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Sound Sanitary Landfilling: A Sustainable Option for Waste Disposal in Harare and Gweru, Zimbabwe

Introduction

The Harare and Gweru City councils are currently facing immense problems in solid waste management, especially waste dump management. In Harare the Golden Quarry dumpsite was opened over 20 years ago when the sites along the Mukuvisi filled up. It is situated about 7 km from the city centre, close to the sources of waste, such as the central business district, the industrial areas and the bulk of the high-density residential areas. As a result of this proximity, Golden Quarry receives about 90% of all waste disposed in Harare (Tevera 1991; 1993). The rest of the waste is taken up by Teviotdale waste dump some 12km from the city center outside the northern frontiers of the city. It was opened up in 1982 to serve the low-density residential areas, and for debris from the construction industry and a bit of industrial waste from Msasa.

According to the City of Gweru Health Department Report (2000), old gravel pits have been used for waste disposal in Gweru since the 1940s. A number of areas have served as disposal sites up to today. These include the following:

1. Thornbrook Plot near Windsor Park

2. The area near Thornhill round- about close to the little kopje

3. Area at the base of the kopje where Enfield and Franklin courts stand today

4. Old gravel pits in Lundi Park

5. Old Gwenoro Road turn off from the old Bulawayo Road

6. Area between Bata Estate and Mkoba Village Eleven

7. Area west of Mudavanhu Centre

8. Mkoba light industrial sites

9. Area near Gweru River at the end of Coventry Road

10. Area where Senga Public Training Centre stands today

11. The present site across the Gweru River

All the above locations in Gweru, just like the case of Harare, disregard environmental concerns. The only effort made was to locate them some distance from built-up areas as the public health concerns were given some priority. The Health Department and Town Planning Development and Control Section went out to identify possible sites for waste disposal and the site chosen was not based on a complete environmental impact assessment (EIA). In 1980 the disposal site was moved from the current location to Mkoba light industrial area and reverted to the original site due in 1990 to pressure from residents of Mkoba high-density residential area. According to the City health Department, such scenarios characterise the rather negative planning approach attached to waste management in general in Zimbabwe.

Environmental Concerns

The processing and dumping of waste needs to be taken far more seriously than is the practice at the moment in Harare and Gweru. The pollution from the smoke is an environmental and health hazard to the residents of Borrowdale, Warren Park and Westlea suburbs in Harare, and Monomotapa and Mambo suburbs in Gweru.

Fires are a serious environmental problem at the two official dumps in Harare. Scavengers start fires inadvertently as they prepare food for themselves and their families. Industrial waste is also flammable and results in fires. Such solid wastes as old tyres, PVC pipes, used batteries, old paints and plastics are also easily converted into toxic material. Leaching is also a potential danger when excess water is used to put out fires and this poses a threat to groundwater sources. The build- up of gases poses a threat to nearby houses. Such landfill gases comprise methane (45%), carbon dioxide (35%), nitrogen (18%), oxygen (1%), and sulphur compounds (1%).

Decomposing matter at the landfills in Harare and Gweru produces a very offensive odour, which is a major environmental nuisance to the nearby suburbs. Dust, blowing paper, and rats are also the other nuisances associated with the landfills. In Gweru, the distance between the old landfill and the town centre is only 2 km. Power lines traverse the dumpsite from south to west and on to the northwest. Gweru River flows through the area and during the rainy season it floods and flows into the landfill. This poses an environmental hazard as the water transports leachate out of the landfill.

Furthermore, domestic and industrial waste is mixed and the slope is too steep in the west, but acceptable in the north, northeast and south. Much of the dumpsite also lacks topsoil, making the surrounding area look very polluted by air- transported material such as plastic and paper.

Another major problem associated with the Gweru dump is that of waste oil management. Different hydrocarbons, i.e crude or refined oil, differ in their toxicology, resistance to degradation and the ability to incorporate into the ecosystem. The waste oil problem involves mainly lubricants such as engine oil and transmission oil. These lubricants have a high viscosity and poor solubility without any degreasers present. The hydrocarbons are usually in the range C26- C40 (see Table 1).

Table 1: Boiling Temperature Related to Molecular Size

Source: Laws (1993)

Eriksson and Nilsson (2000) note that lubricants do not exhibit PAH and Naphtha, but viscosity improper, corrosion and oxidation inhibitors are often added. Hence due to their high viscosity, they are not soluble with water and so are transported slowly into the ground. If the soil has a high solubility, gravity dominates; but if the permeability of the soil is low, capillary force becomes dominant. When oil is spilled on the soil consisting mainly of medium grained sand or finer fractions, capillary force spreads the pollution more horizontally than vertically (SNV 1995). Cheremisinoff (1995) indicates that oils in water resources used for domestic purposes may cause objectionable taste, odours, colours and turbidity, and hence film, making water treatment difficult. A major toxic effect is the disruption of metabolism in living cells. Therefore the aliphatic hydrocarbons (eg. Methane with more than 60% of hydrocarbon content in alkens) are least toxic, and the most toxic are aromatic compounds with at least one benzene ring e.g., that found in crude oil (NRC 1985).

