Wastewater Treatment Systems

Domestic wastewater is primarily contaminated water resulting from daily human activities originating from residences, commercial buildings (offices, schools, restaurants, etc.), and institutions.

This water consists of two main components:

1. Blackwater: Water coming from toilets, containing high levels of fecal matter (feces, urine) and pathogens.
2. Greywater: Water coming from kitchen sinks, bathrooms, showers, and washing machines; containing soap, detergent, grease, and food waste.

Domestic wastewater contains high levels of organic matter, total suspended solids (TSS), nutrients (nitrogen and phosphorus), and potentially pathogenic microorganisms (bacteria, viruses).

Wastewater treatment is a critical necessity for both environmental and public health.

• Protecting Public Health: Untreated wastewater contains pathogens that can cause the spread of serious waterborne diseases such as typhoid, cholera, and dysentery.
• Protecting the Environment (Water Resources): When wastewater is discharged directly into rivers, lakes, or seas, the high nitrogen and phosphorus within it lead to algal blooms known as “eutrophication.” This situation depletes oxygen in the water, causing mass deaths of fish and other aquatic organisms.
• Preventing Oxygen Depletion: The decay of organic matter in the water environment consumes dissolved oxygen, leading to the disruption of the aquatic ecosystem.
• Legal Obligations: Environmental regulations require wastewater to be brought to a certain quality (Discharge Standards) before being discharged into nature.
• Aesthetics and Odor: Untreated water causes serious odor problems and an unsightly appearance in the receiving environment.

Treatment of domestic wastewater generally occurs in three main stages (plus an additional sludge stage). This process is known as the “Conventional Activated Sludge System”:

1. Physical Treatment (Pre-treatment):
   • Screens/Sieves: The first stage where coarse waste mixed with water (toilet paper, bags, solid waste) is trapped.
   • Grit and Grease Trap: The flow of water is slowed down to allow inorganic materials like sand and gravel to settle, and oils on the water surface are skimmed off.
   • Primary Sedimentation: These are basins where a portion of the suspended solids in the water is settled by the effect of gravity.
2. Biological Treatment (Secondary Treatment):
   • Considered the heart of the treatment, microorganisms (bacteria) are used in this stage.
   • Wastewater is taken to aeration tanks. Oxygen is continuously supplied to these tanks via “blowers” (air fans).
   • Bacteria living in the oxygenated environment consume and break down the dissolved organic matter (pollutants) in the wastewater as food. Bacteria multiply this way and form clusters called “activated sludge.”
3. Sedimentation and Disinfection (Advanced Treatment):
   • Final Sedimentation: The water coming out of biological treatment (containing bacterial clusters) is taken to final sedimentation tanks. Here, the bacteria (activated sludge) settle to the bottom, while clarified treated water remains at the top. (A portion of the settled sludge is recycled back to the start of the aeration tank to maintain the bacterial population).
   • Disinfection: The treated water taken from the top is disinfected using chlorination, ultraviolet (UV) rays, or ozonation methods before being released into nature to eliminate any remaining pathogens.
4. Sludge Treatment:
   • The sludge accumulating at the bottom of the primary and final sedimentation tanks is called “sewage sludge.” This sludge has a very high water content. It is passed through dewatering (filter press, decanter, etc.) and stabilization (digestion) processes to reduce its volume and is then disposed of or used as fertilizer/energy source.

The main equipment used in a wastewater treatment plant include:

• Screens (Mechanical or Manual): Bars or sieves used to trap coarse waste.
• Grit and Grease Separators: Usually reinforced concrete or steel tanks.
• Pumps (Submersible, Centrifugal): Ensures the conveyance of water and sludge to desired points within the plant.
• Blowers: Machines that produce the air (oxygen) required for biological treatment.
• Diffusers: Equipment that distributes the air from the blower into the water in the form of fine bubbles at the bottom of the aeration tank.
• Sedimentation Tanks (Reinforced Concrete or Steel): Usually containing slowly rotating scrapers inside.
• Disinfection Equipment: Chlorine dosing pumps or UV lamps.
• Sludge Dewatering Equipment: Filter press, belt press, or decanter (centrifuge).
• Pipes and Valves: Connection elements of the system (usually PVC, HDPE, or metal).

A package treatment system is a factory-manufactured, ready-to-use system that combines all the conventional treatment processes described above (physical, biological, and sedimentation) into a single compact unit.

• Purpose: Used especially in places where a central sewage system is unavailable or plant construction is difficult.
• Usage Areas: Ideal for residential complexes, hotels, holiday resorts, construction sites, military units, factories, and settlements with low populations (usually between 50 – 5000 people).
• Features:
  • Compact: They occupy little space.
  • Modular: Capacity can be increased according to need.
  • Fast Installation: Since they are prepared in the factory, field assembly is very quick.
  • Automatic: Usually operates fully automatically, requiring minimal operator intervention.
  • Portability: Since they are generally made of steel or fiberglass/polyethylene tanks, they can be moved to another location if necessary.

These systems can perform biological treatment using more compact technologies such as SBR (Sequencing Batch Reactor) or MBR (Membrane Bioreactor).

Industrial wastewater is wastewater generated as a result of industrial activities such as factories, production plants, industrial zones, and workshops. Unlike domestic wastewater, the characteristics of industrial wastewater change completely “from sector to sector.”

