EnE 301: ENVIRONMENTAL ENGINEERING 4.0 Solid Waste Management 4.1 Overview of Solid Waste Management 4.2 Collection of Solid Wastes 4.3 Disposal by Sanitary Landfill 4.4 Resource Conservation and Recovery 4.5 Ecological Solid Waste Management Act of 2000RA9003 Perspective Solid waste is a generic term used to describe the things we throw away. It includes things we commonly describe as garbage, refuse, and trash. • It includes any discarded item; things destined for reuse, recycle, or reclamation; sludge and hazardous wastes (EPA). • Characteristics of Solid Waste The terms refuse and solid waste are used more or less synonymously. • The common materials of solid waste can be classified in several different ways. According to point of origin, classification are domestic, institutional, commercial, industrial, street, demolition, or construction. • The nature of material may be important, so classification can be made on the basis of organic, inorganic, combustible, non combustible, putrescible, and non putrescible. • One of the most useful classification also is based on the kinds of material. • Garbage is the animal and vegetable waste resulting from the handling, preparation, cooking, and serving food. It is composed largely of putrescible organic matter and moisture. • Rubbish consists of a variety of both combustible and non combustible solid wastes from homes, stores, and institutions, but does not include garbage. • Trash is a component of rubbish which consists of paper, rags, cartons, boxes, wood, furniture, tree branches, and yard trimmings. • Non combustible materials can not be burned at ordinary incinerator temperatures of 700 to 1,100 oC. • Integrated Solid Waste Management (ISWM) The selection of a combination of techniques, technologies, and management programs to achieve waste management objectives is called integrated solid waste management (ISWM) • ISWM actions and programs, according to hierarchy, includes (1) source reduction, (2) recycling, (3) waste combustion, and (4) landfilling. • Collection Methods 1. Curbside or alley pickup Most common, quickest and economical type of collection. • Usually the city designates what type of containers are to be used. The crews simply empty the containers into the collection vehicles. • Whenever possible, the crews collect from both sides of the street at the same time. • Municipal ordinances usually specify when the containers must be placed at the curb or in the alley for pickup. • 2. Set-Out, Set-Back Collection Eliminates the unsightly appearance of solid wastes in the streets but does require the collector to enter private property. • This method consists of the following operations: (1) set-out crew carries the full containers from the residential storage location to the curb before collection vehicle arrives, (2) collection crew loads the refuse, and (3) the set-back crew returns the empty cans. • 3. Backyard Pickup • Accomplished by the use of tote barrels. In this method, the collector enters the resident’s property, dumps the container into a tote barrel, carries it to the truck, and dumps it. • The collector may collect refuse from more than one house before returning to the truck to dump. • Standard Tasks in Waste Collection: 1. Walk - Time spent by the workers in walking along the road from the truck to the next collection point. Only used in the curb or alley collection method. 2. Drive - Time spent driving the truck from collection point to collection point. 3. Trash - Time spent placing yard wastes from the curb into the truck. 4. Ride - Time the workers spend riding on the truck between collection points. 5. Collect - Time spent collecting from houses in the traditional way in backyard pickup. It includes the time from when the collector leaves the truck, walks to the backyard, dumps the cans into a tub, returns to the truck, and dumps the tub. 6. Dump - Time spent dumping cans or bags from the curb into the truck. 7. Delay - Time spent on any operation other than above. Truck Routing Methods 1. Daily Route Method Simplest and most common method. • The crew has a definite route that must be finished before going home. • When the route is finished the crew can leave, but if necessary, they must work overtime to finish the route. • Advantages are that the homeowner knows when the refuse will be picked up and that route sizes can be adjusted for load to maximize the crew and truck utilization. • Disadvantages are that the crew will work overtime if the route is not finished which mean additional expense and that the crew have a tendency to become careless as they try to finish the job sooner. • 2. Large Route Method The crew has enough work to last the entire week. The route must be completed in one week. • The crew is left on its own to decide when to pick up the route. This method is only good for backyard pickup since the residents don’t know when pickup will be. • 3. Single Load Method Routes are planned to get a full truck load. Each crew is assigned as many loads as it can collect per day. • The biggest advantage of this method is that it can minimize travel time and it can be used for any type of pickup. • The major disadvantage is that it is hard to predict the number of homes that can be serviced before the truck is filled. • 4. Definite Working Day Method The crew works for its assigned number of hours and quits. • Regularity is sacrificed with this method and residents have little idea when pickup will occur. • Estimating Truck Capacity Often, it is desirable to estimate the truck capacity as well as the crew size that’s why simple formulas have been developed to enable such calculations. • The formulas are based on crude averages regarding collection times, and broad assumptions made. • Given that you are able to estimate a large number of factors, the volume of solid waste a truck must be able to carry can be estimated: • V p H VT r t p N d 2x B 2t d tu s Nd where, VT = volume of solid waste carried per trip by truck at a mean density, DT, m3 VP = volume of solid waste per pickup location or stop, m3/stop r = compaction ratio tP = mean time per collection stop plus the mean time to reach the next stop, hr H = length of working day, hr Nd = number of trips to the disposal site per day x = one-way distance to disposal site, km s = average haul speed to and from disposal site, km/h td = one-way delay time, hr/trip tu = unloading time at disposal site, hr/trip B = off route time per day, h The factor 2 in the equation accounts for travel both to and from the disposal site. • average haul speed is a function of the total round trip distance to the disposal site. • The volume carried presumes a mean density, DT which is the density that results after waste has been compacted. • The compaction ratio, r is the density after compaction to and before compaction. • A value for tp can be estimated from empirical data. • tp tb a Cn 60 where, tP = mean time per collection stop plus the mean time to reach the next stop, hr tb = mean time between collection stops, min/stop a = coefficient of regression fit to data points Cn = mean number of containers at each pickup location The factor 60 in the equation accounts for the conversion of min to hr. • The number of pickup locations that can be handled by a given crew is simply the available time after haul divided by pickup time: • H Nd Np 2x B 2t d tu s Nd tp where, NP = number of pickup locations per load Example: The solid waste management division of the local government is to purchase a solid waste collection vehicle. The compactor trucks available from a local supplier are rated to achieve a density of 400 kg/m3 and a dump time of 6.0 minutes. The disposal site is 6.4 km away from the collection route. From past experience, a delay time of 13 minutes can be expected and the time per collection stop plus time to reach the next stop is 1.8 min. The mean density of the uncompacted solid waste is 106 kg/m3. Each stop typically has 3 cans containing 4 kg each. Assume that two trips per day will be made to the disposal site. Also assume that the average haul speed to and from disposal site is 27 km/hr and the length of working hours per day is 8 hrs with off-route time of 30 min. In order to ensure once-a-week pickup, the truck must service 300 locations per day. Determine the truck capacity (in m3) and the no. of garbage crews needed.