The treatment of leachates from domestic wastes in landfills—I: Aerobic biological treatment of a medium-strength leachate

A medium-strength leachate from domestic solid wastes in a landfill (COD 5000 mg l⁻¹, BOD 3000 mg l⁻¹ was treated using aerobic biological processes in continuous-flow, laboratory-scale reactors at low temperatures. Each unit was completely mixed, and mixed liquor was wasted such that solids retention time (SRT) was equal to the hydraulic retention period.At 10 C with addition of phosphate (COD:P less than 100:1) SRT values of 10 days were required to obtained well-clarified effluents, and high removal of BOD (>;98%) and COD (>;92%). Reduction of temperature to 5°C resulted in adverse effects on settling of sludges from units with SRT values of less than 10 days, but in other units good removal of organic materials could still be obtained. These units operated successfully with concentrations of mixed liquor volatile suspended solids (MLVSS) of 1450 mg l⁻¹, equivalent to a ratio of F/M of 0.21 kg BOD kg⁻¹ MLVSS day⁻¹ or less. Removal of ammoniacal nitrogen which took place (influent concentration 80 mg l⁻¹ as N) resulted from incorporation in biomass, and at SRT values of 10 days no nitrification took place at 5 or 10 C. Higher concentrations of ammonia in influent leachates resulted in ammonia in effluents when the ratio of BOD:N was less than about 100:3.6. Increasing the SRT of units to 20 days resulted in erratic conversion to nitrite, but reduced pH-values and possible simultaneous denitrification caused floating sludges and poorly-clarified effluents. Removal of ammonia is identified as a major problem when treating leachates, and further research is recommended.     

Estimation of the mass-balance of selected metals in four sanitary landfills in Western Norway, with emphasis on the heavy metal content of the deposited waste and the leachate

A worst-case simulation of the mass-balance for metals in the waste deposited during 1 year and the levels of cadmium (Cd), lead (Pb), mercury (Hg), chromium (Cr) and iron (Fe) in the leachate was calculated for four sanitary landfills in Western Norway. Estimates of the levels of metal content in mixed municipal solid waste (MSW) were found by using recent literature values calculated in a mass-balance study at a Norwegian waste incinerator plant. Leachate from the landfills were sampled and analyzed monthly during 1 year, and from these measurements the total annual discharge of the selected metals through the leachate was determined. The levels of the measured heavy metals in the leachate were low. For Cd less than 0.06%, for Pb less than 0.01% and for Hg less than 0.02% of the estimated year's deposited mass of metals were leached from the landfills during the year of investigation. The high retention of these metals are most likely due to sulfide precipitation, but also due to the immobile condition of the metals in their original deposited solid state (plastics, ceramics, etc.). The percentage of Cr leached was relatively higher, but less than 1.0% per year. The mass balance of Fe suggests that this element is more mobile under the prevailing conditions. The percentage of Fe leached varied and was estimated to be between 1.9% and 18%. The present study clearly supports the theory that MSW only to a small extent will lead to discharge of metals if deposited at well-constructed sanitary landfills with top layers.     

The influence of a low air pressure environment on human metabolic rate during short‐term (< 2 h) exposures

Passengers in aircraft cabins are exposed to low‐pressure environments. One of the missing links in the research on thermal comfort under cabin conditions is the influence of low air pressure on the metabolic rate. In this research, we simulated the cabin pressure regime in a chamber in which the pressure level could be controlled. Three pressure levels (101/85/70 kPa) were tested to investigate how metabolic rate changed at different pressure levels. The results show that as pressure decreased, the respiratory flow rate (RFR) at standard condition (STPD: 0°C, 101 kPa) significantly decreased. Yet the oxygen (O₂) consumption and carbon dioxide (CO₂) production significantly increased, as reflected in the larger concentration difference between inhaled and exhaled air. A significant increase in the respiratory quotient (RQ) was also observed. For metabolic rate, no significant increase (P > 0.05) was detected when pressure decreased from 101 kPa to 85 kPa; however, the increase associated with a pressure decrease from 85 kPa to 70kPa was significant (P < 0.05). Empirical equations describing the above parameters are provided, which can be helpful for thermal comfort assessment in short‐haul flights.     

