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tions an indigenous microbial population exists and that degradation has already occurred and is continuing. To support or enhance this natural self-curing ability, bioaugmentation and biostimulation technologies are available and sometimes suitable. In all situations, degradation rates, degradation efficiency, and groundwater flow rates should be carefully monitored, and the remediation area should be planned far enough downstream in the groundwater to avoid transportation of contaminants or metabolites out of the remediation field. By construction of funnel- and-gate systems (reactive walls) at the downstream end of the remediation field, nondegraded contaminants and residual metabolites can be adsorbed onto activated carbon or other suitable materials and be prevented from migrating into noncontaminated areas.
19.6
Drinking Water Preparation
If the groundwater contains toxic substances as a consequence of soil pollution by leachates from sanitary landfills, production residues, spillages from industry, overfertilization, or insecticide and pesticide application in agriculture, these substances must be separated quantitatively during water processing for drinking water preparation. Separation, filtration, and sanitizing procedures have been developed and have reached high technological levels. Since contamination of groundwater is still increasing and many contaminants remain for decades, water purification procedures must have high priority now and in the future, especially since drinking water resources are limited.
In arid countries with access to saline seawater, the water must be desalted by membrane-based seawater desalting processes to obtain salt-free process water or drinking water.
Although techniques for complete purification of wastewater are in principle available, the application of these multistep procedures to drinking water preparation is not likely in the near future, because of the very high water processing costs and the availability of less polluted water sources.
19.7
Future Strategies to Reduce Pollution and Conserve a Natural, Healthy Environment
In industrialized countries the main strategy for handling domestic and industrial wastewater seems to be set for years or even decades, due to high investments in sewer systems and in what is considered modern wastewater treatment facilities. High-efficiency removal of carbon, nitrogen, and phosphate was intended in the past as a way to avoid damage to the receiving ecosystems.
In Germany, centralized treatment centers fed with hundreds of miles of sewers and many pumping stations have been almost completed for domestic wastewater treatment. ‘Spot solutions’ for new residential areas, single houses, or small villages
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should be promoted to gain experience with the new small-scale process alternatives.
The real challenge for wastewater purification arises in many developing countries lacking sewer systems and often lacking any wastewater treatment. Central treatment units are unaffordable, and even if they existed the sewer systems would not be capable of handling the masses of rainwater during the rainy season. This is why decentralized wastewater and waste treatment should be favored. ‘Decentralized’ in this context should range from single-house solutions, neighborhood solutions for a few houses, wastewater treatment solutions for a residential area or municipality, to solutions for a certain geologically defined area of human settlement. If the whole infrastructure for wastewater collection and treatment must be designed, the best solution would be the one with the shortest overall sewer length. Due to the still-unreliable electric supply outside the megacities, small-scale treatment systems should be reduced to the basic components as a starting technology, requiring little or no electricity and no skilled personnel for maintenance. Decentralized wastewater management should be favored, not only because imitating the systems of industrialized countries would not be affordable, but because the wastewater resources could be better used. Domestic wastewater and wastes, if properly collected and treated, can be upgraded to yield valuable nitrogenand phosphate-rich fertilizers and thus save money otherwise spent on mineral fertilizers. By decentralized treatment, more nontoxic wastewater, sewage sludge, or waste compost as a source of nitrogen and phosphate is available for treating local farmland, and transport distances are short.
A process development that goes hand in hand with investigations on the respective microbiology is very important for the future development of wastewater treatment. Microbial reaction rates are higher in equatorial countries due to the high average annual temperatures.
Future microbial investigations for wastewater treatment should start with the complex ecophysiology and end with tracing and optimizing single microbial bottleneck reactions. As recently experienced with the Anammox (anaerobic ammonia oxidation) process, microbiology often seems to lag behind technical verification. Other new procedures for the removal of nitrogen from domestic or industrial wastewater are at the stage of pilotor technical-scale testing. In parallel, microbiologists are elucidating the biochemical basis of the relevant reactions.
Although in some branches of the food and feed industries, starter cultures or even enzymes are now essential tools for production, the advantage of a broad application of starter cultures to wastewater treatment (bioaugmentation) in order to improve purification efficiencies or to degrade trace compounds is not yet widely recognized. Most reports refer to laboratory-scale experiments; only a few full-scale tests have been reported. Starter cultures containing genetically engineered specialists for metabolizing certain xenobiotics that periodically appear in more than trace concentrations may, however, help to introduce or stabilize the required metabolic capabilities. Starter cultures containing an ‘omnipotent’ population may be seeded only after complete process failure due to the presence of toxins, to reestablish the microbial degradation potential more quickly in wastewater treatment plants receiv-
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ing wastewater having little indigenous population. Biostimulation of the autochthonic population by addition of extra substrates or electron acceptors is an alternative to be considered.
