wastewater treatment Process and removal of emerging pollutants

1. Introduction of wastewater treatment 

A wastewater treatment plant, . or WWTP, is a water treatment plant dedicated to the purification of wastewater . whose main goal is to collect the water from a population or an industrial sector, . and end the polluting substances from it, and later ,. returned to the water cycle, either by drainage into the sea or by direct reuse. Among the different substances to be end are residues, . oils, sands and different sediment able solids,. compounds with nitrates, ammonia and phosphates, among others. The problem is, . as will mentioned below, . that conventional WWTPs are not designed for the elimination of emergent pollutants.

2. Types of treatment

2.1. Physical treatments
They are those methods in which a physical separation is apply, generally of solids. These methods often depend on the physical properties of the contaminants, . such as viscosity, particle size, buoyancy, etc. Among them we can find the sieving, . precipitation, separation and filtration of solids.
2.2. Chemical treatments
They are those methods that depend on the chemical properties of the contaminant or . reagent incorporated into the water. We can highlight the elimination of iron and oxygen,. the elimination of phosphates and nitrates, coagulation, . electrochemical processes, oxidation, ion exchange, etc.
2.3. Biological Treatments
In these methods biological processes is use,. so that it is try to eliminated the colloidal contaminants. They are microorganisms that act on suspended matter, transforming it into sedimentable solids. They can be aerobic or anaerobic processes, . such as active sludge, trickling filters, anaerobic biodigestion or aerated lagoons.

3. Stages of  wastewater treatment

3.1. Pretreatment
This is the preliminary stage of the treatment of the purifier. This process regulates and measures the flow of wastewater entering the station. In this stage, the larger solids, sand and grease, which are present in the black water, is end. These compounds removed by filtration.
 Among the devices used are the coarse well, . coarse roughing, fine roughing and degreasing-degreasing. 
3.2. Primary treatment
The function of this first stage is to drop suspended solids, . which is carry out by means of a gravitational sedimentation process . or by precipitation, . either assisted or by added chemical substances. Solids removal done by sieving based on particle size.
Compounds such as aluminum, flocculating polyelectrolytes and ferric salts added,. besides to precipitating the phosphorus dissolved. in small colloids or in a very fine suspension, . using hydraulic machinery.
Among the main methods we find the primary . decanter (gravitational sedimentation), . the dissolved air float (separation of suspended particles by bubbles) and chemical treatments, . with the addition of reagent to increase the sedimentation of dissolved solids.
3.3. Secondary treatment
The aim of this second stage is to drop the organic matter dissolved and in a colloidal state,. through biochemical oxidation processes. Besides, biological substances caused by human waste degraded. In these treatments we find aerobic and anaerobic processes. Aerobic processes carried out in the presence of oxygen,. introduced by bubbling into storage tanks.
Anaerobic processes carried out in the absence of oxygen . In these processes, the fermentation reactions of organic matter take place, . which converted into released energy, . CO2, CH4 and C. Some of the most used anaerobic and anaerobic processes. are active sludge, green filters, aerated lagoons, bacterial beds and anaerobic digestion. There are also physical-chemical processes such as particulate beds. These processes reduce a large part of the BOD and end the rest of the sediment able solids. Generally, . there are combinations between these different treatments, . giving rise to biological processes of two or more stages.
Biological reactors, such as moving bed or membrane reactors,. can also used, . although the cost of construction and operation of these is usually more expensive. than that of a conventional filter wastewater treatment system.
This stage also includes secondary settling, separating the treated water . and the sludge generated in the biological process.
3.4. Tertiary treatment
In this final stage of the treatment, . processes carried out to end pathogens, . such as bacteria of fecal origin, . increasing the quality standards required to returned to the water cycle,. by discharge to the sea, in rivers, lakes, . aquifer recharges, reservoirs and other water systems. This type of treatment is only carried out in WWTPs that discharge into a protected area.
Among the processes that is carried out, we first find filtration in sand filters, . which retains a large part of the matter in suspension. The active carbon that left over retains the rest of the toxins.
Lagoon treatment provides the necessary sedimentation, as well as an extra biological advantage. It is an imitation of the natural self-purification processes . that a river or lake performs. In beside to being aerobic lagoons, . which generates a habitual growth of streams, the invertebrates of filter feeding also . aid the process of elimination of solids. but, artificial wetlands consist of a series of cane beds or . similar that generate a process of phytoremediation (decontamination of soils).

Nutrient removal

Nutrient removal is also done at this stage. Nitrogen is remove by biological oxidation of bacteria such as . Nitrobacteria or Nitrosomus, which convert NH 3 into nitrates, and then into N 2 . In this denitrification process,. nitrates and nitrites used by said bacteria under anaerobic conditions, . forming CO 2 and water as final products, also to nitrogen gas.

Phosphorus removal

Phosphorus removed through the enhanced biological phosphorus removal . process in which polyphosphate-accumulating bacteria collect phosphorus from the water within them. The resulting sludge complicated to operate,. which is a slight drawback compared to the. efficiency improvement of the phosphorus removal process.

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