Waste Disposal Methods PDF

Waste Disposal Methods Disposal Surface Disposal Subsurface Disposal Disposal of water Disposal of solids Disposal of liquids Disposal of Solids Onshore Offshore...

Waste Disposal Methods Disposal Surface Disposal Subsurface Disposal Disposal of water Disposal of solids Disposal of liquids Disposal of Solids Onshore Offshore Onshore Offshore Discharges Discharges Discharges Discharges  Surface Disposal The easiest and least expensive method of waste disposal is to discharge the wastes onto the ground or into surface waterways. (i) Disposal of water: ✓ Waste water can be discharged directly into local streams, rivers, or the ocean as long as its quality meets regulatory standards, i.e., its concentration of suspended and dissolved solids, chemicals, and hydrocarbons is sufficiently low. ✓ When wastewater is discharged offshore, the water is typically treated to remove only the hydrocarbons. Although the dissolved solids (salt) concentrations of most produced waters are high enough to be toxic to even marine life, the rapid mixing and dilution of the discharged water makes the resulting environmental impact negligible. ✓ For near-shore discharges in shallow water, there is less opportunity for mixing and dilution of the discharged water, and a toxic plume can exist for some distance away from the discharge point. Such toxic plumes are of particular concern when discharging a dense, high saline, oxygen-deficient brine because it can be trapped in subsurface topographic low areas. Because this trapped brine can significantly impact the local marine life, permits to discharge high-salinity brines near the shore may be difficult to obtain, even if hydrocarbon content is low. ✓ When wastewater is discharged into onshore freshwater locations, both the hydrocarbon and dissolved solid concentrations must be low. ✓ Surface discharges into dry stream beds is a common way to dispose of treated water in arid areas like Wyoming. ✓ Surface discharge into percolation ponds is also used in some areas. ✓ Discharge into evaporation ponds is also an option in many arid areas, particularly if a liner is used to prevent leaching of dissolved solids.  (ii) Disposal of solids Offshore Discharges: Offshore discharges of treated solids, such as drill cuttings and produced solids, are permitted in some areas. Offshore discharges, however, are prohibited within three miles of shore in the unites states, and the discharge of oil-based drilling mud waters are prohibited in all united states waters. Onshore Discharges: Many solid wastes, particularly drill cuttings and produced solids can be discharged by spreading them over the land surface. If the solids have been treated and are not contaminated with hydrocarbons, salt, or heavy metals, then obtaining permits for surface disposal may be relatively simple. The suitability of a solid waste for surface discharge can be assessed through its Electrical Conductivity (EC), Sodium Adsorption Ratio (SAR), the Exchangeable Sodium Percentage (ESP), and the Oil and Grease (O&G) levels. Maximum values generally recommended for these parameters are: EC 4 m mhos/cm EC is a fundamental property of a material that measures how strongly it conducts electricity. SAR 12 ESP 15% O&G 1% The Sodium adsorption ratio (SAR) is a measure of the amount of sodium (Na) relative to calcium (Ca) and magnesium (Mg)in the water extract from saturated soil paste. Oils with a SAR of 13 or more are considered sodic soils. Sodic soils have high levels of sodium adsorbed on clay cation-exchange sites. Soils with high SAR values may experience a degradation in structure, reduced aeration and saturated hydraulic conductivity, and increased dispersion of organic matter and clay particles. The exchangeable sodium percentage (ESP) is the proportion of cation exchange sites in soil that are occupied by sodium. The acceptable limit for ESP is 15%. Soils with an ESP greater than 6 are considered sodic, and soils with an ESP greater than 15 are considered highly sodic. The exchangeable sodium percentage (ESP) is calculated as follows: ESP = Exchangeable {(Na)/(Ca + Mg + K + Na)} x 100 Another measure of the suitability of a solid waste for surface discharge is its heavy metal content. Maximum recommended accumulation of heavy metals in soils are given below: Element Soil Concentration (mg/kg) Arsenic 300 Boron 3 Beryllium 50 Cadmium 3 Cobalt 200 Chromium 1,000 Copper 250 Mercury 10 Manganese 1,000 Molybdenum 5 Nickel 100 Lead 1,000 Selenium 5 Vanadium 500 Zinc 500  ❖ Treated waste solids can be used for road and site construction. ❖ Land treatment can be used for the disposal of solids containing only hydrocarbons, particularly if the treatment is designed to degrade the hydrocarbons by biological processes. Two major forms of Land Treatment Landspreading Landfarming Landfarming is an enhanced version of landspreding in which Wastes are spread over the surface of additional processing of the soil is conducted after the initial the ground and then tilled into the tilling. In Landfarming, the soil is commonly processed for soil. After the initial tilling, no several years after the initial application of the waste solids. This additional processing may include adding fertilizers and further action is usually taken. tilling repeatedly to increase oxygen uptake in the soil. Landfarming  Road Spreading Road spreading is another disposal method for hydrocarbon contaminated solids. The wastes are mixed with other construction materials and spread over gravel roads. The oil helps to hold the road materials together, making such wastes an effective dust suppressant.  Subsurface Disposal (i) Disposal of Liquids ✓ The most common disposal method for waste liquids, such as produced water, is to inject them into a subsurface formation. ✓ Disposal wells must be completed in a formation that is permeable, porous, has low pressure and a large storage volume. The disposal formation must also be geologically isolated from any fresh water aquifers. ✓ To prevent the water from plugging the formation, the water must normally treated to remove free and emulsified oil, suspended solids, and some dissolved solids, such as iron and scale, prior to disposal. ✓ One disposal method that is growing in popularity is annular injection in existing wells. In this process, the waste water is injected down the annulus of an existing production & injection well and into a formation above the existing completion. ✓ A major concern with underground disposal of water is the potential for the well to provide a vertical path from the disposal formation to any overlying fresh water aquifers. Possible communication path include flow up the inside of the casing through leaks in the casing and flow up the outside of the casing through a bad cement bond.  (ii) Disposal of Solids ✓ Subsurface burial is a common method for disposal of solid wastes. Drill cuttings and used mud are typically left in reserves pit after a well is drilled. After the free liquids are removed, the remaining materials are covered by soil and the site is revegetated. ✓ One major concern with the burial of solids is the potential for heavy metals, hydrocarbons, and salts to migrate away from the site. Salt buried in reserve pits can migrate both downward and upward. ✓ The two metals most commonly found in drilling muds at concentration above those found in most soils are barium and chromium. These metals are in a non-soluble form and have a very limited potential for migration or plant uptake. ✓ For pits containing high salts or hydrocarbon levels, regulations may require the use of an impermeable pit liner to prevent leaching. ✓ A developing new technology for the disposal of drill cuttings is to grind them into small particles and inject them into a well as a slurry.