Proper concepts and technologies for attaining a sustainable, robust and social-economically affordable protection of the life environment for all people are available. They consist of concepts of Decentralised Sanitation and Resource Recovery and Reuse that are comprised of the use of treatment methods based on the Natural Biological Mineralization Route. The major difficulty is to get these systems/concepts implemented; it is more sociology than technology. Generally the short-term economic interests of well-established structures comprise the major bottleneck for making progress on the route to sustainable and robust public sanitation. However, regarding the enormous social and economic benefits of the decentralized sanitation and resource recovery-concept, natural mineralization-based treatment systems irrevocably will be substitute, for the nowadays applied, highly centralised sanitation concepts with their complex and expensive treatment methods. This process already is on the way in the industrial sector of environmental technology in many countries, while in the public sanitation sector promising developments occur in India and Latin America. Consequently there are reasons to be optimistic for a drastic improvement of the life conditions of the poor.
Billions of poor attempt to survive under dramatic life conditions; they don't look to be of any value by the prosperous part of the world. An international conference on Environmental Protection (EP) focussing on the issue ‘A good life environment for all people’ challenged its participants to look beyond the borders of their own specific fields, that is, to acknowledge notions like ‘common humanity’ and ‘sustainable development’, both essential for future generations and in essence for all people.
It may seem utopian to speak about the realization of ‘a satisfactory (life) environment for all people’ but in fact it is not; because with respect to provision of potable water and universal public sanitation, in essence all required conceptual and technological tools lay ready on the shelf. They comprise: 1) the use of treatment methods for wastewater and wastes based on the ‘Natural Biological Mineralization Route’ (NBMR), if ecologically and economically profitable, completed with various physical-chemical methods, for example for product recovery and refining and 2) the concept of ‘Decentralized Sanitation and Resource Recovery and Reuse’ (DESAR), that is, a concept incorporating Environmental Protection (EP) where transport of wastes and wastewater is kept at an optimal (minimum) level and where pollutants are brought to value, preferentially at the location.
The major bottleneck in the implementation is not the technology, but the fact that these methods/concepts are diametrically opposed to the present practices in the established world of EP, particularly in the public sanitation (PuSan) sector. As elucidated in Figure 1, the NBMR-treatment system implies the use of the biological degradation (mineralization) sequence of organic residues (wastes) as proceeding under natural conditions, that is: a) anaerobic degradation (AnDegr) processes (anaerobic digestion, sulphate reduction, denitrification) as the first main biological treatment step, because they remove/mineralize the organic pollutants and promote formation of very useful by-products, that is, ‘resources’; b) high-rate micro-aerobic processes(MicroAeWT) as first post-treatment step. These systems will take care of: i) the conversion of reduced S-compounds into elementary sulfur (which can be recovered) on the basis of the oxidative part of the Sbiol-cycle; ii) the degradation of part of the remaining, easily biodegradable organic pollutants; iii) the removal of colloidal matter, including dispersed pathogenic organisms, via a coagulation process and/or entrapment in biofilm; c) conventional aerobic treatment systems (AeWT) as a secondary polishing step for removal of the (very) small amounts of remaining biodegradable matter and, if needed, for nitrification of ammonia and d) a biological N-removal process (i.e. nitrification combined with denitrification) or by a physical-chemical removal/recovery step for N-and P-compounds.
In the light of the NBMR-treatment concept, the application of AeWT as the first treatment step is a waste, even though it is the general practice in the modern centralized mode of sanitation (CENSA), that is, for the treatment of wastewater, waste-slurries, and the stabilization of solid organic wastes such as by conventional composting. Despite its generally good treatment performance, conventional AeWT-treatment methods suffer from a number of serious drawbacks as compared to treatment systems based on NBMR (see Table 1).
The drawbacks (still) brought up against the use of modern AnWT-systems as first treatment step, are either hardly relevant or they gradually vanish. So the presumed slow first start-up, the high susceptibility of anaerobic organisms and the relatively small full-scale experience with these systems belong generally to the past. Inherent to the use of AnWT-systems is that they merely remove biodegradable organic matter; the mineralised nutrients (ammonia salts, phosphates, sulphides) are left behind in the solution. However, rather than considering this as a drawback it is an important benefit. There are a variety of appropriate physical-chemical post-treatment methods available to remove and/or to recover these nutrients. Moreover in various cases, for example, in specific DESAR-settings such as even suburban situations, the effluent can be used directly for irrigation and fertilization!