A major problem at present and in the future is the handling of surplus sludge from wastewater treatment. Dewatering procedures must be improved, and new and better sludge disintegration methods must be developed. Although in some examples the microbiological basis for the formation of bulking sludge is understood, reliable microbiological counteractions to prevent bulking are not yet available. For sludge disintegration, enzyme engineering should in the future create new, stable, and powerful lytic enzymes.
For water management in new residential areas, developments might go in the direction of dual water supply, on-spot treatment of slightly polluted wastewater, and seepage of purified wastewater in especially designed ecosystems. Concentrated wastewater streams should also be treated near to where they are generated. New residential areas must be planned with few paved areas (or existing paved areas should be depaved), so as to retain most of the rainwater for replenishing the groundwater.
Industrial production processes with better product-to-wastes ratios have to be developed by applying new production processes or by more efficient utilization of the water, e.g., by internal water cycling. Tailor-made treatment systems for every wastewater stream should be optimized, with emphasis on production procedures and on microbiological capabilities, including the use of starter cultures (bioaugmentation).
The slogan ‘the waste of one company is the raw material of another’ should be promoted worldwide and may be facilitated by creation of appropriate databanks. Retail prices for all goods, including those imported from developing countries, should include the full, real, or fictive costs for wastewater and residue treatment.
The potential to reduce the total amount of solid wastes in the future must be fully exploited, in particular by the packaging industry. Improvement of distribution logistics may help to prevent one-way single-product packaging, pallet-level packing and another layer of packaging for transport of larger package units.
Since incineration is the most expensive waste destruction system, it should be reserved only for those fractions that cannot be recycled or reutilized. Biowaste composting and biowaste methanation are options for organic waste fractions having a high content of naturally occurring organics. Cofermentation of biowaste fractions with sewage sludge may also be taken into consideration, if excess digester volume is available and the sewage sludge is free of toxins. Combined mechanical and biological waste inertization could be an alternative to incineration, but cannot achieve the low carbon content required by the deposition guideline of the EU.
In developing countries, direct reutilization of wastewater or wastes or product recycling seems to be more distributed than in highly industrialized countries, due to a shortage of raw materials or to restricted production or affordability. This is especially true for, e.g., plastic bottles and containers, which are often one-way articles in industrialized countries, but are reutilized several times in developing countries.
In industrialized countries, drinking water management must in the future take care of trace pollutants that have unknown effects on human health. New methods
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to analyze and separate residual agricultural and household chemicals and their metabolites must be developed.
Due to the high number of contaminated areas in almost every country and due to limited budgets for soil remediation, such areas should be ranked according to environmental risk. Then soil remediation techniques should be chosen that will prevent further migration of the contaminants or their possibly toxic reaction products. In addition to the common techniques for groundwater treatment (pump-and-treat, funnel-and-gate systems and reactive barriers) increasingly have to be used. For natural attenuation of contaminated areas, gen probe methods must be developed to analyze the biological or biochemical potential in-situ or from in-situ samples. In the U.S. the Environmental Protection Agency requires proof of the degradative capability of the in-situ population.
For treatment of sites with low contaminant concentrations, phytoremediation approaches for metals and organics, e.g., nitro compounds and polycyclic aromatic hydrocarbons, increasingly have to be tested. Together with other near-natural processes and the monitored natural attenuation procedures, sustainable strategies have to be developed to overcome the problems of contaminated sites. Furthermore, a variety of bacterial species and enzymes have been the target of genetic engineering to improve the performance of biodegradation, control degradation processes, and detect chemical pollutants and their bioavailability. Avoidance of environmental contamination is the future challenge for which suitable and sustainable strategies can be achieved only by an interdisciplinary collaboration between all protagonists in research and industry. The wide-ranging experience accumulated with respect to the contamination of soils and groundwater must provide a special impetus for testing the environmental impact of new chemical products before they are introduced, thus preventing subsequent contamination and undesirable reactions, such as the endocrine disruption suspected to be caused by Bisphenyl A. A benign ‘design chemistry’ would, therefore, have to concentrate research on identifying forms of bonding that facilitate the development of biodegradable and environmentally sound chemical products.
The supply of good-quality drinking water must especially be improved in developing countries. to reduce mortality, especially in children. Groundwater pumping from deep wells often exceeds the amount of newly formed groundwater, so wells are drilled deeper and deeper. In coastal regions this may lead to salt water infiltration, which contaminates the sweet water reserves.
Wastewater seepage and groundwater pumping often occur close together, too close to maintain a sufficient purification distance for complete degradation and sufficient sanitization. Contamination of well water with pathogenic microorganisms is favored by this mismanagement and in warm climates causes epidemics.
Off-gas purification by biological means has seen much-increased use in the past. For biological off-gas purification, existing gas ventilation, washing, and filtration techniques and the appropriate technical equipment must be improved further.
