Opportunities and Constraints for Resource Efficient ... - CyberLeninka

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Aquatic Procedia 1 (2013) 100 – 119

World Water W Week k, 26-31 Auugust 2012, Stockholm,, Sweden

Opportun O nities andd constraaints for resourcee efficient enviroonmentaal managem m ment in rapidly r developi d ing urban n areas: The exaample off Mexico City M. Starklla*, I. Bisscchopsb, L. Esslc, E. L Lópezd, J.L.. Martínezd, D. Murillloe, T.A. Nann ingab a

Competence C Centrre for Decision Aid A in Environmen ntal Managementt, University of Natural N Resourcess and Life Sciencees, Vienna, Austria b Lettinga a Associates Founndation, The Neth herlands c Centrre of Environmental Management and Decision Sup pport, Vienna, Au ustria d Mexican Institutte of Water Technnology (IMTA), Jiutepec, J Mexico e Center off Research and Advanced A Studies in Social Anthrop pology (CIESAS), Mexico

Absttract This paper comparees two contrastiing approaches to natural resoources managem ment in Xochim milco, a peri-urbban area of Mexico City.. Both are realiistic options thaat were based on o local stakehholder consultattions and trend analyses. One of the alternattives aims at maximizingg conservationn, reuse and reecycling of resoources; the oth her takes a con nventional, cenntralized appro oach. himilco is of sttrategic importaance for Mexico City for rechharge of the dep pleted aquifers supplying the city and featurres a Xoch tradittional form of aagriculture (chiinampas). The environmental e sectors consideered are water supply, s sanitatioon and wastewater, solid d waste and agrriculture. In thee geographical area there hass been a trend towards t urbanization and few w efforts have been b madee to increase rreuse and recyccling of resourrces. Both mannagement altern natives have been complemen ented with a seet of techn nologies suitablle for the purpose of each on ne (local and onn-site technolog gies for the con nservation alterrnative, centrallized techn nologies for thee centralizationn scenario). Th he resource flow ws were calcullated to quantiffy the potentiaal for conservattion, reusee and recyclingg under each sceenario. The soccial impact and the costs of thee proposed tech hnologies were also assessed. The study y shows that a management alternative aim ming at conserrvation, reuse and recycling of resources iis environmenttally beneficial but mayy not necessaarily be financcially cheaper than a conv ventional manaagement approoach. Furtherm more, ntralized technnologies enablinng resource recovery and reusse will have a greater impact on users and aare less compattible decen with existing instittutional system ms. The study concludes witth several poliicy recommend dations on how w to facilitate the impleementation of ddecentralized teechnologies aim ming at reuse annd recycling of resources. r

* Corresponding C autthor. E-ma ail address: [email protected]

2214-241X © 2013 The Authors. Published by Elsevier B.V. Selection and peer-review under responsibility of the Stockholm International Water Institute doi:10.1016/j.aqpro.2013.07.009

M. Starkl et al. / Aquatic Procedia 1 (2013) 100 – 119

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Published by Elsevier B.V. B.V. © 2013 2013The TheAuthors. Authors. Published by Elsevier Selection and under responsibility of theof Stockholm International Water Institute Selection andpeer-review peer-review under responsibility the Stockholm International Water Institute. Keywords: agriculture, organic waste, resource recovery, reuse, recycling, urbanization, water supply, wastewater

