Ohio Pollution Prevention and Waste Minimization Planning Guidance Manual

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Chapter 9
Do a Preliminary Assessment

"Pollution is nothing but the resources we are not harvesting. We allow them to disperse because we are ignorant of their value."

Buckminster Fuller

Understanding Processes and Wastes

To effectively implement a pollution prevention program, it is important to understand the various unit processes and where in these processes waste is being produced. This chapter will explain how to determine the various unit process steps in materials use and will present methods to determine where wastes are being generated. An extensive amount of data gathering may be necessary in this step in order to achieve a complete process characterization.

Two general approaches characterizing processes and waste generation can be used. One method begins with gathering information on total multi-media (air, land, and water) waste releases at the end of each process, and then backtracks to determine waste sources. Another method tracks materials from the point at which they enter the plant until they exit as wastes or products. Both methods provide a baseline for understanding where and why wastes are generated and a basis to measure waste reduced after implementation of pollution prevention projects. The steps involved in these characterizations include gathering background information, defining a production unit, general process characterization, understanding unit processes, and completing a materials balance.

Gathering Background Information

The first step toward understanding processes and waste generation is gathering background information on the facility. This allows for the accurate determination of the type and quantity of raw materials used, the type and quantity of wastes generated, the individual production mechanisms, and the interrelationships between the unit processes. The pollution prevention team should divide up the responsibilities for obtaining this information. A time frame should be established for assembling the data and presenting it to the group. Table 1 provides suggestions on data that should be assembled and where this information might be found.

In addition to these data, useful information can be obtained from line workers, maintenance staff, process engineers, purchasing, inventory, shipping and receiving; and accounting personnel. These employees can be interviewed to determine how the processes are run; what types of raw materials, cleaning agents, lubricants, etc. are used; what types of waste are generated and how they are handled; what other types of records are kept; and what information is not recorded on a regular basis. When gathering this information, begin to track wastes to determine if there are seasonal or shift variations in wastes generated. Once this information is assembled, the general process can be characterized.

Table 1. Possible Sources of Background Information
Raw Materials Use Purchasing records
Inventory records
Vendor information
Production logs
Packaging material discarded
Shipping and receiving logs
Annual report
Waste Generated Waste manifests
TRI data
Sewer records (POTWs)
Flow diagrams
Annual report
Rejected product
Environmental reporting
Waste collection and storage
Production logs
Environmental violations
Laboratory analyses
Obsolete expired stock
Spill and leak reports
Production Mechanisms Operations manuals (SOPs)
Vendor information
Control diagrams
Quality control guidebook
Production logs
Flow diagrams
Product specifications
Process Interrelationships Product-to-raw material data
Flow diagrams
Quality control data
Production logs
Product specifications
Facility layout
Economic Information Cost accounting reports
Operating costs for waste handling and disposal
Pollution control costs
Costs for products, utilities, raw materials, and labor

(adapted from Pollution Prevention: A Guide to Program Implementation, Illinois Hazardous Waste Research and Information Center, 1993)

Define Production Units

To compare the amounts of waste generated during different time periods, and subsequently measure relative waste reductions, a production unit should be defined for each process - either the unit process or the overall process depending on the nature of the facility. A production unit is simply a set quantity of product that is characteristic of the process - tons of plastic, gallons of acid, number of copies, etc. Try to choose a production unit that can be related to later waste generation. Once the production unit is defined, wastes generated can be quantified as waste per production unit. Since total production can vary, comparing the total amounts of waste generated for different time periods will not reflect the reductions achieved due to pollution prevention activities (i.e., waste will increase or decrease with production changes). For example, a printing press may use 1000 copies for a production unit and might then define wastes as "waste per 1000 copies." Alternatively, a company might consider the unit of product per unit of raw material. This measure would be an indicator of yield and process efficiency.

By assembling background information, process flow diagrams for both the general process and individual processes can be developed. These diagrams, along with the materials balance, help provide an understanding of the processes and the wastes generated. The production unit can be used for waste reduction comparisons throughout the pollution prevention program.

Characterize General Process

A typical process has raw material inputs, product outputs, and waste generation. It can be represented by a general process flow diagram. This diagram may not physically resemble the process but will show the movement of raw material through the process as well as the generation of final product and waste. A simple diagram (Figure 3) of a metal parts fabrication facility illustrates this.

Figure 3: A Simple Flow Diagram

In addition to the raw material, final product, and waste flows, other inputs can be represented on the general flow diagram such as lubrication fluids, cleaning agents, cooling water, etc. This will provide an understanding of the overall process and the associated wastes. The general process can then be separated into individual or unit processes.

Understand Unit Processes

Most production operations can be subdivided into a series of unit processes. For example, the general process of metal parts fabrication can be represented by at least seven individual processes.

