Lifecycle Comparison of Mainstream Anaerobic Baffled Reactor and Conventional Activated Sludge Systems for Domestic Wastewater Treatment.

The objective of this study was to evaluate the lifecycle impacts of anaerobic primary treatment of domestic wastewater using anaerobic baffled reactors (ABRs) coupled with aerobic secondary treatment relative to conventional wastewater and sludge/biosolids treatment systems through the application of wastewater treatment modeling and three lifecycle-based analyses: environmental lifecycle assessment, net energy balance, and lifecycle costing. Data from two pilot-scale ABRs operated under ambient wastewater temperatures were used to model the anaerobic primary treatment process. To address uncertain parameters in the scale-up of pilot-scale anaerobic reactor data, uncertainty analysis and Monte Carlo simulation were employed. This study demonstrates that anaerobic primary treatment of domestic wastewater using ABRs can be incorporated with existing aerobic treatment strategies to reduce aeration demand, reduce sludge production, and increase energy generation. The net result of coupling anaerobic primary treatment with aerobic secondary treatment is a more favorable net energy balance, reduced environmental impacts in most examined categories, and lower lifecycle costs relative to conventional treatment configurations; however, the removal and/or capture of dissolved methane is required to reduce global warming impacts and increase on-site energy generation. With further study, anaerobic primary treatment can be a path forward for energy-positive wastewater treatment.

Techno-economic analysis of wastewater sludge gasification: a decentralized urban perspective.

The successful management of wastewater sludge for small-scale, urban wastewater treatment plants, (WWTPs), faces several financial and environmental challenges. Common management strategies stabilize sludge for land disposal by microbial processes or heat. Such approaches require large footprint processing facilities or high energy costs. A new approach considers converting sludge to fuel which can be used to produce electricity on-site. This work evaluated several thermochemical conversion (TCC) technologies from the perspective of small urban WWTPs. Among TCC technologies, air-blown gasification was found to be the most suitable approach. A gasification-based generating system was designed and simulated in ASPEN Plus® to determine net electrical and thermal outputs. A technical analysis determined that such a system can be built using currently available technologies. Air-blown gasification was found to convert sludge to electricity with an efficiency greater than 17%, about triple the efficiency of electricity generation using anaerobic digester gas. This level of electricity production can offset up to 1/3 of the electrical demands of a typical WWTP. Finally, an economic analysis concluded that a gasification-based power system can be economically feasible for WWTPs with raw sewage flows above 0.093m(3)/s (2.1 million gallons per day), providing a profit of up to $3.5 million over an alternative, thermal drying and landfill disposal.