Hydrogen and methane production from household solid waste in the two-stage fermentation process

A two-stage process combined hydrogen and methane production from household solid waste was demonstrated working successfully. The yield of 43 mL H(2)/g volatile solid (VS) added was generated in the first hydrogen production stage and the methane production in the second stage was 500 mL CH(4)/g VS added. This figure was 21% higher than the methane yield from the one-stage process, which was run as control. Sparging of the hydrogen reactor with methane gas resulted in doubling of the hydrogen production. pH was observed as a key factor affecting fermentation pathway in hydrogen production stage. The optimum pH range for hydrogen production in this system was in the range from 5 to 5.5. The short hydraulic retention time (2 days) applied in the first stage was enough to separate acidogenesis from methanogenesis. No additional control for preventing methanogenesis in the first stage was necessary. Furthermore, this study also provided direct evidence in the dynamic fermentation process that, hydrogen production increase was reflected by acetate to butyrate ratio increase in liquid phase.     

Anaerobic digestion of the organic fraction of municipal solid waste: influence of co-digestion with manure

Anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was investigated in two thermophilic (55 degrees C) wet digestion treatment systems R1 and R2. Initially OFMSW was co-digested with manure with a successively higher concentration of OFMSW, at a hydraulic retention time (HRT) of 14-18 d and an organic loading rate (OLR) of 3.3-4.0 g-VS/l/d. Adaptation of the co-digestion process to a OFMSW:manure ratio of 50% (VS/VS) was established over a period of 6 weeks. This co-digestion ratio was maintained in reactor R2 while the ratio of OFMSW to manure was slowly increased to 100% in reactor R1 over a period of 8 weeks. Use of recirculated process liquid to adjust the organic loading to R1 was found to have a beneficial stabilization effect. The pH rose to a value of 8 and the reactor showed stable performance with high biogas yield and low VFA levels. The biogas yield from source-sorted OFMSW was 0.63-0.71 l/g-VS both in the co-digestion configuration and in the treatment of 100% OFMSW with process liquid recirculation. This yield is corresponding to 180-220 m3 biogas per ton OFMSW. VS reduction of 69-74% was achieved when treating 100% OFMSW. None of the processes showed signs of inhibition at the free ammonia concentration of 0.45-0.62 g-N/l.     

Treatment of municipal solid waste leachate using a submerged anaerobic membrane bioreactor at mesophilic and psychrophilic temperatures: Analysis of recalcitrants in the permeate using GC-MS

This study investigated the performance of two submerged anaerobic membrane bioreactors (SAMBRs) operating at a mean solids residence time (SRT) of 30 (SAMBR30) and 300 days (SAMBR300) at mesophilic and psychrophilic temperatures. At 35 °C results showed that SAMBR30 and 300 could achieve 95% soluble chemical oxygen demand (SCOD) removal at 1.5 and 1.1 days HRT, respectively, whereas at 20 °C only SAMBR300 could maintain the same performance. Low temperatures were associated with higher bulk SCOD concentrations, which contributed to reducing the flux, but this was partly reversible once the SCOD was degraded. The utilization rate of compounds was affected differently by the drop in temperature with the concentration of some recalcitrants increasing, while for others such as bisphenol A it decreased when the temperature was decreased. Among the recalcitrants detected in SAMBR30 at 20 °C there were not only long chain fatty acids such as undecanoic acid and dodecanoic acid, but also long chain alkanes such as tetracosane and heneicosane that could not be hydrolyzed at 20 °C. In SAMBR300 these alkanes and acids only appeared at 10 °C, whereas at 20 °C complex compounds such as phenol, 2-chloro-4-(1,1-dimethylethyl), 6-tert-butyl-2,4-dimethylphenol, benzophenone, and n-butyl benzenesulfonamide were found.     

A continuous-flow approach for the development of an anaerobic consortium capable of an effective biomethanization of a mechanically sorted organic fraction of municipal solid waste as the sole substrate