The safe and effective operation of landfills depends on sound planning, administration and management of the entire solid waste management system (Department of Water Affairs and Environment, 1998; Gourlay 1992; Lane and MacDonald 1993; MLGRUD 1995; Tchobanoglous et al 1993; Tevera 1991; 1993; UNEP 1996). In light of this, the Harare and Gweru City Councils need to create institutional and policy environments that view solid waste disposal as a vital element in the cities’ sustainable development plans. In planning for the landfills, the following key considerations need to be taken into account:

The type required – open dumps are not as secure as sanitary landfills;

The required capacity;

The NIMBY (“Not in My Backyard”) syndrome i.e community opposition to the sitting and operation of municipal solid waste facilities close to their neighborhoods. This is due to the health and environmental risks posed by the facilities, their impacts on property values, and the negative impacts on aesthetics, odours and flies.

Landfill Technology Design

A sanitary landfill considers daily cover of soil over the waste, a liner that traps leachate, leachate collection and treatment or recycling, runoff control drainage system and final cover. Pousette and Lagerkvist (1996) pose two basic strategies in the landfilling of waste, i.e. firstly isolation of waste from its surroundings and then to have control over the different effluents leaving the landfill.

The characteristics of the waste generated in Harare and Gweru would need to be examined because this assists in the development of treatment techniques, environmental impact assessment (to predict emissions, gaseous and liquid, from the landfill in future) as well as the design of criteria for operation and monitoring. In Harare and Gweru, the waste generated was characterised as follows:

Inert waste: construction material

Domestic waste: from dwellings and contains high levels of organic matter

Industrial waste: complex and can be anything from oils, scrap metals to hazardous chemicals Leachate: from hazardous industrial waste.

The Controlled Landfill Design

Protective measures need to be taken when depositing materials which leave contaminated leachate and gaseous emissions. This can be achieved using controlled landfills. The objective is to have a cost – effective and environmentally acceptable waste disposal facility. The controlled landfill specifically takes into account the vulnerability of the environment to pollution. In terms of the design of the upslope cut – off drainage systems, the requirements of the Water Act must be met. The system needs to be able to separate unpolluted water from polluted water. Drains should be able to accommodate maximum storm return periods within the given catchment area.

In a sanitary landfill, a minimum permissible separation between the proposed waste body and wet season high elevation of groundwater of 200m is acknowledged (Department of Water Affairs and Forestry 1998). This ensures that waste is not deposited into excavations where the zone of aeration has been reduced or the water table has been affected. However, unlike in clays, the separation is thicker in more permeable sandy soils. In view of all this, the design structure of the lining system is very vital because leachate can be very toxic. The lining system also adds to the separation made by the unsaturated zone between the groundwater and the landfill (Box 1). The minimum accepted plasticity index for a compacted soil liner is 10mm with a maximum particle size not exceeding 25mm (Department of Water Affairs and Forestry, 1998; Lagerkvist and Pousette 1996). If the layer comprises compacted soil of low permeability, the lining layer must not exceed a given maximum rate of leachate outflow to pass through its layers. Hence clay liners would have to be compacted to a minimum dry density of 95% Standard Proctor maximum dry density.

As a result of leachate flow in any landfill, the base of a landfill must be inclined in such a way that the generated leachate is directed to a specific control point. Any leakage passing the barrier of the upper liner is also detected. A leakage collection sump collects the leakage, and its quality and quantity are monitored. A capping layer of the landfill separates the waste body from the atmospheric environment. It thus prevents erosion due to heavy rain and slides, and makes it possible for plants to grow on top of the landfill. Plants increase evaporation from the landfill, hence decrease infiltration, which in turn decreases leachate production (Eriksson and Nilsson 2000).

Adapted from Pousette and Lagerkvist (1996).

Landfill Management

Sanitary landfilling remains the most economically viable, socially acceptable and environmentally friendly waste disposal option; but it has to be done right. The following principles of sanitary landfilling need to be considered by the waste managers of the Harare and Gweru City Councils.

Location of Future Landfills

In the selection of suitable landfill sites there are a number of environmental, economic, social and administrative conditions which have to be satisfied. These include the following:

• Environmental: Groundwater protection areas, water resource conservation areas, stream networks, natural geology, wet land, flood plain, fault area, natural parks, wind direction and soils.

• Socio- cultural: municipal development areas, planning areas, historical and important cultural sites and population areas.

• Administrative: environmental legislation/policies, engineering and economic considerations such as road networks and land cost.

