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write short notes on
-capacity planning
-work sampling
-line balancing
-acceptance sampling
-waste management

A]Capacity Planning

Capacity planning is the process of determining the production  CAPACITY  needed by an organization to meet changing DEMANDS  for its PRODUCTS . In the context of capacity planning, "capacity" is the maximum amount of work that an organization is capable of completing in a given period of time.
A discrepancy between the capacity of an organization and the demands of its customers results in inefficiency, either in under-utilized resources or unfulfilled customers. The goal of capacity planning is to minimize this discrepancy. Demand for an organization's capacity varies based on changes in production output, such as increasing or decreasing the production quantity of an existing product, or producing new products. Better utilization of existing capacity can be accomplished through improvements in OVERALL  EQUIPMENT  EFFECTIVENESS (OEE). Capacity can be increased through introducing new techniques, equipment and materials, increasing the number of workers or machines, increasing the number of shifts, or acquiring additional production facilities.
Capacity is calculated: (number of machines or workers) × (number of shifts) × (utilization) × (efficiency).
The broad classes of capacity planning are lead strategy, lag strategy, and match strategy.
•   Lead strategy is adding capacity in anticipation of an increase in demand. Lead strategy is an aggressive strategy with the goal of luring customers away from the company's competitors. The possible disadvantage to this strategy is that it often results in excess inventory, which is costly and often wasteful.
•   Lag strategy refers to adding capacity only after the organization is running at full capacity or beyond due to increase in demand . This is a more conservative strategy. It decreases the risk of waste, but it may result in the loss of possible customers.
•   Match strategy is adding capacity in small amounts in response to changing demand in the market. This is a more moderate strategy.


   Capacity Planning
   Capacity is the upper limit or ceiling on the load that an operating unit can handle.
   The basic questions in capacity handling are:
   What kind of capacity is needed?
   How much is needed?
   When is it needed?
   Types of Capacity
   Design capacity
   maximum output rate or service capacity an operation, process, or facility is designed for
   Effective capacity
   Design capacity minus allowances such as personal time, maintenance, and scrap
   Actual output
   rate of output actually achieved--cannot
exceed effective capacity.
   Efficiency and Utilization
   Efficiency/Utilization Example
         Actual output          =    36 units/day    
Efficiency =          = 90%
         Effective capacity         40 units/ day
Utilization =          Actual output    =      36 units/day        
         = 72%          Design capacity          50 units/day   
   Objectives of capacity planning
1.   To satisfy the future demand of products without any shortage
2.   To find the optimal capacity of the facility so that the sum of costs of under-capacity & over- capacity is the minimum.
3.   To keep the initial investment in the facility as low as possible to achieve lower break-even volume
4.   Investment in facility capacity are long-term & can’t be reversed easily.
   Variations in Demand Relative to Capacity
   Determinants of Effective Capacity
   Facilities
   Product and service factors
   Process factors
   Human factors
   Operational factors
   Supply chain factors
   External factors
   Steps for Capacity Planning
1.   Estimate future capacity requirements
2.   Evaluate existing capacity
3.   Identify alternatives
4.   Conduct financial analysis
5.   Assess key qualitative issues
6.   Select one alternative
7.   Implement alternative chosen
8.   Monitor results

