Sludge excavation

These observations held true throughout the course of sludge excavation. No groundwater problems were encountered, although surface water from abnormally high rainfall (20.31 in. actual versus... 

Sludge-blanket clarifiers are difficult to start up because the first blanket must be estabUshed, and large-scale units require extensive excavation. Sizes range from 600 x 600 mm to 50 x 50 m. Precipitation and crystallization can be carried out in similar hopper-designed units, having overflow rates of 80 m/h or higher. 

If river cleanup is involved, including dredging, the first estimate of the costs likely to be incurred is on the order of 6.6 Million per kilometer. This includes dredging the bottoms, cleaning and excavating the sides, and thermally treating the sludges after they are dewatered. The sediments will be pumped out at about 2% solids and have to be put into a contained area, the liquid treated, and the solids dried and excavated. 

The commercially available bioremediation process occurs in an engineered land treatment cell or prepared bed. Contaminated soils and sludges are excavated and transported to the treatment ceU (or bed). Nutrients, water, and oxygen (introduced by tilling the soil) are added to the bed to accelerate the treatment process. After bioremediation is complete, the treatment cell is capped and the site is considered suitable for use. 

Bio-Raptor technology uses a combination of ex situ microbial and mechanical processes to treat soils and sludges that are contaminated with hydrocarbons. The Bio-Raptor unit shreds and screens the excavated soil to increase its surface area. Then, the unit sprays and inoculates the soil with a proprietary blend of microorganisms. The soil is heaped into biopiles while the microbes degrade the contaminants. Bio-Raptor systems are commercially available and have been used for full-scale site cleanups. 

Full-scale separation/washing and bioslurry reactor operations have been used to treat creosote-contaminated soil at the former Southeastern Wood Preserving Site at Canton, Mississippi (Jerger et al., 1994 Woodhull Jerger, 1994). Here, an estimated 10 500 yd3 of soil and sludge were excavated from various process areas, stabilized with kiln dust and stockpiled for subsequent treatment. Based on the results of preliminary bench studies, four 680 000 liter reactors were eventually established to handle 7050 yd3 of the screened (200-mesh) soil fraction at a solids content of 20-25%. Other oil fractions and waters were handled separately (data and costs not reported). 

We do not consider transferring the dried sludge to a landfill as an acceptable alternative as this represents only a temporary solution. Thus, we restrict our attention to those processes where most of the PCBs originally present in the sludge are incinerated in one way or another. In every alternative within this class of processes, the sludge has to be excavated, dewatered, and dried. The... 

The US EPA published information on capital cost of constructing sludge lagoons. Using an ENR CC Index equal to 6390.21 (January 2002 Cost), typical excavation and liner costs associated with a two-bedroom residence are as follows ... 

Incineration involves the heating (either directly or indirectly) of excavated soil to temperatures of 880-1200 °C to destroy or detoxify contaminants. Incineration can also be used for the treatment of contaminated liquids and sludges. Incineration results in the destruction of the soil texture and removes all natural humic components. The residues may also have high heavy metal contents. Exhaust gasses need to be treated to remove particulates and any harmful combustion products. A range of methods of incineration are available although the use of rotary kilns is probably the most widespread. Costs of treatment are heavily dependent on the water content of the material being treated and any calorific value that the material may have. 

Excavation Sequence. Excavation commenced with scraping of exposed Lagoon slopes above the sludge level to a depth of six inches. This material was considered potentially contaminated and added to the Lagoon. After the slopes were scraped, benching of adjacent non-dioxin, solvent-contaminated soil was performed by the front loader. This material was transported by clamshell and placed on the staging pad. 

This procedure was utilized successfully until the majority of sludge was removed from the Lagoon. At this point, however, the shallow depth of sludge, approximately six inches, and greatly decreased percentage of solids, made clamshell excavation... 

Sewage sludges, sludges from wastewater and water treatment (dry basis) 883 Building rubble, excavated soil, pavement rubble without harmful contami- 903 nants... 

Over half the quantity of wastes is accounted for by three large groups 27 % wastes not associated with chemical production (building rubble, excavated soil, wastes from energy production facilities) 17% from wastewater and water treatment and 16% inorganic sludges. 

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