• Energy Research

As the world’s population and demand for fresh water increases, new water resources are needed. One commonly overlooked aspect of the water cycle is fog, which is an important part of the hydrology of coastal, high-altitude, and forested regions. Fog water harvesting is being investigated as a sustainable alternative water resource for drinking water and reforestation. Fog water harvesting involves using mesh nets to collect water as fog passes through them. The materials of these nets, along with environmental factors such as wind speed, influence the volume of water collected. In this article, a review of current models for fog collection, designs, and applications of fog water harvesting is provided. Aspects of fog water harvesting requiring further research and development are identified. In regions with frequent fog events, fog water harvesting is a sustainable drinking water resource for rural communities with low per capita water usage. However, an analysis of fog water harvesting potential for the coastal areas of northern California (USA) showed that fog yields are too small for use as domestic water in areas with higher household water demands. Fog water shows particular promise for application in reforestation. Fog water irrigation can increase growth rates and survivability of saplings in reforestation efforts in regions with frequent fog events. Using fog collectors, denuded areas once dependent on natural fog drip can be restored, benefiting local hydrology and ecosystem recovery. Improvement in fog collector designs, materials, and models to increase collection efficiency, perhaps by inclusion of ideas from natural systems, will expand the regions where fog harvesting can be applied.

In the United States, environmentally impaired rivers are subject to regulation under total maximum daily load (TMDL) regulations that specify watershed wide water quality standards. In California, the setting of TMDL standards is accompanied by the development of scientific and management plans directed at achieving specific water quality objectives. The San Joaquin River (SJR) in the Central Valley of California now has a TMDL for dissolved oxygen (DO). Low DO conditions in the SJR are caused in part by excessive phytoplankton growth (eutrophication) in the shallow, upstream portion of the river that create oxygen demand in the deeper estuary. This paper reports on scientific studies that were conducted to develop a mass balance on nutrients and phytoplankton in the SJR. A mass balance model was developed using WARMF, a model specifically designed for use in TMDL management applications. It was demonstrated that phytoplankton biomass accumulates rapidly in a 88 km reach where plankton from small, slow moving tributaries are diluted and combined with fresh nutrient inputs in faster moving water. The SJR-WARMF model was demonstrated to accurately predict phytoplankton growth in the SJR. Model results suggest that modest reductions in nutrients alone will not limit algal biomass accumulation, but that combined strategies of nutrient reduction and algal control in tributaries may have benefit. The SJR-WARMF model provides stakeholders a practical, scientific tool for setting remediation priorities on a watershed scale.

Selective catalytic reduction (SCR) was used to reduce exhaust gas nitrogen oxides (NOx) from the emissions of a 710 kW combined heat and power system fueled by dairy biogas. Exhaust gas NOx was reduced from 63.1 ± 31.9 to 14.2 ± 17.5 ppmvd @ 15% O2 such that emissions were 0.33 ± 0.40 g kW � 1 h � 1 , based on data averaged over 15 min intervals. Online exhaust gas sensors with integrated process control algorithms were effective in improving NOx removal by automated control of urea, the ammonia source used for catal- ysis of NOx reduction reactions. Pre-SCR NOx was most strongly correlated with equivalence ratio (R 2 = 0.39), indicative of the air-fuel ratio. A concave relationship between NOx production and thermal conversion efficiency was not observed since lean-burn operation of the engine was consistent and only altered under low engine load. Following installation of pre- and post-SCR NOx sensors, average daily exhaust gas NOx reduction in the SCR was 82.6 ± 8.5%. Post-SCR NOx emissions were typically impacted by pre-SCR NOx (R

Anaerobic digestion of manure and other agricultural waste streams with subsequent energy production can result in more sustainable dairy operations; however, importation of digester feedstocks onto dairy farms alters previously established carbon, nutrient, and salinity mass balances. Salt and nutrient mass balance must be maintained to avoid groundwater contamination and salination. To better understand salt and nutrient contributions of imported methane-producing substrates, a mass balance for a full-scale dairy biomass energy project was developed for solids, carbon, nitrogen, sulfur, phosphorus, chloride, and potassium. Digester feedstocks, consisting of thickened manure flush-water slurry, screened manure solids, sudan grass silage, and feed-waste, were tracked separately in the mass balance. The error in mass balance closure for most elements was less than 5%. Manure contributed 69.2% of influent dry matter while contributing 77.7% of nitrogen, 90.9% of sulfur, and 73.4% of phosphorus. Sudan grass silage contributed high quantities of chloride and potassium, 33.3% and 43.4%, respectively, relative to the dry matter contribution of 22.3%. Five potential off-site co-digestates (egg waste, grape pomace, milk waste, pasta waste, whey wastewater) were evaluated for anaerobic digestion based on salt and nutrient content in addition to bio-methane potential. Egg waste and wine grape pomace appeared the most promising co-digestates due to their high methane potentials relative to bulk volume. Increasing power production from the current rate of 369 kW to the design value of 710 kW would require co-digestion with either 26800 L d(-1) egg waste or 60900 kg d(-1) grape pomace. However, importation of egg waste would more than double nitrogen loading, resulting in an increase of 172% above the baseline while co-digestion with grape pomace would increase potassium by 279%. Careful selection of imported co-digestates and management of digester effluent is required to manage salt and nutrient mass loadings and reduce groundwater impacts.

