What is Waste Water?

It is used water originating from domestic, industrial, agricultural and medical activities. Upon usage, the quality and composition of the water changes deeming it unfit for further use.

However, the water released from ponds or reservoirs, used for fish farming, is not considered as wastewater.

Types of Waste Water

Domestic Waste Water is all the water used in domestic dwellings (e.g. originating from small trades, schools, private households, and public authorities). Wastewater from domestic dwellings is quite similar in composition (with regard to the substances in the wastewater). Wastewater from hospitals might be of higher concern though, because of the pathogens and medical contaminants it might contain.

Industrial Waste Water is the water that has been used as part of making a commercial product and has a different chemical composition to domestic Waste Water. Whether it’s the food we eat, the beverages we drink, the clothes we wear, or the paper and chemical products we use, water is required for nearly every step of production across a multitude of different industries. The resulting wastewater must be carefully managed. Regardless of how wastewater is treated, the “end product” is called effluent. To comply with environmental protection laws, certain contaminants must be removed from the wastewater. This includes organic matter, inorganics (sodium, potassium, calcium, magnesium, copper, lead, nickel, and zinc), pathogens, and nutrients (most notably nitrogen and phosphorus).

Storm (Rain) Water is the water that originates from precipitation, including snow and ice melt. With less vegetation and more impervious surfaces (parking lots, roads, buildings and compacted soil), developed areas allow less rain to infiltrate into the ground, and more runoff is generated than in the undeveloped condition. Additionally, conveyances such as ditches and storm sewers quickly transport runoff away from commercial and residential areas, carrying along with pollutants like sediments, nutrients, bacteria, pesticides, metals, and petroleum byproducts, into nearby sewers.

Extraneous Water is the unpolluted groundwater and spring water which enter the sewer system due to leakages or due to cross-connections. Roughly 20% of treated wastewater is extraneous water, in some cases, wastewater may increase the fourfold and more.

Agricultural Water Waste is the water from agricultural activities (fertilizers and manure) and stables (animal urine and faces). Due to their high concentration of organic substances and high nitrogen content it may not be drained directly into the sewage system.

How does the municipal wastewater treatment process work?

Step-by-step guide:

Firstly, wastewater is drained to the Wastewater treatment plant (WWTP) through the main sewer system. Strange things end up in the WWTPs, ranging from smaller things like wallets, plants, and watches to bigger things like mattresses and animals. Sometimes even gold ends up at the WWTPs.

Therefore mechanical separation of these objects is required.  This is called preliminary treatment or rather pre-treatment.

The large objects in the wastewater are removed by bar screens. Bar screen consists of various screens to separate various objects. Coarse bar screen racks remove coarse matter like paper, textiles, wood, plastic materials. Medium bar screen racks remove smaller objects (e. g. sanitary articles) to avoid plugging of the plant. Fine bar screen racks reduce the content of the solids in the sludge. Water then flows through the gravel chamber where the flow of the water is slowed down so that grit settles out of the water. The grit is later disposed of at the dump.

The following step is called the primary treatment during which the wastewater flows into primary settling tanks. Water is driven towards the hopper at the base of the tank where the hopper arm moves around the edge of the tank at the velocity of 4 cm/s. Treated water heads towards the edge and the particulates, of higher sedimentation velocity than the flow velocity, settle at the bottom of the tank. The settled particulates form sludge and are transported to a digestion chamber for further treatment. By the end of this step, the contaminant levels are reduced to 60%.

The secondary treatment is a biological step where microorganisms degrade organic carbon and ammonia and assimilate phosphorus. This reduces a load of organic matter and nutrients in the water. The sludge generated in this process (i.e. microorganisms and organic matter) is pumped out and moved back to the primary settling tanks.

Water from secondary treatment flows through the sand filters and activated carbon filters to filter out all the particulate and dissolved compounds in water thereby producing clear service water.

The final step of wastewater treatment is the thorough inspection of service water. This ensures that the treated water has contaminants below the acceptable limit.

Sludge pumped out of the settling tanks is added to the digestion chamber where it is continuously mixed at a higher temperature. Biogas is produced during the digestion process which can be used as a fuel.

When sludge digestion reaches an optimal level the sludge is transferred to thickeners where it is smoothly agitated and interstitial water between the flocs is released. The sludge is compressed by gravity and the clear water rises up.

The digested and dewatered sludge is adequately dried out and ripened. It is either discarded at the dump or if complied with agricultural standards it can be used as fertilizers for crops.

Water Treatment Synopsis:

The aim of treating water is to remove unwanted substances and impurities like pathogens and pollutants thereby producing high quality, clear and tasty drinking water. This also ensures that the water stays consumable for a long time and poses no health risk.

The Treatment Process:

In a typical treatment process, preliminary treatment of raw water is performed to make the water fit for the treatment plant. Coagulation and flocculation are generally the primary treatment steps where the dissolved and suspended particles from the water are separated. Coagulation neutralizes the charges of the particles and forms a gelatinous mass to trap (or bridge) particles thus forming a mass large enough to settle or be trapped in the filter. Generally, alum or ferric salt is used for this purpose. Flocculation is gentle stirring or agitation to encourage the particles formed from coagulation to agglomerate into large masses called flocs which subsequently settle.

During the secondary treatment settled solids are removed by sedimentation. In this process, wastewater flows slowly through a tank allowing suspended particles that are heavier than water to settle to the bottom of the tank. From there, the solids are pumped to digesters for stabilization.

Tertiary treatment may involve clarification, filtration, and disinfection of secondary treated water depending on the desired final quality of water.

Effective Energy Management in Water Treatment:

Drinking water is mainly obtained by purifying groundwater and surface water. This is done through chemical and physical treatment. The type of treatment depends on the quality of the raw water and is determined by its constituents and the contaminants to be removed. The whole process is Energy consuming and thus represents one of the biggest cost factors. Our smart products, services, and solutions help you to achieve transparency in terms of energy demand and meaningfully reduce your costs.

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