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Municipal wastewater treatment
Created on 02.28
The company provides full-process services from wastewater sampling to water quality testing, process design, pilot testing, intermediate testing, construction drawing design, equipment customization and supply, construction, and later operation.
Basic Concepts
Generated during the human living processWastewater, is one of the main sources of water pollution. It is mainly composed of fecal and washing wastewater. The amount of domestic sewage discharged per person per day in cities is 150-400L, which is closely related to the living standard. Domestic sewage contains a large amount of organic matter, such as cellulose, starch, sugars, and fats and proteins; it also often contains pathogenic bacteria, viruses, and parasite eggs; inorganic salts such as chlorides, sulfates, phosphates, bicarbonates, and sodium, potassium, calcium, and magnesium. The general characteristics are high nitrogen, sulfur, and phosphorus content, and under the action of anaerobic bacteria, it easily produces foul-smelling substances. Domestic sewage is also a low-temperature heat source and a source of methane generation, and even more so a potential oil and gas field.
Harm of Wastewater
pathogen pollution
Sources include urban domestic sewage, hospital wastewater, garbage, and surface runoff. The characteristics of pathogenic microorganisms are: ① large quantity; ② wide distribution; ③ long survival time; ④ fast reproduction speed; ⑤ easy to develop resistance, difficult to eliminate; ⑥ after traditional secondary biochemical wastewater treatment and chlorination disinfection, some pathogenic microorganisms and viruses can still survive in large numbers; these pollutants actually enter the human body through various channels, survive in the body, and cause human diseases.
oxygen-consuming organic matter pollution
The common characteristic of these substances is that after entering the water body directly, they are decomposed into simple inorganic substances, carbon dioxide and water, through the biochemical action of microorganisms. During the decomposition process, dissolved oxygen in the water is consumed. Under anaerobic conditions, the pollutants will undergo putrefaction and decomposition, deteriorating the water quality. These organic matters are often called oxygen-consuming organic matters. The more oxygen-consuming organic matter in the water, the more oxygen is consumed, the worse the water quality, indicating that the water pollution is more serious.
eutrophication pollution
A phenomenon of water pollution caused by excessive amounts of plant nutrients such as nitrogen and phosphorus. Eutrophication of aquatic ecosystems can occur through chemical pollutants in two ways: one is an increase in the amount of inorganic nutrients that normally limit plant growth; the other is an increase in organic matter as decomposers.
Malodor
It is a common pollution hazard that also occurs in polluted water bodies. There are more than 4,000 types of malodors that humans can smell, with dozens of them being highly harmful. The hazards of malodor are manifested as: ① Impairment of normal respiratory function, reduced digestive function; mental restlessness, decreased work efficiency, reduced judgment and memory; long-term work and life in a malodorous environment can cause olfactory disorders, damage the central nervous system, and the excitatory and regulatory functions of the cerebral cortex; ② Certain aquatic products are contaminated with malodor and cannot be eaten or sold; ③ Malodorous water bodies cannot be used for swimming, fish farming, or drinking, thus destroying the use and value of water; ④ It can also produce toxic hazards such as hydrogen sulfide and formaldehyde.
Acid, Alkali, and Salt Pollution
Alkali pollution changes the pH of the water body, destroys its buffering capacity, eliminates or inhibits the growth of microorganisms, hinders water self-purification, and can also corrode bridges, ships, and fishing gear. Acids and alkalis often enter the same water body simultaneously. After neutralization, certain salts can be produced. From the perspective of pH, acid and alkali pollution is self-purified through neutralization, but the production of various salts becomes a new pollutant in the water body. Because the increase in inorganic salts can increase the osmotic pressure of water, it has an adverse effect on freshwater organisms and plant growth. In saline-alkali areas, salts in surface water and groundwater will further harm soil quality.