At the Wageningen University, The Netherlands, inspired by the work of the McCarty group (McCarty, 1964; Young and McCarty, 1969) we have been working since 1970 on NBMR-treatment technologies, that is, starting with the development of innovative AnWT systems for low strength industrial wastewaters. Later emphasis was directed to research on systems applying the biological S-cycle (Sbiol), on MicroAeWT post-treatment systems and, particularly, on the development of ‘on-site’ sanitation systems, that is, the DESAR-concept. Worldwide, an increasing number of colleagues in universities, institutes and companies as well as public authorities join in these research issues, frequently inspired by the fact that these systems basically meet all criteria for conservation of mineral resources and other essential criteria for sustainability (see Table 2).
Besides the drawbacks mentioned in Table 1 against the use of AeWT as the first biological treatment step, the present PuSan-CENSA-practice has a number of additional serious drawbacks, mainly due to the excessive extent of centralisation frequently pursued (Table 3).
The implementation of sustainable EP concepts and technologies
With the presently available NBMR-systems a sustainable and robust EP can be realised for everybody. However, unfortunately the implementation of these systems is frequently far from smooth, but there are some reasons for optimism. In the industrial sector enormous progress has been made in the last two decades. Various high rate AnWT-systems have been and still are being successfully implemented, for example, the Anaerobic Filter AF-system, developed in the USA in the sixties by Young and McCarty (1969) and the Upflow Anaerobic Sludge Bed (UASB) system, developed in the Netherlands in the seventies (e.g., Lettinga, 1995, 1996, 2001, 2004), later followed by the expanded granular sludge bed (EGSB) reactor system in the eighties (Kato et al., 1994), a system that is becoming very popular. Moreover, other NBMR-processes have increasingly found their way to full scale application, such as treatment systems based on the Biological S-cycle (Sbiol) (Buisman et al., 1989; Janssen et al., 1995) and new MicroAeWT (Tawfik et al., 2001) and conventional aerobic (post-)treatment systems (Cavalcanti, 2003). Anaerobic waste treatment already is applied for a large variety of industrial wastewaters, including very high and very low strength, easily degradable (e.g., Kato et al., 1994) and ‘highly complex’ wastewaters. These systems are applicable under wide range of temperature conditions, even below 10°C for soluble acidified wastewaters (Rebac et al., 1995, 2001). On the other hand, numerous important useful innovations in the AnWT-process and reactor technology can be foreseen in the near future (Lettinga, 2004) as is certainly the case for the Sbiol–processes, because these offer enormous benefits, such as the removal of H2S from natural gas, of mal-odorous compounds from polluted air, of SO2 from exhaust gases, and for soil remediation and recovery of heavy metals. Similarly, MicroAeWT for post-treatment offers big potentials, and we in these fields are just at the beginning.
Despite the extremely reluctant attitude from the side of the established wastewater treatment world, the UASB process found its way from the university laboratory to full-scale application in the Netherlands in less than six years, first for sugar beet wastewater and later for a large variety of other industrial effluent. This smooth implementation can be attributed to the enforcement of stringent legislation for EP in the Netherlands at that time, because it resulted in a considerable interest of polluting industries in developing and implementing alternative cost economic EP-concepts and technologies. Moreover, it motivated the Dutch ministries to support further research needed for up-scaling and for improvement of the scientific and technological development innovative systems, and of the fundamentals of the anaerobic digestion process, such as the immobilisation of anaerobic bacterial consortia. Polluting industries, the potential users, became highly interested in cheap alternative EP-systems. Some of these industries even became interested to commercialise the new systems. Furthermore, and quite important, the conditions for innovative research at universities were excellent at that time in the Netherlands, that is, with respect to the required infrastructure, such as the formation of lasting research teams and the prospects for researchers to start an academic career. All these factors (some others will be discussed later) were quite positive for the smooth development and implementation of AnWT systems.
