IDRC: Research Programs: Cities Feeding People: Reports
Index |
| IDRC: Research Programs: Cities Feeding People: Reports
Index |
PART I: SANITATION AND WASTEWATER RESOURCE RECOVERY 1.0 INTRODUCTION 2.0 WASTEWATER MANAGEMENT
2.2 COSTS OF (NOT) PROVIDING ADEQUATE SANITATION 2.3 URBAN AGRICULTURE AND WASTEWATER RESOURCES
3.2 MECHANISED VS. NON-MECHANISED WASTEWATER TREATMENT 3.3 ON-SITE SANITATION 3.4 DECENTRALISED URBAN CATCHMENT AREAS 6.0 SEGREGATING URBAN WASTEWATER RESOURCES 7.0 INTEGRATED RECOVERY
7.2 ADVANCED SOLAR TECHNOLOGY 7.3 THE MAYSARA PROJECT: INTEGRATED WASTE MANAGEMENT FACILITY 8.0 LAND-BASED TREATMENT TECHNOLOGIES
8.2 HOUSEHOLD-LEVEL/ON-SITE TREATMENT SYSTEMS
8.2.2 Composting Toilets and Wastewater Garden 8.2.3 DAFF Latrines
8.3.2 Biogas Reactors 8.3.3 Recent developments in biogas technology
9.2 NEIGHBOURHOOD-LEVEL/OFF-SITE CONSTRUCTED WETLANDS
9.2.2 Free Water Surface Wetlands
9.3.2 Disease vector management 9.3.3 Water Hyancinth 9.3.4 Duckweed
9.3.4.2 GreenGold Corporation
9.4.2 Stabilisation ponds and supporting growth media 9.4.3 Advanced integrated ponds systems
10.2 SLUDGE REUSE IN EGYPTIAN AGRICULTURE PART III: CONCLUSIONS AND RECOMMENDATIONS 11.0 CONCLUSIONS AND RECOMMENDATIONS ANNEX II: INTERNET RESOURCES ANNEX III: IDRC PROJECTS IN WASTE MANAGEMENT (1974 - 1997) ANNEX IV: REPORT CONTACTS
Urban environmental management is one of the most pressing issues as the urbanisation trend continues globally. Among the challenges faced by urban planners and managers is the need to ensure ongoing basic human services such as the provision of water and sanitation. The under-management of domestic wastewater in many southern urban areas presents a major challenge. The accumulation of human bio-waste is constant and unmanaged wastewater directly contributes to the contamination of locally available fresh water supplies. Additionally, the cumulative results of unmanaged wastewater can have broad degenerative effects on both public and ecosystem health. The replication of centralised, highly engineered human waste management systems resultant of sanitary reforms of the 19th century have not been successful in many developing world contexts. The report suggests that emergent trends in low-cost, decentralised naturally-based infrastructure and urban wastewater management that promotes the recovery and reuse of wastewater resources are increasingly relevant. The concept of managing urban wastewater flows at a decentralised or "intermediate" level, based on micro-watersheds is explored. The report reveals how innovative and appropriate technologies can contribute to urban wastewater treatment and reuse and reviews the effluent treatment standards that are currently accepted in order to protect public health and safety. The concept of planning integrated wastewater management strategies in conjunction with an urban agricultural "waste-sink" is suggested as a rational approach to waste management and the conservation of valuable urban resources. Urban waste management can and must be transformed from a disposal-based linear system to a recovery-based closed-loop system that promotes the conservation of water and nutrient resources and contributes to public health. Moreover, it is apparent from the literature that both the knowledge and the technology exist that can enable this transformation. There is a gap, however, between the current availability of innovative technology and the promotion/financing of demonstration level projects as well as the development of complementary socioeconomic methodologies to facilitate their implementation. The majority of this report comprises a general technology review and explores a series of wastewater treatment technologies that are low-cost, potentially appropriate for urban environments and will enable the reuse of wastewater in agriculture production. Conventional and highly engineered wastewater management technologies and strategies often focus on electro-mechanical solutions that are capital intensive and require ongoing capital investments for effective operation. Additionally, these systems have shorter life-cycles compared to many alternative and naturally-based technologies which also offer opportunities for resource recovery. This problem necessitates the need for sponsorship and funding of demonstration-level, self-help sanitation systems and treatment technologies that facilitate the reclamation and recycling of urban organic wastewater resources. Overall, the report aims to contribute to the ongoing development of
low-cost options for the closed-loop recovery and reuse of organic waste
resources in urban environments. The development of zero-discharge urban
wastewater management strategies will contribute to a reduction in the
pathogenic contamination of surface and groundwater and aid in protecting
the vitality of urban dwellers. Organic waste recovery can result in
production inputs for urban agriculture, enhance food security and link
different sectors of local economies. De-centralised, organic waste
recovery systems that integrate the best available low-technology in the
recovery of urban domestic wastewater flows are essential and appropriate
components in the promotion of a comprehensive urban ecosystem health
strategy.
This report is the product of a five-month Centre Internship at the International Development Research Centre - Cities Feeding People Programme Initiative (CFP) during the summer of 1999. The report was commissioned to provide CFP team members an overview of emergent trends in environmentally sound and economically viable approaches to wastewater management. The subject of the report relates to the management of domestic human waste in urban environments and focuses on alternatives to centralised electro-mechanical treatment technologies such as activated sludge facilities. The aim of the report is to review recent developments in wastewater treatment and reuse that may contribute to providing low-cost sanitation and improved public health with the added benefit of conserving fresh water resources, improving soil integrity and contributing inputs for urban agriculture. The report presents alternatives to sanitation systems dependent on large distance water-borne conveyance and high-energy inputs for their operation. Natural or naturally-based wastewater treatment technologies are defined in this report as those that employ natural processes (biological, physical or solar elements) to achieve a desired level of treatment. Naturally-based approaches are also defined in this paper as having one or more of the following characteristics:
The report will focus mainly on approaches or treatment technologies capable of three end goals:
ii) to facilitate the recovery of nutrient and water resources for reuse in agricultural production, the irrigation of municipal greenbelts/parks and maintenance of other landscape amenities, and; iii) to reduce the overall user-demand for water resources. The report is organised in the following manner. It is divided into three sections; a conceptual framework describing the organisation of the report is presented in Figure 1.1 (1200K).
(B) Treatment & Recovery Options; and, (C) Conclusions & Recommendations. The report contains 4 annexes.
