For many years, Tetra Tech EC, Inc. (Tetra Tech) has had a continuing waste partnering relationship with Sasol. Our latest project is a basic engineering package for the New Waste Recycling Facility (WRF) in Secunda, Republic of South Africa. The waste is generated from the largest coal to liquids plant in the world that processes 45 million tons of coal a year.

This relationship, aimed at finding technically sound and environmentally safe waste management solutions for Sasol, was established in 1997 with a waste minimization study. This study was very successful, achieving up to an 80% reduction in some waste streams. However, not all waste could be eliminated so the management of waste progressed to the basic design of a WRF.

A conceptual/feasibility study determined the WRF required a wastewater treatment plant, a bioremediation center, and a solidification plant to handle the designated waste streams from the Secunda facility. The WRF recovers, recycles, and reuses all valuable materials from the waste streams including water, a valuable Secunda commodity. Some streams are treated and the recovered sludges are used to produce coke in the Carbo Tar Plant.

What cannot be reasonably reused is bioremediated in the bioreactors and biopiles, or solidified to render it environmentally safe. This produces beneficial use materials which can be used for fill material, landfill cover, and road base. This project benefited from a truly close collaboration and positive synergy between Sasol and Tetra Tech from the outset. Using our Shared Vision® approach as the framework for its collaboration, the integrated team not only achieved Sasol’s commitment to the environment and its Responsible Care Program, but it also laid the foundation for an innovative and sensible waste management program that is new to South Africa, and sure to become a model of environmentally sensitive operation for other industries throughout the country.

The WRF Basic Design Engineering Package (BDEP) is another example of the collaboration between Tetra Tech and Sasol. The objective of the BDEP was to develop a Basic Design and Cost Estimate that could be tailored to specific projects at the facility. The following achievements have been realized using the BDEP: 

• Waste Minimization Study, completed in 1997
• Air Emissions Inventory, completed in 1998
• Waste Minimization Audit, completed in 1999
• WRF Conceptual Package, completed in 2001
• WRF Conceptual Package, revised in 2002
• WRF Construction and Commissioning from 2004-2006

The WRF is a grass roots waste recycling facility designed to receive, store, blend, process, and recycle a variety of waste streams originating from the Sasol Secunda petrochemical complex. The WRF includes all necessary facilities for receiving, storing, processing, and disposing the waste streams, and consists of the following sections:

• Truck Loading/Unloading. This area includes 10 loading/unloading stations for unloading liquid wastes and some of the bulk liquid chemicals used in the WRF. Loading facilities are provided for the liquid wastes that are returned to their originators after partial phase separation for recovery of valuable products. The recovered oil is also loaded into trucks for disposal from this area.
• Waste Water Tank Farm. There are 12 tanks in the Waste Water Tank Farm, 11 for waste waters and one for the recovered oil. Facilities for de-oiling, including addition of emulsion breaker fluid, heating of the wastewater stream, and skimmers on the tanks for oil recovery, are included in this area. The solids are allowed to settle and are pumped into trucks for disposal, or alternatively, are kept in suspension and sent to the equalization tank where solids are separated and sent to the thickener/filter press. The tank farm is designed to normalize the waste streams’ throughput, thereby avoiding sudden changes to the composition feeding the Waste Water Treatment Plant.
• Waste Water Treatment Plant. The Waste Water Treatment Plant is designed for low volume/high toxicity waste water streams. The unit includes phase separation, chemical as well as biological (fixed film and activated carbon) treatment, filtration, and chemical oxidation steps to achieve the desired treated water quality. The treated water from this unit is sent to the Sasol Secunda cooling water make-up or ash water make-up if it is not suitable for cooling water make-up. The main concern regarding the quality of treated water is a high level of salts originating from the chemical cleaning waste streams that are treated in the WRF. This plant also includes a thermal oxidizer that treats vapor emissions from tanks and process equipment within the Waste Water Treatment Plant (API and DAF).
• Bioremediation. The Bioremediation unit treats contaminated solids, including filter cake produced in the Waste Water Treatment Plant. This plant is designed to treat 1442 cubic meters of contaminated solids per year. Wet solids are partially dewatered and mixed with bulking materials. The mixture is biologically degraded in biopiles, which are supplied with nutrients, air, and water to promote biological degradation.
• Solidification and Stabilization. The Solidification/ Stabilization Area is designed to handle 2164 cubic meters of solids per year. Solid wastes are mixed with fine ash, or stored and sent to an external waste treatment contractor for disposal. Although the design is based on only mixing ash with the waste, with minor modifications, other stabilizing reagents such as lime and cement may be added to stabilize the wastes and improve disposal.
• Plant Support Facilities. This includes all facilities provided to support the operation including utilities, laboratory, workshop, administration, weighbridge, and gatehouse. The utilities are supplied from the Sasol Secunda plant and distributed inside the WRF. All the wastes, chemicals, materials, and reagents imported, as well as exported streams, are weighed over the weighbridge. A platform is also provided at the weighbridge to facilitate sampling and testing when required.

WRF construction began in 2004, was completed in 2006, and included engineering support, pilot plant testing, procurement, construction activities, system optimization, pre-commissioning, commissioning, post-commissioning, training, and plant operations. The WRF was awarded Project of the Year at Sasol's Badger Awards in 2006.

Project Highlights:

• Awarded Project of the Year at Sasol's Badger Awards in 2006
• Waste Minimization Study
• Air Emissions Inventory
• Waste Minimization Audit
• WRF Conceptual Package and WRF Basic Design Package