The wastewater is water that can be generate by natural or human actions from liquid waste origin domestic, urban, agricultural, rain or industrial, which may have significant concentrations of organic matter, industrial waste, detergents, fats, waste agro livestock, toxic substances, among others.
This type of water can be treat in the place where it is produced, for example, gray water is treat and reuse directly in the residence that produces it, in addition, primary treatments can be done by installing septic tanks , while in In areas with high population densities, the method to treat them consists of capturing wastewater through the sewerage network to be taken to the city’s treatment plants .
This type of water is generate from organic waste, domestic and commercial waste, rain runoff and infiltration . The main pollutants that appear in this type of water are: large objects in a suspend state, sands, fats, oils, fecal coliforms, among others. If this type of water is not treated properly, it can generate various problems related to the contamination of water sources, the loss of nutrients in growing areas, contamination in the environment, and health problems in the community surrounding the outbreak. of contamination.
Unlike wastewater of urban origin, the wastewater of industrial origin contains chemicals that can not be remove by conventional treatment, either by being in high concentrations or by its chemical nature. The organic and inorganic compounds that are identified in the discharges of this type of water are regulate due to their toxicity or their long-term biological effects. These pollutants come from various industrial activities and due to their nature, concentration, or discharge rate, make these wastewater require intensive treatment before being discharge or reuse.
Wastewater Treatment Process
Treating wastewater includes a series of physical processes – chemical and biological aim, remove contaminant concentrations present in the application so that it can be reuse.
Methods for Removing Suspend Matter from Wastewater:
The suspend matter that can be found in wastewater can be from inorganic particles of several centimeters and very dense, to very stable colloidal suspensions of organic origin. The procedure to reduce the concentrations of this type of particles is the first phase in the wastewater treatment process. The most common suspend matter reduction treatment methods are mention and describe below.
It is a physical method of separation , which consists of retaining the coarse solids that are generally found in wastewater by means of a screen or a sieve and in this way, avoiding technical problems with the equipment use in subsequent treatments of the resource.
In this method, also known as settling, the force of gravity is use, where the densest particles are deposit at the bottom of the settling tank. The main purpose of this primary treatment method is to generate a homogeneous liquid capable of being treated by biological processes and sludge that can be treated separately by other types of treatment.
The shape of the tanks where this process is carried out depends on factors such as the size of the particles, their shape, the concentration of the solids present in the resource, their density, among others. The most common types of sedimentation tanks are as follows:
These types of tanks are use to separate large and dense particles from the water; These are usually shallow tanks since depth does not affect separation efficiency.
It is the type of settlers that is the most common use in treatment plants (WWTP); in them the movement of water is radial, so the speed of movement of the resource decreases towards the edges of the tank. This type of tank is ideal for cases where sedimentation is accompanied by a flocculation of the particles, where the floc size increases when the particles descend to the bottom of the tank, therefore, the sedimentation speed of these tanks is faster. with respect to other types.
They consist of shallow tanks that contain in their interior, plates or tubes incline with respect to the base, through which the water flows, towards the lower surface the particles accumulate, which move downwards and are deposite at the bottom settling tank.
The method of treating wastewater by filtration consists of passing the water through a porous medium, in order to retain as much suspend matter as possible. The porous medium use in this method is generally a sand bed of variable height, arrange in different layers of different particle size.
The sand is contain in containers and the water, under pressure, passes through the filter medium. In this filtration method, slow filtration can be generate, which mixes physical and biological processes or rapid (or deep) filtration which is use for the treatment of industrial wastewater.
This treatment consists of creating air bubbles, which can trap the particles present in the water to later expose it on the surface so that they are drag and eliminate from the resource; This method is ideal in cases where the particles have a density less than or equal to that of water. The air / solids ratio and ml / l of air release into the system for each mg / l concentration of suspend solids present in the resource is the most important parameter when applying this method. The flotation method is use to treat water from refineries, food industries, paint manufacturing industries, among others.
