Solid Waste Management: Current Scenario and Challenges in Bengaluru

Municipal solid waste management (MSWM) has become one of the significant environmental issues, particularly in developing countries. Bengaluru, the state capital of Karnataka, is one of the fastest growing cities in Asia. The Bruhat Bengaluru Mahanagara Palike (BBMP) with an area of 2190 km2 and a population of about 10.18 million generates around 5000 metric tons per day of solid waste at an average generation rate of 0.5 kg per capita per day (kg/capita/d). Presently, Bengaluru City is facing significant problems due to existing disposal practices of generated waste, incurring high cost due to lack of proper infrastructural facilities; also, the open dumping in the expanding zone of the city poses severe problems to the structures constructed on these old dumps. In the meantime, groundwater quality deteriorated due to improper leachate management. Intending to assess the possible impacts on the water environment and suggest a better waste management strategy, the present paper discusses the potential for handling the wastes, thereby reducing the amount of waste to be transported to the landfill. If this waste is used for energy and nutrient recovery, decentralization could also become commercially viable and address the technology-wise deficiencies in the existing MSWM system of Bengaluru City

Optimum lime content of fly ash with salt

The pozzolanic reactivity of fly ash, which plays an important role in its utilisation for geotechnical applications, depends on the reactive silica and the lime content. Fly ashes containing sufficient reactive silica but insufficient lime content improve strength on the addition of lime. The development of strength up to optimum lime content is particularly high. The formation of pozzolanic reaction compounds, which is responsible for improvement of strength, can be enhanced in the presence of sodium chloride. This can possibly be attributed to the higher solubility of silica and the formation of sodium silicate hydrate rather than calcium silicate hydrate. More voluminous pozzolanic compounds with higher water-holding capacity that can bind fly ash particles, leading to increased strength, are formed in the presence of sodium chloride. This paper examines the effect of sodium chloride on the free swell, liquid limit and strength of a lignitic fly ash obtained from Neyveli with different lime contents, and the effect on the optimum lime content. It has been shown that the free swell volume, liquid limit and strength of fly ash increase at every lime content in the presence of sodium chloride compared with lime content alone. The optimum lime content, obtained by any of the methods, has not altered in the presence of sodium chloride. This might be due to the formation of more pozzolanic compounds at every lime content

Electroosmotic flow behaviour of metal contaminated expansive soil

It is important to study the flow behaviour through soil during electrokinetic extraction of contaminants to understand their removal mechanism. The flow through the expansive soil containing montmorillonite is monitored during laboratory electrokinetic extraction of heavy metal contaminants. The permeability of soil, which increases due to the presence of contaminants, is further enhanced during electrokinetic extraction of contaminants due to osmotic permeability. The variations in flow rates through the soil while the extracting fluid is changed to dilute acetic acid (used to control the increase of pH) and EDTA solution (used to desorb the metal ions from soil) are studied. The trends of removal of contaminants vis-a-vis the changes in the flow through the soil during different phases of electrokinetic extraction are established. Chromium ions are removed by flushing of water through the soil and increased osmotic flow is beneficial. Removal of iron ions is enhanced by induced osmotic flow and desorption of ions by electrokinetic processes. © 2007 Elsevier B.V. All rights reserved

Role of moulding water content in lime stabilisation of soil

The role of moulding water content, from the dry side of the optimum to the wet side of optimum, in the strength development in lime-treated soils was investigated in the present study. During compaction, the structure of clay particles can change from a flocculated to a dispersed structure as the water content is increased from the dry side of optimum to the wet side of optimum. For efficient formation of pozzolanic compounds, the water content of the soil-lime mixture should be kept as high as possible. The improvement in the strength of Indian black cotton soil treated with different amounts of lime content at different water contents and cured for varying curing periods was studied. The results clearly showed that the strength of black cotton soil treated with lime content increased better when compacted on the dry side of optimum, the other parameters remaining the same. Further, the optimum lime varied with moulding water content and curing period

Geotechnical behaviour of lime treated sulphatic soils

This study has been under taken to understand the influence of sulphate content on two extreme types of fine-grained soils, namely montmorillonitic black cotton soil and kaolinitic red earth stabilised with optimum lime content of 6.. It has been observed that unusual increase in liquid limit and plasticity index of both types of lime treated soils occurs in the presence of sulphate. However, only the shrinkage limit of expansive soil decreases in the presence of sulphate. Compressibility of lime treated soil containing sulphate increases significantly after curing for one year. The strength of both the lime treated soils decreased considerably due to alteration of soil lime reactions products to swelling ettrengite type of compounds in the presence of sulphate. The strength decrease is more for expansive montmorillonitic black cotton soil than in kaolinitic red earth soil. Use of barium chloride in the proportion of two times the weight of sulphate overcomes the adverse effects of sulphate in lime stabilised soils

Improvement of strength of fly ash with lime and sodium salts

It is often necessary to improve the strength of fly ash to enable its use for many geotechnical applications. Lime in some form or other is normally used as an admixture. Methods are established to determine the optimum lime content for fly ash, as the addition of lime beyond the optimum lime content may not be beneficial or economically viable. This paper examines the use of sodium salts to enhance the effect of lime on fly ash. Based on unconfined compression strength tests on a compacted fly-ash-lime-salt specimen, it has been shown that sodium salts improve the strength of a fly-ash-lime mixture. The improvement is salt-specific. This improvement in strength can be attributed to the formation of a greater volume of sodium calcium silicate hydrate gel as opposed to a calcium silicate hydrate. The improvement in strength is greater for sodium hydroxide than for sodium chloride. The increased pH with sodium hydroxide dissolves more silica and can produce more cementitious compounds after reaction with lime. Although sodium sulphate increases the strength initially, its long-term effect is suspect

Effect of sulphate on the shear strength of lime-treated kaolinitic soil

Lime has been extensively used to improve the strength of fine-grained soils. It has recently been reported that the presence of sulphate in soils causes abnormal volume changes in lime stabilised soil. This paper presents the strength behaviour of lime-treated kaolinitic natural red earth in the presence of varying sulphate contents, up to 3, after curing for periods of up to 365 days. Alteration of soil-lime reactions in the presence of sulphate leads to the formation of ettringite after curing for longer periods. The formation of these compounds affects strength development by cementation. However, after curing for short periods, the strength of lime-treated soil is improved in the presence of sulphate. It is only after curing for longer periods that the strength is decreased. Consequently the stress-strain behaviour and effective stress paths of treated soil cured for long periods show the behaviour of a normally consolidated soil rather than of cemented soils. The reduction in strength is due primarily to a reduction in the effective cohesion intercept. The effective friction angle has not been affected significantly. © 2006 Thomas Telford Ltd

Mitigation of alkali induced heave in rectorite soil with fly ash

Mechanisms that control the volume changes behavior of foundation soils are well understood. The changes that occur in the behavior of soil due to migration of pollutants are not well understood. The extent of changes that occur in the presence of small concentration of contaminants can be predicted based on changes in the thickness of double layer and associated fabric changes. Interactions that occur with strong contaminants depends on the type of soil, type and concentration of contamination and duration of interaction etc It has been shown that different concentrations (1N and 4N) of sodium hydroxide solution causes abnormal changes on volume change behaviour of soil due to mineralogical changes. An attempt is made in this paper to stabilize contaminated soil using fly ash, after establishing its stability in alkali solutions. It was found that the effectiveness of fly ash to control the alkali induced heave increases with fly ash content incorporated into the soil. X-ray diffraction studies reveal that the mineralogical changes that occur in soil due to alkali interaction are inhibited by the presence of fly ash. Copyright ASCE 2008