Introduction

Solid wastes are all the discarded solid materials from municipal, industrial, and agricultural activities.

The objective of solid wastes management (SWM) are to control, collect, process, utilize and dispose of solid wastes in an economical way consistent with the public health protection.

  Background

While most of the focus in waste management is on municipal solid waste management, it is important to note that MSW is a small fraction of the total amount of waste generated. The Resource Conservation AND Recovery Act (RCRA) delineate two categories of waste: hazardous and nonhazerdous waste.

In the united states, 11.7 billions tons of wastes are generated each year, including about 0.7 billions tons of hazardous waste and 11 billions tons of nonhazerdous waste, most of that 11 billions tons is generated by industries during raw material extraction, material processing, and product manufacture, while less than 2% is municipal solid waste.

   Summary of definitions (following the above listed laws):

     Municipal Waste (law 38):

All wastes, solid and/or liquid resulting from population, residential and non residential buildings, as well as transport vehicles.

    Special waste:

Special waste is considered as waste that has to be disposed separately or at least collected separately from residential waste.

   Waste Collector (law 38):

Any person other than those related to the body/authority responsible for public cleanliness, who collects wastes from the sources listed in the definition above, either for his own account, or on the behalf of a contractor, with the purpose of disposal.

   Contractor (law 38):

 Any body delegated by the authority responsible for public cleanliness to collect and transport wastes generated as listed above in bullet point 1.

  Waste Management (law 4):

     The processes of collection, transport, recycling and disposal of wastes

  Waste Disposal (law4):

The processes not resulting in recovery, reuse or recycling of wastes, such as land filling, deep well injection, disposal in surface waster bodies, Physico-chemical treatments, permanent storage or incineration.

  Waste Recycling (law4):

 The processes resulting in recovery, reuse or recycling of wastes, such as use a fuel, metal recovery, organic material recovery, soil remediation, recovery of used oils.

  Sources and classification   

Solid waste is a source of pollution that comes in importance after water Pollution and air pollution. Sources of solid wastes in a community are, in general, related to land use and zoning. The principal sources of solid waste are domestic (Residential), commercial, industrial, and agricultural activities. Although any number of source classifications can be developed, the following categories are the most important:

                              (1)  Residential, Commercial, Institutional.

                              (2)  Industrial.

                              (3)  Agricultural.

                              (4)  Hazardous waste

    Solid wastes are classified as:

            a-    Garbage: it is produced during the preparation of meat, fruit, and vegetables.

          b-    Rubbish: it is combustible or non- combustible solid waste. Combustible wastes include          paper, wood, scrap, rubber and leather. Non- combustible wastes include metals, glass,

               ceramics etc.

         c-     Pathological wastes: like dead animals and human waste.

         d-    Industrial wastes: Chemicals, paints metal ore processing, sludge and flyash.

Agricultural wastes: Farm animal and crop residues.

The following table shows an example of the amount of solid waste that has to be disposed daily In Alexandria.

   Table 1

Waste Generation and waste sources (base year 2000)

 Residential waste and waste that is similar to residential waste

tons/day

m3/day

1. Residential waste

1.642

5.400

2. Market waste 1 (System A +B)

269

880

3. Market waste 2 (System C)

188

600

4. Commercial waste (shops, hotels, restaurants, ( System  A+ B)

269

900

5. Commercial waste (shops, hotels, restaurants System C)

77

260

6. Debrises & dust

136

230

7. Waste from Harbor & Airport

20

70

8. Offices & Governmental Buildings

133

450

9. Medical  waste, similar to household waste

19

60

10. Waste from gardens/parks

50

250

11. Paper bin waste

30

200

12. Waste from street sweeping

176

300

13. Industry 1, similar to household

54

172

Waste quantity during October - May

3.063

9.772

14. Waste from beach cleaning

50

500

15. Summer waste increase

483

1.550

Waste quantity during June - September

3.596

11.822

B. Special wastes

 

 

16. Medical  waste, hazardous

10

50

17. Waste from slaughterhouse

1

5

18. Industry 2, process specific waste

587

1.875

C. Total disposal

4.194

13.752

On average, the solid waste quantity generated only by households in Alexandria is 0, 47 kg/capita per day, or 1,50 lt./capita per day.

