water quality and system

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desires to have the water tested will usually be quoted lab tests based on these ''standard methods."

In general, a facility management professional concerned about the quality of the water supply under his jurisdiction will utilize a certified laboratory to test and verify the adequacy of the water. Bacteriologic monitoring costs between $10 and $50. Volatile organics tests can be expected to cost between $200 and $500. Synthetic organics tests are more expensive, around $2,500. Radionuclides tests cost under $200.

The facility manager's budget should include funds for testing on a periodic basis. Reporting should include the test results.

Public Notification and Right to Know

Finally, the facility manager should be aware of the legal requirements and the public's right to know. If the maximum amount of contaminants allowable drinking water standards are exceeded, then the facility manager must notify the public of the violations (see Chapter 7).

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Chapter 9

Wastewater Systems

Water in, water out ... The facility can treat or partially treat its wastewaters or it can work in close coordination with the utility to make sure its wastes are treated safely. The facility manager does not often need to treat raw sewage. The purpose of this chapter is to provide a basic knowledge that is used by city and county water treatment managers, and cover the fundamentals of treating the facility's own wastewater.

Sewage Treatment

Many facility managers find it necessary to treat their own domestic sewage, while large industrial plants are required to treat sewage.

In addition, recent new trends in water conservation and consumption have generated an interest in "graywater" systems. In a graywater system, the mild waste water from washing hands, bathing, and kitchen waste is reused before being sent to the sewage treatment plant.

The Three-Step Sewage Treatment Process

Sewage treatment is a simple three-step process that makes the most use of natural microbes to decompose and break down human and animal waste. To put it simply, there are bigger bugs out there that like to eat the dangerous pathogenic organisms that contaminate water. A wastewater treatment plant makes it easy for these natural predators to thrive.

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As discussed in Chapter 8, the primary mechanism for serious disease transmission is the fecal/oral route. Wastes from humans, including disease pathogens is inadvertently ingested by other humans who become infected and in turn add more pathogens to wastewaters.

To prevent the spread of disease, the wastewater system carries water from toilets, washbasins, sinks, tubs and floor drains to where it can be treated in a central facility. Wastewaters are carried from the facility in pipes. While Chapter 4 provides a fairly detailed discussion of hydraulics or pipe sizing theory, Table 9-1 provides some quick wastewater pipe-sizing guides from the plumbing codes.

The Two Types of Wastewater Systems

The main types of wastewaters include stormwater and sanitary sewer. Stormwater is the runoff from roofs, gutters, downspouts, parking lots, etc. Sanitary sewers carry the water that goes down the drain or down the toilet. It is carrying waste away from where people are. A new trend is to separate the sanitary waste into graywater from sinks and tubs and blackwater from the toilet and the kitchen garbage disposal unit. The two types of wastes can be conveyed to different areas. In general, the intent is to use graywater for irrigation, plants, fountains and the likewhere it is not used for drinking, but it is also not wasted at the central treatment plant.

Many areas still treat the two systems as one sanitary system.

Wastes are carried through pipes to a central wastewater facility. For many facility managers, this will be the city utility and the facility has little responsibility. For others, the wastes are disposed of on site.

Permits

As discussed in Chapter 7, all wastewater treatment facilities are required to have some sort of permit to release the water from the wastewater treatment system back into the environment. Even lagoons, which would be thought to hold water until it evaporates, are required to have a groundwater discharge permit.

The permit regulates the quantity and the quality of the release and provides requirements for monitoring to assure that the releases do not contaminate the environment.

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Wastewater Treatment Methods

In the past, stormwater and sanitary sewer water were combined but the huge inflow of water to the treatment plant during a rainstorm upset the balance of water chemistry. Often, the stormwaters overflowed the main treatment plant, causing operators to have to dump their raw sewage into the downstream river or lake. As a result, the system designs were changed and the sanitary sewer system was isolated from the stormwater system. Today, the sanitary sewer manholes are solid, while in the past these manhole covers were grated.

Sanitary sewer water is conveyed to a central treatment plant. The amount of wastes in the water is smallperhaps only as much as one-tenth of one percent, while the rest of the water acts as conveyance to carry the small amount of wastes.

Treatment is broken down into two or three components. Primary treatment is where the large particles, grease, paper and debris is separated. Secondary treatment is where microbes are allowed to process the wastes. In a few rare instances, tertiary treatment refines and further purifies the water. Tertiary treatment is expensive and is not required except in a few pristine areas where the local public has decided to take the extra steps.

Treatment of sewage wastes then consists of removing the larger particles, providing a location of the microbes to breakdown the wastes, and final purification and clarification.

Biological Oxygen Demand

The main characteristic for microbe measurement is called biological oxygen demand (BOD, pronounced "Bee Oh Dee"). BOD is used in water treatment studies to measure the presence or number of microorganisms in the water.

BOD is actually the measurement of the amount of dissolved oxygen in a water sample and it represents the amount of wastes that can be consumed by microbes. BOD is usually expressed in milligrams of oxygen per liter of water. As the organic matter, which is what is represented by the BOD, is consumed by the bacteria, the bacteria "breathe" the dissolved oxygen in the water. The demand is representative of the microbes use of the oxygen. The bacteria will grow as necessary to consume the organic matter in the sanitary sewer water.

One of two things can happen to the water as the bacteria colony grows and consumes the organic matter. If enough oxygen is present,

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the bacteria will consume all of the organic matter. After consuming all the organic material, the bacteria, having no further food source will die and sink to the bottom of the vessel. This residual is known as sludge. If there is not enough oxygen in the water to consume the all of the organic matter, a new kind of bacteria that does not need oxygen begins to grow.