Increased groundwater hardness
Water, especially water with high permanent hardness, has multiple harms: it is unpleasant to drink; it can cause digestive dysfunction, diarrhea, and miscarriage in pregnant livestock; it causes inconvenience in daily life; it consumes a lot of energy; it affects the lifespan of kettles and boilers; scale formation in boiler water can easily cause explosions; it requires softening and purification treatment. The loss of acids, alkalis, and salts into the environment will also cause the groundwater hardness to increase, forming a vicious cycle.
Pollution by toxic substances
Substance pollution is a particularly important category of water pollution, with a wide variety of types, but the common characteristic is its toxic harm to biological organisms.
Wastewater Treatment
With the improvement of people's living standards, the discharge of domestic sewage is becoming more and more serious. Under such circumstances,Domestic sewage treatmentprocesses are also constantly improving. The following lists some of theWastewater Treatment Process Flow.
MBR Membrane Process
A novel water treatment technology combining membrane separation technology. There are many types of membranes, classified by separation mechanism, including reactive membranes, ion exchange membranes, osmotic membranes, etc.; classified by membrane properties, including natural membranes (biofilms) and synthetic membranes (organic and inorganic membranes); classified by membrane structure, including flat sheet, tubular, spiral, and hollow fiber types.
The membrane-bioreactor is mainly composed of membrane separation components and a bioreactor. The commonly referred to membrane-bioreactor is actually a collective term for three types of reactors: ① Aeration Membrane Bioreactor (AMBR); ② Extractive Membrane Bioreactor (EMBR); ③ Solid/Liquid Separation Membrane Bioreactor (SLSMBR, abbreviated as MBR).
Characteristics of MBR Process
Compared with many traditional biological water treatment processes, MBR has the following main characteristics:
I. Effluent Water Quality is High and Stable
Due to the efficient separation effect of the membrane, the separation effect is far better than traditional sedimentation tanks. The treated effluent is extremely clear, with suspended solids and turbidity close to zero, and a significant reduction in bacteria and viruses. The water quality of the effluent is superior to the standard for domestic reclaimed water issued by the Ministry of Construction (CJ25.1-89), and can be directly used as non-potable municipal reclaimed water for reuse.
At the same time, membrane separation also completely retains microorganisms within the bioreactor, allowing for a high concentration of microorganisms to be maintained within the system. This not only improves the overall removal efficiency of pollutants by the reaction device and ensures good effluent water quality, but also makes the reactor highly adaptable to various changes in influent load (water quality and quantity), resistant to shock loads, and capable of stably obtaining high-quality effluent water.
II. Low production of excess sludge
This process can operate under high volumetric load and low sludge load, resulting in low excess sludge production (theoretically achieving zero sludge discharge), which reduces sludge treatment costs.
III. Small footprint, not limited by installation location
A high concentration of microorganisms can be maintained within the bioreactor, leading to a high volumetric load for the treatment device and significant savings in footprint. The process flow is simple, the structure is compact, and the footprint is small, making it not limited by installation location and suitable for any occasion. It can be designed as above-ground, semi-underground, or underground.
IV. Can remove ammonia nitrogen and refractory organic matter
Since microorganisms are completely retained within the bioreactor, it is conducive to the retention and growth of slow-growing microorganisms such as nitrifying bacteria, thereby improving the nitrification efficiency of the system. At the same time, it can increase the hydraulic retention time of some refractory organic matter in the system, which is beneficial for improving the degradation efficiency of refractory organic matter.
V. Convenient operation and management, easy to achieve automatic control
This process achieves complete separation of Hydraulic Retention Time (HRT) and Sludge Retention Time (SRT), leading to more flexible and stable operational control. It is a new technology in wastewater treatment that is easy to equip and can achieve microcomputer automatic control, thus making operation and management more convenient.
VI. Easy to upgrade from traditional processes
This process can be used as a tertiary treatment unit for traditional wastewater treatment processes, with broad application prospects in areas such as tertiary treatment of effluent from urban secondary wastewater treatment plants (thereby achieving large-scale reuse of urban wastewater).