Surahammar: a case study of the impacts of installing food waste disposers in 50% of households

This paper reviews 15 years of sewage works' monitoring data to assess the effect of installing in-sink food waste disposers (FWD) and how these effects compare with the published scientific literature. For the first time, it has been possible to assess at full scale the load/cost transfer from solid-waste to wastewater management. Within a period of 10 years, 50% of households in the town of Surahammar in Sweden chose to have FWD installed as their means of managing their kitchen food waste. The drainage from the households feeds a single wastewater treatment works (WwTW) that comprises primary settlement, activated sludge, followed by chemical phosphate precipitation and mesophilic anaerobic digestion. The sewer system is separate but with overflow between foul and surface water in times of surcharge; the diameters and gradients of the sewers are unexceptional. This paper reviews the influent and biogas monitoring data for the years before installation started and the 10 years after the first peak of installations (by which time they had been installed in 30% of households). This provides a unique opportunity to verify the published research on FWD. The operational monitoring data are consistent with the already published research that FWD have little or no impact on water use, sewer blockages, vermin or wastewater treatment. The data are consistent with a hypothesis that in-sewer biological process acclimated to the change in wastewater composition and treated the dissolved and fine particulate load before it reached the WwTW. The digesters produced 46% more biogas than before FWD were installed (P=0.01). There was no significant increase in hydraulic load, or in the loading of BOD₇, COD, N or NH₄. As a result of Surahammar's overall waste strategy, not just the FWD, but the tonnage of waste to landfill from the municipality has also decreased from 3600 tonnes/year in 1996 to 1400 tonnes/year in 2007.     

The effects of food waste disposers on the wastewater system: a practical study

Domestic food waste disposers (FWDs) have recently come to prominence as a possible alternative for disposal of organic waste, to reduce the quantities of this type of waste sent to landfill. There has been little research undertaken on the potential effects of food waste on the wastewater system, and it is believed no previous practical studies have been undertaken in the United Kingdom. In this study, food waste was ground in an FWD and analysed for chemical oxygen demand (COD), biological oxygen demand (BOD), ammonia, total nitrogen, total phosphorus, total suspended solids and rapidly settleable solids to determine their effects on the wastewater system. The largest impacts were on COD, BOD and suspended solids, compared with the amounts of these determinands that currently arrive at sewage treatment works (STW). Experiments using settled samples showed that a relatively high proportion of nitrogen, phosphorus, COD and BOD would pass through to secondary treatment at the STW.     

The effects of unpaved roads on suspended sediment concentration at varying spatial scales – a case study from Southern Brazil

Unpaved roads may induce adverse effects on downstream water resources by increasing suspended sediment concentration (SSC). This study documents the localized impacts on stream SSC of six unpaved road–stream crossings in the rural Guabiroba River Catchment, in southern Brazil. Results demonstrated that SSC values downstream of road–stream crossings was between 3.5 and 10 times higher than upstream SSC at all third‐ and fourth‐order stream locations. However, downstream values were statistically undistinguishable from those collected upstream of road–stream crossings at fifth‐order sampling sites. These findings suggest that localized road effects on stream SSCs are scale‐dependent in that these are important for low‐order headwater streams yet undetectable for their higher order counterparts. Findings point to the importance of low‐order stream crossings in increasing SSC and the need to further explore the role of unpaved roads as agents of water quality degradation in agriculturally active rural settings.     

The impact of cemented layers and hardpans on oxygen diffusivity in mining waste heaps A field study of the Halsbrücke lead-zinc mine tailings (Germany)

This article reports fibre-optic oxygen measurements on a reactive mine waste heap located in the polymetallic sulphide mine district of Freiberg in south-eastern Germany. The heaped material consists of sulphide-bearing tailings from a processing plant of a lead-zinc mine. Mine waste material was deposited in the water phase after separation of mining ores in a flotation process. The tailing impoundment is partly covered with coarse sand and topsoil. Oxygen profiles were monitored during one year at eleven locations showing different physical and mineralogical compositions. At each location a borehole was drilled where the optic sensors were installed at 2-5 different depths. After installation the oxygen profiles were monitored seven times during one year from 2006-2007 and three to five oxygen profiles at each location were obtained. Oxygen measurements were accompanied by physical, chemical and mineralogical data of the tailing material. Additionally, a detailed mineralogical profile was analysed at a location representative for the central part of the heap, where the cemented layers show lateral continuity. Results showed that cemented layers have a significant influence on natural attenuation of the toxic As and Pb species owing to their capacity of water retention. The measured oxygen profiles are controlled by the zone of active pyrite weathering as well as by the higher water content in the cemented layers which reduces gaseous atmospheric oxygen supply. In contrast, gypsum bearing hardpans detected at three other locations have no detectable influence on oxygen profiles. Furthermore, the grain size distribution was proved to have a major effect on oxygen diffusivity due to its control on the water saturation. Temporal changes of the oxygen profiles were only observed at locations with coarse sediment material indicating also an important advective part of gas flux.     