Domestic human waste is defined in this paper as human excreta, urine, and the associated sludge (collectively known as blackwater), as well as, kitchen wastewater and wastewater generated through bathing (collectively known as greywater). The term wastewater will be used through the report to collectivley define domestic human waste. Industrial wastewater is not encompassed in this definition of wastewater. Co-composting of solid organic waste and human faecal sludge is considered a viable approach to human waste management, and advances continue to be made in the development of suitable processes; however, co-composting processes will not be considered in this report (Obeng and Wright, 1987; Lardinois and van de Klundert, 1993; Strauss, 1996). Throughout the report the term on-site will be used synonymously with the term household-level and the term off-site will be used synonymously with the term neighbourhood-level to imply that the technology in mention is best suited for family or communal use.
2.0 WASTEWATER MANAGEMENT In the year 2015 the majority of the global population (over 5 billion) will live in urban environments (UN, 1997). By the year 2000, there will be 23 mega-cities with a population of over 10 million each, 18 of which will exist in the developing world (Black, 1994). Central to the urbanisation phenomena are the problems associated with providing municipal services and water sector infrastructure, including the provision of both fresh water resources and sanitation services. Currently, providing housing, health care, social services, and access to basic human needs infrastructure, such as clean water and the disposal of effluent, presents major challenges to engineers, planners and politicians (Black, 1994; Giles and Brown, 1997). In developing counties, 300 million urban residents have no access to sanitation and it is mainly low- income urban dwellers who are affected by lack of sanitation infrastructure (Forget, 1992; Briscoe and Steer, 1993; Black, 1994; Veenestra and Alaerts, 1996; Giles and Brown, 1997). Approximately two- thirds of the population in the developing world have no hygienic means of disposing of excreta and an even greater number lack adequate means of disposing of total wastewater (Sinnatamby, 1990; Niemczynowicz, 1996). Unfortunately, the International Water Decade paid insufficient attention to the issue of sanitation and wastewater reuse in the developing world (Alaerts el al., 1993). Although fresh water systems have been increasingly developed for the urban poor, urban drainage and sanitation systems have not been scaled-up proportionally; this has led to grossly unsanitary conditions that threaten the re-emergence of plague and pestilence in the developing world (WHO, 1987; Munasinghe, 1992; Black, 1994; Giles and Brown, 1997). The 1992 UNCED Earth Summit and the resultant programme for action or
Agenda 21, emphasized the urgency in addressing the urban
environmental problems of pollution and environmental hazards endemic to
urban areas of the developing world (Leitman, 1994; Alaerts et
al., 1993). Agenda 21 outlined specific actions to promote
environmentally-sound urban waste
management, including the maximisation of waste reuse and
recycling (UNCED, 1992). However, Agenda 21 failed to highlight or
promote specific waste reuse and recycling methods related to
sanitation, and gave no indication as to the level of technology
that would be most appropriate to pursue in the developing world (Sanchez,
1993; Otterpohl et al., 1998).
Innovative approaches and new methodologies for protecting public
health, recovering nutrient resources and protecting water resources from
pollution are necessary (Asano and Levine, 1996; Harremöes, 1997; Sanio
et al., 1998). A resounding expression of the need for immediate
action in the developing world has been made (Chan, 1996; Niemczynowicz,
1993, 1996). Integrated, zero-discharge, and wastewater reuse strategies
are the emerging concept in municipal wastewater reuse at this time and
the development and dissemination of viable alternatives for urban
wastewater reuse is essential (Bouwer, 1993b; ICIBS, 1998).
2.2 Costs of (Not) Providing Adequate Sanitation Conventional conveyance and treatment infrastructure, engineered during 19th century sanitary reform has contributed to the high degree of sanitation and public health experienced in many cities today. Pathogenic waste is isolated and conveyed away from potential human contact and has decreased the threat of major epidemics of less than a century ago (Fahm, 1980; Angelakis et al., 1995). This is not the case in most parts of the developing world. The problem in the developing world today, according to Black (1994:11), is that "public health engineering solutions based on 19th century precepts of centralised systems built and maintained by subsidised public agencies are inappropriate to the extraordinary pace and character ofthe contemporary urbanisation process in the developing world". The initial capital costs of providing effective sanitation services can be high. The approximate cost of constructing sanitation systems ranges from $ 75-150 for a twin pit pour-flush latrine, to $600 - 1,200 for a conventional sewerage system [1990 prices - US$] (Hardoy and Satterthwaite, 1990). According to Grau (1994), countries with a per capita GNP of less than $500 do not have the resources to construct treatment facilities and cannot maintain them (Niemczynowicz, 1996). Additionally, the water resources consumed in some sanitation systems can be very high. In the developing world, flush toilets can consume 20-40 percent of the domestic water resources used in a sewered city (Sanio et al.,1998). Preventing pollution through engineered solutions is often expensive and sometimes inappropriate depending on the context as these solutions often depend on high energy inputs, expert operator skills and continued maintenance expenditures (Edwards, 1985; Chan, 1996; Boller, 1997). The implementation of engineered solutions may also cause external and intangible ecological damage to adjacent ecosystems. Any benefits that may result are often to the advantage of a local region, but often to the disadvantage of the larger society or environment based on the cost of the solution and external impacts (i.e., downstream impacts) (Yan and Ma, 1991; Munasinghe, 1992). The hygienic urban water supply, sewerage systems and many technologies of the last century are now in question with regards to their environmental efficiency and sustainability and new alternatives must be found (Niemczynowicz, 1993; Harremöes, 1997). The human and socioeconomic costs of unmanaged and under-managed domestic waste are also very high (Munasinghe, 1992). In India, the 1994 plague epidemic resulted in a loss of tourism revenue estimated at $US 200 million; in Peru, a recent cholera epidemic resulted in an estimated loss amounting to three times the expenditure on water and sanitation for the entire country over the preceding 10 years; and in Shanghai, China a recent major outbreak of hepatitis A was attributed to sewerage contamination (Munasinghe, 1992; Giles and Brown, 1997). The economic benefits of reusing human wastes in agriculture can be
realised at the farm level through supplementing the use of inorganic
chemical fertilisers with reclaimed organic fertiliser derived from
bio-waste (Sanio et al., 1998). The benefits of reusing these
organic wastes must also be measured against the cost of not doing
so at both the economic and environmental level (Fahm, 1980; Gardner,
1998; Sanio et al., 1998). Marine environment pollution is now
global, and is of key concern top several governmental and
non-governmental organisations (Ahmad, 1990; World Resource Institute
et al., 1996). Munasinghe (1992), has noted that World Bank
data for the Eastern Mediterranean and North Africa region
indicates serious aquatic pollution due to the failures to treat
wastewater flows. Even the discharge of treated sewage presents a
detrimental impact on coastal ecosystems and is a great loss of
nutrient resources (Appasamy and Lundqvist, 1993). However, the costs of
implementing zero- discharge organic waste to agriculture recycling
schemes may be not be expensive. Full-scale implementation of urban
organic waste to agriculture systems could cost as little as US $5 to $6
million for a city of 1 million people (Sanio et al., 1998).
