In this part of the Full Plumbing Course, We will Private on-site Wastewater treatment systems.

Private on-site Wastewater treatment systems

Onsite wastewater treatment systems are considered a last resort because they require a lot of space and maintenance to work properly. However, these systems do have their place in urban settings where space may be limited. They consist of three parts; the pre-treatment unit, the primary treatment unit, and the disinfection unit. Pre-treatment units remove solids and sludge by passing raw sewage through screens. Primary treatment units remove solid matter and pathogens using a series of settling tanks and mechanical filters. Disinfection units kill remaining pathogens using chlorine, ozone, ultraviolet lights, or biological methods.

Why do we need wastewater treatment systems?

The two most important elements when managing a wastewater system are safety and sustainability. These systems help ensure the safety of our environment and surrounding communities while ensuring the highest quality water possible is being produced. A system must be properly designed and installed before its use can begin.

Types of Wastewater Treatment Systems

Wastewater treatment systems can fall under two categories; gravity-based systems and pressurized systems. Both have their advantages and disadvantages. Gravity-based systems are inexpensive to install but require little maintenance. Pressurized systems are more expensive to install than gravity systems, but they provide greater reliability and higher efficiency.

How does a gravity system work?

Gravity-based wastewater management systems work by separating solid matter (such as sediment) from liquid matter (water). In these systems, the solids settle to the bottom of the tank where they collect, and the water flows over the top and out of the tank. Gravity alone is not enough to separate the water and solids, therefore additional filtration processes are necessary. The simplest form of a gravity-based system is just a barrel buried below ground level; however, more sophisticated versions include a series of chambers and filters which create a more effective separation between the different components of the mixture.

What are some advantages of a gravity system?

Gravity-fed systems have many advantages including:

• Low initial cost – Because the cost of installing a gravity system is low, it’s often a great option for smaller projects.

• Easy operation – Once the system is operational, there are rarely any moving parts that could malfunction.

• Simple design – When working correctly, a wastewater system should only take a few hours to install.

• No chemicals – Unlike most chemical-driven systems, gravity-based systems don’t require any added chemicals.

• Reliable performance – If the system is constructed appropriately, it will perform at near 100% efficiency.

• Minimal space requirements – While gravity-based systems may require slightly more surface area than other types of systems, they aren't nearly as much as pressurized systems.

The wastewater treatment system is an essential piece of any residential or commercial building's plumbing construction. It may seem like a small detail, but having a complete sewage system for your home is not only safe, it is expected. A good sewage system should be installed prior to foundation work or major remodeling projects.

A typical sewage system consists of a pumping station, collection tanks, distribution pipes, stormwater sewer, and drainage structures (such as manholes). The following video shows how to install a simple sewage system for residential use. You will need a pump, storage tank, pipe, fittings, and tools to complete the job.

The design should meet local codes/standards, and be approved by local government agencies. If installing a sanitary sewer system, check city requirements.

Wastewater Treatment Systems (WWTS) is designed to remove contaminants from domestic wastewater before it is discharged into surface waters. A WWTS includes three components: a pretreatment unit, a primary clarifier, and a final polishing filter. Depending on the conditions, some additional equipment may be included.

Pretreatment units reduce suspended solids, BOD, and COD. Primary clarifiers remove solid particles. Final Polishing filters remove fine particles. These steps can be combined to provide greater removal efficiency. Each step removes different pollutants from the wastewater.

How does an On-site Wastewater Treatment System work?

An On-Site WWTS works as follows:

a. Pretreatment Unit - Reduces the size of items in the wastewater stream. Most types have screens that operate to remove large debris, while larger items settle out.

b. Primary Clarifier - Removes dissolved solids. Sludge settles to the bottom where it is removed periodically or continuously.

c. Final Polishing Filter - Removes finer particles. Filtering beds are constructed of sand, gravel, or similar material. Sand filtration operates best at high hydraulic loading rates. Gravel filtration has low maintenance costs but requires frequent backwashing to maintain proper bed depth.

d. Discharge Pumping Station - Converts wastewater from the primary clarifier to flow in a dedicated, gravity-fed conduit (discharge line). Discharge pumps move sewage from the primary clarifier and discharge it into a specific sewer line.

e. Storm Water Management Drainage Structure - Manages storm runoff water. Drainpipes often carry stormwater directly to a nearby creek, lake, or other body of water.

f. Secondary Sewer System - Collects and delivers treated sewage to a public sewage collection system.

