Wastewater and sludge control-technology options for synfuels industries

The options examined were those of zero discharge, partial water reuse with restricted discharge of treated effluents, and unrestricted discharge of treated effluents. Analysis of cost data and performance-analyses data for several candidate secondary-wastewater-treatment unit processes indicated that combined activated-sludge/powdered-activated-carbon (AS/PAC) treatment incorporating wet-air-oxidation carbon regeneration is the most cost-effective control technology available for the removal of organic material from slagging, fixed-bed process wastewaters. Bench-scale treatability and organic-constituent removal studies conducted on process quench waters from a pilot-scale, slagging, fixed-bed gasifer using lignite as feedstock indicated that solvent extraction followed by AS/PAC treatment reduces levels of extractable and chromatographable organics to less than 1 ..mu..g/L in the final effluent. Levels of conventional pollutants also were effectively reduced by AS/PAC to the minimum water-quality standards for most receiving waters. The most favored and most cost-effective treatment option is unrestricted discharge of treated effluents with ultimate disposal of biosludges and landfilling of gasifier ash and slag. This option requires a capital expenditure of $8,260,000 and an annual net operating cost of $2,869,000 in 1978 dollars, exclusive of slag disposal. The net energy requirement of 19.6 x 10/sup 6/ kWh/year, or 15.3 kWh/1000 gal treated, is less than 6% of the equivalent energymore » demand associated with the zero-discharge option.« less