Effects of introducing energy recovery processes to the municipal solid waste management system in Ulaanbaatar,Mongolia

Currently, most developing countries have not set up municipal solid waste management systems with a view of recovering energy from waste or reducing greenhouse gas emissions. In this article, we have studied the possible effects of introducing three energy recovery processes either as a single or combination approach, refuse derived fuel production, incineration and waste power generation, and methane gas recovery from landfill and power generation in Ulaanbaatar, Mongolia, as a case study. We concluded that incineration process is the most suitable as first introduction of energy recovery. To operate it efficiently, 3Rs strategies need to be promoted. And then, RDF production which is made of waste papers and plastics in high level of sorting may be considered as the second step of energy recovery. However, safety control and marketability of RDF will be required at that moment.     

Treatment of sewage using an aged-refuse-based bioreactor

The refuse in landfills becomes stabilized or aged after years of placement, and the resultant partly or fully stabilized refuse thus obtained is referred to as "aged refuse" in this work. The aged refuse contains a wide spectrum and large quantity of microorganisms, which have been proved to have a strong decomposition capability for both biodegradable and refractory organic matter present in some wastewaters. In this study, the aged refuse excavated from a 10-year old closed landfill compartment at Shanghai Refuse Landfill was used as the substrate in a bioreactor for the biofiltration of sewage taken from the sewage pipeline systems in Shanghai downtown areas. Typically, 120kg of screened aged refuse with a diameter less than 15mm was used as biofiltration material in a round shaped bioreactor with an inner diameter of 80cm and a height of 150cm. Influent sewage with initial COD, BOD, and NH(3)-N concentrations of 400-500, 240-300, and 45-50mg/L, respectively, was introduced into the bioreactor. The corresponding concentrations in the effluent were reduced to below 80-100, 10-20, and 10-15mg/L, respectively, at a hydraulic load of 1000-1200L/m(3) refuse/day, and the treatment efficiencies decreased with increased hydraulic load. The treatment mechanism was also studied. It was found that the pollutant removal efficiencies dramatically decreased when the aged refuse in the bioreactor was preliminarily disinfected using NaClO solutions, indicating that the pollutants in the sewage were biologically removed. The treatment process developed in this work is cost-effective.     

PCDD/Fs in ambient air collected in Zagreb, Croatia

Levels of PCDD/Fs were measured at four different sites in Zagreb, capital of Croatia. Also one sample was taken during spontaneously initiated open fire on a landfill and one sample where garden waste of unknown content was burnt. Over period 1997–2000, 28 samples were collected and levels ranged between 9 and 306 fg I-TEQ m⁻³, except in the sample collected during landfill fire. Air PCDD/F levels in Zagreb at four sites were different and the highest levels were observed in industrial area. Seasonal variation of levels is also evident with higher levels in winter than in summer. Our results show that PCDD/F levels in ambient air collected in Zagreb are at lower end of the published data range. In general, homologue profiles were quite similar for all locations, the concentration of PCDD homologues increased while the concentration of PCDF homologues decreased with increasing degree of chlorination. PCDD/F levels in the landfill fire sample was 13 200 fg I-TEQ m⁻³ which are much higher than levels in garden waste burning sample or in sample collected at industrial site. During landfill fire, the concentration of 2,3,7,8-TCDF becomes even higher than the concentration of OCDF and is equal to the concentration of 1,2,3,4,6,7,8-HpCDF.     

Identification of a reactive degradation zone at a landfill leachate plume fringe using high resolution sampling and incubation techniques

Vertical small-scale variation in phenoxy acid herbicide degradation across a landfill leachate plume fringe was studied using laboratory degradation experiments. Sediment cores (subdivided into 5 cm segments) were collected in the aquifer and the sediment and porewater were used for microcosm experiments (50 experiments) and for determination of solid organic carbon, solid-water partitioning coefficients, specific phenoxy acid degraders and porewater chemistry. Results from a multi-level sampler installed next to the cores provided information on the plume position and oxygen concentration in the groundwater. Oxygen concentration was controlled individually in each microcosm to mimic the conditions at their corresponding depths. A highly increased degradation potential existed at the narrow plume fringe (37.7 to 38.6 masl), governed by the presence of phenoxy acids and oxygen. This resulted in the proliferation of a microbial population of specific phenoxy acid degraders, which further enhanced the degradation potential for phenoxy acids at the fringe. The results illustrate the importance of fringe degradation processes in contaminant plumes. Furthermore, they highlight the relevance of using high-resolution sampling techniques as well as controlled microcosm experiments in the assessment of the natural attenuation capacity of contaminant plumes in groundwater.     

Recharge processes drive sulfate reduction in an alluvial aquifer contaminated with landfill leachate