2.3 Urban Agriculture and Wastewater Resources According to Scott (1952:21), Winfield defined Agricultural Sanitation as "the successful sanitation of the environment of man and his domestic animals by means which are an integral part of sound agricultural practice". More recently, Otterpohi et al. (1998) defined sanitation as having two functions: i) to maintain the highest level of hygienic standards for humans and, ii) to keep soil fertile. The recycling of organic waste resources is just one aspect of a multi-dimensional and comprehensive approach to upgrading the quality of urban environments and protecting the environmental resources and aesthetic amenities of the hinterlands surrounding urban centres. Cointreau et al. (1984) have stated that sustainable resource recovery and utilization are essential elements of living within finite resources and that resource reuse must be economically justified. Urban Agriculture (UA) may provide that economic justification because producing food and fibre close to urban centres means jobs for people. More importantly, UA can provide the basis for effective wastewater management through providing a sustainable re-distribution of organic nutrients and soil conditioners for agricultural production in urban and peri-urban environments (UNDP, 1996; Gardner, 1998; Furedy, et al., forthcoming). Facilitating two-way organic waste nutrient cycles, from point-of-generation to point-of- production, closes the resource loop and provides a viable approach for the management of valuable wastewater resources (Gardner, 1998; Harsch, 1996; de Zeeuw, 1996; Otterpohl et al., 1997; 1998). Failing to recover organic wastewater from urban areas means a huge loss of life- supporting resources that instead of being used in agriculture for food production, fill rivers with polluted water (Niemczynowicz, 1996). Urban Agriculture draws on the often unmanaged and "un-recovered" urban waste stream inherent to a majority of cities in the developing world and attempts to re-direct these resources toward the toward the production of food and fibre in an economically and environmentally sound fashion. Food production schemes can be augmented and enhanced by recycling human and animal waste if low-cost and reliable waste recovery technologies and approaches can be demonstrated and proven feasible (Chan, 1996). One person can produce as much fertiliser as necessary for the food
needs of one person Table
2.1 Nutrients in Human Waste Compared to Nutrients in
Commercial Chemical Fertiliser (Mid 1990's)
1 Assumes loss of 50% of nitrogen
content to volatilisation.
3.0 PLANNING and IMPLEMENTING WASTEWATER REUSE PROJECTS A functional and sustainable wastewater management scheme begins at the
household level and is largely dependent on the "software" or the human
component (Khouri et al., 1994). Only when perception of need, and
perhaps, anticipation for a wastewater reuse system has been internalised
at the neighbourhood/user level, will planning and implementation be
successfully executed (Khouri et al., 1994). Local level support of
a treatment and recovery scheme can in turn, catalyse pro-active
institutions and vertical support from governments. Once the software
component has been integrated into project development, the "hardware" or
technological component can act to (1) the scheme or technology should be a felt priority in public
or environmental health, and both centralised and de-centralised
technologies should be considered (Veenstra and Alaerts, 1996);
Public acceptance of reuse projects is vital to the overall future of
wastewater reuse and the consequences of poor public perception could
jeopardise future wastewater reuse projects (Asano and Levine,
1996). The selection of any treatment technology must be accompanied in
advance by a detailed examination of the self-sufficiency and
technological capacity of the community. The treatment alternatives must
be manageable by the local community. Boller (1997) suggests that
skilled operation and maintenance are essential to attain
satisfactory performance and that technologies must require the
lowest level of maintenance and control. The overriding criterion is that
the system must be capable of achieving acceptable levels of
pathogen reductions to facilitate the recovery of effluent for
irrigation and organic soil amendment (Yu et al.,1997).
3.2 Mechanised vs. Non-Mechanised Wastewater Treatment Rapid urbanisation and industrialisation in many urban centres of the
developing world pose major challenges to preserving water resources
and the provision of sanitation. In India, like many developing nations,
planning for domestic wastewater reuse is one area that has not received
adequate attention, and to compound the problem, many existent
treatment facilities are in poor repair (Chawathe and Kantawala, 1987).
There are also cases where a mechanised waste management approach has
replaced a low-tech solution, or traditional approach only to malfunction
and cease to operate effectively (Lewcock, 1995).
Mechanised treatment systems (e.g., activated sludge, trickling filter or rotating bio-contactor systems), are efficient, in terms of their spatial requirements (0.5-1 m2 / Person Equivalent (PE) - compared to natural treatment systems at 5-10 m2 PE), but depend on economies of scale to make them economically feasible (Veenstra and Alaerts, 1996). Electro-mechanical wastewater treatment technologies designed to remove high levels of biological oxygen demand (BOD) are not only huge capital investments, but also pose certain dilemmas if reuse of treated effluents is to be an option. Conventional, aerobic, treatment results in maximum reductions in BOD and nutrients while it is desirable to retain biomass BOD and nutrients for agricultural production (Bartone, 1991). Often, the removal of pathogens requires chemical inputs to meet disinfection guidelines, which increases the operation cost and complexity of the system. Dependence on chemical disinfection also complicates effluent reuse in non-restricted irrigation schemes when compared to low-cost solutions such as wastewater stabilisation ponds (WSP), which are economical, produce similar reductions in BOD, nutrients, and greater pathogen reduction, but at a fraction of the cost (Veenstra and Alaarts, 1996; Mara and Pearson, 1998). Highly engineered and mechanised conventional sewerage and wastewater
treatment systems that require large capital investments, demand high
maintenance costs, and are not feasible for the developing world
(Cairncross and Feacham, 1993; Niemcynowicz, 1996; Edwards, 1996). Capital
intensive and highly technological waste disposal solutions utilising
indiscriminate collection and large-scale disposal, do not consider
the value of recovering organic waste resources and do not promote
"front-end" recycling or neighbourhood (local) reuse of organic waste
(Cointreau, 1982; Gunnerson, 1982; Lardinois and van del Klundert,
1993). On-site sanitation has been accomplished through a variety of low-cost measures from bucket latrines to cess-pits, to composting toilets. Bucket latrines and manual collection systems are still in use today; however, in industrialising countries, such as India and China, are phasing-out manual collection and disposal methods (i.e., the "conservancy system") (Giles and Brown, 1997). In China, 0.3 million tonnes of nightsoil are produced daily and collected by more than 200 million people; in most cases the nightsoil is transported out of the city for use as fertiliser in land- based agriculture or fish production (Bo et al., 1993). On-site pit latrines and soak away pits are not a viable solution for
high density urban areas as they depend on the permeability of soil and
multiple systems can overload the infiltration capacity of the local
strata (Alaerts, 1996; Giles and Brown, 1997). Septic tank systems and
vault toilets are effective in containing wastes, providing they are
properly lined, but require frequent servicing, depending on the size, and
are often maximised in their capacity to the state of overflowing across
streets and yards, thus contributing to non-point pollution sources. The
cost to regularly service on-site septic systems is expensive.
