Manual softeners

In cases where there is no water softener available, it is possible to manually soften water by mixing in lime, Borax, or sodium triphosphate. It is good for small-scale projects and does not require electricity or regeneration. However, it must be added to water for every use, and it can irritate your skin.

Desalinization

Desalinization is a special type of water treatment that specifically removes salt from water. Two methods, distillation and RO, have already been described. Two other methods of desalination include electrodialysis and chemical ion exchange.

Electrodialysis

Electrodialysis uses a series of membranes and a current of electricity to remove salt from the water. As saltwater passes through a chamber with a positive anode and a negative cathode, an electrical current is activated, the sodium chloride (NaCl), which is salt, will be split and the anode will attract the negative charged chlorine ion (Cl-). The cathode will attract the positive sodium ion (Na+). This process by itself would not last long because the anode and cathodes would fill with Na+ and Cl-. Two types of membranes are added to the chamber, one is a positive membrane that allows the Cl- to pass but will repel the Na+. The other membrane is negative and will allow the Na+ to pass and will repel the Cl-. If three sets of each membrane are placed in alternating order in the chamber as shown in the pictures below, then the system will be ready. When the electrical current is activated, the salt in the saltwater influent will be split. The Cl- from the first influent will cross the positive membrane on its way to the anode but will be stopped by a negative membrane and then will be removed as effluent. The Na+ from the first influent will pass through the negative membrane and be stopped by the positive membrane. This leaves clean water in the influent channel. The second influent channel reacts in a similar way, also retaining clean water while removing Na+ in the effluent channel and Cl­- through the concentrate channel. The cost of electricity and the membranes limits the use of electrodialysis.

Chemical Ion exchange

Like water softeners, the water is passed through resins and ions exchange places to remove the salt from the water. This is a two-stage process. In the first stage, the sodium chloride (NaCl) crosses through an acidic resin. The acidic resin will give up a hydrogen ion (H+) for a Na+ ion. The result is hydrogen chloride (HCl). In the second stage, the HCl is based through a basic resin where hydroxide ions (OH-) are exchanged for Cl- ions. The H+ joins with the OH- to create HOH or H2O which is pure water.

Wastewater Treatment

Case Example

Jaclyn is the mother of three children; they live in a mobile home trailer. Their trailer is not hooked up to the city sewer system. They could not afford to build a septic system to treat their sewage, so they connected a pipe that took their sewage away from the trailer but deposited it on the ground about twenty feet away. Although they dug a shallow pit for the sewage, the pit quickly filled up. The ground was made up of a thin layer of topsoil on top of a deep layer of clay, so water was slow to percolate into the ground. One day they received unexpected heavy rains and sewage from their pit flowed back through the pipes into their toilet and sinks. The sewage also spread across the backyard where it created puddles of wastewater. While Jaclyn tried to clean up the mess inside the trailer her children went outside to play. Three to four days later, all three children complained about itching feet and discovered a small rash. A week later, it turned into a series of red tracks winding around the feet. The children were taken to the doctor who diagnosed them with Hookworm infection.

Improper treatment of human waste is a public health concern and can lead to serious illness. Proper disposal of sewage can help prevent those types of illnesses.

Introduction

Wastewater Treatment

Human waste has been an issue since the time Adam and Eve left the Garden of Eden. Improperly managed waste can lead to the spread of illness. This idea was made known during the time of Moses. Moses led thousands of Israelites out of Egypt into the desert. While they traveled in the wilderness, Moses received revelations on how to direct, protect, and govern the people. One such revelation that he received is found in Deuteronomy 23:12-13.

12. Thou shalt have a place also without the camp, whither thou shalt go forth abroad:

13 And thou shalt have a paddle upon thy weapon; and it shall be, when thou wilt ease thyself abroad, thou shalt dig therewith, and shalt turn back and cover that which cometh from thee.

The first rule was that people shouldn’t go to the bathroom wherever they wanted but that there should be a designated place that was outside the camp. If they were allowed to go wherever they desired, the camp would soon fill with human sewage and illness and sickness would spread through the people. It could be dangerous outside of camp so the next rule was that when they left camp, they should carry a weapon. Since the Israelites were slaves in Egypt, they probably didn’t have fine weapons like swords and shields, they probably had long sticks and staffs. So, when the rule said put a paddle on thy weapon it essentially turned it into a shovel. Next the scripture says “when thou wilt ease yourself abroad” (go to the bathroom), dig a hole for the waste and cover the hole up. Without a proper waste system to deal with human sewage, their best practice was to bury it in a hole. Even today, in parts of the world where there isn’t proper sewage treatment, the best practice remains to bury it in a hole.

