Planning of disposal sites in Dar es Salaam, Tanzania—A decision support system approach

Waste Management & Research (1992) 10, 1 4 1 -152

PLANNING OF DISPOSAL SITES IN DAR ES SALAAM, TANZANIA-A DECISION SUPPORT SYSTEM APPROACH Michael Yhdego*, Rene V. V. Vidait and Christian M . Overgaard* *Centre for Developing Countries, Building 208, and tInstitute of Mathematical Statistics and Operational Research, Building 321 Technical University of Denmark, DK-2800 Lyngby, Denmark

(Received 2 April 1991 and accepted in revised form 12 August 1991)

A system is developed aiming at supporting the planners in several aspects of solid waste management in developing countries . The system is tailored especially to planning of disposal sites in Dar es Salaam, Tanzania based on a decision support system framework . Emphasis was placed on : applicability for users without particular computer knowledge, a simple and comprehensible system for solid waste planners to use, stressing environmental impact, and introduction of subjective judgements . As an important element of problem formulation and problem solving, the involved decision processes are elaborated . The entire system is implemented within a Lotus 12-3 spreadsheet environment . The developed model illustrates that it is possible to include and emphasize several features that are lacking in many existing commercial computerized models . Key Words-Planning model, decision support system, disposal site, Tanzania

1 . Introduction In any urban society, the collection and disposal of domestic, commercial and industrial waste is a vital service . Without adequate collection and recycling or disposal, solid wastes obstruct drainage, give environmental problems, promote disease vectors and are aesthetically offensive . Numerous obstacles hinder the provision of adequate solid waste management in developing countries . Solid waste services are often given a low political priority. Weak institutional arrangements result from the dispersal of planning and management among multiple agencies . Capital resource shortages also limit service provision, and available equipment often is used inefficiently or is inappropriate for the conditions in which it is operated . As urban areas grow, so do the volumes of wastes generated and the complexities of collecting, transporting, and disposing of them . Given the current growth rates of cities in the developing world, the problems of waste management planning are likely to worsen unless major efforts are undertaken to improve the planning process and strategies (Yhdego 1991b) . Solid waste management planning models and methods are used to analyse performance and costs of alternative waste management strategies . They may address one or more of the following aspects of solid waste management : waste generation, separation of waste components at their source, storage and collection of wastes, transport of wastes from collection areas to intermediate processing systems, transport of waste to landfills, waste disposal at landfills and multiple simultaneous recycling, composting, and resource recovering (Wilson 1981, Rushbrook & Pugh 1987, Energy Systems Research Group 1989) . Applications of microcomputer software in municipal solid 0734-242X/92/020141 + 12 $03 .00/0

©1992 ISWA



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waste management for developing countries have been reviewed and it is suggested that software programmes could bring about cost-effective improvement in planning and management of solid wastes (Light 1990) . The existing models do not consider some of the essential conditions which exist down and upstream of solid waste management in developing countries ; the most important is informal recycling in the form of scavenging (Yhdego 1991 a) . There are several stages of scavenging, very often well organized and controlled by scavengers . This means that at the end, i .e . at the disposal site, where, of course, more scavenging occurs, the amount of waste is reduced, but that the quality of the waste has become very poor for some more sophisticated recycling technologies . Therefore, waste managers and planners need to adopt a broader concept of solid waste management than one that guides most strategy planning models at present . In this paper planning of disposal sites in Dar es Salaam, based on a decision support system framework, is described and the results obtained are presented and discussed . 2 . Problem conceptualization The need for a systemized approach dealing with several aspects of solid waste management and planning in Dar es Salaam has been evident (Yhdego 1988, 1989) . There is no overall solid waste management in the present situation, instead planning is scattered between several departments under the City Council of Dar es Salaam . The present solid waste management is the responsibility of three municipal departments : the City Health Department, the City Engineering Department and the City Planning Department, as shown in Fig . 1 . City Health is the principal executing body for solid waste collection, transport and disposal . City Engineering is engaged in the repair of vehicles and maintenance of the disposal site . City Planning is responsible for the planning of disposal sites . City Finance decides on procurement of vehicles, spares and other equipment . City Personnel administers staffing and related matters .