1. Introduction Latin America is the most urbanized developing region in the world, with 79% of its population living in cities (UNEP, 2010). There are four megacities with more than 10 million inhabitants in Latin America, of which Mexico City is the largest. Urban population has tripled over 40 years and urban growth is continuing (UNFPA, 2008). Development of infrastructure in the cities lagged behind urban growth, leaving a large fraction of the population, mainly in peri-urban areas, without adequate access to water and sanitation services (Engel et al., 2011). Inefficiency of existing infrastructure has been reported to be another cause for the poor water and sanitation services across Latin American cities (UN Habitat, 2012). Even though waste collection services exist, it is common practice to dump waste into natural ecosystems or burn it, which creates problems of air pollution, leaching and transmission of vector-borne diseases (UNEP, 2010). In Mexico City, 30 million m3 of wastewater are discharged every day into surface waters, very often with no treatment or only primary treatment. Currently, Mexico City is even ‘exporting’ wastewater to water bodies outside the city, for example to the Valle de Mezquital, through a deep drain system (Biswas, 2006). Agricultural land is being lost as a result of erosion and change in traditional practices, and demand for land for urbanization is increasing (Ovalles, 2006). Given the above observations, protecting the environment requires a change in practices and a new form of management of natural resources in peri-urban areas to avoid further loss of surrounding ecosystems. This paper compares two contrasting management alternatives, one that maximizes resource conservation, reuse and recycling, the other being a conventional approach based on the extension of centralized services to peri-urban areas with no or little reuse and recycling of resources. These alternatives have been compared under a peri-urban area of Mexico City that faces all the challenges mentioned above (population pressure on resources, overexploitation of groundwater and inadequate urban planning). Both management approaches are very real alternatives that were identified during a scenario workshop that aimed at identifying future development visions for the case-study area. Stakeholders differ in their opinions of which scenario is most likely to happen. Traditional water-service providers favour the centralized solution as it is expected to involve less costs and is better suited to the observed trend of urbanization (ICA, 2012; Olivares, 2010), whereas other stakeholders, such as the Commission of Natural Resources, favour the conservation approach. 2. Case study The case study focuses on the peri-urban area of Xochimilco, one of the 16 boroughs (delegaciones) of Mexico City. Xochimilco covers 3000 ha and includes both flat land used for agriculture and hilly areas. Farmers in Xochimilco practise a traditional form of agriculture, chinampas, in which plots are surrounded by canals. Xochimilco was listed as a World Heritage site in 1986 and as a wetland of international importance in 2004 (Merlín-Uribe et al., 2013). If trends continue, the area is expected to face a large water deficit within the next century (Nanninga et al., 2012). The population of Xochimilco has been increasing rapidly, resulting in a large population and accelerated growth, which has resulted in an increase in urbanization (Fig. 1).

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Figure F 1. Land usse in Xochimilco in 1974 (left) and d trend analysis ffor 2030 (right). Source: S J. Brena, IMTA. Personal Communication

3. Sccenarios A scenario anaalysis conduccted in 2010 identified threee scenarios for the futuree developmennt of Xochimiilco, rang ging from inddividual to cenntralized solu utions. Two oof the scenarios are based on the resultts of a worksshop cond ducted with innhabitants of thhe case-study area, while thhe third is based on current demographic trends. This T paper com mpares a resoource-oriented d scenario idenntified by loccal inhabitantss with a convventional scen nario baseed on current demographic trends. The first of these has the highest recycling and reuse pootential, whilee the seco ond has the llowest recyclling and reuse potential. The contrastt permits disscussion of oopportunities and consstraints for ressource efficiennt managemen nt. Scenario 1 – loocal identity: In this scenaario, individuaal technical so olutions are prreferred over centralized ones. o Thiss would allow w the boroughh to become independent from Mexico o D.F. in its handling of water and waste w man nagement. Com mposting andd use of locaal water resouurces are imp portant components of thiis scenario, as a is prev vention of polllution of channnels used for irrigation. Thhis approach would w strength hen the local identity, whicch is very y much conneected to tradditional agricu ulture. Use oof on-site biogas systems would make households less depeendent on purcchased liquid gas. Fig. 2 illu ustrates the reesource flows in this scenario.


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Figure 2. Resource flows in Scenariio 1 – local identity (blue arrows = water flows; greeen arrows = nutrrient flows; red arrrows = local eneergy flow for houusehold use)

Scenario 2 – ccentralization: All infrastru ucture servicess are centralizeed as far as po ossible. Users are connected d to centralized waterr supply and seewer systems.. Composting is done on ceentralized leveel and composst is supplied to t locaal farmers. Teechnical solutions are selectted at higher aadministrative levels. The reesource flows are limited to o meaasures taken bby Mexico Citty and are not influenced byy measures wiithin the case-study area. Ann illustration of o the concept is shoown in Fig. 3..

Figure 3. Resources flow in Scenario 2 – ccentralization (green arrow = nutriient flow)

T con ncepts 4. Technical Possible P technnical options were discusseed with local stakeholders in a participaatory planningg workshop. They T werre later techniccally assessedd in a feasibiliity study. Morre information n on the particcipatory plannning workshop p and the feasibility stuudy is providedd in Nanningaa et al. (2012) . Corresponding C g technologiess were identifi fied for each oof the two seleected scenarioss (Table 1).

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Table 1. Overview of technologies proposed for scenarios 1 and 2

Scenario 1 On-site rainwater harvesting with UV disinfection Water supply Technologies

Wastewater technologies

Organic solid waste technologies

Improvement of existing centralized water supply (standpipes, tanker trucks) Connection to centralized water supply

A a A

Urine-diverting dry toilet systems

A

Biofilters (constructed wetlands treating grey wastewater)

A

Constructed wetlands for household wastewater (household level)

A

Connection to centralized sewer system and treatment in wastewater treatment plant Biodigester (on-site biogas plant)

A

On-site domestic (vermi-)composting

A

Centralized composting of organic waste (utilization of an existing composting plant located in Xochimilco)