Over the centuries, the management of human waste has progressed significantly from a hole in the ground. The main two ways to manage human waste consist of the use of septic systems or the use of designed sewage systems with sewage treatment facilities.

Septic Systems

Septic systems are onsite sewage treatment systems that can be used at houses or buildings not hooked up to an existing sewage system. They are made of a septic tank which is placed in the ground and a series of pipes called a drainage system.

Septic tanks come in a variety of sizes and designs depending on the soil composition and size of the home or building. Septic tanks have an inlet where wastewater from a building enters the tank, wastewater flows into a settling chamber where light materials float to the top and heavy materials sink to the bottom. Sometimes the tank will have multiple settling chambers. Once the waste is in the tank, intestinal bacteria will begin to consume the solids. If the bacteria are aerobic (use oxygen) then the process will have significantly less odor. If the bacteria are anaerobic (does not need oxygen) then there will be a very strong odor. Some septic systems have aeration systems in them to keep the water oxygenated to reduce the odor. The outlet of the septic system guides the water out to the drainage system. Even with bacteria breaking down the solids, the bacteria cannot consume all the solids and the septic tank will fill up. In this case, owners of the septic system must get the tank pumped out. Under normal conditions, it may take 3–5 years to fill up. If there are fewer people in the building than are designed for the septic system, it may take 6–10 years to fill. If there are more people than it is designed for, it could fill in 1–2 years. A tank can also become overwhelmed if there is a party or event when the number of people in attendance greatly exceeds the design.

Drainage System

Drainage systems, also known as absorption fields, are a series of perforated pipes that allows water to flow into the soil. The pipe is called a lateral and it is laid in trenches. The amount of pipe in the field and each lateral is dependent on the capacity of the building. There are different ways to design the laterals, but they should not be more than 76 feet long and should be separated by at least six feet.

Soil Testing

Before a septic system is constructed, the soil should be tested to assure that the soil can support a system. If the soil is mostly clay, the water will percolate slowly and could back up. If the soil is mostly sand, the water could flow too fast and possibly contaminate the groundwater. Each jurisdiction decides what type of soil testing will be required before approving a septic system. One type of soil test is called a percolation test (perc test). Perc test requirements can vary depending on the jurisdiction.

Perc testing protocol

1. Dig a hole about two feet deep and one foot wide.

2. Put about two inches of pea gravel in the bottom of the hole.

3. Fill the hole with water and let it sit for at least four hours.

4. Maintain water in the hole to assure the soil gets saturated with water.

5. Place a board over the hole and mark the board where the measuring

stick will be placed.

6. Put the yardstick or meter stick in the water. Line it up with the marks on

the board and make sure it extends into the water but does not touch the

bottom.

7. Measure the water level on the measuring stick.

8. Wait 2–30 minutes and take another reading to see how far the water has

dropped.

9. Continue this process until five measurements are taken.

10. Average the five drop measurements and this will be your perc test result.

11. Compare the results to the jurisdiction's standards. A good range of

results would be between six minutes per inch and 60 minutes per inch.

Percolation test calculations

Once the percolation test readings are collected, the result must be calculated. The time in minutes is placed over the amount of drop in inches. The calculation can be done using fractions of an inch or by changing the fraction to a decimal as shown in the two examples below.

The water level drop was measured at 5/8 inch over a 30-minute period.

The water level drop was measured at 1 1/2 inches over a 10-minute period.

In some jurisdictions, instead of perc tests an inspector can conduct a visual hole inspection and ribbon test. Under this type of testing, a ramped hole about six to eight feet (two to three meters) deep is dug in the ground revealing the different soil strata. A trained inspector will visually inspect the strata and could collect soil samples to examine in the lab. An inspection conducting a ribbon test takes a handful of soil from the wall of the hole and tries to form a thin ribbon about two inches (five centimeters) long to see if it holds together. If it stays together, it indicates that the soil has high clay content and water may not properly percolate through it.

