influencing factors, i.e., Fe2+ dosage, n(H2O2/FeSO4) ratio, initial pH, and reaction time, on the removal of fluorescent components were systematically investigated. UV–Vis spectra show the structural transformation of dissolved organic matter (DOM) in SAARB leachate. Results show that SAARB leachate mainly contains two fluorescent components: fulvic-like substances [C1; excitation (Ex)/emission (Em) (nm), (245)280/405] and humic-like substances [C2; Ex/Em (nm), (260)360/435]. A higher Fe2+ dosage, longer reaction time, and acidic conditions increased the degradation efficiency of organics, but excess H2O2 inhibited the treatment process. Under optimum Fenton parameters (Fe2+ dosage of 5 mmol/L, n(H2O2/FeSO4) ratio of 8, initial pH of 4, and reaction time of 60 min), removal rates of C1 and C2 were 52.97% and 77.81%, respectively. UV–Vis spectra indicate that the Fenton reaction can destroy unsaturated conjugated bonds, decreasing the humification degree, hydrophobicity, molecular weight, and condensation degree. Finally, the biodegradability (represented by BOD5 (biochemical oxygen demand for 5-days)/COD) greatly increased (from 0.05 to 0.36), thus benefiting further biological treatment. The results provide suggestions and guidance for practical applications in landfill leachate treatment.

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.

Transformation and degradation mechanism of landfill leachates in a combined process of SAARB and ozonation

Dissolved organic matter (DOM) in mature landfill leachate is significantly different from that in young landfill leachate; the composition of DOM greatly influences both biological treatment and advanced treatment processes. In the present study, the transformation and degradation mechanisms of landfill leachates in a combined semi-aerobic aged refuse biofilter (SAARB) and ozonation process was investigated using organic removal analysis, molecular weight distribution (MWD), 3D-EEM-PARAFAC analysis, UV–Vis spectroscopy, and linear regression. Results revealed that the DOM in mature landfill leachate contained a greater amount of aromatic substances and had higher molecular weight than DOM in young landfill leachate. After the SAARB process, humus contained in the SAARB was discharged with effluent from both mature and young landfill leachate. Due to the differences in composition and structure of organic matter, the COD removal efficiency (17.89%) of SAARB effluent from treating mature landfill leachate (mature SAARB effluent) was much lower than that (45.91%) of SAARB effluent from treating young landfill leachate (young SAARB effluent) under the same operational parameters of the ozonation process. As indicated by PARAFAC analysis, better chemical stability of DOM in mature SAARB effluent resulted in inferior ozone treatment efficiency. Furthermore, the hydrophobicity and the concentration of benzene ring compounds in the mature and young SAARB effluent were reduced significantly by the ozonation process. Therefore, great improvements in the biodegradability of SAARB effluents were achieved in the ozonation process. Overall, the results of this study provide suggestions and guidance for practical applications of these technologies.

Degradation of leachate from a semi-anaerobic aged refuse biofilter by the ZVI/H2O2 process coupled with microwave irradiation: optimization, organics transformation, and reaction mechanisms

The semi-aerobic aged refuse biofilter (SAARB) is highly efficient in removing organic matter and ammonia nitrogen, but the effluent of the SAARB (SAARB leachate) contains high concentrations of recalcitrant organics.

A removal mechanism for organics and nitrogen in treating leachate using a semi-aerobic aged refuse biofilter

A removing mechanism for organics and nitrogen using a semi-aerobic aged refuse biofilter (SAARB) was evaluated based on the space structure, the aged refuse conformation and characteristics, as well as the degradation theories of organic matter and nitrogen-based substances, which could provide a fundamental theory to more effectively treat organic matter and nitrogen-based pollutants in leachate. The experimental results indicated that the average removal rate of chemical oxygen demand and total nitrogen reached 96.61 and 95.46%, respectively. The aerobic–anoxic–anaerobic zones appeared alternately in both the space structure and the granule conformation inside of the SAARB, which promoted various physical, chemical and biological reactions. Most biodegradable organic matter was converted to CO2 and CH4. The average CO2 release rate was 1.567 L/(h m2) in the winter and 1.467 L/(h m2) in the summer during a single-period experiment. The average CH4 release rate was 0.303 L/(h m2) in the summer; however, it could not be detected in the winter. Moreover, the nitrogen-based pollutants were mostly converted to N2 and N2O through denitrification. Some of the refractory organic matter and nitrogen-based pollutants were likely adsorbed by the aged refuse and biodegraded more slowly. The adsorption rate of biologically degradable matter (BDM) was 0.624 g/(kg d) during the first 40 weeks and the largest absorbance of total nitrogen (TN) was about 7.0 g/kg during this experiment. Therefore, the SAARB can maintain stable and highly efficient environment for removing organic matter and nitrogen-based pollutants.

A novel technique of semi-aerobic aged refuse biofilter for leachate treatment

We developed a semi-aerobic aged refuse biofilter (SAARB) for leachate treatment and examined its advantages and disadvantages compared to previous aged refuse biofilters (ARBs). To assess its treatment capability, decontamination mechanisms and optimal performance parameters, a single-period experiment and L 9(3 4) orthogonal array design experiments were conducted on artificial leachate. The SAARB markedly enhanced the treatment capability and removal efficiency of organic matter and nitrogen pollutants due to the alternating aerobic–anoxic–anaerobic zones in situ. The reduction in chemical oxygen demand (COD), ammonia nitrogen ( NH 4 + – N ) and total nitrogen (TN) exceeded 98%, 94%, and 80%, respectively. After the leachate was distributed onto the SAARB surface, the effluent velocity decreased as a logarithmic function, and there was a concomitant reduction in leachate effluent volume. Based on the capacity for removal of COD, NH 4 + – N , and TN, the effective height of aged refuse in a SAARB was enough to be 900 mm. An excellent treatment efficiency could be achieved at 20–35 °C, with a leachate distribution time of 1 h once every period of 2–3 days, hydraulic loading of 11–30 L/(m 3 day), and COD loading of 550–1200 g/(m 3 day). This new SAARB system demonstrates superior efficacy for biofilter compared to other ARB systems, especially for nitrogen removal from leachate.