On-site Wastewater Treatment System (OWTS)

The use of wastewater treatment systems at the point where sewage enters the public sewer system is called “On-Site Wastewater Treatments Systems” (OWTS). OWTS has been proven to reduce the total dissolved solids (TDS), pH, nitrates, phosphates, ammonia, bacteria, heavy metals, pathogens, and pesticides found in wastewater prior to its release into the environment. These contaminants threaten human health by increasing diseases such as cancer, heart disease, kidney damage, birth defects, and reproductive problems. Thus, OWTS helps the environment and reduces potential risks to human health.

Wastewater treatment systems are designed to remove contaminants from wastewater before it enters our environment. There are several types of systems available depending upon the volume of wastewater generated and the type of contaminants present. These range from simple gravity-fed septic tanks to sophisticated chemical and mechanical systems. If properly installed and maintained, these systems can provide reliable service over many years.

Design & Installation

For small systems, including individual homes, a simple pit/well system may work well. However, if your home generates significant amounts of wastewater, you will probably need to install a larger system. A typical system consists of a holding tank (also called a lagoon) that collects wastewater until it reaches a certain level. Once the tank reaches capacity, the wastewater flows into an underground piping network that eventually empties into the public sewer system. In some cases, a pump and filters are added to improve the quality of the treated wastewater.

Maintenance

Most systems require periodic maintenance to ensure they operate efficiently. This includes flushing the pipes periodically to keep them clean, inspecting and cleaning the tank(s), replacing any worn parts, and checking the pH levels in the tank(s). Many systems use chemicals to assist in keeping the tank(s) clear and odorless.

1. On-site wastewater treatment systems (OWTS) require no additional chemicals, equipment, or labor costs to operate. These systems are relatively passive and rely on natural processes to remove solids and dissolved contaminants from the wastewater. In addition, OWTS do not produce sludge, odors, or excess noise, making them perfect for residential and commercial applications.

2. There are two types of conventional treatments: Gravity flow and vacuum filtration. Both methods work well at removing suspended solids, but gravity and vacuum filters cannot adequately handle grease, oils, fats, or heavy metals.

3. Biological treatment uses microorganisms to break down and destroy organic materials in the wastewater. Bacteria consume pollutants and convert toxic substances into less harmful compounds. As an example, nitrification converts ammonia and ammonium ions to nitrate and removes the need for further processing.

4. Filtration systems use sand, gravel, diatomaceous earth, activated carbon, or polymeric membranes to trap particles larger than 0.45 micrometers (the size of a human hair). Filters are effective at removing organic matter, bacteria, heavy metals, and viruses.

5. Biologically active filters treat microbial pathogens using biofilters, constructed wetlands, and aerobic digesters. Biofilters have been proven to reduce pathogens in treated wastewater by 99 percent.

6. A typical biofilter consists of a series of hollow fiber modules that act together to filter out microbes. Wastewater enters the top of the bag and goes through the fibers where the air is introduced via mechanical ventilation fans. Microbes attach themselves to the outside surfaces of the fibers and begin breaking down contaminants. When the oxygen concentration drops below a certain point, the system switches over to a denitrification process.

7. Conventional treatment systems may require periodic chemical additions that add expense and maintenance to the operation.

8. Anaerobic digestion (AD) produces biogas, which can be used for electricity generation. AD works best for treating sewage containing high levels of moisture and organic material.

9. Activated carbon is commonly used as a polishing agent prior to disinfection. The carbon adsorbs toxins, reducing their concentration in the water. However, carbon does nothing to degrade or remove grease or oil.

10. UV treatment uses ultraviolet radiation to kill organisms in the water. UV-C technology kills all forms of bacterial contamination, while UVC-B kills only vegetative bacteria. Ultraviolet radiation breaks bonds in DNA, causing mutations and ultimately death.

11. Disinfection requires a combination of physical and chemical agents to kill pathogenic organisms. Chlorine dioxide gas reacts with organic molecules, oxidizing them and killing any microbes present in the water. Chloramine, combined with chlorine and ozone, degrades organic matter and eliminates microorganisms.