Scenario 2

A

A

A = key technology in this scenario, a = complementary technology

In Scenario 1, potable water would be provided through the application of rainwater harvesting (RWH) systems complemented by an improvement of the centralized water supply system. Wastewater would be treated using onsite technologies, adapted to terrain type and household needs; the effluent would be used in agricultural irrigation. Solid waste would be processed using on-site (vermi-)composting technologies and biodigesters that produce fertilizer and biogas as by-products. In Scenario 2, potable water would be provided by extending the centralized system that already serves the urban zones in the case-study area. Similarly, the centralized sewer system that serves urban zones would be extended into the case-study area and wastewater would will be transported to an existing wastewater treatment plant (WWTP) (San Luis Tlaxialtemalco WWTP, located near the case study) for treatment. Finally, solid waste would be separated by the users and collected by the centralized system. More details on the selected technologies are provided in Nanninga et al. (2012). 5. Assessment methods The criteria selected for the assessments are based on existing studies on sustainability indicators (Zurbrügg et al., 2012; Ashley et al., 2004; Bracken et al., 2004; Balkema, 2003; Kärrman et al., 1998) combined with criteria that appeared to be relevant in the local context of the case study (elaborated in stakeholder workshops). 5.1 Environmental assessment The environmental assessment discussed in this paper encompassed water conservation (water demand covered by rainwater harvesting and wastewater reuse), energy use of technologies and potential nutrient recovery. The assessment used local data for precipitation, household water consumption, waste(water) amounts and composition, treatment technology efficiencies and energy consumption, complemented by literature data and expert estimations where needed. Using this information, the water demand of the area, the available amounts of harvested rainwater and treated wastewater, required energy and amounts of potentially recoverable nutrients were calculated for both scenarios.

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5.2 Economic assessment The economic assessment included costs and benefits of the infrastructure alternatives. Investment, operational and maintenance costs were calculated based on locally available data. Provision of infrastructure for the water and wastewater sector has multiple direct and indirect benefits. This is illustrated for the case of sanitation and wastewater treatment in Fig. 4.

BENEFITS OF SANITATION AND WASTEWATER TREATMENT DIRECT IMPACTS

USE BENEFITS Decreased number of incidences of water related diseases

Improved hygiene

Increased productivity Costs avoided for health treatment Enhanced tourism activities

Cleaner water bodies

Reduced water pollution

NON-USE BENEFITS

Reduced eutrophication

Increased biodiversity Increased fish stock

Increased productivity

Provision of infrastructure

Employment, profit for local economicy and increased capacity

Provision of resources

Reduced cropping costs through saving of fertilizer

Reduced pre-treatment costs for downstream users

Reduced pressure on available resources

Value of by-products

Figure 4. Direct and indirect benefits of improved sanitation and wastewater treatment

This study conducted a quantitative assessment of the use benefits related to provision of resources. Where possible, the market price of resources was used; for example, the market price of compost in the study area is approximately MXN1 or about €0.06 Euro/kg † (INE, 2007). While the market price may not reflect the total economic value of the resource, calculation of the full economic value is a complex task and was not pursued in this study. If no market price was available, as was the case for urine and biogas, the value of nutrients (or energy content, in case of biogas) was calculated by comparing contents with the market price of products that could be substituted.

†

€1 = MXN16.9029 (annual average 2012, European Central Bank, www.ecb.int).

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Using these data, the net present value (NPV) for all options over a period of 30 years was calculated with discount rates of 2% and 10% to see how the costs to the user or the government develop over a longer period. The NPV calculation followed international practise as outlined in Brunner and Starkl (2012). For the centralized system, the number of people who could possibly be connected to the treatment plant was calculated. The costs per user are based on this number. The operational and maintenance costs comprise the costs of personnel or labour input of users, spare parts, transport and energy. The labour input of users was included in the operational costs at a value of MXN16/h, which is based on a local survey. All values were adjusted to the year 2012 by using the inflation rate of the construction sector (INEGI, 2012). The lifespan of various components and resulting reinvestment costs were included in the NPV. 5.3 Social assessment The social assessment encompassed user acceptance, impact on users and institutional compatibility. User acceptance was assessed based on two focus groups (Grudens-Schuck et al., 2004; Krueger and Casey, 2000) that were conducted in the case-study area. Impact on users was assessed through five subcriteria that examined the changes required of users compared with their current practices. Institutional compatibility was assessed using four subcriteria that examined how well suited the options are to the current institutional conditions in the case-study area. The impact on users and the institutional compatibility were judged by local experts, who assessed each criterion on a scale from one to five, with a score of one meaning low impact or high suitability. Table 2 presents the criteria, the method of assessment and the source of information that has been used for the social assessment.