     Composition of Solid Waste:

Composition is the term used to describe the individual components that make up a solid waste stream and their relative distribution, usually based on percent by weight. Typical distributions of components of Solid Waste in Egypt (percent by weight) and the corresponding density is given in table (2)

      Table (2): Typical data of components of MSW and the corresponding density

Component

Density kg/m3

% by weight

Organic:

 

 

Food wastes

290

50-60 %

Paper

85

10-20 %

Plastics

65

3-7 %

Inorganic:

 

 

Glass

195

5-1 %

Ferrous metal

320

2-6%

Nonferrous metal

160

2-4%

MSW

  compacted     300

Uncompacted 130

15-40%

Information about the composition of solid waste is important in evaluating equipment needs, systems, and management programs and plans.

     Solid waste management:

Solid waste management may be defined as the control of generation, storage, collection, transfer and transport, processing, and disposal of solid wastes in a manner that is accord with the best principles of public health, economics, engineering, conservation, aesthetics, and other environmental considerations, and that is also responsive to public attitudes. The first objective of solid waste management is to remove discarded materials from inhabited places in a timely manner to prevent the spread of diseases, to minimize the likelihood of fires, and to reduce aesthetic insults arising from putrefying organic matter.

The goals of M.S.W.M can be summarized as follows:

-To protect environmental health.

-To promote the quality of the urban environment.

-To support the efficiency and productivity of the economy.

-To generate employment and income.

To achieve the above goals, it is necessary to establish sustainable system of S.W.M. The principal of sustainable waste management strategies are to:

-         Minimize waste generation.

-         Maximize waste recycling and reuse.

-         Ensure the safe and environmentally sound disposal of waste.

    Functional Elements of a Waste Management System:

The activities involved in the solid waste management have grouped into six functional                    elements:

1-   Waste generation.

2-   On-site handling, storage and processing.

3-   Collection.

4-   Transfer and transport.

5-   Processing and recovery.

6-   Disposal.

   The interrelationship between the functional elements is shown in Fig. (1)

  1- Solid waste generation:

Solid wastes include all solid or semisolid material that has no longer considered of sufficient value to be retained.

Estimation of solid waste quantities:

The quantity and general composition of the waste material that is generated is of critical importance in the design and operation of solid waste management.

The load-count Analysis: In this method the quantity and composition of solid wastes are determined by recording the estimated volume and general composition of each load of waste delivered to a landfill or transfer station during a specified period of time. The total mass and mass distribution by composition is determined using average density data for each waste category (table 1).

Mass volume analysis is another method that is similar to the above method with the added feature that the mass of each load is also recorded. Unless the density of each waste category is determined separately, the mass distribution by composition must be derived using average density values (table 1).

Mass volume analysis is another method that is similar to the above method with the added feature that the mass of each load is also recorded. Unless the density of each waste category is determined separately, the mass distribution by composition must be derived using average density values (table 1).

The factors that influence generation rate of municipal wastes include: geographic location, season of the year, collection frequency, use of kitchen waste grinders, characteristics pf populace, extent of salvaging and recycling, public attitude and legislation.

 

Fig (1)   : Interrelationship of functional elements comprising SWMS

    2.1 On-site handling:

 On-site handling refers to the activities associated with the handling of solid wastes until they are placed in the containers used for their storage before collection. It may also be required to move loaded containers to the collection point and to return the empty containers to the point where they are stored between collections.

   2.2 On-site storage:

 The factors that mast be considered in the on-site storage of solid wastes include 1- Type of containers. 2- The container location. 3- Public health and aesthetics. 4- The collection method.

   Containers:

 There are different types and capacities of containers commonly used for on-site storage of solid wastes. But because of increasing costs (labor, workers compensation, fuel and equipment costs) there is a strong movement toward the use of large containers that can be emptied mechanically using a vehicle equipped with an articulated pick-up mechanism.

   Container locations:

 In newer residential areas, containers are placed by the side or rear of the house. Fig. (2)

In old residential areas containers are placed in alleys. In high rise apartments storage containers are located in a basement or ground-floor service area.

 

Fig. (2): Typical storage location for on-site containers for an apartment complex

    2-3te processing of solid wastes: On-si

 On site processing methods are used to recover usable materials from solid wastes, to reduce its volume or to alter its physical form. The most common on site processing operations include manual sorting, compaction and incineration.

   3-Collection solid wastes:

    Information of collection is presented in four parts:

1-     The types of collection services.

2-     The types of collection systems.

3-     An analysis of collection system.

4-     The general methodology involved in setting up collection routs.

   3-1  Collection services:

 For municipal solid wastes, the most common collection services are curb, alley and backyard collection. In future the use of large container that emptied mechanically by using a vehicle equipped with an articulated pickup mechanism will be the most common method.

 The collection services provided to large apartment buildings, residential complexes, commercial and industrial activities typically in centered around the use of large movable and stationary containers and large stationary compactors. Compactors are of the type that can be used to compress material directly into large containers or to form bales that are then placed in large containers.