12. Disinfection can cause skin irritation if applied incorrectly.

13. Physical treatment includes sedimentation and separation technologies like belt press and cyclonic separators. Sedimentation relies on gravitational forces to separate solid and liquid components of the wastewater. Most systems utilize some type of media like glass beads, plastic spheres, or synthetic polymer media. Polymer media is preferred due to its low cost, ease of installation, and durability.

14. Separation technologies rely on differences in density between liquids and solids to separate them, much like a centrifuge. Cyclonic separators use induced vortexes to create fluid swirls to enhance the removal of solid particles. Belt presses use a rubber belt to squeeze water through a screen and remove impurities from the water.

On-site wastewater treatment systems (OWTS) help reduce the amount of pollutants discharged into local waterways. Most OWTS consist of two types of devices: primary sedimentation followed by disinfection, and secondary disinfection alone.

Primary sedimentation consists of gravity settling tanks where solids settle out at the bottom of the tank, then the clear liquid flows over the top of the solids back into the system. A clarifier may be added to further remove suspended solids. Primary sedimentation is generally sufficient to provide adequate removal of suspended solids from municipal sewerage. However, some jurisdictions require additional treatments before discharge.

Secondary disinfection consists of either a chlorine contactor or a UV disinfection unit. Both these units create residual disinfectants in the effluent that kill bacteria, viruses, protozoa, and helminths. Chlorine contractors use chemicals to release reactive free chlorine into the effluent. These chemicals react with contaminants in the wastewater to produce nontoxic products that can be easily removed from the treated water.

Chlorination involves adding a chemical known as hypochlorous acid to the water. Once dissolved, the hypochlorous acid reacts with pollutants in the wastewater to make nontoxic compounds called trihalomethanes that can be separated from the treated water. Other reactions between hypochlorous acid and pollutants result in chloramines that may form naturally and can cause problems if they exceed certain concentrations. Therefore, both chlorine contractors and chlorinators should have good control mechanisms to prevent excessive buildup of chloramines.

UV radiation uses electromagnetic waves of shorter wavelengths than visible red light. UV light cannot penetrate water, so it requires air to reach any depth. This results in a highly effective way of removing bacteria, viruses, protozoans, and other microorganisms. In the past, ultraviolet radiation was thought to damage DNA. However, newer technologies have shown that the damaging effects of UV light on DNA do not occur below certain wavelengths and doses. Because of this, UV disinfection systems have become increasingly popular.

Disinfection Units Disinfection units are devices that generate ultraviolet radiation inside a chamber. The radiation passes through the water passing through the chamber. Once outside the chamber, the ultraviolet rays are attenuated by air molecules in the atmosphere. This causes the intensity of the radiation to decrease significantly. UV disinfection does not destroy pathogens, but rather prevents them from multiplying. As a result, the concentration of pathogens in the effluent stream decreases. There are many different kinds of disinfection units that offer varying levels of disinfection. The type of disinfection unit chosen should match the specific requirements of the facility.

Inspecting Your System

Before installing a wastewater treatment system, you should ensure that the system meets all applicable regulations and permits. Inspections are required annually for systems installed in 2002 or later. If your system exceeds three years old, you must schedule inspections every year thereafter. Also, check the manufacturer’s instructions and operating manual. You should know how much flow rate each device provides and what the minimum size of each device should be. Ideally, you should test your system by running untreated wastewater through it. Look for clogs, blockages, leaks, corrosion, and other issues.

You should know whether your system is designed to handle stormwater runoff, sanitary sewage, greywater, blackwater, rainwater, and other substances. To avoid future conflicts, you should know the proper application and location of each device. All electrical outlets should be protected to avoid electrocution hazards. Make sure that the system does not interfere with fire protection equipment or drainage structures. Contact local agencies for more information.

A number of factors affect the performance of a wastewater treatment system. Some of these include system design, materials, and maintenance. For example, if a wastewater treatment system is composed of plastic pipes, it will likely leach chemicals into the environment after a period of time. In addition, if a system is improperly maintained, it may fail to function properly. This could lead to costly repairs and downtime.