M. Starkl et al. / Aquatic Procedia 1 (2013) 100 – 119 Table 2. Criteria, methods and source of information used for assessment of the two scenarios

Criteria Resource conservation Recycling of nutrients Energy use Water conservation Costs Investment costs of technologies Operational and maintenance costs of technologies Social assessment Level of acceptance by users Impact on users: Required changes to cultural habits Operational requirements Required knowledge and skills Required changes in the house Quality of ambience (e.g. noise, aesthetic value, odour, etc.) Institutional compatibility: Compliance of technologies with legal requirements Capacity of existing local institutions to provide technical support Existence of institutions to monitor and control the technologies Information on required institutional support measures

Method of assessment

Source of information

Nutrient flows Energy flows

Literature, general removal efficiencies Information from existing systems, estimations Literature and field data

Water flows Cost calculation Cost calculation

Focus groups Qualitative assessment

Qualitative assessment

Collection of information from existing systems, literature data, own estimations, input for NPV calculation Collection of information from existing systems, literature data, own estimations, input for NPV calculation Users Expert judgement (scale 1-5): 1= low impact (e.g. no change in habits, operation not conducted by user, no changes in house, etc.) 5 = high impact (e.g. large change required in cultural habits or in the house, knowledge, time-consuming operation, etc.) Expert judgement (scale 1-5): 1 = well suited to current institutional framework (e.g. compliance with legislation, existence of all institutions, no external support required, etc.) 5 = not suited to current institutional framework (e.g. no compliance with law, external support required, no institutions for monitoring, etc.)

6. Results and discussion 6.1 Water supply 6.1.1 Environmental assessment (conservation of water) Rainfall in central Mexico is characterized by marked wet and dry seasons, with maximum rainfall in July (172 mm) and minimum rainfall in December (6.6 mm) (SMN, 2012a). Given that consumption of drinking water is low in the study area (less than 1 L/person/d in winter and double that amount in summer [IMTA, 2011]), RWH systems can meet demand for drinking water even in the driest month (based on a collection surface of 36 m²/household, with a collection efficiency of 70%). During the rainy season, RWH could also meet some of the demand for other domestic water uses (laundry, cleaning, etc.). Thus, Scenario 1 offers substantial water conservation with respect to household uses. However, in the dry season it rains only a few days each month, which makes it necessary to have some form of storage and a complementary drinking water source such as a centralized supply or bottled water to ensure that there is enough water available for all household activities.

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Total T water deemand in Xoochimilco is very v much innfluenced by water deman nd for agricul ulture. Sources of agriccultural waterr are precipitaation, treated wastewater, surface wateer from the ch hannels and ssoil water thaat is acceessible to cropp root systemss. The latter is i not includeed in the study y as it could not n be monitoored. Agriculttural wateer demand waas calculated from f local evaapotranspiratioon data (SMN N, 2012b) and an estimationn of the total area destiined for agricculture. The am mount of treaated wastewateer available varies v dependiing on the sceenario, as does its usag ge. In Scenarioo 1, treated grreywater from m the biofilterrs and treated household waastewater from m the constru ucted wetllands are usedd for househoold purposes such as cleanning or laund dry but not fo or drinking. E Effluent from m the centrralized WWT TP in Scenarioo 2 is discharrged to the chhannels betweeen fields as part of the cuurrent practicce in Xoch himilco for suurface water recharge, and is i thus indirecctly reused. However, H this does d not chang nge the discharrged flow w, so the amouunt of water available a is no ot increased. T Therefore, efffectively theree will be no nnet water reusse or nutriient recyclingg in the area. The T types of water w supply soource and their contribution n to total and ddomestic dem mand in th he two scenarrios are shownn in Fig. 5. This shows thee optimal situ uation with resspect to waterr conservation n, in whicch any treatedd wastewater not used forr domestic puurposes is desstined for irrig gation. Shortaages in waterr for dom mestic uses, inccluding drinkiing water, are met by the ceentralized wateer supply systtem.

Figuure 5. Total and household h water supply s and demannd for the entire case-study c area fo or the two scenarrios

In n Scenario 1, in which all households h make use of inddividual RWH H systems, rainwater can m meet about 50% % of the annual a averagge household water w demand d in the area ((Nanninga et al., a 2012). Th he users of a R RWH system will remaain partly deependent on another a sourcce of water tto meet theirr domestic water w demandd. In the casee of Xoch himilco, this alternative soource is the ceentralized watter supply sysstem. For households that ccannot connecct to