Consequently, regular servicing does not occur, and the function of the
system becomes inefficient (Black, 1994). Another problem associated
with septic tanks, is the number of vehicles needed to adequately
maintain and service household-level tanks; the costs associated with
the consumption of fossil fuels can be very high (Strauss, Heinss
and Montangero, 1998).
3.4 Decentralised Urban Catchment Areas Conveyance and treatment in sanitation planning have been approached in two ways: on-site sanitation at the household level and off-site sanitation at the city level (Alaerts et al., 1993). Numerous problems exist in providing effective wastewater collection and treatment systems to dense, highly populated urban areas (Giles and Brown, 1997). Many areas inhabited by the urban poor, especially squatter settlements, are found on marginal land, (i.e., marshes, and steep rocky hillsides) that are difficult to excavate for the implementation of water-borne sewage schemes (Giles and Brown, 1997). Several options have recently been proposed and appear feasible, but necessitate further development. Alaerts et al. (1993) have discussed an "intermediate" level
wastewater management scheme. Intermediate not referring to the technical
level or appropriateness of technology, but intermediate
in terms of conveyance distance between point of waste generation and the
point of treatment. This approach would allow for wastewater management to
be broken down to the neighbourhood-level and to
serve disaggregates of the larger urban areas. Selection of technology
could be made based upon specific site conditions and financial
resources of individual communities. Technology could be more
easily matched to segregate and/or recover individual resources of the
waste stream - including the industrial waste stream (Veenstra and
Alaerts, 1996).
Promoting the development of decentralised wastewater treatment and recovery technologies that are linked with urban agriculture systems, at the neighbourhood level, appear to be a rational approach to solving the human and environmental health dilemmas that result from under- managed wastewater. Decentralised, small-scale systems must be considered in planning and upgrading urban environments (Chan, 1996; Veenstra and Alaerts, 1996). Gravity flow, small bore sewerage, and water borne conveyance systems offer the potential to decentralise urban environments into catchment systems, each with their own integrated treatment plant and at low costs (Alaerts et al. 1993; Mara, 1996; Chan, 1996). These systems could be based on the topography of the local watershed, opposed to sector or citywide collection and treatment schemes, and would result in small-scale facilities equally dispersed through the urban environment. Pathogen reduction and nutrient recovery would occur through the use of integrated biological processes, which are also low-cost. This approach would allow for independent, self-maintained, and self-sustained facilities that are capable of recovering wastewater resources and immediately reusing them in decentralised urban farms (Chan, 1996). In many situations, on-site treatment and storage systems (e.g., anaerobic treatment technologies and septic tanks) can be effectively used for the management of wastewater, but they require periodic emptying and the sludge must be transported to agro-production units. In this case, technologies such as the MAPET may be feasible to promote the decentralised treatment scenario. The MAPET (Manual Pit Latrine Emptying Technology) was developed by WASTE Consultants to facilitate the emptying of pit latrines in low-income, unplanned areas of Dar es Salaam (Muller and Rijnsburger, 1994). The MAPET pump is manufactured locally in Tanzania. The unit is mounted on two pushcarts and is much more hygienic for workers than the previous practice of manually emptying latrine sludge because direct contact between the worker and the sludge is reduced (Muller and Rijnsburger, 1994). Combining this type of innovative sludge removal technology with decentralised, household or neighbourhood level treatment systems that can be directly integrated with agriculture is an area that warrants further exploration. Planning decentralised, intermediate distance treatment facilities in combination with urban agriculture at the corresponding level would allow for the assimilation of wastewater resources and would equally disperse them within urban areas. This strategy would reduce the distance that wastewater is conveyed and would eliminate the need to discharge to receiving bodies. Furthermore, it would reduce the amount of sludge disposed to landfill sites (Strauss, 1996). Bouwer (1993b) has noted that increasingly, small satellite plants are being built to provide reclaimed waste for local use. If small-scale, easily maintained and operated single or multi-residence treatment systems, providing maximum levels of environmental health and public safety, can be developed and easily replicated, then institutional resources can be directed toward education supporting their dissemination and incremental upgrading. National, mid-level, and municipal policies must be action-oriented and support institutional environments that favour the adoption of innovative technologies, otherwise, they are destined to failure.