Methods of Landfilling

General waste: A cell of compacted waste forms the basic landfill unit and is entirely contained by cover material. Dimensions 1.5m to 2.0m high berms made from soil, rubble or slope waste form the dimensions of the sides. Hazardous waste needs to be pre – treated to render it immobile, less toxic and less reactive. Pretreatment involves chemical processes such as neutralization, fixation and oxidation. Physical processes include incineration, blending and encapsulation. Biological processes include aerobic and anaerobic degradation of organic materials.

Co – disposal: Where general waste is disposed in hazardous waste landfills, the standard procedure is to determine the co – disposal ratios. Liquids may be co – disposed with dry waste and hence the landfill needs to be equipped with a leachate management system and the resultant leachate flow must be contained, extracted and treated. The Department of Water Affairs and Forestry (1998) suggested the following approach in the determination of co- disposal ratios:

Co- Disposal Ratio = mass of dry waste /mass of liquid waste disposed

Where:

w = water content of incoming dry waste on a dry mass basis

f = field capacity on a dry mass basis

H = height of lift of landfill above landfill base or nearest intermediate cover layer

Y(kg per cu m) – wet density of dry waste

yw (kg per cu m) density of water

R (m/y) = rainfall or precipitation at site

E = eA (m/y) = A= pan evaporation, e is the factor used to convert pan evaporation from a landfill surface

For a column of waste of unit cross section H, in height, the mass of dry waste is:

YH/1+w and water is Yhw/1+w

The co – disposed liquids as a proportion of dry solids and thus the total mass of liquids is (w+y) yH (kg)/1+w

Mass of liquids at field capacity of waste is:

yH (kg)/1+w

Net precipitation per year per cu m is:

Pn = (R – Ea) Yw (kg)

Therefore liquids in excess of field capacity in the first year after lift H is disposed are:

(w+y) yH/1+w + (R-Ea) w – fyH/1+w = Leachate (kg)

L= (w + y – f) yH +Pn (1+ w) yw/1=w

CR = yH/1+w /y y-H/1+w = 1/y

Combining expressions for L and CR, hence:

CR = yH / L (1+ w) + yH (f-w) – Pn (1+w) yw

Therefore, using expressions for CR, the expressed yearly leachate for any site can be investigated.

Thus for 200mm/year of leachate on average,

If w= 30% f= 0.65 y= 0.75T/cu m H= 5m yw= 1 T/cu m Pn= +0.12m/year;

Hence CR= (L=200)= 0.75(5)/0.20(13)+0.75(5)(0.35)- 0.12(1.3) 1.0=2.6

The implications in variations of co – disposal ratios are both economic and environmental. An increase in volume of dry waste for example reduces leachate generation, potential environmental impacts and thus leachate management costs. Conversely, when the amount of dry waste is reduced, airspace utilisation is also reduced; but there will be greater need for leachate management.

Control of Nuisances

All litter must be contained within the landfill site through compaction and cover. Wind – blown litter is easily picked up and removed from fences and vegetation daily. Good cover and maintenance control odours. Watering unsurfaced roads and ungrassed or unpaved areas can also combat dust. Burning of waste to reduce volume and the attraction of vermin must be considered unacceptable due to its impacts on aesthetics, generation of odours, and potential of health dangers from air pollution.

Landfill Restoration

In the case of Gweru, a number of measures can be recommended for the restoration of the old landfill. In what is known as Area 1 where mostly old buildings and compost material are dumped, not much needs to be done. These waste types are non hazardous with the compost material converting to soil as a result of biological degradation. The building bricks are an inert substance and hence pose no environmental problems. The almost 6, 500 cubic metres of old building bricks and compost could be used as a resource for restoring other parts of the landfill.

In what is known as Area 2, the procedure would be to restore the oil pond by covering the entire pond and making the oil immobile, hence receiving a hydrologically sealed cell (Eriksson and Nilsson 2000). The pond would thus be filled up with larger materials such as stones or scrap metal and then using a top barrier to cover the entire area. Grass and trees would then be planted on top of the soil. The slope angles would also need to be reduced and prevent landfill inhabitants from crop cultivation.

In Area 3 co- disposal of industrial and domestic waste is undertaken. The slope angles of the landfill are appropriate except in the western segment. There is no liner underneath the landfill and this makes it difficult to make the landfill hydrologically secure. Leachate can, however, be countered by lowering the groundwater table through excavating the Gweru River and ditch construction around the area. A top barrier made of a soil layer of about 0.3m to 0.4m thick with a plantation of grass, trees and bushes is also made.

Waste Oil Treatment

The problems of waste oil could be overcome using land farming and solidification technologies.