Designing a drainage field

Once the lot passes a soil test and is deemed adequate to support a septic system, a drainage field must be designed. Although each jurisdiction might have their own tables and requirements, the following steps will use an example to walk through the calculation of a drainage field.

The planned size of the residence is 2100 square feet and will have three bedrooms.

The yard is small so three-foot-wide laterals will be used.

The perc test results were: 24 mpi, 27 mpi, 26mpi, 29 mpi, 27 mpi

Step 1. Average the perc results.

Sum of 24 + 27 + 26 + 29 + 27 = 133

133/5 = 26.6 mpi

Step 2. Did the perc test pass?

The result of 26.6mpi is between 6mpi and 60mpi

Yes, the perc test passed.

Step 3. Determine the type of residence.

Take the square footage of the residence and divide by the number of bedrooms.

Compare your result to the following table to determine residence type.

2100ft2/3bd = 700ft2/bd

700 ft2/bd is between 500 and 800, therefore it is a Type II house.

Step 4. Calculate the estimated water flow per day.

Use the chart below and plug in the number of bedrooms and type of residence.

Three bedrooms and a Type II house = 300 gallons per day

Step 5. Find your Multiplier.

Use your perc result and plug it into the chart below.

26.6 mpi = a multiplier of 1.67ft2/gallon

Step 6. Calculate the area of the drainage system needed for the residence.

Take the Multiplier from Step 5 and multiply by the estimated water flow per

Day from Step 4.

1.67ft2/g X 300 g =501ft2 total drainage area

Step 7. Choose the width of your lateral.

If you have a large lot, choose two-foot-wide laterals.

If you have a small lot, choose three-foot-wide laterals.

Because the lot is small, three-foot-wide laterals were chosen.

Step 8. Calculate how many linear feet of laterals you need.

Take the total drainage area and divide by the width of the laterals.

501ft2 drainage area, laterals 3 feet wide

501ft2/3ft = 167 linear feet of laterals

Step 9. Calculate how many laterals are needed.

No laterals should be over 75 ft long

Divide your linear feet of laterals from Step 8 by 75 and round up

167ft/75ft = 2.226, round up to three Lateral Needed

Step 10. Calculate the actual length of laterals.

Take linear feet of laterals from Step 8 and divide by number of laterals from Step 9.

167ft/3ft = 55.6 feet per lateral

10. Draw a schematic of your drainage field.

Sewer Treatment Systems

Most cities will have dedicated treatment facilities that treat all the human waste (sewage) from the community. The sewer system connects at each residence and the sewage flows through pipes or canals until it reaches the treatment facility. At the facility, the sewage will undergo at least primary and secondary treatment and, in some cases, tertiary treatment. Each sewage or wastewater treatment facility is designed differently but most of them have similar treatment methods.

Primary Treatment

The initial stage of domestic wastewater is known as primary treatment. Coarse solids, floating material, and material that easily settles out are removed from the wastewater (EPA, 2004). Most primary treatments are considered physical as they physically remove the solids from the wastewater. Examples of primary treatment include bar/barrel screens, grit chambers, screws, and primary settling tanks.

Screens

Screens filter out large objects, such as rags, dental floss, plastics, coins, sticks and other objects people flush down toilets. Barrel screens are perforated barrels. The water passes through the perforations and the larger objects are collected in the barrel. The barrel is always rotating so those objects will rotate with the barrel until gravity forces them to fall into a collection device. Most collection devices have an auger of some type to remove those items.

Grit chambers

After the wastewater has been screened, it may flow into a grit chamber where sand, grit, cinders, and small stones settle to the bottom. The grit and screenings removed by these processes must be periodically collected and trucked to a landfill for disposal or incineration (EPA, 2004).

Primary settling tanks

With the screening completed and the grit removed, wastewater still contains dissolved organic and inorganic constituents along with suspended solids (EPA, 2004). The wastewater that enters a settling tank will have a short time for heavy solids to settle to the bottom for removal and light substances such as grease and materials to float to the top where they can be skimmed off.

Secondary Treatment

After the wastewater has been through Primary Treatment processes, it flows into the next stage of treatment called secondary. Secondary treatment processes use bacteria to consume the organic matter and remaining suspended solids in wastewater and can remove up to 90 percent of the organic matter in wastewater (EPA, 2004). Examples of secondary treatment include trickling filters, activated sludge, aeration tanks, oxidation ponds, and secondary clarifiers.