Ci

Counc

Mayo

City D'rec a

Deputy City Directors (Urban and Rural)

I Personnel Affairs

Urban Planning

Three Assistant (Districts) City Directors

Legal Affairs

Engineering

Human Resource Deploymen

Fig. 1 . Urban management structure of Dar es Salaam .



Planning of disposal sites in Dar es Salaam, Tanzania

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The principal executing body for solid waste collection, transport and disposal in Dar es Salaam is the City Cleansing Service . This is one of five subsections under the preventive Health Section of the City Health Department as shown in Fig . 2 . The duties of the city Cleansing Section are : • collection and disposal of solid waste ; • reporting to the City Engineering Department concerning the maintenance of vehicles at Tabata; • policy preparation on solid waste management . The Cleansing Section shares a common aim with the Health Department, i .e . the improvement of health of the city residents . The Cleansing Section is, however, basically a transport organization, a function strange to other Health Department activities . The Cleansing Section lacks autonomy with respect to the procurement of equipment, the maintenance of vehicles, the recruitment and dismissal of personnel, and the proper management of the municipal waste dump . These necessary support functions are scattered throughout the city's urban management structure . This situation necessitates continuous interdepartmental negotiations on priority setting, and management information by a section positioned down the total urban structure . The budgeting process for solid waste management starts with some guidelines from the Ministry of Local Government . Then the Dar es Salaam City Council treasurer is approached . Through interdepartmental discussions in the City Council a total budget is agreed upon, and this is presented to the councillors for approval . They can either extend or reduce financial resources to certain areas . After further interdepartmental meetings the treasurer will present a revised budget, and so this process continues until an agreement is reached . Finally, the budget is returned to the Ministry of Local Government for approval .

Preventive Services

Curative Services

Malaria

Cleans ng

Building

Control

Ser ice

Plans

welfare Services

cad and Inspectorate

Programmes

water

nondoni

Fig . 2 . Organization of the City Health department .



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Rather than entrusting the solid waste management to one professional organization-engaged with policy planning, finance, personnel, operation and maintenancetasks have been diffused over a number of departments, sections and subsections . Inevitably this results in the present poor performance . Management of a collection and transport function is difficult if inputs of personnel, vehicles, equipment and expenditures cannot be evaluated against performance, demand, priorities and the available annual budget . Increased investments and extended operations would provide more reasons for an independent self-contained department for solid waste management operations . Such a department could possibly be a subsection of the City Health Department, but only if the relevant solid waste management tasks were transferred from the other departments (e .g . vehicle maintenance from the City Engineering Department), or the responsible department could be established as proposed in the Masterplan (Marshall Macklin Managhan Limited 1979) : "The responsibility for the collection and disposal of solid waste should be transferred from the City Health Department to the City Engineering Department . However, the Health Department should continue to monitor health hazards ." but this problem still constitutes one of the largest obstacles to satisfactory solid waste management . In the case of Dar es Salaam there was an immediate need to find a new disposal site outside the city centre to replace the Tabata dumping site (located 6 km from the city centre ; Fig . 3), which for some time has been filled beyond an acceptable capacity causing excessive pollution . The masterplan suggested alternative disposal methods, especially a change from crude dumping to sanitary landfilling, but these recommendations have not been followed .

~KUnduehi qugrtle5

/ Ubungo ~Kmwoni Tobato

1 Pugu station Q

Mbggoto

Fig. 3 . Location of possible disposal sites .



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In 1988 the first detailed study on solid waste in Dar es Salaam was undertaken (Haskoning & M-Konsult Ltd 1989) . This work included a lot of data collection, though much of this was quite basic, due to lack of previous studies regarding many of the relevant aspects . The study made by Haskoning recommended the continued use of the Tabata disposal site . The report was ordered by the then Ministry of Water and was never accepted by the City Council of Dar es Salaam . The local councils are under the Ministry of Local Government and are reluctant to accept uncoordinated orders from other ministries . Furthermore, the effect of scavengers in reducing the generated waste was not considered in the report, although this effect was recognized (Yhdego 1991 a) . Several residents have complained about air pollution from the Tabata dumping site (Yhdego 1988) . In particular during the last 3 years there has been intense dispute between the neighbourhood people living around the Tabata site and the City Council . Some of the active persons on behalf of the residents sued the City Council in 1988 . The High Court produced a verdict in June 1990, dictating the closure of the dumping site before the 1 September 1990 .