  3-2   Types of collection systems :

 Based on the mode of operation, collection systems are classified into two categories:

Hauled- container system (HCS).

Stationary container system (SCS).

Hauled- container systems (HCS):

 It is the collection systems in which the containers used for the storage wastes are hauled to the processing, transfer or disposal site, emptied and returned to the original point or to some other location.

 There are two types of hauled container system: 1) tilt -frame container, 2) trash-trailer. Tilt-frame hauled container system has become widespread because of large volume that can be hauled but trash trailer is better for the collection of especially heavy rubbish. The application of both tilt -frame container and trash-trailer are similar, where, the collector is responsible for driving the vehicles, loading full containers, and unloading empty containers, and emptying the contents of the container at the disposal site.

  Stationary container systems (SCS):

It is the collection systems in which the containers used for the storage of wastes remain at the point of waste generation except when moved for collection. There are two types of stationary container systems: 1) self-loading collection vehicles equipped with compactors. 2) Manually loaded vehicles.

Trips to the disposal site, transfer station or processing station are made after the content of the collection vehicle is full.

Examples of typical collection vehicles are shown in fig. (3).

 

Fig. (3): Various trucks for municipal solid waste and recyclable collection

The operational tasks for the hauled container and stationary container systems are shown schematically in Fig (4).

 

 

Figure (4): Definition sketch for waste collection systems

    3-1  Analysis of collection system:

        By separating the collection activities into unit operations, it is possible to develop design data and relationships that can be used to establish vehicles and labor requirements for the various collection systems. The activities involved in the collection of solid wastes can be resolved into four unit operations: pick-up, haul, at-site, and off-routs. So, the time required per trip, which also correspond to the time required per container, is equal to the sum of pick-up, at-site and haul times.

 

   3-4 Collection routs: 

     Once the equipments and labor requirements have been determined, collection rout must be laid out to use the work force and the equipments effectively. The lay out of the collection routs are a four-step processes.

 First: prepare location maps with the data of the pick-up points, their locations, number of containers, collection frequency, if SCS system is used, and the estimated quantity of wastes to be collected at each pick-up collection.

Second: Prepare data summaries; estimate the quantity of wastes to be collected from pick-up location. If SCS system is used, the number of locations that will be serviced during each pick-up cycle must be determined.

Third: Lay-out preliminary collection routes starting from the dispatch station and ending at a location near to the disposal site.

Fourth: Develop balance routes. Determine the labor requirements per day and check against the available work times per day.  

   4 - Transfer and Transport:

 -    Transfer and transport refers to the mean, facilities, and appurtenances used to affect the   transfer of wastes from one location to another.

  -Small collection vehicles are transferred to larger vehicles that are used to transport the    waste over extended distances to disposal sites.

   -  It is very important to calculate the traveling period between the collection areas to the final     disposal area.

   -  Depending on the method used to load the transport vehicles, transfer station may be                classified into three types:

 §    Direct Discharge: The wastes in the collection vehicles are emptied directly into the vehicle to be used to transport them to a place of final disposal area. Used normally in the small communities.

§    Storage Discharge: the wastes are emptied into storage area from which they are loaded into transport vehicles by auxiliary equipments. Then will be transfer to the final disposal sites. It is useful for the large communities.

§    Combined of storage and direct Discharge: in some transfer station both methods are used to serve a broad range of users. In addition, it houses a material salvage operation.

     -  Health, safety, and environmental requirements are needed in the transportation of solid          waste.

  5- Processing and recovery

    - Separation of solid waste could be at the source or at the final stage before disposal of the solid waste.

    - Chemical and biological transformation processes are used to reduce the volume and weight of waste requiring disposal.

     -  It is very important to separate the recyclable materials to reduce the volume of the waste disposal.

    -  Types of separation depend on the types of solid waste. Such as:

 §    Density separation: air classification is the unit operation used to separate light materials          such as paper and plastic from the heavier materials such as ferrous metal, based on the weight difference of he material in an air stream.

§  Magnetic separation: magnetic separation is a unit operation whereby ferrous metals are separated from other waste materials by utilizing their magnetic properties.

    -  Engineering consideration involved in the implementation of waste separation include the  followings:

§    Selection of the materials to be separated.

§    Identification of the material specifications.

§    Development of separation process flow diagrams.

§    Layout and design of the physical facilities.

§    Selection the equipments and facilities that will be used.

§    Environmental control.

§    Safety and healthy impact.