  1. Receiving and storing bulk metal
  2. Cutting, bending, or shaping metal
  3. Cleaning metal
  4. Painting or coating metal
  5. Assembling parts
  6. Packaging
  7. Shipping of assembled parts

Each unit process has its own inputs and outputs. The product from one step becomes the input material for the following step. The raw materials, products, and wastes for each unit process can be shown on a more detailed flow diagram. This diagram should contain the type/composition and quantity of raw materials, products, and wastes to all media. The diagram should also include other inputs (lubrication fluids, tooling water, cleaning agents, etc.) along with the quantities used. The background information obtained previously will be helpful to determine the types/compositions and quantities of these streams. The subdivision of the general process of metal parts fabrication is illustrated in Figure 4.

Figure 4: Simplified general process flow design

The flow diagrams for the unit processes (and in some cases the general process) can be completed using either of two approaches: 1) start with the wastes and products generated and then determine the sources of the waste by going backwards through each of the unit processes, or 2) start with the raw materials and track them through each of the unit processes until products and wastes are generated. For cases where waste streams are not separated but rather are combined prior to handling, the second method may be the preferred initial approach. The two methods may also be combined to complete the unit process flow diagrams and thus a detailed overall process diagram.


It is critical to determine the types/compositions and quantities of raw materials consumed, product yield, and wastes generated as accurately as possible for each unit process. All wastes released to the environment (gas, liquid, and solid) should be characterized. These wastes can include: emissions from stacks; vent emissions from process areas; fugitive emissions from pipes, tanks, or vessels and leaking equipment; spent wash waters/cleaning solvents; cooling water; over spray from painting operations; cleaning rags; material scrap (e.g., metal, packaging, etc.); and other wastes. By subdividing the process into individual components, these types of wastes become more evident. With this information, a materials balance can be performed for the unit processes and then for the overall facility.

Perform Materials Balance

A materials balance accounts for all inputs and outputs into a process; in other words, what goes in must come out. A materials balance should be performed for each unit process and for the overall production line. Although this typically is a very involved procedure, and while it is usually possible to identify sources of waste without having completed a materials balance, there are long term benefits to having done a materials balance. However, because a materials balance can be very involved, your facility may want to consider this an optional step, especially if you operate a small business. You may want to concentrate on developing process flow charts. Companies may also prefer to develop process flow charts in the preliminary assessment and complete a materials balance later in the pollution prevention program.

A materials balance can help determine if fugitive losses are occurring in the process (e.g., fugitive loss from a solvent tank = difference between solvent in and solvent out). In a physical process, one in which there is no chemical change of materials, the raw materials that are not converted to product generally end up as waste. For example, a materials balance can be performed on the metal parts fabrication process as shown in Figure 4. For a chemical process, the materials balance becomes more complicated as raw material inputs are converted to products through one or more chemical reactions. Some unreacted raw materials may also end up as waste along with reaction by-products.

For these processes, a standard materials balance may already be available as part of the daily production log or cycle. Where possible, however, actual measurements of the amounts of materials used and generated should be used to produce the materials balance. The reason for this is that manufacturing processes can change over a period of time to a point where the actual materials balance would differ from that derived from the standard operating procedures.

Once the materials balance has been performed, the actual amount of each waste generated by a process and the source becomes apparent if not already known. These numbers are the baseline amounts of total waste generated at the start of the pollution prevention assessment and can be used for comparison throughout the implementation of the program.

Table 5. Materials Balance
Key Elements of a Materials Balance
Quantity of raw material brought on-site
Quantity produced on-site including amounts produced as production by-product
Quantity consumed on-site
Quantity shipped off-site as, or in, product
Total waste generation (before recycling and treatment) and waste characteristics
Amount of raw material in beginning and ending inventory
An indicator of production levels involving the chemical
Release and transfer rate

(adapted from Pollution Prevention: A Guide to Program Implementation, Illinois Hazardous Waste Research and Information Center, 1993)

Establish Priorities

Before conducting an assessment to identify what pollution prevention opportunities are present, wastes and unit processes should be prioritized to determine which should be examined first. The flow diagrams prepared in this chapter provide a good starting point for prioritization because they show all of the input and output streams for each unit process. Both the pollution prevention team and top management should be involved in this decision-making process since each will have their own ideas of what areas should be addressed initially.

When establishing priorities for pollution prevention, all of the input and output streams should be ranked - beginning with those which require immediate attention, followed by those which are less urgent. Each company will have their own procedures for establishing priorities. Companies should estimate the risks posed each stream and consider the risks in the ranking process. These factors should be considered when ranking the streams:

Once the streams are ranked, candidate input and output streams (especially wastes) can be identified for the initial pollution prevention assessment, keeping in mind the goals set at the beginning of the program. As the assessment proceeds, these priorities may change.

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