The implementation of AnDi processes in the agricultural sector did not proceed successfully in The Netherlands, contrary to countries like China and India, and more recently, Denmark and Germany. The farmers in the field of traditional agriculture in the Netherlands hardly benefited financially from the use of anaerobic digestion mainly due to the low retail prices of energy. Moreover there were few incentives to implement AnDi for reasons of the enforced EP-legislation, because traditional farming generally is a non-polluting sustainable activity. As far as the modern industrialised type of agriculture is concerned (e.g., animal breeding), a serious environmentally polluting activity, the economical benefits for the ‘farmers’ were also marginal, because AnDi cannot solve the enormous EP-problems resulting from this type of farming, that is, dealing with the enormous amounts of mineralised compounds (ammonia, phosphates, potassium) present in the huge amounts of liquid manure produced.
In the public sector of sanitation, PuSan, interest in NMBR-systems so far has remained relatively low and indeed negative, particularly in the prosperous, industrialized parts of the world. Even interest in the progress made in that field with regard to process, technology and possible use under severe conditions is extremely small as can be illustrated by statements of Harremoës (1997), a leading authority during the last decades of the 20th century in the CENSAfield:
‘Local wastewater treatment is not a viable solution in cities, because the approach is either ‘low tech,’ which does not live up to established hygienic requirements and risk assessments, or it is ‘high tech,’ which suffers from energy consumption’ and ‘The present decentralized urban sanitation systems lack adaptability to the urban environment, manageability and control.’
The well established strong consortium of scientists, engineers, contractors, consultancies and water authorities in the PuSan sector that dictates decision making in the field to date has not seriously considered the use of AnWT-systems and/or the DESAR-approach in urban areas as a really feasible option for the treatment of dilute types of complex wastewaters like sewage, particularly not at lower ambient temperatures. A major reason for this negative attitude toward NBMR-systems and the DESAR-approach is on-going ‘big business’ done with the expensive transport and treatment systems used in the CENSA-concept. Initiatives taken from outside the established CENSA-branch to implement DESAR-concepts and NBMR-systems in public sanitation have little chance, because the decisions are mainly made by above-mentioned consortium. Moreover, public environmental protection agencies generally favour the application of proven technologies; they hesitate to take any risk. Therefore, the PuSan-world is not likely to make a very positive contribution with respect to reducing the cost of EP or improving the life environment for the billions of ‘poor’. Rather, the big scale CENSA approach will continue to be pushed and all kinds of developments of expensive sophisticated innovative treatment systems that fit in that approach, for example, the Membrane Bio-reactors (MBR). These may lead to marginal further improvements of the quality of the surface water and possibly to some minor savings in the space requirements of traditional sewage treatment plants, but will not contribute to any improvement of the life conditions of the poor, because they don't meet the criteria for sustainable development (Seghezzo et al., 1998; Seghezzo, 2004).
The matter is quite different in the industrial sanitation sector where the separate industries are capable of rejecting the ‘solutions’ from the established sanitation industry (at least in Europe) and of developing their own systems. The main reason for that is that industries, at least when they are forced by legislation to take adequate measures for waste(water) treatment, can select and/or develop and implement appropriate cost-effective solutions. These systems/concepts are not selected for idealistic reasons but generally simply because they are much more economical. Such a drive, that is, the most economical solution for the society, scarcely exists in the public sector of sanitation. However, in the light of the so much needed ‘sustainable development’, which in essence implies the realisation of a safe world for all people, society has to set the proper priorities (Seghezzo, 2004).