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the water supply network, alternative centralized services such as well-functioning standpipes and/or tanker trucks can be a solution for the months with insufficient rainfall to meet household water needs. No water conservation takes place in Scenario 2, as all households are connected to the centralized supply system and therefore no drinking water demand is covered by rainwater. 6.1.2 Economic assessment Table 3 presents the investment and operational and maintenance costs per user for each of the proposed technologies. Table 3. Economic assessment of water supply under scenarios 1 and 2*

Scenario 1 Scenario 2 Improvement of Connection to centralized system existing system 4,500 1,000 4,500 400 30 200

RWH and tUVo Investment costs** Annual operational and maintenance costs** NPV (after 30 years) @ 2% discount

15,000

9,000

NPV (after 30 years) @ 10% discount

10,000

6,500

* Rounded values. ** See methodology section for details on calculation and components included. Abbreviations: NPV = net present value; RWH = rainwater harvesting; tUVo =

UV disinfection system (Spanish tubo = tube, which refers to the placement of the UV system within a plastic tube). Scenario 1 aims at meeting domestic water demand from RWH. However, as shown in Fig. 5, RWH cannot meet the entire domestic water demand throughout the year, and therefore needs to be supplemented by an extension of the centralized system. The investment costs of the extension in Scenario 1 are only about 25% of those for the connection to the centralized system in Scenario 2 as they comprise only the costs for the primary network. The secondary network, which supplies the standpipes, already exists. Operational costs are slightly higher for the RWH system, as users are required to provide labour for the operation and maintenance of the RWH system and the UV disinfection. Labour costs of users have been calculated assuming that the user spends approximately 90 hours per year operating and maintaining the systems.

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6.1.3 Social assessment Table 4 presents the results of the social assessment of water supply under scenarios 1 and 2. Table 4. Social assessment of water supply under scenarios 1 and 2

Scenario 1 RWH and tUVo Required changes to cultural habits Operational requirements Required knowledge and skills Required changes in the house (e.g. new pipes) Quality of ambience (noise, traffic, aesthetic value, etc.) Impact on users (sum) Compliance of technologies with legal requirements Existence of institutions to monitor and control the technologies Capacity of existing local institutions to provide technical support Required institutional support measures(e.g. awareness raising, education programs) Institutional compatibility (sum)

3 3 2 2

Scenario 2 Connection to centralized system 2 1 1 2

3

2

13 1

8 1

1

1

1

1

3

1

6

4

The technologies have a greater social impact on users under Scenario 1 than under Scenario 2 (Table 4). The reason is that, under Scenario 1, users are responsible for operating and maintaining the technologies, which requires specific knowledge, and have to change their habits to use a new water source and disinfection method. Nevertheless, discussions with potential users in focus groups have shown that users would be willing to make those greater efforts because the additional water the technologies would provide can help them to improve their quality of life, as users would become less dependent on tanker trucks and standpipes. However, overall, users would still prefer a centralized service provision. It also can be seen from Table 4 that the technologies of Scenario 1 are less compatible with the institutional system than are those of Scenario 2. The reason is that implementing the RWH system and the UV disinfection system requires awareness to be raised of the importance of water treatment and training on correct use of the RWH and UV disinfection systems. Standards and institutions for monitoring are available for both options.

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6.2 Wastewater treatment technologies 6.2.1 Environmental assessment (conservation of resources) The results of the environmental assessment of the wastewater management systems are presented in Table 5. Table 5. Conservation of resources in wastewater management under scenarios 1 and 2

Water conservation

Energy use (kWh/person/yr Nutrient recycling****

Scenario 1 (option 1) Grease trap UDDT and biofilter No water is Reuse of used, treated grey conservation wastewater, of flush water 10 13 m3/person/yr m3/person/yr* ** 0 1.4 kg N/person/yr and 0.383 kg P/person/yr

Scenario 1 (option 2)

Scenario 2

Constructed wetland

Centralized WWTP

Reuse of treated household wastewater (black * and grey ** wastewater), 23 m3/person/yr

No reuse

0

0

400***

0

0

0

* Local flush water, 5 flushes/d, 7 L/flush (IMTA, 2011), excreta 1.4 L/d (Arroyo and Bulnes, 2005). ** Greywater use, 27 L/person/d (IMTA, 2011); exact recovery depends on water losses/gains from the biofilter system (leakages, precipitation, evaporation, etc.). *** Based on data of Sánchez-Fuentes et al. (2011) and case-study water flows. **** Based on urine and faeces data from Arroyo and Bulnes (2005). Abbreviations: UDDT = urine-diverting dry toilet; WWTP = wastewater treatment plant.

