No abstract

In the endorheic basins of the Altiplano, water is crucial for sustaining unique ecological habitats. Here, the wetlands act as highly localized evaporative environments, and little is known about the processes that control evaporation. Understanding evaporation in the Altiplano is challenging because these environments are immersed in a complex topography surrounded by desert and are affected by atmospheric circulations at various spatial scales. Also, these environments may be subject to evaporation enhancement events as the result of dry air advection. To better characterize evaporation processes in the Altiplano, the novel Evaporation caused by Dry Air Transport over the Atacama Desert (E-DATA) field campaign was designed and tested at the Salar del Huasco, Chile. The E-DATA combines surface and airborne measurements to understand the evaporation dynamics over heterogeneous surfaces, with the main emphasis on the open water evaporation. The weather and research forecasting model was used for planning the instruments installation strategy to understand how large-scale air flow affects evaporation. Instrumentation deployed included: meteorological stations, eddy covariance systems, scintillometers, radiosondes and an unmanned aerial vehicle, and fiber-optic distributed temperature sensing. Additional water quality and CO2 fluxes measurements were carried out to identify the link between meteorological conditions and the biochemical dynamics of Salar del Huasco. Our first results show that, in the study site, evaporation is driven by processes occurring at multiple spatial and temporal scales and that, even in the case of available water and energy, evaporation is triggered by mechanical turbulence induced by wind.

Wastewater sludge management is a significant challenge for small-scale, urban wastewater treatment plants (WWTPs). Common management strategies stabilize sludge for land disposal by microbial action or heat. Such approaches require large footprint processing facilities or high energy costs. A new approach considers sludge to be a fuel which can be used on-site to produce electricity. Electrical power generation fueled by sludge may serve to reduce the volume of hazardous waste requiring land disposal and create economic value for WWTP operators. To date, no detailed system designs or techno-economic analyses have been found for small scale sludge fueled power plants. Fortunately, a literature base exists describing the fundamentals of applying thermochemical conversion (TCC) technologies to sewage sludge. Thermochemical conversion of sludge is established for large WWTPs, however large system design techniques may not be applicable to small systems.To determine the feasibility of small scale power generation fueled by sludge, this work evaluates several thermochemical conversion technologies from the perspective of small urban WWTPs. Literature review suggests wet oxidation, direct combustion, pyrolysis, and gasification as candidate front-end TCC technologies for on-site generation. Air and steam blown gasification are found to be the only TCC technologies appropriate for sludge. Electrical power generation processes based on both air and steam blown gasification are designed around effective waste heat recovery for sludge drying. The systems are optimized and simulated for net electrical output in ASPEN Plus R . Air blown gasification is found to be superior. Sensitivity analyses are conducted to determine the effect of fuel chemical composition on net electrical output. A technical analysis follows which determines that such a system can be built using currently available technologies. Finally, an economic analysis concludes that a gasification based power system can be economically viable for WWTPs with raw sewage flows of 0.115 m 3 /s, or about 2.2 million gallons per day.

No abstract

Polycyclic aromatic hydrocarbons (PAHs) are a family of organic compounds of widespread presence in the environment. They are recalcitrant, ubiquitous, prone to bioaccumulation, and potentially carcinogenic. Effluent from wastewater treatment plants (WWTPs) constitutes a major source of PAHs into water bodies, and their presence should be closely monitored, especially considering the increasing applications of potable and non-potable reuse of treated wastewater worldwide. Modeling the fate and distribution of PAHs in WWTPs is a valuable tool to overcome the complexity and cost of monitoring and quantifying PAHs. A mechanistic model was built to evaluate the fate of PAHs in both water and sludge lines of a Chilean WWTP. Naphthalene and benzo(a)pyrene were used as models of low-MW and high-MW PAHs. As there were no reported experimental data available for the case study, the influent load was determined through a statistical approach based on reported values worldwide. For both naphthalene and benzo(a)pyrene, the predominant mechanism in the water line was sorption to sludge, while that in the sludge line was desorption. Compared to other studies in the literature, the model satisfactorily describes the mechanisms involved in the fate and distribution of PAHs in a conventional activated sludge WWTP. Even though there is evidence of the presence of PAHs in urban centers in Chile, local regulatory standards do not consider PAHs in the disposal of WWTP effluents. Monitoring of PAHs in both treated effluents and biosolids is imperative, especially when considering de facto reuse and soil amendment in agricultural activities are currently practiced downstream of the studied WWTP.