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The relative success of chemical oxygen demand (COD) removal models to describe measured rates of COD removal in a pilotscale constructed wetland designed for treatment of high-strength winery wastewater are evaluated using retention times determined from tracer studies. Not surprisingly, two-parameter residual and retardation models better fit the measured removal data than single-parameter, first-order decay models for wastewater at average COD loadings up to nearly 5000 mg/L. The residual and retardation models yielded nearly equivalent fits to the measured data. However, the retardation model had more consistent parameters for COD removal data across different depth levels in the constructed wetland and at different loadings, and a slightly smaller sum of least-squared errors. The retardation model seems to be appropriate for constructed wetland design because it allows a steady decrease in COD with increased treatment time rather than a constant residual COD (C*) value. From the least-squares optimization procedure used to estimate model parameters (a volumetric rate constant, K v , range o f3t o1 2d Ϫ1 ), nonrealistic, or physically meaningless, large C* values (C* range of 23 to 450 mg COD/L) that were dependent on COD loading were obtained, potentially underestimating the constructed wetland system's actual winery wastewater treatment potential. The optimal parameters for the retardation model applied to the pilot-scale constructed wetland ranged from 9 to 12 d Ϫ1 for the initial degradation rate constant, K o ,a n d2t o5d Ϫ1 for the time-based retardation coefficient, b. These values should be verified for full-scale field systems based on field measurements currently underway. Water Environ. Res., 73, 597 (2001).

Although in the past, environmental engineering has been primarily concerned with waste disposal, the focus of the field is now shifting toward viewing wastes as potential resources. Because reclamation usually consumes less energy than producing new materials, increasing reclamation not only reduces pollution but saves energy. Technological innovations contributing to this shift are summarized here, and are variously classified as emerging technologies or research topics, as either new departures or incremental improvements, and as opportunistic innovations, or examples of a unifying strategy. Both liquid and solid waste examples are given, such as a recent discovery of effects in disinfecting microfiltered reclaimed wastewater with ultraviolet light. In addition to its value in reducing pollution and conserving energy, this reorientation of environmental engineering could contribute to a more general shift toward greater cooperation among organizations dealing with the environment.

An innovative system for stabilizing the organic fraction of municipal solid waste (OFMSW) has been documented on a pilot scale at the Civil Engineering Department of the University of California at Davis. The system involves the combined methods of high-solids anaerobic digestion and aerobic composting for the recovery of energy and the production of compost from the OFMSW. The performance of the high-solids anaerobic reactor was monitored for three mass retention times. The anaerobic digester was operated under extreme as well as normal conditions. The performance of the aerobic compost unit was monitored based on the physical and chemical characteristics of the final humus by-product. In general, the combined process was very stable at a 30 d retention time and is capable of removing essentially all of the biodegradable fraction of the organic fraction of MSW. A biogas production level of up to 6 liters per liter of active volume of reactor was achieved. The process stability and gas production decreased slightly when the retention time was reduced to 15 d. The output from the second stage is a fine humus-like material with a thermal content of about 14.80 MJ/kg.

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