The urine-diverting dry toilet (UDDT) does not use water for flushing and therefore has no direct emissions to the surface water. Organic matter and nutrients from faeces and urine are collected in a cistern for later usage in agriculture. As it consumes no water, the UDDT contributes to water conservation in Scenario 1. In all scenarios, treated wastewater is either used locally or discharged to the closed canal system. Only the nitrogen (N) and phosphorus (P) and organic matter that are removed from the wastewater in the form of sludge or plant material can be reused locally. In Scenario 2, sewage is treated outside the area and the sludge will be disposed of, or used, outside the study area. The effluent will be discharged to the channels as part of the current practice of surface water recharge in Xochimilco, without causing a change in the amount of discharge. This means that in Scenario 2 effectively all water, nutrients and organic matter will be lost from the area, but that at least part of the water will be recovered indirectly due to the closed canal system.

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6.2.2 Economic assessment Table 6 presents the investment and operational and maintenance costs per user for each of the proposed technologies. Table 6. Economic assessment of wastewater management under scenarios 1 and 2*

Investment costs** Annual operational and maintenance costs** Annual benefit** NPV (after 30 years) @ 2% discount NPV (after 30 years) @ 10% discount

Scenario 1 (option 1) Scenario 1 (option 2) Scenario 2 UDDT Biofilter Constructed wetland Connection to centralized for treatment plant greywater 3,500 1,000 10,000 4,500 200 50 50 100 35

0

0

0

13,000

16,000

7,500

7,500

11,000

6,000

* Rounded values. ** See methodology section for details on calculation and components included. Abbreviations: NPV = net present value; UDDT = urine-diverting dry toilet.

It can be seen in Figure 6 that the centralized option is cheaper than the second cheapest option, depending on the discount rate. The results for NPV also show that a higher discount rate (stronger discounting of future operational and maintenance costs) reduces significantly the difference in the NPV between the options. The annual benefit of option 1 in Scenario 1 (resulting from the monetary value of the resources reused and conserved) is about 15% of the annual operational and maintenance costs. It was assumed that urine replaces chemical fertilizer with a price of MXN18/kg N and MXN22/kg P (based on CEFP, 2012). The reuse of treated wastewater results in no economic benefit because the water price in Mexico City is very low. The operational and maintenance costs for the options of Scenario 1 consist mainly of labour provided by the users and costs to transport by-products to the point of use. The investment costs of the centralized system in Scenario 2 are similar to the costs of the UDDT option. The conventional treatment plant located in the case-study area still has unused capacity; therefore, it was assumed that the people who will be connected to the treatment plant will share the costs for the extension of the primary network. Operational and maintenance costs mainly consist of energy costs (32%) and costs for maintaining the sewer (40%).

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Figuree 6. Net present value v per user oveer a period of 30 yyears for wastewaater treatment opttions, 10% discouunt rate

6.2.3 Social assesssment Tab ble 7 presents the results of the social assessment of waastewater man nagement optiions under sceenarios 1 and 2. 2 Tablle 7. Social assesssment of wastewaater management options under sccenarios 1 and 2

Reequired changges of cultural habits Op perational reqquirements Reequired knowlledge and skillls Reequired changges in the housse (e.g. neew pipes) Qu uality of ambiience (noise, traffic, t aesthetic value, etc.) Im mpact on userrs (sum) Co ompliance of ttechnologies with w leg gal requirements Ex xistence of insstitutions to monitor m an nd control the technologies Caapacity of exissting local insstitutions to provide technnical support Reequired instituutional supporrt meeasures(e.g. aw wareness raisiing, ed ducation progrrams) In nstitutional coompatibility (sum) (

Scenario 1 (opttion 1) UDDT U Biiofilter foor grey w water 3 2 3

Sceenario 1 (optio on 2) nstructed wetlland Con 2 2 2

Scenario 2 C Connection to o centtralized treatm ment plant 1 1 1

2

3

3

3

2

2

13

11

8 1

NA

1

1

1

1

1

1

3

2

6

5

1 1 1

4

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The technologies proposed under Scenario 1 have a greater social impact on users than do those under Scenario 2 (Table 7). The reason for this is that users have to change their current habits and require more skills and knowledge: for the UDDT system, users have to separate urine and faeces and avoid using water for flushing and cleaning. For households using constructed wetlands, it is advisable to throw toilet paper in waste baskets as the pipes are then less prone to clogging. Discussions with potential users in focus groups have shown that the centralized system is the preferred option as it is the most convenient solution. It also can be seen from Table 7 that the technologies under Scenario 1 are less compatible with the institutional system than those under Scenario 2, primarily because external supporting measures such as awareness-raising and training are required. There are no legal requirements for UDDT systems. National wastewater discharge norms and institutions for monitoring exist, but monitoring of household technologies is not common practice in Mexico. 6.3 Organic solid waste management 6.3.1 Environmental assessment (conservation of resources) Whereas the centralized collection and composting facilities envisaged in Scenario 2 require energy for their operation, on-site (vermi-)composting and biogas plants envisaged under Scenario 1 do not. The on-site biogas plant, if properly designed, constructed, operated and maintained, can produce biogas that can be used for household purposes and thus yield a positive net energy (Table 8). The digestate will be dried for subsequent application in agriculture. When available, animal manure can also be processed in the biogas plant. This would increase the total biogas and nutrients production and could improve system stability if, for example, the organic waste contains a large fraction of easily acidifying materials. Table 8. Conservation of resources from organic waste management options under scenarios 1 and 2

