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Home > Natural Water Treatment > Ecological Design > Towards a Post Engineering Perspective
Towards a Post-Engineering Perspective on Wastewater TreatmentPart of a final report to the Environmental Protection Agency and the Mass Foundation about OAI's activities at the South Burlington facilityConventional chemical and biological wastewater treatment systems are in
widespread use. There exists around them a wealth of literature that detail
operational capacities and technological forms. According to Browne et al
(1) this has perpetuated the myth that water treatment, naturally an ecological
process, can be simplified by excluding complexity above a physiochemical
or microbial level. This perspective has stunted the development of whole
systems treatment technologies and the wastewater field in general.
There is a need to define the technological potential of the biophysiological processes integral to water quality change. This involves investigating the bi-directional interactions between water quality and ecological changes. The bi-directional relationship between the abiota and biota of a system represents the self purification capacity of aquatic systems. At a simple level self purification is the microbial breakdown of complex organic molecules into simple organic molecules together with processes of dilution and sedimentation (Mason, 6). However this is much more complex phenomenom to describe at an ecotechnological level as compared with a biotechnical one. Odum described self purification as self-organization and made it clear that nature's capacity to do so was a potentially powerful tool in the design of living technologies (7). Browne et al (1) have begun to map knowledge between the domains within the natural sciences, including between the biochemical, biological and ecological concepts relevant to water treatment and ecological engineering. Their approach was in a sense taxonomic. For them the need was to classify organisms in such a way as to elucidate their roles as a species and their roles within groups or ecologies. Their goal was to map the biochemistry of a system onto the ecology of the same system using as a mapping function a non-Linnaean classification structure. However organism identification, a Linnaean function, is included as a component of their classification structure. Biological or evolutionary classification is not ecological classification, as the former does not define the biota of natural or ecologically engineered system. On a biological level organisms are classified using the Linnaean taxonomic system. What is needed now is an ecological classification system or ecotaxonomy that can be used to define organisms ecotechnologically with respect to their water quality transition potential. The Browne et al (1) taxonomy defines organisms at a primary level as oxygenators or deoxygenators. Another sub- category defines deoxygenators (animals and surface shading plants) as air gulpers or air breathing aquatic animals. These are tolerant of low oxygen and include some insect larvae and fishes such as the Gouramis. Then they break down the air gulpers into another subcategory defined by whether they directly or indirectly remove solids from the water column. This is further broken down into category that states where in the water column the organisms would be found. The process can create an ecological "family tree" for an organism within an ecosystem. Five ecotypes are created in the classification system. Using these simple set of distinctions they come up with: 1: Gross oxygenators 2: Gross deoxygenating direct solids removers 3: Gross deoxygenating indirect solids removers 4: Air gulping direct solids removers 5: Air gulping indirect solids removers Onto these they superimpose spacial and time factors to create 15 ecotaxa or categories. The ecotaxa building process then is next compounded with a Saprobic Index which includes 4 stages and 4 water quality classes. 1: Polysaprobic, the primary process of decomposition in water quality class iv, which is devoid of oxygen and contains hydrogen sulphide. 2: a-Mesosaprobic, a secondary process of decomposition in water quality class iii, where oxygen is less than 50% saturated and hydrogen sulphide is absent. 3: b-Mesosaprobic, involving progressive mineralization in water quality class ii, with oxygen greater than 50% saturation. 4: Oligosaprobic involving completed mineralization in a class i, oxygen saturated environment. This results in a classification system which include 60 ecotaxa. Three examples here will illustrate the scheme. Tubificid worms (Tubifex tubifex) are Polysaprobic, benthic feeding direct solids removing gross deoxygenators. Rotifer (Keratella cochlearis) is a b-Mesosaprobic midwater, direct solid removing, gross deoxygenator. Blue green alga, Oscillatoria planctonica, is an a-Mesosaprobic, algal, gross oxygenator. This classification allows the structuring of valid self-purifying ecologies for waste treatment. First, it defines organisms in terms of their potential self purification functionality by relating them to one another in terms of an ecological treatment hierarchy based upon solids