Numerical model of aerobic bioreactor landfill considering aerobic-anaerobic condition and bio-stable zone development.

Aeration by airflow technology is a reliable method to accelerate waste biodegradation and stabilization and hence shorten the aftercare period of a landfill. To simulate hydro-biochemical behaviors in this type of landfills, this study develops a model coupling multi-phase flow, multi-component transport and aerobic-anaerobic biodegradation using a computational fluid dynamics (CFD) method. The uniqueness of the model is that it can well describe the evolution of aerobic zone, anaerobic zone, and temperature during aeration and evaluate aeration efficiency considering aerobic and anaerobic biodegradation processes. After being verified using existing in situ and laboratory test results, the model is then employed to reveal the bio-stable zone development, aerobic biochemical reactions around vertical well (VW), and anaerobic reactions away from VW. With an increase in the initial organic matter content (0.1 to 0.4), the bio-stable zone expands at a decreasing speed but with all the horizontal ranges larger than 17 m after an intermittent aeration for 1000 days. When waste intrinsic permeability is equal or greater than 10-11 m2, aeration using a low pressure between 4 and 8 kPa is appropriate. The aeration efficiency would be underestimated if anaerobic biodegradation is neglected because products of anaerobic biodegradation would be oxidized more easily. A horizontal spacing of 17 m is suggested for aeration VWs with a vertical spacing of 10 m for screens. Since a lower aeration frequency can give greater aeration efficiency, a 20-day aeration/20-day leachate recirculation scenario is recommended considering the maximum temperature over a reasonable range. For wet landfills with low temperature, the proportion of aeration can be increased to 0.67 (20-day aeration/10-day leachate recirculation) or an even higher value.

Kinetics and removal formula of methyl mercaptan by ethanol absorption without neglecting solute accumulation.

The wet scrubbing process is commonly adopted for organic odor treatment. In this study, methyl mercaptan (CH3SH) was selected as a representative hydrophobic organic odorant which was treated using an ethanol solution in a scrubbing tower. Results showed that the ethanol solution can retain the ideal CH3SH removal effect for 2.0 h. The following experimental conditions were set: intake load of 4,700 m3 m-2 h-1, spraying load of 5,100 L m-2 h-1, and volume ratio of ethanol/water at 1:5. The solute accumulation of CH3SH in the scrubbing liquid exceeded 3.01 × 10-4 kmol CH3SH/kmol ethanol when the scrubbing tower operated for more than 2.0 h. The mathematical formula which neglected solute accumulation in the ethanol solution exhibited poor adaptability to the removal effect of CH3SH by ethanol absorption. The CH3SH removal effect of solute accumulation in the ethanol solution was explored in long-term operation. Meanwhile, the CH3SH removal rate formula which considered solute accumulation in the ethanol solution could be calculated as η = a'-b'X2/Y1. The kinetic parameters of the formula fitting results were phase equilibrium constant m 0.0076, and overall mass transfer coefficient KY 4.98 kmol m-2 h-1 in the scrubbing tower. These findings can serve as a reference for engineering design and operation for the removal of CH3SH by ethanol absorption.

Pilot-scale bioelectrochemical system for simultaneous nitrogen and carbon removal in urban wastewater treatment plants.

This study aims to characterize the performance of a 150 L bioelectrochemical system-based plant, during the simultaneous carbon and nitrogen removal from several waste streams of wastewater treatment plants. The bioelectrochemical system (BES) contained five electrode pairs (operated hydraulically and electrically in parallel) and was fed with either wastewater, centrate (nutrient-rich liquid stream produced during the dewatering of digested biomass), or a mixture of both over 63 days, with a hydraulic retention time of one day. Total organic carbon and total nitrogen removal rates averaged 80% and 70%, respectively, with a specific energy consumption of 0.18 kWh·m-3 (BES + ancillary equipment). This work also underlines the challenges of using BES for nitrogen removal, highlighting the limitations of the current design, and suggesting some strategies for improvement.

Removal of odorous compounds emitted from a food-waste composting facility in Korea using a pilot-scale scrubber.