It is fortunate that gradually some promising drastic changes are occurring in the PuSan-sector. Interest in AnWT for sewage pre-treatment is growing (Seghezzo et al., 1998; Seghezzo, 2004; Table 4) particularly in a number of developing countries; these clearly take a leading position in these developments. For instance, interest in AnWT for sewage pre-treatment in countries like India, Colombia, Brazil, Mexico and Colombia is rapidly growing. Numerous full scale AnWT-plants for sewage (pre-) treatment already have been installed in India (Khan et al., 2001; Draaier et al., 1992; Wiegant, 2001) and increasingly in various Latin American countries, for example, Brazil (Foresti, 2001; Chernicharo et al., 2001, 2004), Colombia (Schellinkhout and Callazos, 1992), and in Africa in Ghana a big UASB-reactor has been put in operation (de Mes et al., 2004). Moreover, gradually compact (high rate) post-treatment systems have found their ways to full-scale application, for example in India (Machdar et al., 1997, 2000; Tandukar et al., 2004). There exists clear evidence that occasionally public decision makers have come to the insight that the solutions for EP have to be found in ‘community on-site systems’, in decentralisation instead of centralisation. In China, millions of compact integrated biogas purification tanks have been installed in buildings, hospitals and public toilets (Wang, 2004). These developments justify optimism because even in some countries in the industrialised world the insight is growing that ‘we all’ have to move in the direction of decentralization, resource recovery and self-sufficiency (Zeeman et al., 2000, 2001; Jefferson and Boler, 2001; Larsen et al., 2001; Niemczynowicz, 2001; Wilderer, 2001; Kujawa-Roerleveld et al., 2004) because this will lead to ‘less dependency on specialists.’ And likely this will not remain restricted to the sector of public environmental protection; also other sectors in society may become ‘infected.’
In the meantime, as a result of the experiences with and scientific insight in AnWT-pre-treatment systems for sewage already available, it is possible to realize major improvements in the economy, the sustainability and robustness of CENSA-oriented sewage treatment plants so far using conventional systems. There exist rational arguments to substitute in conventional sewage treatment plants, the primary settler, the AeWT-step, secondary settlers and the sludge digesters by a UASB-Treatment-Settler–Digester (UASB-TSD) system, which in essence comprises the implementation of a one-step UASB-reactor designed for sewage pre-treatment. Such a one-step AnWT-reactor, when extended with a high rate plate separator for removing remaining settable solids in the effluent, can accomplish a substantial pre-treatment efficiency at liquid detention times of 4 to 8 h at sewage temperatures exceeding 18° C, that is, up to 90% of the settleable total suspended solids (TSS), a very high degree of stabilization of the entrapped solids, a high extent of thickening of the digested solids, (up to values ranging from 3 to 9%) and 80 to 90% removal efficiency of the soluble biodegradable organic matter present in the raw sewage, 60 to 80% of the soluble total-COD, and finally a reasonable, though not sufficient, reduction of pathogens. Moreover a major part of the biogas produced can be collected and the release of malodorous compounds to the environment can be completely prevented.
For post-treatment, generally required for the removal of remaining ‘small’ amounts of biodegradable dissolved/dispersed organic matter, dissolved reduced malodorous sulphur-compounds and remaining pathogens, a compact (i.e. micro-) aerobic reactor system will suffice. A variety of reactors systems are suitable for this purpose, including high rate systems such as (modified) conventional AeWT-reactors, for example, a biorotor system (Tawfik et al., 2001; Tawfik, 2002), micro-aerobic EGSB-type reactors (Vogelaar, 2002) or the Micro-aerobic Upflow Sludge Blanket (MUSB) reactors, and/or low-rate treatment systems like duckweed ponds (El-Shafai, 2001; Gijzen, 2001). These new MicroAeWT systems can be operated at very short liquid retention times of 15 to 30 min; the amount of excess sludge produced in these systems is almost negligible. For those cases where the effluent can be utilized directly for irrigation and fertilization, as likely in specific community on-site (DESAR) settings with urban agriculture practices during the growing season, further treatment will not be needed all the year around. In those cases/periods where a high degree of nutrient N-removal would be required (e.g., Pynaert et al., 2001), some conventional or, possibly, newly developed biological, (e.g., the Anamox) process can be applied for N-removal. The application of compact physical-chemical processes based on ammonia stripping and phosphate precipitation look attractive for the removal and recovery of ammonia and phosphate. Latter physical-chemical systems can be possibly combined with a modern (e.g., the EGSB) version of the MicroAeWT for post-treatment (Vogelaar, 2002).