2 .1 Determination of qualitative elements In September 1990 a questionnaire was distributed to relevant authorities (City Council of Dar es Salaam, Ministry of Lands, and the National Environmental Management Council) to determine possible new disposal sites including a qualitative evaluation . On the basis of the answers received the following factors were identified as important to the local authorities : Political factors : • public acceptance : the local residents acceptance of the disposal site ; • employee acceptance : the employees working at the disposal site ; • cost of land/compensation : compensation to the total residents is not fixed, but is more or less a political decision, and it will be difficult to include in a non-political economic analysis . Environmental factors : • hydrogeology : e .g . the risk of flooding ; • morphology : e .g . the various layers of soil ; • distance from townships, present; • distance from townships, future : e .g . can urban development plans be adapted to the located disposal sites ; • impacts on public health: including the danger of vectors (e .g . insects, rats), smoke, dust, odours etc; • aesthetics : how much will the overall scenery be affected ; • use for land reclamation : e .g . filling a quarry or valley, or making hills for later use as a recreational area; • burden on traffic system : e.g. impact on already congested roads . The answers were aggregated for the most feasible sites-Kunduchi quarries, near Pugu station, and Mbagala Kiburugwa (Fig . 3)-and were transformed to the relative scale . Each factor was weighted with a scale factor 1, 2 or 3, 3 implying the most important factors as these are given most weight . The political and environmental factors were given relative values from 1-3 for each specific disposal site : "1" was chosen to represent the best qualities . For each disposal site the values were added to two total indexes ; one political index and one environmental index (Overgaard 1991) . The results for the three relevant disposal sites are shown in Table 1 . This is a preliminary assessment of disposal technologies that is pertinent in decision making processes .



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TABLE 1 Political and environmental index

Political factors Public acceptance Employee acceptance Cost of compensation Political Index Environmental factors Hydrogeology Morphology Distance townships, present Distance townships, future Impacts on public health Aesthetics Use for land reclamation Burden on traffic system Environmental index

Weighting

Kunduchi

Pugu

3 3

2 3 1

2 2 3

1 2 2

X

12

17

11

3 2 3 3 3 1 2

1

2 1 1 2 2 1 1 1

2 2 2 3 2 2 2 3

2 1 2 2 2 1 1 2

X

27

40

31

1

Mbagala

K

3 . The Dar es Salaam model Two different users of an overall solid waste management model for Dar es Salaam were identified: one within the existing organizational framework, where future presence of an overall solid waste management planner seems inevitable ; the other within the structure of a new independent department for solid waste management . The appropriate approach towards problem solving will depend on the nature of the decision-making processes involved . There are three different types of decision-making processes : structuring, understanding and action (Vidal 1990) . Structuring usually belongs to decision-making at the strategic level . There exists a non-defined problem, where strategies, goals and means need to be stipulated . Understanding is placed at a level between structuring and action . Often a lot of information is available . The objectives are difficult to formulate . Action usually corresponds to the more tactical level . The problem is well-known and well-defined . The planning of disposal sites in Dar es Salaam is a combined "structuring" and "understanding" problem . Many problems were certainly present in advance and some data were available, but on the other hand, several problems needed to be detected, and important supplementary data had to be collected . Objectives had to be formulated, and the interaction with the decision-makers was a central issue . Generally, for the "understanding" and "structuring" type of problems, much of the data describing the problem will be judgemental . The planner needs to develop an understanding of which items require detailed and careful estimation . This knowledge is gained during the planning process . Useful planning aids must support the acquisition of judgemental data and not demand it as a pre-requisite . The idea of studying real-life decision-making processes in such a normative way is to identify the type of computerized tool to be developed, the demands concerning data, and the involvement of decision-makers . In any case, a central element will always be participation and interdisciplinary involving the politicians, citizens, waste managers