Monitoring and control of odorous compound emissions have been enforced by the Korean government since 2005. One of the point sources for these emissions was from food waste composting facilities. In this study, a pilot-scale scrubber installed in a composting facility was evaluated for its performance in the removal of malodorous compounds. The exhaust stream contained ammonia and methylamine as the major odorants detected by the threshold odor test and various instrumental techniques (GC-FID, FPD, MS and HPLC/UV). For the scrubber operation, the column was randomly packed with polypropylene Hi-Rex 200, while aqueous sulfuric acid was selected as the scrubbing solution. To achieve 95% removal, the scrubber must be operated by using H2SO4 solution with pH at < 6.5, liquid to gas ratio > 4.5, gas loading rate < 1750 m3/m3-hr and contact time < 0.94 s. The scrubber performance was further evaluated by determining the mass transfer coefficients and then monitoring for 355 days of operation. The pilot-scale scrubber maintained > 95% ammonia and methylamine removal efficiencies despite the fluctuations in the inlet (from composting facility exhaust stream) concentration. The optimum operating conditions and scrubber performance indicators determined in this study provides a basis for the design of a plant-scale scrubber for treatment of composting facility gas emissions.

Appropriate technologies for upgrading wastewater treatment plants: methods review and case studies in China.

Upgrading existing wastewater treatment plants (WWTPs) is a more challenging task than constructing new plants. The aim is usually to overcome overloading and to reduce pollution concentrations in the effluent. There are various methods that can be used to upgrade WWTPs. This article reviews some of the methodologies, such as inserting new tanks as additional treatment steps and modifying the WWTP by introducing new technologies. A number of effective technologies are reviewed in terms of their basic concepts, operational conditions, and treatment performances. Examples of WWTPs in China that have been successfully upgraded using these technologies are also highlighted.

Tube reactors as a novel ultrasonication system for trouble-free treatment of sludges.

The performance of a novel low-maintenance tube reactor for ultrasonic treatment of sludge has been evaluated. The effects of sonication on the release of soluble chemical oxygen demand (sCOD) and anaerobic digestibility of raw and digested sewage sludge as well as agricultural sludge were studied. Results suggest that solubilization and digestibility is dependent on both type of sludge and the energy input. Digested and raw sludge showed high degree of solubilization, however, methane production was only increased for digested sludge. Agricultural sludge was not significantly affected by ultrasonic treatment neither concerning sCOD release nor methane production. The configuration of the ultrasonic system (serial vs. parallel operation) did not show a significant difference in both sCOD release and methane production. However, parallel operation tends to perform better for digested sludge, while serial operation tends to perform better for raw sludge. The strongest effect was observed for the treatment of digested sludge by increasing the methane production by more than 60%, although with a very intensive energy input of more than 5,000kJ per kg total solids. Hence, tube reactors seem to be an attractive alternative to sonotrode-based systems achieving similar performance at low maintenance with great potential especially for digested sludge.

Microbial community structure in a full-scale anaerobic treatment plant during start-up and first year of operation revealed by high-throughput 16S rRNA gene amplicon sequencing.

High-throughput amplicon sequencing of six biomass samples from a full-scale anaerobic reactor at a Norwegian wood and pulp factory using Biothane Biobed Expanded Granular Sludge Bed (EGSB) technology during start-up and first year of operation was performed. A total of 106,166 16S rRNA gene sequences (V3-V5 region) were obtained. The number of operational taxonomic units (OTUs) ranged from 595 to 2472, and a total of 38 different phyla and 143 families were observed. The predominant phyla were Bacteroidetes, Chloroflexi, Firmicutes, Proteobacteria, and Spirochaetes. A more diverse microbial community was observed in the inoculum biomass coming from an Upflow Anaerobic Sludge Blanket (USAB) reactor, reflecting an adaptation of the inoculum diversity to the specific conditions of the new reactor. In addition, no taxa classified as obligate pathogens were identified and potentially opportunistic pathogens were absent or observed in low abundances. No Legionella bacteria were identified by traditional culture-based and molecular methods.

Enhanced performance of the aerobic landfill reactor by augmentation of manganese peroxidase.

The aim of the work discussed in this article was to determine the ability of an MnP augmented aerobic waste cell to reach stable conditions rapidly in terms of gas production, nutrient content and cellulose and hemicellulose to lignin ratio (C+H/L). Two types of experiments were conducted; small batch and laboratory scale lysimeter experiments. Results from batch experiments showed that enzyme added treatments have the capability to reach a stable C+H/L and lower gas production rates, faster than the treatments without enzyme addition. Enzyme enhancement of the lysimeter increased the rate of biodegradability of the waste; gas production increased more than two times and there was clear evidence of increase in nutrients (nitrogen, dissolved carbon, biological oxygen demand) in the lysimeter ​leachate.

Evaluation of hydrocyclone and post-treatment technologies for remediation of contaminated dredged sediments.

