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Most municipal wastewater treatment plants rely on activated sludge processes, using microorganisms as the core of their wastewater treatment methods. In this approach, the growth needs of these microorganisms become the primary concern. Microorganisms are organic life forms, albeit extremely small and invisible to the naked eye. However, in essence, their life cycle is no different from that of larger life forms like humans on Earth. They also need food to sustain their growth, and their diet consists of the same organic matter necessary for their survival and development as that of larger organisms.   Most municipal wastewater treatment plants rely on activated sludge processes, using microorganisms as the core of their wastewater treatment methods. In this approach, the growth needs of these microorganisms become the primary concern. Microorganisms are organic life forms, albeit extremely small and invisible to the naked eye. However, in essence, their life cycle is no different from that of larger life forms like humans on Earth. They too need food to sustain their growth, and their food composition is the same as that of large organisms—organic matter necessary for their life. However, their food differs from that of large organisms; they require more direct and finer food to meet the specific needs of their tiny individuals. Dissolved organic matter in water is their food, especially organic pollutants in wastewater discharged from human habitation. Microorganisms in activated sludge at wastewater treatment plants survive, grow, and reproduce by consuming large amounts of organic pollutants from wastewater. Organic matter is essentially carbon-containing compounds on Earth; these compounds, containing various complex carbon chains, constitute the rich and diverse world of organisms on Earth. The organic matter needed by microorganisms in wastewater treatment plants can be simply referred to as a carbon source.   However, not all organic pollutants in wastewater are suitable for microorganisms to survive, especially since their life processes require a specific ratio of organic matter to nutrients such as nitrogen and phosphorus. Microorganisms that remove organic pollutants from wastewater need nitrogen and phosphorus for growth and reproduction. Microorganisms need nitrogen to form proteins, cell wall components, and nucleic acids; and they need phosphorus to maintain the energy required for growth. Scientists have expressed the ratio of carbon sources and nutrients required by these microorganisms using a molecular formula: C₅H₇NO₂P₀.₀₷₄. When using the aerobic activated sludge process to treat wastewater, the BOD:N:P ratio in the water is typically required to be approximately 100:5:1 to meet the normal growth needs of the microorganisms in the activated sludge.   The core of wastewater treatment plant management lies in the management of the microorganisms within the plant. Providing these microorganisms with sufficient nutrients and a suitable environment is a crucial task for every wastewater treatment plant operator. However, due to regional differences in dietary habits, industrial wastewater discharge, and the volume of wastewater to be treated, the actual C:N:P nutrient ratio in the wastewater entering the plant is not the 100:5:1 required for microbial growth. It is precisely this imbalance in the influent that leads wastewater treatment plant operators to explore different carbon sources and even nutrients. Some process adjustment personnel believe that artificially added carbon sources, such as methanol, acetic acid, glucose, and flour—simple organic compounds—are easily absorbed and utilized by microorganisms, promoting their growth and reproduction. Therefore, replenishing the carbon source within the wastewater treatment plant is a universal solution, and carbon source replenishment is necessary for any process problem.

 Lower temperatures can affect the normal operation of water treatment equipment. To ensure the equipment operates normally in winter, we need to take protective measures. General Water Treatment Equipment Maintenance Tips:   Lower temperatures can affect the normal operation of water treatment equipment. To ensure the equipment operates normally in winter, we need to take protective measures. General water treatment equipment maintenance tips:   A. Tanks and membrane equipment should be drained and discharged on time as required to prevent stagnant water from freezing and cracking equipment and valves.   B. Equipment and containers that are not in operation should be completely drained of bottom water. Before putting the equipment back into operation, it should be backflushed and then forward washed. Pressure should be avoided in areas where pressure is released. Equipment antifreeze drainage must be properly labeled, registered, and inspected.   C. The area manager is responsible for supervising and inspecting fire prevention, explosion prevention, and antifreeze insulation in the area. They must inspect and approve the antifreeze equipment. After the work is completed, the operator must check and approve the work, ensuring that records are traceable and inquiryable.   D. Pipeline antifreeze: Exposed pipes must be wrapped with insulation material to keep them warm. For severe freezing conditions: In addition to the above measures, maintain water flow in the pipes as much as possible to prevent them from freezing shut.   E. Valve antifreeze: Use insulating materials to wrap and maintain the valves.   After stopping the self-priming sewage pump, drain all remaining water from the pump and pipes, and clean away any external dirt to prevent water from freezing and causing the pump and pipes to crack.   Reverse osmosis system:   In winter, extremely low temperatures can cause pipes to freeze and crack. We generally advise customers to heat the equipment if necessary. If the raw water temperature is very low, it also needs to be heated. Heating the building, such as using a stove or radiator, or an electric heater, is also possible. If the reverse osmosis equipment is not operating in winter, the water in the equipment must be drained, and the reverse osmosis membrane must be removed and placed indoors (with added protective fluid) to prevent damage to the membrane due to freezing.   Reverse osmosis equipment installed indoors must maintain a room temperature no lower than 0 degrees Celsius. Because water expands during freezing, if it freezes, all pipes, filter bottles, and membrane housings in the water purifier will burst, causing leaks.   Ultrafiltration and integrated equipment:   Traditional heating methods are used, employing charcoal stoves in the equipment room. These stoves are placed in the room and monitored by designated personnel who maintain the equipment and add charcoal as needed.   Electric heating plates are used to maintain the temperature, ensuring that the temperature at all points within the equipment room does not fall below 5°C.

