Understanding pH Value in One Article: The “Acid-Base Balance Code” in Wastewater Treatment

pH value is a core indicator for measuring the acidity and alkalinity of water bodies, with a range of 0-14. Essentially, it represents the negative logarithm of the hydrogen ion concentration in a solution. When pH=7, the water body is neutral; pH<7 indicates acidity, with lower values indicating stronger acidity; pH>7 indicates alkalinity, with higher values indicating stronger alkalinity. In the entire process of wastewater treatment, pH value is not simply a “label for acidity and alkalinity”, but a key control parameter that determines treatment efficiency, chemical effect, and system stability, directly affecting the progress of chemical reactions and microbial activity. 1. The graded characteristics of pH value and its suitable application scenarios in wastewater treatment The adaptability of wastewater treatment processes varies significantly across water bodies with different pH ranges. Clarifying the significance of classification can enable precise matching of treatment needs: Strong acidic range (pH 1-3): This range of water has extremely strong corrosiveness, which not only corrodes sewage treatment facilities such as pipelines and reaction tanks, but also completely inhibits microbial activity, leading to the paralysis of biochemical treatment systems. Commonly used in industrial wastewater such as acid washing and electroplating, it needs to be neutralized and pre treated to adjust the pH before entering the subsequent treatment process. Weakly acidic range (pH 4-6): Most microorganisms have low activity in this environment, resulting in a significant decrease in biochemical degradation efficiency. However, it is suitable for specific chemical treatment scenarios, such as the precipitation removal of metal ions – some heavy metal ions are easily combined with anions under weakly acidic conditions to form precipitates, which are easy to separate. Neutral range (pH 6.5-7.5): This is the “golden range” for wastewater treatment, especially suitable for biochemical treatment. Within this range, the activity of microorganisms that degrade organic matter (such as bacteria and bacterial colonies) reaches its peak and can efficiently decompose pollutants; At the same time, mainstream coagulants such as polyaluminum chloride (PAC) can also fully exert their electric neutralization and bridging effects, forming dense alum flowers and improving solid-liquid separation efficiency. Weak alkaline range (pH 8-10): conducive to the stripping treatment of ammonia nitrogen – under alkaline conditions, ammonia nitrogen is easily converted from ionic state to free state ammonia gas, which is removed from the water body by aeration blowing; In addition, this interval is also the optimal operating environment for some chemical phosphorus removal agents (such as lime and polymeric ferric sulfate), which can promote the precipitation and removal of phosphorus. Strong alkaline range (pH 11-14): Similar to the strong acidic range, it has strong corrosiveness and can inhibit microbial activity. However, it can be used for the pretreatment of specific industrial wastewater, such as the alkaline hydrolysis reaction of some difficult to degrade organic compounds. After neutralization and pH adjustment, it can enter the biochemical system. 2、 The influence of pH value on sewage treatment agents and key selection points The effectiveness of sewage treatment agents is closely related to the pH value. Choosing the right agent and matching it with an appropriate pH can avoid agent waste and improve treatment efficiency Coagulants and flocculants: Polyaluminum chloride (PAC) has the best effect at pH 6.5-7.5; Polyferric sulfate (PFS) has a wider range of adaptability and can stably function within pH 5-8.5; Aluminum salt coagulants are more sensitive to pH and need to be controlled within the range of 6-8, otherwise they are prone to form aluminum hydroxide colloids that dissolve and affect the flocculation effect. Biochemical treatment related chemicals: Nitrification reaction (conversion of ammonia nitrogen to nitrate) requires a large amount of alkalinity, with approximately 7.14g of alkalinity consumed for every 1g of ammonia nitrogen oxidized. The optimal pH range is 7.5-8.5, and when alkalinity is insufficient, alkaline supplements such as sodium carbonate and sodium hydroxide need to be added; Denitrification reaction (conversion of nitrate to nitrogen) produces alkalinity, with 3.57g alkalinity generated for every 1g of nitrate nitrogen reduction. The suitable pH range is 7.0-7.5, and there is no need for additional alkalinity. Instead, attention should be paid to adjusting the alkalinity to be too high. Redox agents: The optimal pH range for different oxidants varies greatly: chlorine dioxide has a stable oxidation effect within pH 6-9; Ozone is more stable under acidic conditions and can continuously generate highly oxidizing hydroxyl radicals, improving the removal efficiency of recalcitrant organic compounds; Fenton reagent (ferrous sulfate+hydrogen peroxide) has strict pH requirements and must be in a strongly acidic environment with pH 3-4 to trigger the reaction and generate sufficient hydroxyl radicals for efficient oxidation. Sludge conditioner: Cationic polyacrylamide (CPAM) used for sludge dewatering, with the best dewatering effect in the pH range of 6-8- within this range, the cationic groups of CPAM can fully adsorb the negative charge of sludge colloids, form coarse flocs, and reduce sludge moisture content; If the pH deviates from this range, it is necessary to first adjust the pH of the sludge or replace it with a more adaptable type of conditioner. 3、 Practical suggestions for pH control in sewage treatment In actual operation, scientific control of pH value is the key to ensuring system stability, which can be implemented through the following measures: Establish a continuous monitoring and early warning mechanism: Install pH online monitoring devices at key nodes such as the inlet, reaction tank, and outlet to monitor changes in water quality acidity and alkalinity in real time. When the pH exceeds the appropriate range, issue timely warnings to avoid impacting the treatment system. Regular small-scale verification: By simulating on-site conditions through beaker tests, the optimal dosage and corresponding pH range of various chemicals under different inlet water qualities are determined, providing precise parameter guidance for actual operation. Improve the pH adjustment system: equipped with acid and alkali dosing devices (such as sulfuric acid and sodium hydroxide dosing systems), adjust the pH of the water to a suitable range before adding chemicals according to the pH requirements of different treatment stages; At the same time, optimize the mixing effect of the regulating tank to ensure uniform pH adjustment. summary The pH value is the “invisible regulator” of the sewage treatment system, and its control accuracy directly affects the treatment efficiency, chemical consumption, and facility life. Understanding the characteristics of different pH ranges, mastering the adaptation rules of reagents and pH, and through scientific monitoring and precise adjustment, can significantly improve the stability of sewage treatment systems and achieve the optimal balance between standard discharge and operating costs. The main products of flocculant manufacturer Xinhuan Water Treatment are: White polyaluminium chloride (food grade), drinking grade polyaluminium chloride, industrial grade polyaluminium chloride, anionic polyacrylamide, cationic polyacrylamide, nonionic polyacrylamide, petroleum recycling polyacrylamide, oil recovery polyacrylamide, polyacrylamide, polymer flocculant polymer flocculation coagulant, polymeric ferrous sulphate, polymerized iron and aluminium chloride, and other water treatment chemicals. Welcome customers to write to us to negotiate business! Tel/WhatsApp：86 19139972558 Email：Sunny@xhwtm.com Contact:Sunny