BioCycle February 2005, Vol. 46, No. 2, p. 50
No longer is it a matter of if we will utilize reuse technologies. It is a matter of when in order to sustain economic growth and minimize environmental impact.
Clifford B. Fedler

WATER is one of the most precious of the world’s resources, yet too little effort is made to conserve and preserve the limited available supply. Water resources available for consumption vary considerably around the world with some areas having more than 26.4 million gallons (100,000 m3) per capita. This abundance in some regions tends to create a perception of an infinite supply with minimal need for conservation. Yet, in other regions of the world, the fresh water available is less than 79,000 gallons (300 m3) per capita. These fresh water resources are being withdrawn in some countries at rates that approach 5,000 m3 per capita, while in most countries the withdrawal is about 500 m3 per capita or less. The world’s water resources are being depleted every year due to the fact that most countries are mining their freshwater resources with withdrawal exceeding the rate of recharge.
Approximately 70 percent of the fresh water consumed worldwide is utilized by food production systems. In the most developed countries of the world, the largest consumer of water is industry, which includes many food-related processes. Only approximately 10 percent of freshwater use is for domestic purposes.
CURRENT SITUATION
Almost universally, the fresh water that is consumed is utilized once and then discharged. Water withdrawn from our available resources is used for many purposes, but the bulk of that water is used, treated, and then discharged into a receiving stream. In the northern United States, for example, water is drawn from both surface and ground sources. That water is used for domestic purposes and then enters a collection system. All of that water is then diverted to some form of treatment system and eventually discharged into a nearby receiving stream. Once in that stream, the water is essentially sent to the coast and discharged into the ocean. When examining this scenario from the systems approach, water is mined from our freshwater resources and the resulting waste is then discharged into our coastal waters.
The quality of coastal waters is also problematic in this scenario. It was commonly thought that coastal water quality was dependent only upon the discharges that came from local areas surrounding the coast. However, upstream discharge may be an additional contributing factor. Not all of the coastal water quality problems stem from upstream domestic usages because there are many industries discharging their “consumed and treated” water into the same streams. In addition, runoff from agricultural systems also ends up within the same streams. Therefore, solving some of the coastal water quality problems requires serious examination of activities far upstream from the coast.
From a global perspective, water quality means the difference between having an acceptable quality of life and something below international poverty level standards. The most common figure put forth by such organizations as the International Food Policy Research Institute is that over one billion people are without satisfactory access to safe drinking water. Inadequate sanitation is the primary cause for this. In the urban areas of the world, nearly 100 percent of the industrialized nations have adequate sanitation and about 70 percent of the nonindustrial nations have appropriate sanitation available. Adequate sanitation is available in 95 percent of the rural sectors in the industrialized nations, but in only 20 percent of the rural sectors of the nonindustrialized nations, according to UNESCO data. This lack of adequate sanitation is unfathomable considering the technology available to society. In fact, there is sufficient low-tech technology available that there should be no segment of the population without adequate sanitation. The integrated facultative pond is one approach that has tremendous potential for solving this problem.
With our population continuously growing, causing ever-increasing demands upon our natural resources, the future of our water resources will be reduced even further. It is time for a shift in our thinking. All water should be reused to produce a multitude of valuable products while reducing the demands on our fresh-water resources. For every gallon of water recycled, a gallon of fresh water is reserved for future human consumption. Furthermore, the recycling process itself will contribute to sustained economic development.
RECYCLING OUR WATER
One example of the multiple-use concept is the recycling of water into various aquatic and terrestrial based products. To allow water to be used multiple times, it is necessary to treat the used water to a level suitable to sustain the development and growth of various products. The level of treatment necessary varies depending upon the level of use of the water and the species of the fish and plants being produced. Each level of treatment of the water can be used to produce another valuable product. Based upon the resources available in a region and the potential products the area market can support, specific processes can be enlisted to recycle output water from one process as the input water for another process to create marketable products to grow the rural economy.