Natural attenuation of contaminants in groundwater depends on an adequate supply of electron acceptors to stimulate biodegradation. In an alluvial aquifer contaminated with leachate from an unlined municipal landfill, the mechanism of recharge infiltration was investigated as a source of electron acceptors. Water samples were collected monthly at closely spaced intervals in the top 2 m of the saturated zone from a leachate-contaminated well and an uncontaminated well, and analyzed for delta(18)O, delta(2)H, non-volatile dissolved organic carbon (NVDOC), SO(4)(2-), NO(3)(-) and Cl(-). Monthly recharge amounts were quantified using the offset of the delta(18)O or delta(2)H from the local meteoric water line as a parameter to distinguish water types, as evaporation and methanogenesis caused isotopic enrichment in waters from different sources. Presence of dissolved SO(4)(2-) in the top 1 to 2 m of the saturated zone was associated with recharge; SO(4)(2-) averaged 2.2 mM, with maximum concentrations of 15 mM. Nitrate was observed near the water table at the contaminated site at concentrations up to 4.6 mM. Temporal monitoring of delta(2)H and SO(4)(2-) showed that vertical transport of recharge carried SO(4)(2-) to depths up to 1.75 m below the water table, supplying an additional electron acceptor to the predominantly methanogenic leachate plume. Measurements of delta(34)S in SO(4)(2-) indicated both SO(4)(2-) reduction and sulfide oxidation were occurring in the aquifer. Depth-integrated net SO(4)(2-) reduction rates, calculated using the natural Cl(-) gradient as a conservative tracer, ranged from 7.5x10(-3) to 0.61 mM.d(-1) (over various depth intervals from 0.45 to 1.75 m). Sulfate reduction occurred at both the contaminated and uncontaminated sites; however, median SO(4)(2-) reduction rates were higher at the contaminated site. Although estimated SO(4)(2-) reduction rates are relatively high, significant decreases in NVDOC were not observed at the contaminated site. Organic compounds more labile than the leachate NVDOC may be present in the root zone, and SO(4)(2-) reduction may be coupled to methane oxidation. The results show that sulfur (and possibly nitrogen) redox processes within the top 2 m of the aquifer are directly related to recharge timing and seasonal water level changes in the aquifer. The results suggest that SO(4)(2-) reduction associated with the infiltration of recharge may be a significant factor affecting natural attenuation of contaminants in alluvial aquifers.     

Monitoring of Gin Drinkers' Bay landfill,Hong Kong: II. Gas contents,soil properties,and vegetation performance on the side slope

This second part of the study concerned the plant cover, gas contents, and soil properties of the side slope area of the landfill, which is not protected against gas infiltration. Five different sites on the slope and a control site outside the landfill were chosen, and pipes were installed in the region. Gas contents were tested, and plant cover recorded by quadrat analysis Over 20 species of grasses, herbs, and vines were present on the slope The relative adaptabilities of the species were ranked according to the abundance of the plants Plant cover was found to be negatively correlated with landfill gas contents. The landfill soil had elevated contents of nitrogen, organic carbon, and extractable metals Total nitrogen, ammonia nitrogen, and extractable lead were further identified to be negatively correlated while available phosphate was positively correlated with plant cover     

Solid Waste Management Practices in the Eastern Province of Saudi Arabia

Solid waste management practices in the Eastern Province of Saudi Arabia are reviewed. The officials of various municipalities and agencies responsible for collecting and disposing of municipal waste were interviewed. The refuse generation rate found is in the range of 1.61–2.72 kg per capita per day. The refuse composition data indicate a high percentage of glass, metals, and wood. For storage purposes, 0.2-m³ barrels are used in residential areas and 0.75 to 1.50 m³-capacity containers are used in commerical areas. The present solid-waste collection system is labor-intensive, and a significant part of the budget is spent on collection and haul operations. The unit collection and haul cost is much higher than the unit disposal cost of refuse. The direct haul of refuse is the common practice, and the use of transfer stations has not yet been considered. It is also observed that the disposal methods used at these sites are not in line with modern techniques for refuse disposal. Landfilling and combined burning and landfilling are the common disposal methods at all the sites.     

吹脱-水解酸化-SBR法处理垃圾渗滤液的试验研究

研究采用吹脱—水解酸化—SBR工艺处理含高浓度氨氮的垃圾渗滤液。结果表明，采用吹脱预处理可去除废水中60％以上的氨氮，有利于后续生物脱氮和脱碳的进行。生物水解酸化处理在降低废水CODCr值的同时，可以提高废水的可生化性。该方法将曝气期分为二段，并设置缺氧反硝化期，可明显提高氨氮的去除率。     

Recycling, landfill consumption, and CO2 emission: analysis by waste input–output model

The emission of waste in an economy, including landfill, is to a large extent determined by its patterns of technology, institutions, and lifestyle. A mathematical model (the waste input–output model) is presented that gives a simple analytical representation of this interdependence. The model was used to evaluate the effects of alternative waste disposal and recycling options on the levels of industrial production, landfill consumption, and the emission of carbon dioxide, and also to analyze the overall dependence on landfill of individual industries. It was found that a systematic combination of the options could be effective in reducing the overall landfill consumption and carbon dioxide emission. Received: November 4, 2000 / Accepted: August 2, 2001     

An evaluation of landfill disposal of asbestos-containing waste and geothermal residues within a risk-assessment framework

 The public perception of risks related to waste disposal facilities appears to reflect general societal anxieties and fears, which may not have a reasonable basis. A three-tier risk assessment study was therefore conducted to evaluate the landfill disposal of asbestos-containing waste (ACW) and geothermal residues. From the tier-1 analysis, the dominant asbestiform phase was identified as chrysotile, that is tightly bound in the matrix of calcite, while arsenic, cadmium, chromium, and lead were identified as the chemicals of potential concern associated with geothermal residues. From the tier-2 analysis, none of the possible exposure pathways associated with the landfill disposal of ACW was found to be potentially significant. On the other hand, there were potentially significant pathways associated with landfill disposal of geothermal residues because of the considerable potential pollution impact of leachate on soil and groundwater quality. From the tier-3 analysis, the health risk associated with landfill disposal of geothermal residues was found to be time-dependent, since the contributions to risk from water-dependent and water-independent pathways occur at different times, as indicated by RESRAD–Chem simulations. Component pathway analyses were performed to identify critical exposure pathways. The results from model sensitivity analysis have identified the input parameters that have the most influence on the time of peak risk, and the cancer risk associated with water-dependent and water-independent pathways. Received: July 9, 2002 / Accepted: October 17, 2002