4.1 Effluent Quality Standards As water demand and technologies improve, it is likely that wastewater reuse will continue to expand in the future (Asano and Levine, 1996). This is especially true in the Mediterranean basin countries of North Africa, the Middle East, and Southern Europe where wastewater reuse for farming has always existed (Bahri and Brissaud, 1996). The most critical issues regarding reclaimed wastewater is the protection of public health. Unlike fresh water irrigation, reclaimed wastewater is restricted to certain uses due to public health or water quality concerns (Asano et al., 1996; Mills and Asano, 1996). The effectiveness of any treatment technology must be directly correlated to the end-use and the associated water requirements (Bouwer, 1991; Asano and Levine, 1996). The recovery and reuse of wastewater and protection of public health are achieved through following a control algorithm that includes: (1) wastewater treatment to reduce pathogen concentrations to meet the WHO (1989) guidelines; (2) crop restrictions to prevent direct exposure to those consuming uncooked crops; (3)application methods (irrigation) reducing the contact of wastewater with edible crops; and, (4) human exposure control for workers, crop-handlers and final consumers (WHO, 1989; Mara and Cairncross, 1989; Strauss and Blumenthal, 1990). The most recent guidelines directing the reuse of wastewater to a level considered safe to protect human health are those outlined in the Engelberg Standards, later adopted as the WHO (1989) "Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture". These guidelines outline acceptable microbial pathogen levels for treated wastewater for use in restricted and unrestricted irrigation (see Table4.1) (IRCWD, 1985; Mara and Cairncross. 1989; Khouri et al. 1994). Restricted irrigation refers to the irrigation of crops not directly
consumed by humans (e.g., trees, fodder crops). For restricted
irrigation, wastewater effluent must contain Table
4.1 Guidelines for Treated Wastewater in Agricultural
Irrigation
The standards are expected to be achievable with simple, inexpensive treatment methods that are appropriate for the developing world (Khouri et al., 1994). The guidelines aim to prevent disease transmission while facilitating the recovery and reuse of resources (Mara and Cairncross, 1989). The WHO (1989) guidelines offer a starting point for wastewater reuse efforts. These guidelines are widely accepted and should offer public health protection if they are applied (Bartone, 1991; Khouri et al., 1994). It is most beneficial to combine the recommended guidelines with a series of control measures (see Figure 4.1 488K). In countries where agricultural exportation is possible, higher standards than the WHO guidelines may be considered. Shelef and Azov (1996) have noted that where the reuse of wastewater irrigation is practised or planned, such as in the exportation of agricultural crops for economic development, the WHO (1989) quality criteria are considered too lenient and higher standards such as those promulgated by the U.S. Environmental Protection Agency (1992) and the Israel Ministry of Health (1978) are often followed. This should be noted where the international export of agricultural products is expected to occur.
5.0 INSTITUTIONAL and COMMUNITY-RELATED ISSUES Institutional and social dimensions cannot be overlooked in the implementation of resource-conserving alternative wastewater technologies. The adoption of an alternative technology corresponds directly to the level of acceptance it gains from both the household user and the institutional framework from which the technology is supported and developed (Frijns and Jansen, 1996; Khouri et al., 1994; Veenstra and Alaerts, 1996). Frijns and Jansen (1996) have pointed out that although alternative technologies may be less expensive per capita, they often require community "investment" efforts and resources from residents. However, decentralised, alternative sanitation strategies also offer the opportunity to extend services in an incremental fashion. Marks (1993) has noted that incremental sanitation schemes encourage self-help wherever possible. Partnerships among neighbourhood-level users, private sector contractors and government officials must be equitable and pre-determined. Community ownership and participation are essential components for the implementation and success of any large-scale project - centralised or decentralised. Frijns and Jansen (1996) have pointed out that an institutional framework should guide responsibilities among stakeholders. If greater private sector involvement evolves out of this model, it is necessary to pre-determine the roles and responsibilities of each party. Elmendorf (1992) noted that the implementation of decentralised sanitation systems, particularly those that prove self-sustaining and perhaps generate income through sale of reclaimed resources, may threaten government officials, contractors and local leaders who may fear a loss of jobs, money or patronage. Friction can potentially develop in the community , and it is, therefore, advisable that an attempt be made to include a broad cross-section of community groups and public and private organisations. Whether the wastewater treatment system is biological or mechanical, on-site or intermediate-level off-site, collaboration and rewards, both economic and environmental, can be realised if strong collaborative relationships can be developed among the community, the construction and servicing groups and supporting institutions. In Rufisque, Senegal, success of a locally-developed ecological
wastewater purification system using water hyacinth / water lettuce
(pistia stratiotes) has resulted in multiplier effects. Maintenance
and operation staff have been able to gain skills allowing them to
assist other districts and towns in upgrading their services (Gaye and
Diallo, 1997). Dissemination of this locally-managed and low-cost
sanitation technology has stimulated a growth sector of the local economy
while increasing public awareness of the issue and improving the
environmental health of the community.
6.0 SEGREGATING URBAN WASTEWATER RESOURCES 6.1 Isolation of the Domestic Wastewater Wastewater-related diseases can be divided into those caused by chemical substances such as heavy metals and other toxins in mismanaged industrial effluent, and those caused by biological agents or pathogens (Giles and Brown, 1997). Both chemical substances and biological pathogens are a threat to public health as they can be transferred up the food chain when contaminated wastewater is used to irrigate crops or used in aquaculture (Furedy et al. forthcoming; Beck et al., 1994; Asano and Levine, 1996; Bartone, 1991). It is suggested that industrial pollution may pose an even greater risk to public health than pathogenic organisms (Edwards, 1996). Therefore, increasing emphasis is being placed on the need to separate the domestic and industrial waste stream in order to differentiate urban waste resources and to treat them individually for ease of recovery and reuse (Otterpohl et al., 1997, 1998; Niemczynowicz, 1993). Approaches must be found to isolate industrial toxins, pathogens, carbon, and nutrients if future societies are to be sustainable (Niemczynowicz, 1993). As Gardner (1998) has stated: Otterpohl et al. (1998) have stated that the central issue regarding centralised vs. decentralised sanitation systems is not a question of structure, but rather a question of mixing different qualities of urban resources. They have also stated that the centralised approach leads to: (2) the loss of nutrient resources (N)(P)(K) and (S) and trace nutrients inherent to domestic waste, and loss of opportunity to maintain the fertility of soil through recovery and reuse, thereby, perpetuating the need for producers to purchase inorganic fossil fertiliser; and, (3) the mixing domestic waste with industrial wastewater, which results in a contaminated sludge that is not valuable as a fertiliser for use in agricultural production. 6.2 Industrial, Municipal and Domestic Reuse of Wastewater Municipal uses of treated wastewater include the irrigation of road plantings, parks, playgrounds, golf courses and toilet flushing etc. (Bouwer, 1993a). Industrial reuses of wastewater include cooling systems, agricultural uses (irrigation and aquaculture), the food processing industry and other high-rate water uses (Bouwer, 1993b; Khouri et al. 1994; Asano and Levine, 1996). In Middle Eastern countries, where water is scarce, dual distribution systems will, in the near future, provide high quality, treated effluents for toilet flushing to hotels, office buildings, etc. (Shelef and Azov, 1996). In India, wastewater is currently being used for irrigation, gardening, flushing, cooling of air conditioning systems, as a feed for boilers, and as process water for industries (Chawathe and Kantawala, 1987). In China, national policy has been developed that promotes the development of water-efficient technologies, and encourages the reuse of reclaimed municipal wastewater in agriculture first, and then for industrial and municipal uses (Zhongxiang and Yi, 1991). In Japan, reclaimed wastewater is used for toilet flushing, industry, stream restoration and flow augmentation to create "urban amenities" such as green space (Asano, Maeda, Takaki, 1996).