Strategies for Shifting Demand
to Match Capacity
•   Use signage to communicate busy days and times
•   Offer incentives to customers for usage during non-peak times
•   Take care of loyal or regular customers first
•   Advertise peak usage times and benefits of non-peak use
•   Charge full price for the service--no discounts
Strategies for Flexing Capacity
to Match Demand
•   Stretch time, labor, facilities and equipment
•   Cross-train employees
•   Hire part-time employees
•   Request overtime work from employees
•   Rent or share facilities
•   Rent or share equipment
•   Subcontract or outsource activities
   Production planning & control
   Production planning implies formulation, co-ordination & determination of activities in a manufacturing system necessary for the accomplishment of desired objectives
   Production control is the process of maintaining a balance between various activities evolves during production planning providing most effective & efficient utilization of resources.
   Objectives of PPC
1.   Determining the nature & magnitude of various input factors to manufacture desired output.
2.   To co-ordinate labor, machines in the most economic manner
3.   Setting targets & checking these against performance.
4.   Ensuring smooth flow of material by eliminating bottlenecks if any
5.   Utilization of under employed resources
6.   To produce desired output of right quality & quantity at right time.
   Importance of time horizon
Depending on the time horizon, the plan is of 3 types-
   Long-term Planning: Strategic Planning – normally more than an year’s time.
   Medium-term Planning: Aggregate Planning – up to an year’s time.
   Short-term Planning:  Routine Planning – monthly/weekly.
Dovetailing (fit together) of Plans-
Shorter-range plans are always made within the framework of the longer-range plans. Production planning as it is generally understood, is really the intermediate-range and short-range plan. That is why. production planning is said to follow from the marketing plan. The production plan is the translation of the market demands into production orders. The market demands have to be matched with the production capacities  
Need for Detailed Plans-
At a gross level, one must balance the gross demand into gross level availability of resources in machine-hours or man-hours, etc. At the detailed level one needs to balance the requirements of indi¬vidual products with the availability of individual machines/equipments and labor of different skill categories.
Centralization & decentralization-
concentrate of authority (esp. administration) at a single centre & transfer (power etc.) from central to local authority.
B]Work Sampling
Work Sampling
Work Sampling (also sometimes called ratio delay study) is a technique of getting facts about utilization of machines or human beings through a large number of instantaneous observations taken at random time intervals. The ratio of observations of a given activity to the total observations approximates the percentage of time that the process is in that state of activity. For example, if 500 instantaneous observations taken at random intervals over a few weeks show that a lathe operator was doing productive work in 365 observations and in the remaining 135 observations he was found 'idle' for miscellaneous reasons, then it can be reliably taken that the operator remains idle (135/500) x 100 = 27 % 0f the time. Obviously, the accuracy of the result depends on the number of observations. However, in most applications there is usually a limit beyond which greater accuracy of data is not economically worthwhile.
Use of Work Sampling for Standard Time Determination
Work sampling can be very useful for establishing time standards on both direct and indirect labor jobs. The procedure for conducting work sampling study for determining standard time of a job can be described step-wise.
Step 1 . Define the problem.
• Describe the job for which the standard time is to be determined.
• Unambiguously state and discriminate between the two classes of activities of operator on the job: what are the activities of job that would entitle him to be in 'working" state.
This would imply that when operator will be found engaged in any activity other than those would entitle him to be in "Not Working" state.
Step 2. Design the sampling plan.
• Estimate satisfactory number of observations to be made.
• Decide on the period of study, e.g. two days, one week, etc.
• Prepare detailed plan for taking the observations.
This will include observation schedule, exact method of observing, design of observation sheet, route to be followed, particular person to be observed at the observation time, etc.
Step 3. Contact the persons concerned and take them in confidence regarding conduct of the study.
Step 4. Make the observations at the pre-decided random times about the working / not working state of the operator. When operator is in working state, determine his performance rating. Record both on the observation sheet.
Step 5. Obtain and record other information. This includes operator's starting time and quitting time of the day and total number of parts of acceptable quality produced during the day.
Step 6. Calculate the standard time per piece.
We will now briefly discuss some important issues involved in the procedure.
Number of Observations
As we know, results of study based on larger number of observations are more accurate, but taking more and more observations consumes time and thus is costly. A cost-benefit trade-off has thus to be struck. In practice, the following methods are used for estimation of the number of observations to be made.
(i) Based on judgment. The study person can decide the necessary number of observations based on his judgment. The correctness of the number may be in doubt but estimate is often quick and in many cases adequate.
(ii) Using cumulative plot of results. As the study progresses the results of the proportion of time devoted to the given state or activity, i.e. Pi from the cumulative number of observations are plotted at the end of each shift or day. A typical plot is shown in Figure. Since the accuracy of the result improves with increasing number of observations, the study can be continued until the cumulative Pi appears to stabilize and collection of further data seems to have negligible effect on the value of Pi.
(iii) Use of statistics. In this method, by considering the importance of the decision to be based on the results of study, a maximum tolerable sampling error in terms of confidence level and desired accuracy in the results is specified. A pilot study is then made in which a few observations are taken to obtain a preliminary estimate of Pi. The number of observations N necessary are then calculated using the following expression.
The number of observations estimated from the above relation using a value of Pi obtained from a preliminary study would be only a first estimate. In actual practice, as the work sampling study proceeds, say at the end of each day, a new calculation should be made by using increasingly reliable value of Pi obtained from the cumulative number of observations made.
Determination of Observation Schedule
The number of instantaneous observations to be made each day mainly depends upon the nature of operation. For example, for non-repetitive operations or for operations in which some elements occur in-frequently, it is advisable to take observations more frequently so that the chance of obtaining all the facts improves. It also depends on the availability of time with the person making the study. In general, about 50 observations per day is a good figure. The actual random schedule of the observations is prepared by using random number table or any other technique.
Design of Observation Sheet
A sample observation sheet for recording the data with respect to whether at the pre-decided time, the specified worker on job is in 'working' state or 'non-working' state is shown . It contains the relevant information about the job, the operators on job, etc. At the end of each day, calculation can be done to estimate the percent of time workers on the job (on an average) spend on activities, which are considered as part of the job.
Conducting Work Sampling Study
At the predecided times of study, the study person appears at the work site and observes the specific worker (already randomly decided) to find out what is he doing. If he is doing activity which is part of the job, he is ticked under the column 'Working' and his performance rating is estimated and recorded. If he is found engaged in an activity which is not a part of job, he is ticked under the column 'Not Working'. At the end of day, the number of ticks in 'Working' column is totaled and average performance rating is determined.
The observed time (OT) for a given job is estimated as