There are many disposal and treatment methods for contaminated dredged sediments, depending on their properties. In this study, treatment methods for the remediation of dredged sediments as well as the reduction of pore water generated from dredged sediments were optimized. The efficiency of separation using hydrocyclone as the pre-treatment increased with greater inflow velocity of hydrocyclone, deeper insertion of the vortex finder, and smaller hydrocyclone diameter. In the post-treatment of hydrocyclone overflow, the chemical coagulation and membrane filtration methods had high efficiency with regard to the removal of solid and organic compounds, but the former was less feasible, due to its excessive operation and sludge disposal costs. The membrane filtration was easily applicable in the field, based on its convenience of installation and lower cost of operation despite low removal efficiency of trace organic contaminants.

Examining Screening-Level Multimedia Models Through a Comparison Framework for Landfill Management.

Two models for evaluating transport and fate of benzene were studied and compared in this paper. A fugacity model and an analytical environmental multimedia model (AEMM) were used to reconcile fate and mass transfer of benzene observed in a landfill site. The comparison of two models were based on average concentrations and partition behavior of benzene among three different phases i.e., air, soil, and groundwater. In the study of fugacity method about 99.6 % of the total benzene flux was distributed into air from landfill source. According to AEMM the diffusion gas flux was also predominant mechanism for benzene released from landfill and advection of gas and liquid was second dominant transport mechanism at steady-state conditions. Overall study of fugacity modeling (Level I and II) confirms the fate and transport mechanism of benzene released from landfill by comparing it with AEMM. However, the values of predicted concentrations, advection, and diffusion flux of benzene using fugacity model were different from AEMM results due to variation in input parameters. In comparison with experimental observations, fugacity model showed more error difference as compared to AEMM as fugacity model is treated as a single unit box model. This study confirms that fugacity model is a screening level tool to be used in conjunction with detailed remediation followed by AEMM that can be evolved as strategic decision-making stage.

Investigation of an Accidental Radiological Release in an Underground Disposal Facility.

A radioactive release took place at the Waste Isolation Pilot Plant near Carlsbad, New Mexico, on 14 February 2014. An alarm from a Continuous Air Monitor caused a switch from unfiltered to filtered air exiting the facility through High-Efficiency Particulate Arrestance filters. The activity measured on the filters demonstrated first order decay, indicating that the release was a single release. The facility was reentered in April 2014 and photographic evidence pointed to a single breached 55-gallon drum that originated at Los Alamos as the source of the release. Data were collected and analyzed to verify the source and cause of the release.

Assessing the performance of gas collection systems in select Chinese landfills according to the LandGEM model: drawbacks and potential direction.

In China, municipal solid waste (MSW) is primarily treated by landfilling. Landfill gas (LFG) collection effectively reduces methane emission from MSW landfills. An accurate system of LFG collection is important in landfill planning, design, and operation. However, China has not developed such systems. In this study, the efficiency of methane collection is calculated in three Chinese landfills with different collection systems (A: vertical wells for MSW before 2010; combined horizontal trenches and under-membrane pipes for MSW from 2011 onwards; B: combined horizontal trenches and vertical wells; C: vertical wells only). This efficiency was computed by dividing the quantity of methane obtained from landfill operation records by the quantity estimated based on the LandGEM model. Results show that the collection efficiencies of landfills with vertical wells and/or horizontal pipes ranged from 8.3% to 27.9%, whereas those of a system equipped with geomembrane reached 65.3%. The poor performance of the landfills was attributed to the open burning of early-stage LFG, LFG release from cracks in high-density polyethylene covers, and high levels of leachate within a landfill site. Therefore, this study proposes an integrated LFG collection system that can remove leachate and collect gas from landfills that accept waste with high moisture content.

A New Storage Facility for Institutional Radioactive Wastes at IPEN.

IPEN, the Nuclear and Energy Research Institute in Sao Paulo, Brazil, has been managing the radioactive wastes generated in its own activities of research and radioisotope production as well as those received from many radioisotope users in the country since its start up in 1958. Final disposal options are presently unavailable for the wastes that cannot be managed by release after decay. Treated and untreated wastes including disused sealed radioactive sources and solid and liquid wastes containing radionuclides of the uranium and thorium series or fission and activation products are among the categories that are under safe and secure storage. This paper discusses the aspects considered in the design and describes the startup of a new storage facility for these wastes.

Steady-state analytical models for performance assessment of landfill composite liners.