Diving into Deep Water The Deepwater Horizon oil spill in the Gulf of Mexico was one of the largest oil spills on record. Its setting at the bottom of the sea floor posed an unanticipated risk as substantial amounts of hydrocarbons leaked into the deepwater column. Three separate cruises identified and sampled deep underwater hydrocarbon plumes that existed in May and June, 2010—before the well head was ultimately sealed. Camilli et al. (p. 201 ; published online 19 August) used an automated underwater vehicle to assess the dimensions of a stabilized, diffuse underwater plume of oil that was 22 miles long and estimated the daily quantity of oil released from the well, based on the concentration and dimensions of the plume. Hazen et al. (p. 204 ; published online 26 August) also observed an underwater plume at the same depth and found that hydrocarbon-degrading bacteria were enriched in the plume and were breaking down some parts of the oil. Finally, Valentine et al. (p. 208 ; published online 16 September) found that natural gas, including propane and ethane, were also present in hydrocarbon plumes. These gases were broken down quickly by bacteria, but primed the system for biodegradation of larger hydrocarbons, including those comprising the leaking crude oil. Differences were observed in dissolved oxygen levels in the plumes (a proxy for bacterial respiration), which may reflect differences in the location of sampling or the aging of the plumes.

Abstract Previous experience has demonstrated the tenuous nature of biomass energy projects located at livestock facilities in the U.S. In response, the economic sustainability of a 710 kW combined heat and power biomass energy system located on a dairy farm in California was evaluated. This biomass energy facility is unique in that a complete-mix anaerobic digester was used for treatment of manure collected in a flush-water system, co-digestates were used as additional digester feedstocks (whey, waste feed, and plant biomass), and the power plant is operating under strict regulatory requirements for stack gas emissions. Electricity was produced and sold wholesale, and cost savings resulted from the use of waste heat to offset propane demand. The impact of various operational factors was considered in the economic analysis, indicating that the system is economically viable as constructed but could benefit from introduction of additional substrates to increase methane and electricity production, additional utilization of waste heat, sale of digested solids, and possibly pursuing greenhouse gas credits. Use of technology for nitrogen oxide (NO x ) removal had a minimal effect on economic sustainability.

In 1952, Isaac Asimov wrote a vivid tale about human explorers engineering the ecosystem of Mars to make it habitable for humans (Asimov 1952). In science fiction, engineers use terraforming machines to modify the atmosphere, landscape, and hydrology of Mars to create ecosystems that sustain earth-based life-forms. Since that time, rapid advances in population density, combined with ideas concerning engineering and finance, have allowed us to recreate the ecosystem of our home planet. However, our Earth-based ‘‘terraforming’’ efforts have not sufficiently included ecosystem function in our engineering designs and, as a result, a number of negative consequences are occurring. Engineering has had a great history of achievement in designing and building hydrologic structures and actualizing fantastic ideas, such as the Roman aqueducts, the canals of Angkor Wat, or the Bhakra Nangal dam. Engineering over the ages has transitioned from a focus on structural greatness to engineering the manipulation of natural cycles and systems, including the hydrologic cycle. These designs and manipulations typically regard only the immediate application (e.g., flood control, water supply), not the needs of the regional and global ecosystem, and therefore impart unintended consequences as a result of this oversight. In the last 50 years, the world population has more than doubled, from less than 3 billion people to an estimated 6.8 billion people today (United States Census Bureau 2010). Current projections are for the world population to reach nine billion within the next generation. Despite the potential for disaster, arguably the human condition has improved as population density increased. The Human Development Index (HDI), a measurement that incorporates life expectancy, access to education, and standard of living, has risen for all of the 82 UN member states for which there is comparative data between 1980 and 2007 (United Nations Development Programs, 2009). The average increase for states ranked as having low development (scores less than 0.50) in 1980 was almost 140%, with ten out of 21 states moving from the low development to medium development categories. The HDI also increased in countries ranked in 1980 as medium development (120%) and high or very high development (110% of the 1980 values). Other measurements of the human condition, such as access to drinking water, undernourishment, and poverty rates, show trends that indicate the human condition is improving (United Nations 2008; United Nations Environmental Programs 2010). The human condition has been uplifted in large part due to engineering that has transformed our landscape and hydrology on a local, regional, and global scale. W. T. Stringfellow (&) R. Jain Ecological Engineering Research Program, School of Engineering and Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA e-mail: wstringfellow@pacific.edu