The normal time (NT) is found by multiplying the observed time by the average performing index (rating factor).

Where =  is average rating factor to be determined as  ,  
The standard time is determined by adding allowances to the normal time.
A work sampling study was made of a cargo loading operation for the purpose of developing its standard time. The study was conducted for duration of 1500 minutes during which 300 instantaneous observations were made at random intervals. The results of study indicated that the worker on the job was working 80 percent of the time and loaded 360 pieces of cargo during the study period. The work analyst rated the performance at 90 %. If the management wishes to permit a 13 % allowance for fatigue, delays and personal time, what is the standard time of this operation?
Here, total study period = 1500 minutes
Working fraction = 80 percent
Average rating = 90 percent
Number of units loaded = 360
Allowances = 13 %
Advantages and Disadvantages of Work Sampling in Comparison with Time Study.
• Many operators or activities which are difficult or uneconomical to measure by time study can readily be measured by work sampling.
• Two or more studies can be simultaneously made of several operators or machines by a single study person. Ordinarily a work study engineer can study only one operator at a time when continuous time study is made.
• It usually requires fewer man-hours to make a work sampling study than to make a continuous time study. The cost may also be about a third of the cost of a continuous time study.
• No stopwatch or other time measuring device is needed for work sampling studies.
• It usually requires less time to calculate the results of work sampling study. Mark sensing cards may be used which can be fed directly to the computing machines to obtain the results just instantaneously.
6. A work sampling study may be interrupted at any time without affecting the results.
7. Operators are not closely watched for long period of time. This decreases the chance of getting erroneous results for when a worker is observed continuously for a long period, it is probable that he will not follow his usual routine exactly during that period.
Less Erroneous
8. Observations may be taken over a period of days or weeks. This decreases the chance of day-to-day or week-to-week variations that may affect the results.
Operators Like It
9. Work sampling studies are preferred to continuous time study by the operators being studied. Some people do not like to be observed continuously for long periods of time.
Observers Like It
10. Work sampling studies are less fatiguing and less tedious to make on the part of time study engineer.
• Work sampling is not economical for the study of a single operator or operation or machine. Also, work-sampling study may be uneconomical for studying operators or machines located over wide areas.
• Work sampling study does not provide elemental time data.
• The operator may change his work pattern when he sees the study person. For instance, he may try to look productive and make the results of study erroneous.
• No record is usually made of the method being used by the operator. Therefore, a new study has to be made when a method change occurs in any element of operation.
• Compared to stop watch time study, the statistical approach of work sampling study is difficult to understand by workers.
Computerized Work Sampling
Use of a computer can save as much as 30 to 40 percent of the total work sampling study cost. This is because too much clerical effort is involved in summarizing work sampling data, e.g. in determining the number of observations required, determining the daily observations required, determining the number of trips to the area being studied per day, determining the time of each observation, calculating the accuracy of results, plotting data on control charts and like that. Computers can be used for mechanization of the repetitive calculations, display of control charts and calculation of daily as well as cumulative results.

