Building sewage systems is an indispensable requirement in protecting the environment in residential areas or industrial plants. Wastewater collection and proper treatment is an issue that needs to be addressed to minimize the current surface water pollution, and to meet the provisions of the Law on discharge.
Classification of wastewater treatment systems
The wastewater treatment system is designed based on the composition of waste contained in the wastewater. Each different type of wastewater has different components such as liquid and solid waste discharged from apartments, industrial plants, and agricultural facilities …. Wastewater contains a range of contaminants in different concentrations.
The characteristics of wastewater vary depending on the source. Types of wastewater include: domestic wastewater from households, urban wastewater and industrial wastewater
Domestic wastewater treatment system
Domestic wastewater treatment systems can be installed in households, offices, schools, hospitals or other public places …
Domestic wastewater treatment systems are classified into levels:
Small scale: like households, the system is designed to be simple but still ensure the quality of water discharged into the common waste water system.
Medium scale: apartment buildings, companies, offices, high buildings have centralized wastewater treatment systems for many small waste areas to ensure environmental sanitation.
Large scale: Urban areas, residential areas, … with the system built carefully, intricately and should be carefully surveyed before construction.
The characteristics of domestic wastewater vary by hour, by day, with the flow depending on the level of water use per capita according to habits, diet, living standards and lifestyle.
Chemically, wastewater is composed of organic (70%) and inorganic (30%) as well as various gases. Organic compounds include mainly carbohydrates (25%), proteins (65%) and fats (10%), soaps, synthetic detergents, and their breakdown products. Inorganic components may include heavy metals, nitrogen, phosphorus, pH, sulfur, chloride, alkali, toxic compounds, etc. The dissolved gases in wastewater are hydrogen sulfide, methane, ammonia, oxygen, carbon dioxide and nitrogen. Solid waste content of domestic raw sewage is very low, on average about 0.1%. This usually includes waste organic matter, some inorganic solids, heavy metals, sand and debris and floating debris.
Industrial wastewater treatment system
Industrial wastewater treatment systems are an integral part of the industrial plant chain. Unlike domestic or municipal wastewater, industrial wastewater as a by-product of commercial or industrial activity may contain:
Heavy metal components such as metallurgy and plating
Organic ingredients, as in the industry: food industry
Complex organic chemicals such as pesticides, pharmaceuticals, paints, dyes, petrochemicals, etc.
Wastewater generated during the production process, cleaning machinery, … containing specific substances of that industry should be treated before the commune enters the common drainage network to avoid causing environmental pollution.
The construction of wastewater treatment systems applies to many industries such as livestock, healthcare, textile and dyeing, hospitals, fisheries …. Each system will have different designs and operating procedures in accordance with waste characteristics.
Process system of wastewater treatment with high organic matter such as daily life, food
The main objective of wastewater treatment in general is to allow human and industrial wastewater to be treated without endangering human health or damage to the natural environment. The design of wastewater treatment systems often characterizes wastewater sources. Procedures should be selected and designed to be technically and economically feasible. Conventional wastewater treatment includes a combination of physical, chemical and biological processes and activities to remove solids and organic matter from basic wastewater including the following:
Garbage screens: usually made of metal, placed at the entrance of the canal will retain the raw impurities such as rags, trash, plastic bags, and other wastes are retained, to protect the treatment equipment. such as pumps, pipes, ditches …
Collecting tank: is the place where wastewater is received before going to the next wastewater treatment facilities. Collecting tanks are usually made of concrete and built of bricks.
Used to maintain a nearly constant inflow, it is important to adjust the pH to an appropriate value for biological treatment. In the tank, there is a system of stirring equipment to ensure the dissolution and leveling of the concentration of contaminants in the whole volume of the tank and without sedimentation in the tank, diluting the concentration of toxic substances if any. There is also a device to collect and discharge foam, floating scum. At the regulating tank, the wastewater is neutral, that is, the pH is about 6.5 – 8.5.
GAS BIODIVERSITY HANDLING
Here decomposition takes place the organic and inorganic substances in the wastewater without oxygen. Wastewater is directed directly to the bottom of the tank and distributed evenly there, then flows back up through the small layer of biological sludge and organic and inorganic matter consumed here.
The process of converting contaminants in wastewater by anaerobic microorganisms takes place in three steps:
Stage 1: a group of natural microorganisms present in the hydrolysis of hydrolyzed complex organic compounds and lipids into simple organic substances such as monosaccharides, amino acids to create food sources and energy for microorganisms to function.
Stage 2: a group of acid-producing bacteria that convert simple organic compounds into organic acids usually acetic, butyric acid, Propionic acid. At this stage the pH of the solution decreases.
Stage 3: methane-producing bacteria convert hydrogen and acetic acid into methane gas and the carbon dioxide of the environment increases.
Aerobic biological method uses a group of aerobic microorganisms, operating under conditions of continuous oxygen supply. The process of decomposing organic matter by microorganisms is called biochemical oxidation. Aerobic microorganisms will decompose the organic matter in wastewater and collect energy to convert into new cells, only partially organic matter is completely oxidized into CO2, H2O, NO3-, SO42- , … Microorganisms existing in the activated sludge of biological tanks include Pseudomonas, Zoogloea, Achromobacter, Flacobacterium, Nocardia, Bdellovibrio, Mycobacterium, and two types of nitrifying bacteria Nitrosomonas and Nitrobacter. In addition, many types of filamentous bacteria such as Sphaerotilus, Beggiatoa, Thiothrix, Lecicothrix, and Geotrichum also exist.
To carry out biochemical oxidation of dissolved organic substances, colloids and small dispersants in wastewater, it is necessary to move inside the microorganism cell in three main stages as follows:
Transfer of pollutants from liquid phase to micro-cell surface;
Diffuse from cell surface through semi-permeable membrane due to difference in concentration inside and outside the cell;
Metabolizes substances in microbial cells, produces energy and synthesizes new cells.
The rate of biochemical oxidation depends on the concentration of organic substances, the concentration of impurities, the density of microorganisms and the stability of the flow of wastewater at the treatment plant. Under certain treatment conditions, the main factors affecting the biochemical oxidation reaction are hydrodynamic regimes, oxygen content in wastewater, temperature, pH, nutrition and trace elements. … The organic loading of traditional aerobic biological tanks usually ranges from 0.32 to 0.64 kg BOD / m3.day and night. Dissolved oxygen concentration in wastewater in aerobic biological tanks should always be maintained at values greater than 2.5 mg / l.
Wastewater after going through aerobic biological treatment tank is distributed into water distribution area of sedimentation tank. Clean water is collected on the surface of the sedimentation tank through a spill, the microorganism sludge is collected and collected to the aerobic tank, a part of circulating sludge to the sludge storage tank.
Treatment under artificial conditions does not eliminate bacteria, especially pathogenic and contagious bacteria. Therefore, after the biological treatment stage under artificial conditions, it is necessary to disinfect the waste water before discharging into the environment. When chlorine is added to water, chlorine is highly oxidized which will diffuse through the cell wall of microorganisms and react with the internal enzyme of the microbial cell to destroy the metabolism leading to microorganisms. exterminated objects.
Sludge in sedimentation tanks will be transferred to collection tanks and will be periodically removed by specialized vehicles for industrial wastewater treatment.
Operation diagram of wastewater treatment system
With the above wastewater treatment system process, it can be described in the form of operation diagram as shown below:
Toan A Environment Technology Joint Stock Company provides products for industrial waste water treatment system, medical waste water, domestic waste water. Refer to the articles about the highlight product for more details.
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