Carbon Adsorption

Adsorption is the process of removing chemicals from a solution by accumulating the chemicals on a solid surface. Engineers refer to this as the transition from an aqueous environment to a solid environment. Large wastewater treatment plants have more than one method for removing hazards from wastewater; adsorption supplements these treatments because of its efficiency and ease of use. Sustainable wastewater treatment plants, small rural plants on a strict budget, and sustainable homes act as ideal places to use adsorption for cleaning wastewater.

Three types of adsorbents, substances that adsorb materials from water, work in treatment: activated carbon, synthetic long-chain compounds called polymers, and silica-based adsorbents. Polymers and silicabased compounds are expensive, but inexpensive activated carbon has been important in wastewater treatment for many years. Activated carbon consists of any material with high carbon content, which is treated to increase its capacity to draw contaminants from water. Also important, activated carbon holds onto the contaminants and does not release them back into the water.

Makers of activated carbon use any of the following high-carbon materials as precursors: almond, coconut, or walnut hulls; wood; bone; or coal. The activation process contains the following two steps: (1) heating the material to 700°F (371°C) to burn off hydrocarbons and make a material called char; and then (2) activating the char by exposing it to steam and carbon dioxide to create a porous structure. The extensive pore system in the carbon greatly increases surface area and thus makes the material much more efficient as an adsorbent. Activated carbon tends to contain the following pore sizes:

1. macropores—greater than 25 nanometers (nm)
2. mesopores—greater than 1 nm and less than 25 nm
3. micropores—less than 1 nm

 Wastewater treatment systems use either of two types of activated carbon: (1) powdered activated carbon (PAC) that contains small particles (less than 0.075 mm diameter), or (2) granular activated carbon (GAC) that contains larger particles of about 0.1–2.4 mm diameter. Smaller particle sizes also increase the adsorbing surface area compared with large particles.

Carbon adsorption works by exposing the solid surface to a flowing liquid. Contaminants drift toward the solid-liquid interface located adjacent to the solid adsorbent. Contaminant molecules diffuse through this static interface and enter the particles’ pores where they attach to sites called available adsorption sites, which are spaces on the adsorbent’s surface that are unclaimed and available to catch and hold onto a contaminant. Because water flows in and around the adsorbent’s pores, the method is often called carbon filtration. A variety of chemical interactions create the force that holds a contaminant on the surface: charge, covalent bonding, hydrogen bonding, or van der Waals forces. Covalent bonds occur when two atoms share electrons, while van der Waals forces develop when adjacent atoms share a weak attraction to each other because of an electromagnetic field.

Carbon adsorption offers an inexpensive and easy-to-maintain water cleaning method for sustainable homes, especially for treating gray water. The carbon can be reactivated once it has filled up with contaminants and no longer has many available adsorption sites remaining. Reactivation uses the same process as that used to activate char, that is, heating. For home systems, homeowners can simply replace the activated carbon filter every six months to a year after installing it rather than reactivate a used filter.

Energy from Wastewater

Sustainable wastewater treatment involves the reuse of the process’s byproducts for the treatment plant’s operations. A typical wastewater treatment plant offers several options for generating energy or carrying out other conservation measures. Carefully planned wastewater treatment can provide the following benefits: (1) the natural flow of water due to gravity can act as an energy source; (2) methane and hydrogen production from anaerobic digestion serve as energy sources for powering the facility; (3) the reactions inside the digester produce heat that can be rerouted to other biological processes; (4) the treatment plant’s gray water may be reused for flushing toilets; and (5) nutrient-rich sludge exiting the digester serves for landscaping the facility’s grounds or may be sent to local farmers. In summary, in sustainable wastewater treatment, everything is used and reused to the maximum.

The wastewater industry resembles other industries today in trying to meet stricter pollution requirements while reducing energy use. Water and wastewater treatment in the United States uses only 2 percent of the country’s total amount of energy, but with concerns over fuel and energy costs the industry faces the need to build more sustainable operations. Electricity needs of wastewater treatment plants vary by the amount of incoming wastewater they treat each day and the concentration of waste in the water.