C]Line Balancing
Line Balancing
Line: an assembly line composed of several work stations, at which specific operations are performed.
To work effectively, with no work pile-ups between stations, the line must be balanced, e.g. work must get through each workstation in roughly the same amount of time.
Line Balancing
To meet production goals,
Maximize output.
Common Approaches to Line Balancing:
1.   Estimating the number of operators for a given number of stations,
2.   Work element sharing: grouping “activities” per work elements into “stations” or jobs performed by a single person (some times multiple people work in concert at a single station or machine)
Estimating the
number of operators
In a perfectly balanced line, all operations at all station would take identical time.
Efficiency would be 100 %
However, this rarely happens!!
100 % efficiency is rarely achievable,
A more reasonable goal is 95 % efficiency.  (However, even that may not be achievable depending on the nature of the operations).
Estimating the number of Operators
To achieve a given rate of production, R,
N operators are needed (total).
(1)      N  = R  x  Σ AM   =  R x Σ SM
Procedure for Determining
the Number of Operators
needed to meet production goals.
Assumptions. You have already determined:
the number of workstations,
their sequence
the operations that will be performed at each one.
Goals.  To:
Meet production goals given to you by your management,
Balance the workload between stations by putting more workers at the slower stations,
Reduce idle time
Procedure: Estimating the Number of Operators  
Givens: Production goal, operation sequence.
Step 0: (Prior to the analysis) Perform time studies for each operation using experienced operators in order to obtain standard times (SM).
Step 1: Convert the production rate, R, into the same time units as your standard times.
Step 2: (optional) Estimate the total number of operators for the line using Equation (1) (see previous slides)
Step 3: Estimate the number of operators needed for each operation,
Step 4: Identify the slowest operation given the number of operators computed in previous step,
Step 5: Test: have you met the production goal?
Step 6: Adjust.  Add more operators, negotiate to reduce the production goal, or try additional methods.
Example: Estimating the Number of Operators  
Production goal: 700 units/day  where 1 day = 8 hours.
Operation sequence:  Op1, Op2, Op3, Op4, Op5, Op6, Op7, Op8.
Step 0: (Prior to the analysis) Perform time studies for each operation using experienced operators in order to obtain standard times in minutes (SM).
Estimating the Number of Operators
Step 1: Convert the production rate, R, into the same time units as your standard times.
  The standard times, SM, have been expressed in minutes, while R is in days, so:
         R = 700 units/day  =  1.458 units/min
         480 min/day
  Also compute the desired cycle time (rate at which units exit line)
         cycle time = 1 = 0.685 min/unit  
Estimating the Number of Operators  
Step 2: (optional) Estimate the total number of operators, N, required to meet production goal, using Equation (1) :
Estimating the Number of Operators
Step 3: Estimate the number of operators needed for each operation,
Step 4: Identify the slowest operation given the number of operators computed in previous step,
Step 5: Test: have you met the production goal?
Number of operators needed
for each operation
to achieve production goals
Calculate reduced cycle times at each station when using multiple operators
Calculate reduced cycle times at each station when using multiple operators
Work Element Sharing
A line can sometimes be balanced with less cost by rearranging the sub-work elements (e.g. activities composing a work element)
For example, by giving activities from the busiest element to elements with idle time.
Properties of Work Elements
What is a work “element”?
How big should a work element  be?
Work Element Properties
Work elements can be represented at various levels of abstraction or detail
Work elements can almost always be sub-divided into smaller elements.
The appropriate representation depends on the task and situation.
Work Element Sharing:
GE’s Line Balancing
 A Procedure for Assigning
Work  Elements to Stations
Precedence graph
Production goal (e.g. 300 units per shift)
Shift duration (e.g. 450 minutes)
Number of workstations (e.g. 6 workstations)
Decided how to assign elements to workstations so as to meet production goals without violating precedence constraints!
A Precedence Graph for Assembly Operations
The graph should only contain necessary orderings.
Any unnecessary constraints make it harder to achieve efficiency.
Compute positional weighs,
Record immediate predecessors,
Sort from biggest positional weight
The Final Assembly Line
A stream-lined version of the Assembly line