Membrane Bioreactors (MBRs) also have some shortcomings. These are mainly reflected in the following aspects:
o High membrane cost, resulting in higher capital investment for MBRs than traditional wastewater treatment processes;
o Membrane fouling occurs easily, causing inconvenience in operation and management;
o High energy consumption: Firstly, the MBR sludge-water separation process requires maintaining a certain membrane driving pressure. Secondly, the MLSS concentration in the MBR tank is very high, and to maintain sufficient oxygen transfer rate, the aeration intensity must be increased. Furthermore, to increase membrane flux and reduce membrane fouling, the flow rate must be increased to scour the membrane surface, resulting in higher energy consumption for MBRs compared to traditional biological treatment processes.
Integrated equipment
Integrated reclaimed water treatment equipmentThe use of Membrane Bioreactor (MBR) technology is a new process that combines biological treatment technology withmembrane separationtechnology, replacing thesecondary clarifierIt can efficiently perform solid-liquid separation, producing stable reclaimed water ready for direct use. It can also maintain a high concentration of microbial biomass within the biological tank, a processsludgelow, highly effective removal ofammonia nitrogen, effluentsuspended solidsandturbidityare close to zero, bacteria and viruses in the effluent are significantly removed, energy consumption is low, and the footprint is small.
AAO process
AAO process is the abbreviation for Anaerobic-Anoxic-Oxic combined process, which consists of three stages of biological treatment units. Its difference from the single-stage AO process lies in the pre-stage anaerobic reactor, which aims to degrade and remove some refractory organic matter in the wastewater through anaerobic processes, thereby improving the biodegradability of the wastewater and providing a suitable carbon source for denitrification in the subsequent anoxic stage, ultimately achieving efficient removal of COD, BOD, N, and P. The process flow of the AAO system is: wastewater enters the anaerobic reactor after pretreatment, where high COD substances are partially decomposed. It then enters the anoxic stage for denitrification, followed by the aerobic stage for oxidative degradation of organic matter and nitrification. To ensure the efficiency of denitrification, a portion of the effluent from the aerobic stage is returned to the anoxic stage and mixed with the effluent from the anaerobic stage to fully utilize the carbon source in the wastewater. Another portion of the effluent enters the secondary clarifier, where activated sludge is separated and discharged as effluent. The sludge is directly returned to the anaerobic stage.
Contact Oxidation Process
Contact oxidation is a new biochemical wastewater treatment method that combines features of both activated sludge and biofilm processes. The main equipment for this method is the biological contact oxidation filter. In an airtight aeration tank, fillers such as coke, gravel, and plastic honeycomb are installed. The fillers are submerged in water, and air is supplied from the bottom of the fillers by a blower for aeration and oxygenation, which is called forced aeration. Air passes freely through the filter media from bottom to top, carrying the wastewater to be treated, and reaches the surface. After the air escapes, the wastewater flows back to the bottom of the tank from top to bottom between the filter media. Activated sludge adheres to the surface of the fillers and does not flow with the water. Because the biofilm is directly and strongly agitated by the upward airflow, it is constantly renewed, thus improving the purification effect. The biological contact oxidation method has advantages such as short treatment time, small footprint, good purification effect, good and stable effluent quality, no sludge return or bulking, and low power consumption.
Advantages
(1) High volumetric load, strong impact load resistance, short treatment time, saving land area;
(2) High biological activity, high microbial concentration;
(3) Low sludge production, no sludge return required;
(4) Good and stable effluent quality;
(5) Low power consumption, saving energy and operating costs;
(6) Easy to form biofilm, can operate intermittently;
(7) No sludge bulking problem.