Coagulation – Flocculation
This method is a process of chemical destabilization of colloidal particles that are produce by neutralizing the forces that keep them separate, through the addition of chemical coagulants and the application of energy at the time of mixing. Coagulation – Flocculation, is the most effective treatment in reducing polluting particles present in water, being the universal method in wastewater treatment because it removes a large amount of particles of various sizes and components at a lower cost, in comparison. with other treatment methods.
Methods To Remove Dissolve Matter In Wastewater:
The dissolve matter found in wastewater has different concentrations and characteristics: either concentrations of dissolved inorganic salts such as brines, organic salts such as biodegradable organic matter which is use in the food industry, up to low concentrations of inorganic matter such as heavy metals and organic matter such as pesticides (present in agricultural wastewater ) but that need to be remove from the resource given their polluting nature.
Next, the different processes carried out in wastewater treatment will be describe in order to reduce and eliminate the concentrations of dissolve matter present in them:
Precipitation consists of the subtraction of the dissolve substance present in the water, by means of the addition of reagents that form an insoluble compound with it, thus facilitating its removal by any of the methods of elimination of the suspended matter. The most frequent reagent to carry out this procedure is Ca2 + since this compound has coagulant characteristics, which causes the use of this compound in both urban and industrial wastewater treatment .
Electrochemical processes, as their name indicates, are base on the use of electrochemical techniques, where an electrical current through an electrolyte passes through the wastewater, generating oxidation-reduction reactions both at the cathode and at the anode. The main advantage of this method is the absence of the use of reagents and that this method controls the potential of the electrode, allowing to select of the dominant electrochemical reaction that the resource requires for its treatment.
The electrochemical reactor use is generally a filter-press type, similar to fuel cells; This system allows a modular growth of the area where each module is compose of a cathodic element with low hydrogen overvoltage, such as Silver, Gold, Stainless Steel, Nickel, among others, and an anodic element that uses noble metal oxides as a base. .
It uses a material, known as ion exchange resins, which selectively retains the ions dissolve in the wastewater on its surface, keeps them temporarily attach to the surface, and releases them to a regenerating solution. It is usually use to eliminate salts when they are in low concentrations, its application being usual for the demineralization and softening of water, as well as the retention of certain chemical products and the demineralization of sugar syrups.
The use of disinfectants in wastewater treatment seeks to produce water free of pathogens or living organisms that can contaminate water sources, avoid the production of undesirable by-products of disinfection and maintain bacteriological quality in the subsequent conduction network.
Chlorine (Cl2) disinfection:
It is the most widely use oxidant in wastewater treatment , since it destroys the organisms present in the resource by oxidizing the cellular material; disinfection with this compound is reliable and effective since it eliminates a wide spectrum of pathogenic organisms that can be find in water. Chlorine can be supplly by chlorine gas, hypochlorite solutions, and other chlorine-containing compounds in solid or liquid form.
Biological Methods for Wastewater Treatment
Biological treatment of wastewater, perform mainly by gaps of oxidation, has a series of processes that have in common the use of microorganisms such as bacteria to carry out the reduction of concentrations of soluble components in water; These processes use the assimilation capacity of organisms to consume organic matter and nutrients present in the resource for their own growth and development.
In the process use to treat wastewater at a biological level, the following systems are distinguish:
The presence of O2 in this type of system makes this compound a receptor for electrons, for which high energy yields are obtain, causing high production of sludge, due to the high degree of growth of aerobic bacteria. Its application in wastewater treatment is condition by the low solubility of oxygen in the water.
In this type of system, the electron receptor is the CO2 present in the organic matter find in the wastewater , generating as a product, the reduction of carbon in the form of methane gas (CH4). The main advantage of using this system is obtaining combustible gases.
Anoxic systems are systems with the absence of O2 and the presence of high concentrations of nitrates (NO3-), generating that this compound is the electron receptor, and mainly generating N2, which is an inert element. Therefore, depending on the environmental conditions, a wastewater treatment can be obtain that performs denitrification (biological reduction of nitrates).