One-dimensional mathematical models were developed for organic contaminant transport through landfill composite liners consisting of a geomembrane (GM) and a geosynthetic clay liner (GCL) or a GM and a compacted clay liner (CCL). The combined effect of leakage through GM defects, diffusion in GM and the underlying soil liners, and degradation in soil liners were considered. Steady state analytical solutions were provided for the proposed mathematical models, which consider the different combinations of advection, diffusion, and degradation. The analytical solutions of the time lag for contaminant transport in the composite liners were also derived. The performance of GM/GCL and GM/CCL was analyzed. For GM/GCL, the bottom flux can be reduced by a factor of 4 when the leachate head decreases from 10 to 0.3 m. The influence of degradation can be ignored for GM/GCL. For GM/CCL, when the leachate head decreases from 10 to 0.3 m, the bottom flux decreases by a factor of 2-4. Leachate head has greater influence on bottom flux in case of larger degradation rate (e.g., half-life = 1 year) compared to the case with lower degradation rate (e.g., half-life = 10 years). As contaminant half-life in soil liner decreases from 10 to 1 year, bottom flux decreases by approximately 2.7 magnitudes of orders. It is indicated that degradation may have greater influence on time lag of composite liner than leachate head. As leachate head increases from zero to 10 m, time lag for GM/CCL can be reduced by 5-6 years. Time lag for the same composite liner can be reduced by 10-11 years as contaminant half-life decreases from 10 to 1 year. Reducing leachate head acting on composite liners and increasing the degradation capacity of the soil liner would be the effective methods to improve the performance of the composite liners. The proposed analytical solutions are relatively simple and can be used for preliminary design and performance assessment of composite liners.

A case-study of landfill minimization and material recovery via waste co-gasification in a new waste management scheme.

This study evaluates municipal solid waste co-gasification technology and a new solid waste management scheme, which can minimize final landfill amounts and maximize material recycled from waste. This new scheme is considered for a region where bottom ash and incombustibles are landfilled or not allowed to be recycled due to their toxic heavy metal concentration. Waste is processed with incombustible residues and an incineration bottom ash discharged from existent conventional incinerators, using a gasification and melting technology (the Direct Melting System). The inert materials, contained in municipal solid waste, incombustibles and bottom ash, are recycled as slag and metal in this process as well as energy recovery. Based on this new waste management scheme with a co-gasification system, a case study of municipal solid waste co-gasification was evaluated and compared with other technical solutions, such as conventional incineration, incineration with an ash melting facility under certain boundary conditions. From a technical point of view, co-gasification produced high quality slag with few harmful heavy metals, which was recycled completely without requiring any further post-treatment such as aging. As a consequence, the co-gasification system had an economical advantage over other systems because of its material recovery and minimization of the final landfill amount. Sensitivity analyses of landfill cost, power price and inert materials in waste were also conducted. The higher the landfill costs, the greater the advantage of the co-gasification system has. The co-gasification was beneficial for landfill cost in the range of 80 Euro per ton or more. Higher power prices led to lower operation cost in each case. The inert contents in processed waste had a significant influence on the operating cost. These results indicate that co-gasification of bottom ash and incombustibles with municipal solid waste contributes to minimizing the final landfill amount and has great possibilities maximizing material recovery and energy recovery from waste.

Migration of inorganic ions from the leachate of the Rio das Ostras landfill: a comparison of three different configurations of protective barriers.

Batch tests and diffusion tests were performed to analyze the efficiency of a protective barrier in a landfill consisting of compacted soil with 10% bentonite compared to the results obtained for only compacted soil and for compacted soil covered with a 1-mm-thick HDPE geomembrane; the soil and leachate were collected from the Rio das Ostras Landfill in Rio de Janeiro, Brazil. The diffusion tests were performed for periods of 3, 10 and 60 days. After the test period, the soil pore water was analyzed and the profiles for chloride, potassium and ammonium were determined along a 6-cm soil depth. The results of the batch tests performed to define sorption parameters were used to adjust the profiles obtained in the diffusion cell experiment by applying an ion transfer model between the interstitial solution and the soil particles. The MPHMTP model (Multi Phase Heat and Mass Transfer Program), which is based upon the solution of the transport equations of the ionic contaminants, was used to solve the inverse problem of simultaneously determining the effective diffusion coefficients. The results of the experimental tests and of the model simulation confirmed that the compacted soil with 10% bentonite was moderately efficient in the retention of chloride, potassium and ammonium ions compared to the configurations of compacted soil with a geomembrane and compacted soil alone, representing a solution that is technically feasible and requires potentially lower costs for implementation in landfills.

Waste degradation and gas production with enzymatic enhancement in anaerobic and aerobic landfill bioreactors.

The presence of lignin is the limiting factor at later stages of biodegradation of municipal solid waste under aerobic or anaerobic conditions. Supplying enzymes into the system could facilitate lignin degradation, thereby aiding anaerobic and aerobic waste degradation processes. A comprehensive set of laboratory experiments were conducted under both anaerobic and aerobic conditions to evaluate the feasibility of using enzymes in accelerating lignin-rich waste degradation. After 30 days of anaerobic operation, MnP and LiP enzyme treated reactors produced 36 and 23 times higher cumulative methane (CH4), respectively, compared to that of the control reactor devoid of enzyme treatments. The carbon dioxide (CO2) yield of MnP enhanced aerobic reactor showed more than two-fold increase.

