Objective: This section analyzes wastewater in terms of its major sources.
As discussed with drinking water, our knowledge about the sources of wastewater constitutes a major diagnostic tool that helps determine how we manage wastewater. This knowledge, combined with wastewater testing, can give Environmental Health Professionals a major role in this area.
1. Point sources of wastewater are discrete and identifiable sources that are divided into domestic and industrial sources. Domestic sources include residences and small businesses. Compared with industry, these are relatively small sources. As a result, a major issue in this category is the collection of wastewater (i.e., it is a major expense when added up for the entire community). Nationwide, about 80% of domestic wastewater is sent to sewerage systems, and about 20% to private systems (e.g., septic tanks). Industrial sources are relatively large sources that include such sub-categories as the chemical, pharmaceutical, oil, mining, and metal industries. Because of their size, these sources are generally easier to collect, but harder to treat (e.g., their chemical content can vary tremendously). Of course, collection is not always easy: a special sub-category includes the shipping industry, and shipping accidents can occur during transport (e.g., the Exxon Valdez).
2. Non-point sources are diffuse and generally occur from water runoff. Because they are spread over large areas, they tend to be more difficult to control, and in recent years they have gained greater attention from legislators. They are divided into agricultural, urban, and atmospheric sources. Agricultural sources include farms, which can contribute fertilizers, pesticides, soil erosion, and plant and animal wastes to water runoff. Collectively, they usually constitute the largest source of pollutants to water, and the erosion contributions are being worsened by the deforestation occurring in various parts of the world. Urban sources include the storm water systems that collect water from the gutters of streets in towns and cities. The true scope of the problem from urban sources is still not very well understood, but it is clearly a major contributor. Atmospheric sources include air pollution's contribution during precipitation (e.g., acid rain). We do not discuss it in detail here because we have already covered it in a previous section. Nevertheless, it is a classic example of the multi-media role of wastewater pollution.
Wastewater Characteristics I. Physical characteristics
A. total solids content: solid residual matter that remains after evaporation.
We determine this value by simply boiling off the water -- whatever remains is the "total solids content." Perhaps the biggest surprise to most people about wastewater is that it is, in fact, mostly water! By analyzing the total solids content of wastewater, we know that it is typically 99% water and 1% solids. We can learn more, however, by dividing this value into two sub-categories described below: suspended solids and filterable solids.
1. suspended solids: this includes solids that are basically larger than1 micron in diameter.
When we flush the toilet, the fecal wastes have to go somewhere! Such wastes are, of course, part of the suspended solids. These wastes break up fairly quickly due to the action of water during transport. While fecal wastes are certainly part of this group, there may be many other sources (e.g., industrial wastes) depending on the sources of wastewater.
settleable solids: removed by gravity (usually in about one hour).
This is a sub-category of suspended solids. It is useful for us to know how much of the suspended solids will settle out in an hour, because these wastes are the easiest to remove.
2. filterable solids: This includes solids that are basically less than 1 micron in diameter.
These solids are much more difficult to remove from wastewater, because smaller particulates can remain suspended in water for a much longer time. In fact, they can pass through wastewater treatment facilities relatively unchanged. They generally fall into two sub-categories: colloidal and dissolved solids.
colloidal solids: This generally includes solids between 1 - 100 millimicrons in diameter.
dissolved solids: This generally includes wastes less than 1 millimicron in diamter.
II. Chemical characteristics
Without a doubt, we have historically devoted most of our attention to the removal of organics from wastewater. This is reflected by the different measures of organic pollution as described below. The first three measures are all labelled "oxygen demand." This refers to the amount of oxygen it takes to break down these organic wastes. In other words, instead of measuring all of the individual organic compounds, we have a general indicator (oxygen) for the strength of these wastes. As you'll see below, the oxygen plays a different role in each measure.
A. BOD (Biochemical Oxygen Demand)a measure of dissolved oxygen used by micro-organisms in the biological oxidation of organic matter.BOD is perhaps the most relevant measure of organics, because most treatment methods for organic wastes involve the use of microbes to digest the wastes.
B. COD (Chemical Oxygen Demand)a measure of dissolved oxygen used by an chemical oxidizing agent (potassium dichromate) in the chemical oxidation of organic matter.COD is faster than BOD, because a powerful chemical oxidizing agent can oxidize organics faster than microbes. This makes it a more convenient measure, but less relevant to many treament methods.
COD is generally higher than BOD, because there are some organics that cannot be digested by microbes, but can be oxidized by powerful chemical agents.
C. TOD (Total Oxygen Demand)a measure of oxygen used in the incineration (physical oxidation) of organic matter.This is typically achieved by injecting wastes into a platinum catalyzed combustion chamber, where we measure the amount of oxygen present before and after incineration. The incineration techniques are the fastest of all. It's a useful measurement technique, but in terms of practical treatment methods, we would never actually be able to incinerate millions of gallons of wastewater every day.
D. TOC (Total Organic Carbon)a measure of the carbon that remains after the incineration (physical oxidation) of organic matter.Instead of using oxygen as the unit of measure, carbon becomes the unit of measure for this method, mostly from carbon dioxide that remains after complete combustion. We can measure this by infrared techniques. TOC is often used in the various models that predict the fate of different wastes, because it represents a more direct measure of the organics (i.e., all organics are composed of carbon).
A parting thought: we refer to each of the above measures as an "indicator." That is, they are general indicators of the level of organic pollution, and they help us calculate the amount of treatment that will be needed. There is a tremendous advantage in expressing the complex mix of organics in a single practical measure.
However, by the time we talk about inorganic wastes, there is no such common indicator! We generally have to measure these contaminants one chemical at a time. And that's expensive!
Objective: The purpose of this assignment is to analyze soils in terms of the content (elements), horizons, profiles, soil types, and biological components. This section also analyzes types of wells.
1. The earth's crust is composed of the following elements (given in the order of average % of soil content):
O2: 46%
Si: 28% (mostly as SiO2)
Al: 8%
Fe: 5%
Ca, Mg, Na, and K: 11%
all others: about 1.5%
2. Horizons are horizontal layers of different soils. Examples are shown in the diagram below:
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Horizon
A:
topsoil: zone of maximum bioactivity Horizon B: subsoil: zone of eluviation (washing in)
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3. Profiles refer to different patterns of soil horizons.
For example, the topsoil may be very thin or even missing in some soil profiles.
4. Soil types: soils are made of combinations of three different grains:
5. Humus refers to the organic material in soil
6. Biological components include such diverse components as:
7. Wells fall into at least three basic categories:
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