During the early 1980s, the Tokyo branch of the United Nations University conducted a special study on ecological engineering and integrated farming systems in China (Chan, 1993). Interest in these systems has been renewed. Recently, the Integrated Bio-Systems conference, jointly organised by the Institute of Advanced Studies (IAS) of the United Nations University (UNU-Tokyo) and the UNESCO Microbial Resource Centre at Stockholm, as an activity of the UNU/Project Zero Emissions Research Initiative, focused on the recovery and reuse of biological waste. Some of the more salient examples and topics to arise during the
conference related to how ecological engineering is being used in the
conservation of natural resources and in the production of primary
agricultural products. Ecological engineering integrates organic waste
management strategies to improve the integrity and productivity of soils
for food production. Numerous case studies were presented which provided
examples for small-scale sewage wastewater treatment systems for
production of crops and livestock in multiple-products systems based on
the recovery and reuse of organic waste (Foo and Della Senta, 1998).
Ecological engineering has emerged as a field with the potential to conserve the natural environment while at the same time adapting to and solving sometimes intractable environmental pollution problems (Mitsch and Jorgensen, 1989). Todd and Josephson (1996) have stated that ecological engineering will influence the future of waste treatment, environmental restoration and remediation, food production, fuel generation, architecture, and the design of human settlements. Wang et al., (1998) and Qixing et al., (1996) have stated that the systematic planning of wastewater reuse schemes employing a combination of technology, (e.g., anaerobic reactor systems and constructed agriculture) (see Figure 7.1 288K) for food and fibre production, may offer one solution to solving food shortages and water pollution. Yan and Ma (1991) have described the benefits of ecological engineering in contrast to other approaches, such as environmental engineering and mechanised treatment systems, as a method to produce environmental, ecological, economic and social benefits not only in the locality of the intervention, but with benefits extending to the larger society and the environment as well. In terms of domestic wastewater treatment, Ma and Yan (1989) have stated that ecological engineering can have the highest economic benefits in wastewater treatment because it does not depend on high operation and maintenance costs and involves the regeneration of abandoned resources (Mitsch, 1991). The goal of ecological engineering is to attain high environmental quality, high yields in food and fibre, low consumption, good quality, high efficiency production and full utilisation of wastes. This is in clear contrast to the mono-objectives of "environmental engineering" where mitigation or remediation are the goals and mechanised components, such as scrubbers, filters, settling tanks and precipitators, are used (Yan and Ma, 1991; Mitsch, 1991; Chan, 1993). China is one developing country that has made major advances in
optimising approaches to recovering and reusing primary human and animal
waste products to maximise production. Historically, China and Asia have
always treated wastes as valuable resources - wastes are consistently
returned to the environment to replenish earlier removal (Chan, 1993). The
Chinese government has supported the emerging practice of ecological
engineering that combines waste management with livestock rearing,
aquaculture, agriculture and agro-industry, and uses locally-available
natural resources in ecologically-balanced systems for food production
(Chan, 1993). Admittedly, sustainable traditions in China are under
increasing pressure from industrialisation and urbanisation. However, as
late as 1998, it appears that the Chinese government is actively promoting
the efficient reuse of waste resources in integrated production systems
such as aqua-culture (Wang et al., 1998). Currently, there are more
than 2,000 active ecological engineering projects involving 10% of the
Chinese population (Wang et al., 1998). These systems promote the
multi-layer utilisation of spatial and energy resources to maximise
production capacity. Pilot projects have included:
Ghosh (1991) postulates that the wetland treatment technology for wastewater treatment in developing countries offers a comparative advantage over conventional, mechanised treatment systems because the level of self-sufficiency, ecological balance and economic viability is far greater. Furthermore, he states that these systems enable total resource recovery and herald a new era in self-help sanitation for municipalities of developing countries. In a wider and longer-term vision, ecological engineering can offer the opportunity for integrated urban sanitation schemes where wastewater treatment, resource recovery and improved socioeconomic status of the urban poor can become a reality in the developing world. Ghosh (1991:78) has stated, in relation to integrating wastewater resources for urban sanitation, that: Most recently, the term ecological engineering has been used to describe the treatment of wastewater in ecologically-based "green machines" or "living machines" (Guterstam and Todd, 1990; Mitsch, 1991). The development of solar technologies and an increased understanding of the role of organisms in the water purification process is providing both economic and environmental benefits (Todd and Todd, 1994). Capturing the same natural forces occurring in natural wetland treatment systems, these facilities treat wastewater in confined space environments and are, therefore, suitable for densely populated urban areas. In these systems, enclosed greenhouses enhance the growth of algae, plants and bacteria which, in turn, act to degrade the biological and pathogenic components of the wastewater effluent. Wastewater effluent flows through a series of clear-sided tanks, engineered streams, and constructed marshes where contaminants are metabolised or bound up (Eco-Tek, 1998). Recovered wastewater effluent from these systems can be used for landscape irrigation, and for the propagation of horticultural plants for resale (Farrell, 1996, WEF, 1995). Whether these systems can become affordable in a developing-world context, and specifically in urban regions, is not apparent at this time. However, implementing these facilities in tropical climates would eliminate the need for permanent enclosed greenhouse superstructure. In tropical climates, less expensive enclosures (e.g., tents, or roll-away translucent tarp systems) may be adequate to account for seasonally low-temperature variations. This would result in lower capital construction costs and would potentially enable the implementation of larger systems, designed to serve more users. Solar Aquatics is ideal for distributed treatment in urban environments (multiple smaller plants versus one large end-of-pipe solution). Environmental Design and Management (EDM) Limited is a Canadian design company specializing in the development of alternative environmental solutions. EDM designed and built the first two Solar Aquatics facilities in Canada, and is currently designing a system for Quyon, Quebec and Meze, France. The Bear River, Nova Scotia, Canada facility was the first municipal system in the world, and has won four national and international awards. The system treats to a very high level of water quality with virtually no odor. With few mechanical systems and no required chemicals, the system requires minimal "first world" inputs (e.g., chemicals, power, etc.). This is especially true in warm climates where heating requirements are negligible. For example in the dry arid climate of La Paz, Mexico, the system processes 180,000 US gallons per day and the tanks sit outside without enclosure and are protected solely by sunscreens. In Meze, France (under construction) the enclosed greenhouse will require only minimal external energy to heat the system (R. Cantwell [EDM] 1998: personal communication). Solar Aquatics has numerous advantages for developing countries.
