No abstract

No abstract

The combination of enhanced biological phosphorus removal (EBPR) with sidestream struvite precipitation is a synergistic treatment approach for P removal and recovery. However, periodic disruption events in crystallization reactors can cause fine struvite particle washout followed by P solubilization, leading to decreases in EBPR effluent quality, yet modeling tools do not exist to quantify plantwide impacts of struvite loss. To understand the impacts of struvite loss and dissolution on EBPR, this work first quantifies the dissolution rate of field-harvested struvite using the surface area-dependent shrinking object model and presents a novel particle population balance dissolution modeling tool for integration with a plantwide process simulator (SUMO). Analysis of time series P concentration data from dissolution experiments yields a rate constant of 1.14 mm min–1. Simulations of intra-plant phosphorus dynamics indicate that when struvite reactors operate with a high capture efficiency, the majority of influent orthophosphate can be captured through sidestream precipitation. In the event of struvite loss, large particles would not fully dissolve and are removed through sedimentation during primary clarification without significant disruption of EBPR. In contrast, the loss of 200 μm-sized struvite particles can lead to a difference in effluent phosphate of up to 0.8 mg P/L. Our results suggest that surface area-dependent models are essential to quantify the impacts of struvite loss and that reactor design should center on particle retention, rather than conversion of soluble P to struvite.

While most areas of the US are serviced by inexpensive, dependable grid connected electrical power, many areas of Alaska are not. In these areas, electrical power is provided with Diesel Electric Generators (DEGs), at much higher cost than in grid connected areas. The reasons for the high cost of power are many, including the high relative cost of diesel fuel delivered to the villages, the high operational effort required to maintain DEGs, and the reverse benefits of scale for small utilities.Recent progress in fuel cell technologies have lead to the hope that the DEGs could be replaced with a more efficient, reliable, environmentally friendly source of power in the form of fuel cells. To this end, the University of Alaska Fairbanks has been engaged in testing early fuel cell systems since 1998. Early tests were conducted on PEM fuel cells, but since 2001, the focus has been on Solid Oxide Fuel Cells.In this work, a 5 kW fuel cell was delivered to UAF from Fuel Cell Technologies of Kingston, Ontario. The cell stack is of a tubular design, and was built by Siemens Westinghouse Fuel Cell division. This stack achieved a run of more than 1 year while delivering grid quality electricity from natural gas with virtually no degradation and at an electrical efficiency of nearly 40%. The project was ended after two control system failures resulted in system damage.While this demonstration was successful, considerable additional product development is required before this technology is able to provide electrical energy in remote Alaska. The major issue is cost, and the largest component of system cost currently is the fuel cell stack cost, although the cost of the balance of plant is not insignificant. While several manufactures are working on schemes for significant cost reduction, these systems do not as yet provide the same level of performance and reliability as the larger scale Siemens systems, or levels that would justify commercial deployment. Executive summaryWhile most areas of the US are serviced by inexpensive, dependable grid connected power, many areas of Alaska are not. In these areas, electrical power is provided with Diesel Electric Generators (DEGs), at much higher cost than in grid connected areas. The reasons for the high cost of power are many, including the high relative cost of diesel fuel delivered to the villages, the high operational effort required to maintain DEGs, and the reverse benefits of scale for small utilities. This problem has been exacerbated by the recent price spike in diesel fuel, resulting in cost of electrical power to levels several times that of urban areas.Recent progress in fuel cell technologies have lead to the hope that the DEGs could be replaced with a more efficient, reliable, environmentally friendly source of power in the form of fuel cells. To this end, the University of Alaska Fairbanks has been engaged in testing early fuel cell systems since 1998. Early tests were conducted on PEM fuel cells, but these proved expensive, unreliable, and thermodynamically less...

No abstract