In recent years, rapid industrial development has led to increasingly severe environmental problems, especially water pollution. Heavy metal pollution is one of the important factors causing water pollution. Heavy metal ions in water bodies exhibit high toxicity and carcinogenicity even at trace levels. They can accumulate in animals through bioaccumulation in the food chain, causing persistent harm and inducing various diseases. Therefore, exploring methods for removing heavy metals from water bodies is an effective means to ensure water safety and improve the reusability of water resources.     1. Introduction   In recent years, rapid industrial development has led to increasingly severe environmental problems, especially water pollution. Heavy metal pollution is one of the important factors causing water pollution. Heavy metal ions in water bodies exhibit high toxicity and carcinogenicity even at trace levels. They can accumulate in animals through bioaccumulation in the food chain, causing persistent harm. Heavy metals can induce various diseases. Exploring methods for removing heavy metals from water bodies is an effective means to ensure water safety and improve the reusability of water resources.   The main heavy metal ions polluting water bodies in my country include cadmium (Cd), chromium (Cr), lead (Pb), and arsenic (As), among which Cd(II) and Cr(VI) are extremely toxic. Methods for removing heavy metals from water bodies mainly include chemical precipitation, ion exchange, membrane separation, and adsorption. Among these, adsorption has attracted much attention due to its high efficiency, low cost, and ease of operation. Wu et al. (2000) and Zan et al. (2006) reported the use of liquid membranes to adsorb heavy metal ions while simultaneously synthesizing nanoparticles, thus "turning waste into treasure" while removing heavy metal ions. Ge et al. (2013) found that Al2O3 nanoparticles have good adsorption performance for Cr(VI) in aqueous solution, with an adsorption rate of up to 90%. However, after adsorption, the tiny metal oxide particles are difficult to recover. Often, this leads to loss or even new pollution. Immobilizing Al2O3 nanoparticles on materials such as hydroxyapatite, montmorillonite, and chitosan can effectively solve the above problems. However, the organic carrier is prone to irreversible decomposition during adsorbent regeneration, resulting in the loss of nanoparticles, which limits the practical application of these materials. 316L porous stainless steel (PSS, 022Cr17Ni12Mo2) is a porous membrane tube with high mechanical strength, and is a relatively ideal carrier for immobilizing metal oxide nanoparticles. This study aims to synthesize Al2O3 nanoparticles by hydrothermal method and immobilize them on 316L PSS using a suspended particle dip-coating method to prepare a porous stainless steel-based alumina membrane. At the same time, using this membrane as an adsorbent, its adsorption performance for Cr(VI) and Cd(II) in aqueous solution will be investigated.   2. Experimental Part 2.1 Instruments and Reagents   Instruments: Field Emission Scanning Electron Microscope (FESEM, JEOL S-4800, Hitachi, Japan) X-ray diffractometer (D/MAX-3C, Ricoh Corporation, Japan), hollow fiber membrane pilot-scale equipment (HFM-0530, Xiamen Shida Membrane Technology Co., Ltd.), graphite furnace atomic absorption spectrometer (AAS-9000, Jiangsu Tianrui Instrument Co., Ltd.), high-speed centrifuge (ZONKIA, HC-3018, Anhui Zhongke Zhongjia Co., Ltd.). The experimental materials were self-made γ-Al₂O₃ nanoparticles and 316L porous stainless steel (steel grade: 022Cr17Ni12Mo₂, pore size 1 μm, length 30 cm, inner diameter 8 mm, outer diameter 12 mm).   