Line-balancing strategy is to make production lines flexible enough to absorb external and internal irregularities. There are two types of line balancing,
– Static Balance – Refers to long-term differences in capacity over a period of several hours or longer. Static imbalance results in underutilization of workstations, machines and people.
Dynamic Balance – Refers to short-term differences in capacity, like, over a period of minutes, hours at most. Dynamic imbalance arises from product mix changes and variations in work time unrelated to product mix.
Labour Balancing and Assignments Strategy of production line stability is the tendency for labour assignments to be fixed. Labour feasibility is an important feature in the strategy of production line flexibility linked to individual skills and capabilities – When one worker is having problem in performing his assigned task and experiencing delay due to technical problem(s), other worker(s) should move into help. The management practice of deliberately pulling worker’s of the line when the line is running smoothly. The movement of whole crews from one dedicated line to another as the model mix changes. Group Technology – In which one worker can handle variety of tasks (automation) in a single work centre. Equipment Balancing While balancing equipment, attempt to ensure that each piece of equipment in the work cell has the same amount of work. Now days every manufacturer is attempting to maximize the utilization of all available equipments. Such high utilization is often counterproductive and may be the wrong goal because; high utilization is usually accompanied by high inventory. Equipment Failure An equipment failure is a major serious matter, with the potential to shut down a production line. To avoid such failures one should not overload the equipments, and workers should be trained to perform a daily machine checking (preventive maintenance) and following standard operating procedures. The advantage for Maintenance and Engineering Department does not lye in running late shifts, hence calculate the preventive maintenance time and schedule the activity.
Analysis Analysis is generally performed by Competent Technical Staff. Begin the analysis with division of production-line work into small tasks, determination of task time standards, specification of required task sequencing and notation of constraints. If bottle neck task is in the way of good balance, the Competent Technical Staff should analyze the task to reduce the time it takes to perform. Line Balancing Leadership Workmen should lead the production line balancing effort, so that they can react quickly when line imbalances (static and dynamic) crop up as a result of changeover to make a different item or changes in the output rate. Conclusion Production-line balancing study tends to employ thought and ingenuity to change conditions. Production-line design and operation is more art than science. Labour flexibility is the key to effective resource management. The idea of worker’s checking and doing minor repair work on their own equipment possibly decreases the risk of equipment failure. Selecting an appropriate set of balancing mechanism is a part of work cell design and it must be linked with many other decisions for the system to function well. -

D]Acceptance Sampling
A statistical measure used in quality control. A company cannot test every one of its products due to either ruining the products, or the volume of products being too large. Acceptance sampling solves this by testing a sample of product for defects. The process involves batch size, sample size and the number of defects acceptable in the batch. This process allows a company to measure the quality of a batch with a specified degree of statistical certainty without having to test every unit of product. The statistical reliability of a sample is generally measured by a t-statistic.