Influence of eco‐hydrological factors on aquatic plant succession in a regulated river: a case study of the Petchburi River,Thailand

Monitoring of aquatic plant biomass in the Petchburi River, a regulated river system in Thailand, was carried out together with the examination of eco‐hydrological characters and the sedimentary organic content. The surveys were performed during May, August and November of 2010 and 2011. The results indicated temporal variation in water velocity (0.08–2.51 m/s) and medium to low organic levels (0.58–4.68%) of the benthic substrates. Dominant aquatic plants were Hydrilla verticillata (L.F.) Royle and Potamogeton malaianus Miq. with the highest biomass of 70.84 and 182.72 g/m², respectively. The biomass was substantially decreased during the flood‐induced discharge period. This study indicates that Potamogeton has more adaptive potential to high water velocities than Hydrilla, while Hydrilla prefers lower water velocities. Discharge velocities of less than 0.5 m/s could provide positive growth rates of such submerged plants. Approaching the discharge control from this ecological point of view can further contribute to river habitat conservation.     

Impacts of climate and land‐cover changes on water resources in a humid subtropical watershed: a case study from East Texas,USA

This study investigates the response of water resources regarding the climate and land‐cover changes in a humid subtropical watershed during the period 1970–2009. A 0.7°C increase in temperature and a 16.3% increase in precipitation were observed. Temperature had a lower increase trend, and precipitation showed definite increasing trend compared to previous studies. The main trend of land‐cover change was conversion of vegetation and barren lands to developed and crop lands affected by human intervention, and forest and grass to bush/shrub which considered to be caused by natural climate system. Hydrologic responses to climate and land‐cover changes resulted in increases of surface run‐off (15.0%), soil water content (2.7%), evapotranspiration (20.1%) and a decrease in groundwater discharge (9.2%). We found that surface run‐off is relatively stable with precipitation, whereas groundwater discharge and soil water content are sensitive to changes in land cover, especially land cover brought about by human intervention.     

Use of 222radon as a simple tool for surface water–groundwater connectivity assessment: a case study in the arid Limarí basin,north‐central Chile

We report the results from a pilot study on the use of ²²²Rn (²²²radon) for river–aquifer interaction assessment in the Limarí watershed, north‐central Chile. Previous studies on this tool for such applications are not abundant at international level, and no records exist for Chile. The lowest ²²²Rn levels (less than 1000 Bq/m³) were found in water reservoirs, thus indicating that this isotope is easily lost (and therefore usually absent) in surface waters. Conversely, the highest levels of ²²²Rn were found in groundwater, with maxima activities around 20 000 Bq/m³. This remarkable contrast allowed clear identification of zones of surface water–groundwater connectivity in the searched watershed domain.     

Influence of fracture orientation on excavatability of soft sedimentary rock using a hydraulic impact hammer: A case study in the Horonobe Underground Research Laboratory

In the Japanese deep geological disposal project for high-level radioactive waste, the ease of excavation of a potential host rock is a key issue for the economics of project implementation. This is because it is estimated that about 300-km of disposal drifts will need to be excavated for the disposal of 40,000 waste packages deep underground. In this study, the influence not only of the mechanical properties of intact host rock, but also fracture characteristics and their effect on the practical excavation rate of drifts using a hydraulic impact hammer were analyzed. The drifts were excavated through soft sedimentary rock in the Horonobe Underground Research Laboratory. Fracture mapping was conducted at the excavation face before every excavation round for the evaluation of fracture characteristics. Equotip hardness testing was also conducted to estimate the strength of intact rock. The results indicate that the excavation rate of the drift excavated in the direction perpendicular to natural fractures was faster than the excavation of the drift excavated in the direction parallel to natural fractures. In addition, the drift excavated in the direction perpendicular to natural fractures had a good correlation with fracture density. This result suggests that the preferred direction of disposal drifts should be perpendicular to the major natural fractures in the host rock to optimize excavatability in any deep geological disposal project.     