An effective mesophilic continuous anaerobic digestion process fed only with a mechanically sorted organic fraction of municipal solid waste (MS-OFMSW) was developed. During a preliminary 3-month experimental phase, the microbial consortium was acclimated toward MS-OFMSW by initially filling the reactor with cattle manure and then continuously feeding it with MS-OFMSW. The Hydraulic Retention Time (HRT) and Organic Loading Rate (OLR) were 23 days and 2.5 g/L/day, respectively. After 4 weeks, the reactor reached stationary performances (84% COD removal yield, 0.15 L₄CH/g_CODremoved methane production yield). The acclimated consortium was then employed in a second run in which the reactor was operated under steady state conditions at the previous HRT and OLR for 73 days. The COD removal and the methane production yield increased up to 87% and 0.25 L₄CH/g_CODremoved, respectively. The capability of the acclimated consortium to biomethanize MS-OFMSW was further studied via batch digestion experiments, carried out by inoculating the target waste with reactor effluents collected at the beginning of first run and at the end of the first and second run. The best normalized methane production (0.39 L₄CH/g_{initial COD}) was obtained with the inoculum collected at the end of the second run. Molecular analysis of the microbial community occurring in the reactor during the two sequential runs indicated that the progressive improvement of the process performances was closely related to the selection and enrichment of specific hydrolytic and acidogenic bacteria in the reactor.     

浅谈生活垃圾卫生填埋场选址中应注意几个问题

生活垃圾卫生填埋场多处于农村或城乡结合部,其选址涉及多方面因素,不仅要分析其是否符合相关政策、规划、规范、标准等要求,而且还要紧密结合所选场址各方面特征因素,全面分析其可能存在的影响,尤其应关注对农村、农业和农民的影响,并提出解决办法。本文结合环评实践,阐述选址中应该注意几个问题。     

High-concentration food wastewater treatment by an anaerobic membrane bioreactor

The viability of treating high-concentration food wastewater by an anaerobic membrane bioreactor (AMBR) was studied using polyethersulfone (PES) ultrafiltration membranes PES200, PES300, PES500 and PES700 with norminal molecular weight cutoff (MWCO) ranging from 20,000 to 70,000 Da. Hydraulic and solid retention time significantly affected the treatment performance of the AMBR kept at 60 h and 50 days in the study. The four membranes exhibited a similar efficiency in removal of suspended solids, color, chemical oxygen demand (COD) and bacteria. When the volumetric loading rate was below 4.5 kg/m3d, COD removal rate was in the range of 81-94% and the gas yield stabilized at 0.136 m3/kg COD. The effect of membrane properties including MWCO, hydrophobicity and surface morphology on membrane fouling and cleaning was evaluated. The PES200 membranes with the smallest MWCO and smoothest surface exhibited a serious initial flux decline, whereas the PES700 membranes with the largest MWCO and roughest surface were observed related to the highest flux decline and the lowest recoverable flux rate during long-term operation. Membrane autopsy revealed that the significant flux decline was caused by the formation of a thick biofouling layer onto the membrane surfaces.     

A comparison of wet and dry anaerobic digestion processes for the treatment of municipal solid waste and food waste

A main distinction between anaerobic digestion (AD) technologies for treatment of municipal and industrial biodegradable wastes is the operating process solids content. Wet AD systems operate at low total solids (<10–20% TS) and dry systems have high operating solids (20–>40% TS). The performance of wet and dry AD systems was quantified in relation to: technical operation (footprint, capacity, feedstock characteristics, pretreatment and post‐treatment, retention time, water usage), energy balance (biogas productivity, parasitic energy, methane [CH₄] content, utilization of biogas and produced energy), digestate management and economic performance (capital and operational costs, revenues, specific capital costs [per t of waste and per m³ biogas]). Wet AD plants had improved energy balance and economic performance compared to dry AD plants. However, dry AD plants offered several benefits, including greater flexibility in the type of feedstock accepted, shorter retention times, reduced water usage and more flexible management of, and opportunities for marketing, the end‐product.     

Contaminant mitigating performance of Chinese standard municipal solid waste landfill liner systems

In 2004, Chinese Government prescribed standard municipal solid waste (MSW) landfill bottom liners. However, very limited research has been conducted to evaluate the performance of the standard MSW landfill bottom liners prescribed by the Chinese Government. In this paper, the performance of the two types of Chinese MSW landfill bottom liner systems was evaluated based on: (1) the maximum leachate head; (2) leakage rate; (3) peak concentration of the target contaminant in an aquifer which was underlain the assumed landfill, and (4) total mass per unit area of the target contaminant discharged into the aquifer. The performance of the German standard MSW landfill bottom liner system was evaluated and compared with that of Chinese ones. It is found that the calculated maximum leachate head for the Chinese landfill liner systems was much higher than that for the German one. The calculated leakage rate, peak concentration and the maximum total mass per unit area in the aquifer of the target contaminant show that the performance of the Chinese standard landfill liner Type 2 is practically the same as that of the German standard landfill liner with holed geomembrane wrinkles, while the Chinese standard liner Type 1 is less effective, with regarding the mitigation of the impact of landfills to the groundwater quality. It is concluded that the overall performance of the Chinese standard landfill liner systems is less strict than that of the German standard landfill liner system.     