A representative illustration is the production of cattle. In this case, the resources required to produce and market a product (the cattle) are land, water, feed, energy and labor. Typical thinking is that the only product that is marketed is the cattle itself; but, that is not truly the case. When all the potential products are recycled, the products become not only the cattle, but also water, nutrients and energy (Figure 1). Now, the water, nutrients and energy are resources that, when combined with plants or fish, can be used to produce another product that has marketable value. In this case, the products are not only the fish or plants produced but also energy and, once more, water. These products can then be used in another business to produce other products of value. The key is completing the mass balance on the water, nutrients and energy to determine what will become the total structure of the system.
A modular production system concept can be used to explain how water recycling can be used to integrate businesses in such a way as to provide sustainable development in terms of both economic development, particularly rural development, and a sustainable environment. The technology used in the modular production system is easily transferable world-wide, making the processes usable even in the least developed regions of the world.
MODULAR PRODUCTION SYSTEM
Recycling livestock waste, both the solid and liquid fractions, into various products is one example of a multiple-use concept. To accomplish this task, it is necessary to treat the livestock waste to a level suitable to sustain the growth of the various plants and fish. The level of treatment necessary varies greatly depending upon the species of both the fish and the plants. In any scenario, each level of treatment of the wastewater can produce another valuable product, many of which can contribute to the fish production system. The basics of the overall process are illustrated in Figure 2. Based upon the resources available in a region and the potential products the local and even global market can support, specific processes will be enlisted to recycle output waste from one process as the input product for another process.
If not properly handled, wastewater generated by livestock, extremely high in organic matter, causes the degradation of water resources through leaching into the water table and nonpoint source pollution of surface waters. This wastewater also contains large quantities of nutrients that are valuable resources for producing various aquatic and terrestrial products. If the wastewater is treated in an anaerobic system (e.g., an anaerobic digester or an integrated facultative pond), the effluent will be high in ammonia-nitrogen. However, a valuable by-product is also produced-methane gas. This ammonia-nitrogen is quite toxic to many species of fish and must, therefore, be either converted or removed. A plant-based system is highly effective in recycling those available nutrients.
Some algae, such as Phormidium boneri, can be grown on the treated wastewater effluent and can remove most of the ammonia-nitrogen present in that effluent within less than two days. The algae are a valuable resource as a food for the fish or it can be used as a protein source for the livestock that supply the wastewater. Note that, in this case, the waste being recycled back to the originating animals goes through two process steps before the recycling process occurs, thus eliminating potential biotoxicity or bioaccumulation problems. Since the wastewater may not be suitable, at this point, for the survival of some species of fish, another process step may be required which will lead to the production of even more valuable by-products such as duckweed (for example Lemna, Spirodela, or Wolffia). Once again, these products can be used as feed for fish or livestock and continue to support sustainable economic growth.
For the fish production process, it is desirable to allow the water to flow through the production facilities continuously as a means of flushing out waste produced by the fish. The effluent water from the previous flow process step is stored in a tank where either algae or more duckweed is grown and harvested. This water is then pumped into the fish tanks while the fish tank effluent flows back into this same storage tank and is recirculated back into the fish tanks. In a properly operating system, this recirculating tank of water supports the growth of algae, which is a highly marketable feed source for fish. In fact, algae are the elements that provide the color to tropical fish, which increases their value substantially in the marketplace. When discussing the need to include algae in the diets of tropical fish, many producers explain that inclusion results in a marketable product while exclusion often results in unmarketability. For this reason, most tropical fish producers either purchase a source of feed that includes an algal product, or they formulate diets with purchased algae.
Tropical fish are not the only fish that can be produced in this type of system. The species tested were koi (Cyprinus carpio), molly (Poecilia latipinna), Platty (Xipmophorus maculatis), Tilapia (Tilapia aurea), Channel catfish (Lctalurus punctatus), Bluegill (Lepomis macrochirus), Fathead minnow (Pimephales promelas), and Redfin shiner (Notropis umbratilis). Each species tested maintained survival rates equivalent to or better than the control tests.
