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Ecological Water Management in Cities  

Timothy Beatley

Managing water in cities presents a series of intersecting challenges. Rapid urbanization, wasteful consumption, minimal efforts at urban or ecological planning, and especially climate change have made management of urban water more difficult. Urban water management is multifaceted and interconnected: cities must at once address problems of too much water (i.e., more frequent and extreme weather events, increased riverine and coastal flooding, and rising sea levels), but also not enough water (e.g., drought and water scarcity), as well as the need to protect the quality of water and water bodies. This article presents a comprehensive and holistic picture of water planning challenges facing cities, and the historical approaches and newer methods embraced by cities with special attention to the need to consider the special effects of climate change on these multiple aspects of water and the role of ecological planning and design in responding to them. Ecological planning represents the best and most effective approach to urban water management, and ecological planning approaches hold the most promise for achieving the best overall outcomes in cities when taking into account multiple benefits (e.g., minimizing natural hazards, securing a sustainable water supply) as well as the need to protect and restore the natural environment. There are many opportunities to build on to the history of ecological planning, and ecological planning for water is growing in importance and momentum. Ecological planning for water provides the chance to profoundly rethink and readjust mankind’s relationship to water and provides the chance also to reimagine and reshape cities of the 21st century.

Article

Mining, Ecological Engineering, and Metals Extraction for the 21st Century  

Margarete Kalin, William N. Wheeler, Michael P. Sudbury, and Bryn Harris

The first treatise on mining and extractive metallurgy, published by Georgius Agricola in 1556, was also the first to highlight the destructive environmental side effects of mining and metals extraction, namely dead fish and poisoned water. These effects, unfortunately, are still with us. Since 1556, mining methods, knowledge of metal extraction, and chemical and microbial processes leading to the environmental deterioration have grown tremendously. Man’s insatiable appetite for metals and energy has resulted in mines vastly larger than those envisioned in 1556, compounding the deterioration. The annual amount of mined ore and waste rock is estimated to be 20 billion tons, covering 1,000 km2. The industry also annually consumes 80 km3 of freshwater, which becomes contaminated. Since metals are essential in modern society, cost-effective, sustainable remediation measures need to be developed. Engineered covers and dams enclose wastes and slow the weathering process, but, with time, become permeable. Neutralization of acid mine drainage produces metal-laden sludges that, in time, release the metals again. These measures are stopgaps at best, and are not sustainable. Focus should be on inhibiting or reducing the weathering rate, recycling, and curtailing water usage. The extraction of only the principal economic mineral or metal generally drives the economics, with scant attention being paid to other potential commodities contained in the deposit. Technology exists for recovering more valuable products and enhancing the project economics, resulting in a reduction of wastes and water consumption of up to 80% compared to “conventional processing.” Implementation of such improvements requires a drastic change, a paradigm shift, in the way that the industry approaches metals extraction. Combining new extraction approaches, more efficient water usage, and ecological engineering methods to deal with wastes will increase the sustainability of the industry and reduce the pressure on water and land resources. From an ecological perspective, waste rock and tailings need to be thought of as primitive ecosystems. These habitats are populated by heat-, acid- and saline-loving microbes (extremophiles). Ecological engineering utilizes geomicrobiological, physical, and chemical processes to change the mineral surface to encourage biofilm growth (the microbial growth form) within wastes by enhancing the growth of oxygen-consuming microbes. This reduces oxygen available for oxidation, leading to improved drainage quality. At the water–sediment interface, microbes assist in the neutralization of acid water (Acid Reduction Using Microbiology). To remove metals from the waste water column, indigenous biota are promoted (Biological Polishing) with inorganic particulate matter as flocculation agents. This ecological approach generates organic matter, which upon death settles with the adsorbed metals to the sediment. Once the metals reach the deeper, reducing zones of the sediments, microbial biomineralization processes convert the metals to relatively stable secondary minerals, forming biogenic ores for future generations. The mining industry has developed and thrived in an age when resources, space, and water appeared limitless. With the widely accepted rise of the Anthropocene global land and water shortages, the mining industry must become more sustainable. Not only is a paradigm shift in thinking needed, but also the will to implement such a shift is required for the future of the industry.