Reagents: Sodium aluminate (NaAlO₂), urea (CON₂H₄), potassium nitrate (KNO₃), and anhydrous ethanol (C₂H₅OH) were all analytical grade; polyethylene glycol (PEG 2000) and sodium polyacrylate (PAAS 20M) were chemically pure. All reagents were purchased from Tianjin Kemei Chemical Reagent Factory; the test water was deionized water.   2.2 Experimental Methods   316 L PSS was ultrasonically cleaned sequentially with 0.1 mol·L⁻¹ NaOH and HNO₃ solutions for 10 min, then washed with deionized water until neutral, and finally ultrasonically cleaned with anhydrous ethanol for 5 min. After drying, γ-Al₂O₃ powder was prepared according to the method described in the literature (Zhang et al., 2016). Specifically, a certain amount of sodium aluminate, urea, and sodium polyacrylate were sequentially added to 50 mL of deionized water, stirred for 30 min, and then poured into a stainless steel hydrothermal reactor and reacted in an oven at 140 ℃ for 10 h. After the reaction, the product was removed, washed, and vacuum dried for 12 h. The resulting white powder was then calcined in a muffle furnace at 500 ℃ for 3 h to obtain γ-Al₂O₃ powder. Next, a certain amount of polyethylene glycol was dissolved in 1000 mL of deionized water to prepare a dispersion, and 2 g of [unspecified ingredient] was added. γ-Al₂O₃ powder (polyethylene glycol to γ-Al₂O₃ mass ratio 1:7.9) was used. The particle strength of the solution was adjusted to C(KNO₃) = 1 mmol·L⁻¹ with KNO₃. The pH of the suspension was then adjusted to 7.0 with 0.1 mol·L⁻¹ NaOH and 0.1 mol·L⁻¹ HNO₃ solutions. After ultrasonic dispersion at room temperature for 15 min, the suspension was coated onto a porous stainless steel substrate using a suspended particle dip-coating method, followed by sintering at 400 ℃ for 3 h. The sintering program was: 250 ℃ for 1 h, then 400 ℃ for 3 h. To prevent cracking of the alumina film due to excessively rapid heating, the heating rate during sintering was 1 ℃·min⁻¹. After sintering, the film was cooled with the furnace.   2.3 Adsorption Experiment   The adsorption performance of the membrane was studied using a classical batch process. The porous stainless steel-based alumina membrane module was connected to a hollow fiber membrane pilot-scale device. Adsorption was performed under constant pressure (0.1 MPa). All experiments were repeated three times.   The temperature was set to room temperature, the initial concentrations of Cr(VI) and Cd(II) were both 5 mg·L⁻¹, and the adsorption time was 8 h. Under these conditions, the effect of the initial pH of the solution on the adsorption capacity was investigated. The initial pH values ​​for Cr(VI) were 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, and 11.0, and for Cd(II) were 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0. The initial concentrations of Cr(VI) and Cd(II) were set to 2, 5, 10, and 20 mg·L⁻¹, respectively. The initial pH was considered the optimal adsorption pH. The adsorption time was investigated at (0, 1, 5, 10, 15, 20, 80, 100, 120, 140, 210, 270, 360, and 480 h). The effect of initial concentrations (0, 5, 10, 15, 20, 25, 30, 40 mg·L⁻¹) of Cr(VI) and Cd(II) on the adsorption capacity was investigated under optimal adsorption pH, room temperature, and adsorption time of 8 h. Adsorption isotherms were plotted and a fitting model was obtained. The concentrations of Cr(VI) and Cd(II) were determined by graphite furnace atomic absorption spectrometry. All experiments were repeated three times.   The adsorption capacity was calculated using equation (1), and the adsorption percentage r was calculated using equation (2). Adsorption kinetic data were fitted using pseudo-first-order and pseudo-second-order adsorption kinetic models (Ho et al., 1999), and their equations are shown in equations (3) and (4). Adsorption thermodynamic data were fitted using Langmuir (Langmuir, 1918) and Freundlich (Freundlich et al., 1939) adsorption isotherm models. The equations are shown in equations (5) and (6), respectively.