   Recycling:

 After source reduction, the recovery of materials for recycling and composting is the next important component of integrated SWM program.

  Definition :

Resource recovery: means that the materials have not only been removed from the municipal waste stream, but also, purchased by an end user. The materials are recovered or recycled.

Recycling include activities such as refilling bottles for reuse and remanufacturing products for resale to consumers but it is better to use  the term recycling only when materials are collected and used as raw materials for new products. The process of recycling includes collecting recyclables, separating them by type, processing them into new forms that are sold to manufacturers, and finally, purchasing and using goods made by reprocessed materials. Example for products that can be recycled and typical applications of the raw materials that are so produced, are illustrated in fig. (5)

Fig (5): Recyclable in the waste stream (Source: U.S. EPA, 1989)

  Composting:

Yard trimming and food waste account for almost 25% of the mass of all municipal generated solid waste. Prior to the 1990s, essentially all of that ended up as discards sent to the landfill or incinerator. But as the life of landfills becomes critical, it is apparent that source reduction, recycling program and composting should be implemented.

Composting is a term used to describe the aerobic degradation of organic materials under control conditions yielding a marketable soil amendment or mulch.

Composting can be carefully controlled to shorten the composting time and space required and to minimize offensive odors. The end product is rich in organic matter but low in nutrients.

The composting process can be carried out by spreading the domestic wastes in thin layers to a depth of 1.0 meter deep. The wastes are decomposed under aerobic conditions whereby decomposition is completed in a few months.

The composting process is affected by temperature, moisture, nutrients supply and availability of oxygen. Bacteria, fungi and microorganisms are the principal players in the decomposition process.

   5-Disposal

Disposal on or in the earth mantel is the viable method for the long- term handling solid wastes. Sanitary lanfilling is the method of disposal used most commonly for municipal wastes.

    Land filling with solid waste

 Sanitary landfilling: The controlled disposal of solid waste on the upper layer of the earth mantle in a manner the environmental hazards is minimized. Important technical aspects in the implementation of sanitary landfills include:

1 - Site selection.

2 - Landfilling methods and operation.

3 - Occurrence of gasses and leachate.

4 - Movement and control of gases and leachate.

   1 – Site selection:

 Available land area, haul distance, soil condition and topography, surface water hydrology, geologic and hydraulic condition, climatologic condition, local environmental condition and ultimate use of site are the factors that should be considered in evaluating potential solid-waste disposal sites.

  2 – Landfilling methods and operations:

 The principal methods used for landfilling dry areas may be classified as

 1- area.                                 2- Trench.                               3- Depression.

  Area method:

 It is used when the terrain is unsuitable for excavation. The filling operation is started by:

       1- Building an earthen levee (berm) against which wastes are placed in thin layers.

       2- Each layer is compacted and covered with a thin layer of compacted soil (20cm) until the           thickness of the compacted wastes reaches a height of 2-3 m. (See fig.6)

       3-  A final cover of soil (15-30cm) is placed and compacted.

       4-  A complete lift including the cover material is called a cell.

       5-  Successive cells are placed on top of one another; a finial cover material is placed when the       fill reaches the final design height.

Fig. (6) Area method of land filling solid wastes

  Trench method:

 It is suitable for the site where the water table in well below the surface. The operation starts by:

       1- A portion of the trench is dug with a bulldozer and the dirt is stockpiled to form an embankment behind the first trench.

       2- Wastes are spread in thin layers and compacted until the desired height is reached.

       3- Cover material is obtained by excavating adjacent trench or continuing the trench that is being filled and the access to the site.

 Depression Method:

 At locations where natural or artificial depressions exist, it is often possible to use them effectively for land filling operation. The techniques to place and compact solid wastes in depression landfills vary with the geometry of the site, the characteristics of the cover materials, the hydrology and geology of the site.

 3 – Occurrence of gases and leachate in landfills:

     When solid wastes are placed in a sanitary landfill, the following events take place:

   1- Biological decay of organic materials, either aerobically or anearobically, with the evolution of gases.

   2- Chemical oxidation of waste material.

   3- Escape of gases from landfill.

   4- Movement of liquids caused by differential head.

   5- Dissolving of organic and inorganic materials by water and leachate moving through the fill.

   6- Movement of dissolved material by concentration gradient material into voids.

   Gases in landfills:

 Carbon dioxide (CO2) and methane (CH4) are the main gases produced by anaerobic decomposition of organic solid waste components.

   Leachate in landfills:

 Leachate is defined as liquid that has percolated through solid waste and extracted dissolved or suspended material from it. The liquid portion of leachate is composed of the liquid produced from decomposition of the wastes and liquid that has entered the landfill from external sources such as rainfall, surface drainage and ground water.