Planning of disposal sites in Dar es Salaam, Tanzania

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and specialists working together to design the most suitable tools . One of these tools is a decision support system (Yhdego & Vidal 1991) . A main purpose in the development of the waste management model for Dar es Salaam was to create a system that could be used by planners in developing countries . As a consequence the system had to run on a personal computer. The system was developed on the basis of existing obtainable data and not on future possible data, but with a flexible structure so that new data could be easily adapted to the problem solving process . This consideration had a significant influence on the development of the system, especially on the choice of how to model the various modules . The model must also be comprehensible, easy to utilize for the user, and be able to rapidly produce "what-if" scenarios and sensitivity analyses . All these considerations, and especially the dependence on existing data, implied a fairly simple model and it was decided to develop the entire model with a Lotus 1-2-3 spreadsheet . The force of spreadsheets is that input parameters can be viewed and modified merely by scrolling through the spreadsheet and replacing an existing number with the desired one . In a spreadsheet the sensitivity of the result can be explored in few minutes by simply making changes in some of the judgemental data, and the new result will appear immediately . Finally, the spreadsheet environment is fairly easy to learn and to use . Demographic and technical data was obtained through interviews, previous studies, statistical material and maps . Only very limited information was available on the financial constraints, hence the technical constraints became "bottlenecks" in the model . Table 2 depicts the structure of the developed spreadsheet . The "Disposal sites" (Table 3) and the "Vehicles" (Table 4) modules contain technical data, including for example the effect of scavenging as an annual percentage reduction . In columns O-Y the generated waste in each category is distributed between wards . Each module has a structure as outlined in Table 5 . The generated quantity of waste for each ward was estimated from demographic information on relevant "generation factors", e .g . population, hospital beds etc . A more complex model could easily be included if data were available . The general procedure for using the system is to allocate waste to the cheapest possible according to a priority setting of the various waste categories until one the constraints becomes restrictive . If the "bottleneck" is a disposal site capacity, the system indicates the cheapest redistribution of waste . The procedure is terminated when no more waste can be collected due to either disposal site capacity, vehicle capacity, or financial constraints . The principal decision parameters are : (1) the quantities of waste in a specified category to be collected from a specified ward (point of generation) ; (2) the disposal site for the above specified waste . Yet the decision parameters can be extended to all input data that is not fixed . For example, the lifespan of the disposal sites is a political decision and the investment in new vehicles might be determined according to the need . Different scenarios and the sensitivity of the model can be tested by changing any data in the model . 4 . Results and discussion Nine scenarios were applied to the developed solid waste management model for Dar es Salaam to investigate different strategies concerning the allocation of one or more disposal sites in two different years ; the base year 1988, and 5 years later in 1993 . The



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TABLE 2 Structure of the spreadsheet Row

Column A-M

Row

1-20 Introduction screen picture

Column O-Y

Row

Column AA-AG

Domestic waste

55-90

Help columns for vehicle capacity calculation

1-47 48-78 Commercial waste 79-101 Institutional waste

21-34 35-45 46-94

Disposal sites Vehicles Distances and transport volumes 95-113 Constraints 114-135 Service level 136-163 Political and environmental index

102-128 Street and drain 129-162 Market waste 163-183 Hospital waste 184-195 Privately transported waste

TABLE 3 The "Disposal sites" module

Disposal sites

Total capacity (100 m 3 )

Life span (years)

Annual capacity (100 m 3)

Annual scavenging (%)

Fixed costs (Tsh y - ')*

Variable cost (Tsh y - ')

Kunduchi Pugu Mbagala

102 1155 1470

4 20 25

25 .5 57 .8 58 .8

3 5 5

0 0 0

0 0 0

* Tsh : Tanzania shillings .

TABLE 4 The "Vehicles" Module Type I (1 shift)

Collection vehicles

Quantity Life Variable cost Capital cost Shift Workday Operation Loading time Average speed * Tsh : Tanzania shillings .

(vehicles) (years) (Tsh t - ' km - ')* (Tsh vehicle - ') (shifts day - ') (hours day - ') (%) (hours) (km h - ')

28 5 120 9 million 1 7 65 1 .5 25

Type 2 (2 shifts) 2 5 120 9 million 2 7 100 1 .5 25



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TABLE 5 Structure of waste type module . Generation rate : 0 .4 kg capital -' day - ' 500 t d - ' . Growth rate : 0% . Density : 350 kg m -3

or

Wards

Collected waste

Generation Generated factors waste (t d - ')

Transport to sites (%) Kunduchi

Kariakoo Mcafukoge

Totals

X

Pugu

Mbagala K

total quantity :

(%)

(t d - ')

60

20

40

100

0 0

50 0

70 100

42 40

500

X

X

X

40

200

strategies were selected because they seemed to be the most likely to be implemented in the future . Finally, an extra scenario was run to illustrate sensitivity analysis . Scenario 1 : Scenario 2 : Scenario 3 : Scenario 4 : Scenario 5 : Scenario 6 : Scenario 7 : Scenario 8 : Scenario 9 :

Kunduchi, 1988 Kunduchi, 1993 Pugu, 1988 Pugu, 1993 Mbagala K, 1988 Mbagala K, 1993 Pugu & Mbagala K, 1988 Pugu & Mbagala K, 1993 Pugu & Mbagala K, 1988 and changed domestic generation rate .