Determine the Optimal Dosage The dosage of coagulant is prioritized because it directly affects coagulation performance and operational costs. There is no universal standard for dosage. The optimal amount must be determined through coagulation and stirring tests according to the actual water quality, as appropriate coagulant types and dosages vary for different water sources. Specific Procedures for Beaker Coagulation and Sedimentation Test to Confirm the Optimal Coagulant Dosage Required tools: Beakers, coagulation test stirrer, graduated cylinder, raw water sample, turbidimeter, pH meter and thermometer. Measure and record the characteristics of raw water, including turbidity, pH value, temperature and other indicators. Take six 1000mL beakers and fill each with an equal volume of raw water sample. Place the six beakers on fixed positions of the coagulation test stirrer, and set different stirring speeds and durations for each beaker. Use a pipette to add the prepared coagulant into each beaker in equal amounts sequentially, then start the stirrer. After stirring is completed, turn off the equipment. Observe and record the formation of alum flocs during static sedimentation in each beaker. After 10 minutes, draw 30-50mL of supernatant from each beaker with a 50mL syringe or pipette, and transfer the liquid into separate 500mL stirring beakers. Immediately test the turbidity of each sample with a turbidimeter and record all data for comparison. Select the group with the lowest turbidity, which corresponds to the optimal coagulant dosage. There are other methods to calculate coagulant dosage. A convenient way is to refer to the operational data of existing wastewater treatment plants with similar water quality, and make appropriate adjustments on this basis. Coagulant Dosage Calculation Formula T=aQ/1000 T — Daily dosage of coagulant (kg/d) a — Maximum dosage of coagulant per unit volume (mg/L) Q — Daily water treatment capacity (m³/d) Differences Between Solid and Liquid Coagulants Coagulants are divided into solid and liquid forms, corresponding to dry feeding and wet feeding methods respectively. Taking aluminum sulfate as an example: Solid Aluminum Sulfate Advantages: Easy to store and requires smaller space for chemical storage tanks. Disadvantages: Higher labor demand and greater labor intensity in wastewater treatment plants. Woven bag debris may fall into the dissolving tank during unpacking, resulting in pipeline blockage. Uneven mixing between solid chemicals and water may weaken the coagulation effect. Chemical storage and handling will adversely affect the sanitation of the dosing room. Liquid Aluminum Sulfate It can solve most drawbacks of solid chemicals, featuring labor savings, better sanitary conditions and lower costs. Meanwhile, liquid coagulant also has limitations: the dosing system is more complicated, occupies larger floor space, and the equipment is prone to corrosion. Improvement Measures for Liquid Coagulant Dosing System Adopt an integrated dosing system. Optimize the spatial layout of chemical dissolving, stirring, quantitative control and dosing units to save floor space. For example, place the liquid storage tank at the bottom, install dissolving and stirring devices above it, and build a platform on the upper space of the storage tank to arrange quantitative control and dosing equipment. Select paddle agitators equipped with baffles and draft tubes for chemical dissolving and stirring units. This design eliminates overall rotation of the liquid, enhances axial and radial flow, increases turbulence intensity, improves stirring performance and boosts dissolution efficiency. Implement anti-corrosion treatments. Coat stirring components with epoxy primer and epoxy topcoat. For highly corrosive chemicals, use anti-corrosion materials such as fiberglass reinforced plastic, rubber and enamel. Select plastic pipes or rubber hoses for chemical delivery pipes according to the actual dosing volume.

 Colloidal particles in water carry a negative charge. Like charges repel each other, and they are constantly undergoing Brownian motion, making them extremely stable and difficult to settle. When an appropriate amount of coagulant is added, these tiny colloidal particles destabilize, creating an adsorption bridging effect, flocculating into flocs that quickly settle. This process is called coagulation.     What are the main measures to reduce acid and alkali consumption?   (1) Ensure the quality of the influent;   (2) Ensure the quality of regeneration and extend the water production cycle;   (3) Ensure the quality and purity of the regenerated solution and strictly control the regeneration operation procedures;   (4) Ensure the safe, reliable, and normal operation of the equipment.     What is the purpose of using coagulant aids?   (1) Improve the floc structure, making the particles larger, stronger, and heavier;   (2) Adjust the pH and alkalinity of the treated water to achieve optimal coagulation conditions and improve the coagulation effect; coagulant aids themselves do not have a coagulation effect, but they can promote the coagulation process of impurities in the water.   Basic Concepts of Coagulation:   Colloidal particles in water carry a negative charge, causing them to repel each other. Simultaneously, they undergo Brownian motion, making them extremely stable and difficult to settle. When an appropriate amount of coagulant is added, these tiny colloidal particles destabilize, creating an adsorption-bridging effect, flocculating into flocs that quickly settle. This process is called coagulation.     What are the main factors affecting coagulation effectiveness?     (1) Water pH: For example, adding PAC hydrolyzes to produce Al(OH)3 colloids. When the pH is between 6.5 and 7.5, the solubility is low, resulting in good coagulation.     (2) Water alkalinity: When alkalinity is insufficient, the coagulant continuously produces H+ during hydrolysis, causing the pH to drop, thus reducing the coagulation effect.     (3) Water temperature: At low temperatures, water viscosity is high, hydrolysis is slow, floc formation is slow, and the structure is loose, with small particles that are difficult to settle.     (4) Composition of impurities in water: The properties and concentration of these impurities have a significant impact on coagulation effectiveness.