The influence of spent household batteries to the organic fraction of municipal solid wastes during composting

The objective of this work was to investigate the potential transfer of 9 heavy metals from spent household batteries (zinc-carbon and alkaline-manganese batteries) to the organic fraction of municipal solid wastes during active composting. Six runs were performed including one control and 2 replications. Eleven types of alkaline and non-alkaline batteries were added at 3 different levels to the organic fraction of municipal solid wastes, namely at percentages equal to 0.98% w/w (low), 5.2% w/w (medium) and 10.6% w/w (high). Experiments were performed in 230 l insulated plastic aerobic bioreactors under a dynamic air flow regime for up to 60 days. Iron, copper and nickel masses contained in the organic fraction of the wastes were found significantly higher in the high level runs compared to the corresponding masses in the control. No metal transfer was obtained in the low and medium level runs. Metal mass balance closures ranged from 51% to 176%. Metals' concentrations in the leachates were below 10 mg l⁻¹ for most metals, except iron, while an increasing concentration trend versus time was measured in the leachates of the high level runs. In all cases, the contents of 5 regulated heavy metals in all end products were below the Hellenic limits.     

Thermophilic anaerobic digestion of source-sorted organic fraction of household municipal solid waste: start-up procedure for continuously stirred tank reactor

Two feeding strategies for start-up of continuously stirred tank reactors (CSTR) treating source-sorted organic fraction of household municipal solid waste (SS-OFMSW) at 55 degrees C were evaluated. Two reactors were started up separately with a limited amount of initial inoculum (i.e. 10% of the final volume of 3.5l) and operated in a fed batch mode until the reactors were filled (30 days). A reference reactor was filled up with 3.5l of inoculum and fed at a constant rate (11.4 g volatile solids (VS)/d). Loading at progressively increasing rate (from 1.7 to 15 gVS/d), as calculated based on an activated biomass concept, showed superior process performance compared to a fixed feed rate (5.7 gVS/d). Methane yield of 0.32 m(3)/kg VS was produced during the start-up in reactor filled at progressively increasing rate and was comparable to the reference reactor. On the contrary, significant inhibition due to volatile fatty acid (VFA) build-up, mainly due to butyrate, was noticed in the reactor filled at constant rate. Thus, low initial and progressive increasing inoculum loading rate could be used as a strategy for a successful start-up of CSTR treating SS-OFMSW as it allowed a gradual acclimation of the biomass. Lab-scale results were further reaffirmed from the start-up of a full-scale plant (7000 m(3) total capacity) which was supplied with inoculum corresponding to approx. 16% of final volume and operated in a fed batch mode until the reactors were filled (58 days). Stable biogas production with low VFA (<3 g/L; based on titration method) were noticed during the start-up period when fed at progressively increasing rate. Thus, a controlled and reliable start-up procedure was found essential, which could allow rapid process stabilization and time to focus on other technical aspects of plant operation. In addition, the influence of substrate to inoculum amount (1.5-30% TS) and temperature (5-65 degrees C) on anaerobic degradation and methane production of SS-OFMSW was investigated in batch assays as a protocol for start-up procedure.     

In‐vessel composting under air pressure of organic fraction of municipal solid waste in Azemmour,Morocco

This study aims to evaluate the performance of laboratory‐scale in‐vessel composting bioreactor for the Organic Fraction of Municipal Solid Waste treatment in Azemmour, Morocco. The bioreactor was specially designed and used for this study, and it was operated semicontinuously under 0.6 bar pressure. The evaluations studied included the operational indices, the compost maturity indices and the quality of the final compost. Obtained results showed that organic fraction of municipal solid waste could be composted successfully in 12 days. Moreover, high CO₂ generations involve high temperature and high internal air pressure change, revealing vigorous microbial activity. The final compost was satisfactory for its agricultural application.     

Geo-environmental application of municipal solid waste incinerator ash stabilized with cement

The behavior of soluble salts contained in the municipal solid waste incinerator (MSWI) ash significantly affects the strength development and hardening reaction when stabilized with cement. The present study focuses on the compaction and strength behavior of mixed specimens of cement and MSWI ash. A series of indices such as unconfined compressive strength, split tensile strength, California bearing ratio (CBR) and pH value was examined. Prior to this, the specimens were cured for 7 d, 14 d, and 28 d. The test results depict that the maximum dry density (MDD) decreases and the optimum moisture content (OMC) increases with the addition of cement. The test results also reveal that the cement increases the strength of the mixed specimens. Thus, the combination of MSWI ash and cement can be used as a lightweight filling material in different structures like embankment and road construction.     