While domestic wastewater contains largely predictable organic pollution, industrial wastewater may include:

• Heavy metals (Mercury, lead, chromium, cadmium, etc.)
• Toxic chemicals
• Petroleum and oil derivatives
• High or low pH values (highly acidic or basic)
• High temperatures
• Color (especially in textile and dye industries)
• Very high organic load (especially in the food industry)
• Solvents

Therefore, the wastewater of a metal plating plant and a dairy factory are as different as night and day.

The treatment of industrial wastewater is based on reasons even more critical and mandatory than domestic wastewater:

• Legal Obligations and Heavy Penalties: There are very strict “Discharge Standards” (Water Pollution Control Regulation, etc.) determined for every industrial branch. Plants that do not comply with these standards face heavy fines, suspension of production, and even closure.
• Preventing Environmental Disasters: Toxic chemicals and heavy metals in these wastewaters can cause “mass biological deaths” and irreversible destruction of the ecosystem in the rivers, lakes, or seas where they are discharged.
• Soil and Groundwater Pollution: Untreated water can seep into the soil, poisoning agricultural areas and contaminating groundwater used as drinking water.
• Human Health: These chemicals reach humans through the food chain (e.g., fish) or drinking water, leading to cancer, neurological disorders, and many chronic diseases.
• Protecting the Sewage System: If a plant is to discharge its wastewater into the municipal sewage system (and from there to central treatment), it must perform “pre-treatment.” Otherwise, acidic/basic or chemical-laden water can damage both the pipes (corrosion) and the beneficial bacteria in the municipality’s biological treatment plant, collapsing the entire city system.
• Water Recovery: Due to increasing water scarcity and water costs, many modern plants prefer to treat their wastewater and “reuse” it in their own production processes (e.g., cooling tower, boiler water). This provides a significant cost advantage.

Industrial wastewater treatment is a “tailor-made” job. A process is designed specifically for the wastewater characteristics of each plant. Unlike domestic treatment, chemical processes are generally much more dominant.

The main treatment methods are:

1. Physical Treatment:
   • Screens, Sieves, Grit Traps: Trapping of coarse solids and settleable matter.
   • Oil Separators (DAF): “Dissolved Air Flotation” (DAF) systems are used especially for plants with high oil and grease content (food, petrochemical).
   • Equalization Tanks: Since production in industrial plants changes according to shifts, wastewater volume and pollution fluctuate greatly during the day. Equalization tanks collect and mix this water to send a homogeneous (balanced) flow to the treatment plant.
2. Chemical Treatment (Most commonly used method):
   • Neutralization: Adding acid or caustic (base) to adjust the pH of the wastewater.
   • Coagulation and Flocculation: Chemicals (coagulant and flocculant) are added to the water to allow dissolved or suspended pollutants (e.g., heavy metals) to combine, clot, and form “flocs” that can settle.
   • Chemical Sedimentation: Settling these formed flocs in a sedimentation tank to separate them from the water.
3. Biological Treatment:
   • If the wastewater contains a high rate of “organic matter” (e.g., food, beverage, paper industry), biological treatment (activated sludge, etc.) is applied before or after chemical treatment.
   • Sometimes “Anaerobic Treatment” (oxygen-free) is preferred for very high organic loads, from which biogas (energy) can be obtained.
4. Advanced Treatment (For Recovery):
   • Used if the plant’s discharge standards are very strict or if it wants to recover water.
   • Filtration: Sand filters, multimedia filters.
   • Activated Carbon: Removal of color, odor, and dissolved chemicals.
   • Membrane Systems: Purification of water to process water quality using Ultrafiltration (UF) and Reverse Osmosis (RO) systems.
   • Ion Exchange: Used especially to remove specific metals or hardness from water.

Equipment used in industrial plants must be resistant to the aggressive (corrosive, chemical) nature of the wastewater.

• Dosing Pumps and Tanks: Pumps that accurately deliver chemicals (acid, caustic, flocculant) required for neutralization, coagulation, etc., into the system.
• pH and ORP Meters: Sensors that measure the pH and oxidation potential of water in real-time and automate the dosing.
• Fast/Slow Mixers: Used for homogeneous mixing of chemicals with water.
• DAF (Dissolved Air Flotation) Units: Systems that produce air bubbles to separate oil.
• Sedimentation Tanks (Chemical/Physical): Generally conical-bottomed or scraper-equipped tanks.
• Blowers and Diffusers: Used if biological treatment is present.
• Filter Presses or Decanters: Used to dewater the chemical sludge resulting from treatment (which often falls into the hazardous waste category).
• Advanced Treatment Equipment: Activated carbon columns, Reverse Osmosis (RO) membrane modules.
• Piping and Valves: Usually chemical-resistant PVC, HDPE, C-PVC, or Stainless Steel materials are preferred.

As with domestic wastewater, “package” solutions exist for industrial wastewater as well, but they are more specific:

• Industrial Package Treatment: Generally factory-manufactured, compact systems for smaller-scale industrial plants or focused on a specific type of pollution (e.g., only oil separation or only pH neutralization).
• Examples: A DAF (oil separation) unit installed inside a container, a chemical treatment unit (dosing, mixing, sedimentation) mounted on a chassis, or small-capacity MBR (Membrane Bioreactor) systems can be given as examples of industrial package treatment.
• Advantages: They occupy less space, their installation is fast, and they are designed for a specific, standard wastewater character (e.g., car wash, small food workshops, concrete plants). For large and complex chemical plants, package systems are usually insufficient.