Energy use (KWh/person/yr Recycling of nutrients (kg N & P/person/yr

Scenario 1 (option 1) Composting

Scenario 1 (option 2) Vermicomposting

Scenario 1 (option 3) Biogas plant

Scenario 2

0

0

0*

Centralized collection and composting 14

1.5 & 0.3

1.5 & 0.3

1.7 & 0.3

1.5 & 0.3

* Biogas plant produces 57 m3 of methane/person/yr, which corresponds to approximately 600 kWh/person/yr.

6.3.2 Economic assessment Table 9 presents the investment and operational and maintenance costs per user for each of the proposed technologies. Table 9. Economic assessment of solid waste management under scenarios 1 and 2*

Scenario (option 1) Composting Investment costs** Annual operational and maintenance costs** Annual benefit**

200 400 200

Scenario 1 (option 2) Vermicomposting

Scenario 1 (option 3) Biogas plant

Scenario 2

Centralized collection and composting 1.500 2.500 100 800 500 300 200

550

200

115


NP PV (after 30 yyears)@ 2% % discount NP PV (after 30 yyears) @ 10 0% discount

4.500

14.0000

2.500

900

2.000

7.0000

2.000

500

* Ro ounded values. ** See methodology section for details on calculation and a components iincluded. Abbrev viation: NPV = ne et present value.

All A options prrovide valuablle side produccts in the form m of compost or o biogas. In Scenario 2 invvestment costts are halff those of the cheapest option of Scenariio 1 as they coonsist of only costs for land d. Operationall and mainten nance costts of the optioons of Scenariio 1 are mainlly personnel ccosts, whereass in Scenario 2, 45% of thee operational costs are for transport: organic waste is separated d by the users and transporteed to the treattment plant; thhe compost is then disttributed in thee case-study area. For all composting options, the annual benefiit totals MXN N200, assumiing a com mpost price off MXN1/kg (IN NE, 2007). The T NPV of the vermicom mposting systtem is higherr than of the other option ns (Fig. 7), buut users havee the opp portunity to seell the worms or use them as a cattle feed. This benefit was w not considered in the aassessment, ass it is not known whethher all users would w be intereested or willinng to sell theirr worms. The benefit from selling wormss can be greater g than tthe operationaal and mainten nance costs aas they multip ply at least ten nfold within oone year (Gó ómez, 200 08). Other bennefits of verm micomposting are that it reequires less space than con nventional coomposting and d the com mpost produceed contains lesss salt (de Kofff et al., 2008)).

Figuree 7. Net present value v per user oveer a period of 30 yyears for solid waaste treatment opttions, 10% discouunt rate

The T value assigned to bioggas is based on n the cost of lliquid gas in Mexico. The heating valuee of methane is 10 kW Wh/m3 (Cerbe, 1999) and thee total producttion is approxximately 60m3/person/yr. Th herefore, the ttotal heating value v thatt can be obtainned is approxximately 600 kWh k (or approoximately 46 kg of liquid gas/person/yr. g The price of 1 kg of liquid gas is M MXN12 (SENE ER, 2008). Affter 20 years, rreinvestment is necessary for f the biogas system. However, he biogas is ussed. the NPV is still inn the range off the compostiing system, prrovided that th The T biogas syystem is thereffore an econo omically attracctive option because of the benefit it prooduces in the form of by-products. b A An even cheaaper option would w be to ccombine black k water and organic o wastee treatment in n the biod digester; this w would reduce construction costs and yielld more biogas.

