The Complete Guide to Wastewater Treatment and How It Affects the Environment.
- Definition and Sources:
Wastewater as the name suggests is a byproduct of human activity either directly as human waste or as a result of human activities both domestic and industrial. Waste water may infiltrate the sewer system as groundwater infiltration or as stormwater that enters from roof drains, foundation drains, submerged man-holes, or Runoff from rainfall and snow melt.
Domestic wastewater sources are categorized as grey water discharged from the Kitchen, general washing, and the bathroom. The foul water source is from the toilet, latrines, and exhaust tracks.
Industrial wastewater sources are majorly discharged from factories e.g., manufacturing and chemical processes.
- Key facts about wastewater:
Wastewater has chemical and physical characteristics
Domestic wastewater’s physical Characteristics are: Fresh and aerobic domestic wastewater has been said to have the odor of kerosene or freshly turned earth. The smell of old sewage gets steadily more unpleasant. Hydrogen sulfide smells awful and its presence means there’s septic sewage in the area. Fresh sewage is usually some shade of gray, whereas septic sewage is usually black.
Wastewater temperatures normally range between 10°C and 20°C. In general, the wastewater is warmer than the potable water supply. This is because of the addition of water from households and heating within plumbing systems
One cubic meter of wastewater weighs approximately 1tonne. It will contain about 500 grams of solids. One-half of the solids will be dissolved solids such as calcium and sodium salts as well as soluble organic compounds. The remaining 250 grams will be insoluble. The insoluble fraction usually occupies about 125 grams of material which settles out of the bulk liquid in a time span of approximately 30 minutes when left under quiescent conditions. The other 125 grams of water will take a long time to settle to the bottom, resulting in high levels of turbidity in the tank.
Domestic wastewater has a number of chemical compounds and describing all of them would be next to impossible. In practical use, we usually consider only a few general classes of compounds. These classes often are better known by the name of the analytical procedure used to measure them than by what is included in the class. The biochemical oxygen demand (BOD 5) test is a good example. The other test is chemical oxygen demand (COD). This is a measure of the reactivity of organic substances relative to that of only oxygen in the water.
- Famous Myths about wastewater:
Myth #1: Resolving urban sanitation is all about toilets.
In fact: Providing access to a toilet, a latrine, or a sewer connection is only one important step of the solution. To help achieve SDG number 6-clean water and sanitation, it has been established that human waste needs to be dealt with safely and sustainably.
Myth #2: Domestic wastewater produces waste that is a nuisance to be eliminated
In fact: Human waste contains important nutrients that can be reused as a soil conditioner or fertilizer. Energy can be generated from heat recovery and biogas combustion. Recycled wastewater can also be reused for other purposes, such as for making potable water, using in industrial applications, or in agriculture. There is a return on investment when the proceeds of the recycled wastewater are compared with the whole treatment process.
- What might go wrong without an efficient wastewater system:
Poor sanitation standards can lead to a whole host of problems, from diseases and epidemics to soil and water contamination. One effective way of tackling sanitation problems is wastewater treatment. There can be a variety of microbes in wastewater, including bacteria, viruses, and parasites (such as worms or protozoans). These are all harmful to humans.
Certain fungi can cause skin, eye, and respiratory infections. Studies have shown that various disease-causing organisms can also be found in sewage and wastewater.
It may be a good idea to filter your water because drinking it could lead to an infectious disease. According to a recent report, 80% of water-related diseases around the world are caused by infectious organisms. Diarrheal diseases caused by contaminated water lead to around 2 million child deaths and 900 million illnesses each year.
Treating wastewater consists of a sequence of processes. The result is clean and disease-free water.
- The Modern wastewater treatment Process:
Sewage water both domestic and industrial can be treated and reclaimed for reuse and discharged back into the natural water system. There are several steps involved in this treatment process as outlined as follows:
Step 1: Screening and Pumping:
Incoming wastewater is first screened to remove objects such as plastics, wood and fabric fragments, grits, and grease. The material removed is washed and transported to a landfill for disposal. The wastewater then moves to the next step: grit removal.
Step 2: Grit Removal:
At this stage, heavier and finer materials like sand and gravel are removed from the wastewater. These materials are also disposed of in a landfill.
Step 3: Primary Settling:
Sludge that settles at a slower rate than step two is needed to be taken out using clarifiers. Here, the sludge, which is called primary sludge, gathers at the bottom and wastewater exits the tank from the top. Floating debris such as grease is skimmed off the top and combined with settled debris. Chemicals are also dossed into the tank to remove phosphorus and all its elements at this point.
Step 4: Aeration / Activated Sludge:
At this stage, the wastewater has had most of its treatment. Biological degradation will turn pollutants into cells, water, and nitrogen. The same chemical process takes place on the ocean floor as on the bottom of lakes and rivers, but it takes years to occur.
Step 5: Secondary Settling:
Large tanks, called secondary clarifiers, help to separate the wastewater and then break down the organic sediment from the aeration tanks. This yields an effluent that is over 90% treated.
Clarified sludge is consistently returned to the aeration tanks in step four in a cycle to increase efficiency
Step 6: Filtration:
The clarified water is polished at this step by filtering through 10-micron polyester media. The material captured on the surface of the discs is periodically pumped back to the plant head for treatment.
Step 7: Disinfection/Chlorination:
After the bacteria has been removed by filtration, the treated wastewater is then subjected to ultraviolet treatment. Ultraviolet treatment kills any remaining bacteria, ensuring levels are within the discharge permit.
Step 8: Oxygen Uptake, Water Analysis & Testing, and Final Disposal:
The water is now stabilized and of a higher quality. It’s aerated if necessary to bring the dissolved oxygen up to a safe level, and tested for pH, ammonia, nitrates, phosphates, dissolved oxygen, and residual chlorine level.
After treatment, water is released back into the natural flow of things. The water discharged into the river must meet stringent requirements set by the EPA and Clean Water Act. Pollutant removal is maintained at 98% or greater.