and nutrient transfer. Secondly, it divides organisms in terms of spatiality of their feeding position and to other organisms in that space. Thirdly, it divides into saprobic types which indicates the biochemical tolerance/intolerance of organisms to the parameter which dictates their functionality, such as BOD. Finally, it enables Linnean species as biomonitors to be classed in accordance to a water quality or water quality change parameter. The overall classification scheme is a beginning insofar as it amalgamates ecological and waste state data. From the ecological designer's point of view it classifies and defines the important niches. It can identify the presence or absence of key species groups in any system. It is the beginning of a new functional taxonomy for ecological engineering. TROPHIC MANAGEMENT In limnology there is a concept which should have great value in ecological engineering of the future. It is called the trophic cascade concept and the extensive research has been summarized by Carpenter and Hall (8). The concept states that nutrient inputs set the potential productivity of lakes and that deviations from the potential are due to food web effects. Nutrient and food web effects are complimentary, not contradictory, but they act at different time scales. Food web effects stem from variability in predator-prey interactions and their effects on community structure. Acting through selective predation variability at the top of the food web cascades through zooplankton down to phytoplankton and microbial communities to influence ecosystem processes. Contemporary population biology and community ecology has determined that consumers are typically selective in the types and sizes of resources they consume. The result is that selective predation from the top down plays a major role in community composition at each trophic level. Predatory fish, for example, determine the size and species composition of planktivorous feeders below them, and these organisms in turn influence the community of herbivorous zooplankton, which in turn regulate the amounts and kinds of phytoplankton which compete for nutrients. This in turn influence the protozoan and microbial community structure. Protozoa can be dramatically reduced by large zooplankton and bacterial division and population growth has been shown to be surpressed by the presence of phytoplankton. Even nutrient levels are determined by cascade concepts. In one lake system for example predatory insects (Chaoborus) and piscivorous bass contained 20-25% of the phosphorus (8). Trophic cascade concepts have been applied to the biomanipulation of lakes towards humanly determined ends (Gulati et al, 9). This included reducing hypolimnetic oxygen depletion, blue green algae blooms and littoral macrophytes. They have rarely been applied to the management of wastewater mesocosms. The cellular design of the living machines allows for a high degree of trophic management. For example, snails, whose eggs are eaten by fish, can be physically separated from fish confined to specific cells. As a result snail numbers numbers can increase to the point where they can reduce sludge volumes dramatically. This has been demonstrated in the test train at South Burlington. Oxygen can be regulated to favor bacteria over protozoa and further downstream to reverse the relationship favoring protozoa over bacteria. Detritivorous fishes and zooplankton be placed at various stages in the process to influence the ecology and performance. Algae and attached algae communities can be favored in certain cells to increase nutrient uptake, increase pH, sequester metals and generate oxygen for free through photosynthesis. All of these strategies can be made to work on behalf of the performance of the living system. They do however need to be codified and confirmed through population--performance studies. To my knowledge no research support has ever gone to a combined taxonomic and treatment performance study of a mesocosm designed to treat wastes. SUCCESSION AND THE ECOLOGY OF INVASIONS If a field is plowed and then left alone, re-invasion takes place. First, annual weeds take hold, followed by grasses and perennials. After a time a meadow appears after the major plant groups, cool season grasses, warm season grasses, legumes and members of the sunflower family become established. Then in ensuing years woody shrubs invade which set the stage for trees. First fast growing invasive tree species become established followed in subsequent years by the forest dominants which provide the framework for an emerging woods. Each step in this succession is predicated on the stage before it. Each stage lays the template for the next. This dynamic process creates structure and organization, and at each stage the ability of the system to close loops and manage perturbations increases. No Living Machine has ever been given the opportunity to go through a successional process like the one just described. The reason for this is that Living Machines are relatively isolated from the ecology of invasions. This is due in part to the fact that they are housed in greenhouses and screen houses or are located in very urban settings. During ramp up, the