Multiple, connected treatment systems in an urban environment offer
redundancy so that a problem in one area doesn't take the whole sewage
treatment system off line. This is especially critical if the water
recycling time is short. The primary maintenance (input) to the system is
unskilled labor to harvest and maintain the profuse growth of plant
material; an easy requirement in most developing countries. Current Solar
Aquatics applications in Europe and North America have not tested the
potential for food production; however, the system is a nutrient rich
hydroponic environment that produces rapid growth of biomass. The
un-demonstrated potential for food production necessitates further
research in association with Solar Aquatic treatment systems.
7.3 The Maysara Project: integrated waste management facility The Government of Jordan and the Canadian International Development Agency (CIDA) have identified the East Bank of the Jordan River as the site for a pilot integrated waste management facility. This project will contribute to an overall decrease in environmental contamination of the Jordan River. The facility will recover operation and maintenance costs in addition to a substantial fraction of the capital costs, through the sale of value-added agricultural products produced on-site through the recovery of resources recovered in the wastewater influent. The main objectives of the Project are to:
This
concludes Part i:
8.0 LAND-BASED TREATMENT TECHNOLOGIES Wastewater reuse has been growing over the previous three decades and is now considered an essential management strategy in areas of the world where water is in short supply (Mara and Cairncross, 1989, Khouri et al, 1994). Many countries now consider wastewater reuse as a method to secure water resources (Shelef and Azov, 1996). The benefits of reclaimed wastewater for irrigation are several, including:
8.1 Dry vs. Wet Sanitation System As a shortage of water becomes a reality in many parts of the world, the disadvantages of large-scale water-based conveyance or sewerage systems that lead to a consumption of a valuable water resources are heighten. This section will discuss alternative options to the conventional water-borne conveyance or wet-sanitation systems that, unfortunately, are aspired to by many countries of the developing world. Urban areas can consume up to 50% of the total water demand strictly
for hygiene-related human activities and toilet flushing (Rogers, 1998). A
re-thinking of the water-borne approach to human waste conveyance is
occurring especially in arid climates where water resources are at a
premium. Certainly, in areas such as the Middle East, a rational
alternative would be to phase-out the water-borne sewerage systems in
exchange for dry-sanitation systems. The concept of dry sanitation in the
Middle East is in no way new (see Box
8.2) (Winblad and Kilama, 1995). In suburbs and new developments,
intermediate-scale collection and treatment schemes should be
promoted. Edwards (1985) differentiates between various sanitation options by the amount of water used and states that this leads to a major distinction between "dry" and "wet" sanitation systems. When human waste is disposed of in buckets, pits, or vaults, it is referred to as nightsoil and must be removed and treated away from the site of collection (Obeng and Wright, 1987). Collection can occur daily or frequently as in the case of bucket latrines or periodically as in the case of a septic tank where a larger capacity exists. In the dry sanitation system, the degree of waste treatment increases with detention time, but must eventually be carted away from point from point of generation and treatment. The compost or humus can then be used in agricultural production (Edwards, 1985). Conventional sewerage results in the excreta being removed off-site immediately through sewerage systems, compared to dry sanitation systems, that store the excreta on-site. Asano and Levine (1996) have stated that as wastewater reuse is better
defined and understood, shorter recycling loops are possible. There is no
shorter closed-loop system than household or neighbourhood-level reuse of
domestic wastewater. New approaches and novel technologies must be
identified that are environmentally-sound for wastewater treatment and
recycling must be developed and implemented (Niemczynowicz, 1993; 1996).
Many would agree that these solutions already exist and that it is simply
necessary to disseminate the technology and for it to gain credibility
though demonstration in the developed or newly industrialised countries
(Parr, 1996; Niemczynowicz, 1993). 8.2
Household-Level/On-Site Treatment Systems 8.2.1 Double Vault Batch Composting Systems Several variations of composting toilets and innovative options will be discussed here. Composting toilets cost as little as one-seventh the cost of implementing a sewerage system in the developing world (Gardner, 1998). Pathogen reduction in composting toilets occurs through containment of the faecal waste; competition among organisms for available carbon and other nutrients; antagonism between different organisms; and, adverse environmental conditions such as pH, temperature, moisture and ammonia (D. Del Porto, [Sustainable Strategies] 1999: personal communication). Two main types of composting toilets exist, they are continuos and batch. Continuous composting toilets must be removed from service once the unit is full so that the fresh excreta can be degraded biologically in order to promote maximum pathogen reduction - which usually takes up to one year. Double Vault Batch composting systems (see Figure 8.1 201K), which are commonly used, facilitate the reuse of excreta more easily than continuous systems. They have two adjacent vaults that are used alternately. As the first vault becomes full, the second vault is put into operation. Each vault in the system should be designed large enough to store excreta for 1 year. This will provide adequate time for biological decomposition of the faecal waste, which makes the organic material available for plants, and also provides for adequate pathogen reduction. Double Vault Batch composting systems, though commonly used, are not
generally feasible in densely populated urban areas unless the system is
sealed (i.e., blind and impermeable) to protect local groundwater
resources. The superstructure can be built from locally-derived materials
and should follow design guidelines that include ventilation to decrease
odours and low light conditions which allow insects to be attracted to and
trapped in the ventilation chamber. These systems should also be designed
large enough to store excreta for 1 year. This management practice will
afford safe handling of the resulting humus and ease of application for
use in agriculture. Triple vault systems provide even more assurance of
pathogen kill because the duration of microbiological activity is