Sustainable wastewater treatment plants allow water to naturally purify and consume minimal energy for pumping water. Methane gas from the treatment plant’s anaerobic digester can provide some or all of this energy. The Earth purifies the water due to the soil’s ability to remove particles and bind to many organic compounds.

Sustainable practices in wastewater treatment provide some or all of the energy needs for running pumps for the aeration step and other pumps, heating, and lighting. Methane serves as the most efficient energy source for these purposes, helped to a smaller degree by hydrogen gas. Wastewater-to-energy plants recover methane in a three-step process that involves (1) dehydration, (2) gas cooling, and (3) removal of hydrocarbon compounds heavier than methane. This process results in pure methane of natural gas quality. Methane contains a heating value of 55.5 megajoules per kg of material compared with natural gas’s 53.0 MJ/kg. Other fuels do not provide as much energy as methane: gasoline (48.1 MJ/kg); home heating oil (45.5); coal (28.5 MJ/kg); and wood (about 15 MJ/kg). Wastewater-to-energy therefore holds exciting promise for leading the way in new waste-to-energy technologies.

Ecological Wastewater Treatment

Ecological wastewater treatment encompasses three control methods for keeping wastewater from harming the environment: odor control, methane control, and discharge cleanliness. Odors from gases like hydrogen sulfide emitted from anaerobic digestion do not harm human health but make the surroundings unpleasant for neighbors of treatment facilities. Anaerobic digesters help solve most of this problem, and methane collection devices over manure tanks also reduce odors. Methane collection as previously discussed in this chapter is a critical part of ecological wastewater treatment because it can have a meaningful effect on greenhouse gas levels. The third factor, discharge of cleaned water, represents the wastewater industry’s major responsibility and the U.S. Environmental Protection Agency (EPA) enforces strict laws on the quality that treated wastewater must achieve. The government expects treatment plants to keep the amounts of treated wastewater constituents within certain predetermined limits. The following table describes the constituents in wastewater that the EPA monitors to avoid harm to the environment. These constituents must be controlled within the EPA’s acceptable limits whether a treatment

 facility runs traditional wastewater treatment or wastewater-to-energy processes.

 Wastewater treatment methods offer the following advantages: (1) easy to install and use; (2) small energy demand by most methods; and (3) inexpensive, except for ozone disinfection, ultraviolet disinfection, and ion exchange.

Methane—Cow Power

Cattle, meaning dairy cows and beef animals, belong to a diverse group of animals called ruminant animals, or simply ruminants. Ruminants possess a four-part digestive system composed of a stomach similar to a human stomach and three additional chambers that carry out a different digestion than found in the stomach. Ruminants exist on a diet of fibrous plants that require a good deal of chewing to digest. These animals do this by swallowing partially chewed food, regurgitating it, chewing it again to further break up the pieces (called chewing the cud), and then re-swallowing the material. The smaller, chewed pieces move into the other compartments that contain enormous numbers of anaerobic bacteria and protozoa, especially the biggest compartment called the rumen. Rumen microbes degrade fibers into organic acids that the animal relies on for energy. As the microbes work they release methane, which the animal must constantly eliminate by belching or passing along to the large intestines. The methane drifts upward into the atmosphere and mixes with other greenhouse gases.

CO2 receives most of the blame for the crisis of greenhouse gases and global warming, but, in fact, other gases cause much more harm to the environment. Methane contributes about 20 times more to global warming than CO2. The EarthSave environmental organization has calculated that animal agriculture produces 100 million tons (91 million metric tons) of methane a year. Cattle produce about 20 percent of the methane emissions in the United States, and, unlike new methane-reducing technologies for factories and wastewater treatment plants, these cattle must keep producing methane as long as they live.

Environmental scientists have considered two divergent solutions to cattle methane: capturing the methane for energy or altering normal ruminant digestion to produce less methane. Capturing the methane from belching cows presents an understandably difficult task, so engineers have turned their attention to the large amounts of methane that come from cattle manure. Pacific Gas and Electric Company has embarked on a program to capture this “cow power.” Roy Kuga, its vice president of energy supply said, “With nearly 2 million dairy cows in California, there is great potential for the state’s agriculture and power sectors to work together to address the challenges of climate change.” Cattle have become a hot topic among environmental scientists due to their enormous production levels of a renewable energy source.