Disadvantages
(1) The biomass on the packing varies with the BOD load;
(2) The biofilm can only fall off by itself, and the excess sludge is difficult to discharge. If it is retained between the filter materials, it can easily cause water quality deterioration and affect
treatment effect;
(3) When honeycomb packing is used, if the load is too high, the biofilm will be thicker, which can easily block the packing;
(4) Large production of protozoa (e.g., rotifers);
(5) Combined contact media can sometimes affect aeration and mixing.
Aerated Biofilter
Process Flow Introduction:Aerated Biofilter, which is to set up in the biological filter treatment devicepacking, by artificial oxygen supply, a large number of microorganisms grow on the packing. This wastewater treatment process flow device consists of a filter bed, a gas distribution device, a water distribution device, a drainage device, etc.aeration deviceadopts supporting specialaerator, the medium and small bubbles produced are repeatedly cut by the packing, reaching near micro-controlaerationeffect. Due to the high sludge concentration in the reaction tank and the compact treatment facility, the land area can be greatly saved and the reaction time can be reduced.
SPR Process
The SPR wastewater treatment system first uses chemical methods to precipitate pollutants in dissolved state from true solution state, forming colloidal particles or tiny suspended particles with solid interfaces; it then uses highly efficient and economical adsorbents to separate organic pollutants, color, etc. from wastewater; subsequently, it uses microscopic physical adsorption method to condense various colloidal particles and suspended particles in wastewater into large, dense flocs; then, relying on fluid mechanics principles such as swirl and filtration hydraulics, the flocs are rapidly separated from water in the self-designed SPR high-turbidity wastewater purifier; the clean water passes through the dense suspended mud layer formed within the tank, reaching the level of tertiary treatment, and the effluent is reused; the sludge is highly concentrated in the concentration chamber and discharged under pressure periodically. Due to the low moisture content and good dewatering performance of the sludge, it can be directly sent to mechanical dewatering equipment. The dewatered sludge cake can also be used to manufacture sidewalk paving bricks, eliminating secondary pollution.
SBR Phosphorus Removal Process
Introduction to Wastewater Treatment Process: The main cause of eutrophication of water bodies is the large amount of discharge into water bodies by humans.Ammonia nitrogenand phosphorus. Phosphorus is the most important factor for eutrophication of water bodies. Looking at the domestic wastewater treatment process, phosphorus removal technology has always been a challenge.Wastewater treatment plantsoperational challenges. Traditional physicochemical phosphorus removal technologies require a large amount of chemicals, with the disadvantages of high operating costs and large sludge production; biological phosphorus removal processes with pre-anaerobic stages have the advantage of low operating costs, but due to complete reliance on the phosphorus uptake and release of microorganisms, it is difficult to meet the requirements of national wastewater treatment process standards. When consideringReclaimed water reuse, it is even more difficult to meet the requirements.
Enhanced biological phosphorus removal
During the treatment process, major rivers and lakes in China are severely eutrophic due to phosphorus pollution. The National Environmental Protection Agency has formulated relatively strict standards for phosphorus discharge to control and reduce phosphorus pollution. Chemical enhanced biological phosphorus removalWastewater Treatment Processto remove from wastewaterorganic pollutantsand phosphorus in various forms. This wastewater treatment process integrates chemical phosphorus removal and biological phosphorus removal. Through anaerobic digestion,biological systemactivated sludge produces volatile organic acids, which serve as substrates or nutrients for the growth of phosphorus-accumulating organisms (PAOs). This leads to the selective proliferation of PAOs in the activated sludge, and their return to the biological system, allowing the biological wastewater treatment system to operate in a high-efficiency phosphorus removal state; meanwhile, phosphorus released from sludge under anaerobic conditions is eliminated through chemical phosphorus removal. This is a highly efficient municipal wastewater treatment process technology that meets the current requirements in China for further phosphorus removal on the basis of conventional secondary wastewater treatment to addresswater eutrophication.