Living Machines are seeded with organisms from wild aquatic environments. This seeding is continued sporadically for perhaps the first year. After this the systems are typically left to self organize and self design. They are truncated in successional terms, remaining at the ecological equivalent of the weedy field. As a consequence the vast majority of species originally seeded do not find the appropriate conditions for their survival. System extinction rates are high because the state of the system is not analagous to the successional stage of the parent or "wild"systems from which the organisms were derived. James Drake and Stuart Pimm at the University of Tennessee study what it takes to arrive at an assembly of species that remain in equilibrium a condition that would be desirable for a Living Machine (10). They undertake experiments with ecosystems, in computer based artificial life systems and with aquatic organisms in aquaria. They begin by adding species in various combinations and then letting them work out who will survive and in what ratio. Eventually, without intervention, the community shakes down into something that is both complex and persistent-order for free. According to Pimm "We don't get order immediately. We get it after a long period of adding species to communities and watching them come in, displace other species, and go extinct in turns" In other words, having a history is what makes a community last. Stuart Pimm has a "Humpty Dumpty" hypothesis which is relevant to the ecological design of living technologies. Pimm maintains that once a community assembly is destroyed, a forest for example, you can't just plant the same species back and expect to put it together again. There is no such thing as an instant forest. It needs a successional history. Some plants will invade and others will drop out. All the species change the soil and the fauna and flora around them. They make it possible for the final assembly to be there. For the ecological engineer the challenge is to get that order relatively quickly. Complex persistent systems that shake down within a very few years are the goal to which we must aspire. We do not yet know the capabilities or capacities of a highly evolved, species rich and persistent Living Machine. There is little doubt that its performance will surprise us. LIGHT AND PHOTOSYNTHETIC MANAGEMENT Except for the deep water oceanic thermal vents, sunlight is the primary driver for all persistent ecosystems. Contemporary waste treatment does not use solar energy as a determinant in the waste conversion process. The original Solar Aquatic™ patents, developed by Todd and Silverstein, used clear-sided tanks to allow for sunlight to penetrate into the cells. These patents have closely held by their corporate owners and few Solar Aquatic™ systems have been built. However Solar Aquatic systems have proven effective at removing heavy metals via uptake into algae communities which attach to the tank sides, and for breaking down many of the EPA priority pollutants (3). At South Burlington sunlight is a primary energy source having supported over three hundred species of higher plants rafted and grown on the surface of the tanks and in constructed wetlands within the greenhouse. Supplemental lighting has not been used at South Burlington other than for visibility after dark. Horticulture in northern climates is based upon supplemental lighting. Applying supplemental lighting in the operation of Living Machines should be investigated in the future. If commercial crops are part of the treatment process, the additional energy required would be cost effective. Supplemental lighting could also boost performance through increased plant root growth and production of exudates or saps from the plant roots which benefit the attached growth microbial communities. Living Machines need to utilize sunlight and supplemental light in other ways to diversify their ecologies. Algae growth in certain cells within the treatment train needs to be promoted for ecological reasons. Algae are environmental oxygenators " for free", have the ability to neutralize and stabilize pH, consume excess carbon dioxide, uptake heavy metals and utilize nutrients including ammonia and phosphorus. It would be wise to direct natural daylight and artificial light onto selected cells in which no higher plants, which ordinarily shade the water column, grow. It is proposed that artificial substrates be established, such as screening, to allow attached algae communities to become part of the Living Machine community of organisms. These attached algae systems are potent water purifying systems (2). They belong at about the midpoint in the treatment process. Algae in the system could be harvested by grazing snails and native fishes of the Catostomidae family. It would be interesting to experiment with light concentrators to beam intense light into algae based cells. Fiber optics might be used here. This would help compensate for the shading caused by turbidity at the midpoint in the treatment process. The intense light would allow for a more diverse photosynthetic community and possibly even more persistent biological structure in the algae based cells. As long