The use of the UASB-TSD-system certainly is not restricted to tropical regions (Lettinga et al., 1983). Results of recent research (Mahmoud et al., 2004; Kujawa-Roeleveld et al., 2004) show that the system is applicable under moderate climate conditions, that is, likely even at low sewage temperatures of about 10°C during the winter season. The UASB-reactor then needs to be combined (integrated) with a sludge digester that, contrary to the UASB-reactor, is operated under optimal mesophilic temperature conditions in order to accomplish a sufficient stabilisation of the sludge accumulating in the UASB-ST system and maintain a sufficiently high methanogenic activity in this treatment unit. For the latter purpose, part of the stabilised sludge needs to be returned to the UASB-TSD reactor. The implementation of the UASB-TSD systems in a ‘conventional’ sewage treatment plant will lead to substantial reductions of the treatment costs and to about 50% savings in the land requirements. Provided that it will be implemented in DESAR-settings, UASB-TSD systems will offer excellent perspectives for realising a good life environment of the poor. It opens the door for these people to more self-sufficiency, not merely in the protection of their environment but also in other respects, such as the production of food. For improving the quality of life of the billions of poor everything possible should be done to prevent the further implementation of the traditional CENSA-approach. In order to realise this, obviously, a strong, independent and objective governmental decision making organisation is needed. This apparently happened in India in the late eighties with the ‘Ganga action plan’; the responsible Indian decision making governmental organisation selected AnWT as pre-treatment for the sewage; the conventional Western solutions (low tech as well as high tech) were considered as technically and economically not feasible and/or affordable for the Indian society. More recently similar developments occurred in Latin American countries. In various of these countries university professors increasingly succeeded in convincing national, state and regional politicians and policymakers of the big social-economic potentials of applying AnWT for achieving a sustainable and robust EP. As in India, established contractors and consultants so far working with the conventional PuSan-systems were forced to start working with the new concepts; if they did not, new contractors would take over their tasks, as happened in the industrial sector of environmental protection in the Netherlands!
The role of entrepreneurs starting the commercialisation of the newly developed systems, generally new comers in the field of environmental technology, has been (and still is) very positive for both the implementation of AnWT and the development of innovative systems in the field of NBMR as well. Some of these entrepreneurs started their activities in the late seventies with the commercialisation of the UASB-process, followed in the eighties with the EGSB-process and later of processes based on Sbiol-cycle and NBMS-post-treatment systems. This could hardly have happened if the field of EP had remained the exclusive monopoly of established consultants and contractors working with the conventional systems, as is the case in the USA, where the implementation of the AnWT, even for treatment of industrial wastewaters, proceeds extremely slowly. As mentioned before, in general also the input of polluting industries in the Netherlands has been positive, mainly because they are keen to implement systems that benefit the economy of the company. On the other hand, as explained above in connection with the developments in the PuSan sector in the industrialised world, the role of the private sector of trade and industry can also be obstructive. This is the case when the introduction of an innovative technology and/or concept might detrimentally affect the market position of the company, even when its impact would be very profitable, socially and economically, for the society as a whole, and particularly for the life conditions of the poor and those of future generations. The ever-ongoing building activities of civil engineering sector, generally advertised under the flag of ‘improvement of infrastructures,’ not only will lead to an unacceptable expensive heritage for coming generations, but also to an unacceptable high vulnerability, in essence to less and less sustainability.
With respect to the protection of the life environment, the PuSan sector in the prosperous world likely will be forced to follow the developments taking place there in the industrial sector and those happening in PuSan sector in developing countries like India, Brazil, Mexico and Colombia. Ultimately citizens, and consequently their representatives in governmental institutions, will become aware that we have available cheap and sustainable alternatives for the expensive and resource wasting established concepts and technologies of environmental protection presently applied in and pushed by the industrialised part of the world. Likely also many of the extremely severe (frequently absurd) standards set for the quality of treated sewage, as proposed by governmental institutions or international organisations will be rejected. Citizens gradually will understand that too severe standards are highly contra-productive for realising a satisfactory quality of the environment for all people at global scale. The AnWT-systems, together with the other technologies based on NBMR, are going to act as a crowbar for getting the required drastic changes, not merely in the way we should protect our life environments, but likely also in other fields in society. There are reasons to believe in the utopia that society is on the route to create better conditions for the well being of all humans, consequently to the development of the creative talents of humans. It will lead to an exciting, inspiring world, where emphasis is put on the conservation and further development of the best renewable source we have!