Cyclic Intermittent Aeration
Economic development levels vary greatly across regions. Cities with lagging economic development cannot allocate much funding for wastewater treatment. Therefore, how to use limited funds to reduceenvironmental pollution, which is a problem faced by many city governments. In terms of wastewater treatment, until recently, some cities still used primary or intensified primary treatmentprocess technology, and the effluent did not meet the national secondary discharge standard for the removal of organic pollutants. The circulating intermittent aeration process fully utilizes the high-loadoxidation ditch's high treatment efficiency, and fully utilizes the characteristic of good effluent from the sequencing batch activated sludge wastewater treatment process, ensuring that the system's effluent meets the national wastewater discharge Class I standard for the removal of organic pollutants. The investment and operating costs are about 30% lower than those of typical secondary biological wastewater treatment systems that primarily remove organic pollutants, making it a process technology suitable for the current stage of wastewater treatment requirements in China.
Rotating biological contactor
The rotating biological contactor wastewater treatment process technology is based onrotating biological contactorbased on technology, combined with biological contact oxidationtechnical advantagesa new generation of aerobic biofilm treatment technology developed. Rotating biological contact oxidation wastewater treatment technology andcomplete sets of equipmentprovide a simple and reliable wastewater treatment method. The rotating shaft in the entire wastewater treatment system is the only moving part, and if the machine fails, general mechanical personnel can perform repairs. The system biomass will automatically compensate according to the changes inorganic loadAttached microorganisms on the rotating discs are living organisms. When the organic matter in the wastewater increases, the microorganisms increase accordingly. Conversely, when the organic matter in the wastewater decreases, the microorganisms decrease. Therefore, the working efficiency of this wastewater treatment system is not easily affected by sudden changes in flow rate and load, or power outages. Operating costs are low, only one-eighth to one-third of the electricity consumption of other aerated wastewater treatment systems. The footprint is only half that of conventionalactivated sludge methodDue to the diverse types of microorganisms growing in the biological system, it can efficiently treat various refractory industrial wastewaters.
Continuous circulating aeration
CCAS process, namely Continuous Cycle Aeration System, is a continuous inflow SBR aeration system. This process is an improvement based on SBR (Sequencing Batch Reactor). The SBR process was successfully researched and developed as early as 1914, but it was difficult to promote and apply in large wastewater treatment plants due to the cumbersome manual operation and management, backward monitoring methods, and easily clogged aerators. The SBR process was generally considered suitable for small-scale wastewater treatment plants. After the 1960s, automatic control technology and monitoring technology developed rapidly, and new non-clogging micro-pore aerators were successfully developed, creating conditions for the widespread adoption of intermittent treatment methods. In 1968, the University of New South Wales in Australia and ABJ Company in the United States collaborated to develop the "continuous inflow, periodic discharge, and delayed aeration aerobic activated sludge process using an intermittent reactor system." In 1986, the U.S. Environmental Protection Agency officially recognized the CCAS process as an innovative alternative technology (I/A), becoming the most advanced computer-controlled biological phosphorus and nitrogen removal treatment process today [1].
The CCAS process has low requirements for wastewater pretreatment, only requiring mechanical screens with a 15mm gap and a grit chamber. The core of the biological treatment is the CCAS reaction tank, where functions such as phosphorus removal, nitrogen removal, organic matter degradation, and suspended solids removal are all completed within this tank, allowing for compliant discharge of effluent.
Pretreated wastewater continuously enters the pre-reaction zone at the front of the reaction tank. In this zone, most of the soluble BOD in the wastewater is adsorbed by activated sludge microorganisms and enters the reaction zone through the openings below the partition between the main and pre-reaction zones at a low flow rate (0.03-0.05m/min). In the main reaction zone, it operates cyclically according to the "Aeration, Idle, Settle, Decant" program, completing carbon removal and nitrogen removal through repeated "aerobic-anoxic" cycles, and phosphorus removal through repeated "aerobic-anaerobic" cycles. The duration of each process and the operation of corresponding equipment are programmed in advance, adjustable, and centrally controlled by computer.
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