Management and design of biogas digesters: A non-calibrated heat transfer model.

A thermal balance modeling framework is developed, based on heat transfer-resistance networks. The heat transfer model accounts for effects of digester- design, location and operation, including effects of solar irradiance, external heating and ambient climate. We demonstrate extendibility of the framework by using the model in dynamic simulations of substrate temperature for digesters comprising two very different designs. Digester designs modeled include fixed-dome, buried, uninsulated and unheated household digesters in Hanoi, Vietnam, and an industrial-scale anaerobic digester located at a wastewater treatment plant in Esbjerg, Denmark. The modeled temperature profiles were evaluated against measured substrate temperatures over long periods, from 7 months and up. For the two Hanoi digesters, root-mean-square-error were 1.43 °C and 0.92 °C, with Nash-Sutcliffe model efficiency coefficients (NS-C) of 0.87 and 0.93 respectively. For the industrial digester in Esbjerg root-mean-square-error was 0.48 °C with an NS-C of 0.94. The model was not calibrated prior simulation, suggesting good predictive performance.

Long-term trends in sodium and chloride in the Mohawk River, New York: the effect of fifty years of road-salt application.

Ecological studies have demonstrated the adverse effects of road-salt, primarily NaCl, on water quality, flora, and fauna. In this study, we quantified changes in ionic composition and solute flux of water draining the Mohawk River Basin (9103 km(2)) in New York State, from 1952 to 1998. Using various statistical, graphical, and modeling techniques, we showed that concentrations ofNa+ and Cl- have increased by 130 and 243%, respectively, while other constituents have decreased or remained constant. The use of de-icing salt on roads within the watershed, which we estimate at 39 kg km(-2) day(-1), appears to be the primary mechanism responsible for reported increases, accounting for the increase in NaCl export from 16 to 46 kg km(-2) day(-1) over the 47-year period.Moreover, despite population decline within this rural upstate watershed, increased environmental stewardship, and The Clean Water Act, concentrations of Na+ and Cl- still increased during the 1990s.