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6.3.3 Social assessment The results of the social assessment are summarized in Table 10. Table 10. Social assessment of organic waste management under scenarios 1 and 2

Required changes of cultural habits Operational requirements Required knowledge and skills Required changes in the house (e.g. new pipes) Quality of ambience (noise, traffic, aesthetic value, etc.) Impact on users (sum) Compliance of technologies with legal requirements Existence of institutions to monitor and control the technologies Capacity of existing local institutions to provide technical support Required institutional support measures (e.g. awareness raising, education programs) Institutional compatibility (sum)

Scenario 1 (option 1) Composting

Scenario 1 (option 2) Vermicompost ing

Scenario 1 (option 3) Biogas

Scenario 2

2 3 2

2 4 3

2 4 3

Centralized collection and composting 2 2 1

2

2

2

1

3

3

3

3

12

14

14

9

NA

NA

NA

NA

1

1

1

1

1

1

1

1

2

3

3

2

4

5

5

4

The technologies proposed under Scenario 1 have a greater social impact than those under Scenario 2. The reasons for this are that the system requires users to have the skill to operate the system and the time to do so, and that the treatment system is located within the homestead. However, the focus groups have shown that potential users are interested in the biogas option as they see a benefit in the use of biogas for cooking. The preferred option was the centralized system as it is perceived as most convenient. There are no legal requirements concerning the quality of compost, biogas or digested sludge. Institutional support measures are needed for all technologies as all require separation of organic waste, which is not yet common practice in Mexico. As the vermicomposting unit and the biodigester are more complex than normal composting, they require more training than composting and the centralized system. 7. Conclusions and recommendations The study has shown that a natural resources management option that aims at maximization of resource conservation may not be cheaper than a conventional management approach. Even if prediction of future costs is subject to significant uncertainty, this result is interesting given that the cost calculation included the monetary values of conservation, reuse and recycling of resources. The calculations show that the monetary value of resources is greatest for energy (with about MXN550person/yr for a biogas plant for organic solid waste) and lowest for water, which has no monetary value in peri-urban Xochimilco because water is provided for free from tankers, standpipes or illegal connections. The price of water is low throughout Mexico City, averaging only MXN5.45 /m3 (Ortega Font, 2011). The water tariff in Mexico City is a complex issue, as each block is classified


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according to a development index based on various socio-economic parameters. Depending on the value of the development index, households receive up to 91% subsidy of the water price. Valuing the reused wastewater at the unsubsidized water price of MXN25.8/m3 (SACMEX, 2013) would make the constructed wetland of Scenario 1 as economically as attractive as the centralized system. Issues such as a too low a price for water are well known but this may also be the case for the price of nutrients and energy. If the price of nutrients and energy were to increase, the conservation and reuse and recycling alternatives would increase in value relative to the conventional, centralized approach. An increase in the price per kilogram for liquid gas of around 40% (from MXN12 to MXN17) would make the biogas digester as cheap as the centralized composting system. The price of nutrients provided by the UDDT would have to increase by around 600% (from MXN18.4 to MXN110/kg for N and from MXN22 to MXN132/kg for P) for the system to reach the same cost as the centralized system. The study has also shown that technologies proposed under Scenario 1 would have a greater impact on users than those proposed under Scenario 2 as they would impose more responsibility on the users. However, focus groups have shown that users would be prepared to take on those responsibilities, even though the overall preference was still for centralized services. Therefore, it is unclear whether users would really be willing to operate such systems themselves over a longer period and mechanisms whereby professional organizations could take over the operation need to be explored, although this would increase costs. Finally, the study has confirmed that the technologies proposed under Scenario 1 are less compatible with the existing institutional system (regulations, laws, capacity of existing institutions) than is the conventional, centralized system. Therefore, substantial investment would need to be provided for training and awareness-raising activities and existing regulations and laws would need to be modified to cater to the needs of alternative technologies. A policy workshop with national and local stakeholders from the public and private sector was conducted to elaborate and suggest policy changes that would facilitate the implementation of alternative technologies. As a result of this policy workshop, the following key policy recommendations were elaborated: More information needs to be provided on the advantages and possible risks of alternative technologies that are easily accessible to local stakeholders and interested users, and guidelines for their application must be made available. The scope of application of such alternative technologies should be actively promoted among stakeholders (including providers of centralized services). Laws and regulations need to be reviewed with respect to their compliance to the needs of such alternative technologies. A mixture of public and private funding should be mobilized for financing (alternative) infrastructure. The public and private sectors should work together in this area. Awareness about the economic value of water services needs to be increased. Studies that identify the full economic value of direct and indirect benefits should be supported. Recognizing that operation and maintenance are crucial for long-term sustainability of any infrastructure, and therefore also for alternative technologies, funding policies should allow for funding of training activities and for funding of operation and maintenance work. In this context, policies should be elaborated that make it mandatory for infrastructure to be subject to follow up and monitoring even years after implementation. Financial resources need to be provided for that purpose. A planning framework like that applied in this project, which includes participatory planning and scenario building, technical feasibility studies and the assessment of environmental, economic and social aspects for different technically feasible options, can help to identify sustainable solutions. These key policy recommendations have been endorsed by some of the key stakeholders such as the Asociación Nacional de Empresas de Agua y Saneamiento, the Comisión Nacional de Agua and UNHabitat (Mexico).

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