Article

Review of Rain and Atmospheric Water Harvesting History and Technology  

Nathan Ortiz and Sameer Rao

Water is an essential resource and is under increased strain year after year. Fresh water can be a difficult resource to come by, but the solution may lie in the invisible water source that surrounds us. The atmosphere contains 12.9 trillion m3 of fresh water in liquid and vapor forms. Rain and fog harvesting were the first solutions developed in ancient times, taking advantage of water that already existed in a liquid state. These technologies do not require energy input to overcome the enthalpy of condensation and thus are passive in nature. They are, however, limited to climates and regions that experience regular rainfall or 100% relative humidity (RH) for rainwater and fog harvesting, respectively. People living in areas outside of the usable range needed to look deeper for a solution. With the advent of refrigeration in the 20th century, techniques came that enabled access to the more elusive water vapor (i.e., <100% RH) that exists in the atmosphere. Refrigeration based dewing (RBD) is the most common technique of collecting water vapor from the atmosphere and was first developed in the 1930s but found greater adoption in the 1980s. RBD is the process of cooling ambient air to the dew point temperature. At this temperature water vapor in the atmosphere will begin to condense, forming liquid droplets. As the humidity ratio, or amount of water in a given quantity of air (gwater/kgdry-air) continues to decrease, RBD becomes infeasible. Below a threshold of about 3.5 gwater/kgdry-air the dewpoint temperature is below the freezing point and ice is formed during condensation in place of liquid water. Since the turn of the century, many researchers have made significant progress in developing a new wave of water harvesters capable of operating in much more arid climates than previously accessible with RBD. At lower humidity ratios more effort must be expended to produce the same amount of liquid water. Membrane and sorbent-based systems can be designed as passive or active; both aim to gather a high concentration of water vapor from the ambient, creating local regions of increased relative humidity. Sorbent-based systems utilize the intrinsic hydrophilicity of solid and liquid desiccants to capture and store water vapor from the atmosphere in either their pore structure (adsorbents) or in solution (absorbents). Membrane separators utilize a semipermeable membrane that allows water vapor to pass through but blocks the free passage of air, creating a region of much higher relative humidity than the environment. Technologies that concentrate water vapor must utilize an additional condensation step to produce liquid water. The advantage gained by these advancements is their ability to provide access to clean water for even the most arid climates around the globe, where the need for secure water is the greatest. Increased demand for water has led scientists and engineers to develop novel materials and climb the energy ladder, overcoming the energy requirements of atmospheric water harvesting. Many research groups around the world are working quickly to develop new technologies and more efficient water harvesters.

Article

Wastewater Reclamation and Recycling  

Soyoon Kum and Lewis S. Rowles

Across the globe, freshwater scarcity is increasing due to overuse, climate change, and population growth. Increasing water security requires sufficient water from diverse water resources. Wastewater can be used as a valuable water resource to improve water security because it is ever-present and usually available throughout the year. However, wastewater is a convoluted solution because the sources of wastewater can vary greatly (e.g., domestic sewage, agricultural runoff, waste from livestock activity, and industrial effluent). Different sources of wastewater can have vastly different pollutants, and mainly times, it is a complex mixture. Therefore, wastewater treatment, unlike drinking water treatment, requires a different treatment strategy. Various wastewater sources can be reused through wastewater reclamation and recycling, and the required water quality varies depending on the targeted purpose (e.g., groundwater recharge, potable water usage, irrigation). One potential solution is employing tailored treatment schemes to fit the purpose. Assorted physical, chemical, and biological treatment technologies have been established or developed for wastewater reclamation and recycle. The advancement of wastewater reclamation technologies has focused on the reduction of energy consumption and the targeted removal of emerging contaminants. Beyond technological challenges, context can be important to consider for reuse due to public perception and local water rights. Since the early 1990s, several global wastewater reclamation examples have overcome challenges and proved the applicability of wastewater reclamation systems. These examples showed that wastewater reclamation can be a promising solution to alleviate water shortages. As water scarcity becomes more widespread, strong global initiatives are needed to make substantial progress for water reclamation and reuse.