Trickling filters

A trickling filter is a bed of rocks or plastic through which the wastewater passes. Newer facilities may use beds made of plastic balls, interlocking sheets of corrugated plastic, or other types of synthetic media. The media ranges from three to six feet (one to two meters) deep and allows large numbers of microorganisms to attach and grow. Bacteria, algae, fungi, and other microorganisms grow and multiply, forming a microbial growth or slime layer on the media. In the treatment process, the bacteria use oxygen from the air and consume most of the organic matter in the wastewater as food (EPA, 2004).

Activated sludge and aeration tanks

Activated sludge is a process for removing organic matter from sewage by saturating it with air and microorganisms that can break down the organic matter. An adequate supply of oxygen is necessary for the activated sludge process to be effective. The oxygen is generally supplied by mixing air with sewage and biologically active solids in aeration tanks (EPA, 2004). The air is often forced in at the bottom of the tank bubbling up through the activated sludge and wastewater.

Oxidation ponds

Oxidation ponds, stabilization ponds, and sometimes lagoons are scientifically constructed shallow ponds that allow sunlight, algae, bacteria, and oxygen to interact. Biological and physical treatment processes occur in the lagoon to break down organic matter and improve water quality (EPA, 2004).

Secondary clarifiers

During the last step of secondary treatment, wastewater flows to a secondary clarifier or sedimentation tank. Like a primary settling tank, heavy solids settle to the bottom where they are scraped off and removed while light substances on top are skimmed off. After water leaves the clarifier, it is generally ready to enter a river.

Tertiary Treatment

After the water leaves secondary treatment, either by choice or jurisdictional requirement, it may proceed to tertiary treatment. Examples of tertiary treatment are disinfection and further filtering.

Disinfection

Disinfection means killing or inactivating pathogenic microorganisms that remain in the water. Chlorine is the most widely used disinfectant, but ozone and ultraviolet radiation are also frequently used for wastewater effluent disinfection (EPA, 2004). Chlorine kills microorganisms by destroying cellular material. This chemical can be applied to wastewater as a gas, a liquid, or in a solid form. However, any unused chlorine remaining in the water, even at low concentrations, is highly toxic to aquatic life (EPA, 2004). Facilities can add a chemical to dechlorinate the water, but it takes time, so the water is sent through a chlorine maze until the chlorine is no longer active. Ozone is produced from oxygen that is exposed to a high-voltage current. Ozone is very effective at destroying viruses and bacteria and decomposes back to oxygen rapidly without leaving harmful by-products. Ozone is not very economical due to high energy costs. Ultraviolet (UV) disinfection occurs when UV in the form of light penetrates the cell wall of exposed microorganisms. The UV radiation retards the ability of microorganisms to survive by damaging their genetic material. UV disinfection is a physical treatment process that leaves no chemical traces (EPA, 2004).

Further filtering

Water can also be passed through an activated carbon filter or reverse osmosis system. Wastewater passing through a bed or canister of activated carbon can remove more than 98 percent of the trace organic substances still in the water. Water can also be forced through the tiny pores of membrane filters in a process called reverse osmosis. This removes anything left in the water larger than the pores.

Sludge Treatment

Water treatment is not the only process going on at a wastewater treatment facility. While a lot of sludge can be present through many of the treatments, some sludge is removed. There are many ways to treat sludge. One way is sending it through a digester that uses bacteria to break it down. Before sludge from the digester can be removed from the facility it must be de-watered. De-watering can be done through gravity belt thickeners, centrifuges, and presses. Sometimes, a polymer is added to speed up the process. After de-watering, the sludge is transported to drying beds where any remaining water can evaporate. Eventually, the sludge will turn into a nutrient-rich compound that can be used as fertilizer or fill for landfills.

Additional Resources

How to Create a Flow Chart

This week, in the virtual lab, you will need to create a flow chart. The following videos are directions on how to create flow charts within MS Word and Google Docs.

How to create Flow Charts in MS Word: How to Create a Flowchart in Word

How to create flow charts in Google Docs: Create a flowchart in Google Docs & Drive

References

EPA. (2004). Primer for Municipal Wastewater Treatment Systems. Retrieved Feb 8, 2023, from https://books.byui.edu/-iByQ

WHO. (2022a). Drinking-water. Retrieved Feb 4, 2023, from https://books.byui.edu/-LGeM