The data output data includes utilization and capacity of disposal sites, utilization and capacity of collection vehicles, cost figures, service levels, and the final distribution of wastes within the last "served" category according to the priority setting . Output data for the nine selected scenarios is summarized in Table 6 . The scenarios in Table 6 provide two clear messages : (1) the use of Kunduchi as the only disposal site seems as a very bad solution because it is by far the most expensive from a transport-economical point of view with more than 50% higher costs per collected tonne ; (2) if a reasonable amount of the generated domestic waste is to be collected (in accordance with the priority setting) in the future, it is absolutely necessary to find extra disposal methods. Alternatively, the lifespans of Pugu and Mbagala K can be reduced . This is a short-term solution, and as a consequence new means of disposal need to be identified sooner . On the basis of statement (1) it is recommended that consideration be given to operation of Pugu and Mbagala K instead of the very expensive (measured in costs per tonne) Kunduchi disposal site . In any case it would be necessary to find a new disposal site to replace Kunduchi in a few years . It would be preferable to use Pugu and Mbagala K (both would also be individually preferable) and to try to find alternative treatment possibilities, which would be needed some years earlier, as stated in (2) . Anyway, it will be necessary to find extra disposal sites in the future . Finally, the political and environmental indices should be given attention . Pugu has

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TABLE 6 Central figures for the nine scenarios Municipal collection (%)

Disposal' (t d - ')

Total costs (million Tsh y - ')

Vehicle utilization (t d - ')

Cost t-' (Tsh x 10' t - ')

1*

11

3* 5* 7* 9* 2t 4t

25 25 31^ 26 5 7 17 18

86 .4 199 .9 203 .5 294 .4 292 .9 86 .3 199 .5 203 .3 402 .2

135 .4 208 .5 147 .9 166 .0 167 .6 135 .4 206 .2 147 .1 232 .4

70 .1 144 .5 119 .8 145 .4' 145 .5' 59 .3 120 .3 119 .4 169 .3

4 .29 2 .86 1 .99 1 .54 1 .57 4 .30 2 .83 1 .98 1 .58

Scenario No .

6t 8t

306

2

* 1988 . t 1993 . ' The disposed quantities can be a little larger than the annual capacities due to the reduction from scavenging ; for example for Kunduchi : 86.4 td - ' x 97%=83 .6 td - ' . 2 Calculated by dividing column 4 by column 3 after converting to the same time unit . I Scenarios where the vehicle constraint was the limiting factor, i .e . disposal capacity was not fully utilized . " Here privately disposed waste is accepted giving an overall collection of 34% of all wastes generated . Overall collection of 29% of all wastes generated . 6 Overall collection of 33% of all wastes generated . Tsh : Tanzania shillings .

both the highest political and the highest environmental index as shown in Table 1 . This indicates that this disposal site is generally not favoured, and that extra attention should be given to the preparation of this site . In this connection it is recommended that further investigations of the qualitative factors affected by operating a disposal site at Pugu be undertaken . It is emphasized that the results are obtained under some significant assumptions . First, the allocation of wastes strictly follows the theoretical priority setting . As a consequence a priority class is not entered before all lower classes have been served satisfactorily . This effect is quite evident in the very low collection rate of domestic waste (last on the priority list) in all nine scenarios . Secondly, disposal costs are not included in the model, due to lack of information . Neglecting capital costs for disposal sites may be acceptable if the expected lifetime is quite long . In this case, the daily expenses of collection, transportation and operation of the disposal sites are much more critical . Usually, collection and transportation costs are estimated to account for 70-90% of the daily costs . Thirdly, a much more severe financial limitation of the model is the lack of a budgetary constraint . This is likely to be a very vital factor for the decision-makers in Dar es Salaam . Furthermore, such a constraint might be the limiting factor, rather than either vehicle capacity or disposal capacity . Nevertheless, the developed model and the studied scenarios may possibly imply several qualitative aspects such as trends, critical factors (e .g. bottlenecks), and a sensible allocation of the waste that can be collected and disposed of .