Probability is a key factor in acceptance sampling, but it is not the only factor. If a company makes a million products and tests 10 units with one default, an assumption would be made on probability that 100,000 of the 1,000,000 are defective. However, this could be a grossly inaccurate representation. More reliable conclusions can be made by increasing the batch size higher than 10, and increasing the sample size by doing more than just one test and averaging the results. When done correctly, acceptance sampling is a very effective tool in quality control.

  Acceptance sampling is "the middle of the road" approach between no inspection and 100% inspection. There are two major classifications of acceptance plans: by attributes ("go, no-go") and by variables. The attribute case is the most common for acceptance sampling, and will be assumed for the rest of this section.

A point to remember is that the main purpose of acceptance sampling is to decide whether or not the lot is likely to be acceptable, not to estimate the quality of the lot.
Acceptance sampling is employed when one or several of the following hold:
•   Testing is destructive
•   The cost of 100% inspection is very high
•   100% inspection takes too long
E]Waste Management
WASTE   is   a  general  term.

It means an object ---the  holder  discards or  intends to discard.
THIS  UNWANTED  OBJECTS  could  include
-junk  materials
-plastics  materials
-glass  materials
etc etc

There are a number of   concepts of  waste management  systems which vary in their usage between countries or regions. This presents some of the most general, widely-used concepts.


The waste hierarchy refers to the "3 Rs" reduce, reuse and recycle, which classify waste management strategies according to their desirability in terms of waste minimization. The waste hierarchy remains the cornerstone of most waste minimization strategies. The aim of the waste hierarchy is to extract the maximum practical benefits from products and to generate the minimum amount of waste




Waste management  system  is the collection, transport, processing, recycling or disposal of waste materials. The term usually relates to materials produced by human activity, and is generally undertaken to reduce their effect on health, aesthetics or amenity. Waste management is also carried out to reduce the materials' effect on the environment and to recover resources from them. Waste management can involve solid, liquid or gaseous substances, with different methods and fields of expertise for each.
Waste management practices differ for developed and developing nations, for urban and rural areas, and for residential and industrial, producers. Management for non-hazardous residential and institutional waste in metropolitan areas is usually the responsibility of local government authorities, while management for non-hazardous commercial and industrial waste is usually the responsibility of the generator.
Waste management system methods
Waste management methods for vary widely between areas for many reasons, including type of waste material, nearby land uses, and the area available.