Cow power farms work by conveying the manure to covered tanks or lagoons. Gas collecting devices receive the methane as it rises out of the waste load and, with a small amount of processing, pipe the natural gas to an energy utility company’s distribution system. On the other side of the country, Central Vermont Public Service, an electric utility company, uses manure methane to fuel an energy generator and converts the output to electricity for its customers. A Vermont environmental planner Jason Bregman has predicted, “The next generation of renewable energy systems will seek out organic matter in municipal, commercial and agricultural waste streams as a relatively easy source of fuel to obtain and process energy.” Other states and many other countries have begun their own methane waste-to-energy programs.

Reducing the methane a cow produces requires adjustments to the cow’s diet. Grasses that cattle graze contain a stringy fiber called lignin that can only be digested with cud chewing and the action of the rumen’s anaerobes. Laboratories have begun to develop new grasses that contain less lignin so that grass-fed beef and dairy cows emit less methane. The Carnegie Mellon University engineer Christopher Weber explained to Discovery magazine in 2008, “Genetically modified grass could be an appealing solution. It could be more acceptable to the carnivores among us than meat grown in test tubes or giving up meat altogether.” The promise of adjusting cattle’s diets offers some promise, but it is still a long way from helping solve climate change. A more daunting obstacle comes from the fact that cattle are not the world’s only methane producers. The following ruminant animals all produce methane: alpacas, antelopes, bison, camels, deer, giraffes, goats, llamas, oxen, pronghorns, sheep, water buffalos, wildebeests, and yaks.

Methane use and methane reduction are two rapidly emerging technologies. If environmental engineers can design successful means of capturing methane for energy use, they will certainly help in advancing sustainable energy sources. Overall, methane will continue to be a problem in global warming.

Gray Water Reuse

Gray water is water that has been used for showering, faucet uses, and clothes washing, and it usually disappears down drains as a wasted resource. Sustainable wastewater treatment involves the recapture of gray water for additional uses, a process better known as water reclamation. These recovery systems do not collect kitchen sink water or toilet water because these can be health hazards due to the presence of disease-causing microbes.

Sustainable houses collect gray water in pipes that run separate from toilets and the kitchen sink. After collection, building designers have options regarding how and where the gray water will be best used. The three main options for gray water use are: (1) as irrigation water; (2) for flushing toilets; or (3) in the home’s fire suppression system.

Two new technologies may soon join the three main uses for gray water. The first involves the routing of gray water into wetlands constructed near the building to naturally degrade liquid wastes. These constructed wetlands work similarly to natural wetlands in which wastes move very slowly through the site so that plants and microorganisms have time to degrade the organic matter. Lori Ryker explained in her 2005 book Off the Grid, “The goal of a man-made wetland is to replicate a natural wetland’s ability to clean and filter water. A constructed wetland system’s selected plants filter gray water in a specific order, and then return the water to the earth, eliminating the need for a fully developed septic system.” The second technology uses very efficient filtration systems to make the water suitable for drinking, known as potable water. The following filtration technologies may soon produce drinking water for direct reuse as potable water: ultrafiltration in which filters contain extremely small pores to capture all contaminants; nanotechnology in which nanoscale materials act to clean or even sterilize water; and reverse osmosis in which water is forced through a fine membrane to clean out all impurities.

A sustainable home manages three different water sources: (1) rainwater, which is usually captured in a cistern such as the 60-gallon (227-l) size shown here; (2) gray water, which is wastewater from showers, sinks, and washers that is not expected to contain diseasecausing microbes; and (3) blackwater, which is wastewater from toilets, sinks, or any other source expected to be contaminated with disease-causing microbes. (Natural Rainwater.com)

Most houses that recover gray water today send the water to a holding tank that degrades waste in a manner similar to a septic tank. The cleaned water moves out of the tank by passive energy; it is pushed along by the force of new gray water entering the system. The cleaned water flows through a short series of baffles that prevent most of the dirty gray water from mixing with the cleaner water, and then the cleaned water goes through the outflow pipe. After completing this cleanup process, the two main current uses for gray water are garden irrigation or flushing toilets. Gray water reclamation does not need to be confined to houses; these closed-loop systems can work in large office buildings, schools, and manufacturing plants.