The bacteria that grow in oxygen-starved water are called anaerobic bacteria (growing without oxygen). Anaerobic bacteria can process more concentrated wastes and do not need light or air to work. However, the by-products of their consuming of the organic matter include methane and hydrogen sulfide gas. Hydrogen sulfide is a foul-smelling, unpleasant odor, while methane is flammable. Both require large amounts of fresh air to dilute the gases to safe and acceptable levels. The gases that are a product of anaerobic bacteria are why sewage treatment plants are remotely located.

Finally, facility managers should know that hydrogen sulfide gas is insidious. At low levels, it is malodorous, but the nasal passages become desensitized to it at low levels. This accounts for not being able to smell the foul odors after just a few moments.

Primary Treatment

At the treatment plant, primary treatment consists of filtering out large particles, dirt, stones, paper and bits of plastic. The primary design requires the flow to slow down enough so that heavy material can settle to the bottom. In addition, any floating debris is removed. Grinder pumps chop and break up most large pieces of debris. The sludge that settles is removed periodically.

Secondary Treatment

Secondary treatment is essentially the biological process and there are two basic methods for removal of the organic matter. Both methods provide air and microorganisms to interact and reduce the solids into sludge, carbon dioxide and water. The two methods mentioned here are trickling filters and activated sludge.

Trickling Filters - For most medium-sized communities, a trickling filter system is used. The trickling filter sprays sewage, after it has been through primary treatment, onto a bed of loose rocks or in some cases plastic saddles similar in surface area to rocks. Microorganisms form a slime layer on the rocks and as the sewage trickles over them, the large microorganisms consume the organic matter.

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After the water passes through the rock layer, the treated water is collected at the bottom and is released to ponds, rivers or streams. Trickling filters are usually round, 30-80 ft. in diameter and require pumps to push the sewage through the sprinkling mechanism (see Figure 9-1 ).

Activated Sludge - Like the trickling filter process, the activated sludge process uses air to encourage microbes to grow and consume organic matter in raw sewage. After primary treatment, mixed sewer water and activated sludge is pumped into a tank where compressed air is bubbled up through the sludge. The air feeds the microorganisms which consume the organic matter. As the matter is consumed, sludge settles to the bottom of the tank where it is siphoned off to drying beds or to a second anaerobic process.

Anaerobic Digester - The activated sludge, in the form of a slurry, flows into another large tank called an anaerobic digester. In this tank the growth of anaerobic (non-oxygen) bacteria is encouraged. These microbes consume the remaining organic matter. The remaining water is released to lagoons to evaporate, or to rivers or streams. The other by-product of the anaerobic digestersludgeis a more concentrated form than the product of the activated sludge tank. The sludge is pumped to drying beds.

Sludge - After drying, the sludge is picked up using earth-moving equipment. Front-end loaders scoop up the dried sludge where it is placed in dump trucks. The trucks can haul the dried sludge to a disposal site or in some areas of the country, the sludge is incinerated. It can even be recycled for agricultural use because it is rich in humus, a product that aids in plant growth (if allowed by the local government).

Problems Of Secondary Treatment - The trickling filter, the activated sludge digester and even to some extent the anaerobic digester are subject to poisoning of the microbes by strong chemicals. In effect, the chemicals kill or severely reduce the life of the microorganisms. When this happens, the treatment plant has no choice but to store the sewage until a new batch of microbes is ready. For this reason, many treatment facilities have more than one of these systems. In addition, the tanks and filters have to be taken down periodically for maintenance and for cleaning.

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Figure 9-1.

Typical trickling filter for treatment of wastewater. Reprinted (wit minor adaptation) from Microbiology: An Introduction with permission of Benjamin/Cummings Publishing Co., Inc.

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Other Sewer Treatment Facilities

Wastewater may be treated in a number of other facilities, including lagoons, septic tanks, storage tanks and others.

Lagoons

For many small facilities, simple sewer lagoons provide the necessary treatment. The raw sewage flows through grinders to chew up the solids. The remaining effluent flows into a pond where aerators stir the water and mix in air. The organic matter is removed via the microbial action discussed above. From the lagoon, wastewater is held until it evaporates, or it flows through a successive series of ponds until it is clean enough to be released back into rivers, a lake or the ocean. By comparison, lagoons are the simplest to operate but require much more room than either trickling filters or activated sludge digester.

Septic Tanks

For small residential or business users located a considerable distance from a sewer main or in an area that is not served by a central treatment plant, a septic tank is a simple, economical waste treatment alternative provided it is allowed by the regulating agency.

A septic tank is essentially an on-site disposal process that uses anaerobic bacteria. The septic tank is a vault with a dividing wall. Septic tanks can be made from concrete, fiberglass or other suitable leak proof materials (see Figure 9-2). The septic tank is buried sufficiently far from the facility to provide a margin of safety from any fumes coming from the tank and to prevent leaching back from the septic tank into the facility. Recommended distances for building sewers and septic tanks are provided in Table 9-2.

Raw sewage flows into the first portion of the septic tank as shown in the figure. Here, the large heavy solids drop out, and any grease or other floating debris is skimmed. In the second part, the anaerobic process takes place and the organic matter in the sewage is consumed.

From the septic tank, the water or effluent flows to a leach field. The septic tank leach field is a series of slotted or holed pipes where the waste water flows. The released water irrigates sod or other vegetation. Usually, the leach field does not supply vegetable gardens because on occasion the decomposition process is not completed in the septic tank. The sizing and function of the drain field is dependent upon the soil conditions in the area.