Disposal  system
Landfill  system
Disposing of waste in a landfill involves burying waste to dispose of it, and this remains a common practice in most countries. Historically, landfills were often established in disused quarries, mining voids or borrow pits. A properly-designed and well-managed landfill can be a hygienic and relatively inexpensive method of disposing of waste materials. Older, poorly-designed or poorly-managed landfills can create a number of adverse environmental impacts such as wind-blown litter, attraction of vermin, and generation of liquid leachate. Another common byproduct of landfills is gas (mostly composed of methane and carbon dioxide), which is produced as organic waste breaks down anaerobically. This gas can create odor problems, kill surface vegetation, and is a greenhouse gas.
Design characteristics of a modern landfill include methods to contain leachate such as clay or plastic lining material. Deposited waste is normally compacted to increase its density and stability, and covered to prevent attracting vermin (such as mice or rats). Many landfills also have landfill gas extraction systems installed to extract the landfill gas. Gas is pumped out of the landfill using perforated pipes and flared off or burnt in a gas engine to generate electricity.
Incineration  system
Incineration is disposal method that involves combustion of waste material. Incineration and other high temperature waste treatment systems are sometimes described as "thermal treatment". Incinerators convert waste materials into heat, gas, steam, and ash.
Incineration is carried out both on a small scale by individuals, and on a large scale by industry. It is used to dispose of solid, liquid and gaseous waste. It is recognised as a practical method of disposing of certain hazardous waste materials (such as biological medical waste), though it remains a controversial method of waste disposal in many places due to issues such as emission of gaseous pollutants.
Incineration is common in countries such as Japan where land is more scarce, as these facilities generally do not require as much area as landfills. Waste-to-energy (WtE) or energy-from-waste (EfW) are broad terms for incinerator facilities that burn waste in a furnace or boiler to generate heat, steam and/or electricity.
Recycling  system
The process of extracting resources or value from waste is generally referred to as recycling, meaning to recovery or reuse the material. There are a number of different methods by which waste material is recycled: the raw materials may be extracted and reprocessed, or the calorific content of the waste may be converted to electricity. New methods of recycling and are being developed continuously, and are described briefly below.
Physical Reprocessing  system
The popular meaning of ‘recycling’ in most developed countries refers to the widespread collection and reuse of everyday waste materials such as empty beverage containers. These are collected and sorted into common types so that the raw materials from which the items are made can be reprocessed into new products. Material for recycling may be collected separately from general waste using dedicated bins and collection vehicles, or sorted directly from mixed waste streams.
The most common consumer products recycled include aluminium beverage cans, steel food and aerosol cans, HDPE and PET bottles, glass bottles and jars, paperboard cartons, newspapers, magazines, and cardboard. Other types of plastic (PVC, LDPE, PP, and PS: see resin identification code) are also recyclable, although these are not as commonly collected. These items are usually composed of a single type of material, making them relatively easy to recycle into new products. The recycling of complex products (such as computers and electronic equipment) is more difficult, due to the additional dismantling and separation required.
Biological processing  system
Waste materials that are organic in nature, such as plant material, food scraps, and paper products, can be recycled using biogical composting and digestion processes to decompose the organic matter. The resulting organic material is then recycled as mulch or compost for agricultural or landscaping purposes. In addition, waste gas from the process (such as methane) can be captured and used for generating electricity. The intention of biological processing in waste management is to control and accelerate the natural process of decomposition of organic matter.
There are a large variety of composting and digestion methods and technologies varying in complexity from simple home compost heaps, to industrial-scale enclosed-vessel digestion of mixed domestic waste (see Mechanical biological treatment). Methods of biological decomposition are differentiated as being aerobic or anaerobic methods, though hybrids of the two methods also exist.
Energy recovery  system

The energy content of waste products can be recycled by using them as fuel. Recycling through thermal treatment ranges from using waste as a fuel source for cooking or heating, to fuel for boilers to generate steam and electricity in a turbine. Pyrolysis and gasification are two related forms of thermal treatment where waste materials are heated to high temperatures with limited oxygen availability. The process typically occurs in a sealed vessel under high pressure. Pyrolysis of solid waste converts the material into solid, liquid and gas products. The liquid and gas can be burnt to produce energy or refined into other products. The solid residue (char) can be further refined into products such as activated carbon. Gasification is used to convert organic materials directly into a synthetic gas (syngas) composed of carbon monoxide and hydrogen. The gas is then burnt to produce electricity and steam.
Avoidance and Reduction  system
Another important method of waste management is the prevention of waste material being created. Methods of avoidance include reuse of second-hand products, repairing broken items instead of buying new, designing products to be refillable or reusable (such as cotton instead of plastic shopping bags), encouraging consumers to avoid using disposable products (such as disposable cutlery), and designing products that use less material to achieve the same purpose (for example, lightweighting of beverage cans.
Waste handling and transport  system
Waste collection methods vary widely between different countries and regions. Domestic waste collection services are often provided by local government authorities, or by private industry. Some areas, especially those in less developed countries, do not have a formal waste-collection system.
The waste hierarchy refers to the "3 Rs" reduce, reuse and recycle, which classify waste management strategies according to their desirability in terms of waste minimization. The waste hierarchy remains the cornerstone of most waste minimization strategies. The aim of the waste hierarchy is to extract the maximum practical benefits from products and to generate the minimum amount of waste









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