Anaerobic Digesters

An anaerobic digester is any equipment or site that holds waste materials in an oxygen-free environment so that anaerobic bacteria can degrade the wastes. On a wastewater treatment plant’s property, the digester is a large tank that holds several thousand gallons of liquid and semiliquid material. Wastewater digestion also takes place in a similar way in lagoons or ponds even though these places are exposed to the air. Though the upper layers of the water contain some dissolved oxygen, the deeper layers become less aerobic and more anaerobic. If the contents of an anaerobic digester or pond receive little mixing, oxygen does not penetrate the depths and so anaerobic bacteria work at their best.

Anaerobic decomposition occurs naturally in swamps, bogs, stagnant ponds, deep bodies of water, and waterlogged soils. The bacteria in these places degrade organic matter to the simplest of compounds, which allows the nutrients to be recycled. For example, amino acids degrade to carbon dioxide (CO2), methane (CH4), hydrogen (H2), and small amounts of nitrogen and sulfur compounds.

Digestion of organic matter—in nature as well as in a digester—takes place in three stages. First, aerobic bacteria degrade complex compounds such as starches, proteins, and fibers into smaller carbohydrates or peptides. A second group of bacteria use these compounds as food and produce organic acids as end products of their enzyme reactions. The organic acids all have in common a carboxylic group as part of their structure (COOH). This section of the molecule contains a carbon that is linked both to an oxygen molecule and to an oxygen-hydrogen complex, called a hydroxyl group. Examples of the organic acids produced in this step are acetic acid (two total carbons), propionic acid (three carbons), and butyric acid (four carbons). As a third and final step, anaerobic bacteria use the acids for energy and produce methane, carbon dioxide, and a small amount of other gases (hydrogen, carbon monoxide, hydrogen sulfide, and nitrogen).

Anaerobic digesters at wastewater treatment plants make fuel in the form of methane gas, which can be burned to release its energy. Many sustainable wastewater treatment plants use the methane to provide heat for the digester so that the entire process can continue. This is an example of a sustainable loop.

The methane and the other biogases produced by anaerobic digestion serve as an energy source that can be used to run the treatment plant or do other work. Burning one cubic foot of biogas yields 10 Btu of heat energy. The amount of methane in the biogas mixture affects the energy production because methane is the main energy source. Each percentage of methane results in 10 Btu, so that a biogas containing 65 percent methane produces 650 Btu per cubic foot. Very active anaerobic digesters can produce enough methane to run a treatment plant’s heating, refrigeration, and electricity. Anaerobic digesters therefore play a role as the main powerhouse when designing a sustainable wastewater treatment plant.

Methane cannot solve every environmental problem. For one thing, though methane can be used for making energy, it is also a predominant greenhouse gas that causes global warming. Sustainable wastewater treatment plants help reduce this problem by capturing all the methane emitted by a digester and using it, but methane come from additional sources in the world. Human activities that lead to methane production are waste treatment, biomass burning facilities, energy plants, and landfills. Methane also comes from natural sources: anaerobic soil and water bacteria, some vegetation, fossil fuel deposits such as coal mines and natural gas fields, and certain animals. Scientists have begun to realize in the past decade or so that the animal sources of methane contribute a significant amount of greenhouse gas to the atmosphere.

Kufunda Learning Village, Zimbabwe

Kufunda Learning Village in Zimbabwe, located near the capital of Harare, was created in 2005 by Marianne Knuth for the purpose of creating strong, healthy communities that are responsible for their own future. In addition to cultural growth, Kufunda has embarked on an exploration of technologies to meet its most immediate needs. Kufunda residents focus on building self-sufficiency in two main areas: agriculture and community infrastructure. Knuth explained, “We are a small group of people who have decided to create a learning village aimed at the creation of locally rooted solutions to community self-reliance challenges. A starting assumption for my work here is that people already know how to work in creative and self-sufficient ways, and that the challenge is to help them access that knowledge—and the self-confidence to act on it—generating concrete and often surprising results in the process.” In time, Kufunda’s residents hope they can transfer their knowledge to neighboring villages that wish to create similar self-sufficiency.