Land farming is a method used to decompose organic nonhazardous waste by microorganisms and fungus (Ewiis 1998; Crawford and Crawford 1996). Tilling equipment is used to turn and aerate the soil, and hence thin layers of soil are treated. When liquid waste is deposited on a land farming unit, soil acts as a treatment medium and can thus be used for a long period without being replaced. The waste is applied using sprinklers, irrigation, or overland flow. The essential parameters for land farming include the following:

• A temperature regime of 0 degrees to 70 degrees (Bengstsson 1996) for a macro – organism field of life;

• Compost temperature parameters of 48 to 71 degrees celcius as being the optimum (Mather 1991; Hellden 1996);

• Optimum Ph for oil degradation at a range of 605 to 7.5 (Hellden 1996);

• Nutrition for micro – organisms is also essential in the form of nitrates, ammonium, phosphates, sulphur, potassium, sodium, magnesium and iron (Brock and Madigan 1991);

• A suitable C/N ratio of 60/1 for oil reduction;

• An oxygen level of 0.45 gm per gram of carbohydrate to remove surplus products as carbon dioxide, water and heat (Haug 1993).

The hot dry climate of Gweru makes oil reduction by biodegradation appropriate and cost effective.

EMS Implementation

In the Editorial of The Herald newspaper of August 30 2000 it was observed: “It is a disgrace that a city of the size of Harare does not have a proper waste management plan. It is time that one is thought out and implemented swiftly.”

The starting point for the cities of Harare and Gweru would be the introduction of well-managed Environmental Management Systems (EMS). An EMS integrates environmental considerations into council activities and decisions. This is because an EMS is an organizational framework for systematic identification, control and improvement of environmental aspects and impacts (SAZ 1996; Nath 1984). It is a continuous cycle of planning, implementing, reviewing and improving the actions that an organization takes to meet environmental obligations. The development, implementation and revive process of the EMS Cycle.

The Environmental Review provides the base for the EMS as it identifies the weaknesses of the current waste management systems in Harare and Gweru. Based on the environmental review, an environmental policy is established for the particular council. This is a statement of intentions and principles in relation to overall environmental performance. The policy provides a framework for action and sets objectives and targets. In the case of Harare and Gweru City Councils, the inputs into the environmental policy would emanate from the environmental review of the landfills, views of stakeholders (including residents) and the city by-laws and the current Environmental Management Act. The planning stage in the EMS cycle sets the criteria to meet environmental management goals. It comprises measurable objectives and targets as the basis to measure environmental improvement in the council. A waste management plan for any town is essential because waste needs to be managed at all stages from its generation to disposal (UNEP 1999; Swedish Association of Waste Management 2000). The decisions made on one aspect affect other aspects, e.g. the amount of waste reduction carried out affects the rate at which landfill space is filled up. 

The implementation and organizational phases of the EMS involve setting out responsibilities right from involving the city mayor as the chief executive down to the general workers. For this phase to be successful employees need to know what to do, when, how, and why. A training and awareness raising programme needs to be put in place and a documentation system also needs to be maintained.

When implemented procedurally within the city councils of Gweru and Harare, an EMS would offer the following advantages:

Consistency in approach across the whole council;

Raising of awareness of environmental issues amongst all staff and elected members;

Demonstrates to the public and other organizations that the council takes environmental issues seriously;

Helps identify problem areas within an organisation where the existing standards are low;

The organisation can have an on-going process and thereby keeping staff on their toes

Enables compliance with waste management legislation such as the city by-laws and the Environmental Management Act (2003); and

Enables improved community relations with stakeholders, environmental groups and the media- hence improving the corporate image of the organisation.

Concluding Remarks

Integrated solid waste management is based on the idea that all aspects of a waste management system must be analysed together since developments in one sector frequently affect practices or activities in another. This approach therefore allows for public, private and informal sector participation in waste management. The universal approach related to the integrated approach is the waste management hierarchy. It ranks waste management operations according to their environmental benefits. Its principles also abound in international conventions and protocols dealing with management of toxic wastes. The universal waste management hierarchy entails the following stages:

Prevent creation of waste or reduce the amount of generation;

Reduce the toxicity or negative impacts of waste that is generated;

Re-use in their current forms the materials recovered from the waste stream;

Re-cycle, compost or recover materials for use as indirect inputs to new inputs;

Recover energy by incineration anaerobic digestion or similar processes;

Reduce the volume of waste prior to disposal; and

Dispose of waste in an environmentally sound manner, generally in landfills.

The waste management hierarchy provides a useful tool for situations where the landfill forms the final repository for solid waste.

Land filling as a waste disposal option minimizes the problems associated with open or crude dumping. For any local authority, the sanitary landfill offers many advantages. Landfills should therefore be considered part and parcel of the integrated waste management strategies of the cities of Harare and Gweru. This is because the landfill is the ultimate means of waste disposal.

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