   4- Movement and control of gases and leachate 

   Gas movement:

 Under ideal conditions, the gases generated from landfills either vented to the air or, in larger landfills, collected to produce energy.

 In most cases, the gases generated from a solid waste decomposition consist of carbon dioxide and methane. If both gases vented to the air in an uncontrolled manner, methane accumulate below building or enclosed spaces close to a sanitary landfill because its specific gravity is less than that of air.

Because carbon dioxide is 1.5 times as dense as air and 2.8 times as dense as methane, it tends to move toward the bottom of the landfill. Ultimately, because of its density, it will also move downward through the under laying formation until it reaches the groundwater and dissolve in water lowering the PH which result in the hardness of water.

   Control of gas movement:

 The movement of gases can be controlled by constructing vents, barriers and recovery wells.

 Gas vents are constructed of gravel (Fig.7a). The spacing between vents varies from 18 to 60m depending on the width of the waste cells and the thickness of the vents varies between 0.3 to 0.45m.

 Barriers or well vents: (Fig.7b) are also used to control the lateral movement of gases.

 Well vents :( Fig.7C) are used in conjunction with lateral - surface vents buried below grade in a gravel trench.

 The prevention of the movement of gases through the adjacent soil formations can be achieved by constructing barriers of clay with thickness ranging from 0.15-1.25m Fig. (9)

 

 

Fig. (7): Typical method for venting landfill gases :(a) cell (b) barrier (c) well

Gas recovery wells: The movement of gases in landfill can also be controlled by installing Gas recovery wells in complete landfill. Fig. (8)

   

Fig: (8): Well system used for the recovery of gases from landfill

    Control of leachate movement:

 Because of the potential risk involved in allowing the percolation of leachate to the groundwater, it may be necessary to collect and treat the leachate.

 Impervious clay liner is used to prevent the movement of leachate.

Membrane liners are used also, but they are expensive and require care so that they will not be damaged during the filling operations. (See fig 9).

 Equally important in controlling the leachate movement is the elimination of surface water infiltration which is the major contributor to the total volume of leachate.

Fig. (9): Landfill designed to prevent the movement of gases and leachate

   Settlement and structural characteristics of landfills: 

 The settlement of landfills depends on the following factors: the initial compaction, characteristics of wastes, degree of decomposition, effects of consolidation after formation of the leachate and gases and the height of the completed fill.

   Empirical methods for waste settlement:

       b1.  Logarithmic function (Yen and Scanlon, 1975)

                             

Where:   S = settlement between time interval, i.e., S = Si – So (m);

                 t = difference between time of interest and time of the

                    start of measurement, i.e., t = ti – to (days);

                 m=empirical constant, n =empirical constant

  

        b2.  Power function (Edil, et al., 1990)

                              

Where:   S =    settlement between time interval, i.e., S = Si – So (m);

              t = difference between time of interest and time of the

                start of measurement, i.e., t = ti – to (days);

               p =empirical constant, p = pĒ/q;        

               q=empirical constant, q = 1 - qĒ

  

        b3.  Hyperbolic function (Ling, et al., 1998)

                    

 
Where:     S  = difference between settlement at time t1 and that

                   measured at time to, i.e., S = Si – So (m);

                  t   = difference between time of interest and time of the

                     start of measurement, i.e., t = ti – to (days);

                   ro   =initial rate of settlement at t = to;

                   Sult   =ultimate settlement, i.e., t Ū Ĩ

      Design and operation of landfills:

 The consideration that must be considered in the design and operation of landfills include:

1- Land requirements.

2- Types of wastes.

3- Evaluation of seepage potential.

4- Design of drainage and seepage control facilities.

5- Development of a general operation plan.

6- Design of solid-waste filling plane.

7- Determination of equipment requirements.

    Landfill operation plan:

 In planning the layout of a landfill site, the location of the following must be determined:

1-     Access roads.

2-     Equipment shelters.

3-     Scales if used.

4-     Storage sites for special wastes.

5-     Topsoil stockpiles sites.

6-     The landfill areas.

7-     Planting.

 Typical landfill operation plan is shown in Fig. (10)

 

 

Fig. (10): Typical landfill operation plan..

   Solid waste filling plan:

 Figure (11) shows typical plan for filling landfill. The specific method of filling depends on the characteristics of the site, the amount of cover material, topography, local hydrology and geology and the method of operation (e.g. gas recovery), methods of controlling gases and leachate).

 

Fig. (11): Typical plan for filling landfill.