Analysis of fouling mechanisms in anaerobic membrane bioreactors

In this paper, we investigate the fouling mechanisms responsible for MF and UF membrane flux decline in Anaerobic Membrane Bioreactors (AnMBR). We have used the fouling mechanism models proposed by Hermia (1982), namely pore constriction, cake formation, complete blocking and intermediate blocking. Based on an optimization approach and using experimental data extracted from the literature, we propose a systematic procedure for identifying the most likely fouling mechanism in play. Short-term as well as long-term experiments are considered and discussed. It was found that short-term experiments are usually characterized by two fouling phases during which the same fouling mechanism or two different mechanisms affect the process. In contrast, in long-term experiments involving cleaning cycles, membrane fouling appears to be better ascribed to one phase only.The impact of abiotic parameters on membrane fouling mechanisms is reviewed and discussed in the light of these results. Finally, it is shown that the mechanism most responsible for membrane fouling in an AnMBR is cake formation. This main result will be useful for the future development of simple integrated models for optimization and control.     

Life cycle assessment of municipal solid waste management with regard to greenhouse gas emissions: Case study of Tianjin, China

The environmental impacts of municipal solid waste (MSW) management have been highlighted in China, due to the continually increasing amount of MSW being generated and the limited capacity of waste treatment facilities. Of particular interest is greenhouse gas (GHG) mitigation, aided by the Kyoto Mechanisms. China is an important case study for this global issue; however, an analysis of the entire life cycle of MSW management on GHG emissions is not available for China. This study evaluates the current and possible patterns of MSW management with regard to GHG emissions, using life cycle assessment (LCA), based on the Tianjin case. We assess the baseline scenario, reflecting the existing MSW management system, as well as a set of alternative scenarios, five exploring waste treatment technology innovations and one exploring integrated MSW management, to quantitatively predict potentials of GHG mitigation for Tianjin. Additionally, a sensitivity analysis is used to investigate the influence of landfill gas (LFG) collection efficiency, recycling rate and methodological choice, especially allocation, on the outcomes. The results show GHG emissions from Tianjin's MSW management system amount to 467.34 Mg CO₂ eq. per year, based on the treatment of MSW collected in the central districts in 2006, and the key issue is LFG released. The integrated MSW management scenario, combining different improvement options, shows the highest GHG mitigation potential. Given the limited financial support and the current waste management practice in Tianjin, LFG utilization scenario would be the preferred choice. The sensitivity analysis of recycling rate shows an approximately linear relation of inverse proportion between recycling rate and total GHG emissions. Kitchen waste composting makes a considerable contribution to total GHG emissions reduction. Allocation choices result in differences in total quantitative outcomes, but preference orders and contributions analysis are found to be robust, suggesting LCA can support decision making.     

Statistical estimate of mercury removal efficiencies for air pollution control devices of municipal solid waste incinerators

Although representative removal efficiencies of gaseous mercury for air pollution control devices (APCDs) are important to prepare more reliable atmospheric emission inventories of mercury, they have been still uncertain because they depend sensitively on many factors like the type of APCDs, gas temperature, and mercury speciation. In this study, representative removal efficiencies of gaseous mercury for several types of APCDs of municipal solid waste incineration (MSWI) were offered using a statistical method. 534 data of mercury removal efficiencies for APCDs used in MSWI were collected. APCDs were categorized as fixed-bed absorber (FA), wet scrubber (WS), electrostatic precipitator (ESP), and fabric filter (FF), and their hybrid systems. Data series of all APCD types had Gaussian log-normality. The average removal efficiency with a 95% confidence interval for each APCD was estimated. The FA, WS, and FF with carbon and/or dry sorbent injection systems had 75% to 82% average removal efficiencies. On the other hand, the ESP with/without dry sorbent injection had lower removal efficiencies of up to 22%. The type of dry sorbent injection in the FF system, dry or semi-dry, did not make more than 1% difference to the removal efficiency. The injection of activated carbon and carbon-containing fly ash in the FF system made less than 3% difference. Estimation errors of removal efficiency were especially high for the ESP. The national average of removal efficiency of APCDs in Japanese MSWI plants was estimated on the basis of incineration capacity. Owing to the replacement of old APCDs for dioxin control, the national average removal efficiency increased from 34.5% in 1991 to 92.5% in 2003. This resulted in an additional reduction of about 0.86 Mg emission in 2003. Further study using the methodology in this study to other important emission sources like coal-fired power plants will contribute to better emission inventories.     