Numerical study of the THM effects on the near-field safety of a hypothetical nuclear waste repository—BMT1 of the DECOVALEX III project. Part 2: Effects of THM coupling in continuous and homogeneous rocks

An evaluation of the importance of the thermo-hydro-mechanical couplings (THM) on the performance assessment of a deep underground radioactive waste repository has been made as a part of the international DECOVALEX III project. It is a numerical study that simulates a generic repository configuration in the near field in a continuous and homogeneous hard rock. A periodic repository configuration comprises a single vertical borehole, containing a canister surrounded by an over-pack and a bentonite layer, and the backfilled upper portion of the gallery. The thermo-hydro-mechanical evolution of the whole configuration is simulated over a period of 100 years. The importance of the rock mass's intrinsic permeability has been investigated through scoping calculations with three values: 10⁻¹⁷, 10⁻¹⁸ and 10⁻¹⁹ m². Comparison of the results predicted by fully coupled THM analysis as well as partially coupled TH, TM and HM analyses, in terms of several predefined indicators of importance for performance assessment, enables us to identify the effects of the different combinations of couplings, which play a crucial role with respect to safety issues. The results demonstrate that temperature is hardly affected by the couplings. In contrast, the influence of the couplings on the mechanical stresses is considerable.     

A numerical study of THM effects on the near-field safety of a hypothetical nuclear waste repository—BMT1 of the DECOVALEX III project. Part 3: Effects of THM coupling in sparsely fractured rocks

As a part of the international DECOVALEX III project, and the European BENCHPAR project, the impact of thermal–hydrological–mechanical (THM) couplings on the performance of a bentonite-back-filled nuclear waste repository in near-field crystalline rocks is evaluated in a Bench-Mark Test problem (BMT1) and the results are presented in a series of three companion papers in this issue. This is the third paper with focuses on the effects of THM processes at a repository located in a sparsely fractured rock. Several independent coupled THM analyses presented in this paper show that THM couplings have the most significant impact on the mechanical stress evolution, which is important for repository design, construction and post-closure monitoring considerations. The results show that the stress evolution in the bentonite-back-filled excavations and the surrounding rock depends on the post-closure evolution of both fields of temperature and fluid pressure. It is further shown that the time required to full resaturation may play an important role for the mechanical integrity of the repository drifts. In this sense, the presence of hydraulically conducting fractures in the near-field rock might actually improve the mechanical performance of the repository. Hydraulically conducting fractures in the near-field rocks enhances the water supply to the buffers/back-fills, which promotes a more timely process of resaturation and development of swelling pressures in the back-fill, thus provides timely confining stress and support to the rock walls. In one particular case simulated in this study, it was shown that failure in the drift walls could be prevented if the compressive stresses in back-fill were fully developed within 50 yr, which is when thermally induced rock strain begins to create high differential (failure-prone) stresses in the near-field rocks.     

The effects of building‐related factors on classroom relative humidity among North Carolina schools participating in the ‘Free to Breathe,Free to Teach’ study

Both high and low indoor relative humidity (RH) directly impact Indoor Air Quality (IAQ), an important school health concern. Prior school studies reported a high prevalence of mold, roaches, and water damage; however, few examined associations between modifiable classroom factors and RH, a quantitative indicator of dampness. We recorded RH longitudinally in 134 North Carolina classrooms (n = 9066 classroom‐days) to quantify the relationships between modifiable classroom factors and average daily RH below, within, or above levels recommended to improve school IAQ (30–50% or 30–60% RH). The odds of having high RH (>60%) were 5.8 [95% Confidence Interval (CI): 2.9, 11.3] times higher in classrooms with annual compared to quarterly heating, ventilating, and air‐conditioning (HVAC) system maintenance and 2.5 (95% CI: 1.5, 4.2) times higher in classrooms with HVAC economizers compared to those without economizers. Classrooms with direct‐expansion split systems compared to chilled water systems had 2.7 (95% CI: 1.7, 4.4) times higher odds of low RH (<30%). When unoccupied, classrooms with thermostat setbacks had 3.7 (95% CI: 1.7, 8.3) times the odds of high RH (>60%) of those without setbacks. This research suggests actionable decision points for school design and maintenance to prevent high or low classroom RH.     