In the face of periodic political unrest, villages like Kufunda have a greater need for self- reliance, perhaps, than any other communities. Residents have begun to investigate the developmentment of ecological projects such as renewable energy, organic farming, ecological building, and composting toilets. The Kufunda Learning Village Web site has reported, “Ecological sanitation is a system that makes use of human excreta and turns it into something useful, which can be used to grow plants or trees. By now all the toilets at the village are of this type. Our simplest compost toilet can now be built for roughly 10 U.S. dollars—an important factor when working with financially poor rural communities.” Not only are Kufunda’s plans cost-effective, but they make every use of natural clean-running systems.

The Kufunda Learning Village has already begun to run its main electronic systems on solar power—the satellite Internet was the village’s first system to run on solar energy. Kufunda’s residents have an advantage over richer, more industrialized communities: They own no preexisting energy or waste management systems to tear down. The Kufunda Learning Village continues to find the best solutions to its specific environmental issues and, in the process, provides a good example of building efficient and simple technologies that foster sustainability.

Wastewater in Developing Countries

Numerous developing parts of the world contend with a high incidence of infectious disease because of poor drinking water quality and poorly functioning wastewater systems. Leaks and contamination of either system come from faulty or missing infrastructure, meaning distribution pipes, collection pipes, treatment facilities, and disinfection methods. Because of serious health threats to humans, many developing countries that already struggle with poor infrastructure make wastewater treatment their priority. The World Health Organization (WHO) has warned that the problem will get worse in developing countries. Because these places have clean water shortages, wastewaters substitute for treated water for irrigation, fishing, and cleaning clothes.

Sustainable wastewater treatment refers to the production of energy from the wastewater treatment process. This method of energy production offers an opportunity for developing countries for two reasons: the efficiency in converting biomass’s chemical energy to other forms of energy, and low cost compared with other energy technologies. Sustainable wastewater treatment therefore relieves two problems that plague many developing parts of the world: energy and waste management.

Nonindustrialized countries have a great need for inexpensive, easyto- build waste treatment technologies. Some of these countries have adopted inventive and sustainable solutions to waste treatment. The Internet reporter Andrea Millar provided an example in a 2008 article: “A Kenyan jail has confronted the issue of its waste production by creating a sustainable wastewater treatment facility staffed by inmates and designed by both local and international organizations. Rather than employ hightech engineering, the bulk of the [treatment is] handled by natural processes in the facility’s man-made wetlands. Acting as a vast filtration system, the sustainable processes of anaerobic microbes convert human waste into materials for biogas and water for use on the jail’s vegetable fields.” Millar’s example illustrates a situation in which wastewater handling is done in a manner that requires no energy input at all other than a small amount of manual labor.

The next step in sustainable wastewater use involves methods for producing energy. Treatment plant anaerobic digesters offer the most efficient way to make energy-containing methane gas, but some villages may not have the funds to build a new plant from the ground up. A waste treatment pond offers an inexpensive option because it contains conditions similar to those found inside treatment plant anaerobic digesters. Treatment ponds contain anaerobic activity in the deepest parts of the pond where aerobic bacteria have depleted the oxygen. Anaerobic bacteria live naturally in these types of places so setting up a wastewater treatment pond carries little expense. Methane gas drifts up from the bottom of the pond and can be captured and piped to an energy-generating plant so that the pond produces energy rather than consumes it.

Some ponds tend to grow heavy mats of algae on the water surface. Rather than spend efforts to get rid of the algae, workers remove the algae layer and add it to a small anaerobic digester to produce heat. In fact, treatment ponds provide the same advantages of mechanical anaerobic digesters: They help in waste management and treatment and recycle nutrients. One disadvantage of ponds compared with closed anaerobic digesters comes from odors emitted by the bacteria in their normal digestion of organic matter. The odors do not cause a health problem, but smell unpleasant.