Critical flux and chemical cleaning-in-place during the long-term operation of a pilot-scale submerged membrane bioreactor for municipal wastewater treatment

The critical flux and chemical cleaning-in-place (CIP) in a long-term operation of a pilot-scale submerged membrane bioreactor for municipal wastewater treatment were investigated. Steady filtration under high flux (30 L/(m² h)) was successfully achieved due to effective membrane fouling control by sub-critical flux operation and chemical CIP with sodium hypochlorite (NaClO) in both trans-membrane pressure (TMP) controlling mode (cleaning with high concentration NaClO of 2000-3000 mg/L in terms of effective chorine was performed when TMP rose to 15 kPa) and time controlling mode (cleanings were performed weekly and monthly respectively with low concentration NaClO (500-1000 mg/L) and high concentration NaClO (3000 mg/L)). Microscopic analysis on membrane fibers before and after high concentration NaClO was also conducted. Images of scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that NaClO CIP could effectively remove gel layer, the dominant fouling under sub-critical flux operation. Porosity measurements indicated that NaClO CIP could partially remove pore blockage fouling. The analyses from fourier transform infrared spectrometry (FTIR) with attenuated total reflectance accessory (ATR) and energy dispersive spectrometer (EDS) demonstrated that protein-like macromolecular organics and inorganics were the important components of the fouling layer. The analysis of effluent quality before and after NaClO CIP showed no obvious effect on effluent quality.     

Numerical study of strain development in high-density polyethylene geomembrane liner system in landfills using a new constitutive model for municipal solid waste

Tensile strain development in high-density polyethylene (HDPE) geomembrane (GMB) liner systems in landfills was numerically investigated. A new constitutive model for municipal solid waste (MSW) that incorporates both mechanical creep and biodegradation was employed in the analyses. The MSW constitutive model is a Cam-Clay type of plasticity model and was implemented in the finite difference computer program FLAC?. The influence of the friction angle of the liner system interfaces, the biodegradation of MSW, and the MSW filling rate on tensile strains were investigated. Several design alternatives to reduce the maximum tensile strain under both short- and long-term waste settlement were evaluated. Results of the analyses indicate that landfill geometry, interface friction angles, and short- and long-term waste settlement are key factors in the development of tensile strains. The results show that long-term waste settlement can induce additional tensile strains after waste placement is complete. Using a HDPE GMB with a friction angle on its upper interface that is lower than the friction angle on the underlying interface, increasing the number of benches, and reducing the slope inclination are shown to mitigate the maximum tensile strain caused by waste placement and waste settlement.     

Impact of open dumping of municipal solid waste on soil properties in mountainous region

This paper presents the effect of open dumping of municipal solid waste (MSW) on soil characteristics in the mountainous region of Himachal Pradesh, India. The solid waste of dumpsite contains various complex characteristics with organic fractions of the highest proportions. As leachate percolates into the soil, it migrates contaminants into the soil and affects soil stability and strength. The study includes the geotechnical investigation of dump soil characteristics and its comparison with the natural soil samples taken from outside the proximity of dumpsites. The geochemical analysis of dumpsite soil samples was also carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Visual inspection revealed that the MSW consists of high fraction of organics, followed by paper. The soil samples were collected from five trial pits in the dumpsites at depths of 0.5 m, 1 m and 1.5 m. Then the collected soil samples were subjected to specific gravity test, grain size analysis, Atterberg's limit test, compaction test, direct shear test, California bearing ratio (CBR) test and permeability analysis. The study indicated that the dumpsite soils from four study regions show decreasing trends in the values of maximum dry density (MDD), specific gravity, cohesion and CBR, and increasing permeability as compared to the natural soil. The results show that the geotechnical properties of the soils at all four study locations have been severely hampered due to contamination induced by open dumping of waste.     

生活垃圾填埋场渗滤液处理站改造可行性的初步调研

张桥庄生活垃圾填埋场渗滤液处理站自2008年8月建成以来,由第一污水处理厂接管运行,由于存在诸多问题,一直难以正常运行,于2009年7月组织了一次现场专家研讨,确认了问题症结。就该垃圾渗滤液处理站能否改造运行的问题,第一污水处理厂有关技术、管理人员专程赴京走访了有关部门的专家或技术管理人员。