lengthened to a three year cycle (Simbeye, 1980). 8.2.2 Composting Toilets and Wastewater GardenTM Sustainable Strategies of Massachusetts, USA (see Annex IV: Report Contacts) has had considerable success in implementing composting toilet systems combined with an add-on Wastewater GardenÔand with minimal capital start-up costs. The Wastewater GardenÔ; is the result of decades of research by the University of Toronto (Sustainable Strategies, 1998). The Wastewater GardenÔtreats the urine component of human waste. The Wastewater GardenÔassimilates and evapo-transpires the liquid leachate (mainly urine) that is drained from the toilet through a small tube to the exterior of the residence or latrine housing and into the "garden". The filter is capable of assimilating any greywater that may be generated from the dwelling as well. A distinction is made here between a Wastewater GardenÔand a reed bed filter. Del Porto (Sustainable Strategies, 1999: personal communication) states that the Wastewater GardenÔis usually less saturated than typical reed bed filters which allows treatment to occur under aerobic conditions opposed to anaerobic conditions. In reed bed filters, wastewater effluent percolates or flows through the subsurface root system. In the root system, impurities are removed by combining microbial, chemical and physical processes (Price and Probert, 1997). The composting toilet and reed bed filter combination could potentially be implemented in densely populated urban areas if the compost toilet - reed bed filter combination technology can be further developed and demonstration projects implemented. Leeflang (1996) has stated that only 1 m2 of surface area is required per toilet user and that research continues in the development of substrate bedding materials that are lightweight and can be used on urban balconies and roof-tops. This alternative certainly warrants further research. Ecological latrine systems, combining composting toilets and reed bed filters, have been implemented in the South Pacific island states of Fiji, Palau, Yap and Kosrae (Sustainable Strategies, 1998). The composting toilet that was used is the Soltran II Non-Polluting Toilet with Carousal Compost System (see Figure 8.2 386K )which is also combined with a Wastewater GardenÔ. The Soltran II is a rather expensive unit for a low-income context. Locally built units constructed from 45 gallon drums that have been cut in half and adapted accordingly would be much more affordable if local fabrication capacity could be developed. Sustainable Strategies has also built innovative low cost composting systems for Fiji, Yap, Kosrae, and Pohnpei. The CEPP Net Batch Composting Toilet System is a concrete 2-vault block composting reactor system using a suspended fishing net basket for excrement collection and costs less than $500 - less if recycled materials are used (see Figure 8.3 275K ). The system appears to have the capability of managing the waste of about 20-40 people per day on a 6-year cycle (three years to fill the first chamber and then three for the second so that removal of the first chamber is after 6 years). Using the net to catch and suspend the faeces, separates solids and leachate, and optimizes aeration, which allows composting to occur (D. Del Porto, [Sustainable Strategies] 1998: personal communication). In Fiji, Sustainable Strategies designed a latrine system using fishing nets (as above) in recycled 55-gallon polyethylene drums with quick disconnects to a pint flush toilet. Settled leachate is combined with filtered greywater and applied subsurface into an aerobic evapo-transipration bed planted with indigenous reeds. The total cost for a 7.5 cubic foot composting system is approximately $US 40 (Recycled drums - $6-10/each, fixtures and net - $US 30). Capacity and filling time is determined by variables affecting composting plus load factors (D. Del Porto, [Sustainable Strategies] 1998: personal communication). Sustainable Strategies has also designed "movable batch systems" from all sizes of polyethylene barrels compared to fixed batch system. Complete plans, specifications and operation manual for the CEPP Net Batch Composting Toilet System with greywater treatment (i.e., Fiji project - above) can be purchased through Sustainable Strategies' non-profit Center for Ecological Pollution Prevention (see Annex IV: Report Contacts). Recently, the United States Department of Agriculture contracted Sustainable Strategies to design and demonstrate a small-scale piggery waste pollution prevention system in Micronesia in the Federated State of Pohnpei. The system will utilise a Wastewater GardenÔto convert pig waste (manure, urine and spilled feed) back into valuable feed plants such as kangkon and water hyacinth. Furniture grade bamboo will also be irrigated and grown from the reclaimed wastewater, and will be harvested and sold (Sustainable Strategies, 1998). Composting toilets have been in use in northern communities since the
1970's. One case study in Sweden demonstrated the problems of integrating
three different types of dry composting systems into domestic households
(Fittschen and Niemczynowicz, 1997). Their study suggested that aspects of
planning, maintenance and training need considerable research if these
systems are to be integrated into cold climates. In southern tropical
climates, composting toilets or dry sanitation systems may be more
feasible and efficient at the site-specific level as they can be combined
with a Wastewater GardenÔ (see Box 8.3). Combined
composting toilets and filter systems may be appropriate for many Middle
Eastern countries where sanitary ablution is practised. The filter is
capable of treating and assimilating the additional water while the faecal
waste is retained in the composting toilet, where it degrades
biologically. The reed bed filters have demonstrated consistent effluent
quality in terms of BOD, total suspended solids (TSS) and ammonia-N
removal (Green and Upton, 1994 in Yu et al., 1997).
The Dry Alkaline Family Fertiliser (DAFF) latrine is a variation of the Vietnamese latrine and was introduced by the Centro Mesoamericano de Estudios sobre Tecnolgia Apropiado (CEMAT) in Guatemala. The DAFF latrine has two alternating chambers where excreta are deposited separate from urine. To ensure stabilisation of degradation of the faecal waste, soil or lime can be added instead of or in addition to ash in order to keep an optimal moisture content of the system at around 50% (Mara and Cairncross, 1989). The urine component is conducted to a container and stored for future application to crops (Chavez, 1987). When the first composting chamber is filled, the other has previously been emptied and is then put into use. The main advantages associated with the DAFF are that it produces fertiliser, no sub-surface digging is needed, it consumes little space, it is comfortable, and it can be constructed with local materials (Caceres, 1988). DAFF latrines cost approximately $US 140 including construction materials, and the associated educational program that should accompany the implementation of the system. The latrine produces approximately 500 kg. of compost annually that can be sold for $US 120 (US$ 1989) (Mara and Cairncross, 1989). DAFF latrines produce a compost comprised of 3-10% organic matter, 0.3-1.1% total nitrogen, 150-410 mg/kg. of total phosphorus and 700-7600 mg/kg. of potassium; the pH is 9.8-11.2 (high) due to the supplemented ash. The faecal coliform count (FCC) is less than 4000 per gram (wet weight), and helminth eggs less than 8500 per gram with a viability of less than 30% (Zandstra, 1986; Mara and Cairncross, 1989). A FCC of 4000 per gram (wet weight) may; however, be high. The current standard promoted by NSF International (ANSI/NSF 41-1998) for treated solid waste derived from Non-liquid Saturated Treatment Systems is a 200 MPN (most probable number) faecal coliform content per gram and that the liquid component, if any, shall have a fecal coliform content that does not exceed 20 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 viable
intestinal nematode egg per litre, implying a > than 99% treatment
level. This guideline has been introduced to protect the health of field
workers and to indirectly protect consumers and grazing cattle (beef
tapeworm) (Mara and Cairncross, 1989). Unrestricted irrigation refers to
the irrigation of vegetable crops eaten directly by humans, including
those eaten raw, and also to the irrigation of sports fields, public
parks, hotel lawns, and tourist areas (Mara and Cairncross, 1989). The
criteria for unrestricted irrigation, contains the same helminth criteria
as restricted irrigation, in addition to a restriction of no more than a
geometric mean concentration of 