Utilization of the duckweed for animal feeds appears to have benefits that go beyond the value of the protein within the duckweed. Feeding trials conducted with both swine and cattle showed positive benefits when duckweed was included as the protein source vis-à-vis the typical soya or corn based diet. Swine fed the duckweed not only show an increase in average daily gain during a short trial period of 21 days, but they also continued to maintain a higher growth rate even after being removed from the duckweed diet and placed back on the basal diet. For the sheep tested, there was no significant (P In some production systems, an abundance of water flowing through a fish production system provides excess water that can be recycled back into the livestock operation. In view of the fact that fish require a much higher quality of water than cattle and since the water has been treated through several processing steps, the quality is more than sufficient to be used as drinking water for livestock. Another alternative for the discharge water is use on a terrestrial-based crop.
In all the modular production components of a system, there is a certain quantity of biomass that is generated and often requires disposal. Normal disposal in a landfill or similar system is usually expensive and justifies the need to seek an alternative solution. Since the biomass is an organic source, the most likely solution to disposal is the conversion of that biomass to electricity. When this type of process is utilized, the production system has its own power source and, in many situations, will be able to generate more power than is required by the system. The excess energy can then be sold as another marketable product. An additional potential benefit is the utilization of the heat normally emitted by an electrical production system. If aquatic plants or fish are being produced, this excess heat can be utilized to maintain a specific temperature for the production of some higher valued products.
In the U. S., the total quantity of biomass produced annually is sufficient to produce about 800,000 MW of electricity. The total amount of electrical power generation is currently just under 800,000 MW with a current average usage of approximately 550,000 MW. If individual production systems were combined with other production systems to utilize this valuable resource of biomass, the reduced disposal problem would contribute significantly to the profitability of the cooperating industries. In addition, recycling much of this biomass would greatly reduce the negative environmental impact we are experiencing on our water resources via leaching, nonpoint source pollution, etc. Furthermore, the use of biomass for electrical power generation will contribute to the economic development of underdeveloped nations that have neither the fossil fuel resources for energy production nor the economic and technological resources necessary for nuclear production of energy. (See the report in this issue, “Biomass In Green Power Markets.”)
FUTURE OUTLOOK
In the United States alone, if all of the livestock waste produced was recycled by applying it to land for the purpose of growing a crop and the nitrogen and phosphorus were to be applied at average agronomic rates, the land required for utilizing the nitrogen ranges from 1 percent to 13 percent of the total available farmland. When you consider phosphorus, the requirement increases to nearly 30 percent of the available farmland. Not all of the livestock waste can be recycled on the land because the hauling distance often prevents this recycling method from being cost effective. This is the first component of the analysis that explains the need for finding alternative solutions to the handling of generated waste in order to maintain the current quality of life we all enjoy. Now consider the future need. Current projections indicate that our population is expected to double within the next 30 to 50 years. If we expect to maintain the same quality of life we enjoy today, over 60 percent of the available farmland will be required for merely handling the waste generated by our livestock industry. And, this has yet to factor in the need for land used to recycle municipal wastewater.
If only half of the water from our municipal wastewater treatment systems in the U.S. were utilized to irrigate crops, over 4 million acres of crops could be produced. In addition, sufficient freshwater would be saved to permit our population to grow by 40 percent without adding any strain on our currently available resources. Similarly, on a global perspective, if only half of the municipal wastewater was treated and used to produce a crop, over 180 million acres of land could be irrigated. This is equivalent to supplying over two billion people with the levels of water currently used per person in the U.S.
The outlook for the future of our available natural resources, especially water, does not have to be bleak. In parts of the world, water is limited and in many cases the quality of that water is compromised, which leads to major health concerns. Much of that compromised water is the result of a lack of adequate sanitation, yet adequate technology is available to solve the problem in even the most underdeveloped regions of the world. Sufficient low-technology waste treatment systems exist that can be used to significantly reduce the environmental impact caused by not treating wastewater before discharge into our natural streams. If recycling of the waste is considered, the cost of providing treatment is significantly reduced and can provide tremendous economic benefit to the community.
Taking into consideration the facts that available natural resources are finite and that the population will continue to grow, it is appropriate to consider the mechanisms of incorporating water reuse technology in every facet of life. It is not a matter of if we will utilize reuse technology in the future; it is a matter of when we will use it to sustain economic growth and minimize environmental impact.
Clifford Fedler is a Civil Engineering Professor at Texas Tech University in Lubbock as well as Associate Dean of the Graduate School.