Steel slags in a landfill top cover--experiences from a full-scale experiment.

A full scale field study has been carried out in order to test and evaluate the use of slags from high-alloy steel production as the construction materials for a final cover of an old municipal landfill. Five test areas were built using different slag mixtures within the barrier layer (liner). The cover consisted of a foundation layer, a liner with a thickness of 0.7 m, a drainage layer of 0.3 m, a protection layer of 1.5 m and a vegetation layer of 0.25 m. The infiltration varied depending on the cover design used, mainly the liner recipe but also over time and was related to seasons and precipitation intensity. The test areas with liners composed of 50% electric arc furnace (EAF) slag and 50% cementitious ladle slag (LS) on a weight basis and with a proper consistence of the protection layer were found to meet the Swedish infiltration criteria of ⩽50 l (m(2)a)(-1) for final covers for landfills for non-hazardous waste: the cumulative infiltration rates to date were 44, 19 and 0.4 l (m(2)a)(-1) for A1, A4 and A5, respectively. Compared to the precipitation, the portion of leachate was always lower after the summer despite high precipitation from June to August. The main reason for this is evapotranspiration but also the fact that the time delay in the leachate formation following a precipitation event has a stronger effect during the shorter summer sampling periods than the long winter periods. Conventional techniques and equipment can be used but close cooperation between all involved partners is crucial in order to achieve the required performance of the cover. This includes planning, method and equipment testing and quality assurance.

Inventory and treatment of compost maturation emissions in a municipal solid waste treatment facility.

Emissions of volatile organic compounds (VOCs) from the compost maturation building in a municipal solid waste treatment facility were inventoried by solid phase microextraction and gas chromatography-mass spectrometry. A large diversity of chemical classes and compounds were found. The highest concentrations were found for n-butanol, methyl ethyl ketone and limonene (ppmv level). Also, a range of compounds exceeded their odor threshold evidencing that treatment was needed. Performance of a chemical scrubber followed by two parallel biofilters packed with an advanced packing material and treating an average airflow of 99,300 m(3) h(-1) was assessed in the treatment of the VOCs inventoried. Performance of the odor abatement system was evaluated in terms of removal efficiency by comparing inlet and outlet abundances. Outlet concentrations of selected VOCs permitted to identify critical odorants emitted to the atmosphere. In particular, limonene was found as the most critical VOC in the present study. Only six compounds from the odorant group were removed with efficiencies higher than 90%. Low removal efficiencies were found for most of the compounds present in the emission showing a significant relation with their chemical properties (functionality and solubility) and operational parameters (temperature, pH and inlet concentration). Interestingly, benzaldehyde and benzyl alcohol were found to be produced in the treatment system.

Optimization of micro-aeration intensity in acidogenic reactor of a two-phase anaerobic digester treating food waste.

Micro-aeration is known to promote the activities of hydrolytic exo-enzymes and used as a strategy to improve the hydrolysis of particulate substrate. The effect of different micro-aeration rates, 0, 129, 258, and 387 L-air/kg TS/d (denoted as LBR-AN, LBR-6h, LBR-3h and LBR-2h, respectively) on the solubilization of food waste was evaluated at 35°C in four leach bed reactors (LBR) coupled with methanogenic upflow anaerobic sludge blanket (UASB) reactor. Results indicate that the intensity of micro-aeration influenced the hydrolysis and methane yield. Adequate micro-aeration intensity in LBR-3h and LBR-2h significantly enhanced the carbohydrate and protein hydrolysis by 21-27% and 38-64% respectively. Due to the accelerated acidogenesis, more than 3-fold of acetic acid and butyric acid were produced in LBR-3h as compared to the anaerobic treatment LBR-AN resulting in the maximum methane yield of 0.27 L CH4/g VS(added) in the UASB. The performance of LBR-6h with inadequate aeration was similar to that of LBR-AN with a comparable hydrolysis degree. Nevertheless, higher aeration intensity in LBR-2h was also unfavorable for methane yield due to significant biomass generation and CO2 respiration of up to 18.5% and 32.8% of the total soluble hydrolysate, respectively. To conclude, appropriate micro-aeration rate can promote the hydrolysis of solid organic waste and methane yield without undesirable carbon loss and an aeration intensity of 258 L-air/kg TS/d is recommended for acidogenic LBR treating food waste.