R. Otterpohl wrote an online article in 2007 for the Swiss Federal Institute of Aquatic Science and Technology describing new processes for wastewater treatment that seem suited for developing countries: “The conventional wastewater management concept, consisting of a waterborne wastewater collection system leading to a central treatment plant, has been successfully applied over many decades in densely populated areas of industrialized countries . . . However, the appropriateness of this model in the context of developing world cities must be questioned, given the urgent need for affordable, sustainable infrastructure. During the last decade, various researchers and institutions, including the World Bank, have started to consider the decentralized wastewater management approach as an alternative to conventional centralized systems, but these approaches have struggled to gain acceptance.” Part of the resistance comes from the worry that treatment plants intended for the use of only one or two towns might not be as efficient to run as big centralized wastewater treatment plants. But small, decentralized treatment plants also offer advantages to communities, as follows:

1. smaller treatment systems tailored to a community’s specific needs
2. experimentation with different wastewater treatment methods
3. reduces accidents that may occur in long-distance wastewater shipment
4. increases opportunities for treated water reuse
5. makes incremental changes and improvements manageable

 Today, the Engineers Without Borders-International (EWBI) organization helps communities in developing regions adopt new technologies to improve their health, income, and lives. The EWBI stresses sustainable methods in energy use, water management, and native natural resource conservation. EWBI engineers and other volunteers help disadvantaged communities build needed structures and teach residents basic engineering skills for future projects. The founder of the Engineers Without Borders-United States, Bernard Amadei, revealed his view of the organization’s purpose in a 2007 interview with the correspondent Spencer Michels. Amadei described San Pablo, Belize, as a village “where I noticed a lot of little girls, young girls, who were carrying water—that was their job—from the river to the village, back and forth, back and forth. And as a result, they could not go to school. It broke my heart. And I decided I was going to do something about it.” EWBI develops projects with a community, not for it, so that the community solves its own environmental engineering needs. EWBI helps train residents how to build a structure, how to fix it, and how to keep it running.

Developing countries therefore have options for the type of wastewater treatment they choose. Because of the health needs for safe wastewater management and the need to produce inexpensive energy, sustainable wastewater systems are ideal for developing parts of the world.

The Energy-Water Connection

Environmental engineers apply the first and second laws of thermodynamics in every project they plan and develop. The first law of thermodynamics states that energy can neither be created nor destroyed. The form of energy, however, can change. For example, the motion energy inside a turbine changes to electricity. The second law of thermodynamics states that energy flows from a region of high concentration to a region of lower concentration, much as water flows downhill. By the second law of thermodynamics, water at the top of a waterfall contains a high concentration of energy. As it pours over the waterfall and fills a basin, the energy concentration changes. The water that settles into the basin at the bottom of the waterfall holds a lower concentration of energy. This principle has been used for centuries to power daily operations.

Flowing water illustrates another component of energy—potential energy versus kinetic energy. Water at the top of the waterfall before flowing over the edge contains potential energy, that is, a form of stored energy. As the water pours downward it loses potential energy and gains kinetic energy, the energy of motion. All of the different types of energy

Operations that generate energy from flowing water—hydroelectric dams, wastewater treatment plants, mills— rely on capturing water’s kinetic energy. Water at the top of the waterfall in this diagram holds high potential energy, but after it reaches the bottom of the waterfall it contains low potential energy. Power plants take advantage of this transition.

in the solar system can be classified as either potential or kinetic, as the following table shows.

Energy can change from one type to another, as mentioned, illustrated by the following example:

1. A racehorse converts the chemical energy in hay to motion energy.
2. A person converts electrical energy to thermal energy by turning on an oven.
3. Plants convert radiant energy from the Sun into chemical energy through photosynthesis.

Water’s use as an energy source throughout history has usually been as motion energy. Wastewater treatment plants can take advantage of the natural flow of water to power operations, but wastewater offers an additional energy source in the form of biomass. Biomass is organic matter in wastewater that comes from plant and animal wastes. In the wastewater treatment industry, biomass represents a source of chemical energy that can be converted to other forms such as thermal energy.

Sustainable Wastewater Treatment

Hydrology, the science of water systems, has always been a central part of environmental engineering. Ancient societies used flowing water as a means of travel, a conveyance for moving timber and other goods downstream, and a waste disposal system. During the growth of civilization, people learned that bodies of water held a significant amount of force. Villages constructed mills next to fast flowing rivers to let the force of the water supply power for the milling operations. The next generation built enormous dams to control the force of water that powered turbines and produced electricity. Water systems will become part of new energy-generating systems in sustainable communities in the near future, mainly because water avoids the use of nonrenewable and pollution-causing fossil fuels.