as clear sided tanks are not permitted (patent protection) in wastewater treatment, concentrating light makes sense and should be explored technologically. Light is a limiting factor in wastewater treatment. Large amounts of electrical energy to oxygenate the water are required in conventional systems to compensate in part for the absence of internal photosynthesis. ECONOMIC ANALOGS The botanical research at South Burlington involving several hundred species of plants has yielded important information about plant groups and their adaptability to use in wastewater treatment. Ten families of plants have representatives in the most favored category. These include Salicaceae (ten species), Araceae (five species), Cyperaceae (three species) Gramineae (two species) and Iridaceae, Juncaceae, Marantaceae, Ranunculaceae, Saururaceae, Zingiberaceae each with one species to date. The majority of these families have representatives that have commercial value. An example of an economic crop that is a top ranked plant in the system is the Calla Lily , Zantedeschia aethiopica, in the Araceae family, It blooms widely throughout the year and most prolifically in May and June. The flowers retail locally for $ 5 to $ 8 per stem. Calla Lilies represent the tip of the economic iceberg. Medical, herbal and floricultural plants as well as valuable trees such as the bald cypress, Taxodium distichum, can be readily grown in the system. Any effort to link higher plant based waste treatment with economic crops will pay off and multiple revenue streams for Living Machines. The same approach can be applied to the water column. Many species of ornamental fish, pet feed species and bait fish can derive their dietary needs from biosolids generated within the facility. We have demonstrated in the Frederick, Maryland, Providence, Rhode Island and San Francisco, Living Machines that Koi, goldfish, fathead minnows and golden shiners grow well on solids pumped from clarifiers to fish holding tanks. In the case of Koi and goldfish they have done well in the clarifiers themselves. Koi purchased in bulk for ninety-nine cents apiece had a wholesale value just under ten dollars after nine months in the Frederick Living Machine. Fish culture was not an interest for the Living Technologies Inc. team operating the South Burlington facility. However the potential for growing fish on waste cycles is being developed by the Ocean Arks group at the Intervale Living Machine in Burlington, Vermont. It is our view that Living Machines that treat wastes can become economic engines in their own right. This should be a major direction for technological innovation. CONCLUSION Guterstam rightly criticized many facets of contemporary waste treatment (5). Many of the criticisms have been countered and solved by the development of Living Machines, since the first facility was built in Warren, Vermont in 1986. At South Burlington, as well as at other facilities, the volumes of sludge wasted have been dramatically reduced. The Living Machine at Findhorn in Scotland has yet to waste any solids after almost five years of operation. On site management and treatment of solids has proven feasible at a number of facilities, including commercial facilities treating food industry wastes. The test train research at South Burlington suggests that Living Machines can utilize biosolids within internal food webs. Guterstam's concern about the use of toxic chemicals is avoided through the use of Living Machines. The only chemical used in South Burlington is methanol. This source of organic carbon to support denitrification has been eliminated in treatment line B through the use of endogenous carbon in anoxic reactors. Work at Providence, Rhode Island and has shown that Living Machines can sequester heavy metals and produce an effluent that meets drinking water standards for these elements. The Harwich, Massachusetts Living Machines demonstrated the removal of synthetic organic chemicals, including fourteen EPA priority pollutants. Guterstam was concerned with engineering difficulties within the waste treatment industry associated with dealing with fine suspended solids and colloidal materials. These may have been solved, in part, through the incorporation into Living Machines of higher plants and their root communities, as well as through the use of ecological fluidized beds (EFB's) and constructed wetland filters. Finally, Guterstam was critical of the costs of conventional waste treatment including capital costs, energy, chemicals and labor. While Living Machines to date have not dramatically reduced the capital or energy costs, they have all but eliminated the chemical costs. Labor, in most cases, is comparable with the Living Machine. However as Living Machines increasing become economic engines, labor costs will be seen as an asset and a resource, rather than a liability. The future of Living Machine development lies in improving the ecological communities within the systems themselves, and in converting them to integrated resource utilization technologies that are economically defined. Through ecology and economics lies the future of waste treatment. REFERENCES
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