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5 . Summary and conclusions A simple decision support system for solid waste management disposal sites planning has been developed for the case of Dar es Salaam . The entire model was developed on a Lotus 1-2-3 spreadsheet . The system is applicable on a PC and is easy to understand and use without a background in computer or system sciences . In general several features that are found to be unsatisfactorily handled in existing models have been included in the developed system . The two most important and innovative of these are : (1) the use of a priority-procedure that encounters the problem of evaluating uncollected wastes ; (2) introducing a measurement of qualitative factors for each treatment facility in the model by the use of a political and an environmental index . The latter secures one of the most essential objectives of the system ; to serve as a guiding tool for the waste management planner . The user is directed towards an understanding of the planning problem in a wide context where economic aspects need to be integrated with political, environmental, social and technological aspects . This feature could be important in the case of Dar es Salaam where the lack of an integrated overview seems evident . Along with a possible new organizational structure, where one department is responsible for the solid waste management, such a computerized tool could prove to be valuable, especially during the initial learning process . The decision support system conceptualized in this study, could be considered as an appropriate transfer of technology (Ravn & Vidal 1986) . The "appropriateness" is secured by the interdisciplinary function of the system and by requiring participation of the local planners who are to use the system . If successful, such a transfer of technology could undergo a further diffusion process to areas other than solid waste management .

Acknowledgements The authors wish to thank the City Council of Dar es Salaam for supporting and allowing to undertake this study . The assistance of the National Environmental Management Council and Ministry of Lands, Department of Town Planning and that of Hans Ravn, is gratefully acknowledged .

References Energy Systems Research Group Inc . (1989), WastePlan- The Solid Waste Management Planning Tool. User Guide Version 98 .7 . Boston : Energy Systems Research Group Inc . Haskoning & M-Konsult Ltd (1989), Masterplan on Solid Waste Management for Dar es Salaam . Volume I : Main Report & Volume II : Annexes . Tanzania . Light, G . L. (1990), Microcomputer Software in Municipal Solid Waste Management : A Review of Programs and Issues for Developing Countries . Water and Sanitation Discussion Paper Series . Washington : UNDP/World Bank . Marshall Macklin Monaghan Limited (1979), Technical Supplements 1,2,3 & 4-Dar es Salaam Masterplan . Ontario, Canada: Marshall Macklin Monaghan Limited . Overgaard, C . M . (1991), Solid Waste Planning in Tanzania-A Decision Support System for Dar es Salaam . MSc Thesis, Institute of Mathematical Statistics and Operations Research, The Technical University of Denmark . Ravn, H . F . & Vidal, R . V . V . (1986), Operational research for developing countries---A case of transfer of technology, Journal of Operations Research Society 37, 205-210 . Rushbrook, P . E . & Pugh, M . P . (1987), An illustrated description of Harbinger, Wastes Management 6, 348-361 .



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Vidal, R . V . V. (1990), Computerized Toolsfor Decision-Making . Paper for Gulbenkian Lecture on "Science and the Modern World" . Lyngby : Institute of Mathematical Statistics and Operations Research, The Technical University of Denmark . Wilson, D . C . (1981), Waste Management : Planning, Evaluation, Technologies . Oxford : Clarendon Press . Yhdego, M . (1988), Urban solid waste management in Tanzania, Waste Management & Research 6, 175-180 . Yhdego, M . (1989), Environmental epidemiology in a market place . Waste disposal in Kairakoo market . The Tanzania Engineer 2, 4, 20-26 . Yhdego, M . (1991a), Scavenging of Solid Wastes in Dar es Salaam, Tanzania . Waste Management & Research 9, 259-265 . Yhdego, M . (199lb), Africa's waste dilemma . ISWA Times, No . 2, I . Yhdego, M . & Vidal, R . V . V . (1991), Computerized tools for solid wastes decision making process . Lyngby : Centre for Developing Countries, The Technical University of Denmark .