Wastewater treatment follows a standard process that turns raw sewage into disinfected water safe for return to the environment. Almost all modern wastewater treatment plants conduct the following steps to treat wastewater: (1) wastewater passes through screens that remove large solids; (2) wastewater enters a grit chamber where heavy wastes settle out of the water by gravity; (3) water enters a larger settling tank where light, small particles slowly settle out of the water; (4) the water enters an aeration tank containing aerobic (oxygen-requiring) bacteria that digest organic substances, aided by a constant bubbling of air through the contents; (5) the water enters another settling step and then passes through a filtration tank, which removes very fine particles; (6) disinfectant kills the bacteria in the water; and (7) the treated water discharges into the environment.


Pipes carry much of the heavy organic sludge that collects in the settling tanks to another tank called an anaerobic digester. This digester contains anaerobic (requiring the absence of oxygen) bacteria that slowly degrade the heavy sludge and produce methane and small amounts of other gases. The wastewater treatment industry calls the methane biogas, and both biogas and solid biomass serve as energy sources produced by wastewater treatment.

Landscape Design Skills

The landscape design profession combines art and science for the purpose of planning and shaping the land that surrounds a structure. Ecological landscape design focuses on meeting a customer’s needs while also planting trees and plants, gardens and ponds, and other features that create a relationship between the building and the environment. Landscape designers must understand many of the same principles as environmental engineers, that is, hydrology, geography, topography, and climatology. The landscape designer, however, emphasizes the artistic use of plants, water, and land. The following table summarizes the basic skills that landscape designers call upon when they develop a new but natural look for a parcel of land.

Environmental landscaping begins with a plan agreed upon between a house’s architect and the property’s landscaper. A landscape designer also gives input to this process in order to create a visual meaning to an entire property. For instance, a country cottage would look out of place nestled among large rock formations and towering pines, and the property would be further confused by a modernistic landscape design including sculpted shrubbery and enormous fountains. Landscaping in harmony with nature eliminates most of these pitfalls: Nature always produces the best balance between art and design.

The landscape design process entails the following six steps:

1. Develop a design for a given parcel of land.
2. Conduct a site analysis to assess existing tree and plant life and physical features.
3. Assess the house design, landscaping objectives, and the residents’ desires.
4. Locate areas of the property that will be designed.
5. Create design plans for those individual areas.
6. Select the plants to be used and plant them in the designated areas.

 In order to carry out the tasks listed here, landscape designers depend on strong skills in horticulture. In this way they help eco-landscapers select plant life that blends with the following factors: local climate and any microclimates; soil conditions; wind and storm incidence; and potential freezing or drought. Landscape designers today also design biodiversity gardens and edible gardens.

America’s Scenic Byways

Since 1991 the U.S. Department of Transportation (DOT) National Scenic Byways Program has designated specific roads that lead to archaeological, historical, cultural, natural, recreational, or scenic locations. The DOT has so far designated 125 such roads in 44 states. All of the scenic byways encourage travelers to gain greater appreciation of the land and its local trees, plants, and wildlife. Because scenic byways often call attention to nature, they seem to be a perfect place to adopt ecolandscaping. But heavily traveled roads have also caused harm to biodiversity by breaking up habitats, blocking migration routes, and killing wildlife in road accidents. Current and future scenic byways hold an important opportunity to establish ecologically friendly methods to construct and maintain popular roads.

Scenic byways range in rustic quality from the Beartooth Highway that meanders through Montana’s mountains and forests to Delaware’s Brandywine Valley Scenic Byway that travels past large estates and magnificent botanical gardens. Regardless of the terrain that a scenic byway traverses, the program ensures that all portions of the highway minimize the presence of billboards, telecommunications towers, fast food restaurants, or other clutter. One goal of the scenic byways program involves saving open space, and keeping human activities away from the roads helps preserve open space. In many instances, scenic byways probably provide some people with a look at nature that they would otherwise miss entirely in their urban lifestyle.