Effect of water and geological factors on the long-term stability of fracture zones in the Päijänne Tunnel, Finland: a case study

Potable water to the Helsinki metropolitan area in Finland is conveyed through Precambrian bedrock along the mostly unlined, rock-surfaced Päijänne Tunnel which has been in use since 1982. Two cave-ins in recent years and the damage observed during the inspection preceding the repair of the northern 64 km of the tunnel in 2001 demonstrates the active eroding processes. The extent of block falls inside the tunnel, interpreted from a recording made by a submersible robot, is compared with both measured and semi-quantitatively documented groundwater inflow and characteristics of fracture zones intersecting the tunnel that commonly appear as linear depressions in topography.Most of the damage observed in the tunnel is inferred to result from weathering, swelling clays, erosion and changes in groundwater or pressure conditions. The main factor in triggering these physical and chemical changes is water that flows both along the tunnel and in the fractures of the surrounding bedrock. Foliation sub-parallel to the tunnel orientation seems to be a factor making tunnel sections more prone to the occurrence of block falls.A high rate of groundwater inflow correlates to some degree with the level of original reinforcement. Even though groundwater inflow does not necessarily indicate support need, increased fracturing in bedrock generally provides more flow paths to water. Hydraulic properties of fracture zones are inferred to contribute to the deterioration in the tunnel but probably as a relatively minor factor compared with the rock support solutions and structural orientation sub-parallel to the tunnel. The orientation of fractures is inferred to play a role as variation is observed in inflow when linked with the strike of the fracture zone. The damage concentrates to zones of existing weakness and sections that have not been lined with shotcrete. Shotcrete prevents leaching of fracture fillings which can lead into loosening and falling of key-blocks. The application of steel-supported reinforcement in the fractured sections is a plausible explanation to why no consistent connection was observed between the occurrence of large block falls and fracture zone intersections. The impairment of the tunnel's condition, revealed during the repair inspection, is considered to have been influenced by the initially low level of reinforcement.     

A study on a porous residential building model in hot and humid regions: Part 1—the natural ventilation performance and the cooling load reduction effect of the building model

This study targets environmental load reduction in hot and humid regions. It reveals the effects that porous residential buildings have on the natural ventilation performance and, consequently, the cooling load reduction. Two residential building models, namely a model with a void ratio of 0% and a model with a void ratio of 50%, are evaluated using computational fluid dynamics (CFD) analysis and thermal and airflow network analysis. The analysis on components of the heat load indicates that improvements in the natural ventilation performance would significantly reduce the cooling load.     

The structural variability of quarters and residential areas in the historical texture of the city of Yazd based on Islamic rules and jurisprudence: a case study of Golchinan quarter

According to many researchers and scholars, religious beliefs can be considered as the most influential factor in forming Muslim urban spaces and their architectural elements. In fact, historical cities reflect the culture and beliefs of their residences. Among all historical places in Iranian cities, the historical texture of the city of Yazd, especially the quarters since the age of Qajar dynasty, are well preserved. The present study aims at identifying the Islamic principles and values influencing the formation of architectural spaces and the extent of their applications in one of the historical quarters known as Golchinan. The results of the conformation of the theoretical findings with the data acquired from field studies revealed that almost 90% of the urban and architectural spaces (e.g. residential areas, mosques, bazaars, and pathways) in Yazd are directly influenced by Islamic principles. In other words, there is a strong conformity between the accepted Islamic values of the society and what actually was applied to urban constructions during Qajar dynasty.     

The effect of a redesigned floor plan, occupant density and the quality of indoor climate on the cost of space, productivity and sick leave in an office building–A case study

The aim of this study was to examine changes in the overall costs of an office when the efficiency of space use is increased. The variable in the examination was a space index, calculated as the floor area per employee. The quality of indoor climate was also a variable in the analysis. The overall cost analysis of a given case building showed that when space use is boosted significantly, measures must be taken to guarantee a sufficient quality of indoor climate. The study indicates that investment in the quality of indoor climate is cost-effective when the economic effect of indoor climate to health and productivity are taken into account in addition to the costs of investment, operation and maintenance. Insufficient ventilation without mechanical cooling may cause a substantial loss of productivity. The importance of good ventilation and air-conditioning increases with a more efficient use of space especially in conjunction with high value of work.