The common malfunctions of manganese sand filter aeration systems and their specific impacts on effluent quality can be categorized into four types: "iron and manganese removal failure, increased turbidity, microbial contamination, and chemical imbalance." Considering the characteristics of high-temperature, high-hardness water in the Dazu area of Chongqing, the specific impacts are as follows:
I. Decreased iron and manganese removal rate (core water quality deterioration)
Incomplete oxidation
Symptoms : Yellowish effluent (excessive iron, Fe > 0.3 mg/L) or blackish effluent (excessive manganese, Mn > 0.1 mg/L).
Insufficient aeration (DO < 5 mg/L) prevents ferrous manganese from being fully oxidized to trivalent oxides;
In water with high hardness, calcium and magnesium scale can clog aeration heads, reducing aeration efficiency by more than 40%.
Impact : Iron and manganese oxides are not retained, and long-term consumption may cause skin discoloration and gastrointestinal diseases.
Symptoms : Yellowish effluent (excessive iron, Fe > 0.3 mg/L) or blackish effluent (excessive manganese, Mn > 0.1 mg/L).
Insufficient aeration (DO < 5 mg/L) prevents ferrous manganese from being fully oxidized to trivalent oxides;
In water with high hardness, calcium and magnesium scale can clog aeration heads, reducing aeration efficiency by more than 40%.
Impact : Iron and manganese oxides are not retained, and long-term consumption may cause skin discoloration and gastrointestinal diseases.
Filter media failure
Symptoms : The filter media surface turns white and loses its stickiness, indicating a loss of catalytic oxidation ability.
Cause : Aeration failure causes the active filter membrane (MnO₂) on the filter media surface to fall off, shortening the filter media life by 50% (e.g., from 5 years to 2-3 years).
Impact : Frequent replacement of filter media is required, and the iron and manganese content in the effluent continues to exceed the standard.
Symptoms : The filter media surface turns white and loses its stickiness, indicating a loss of catalytic oxidation ability.
Cause : Aeration failure causes the active filter membrane (MnO₂) on the filter media surface to fall off, shortening the filter media life by 50% (e.g., from 5 years to 2-3 years).
Impact : Frequent replacement of filter media is required, and the iron and manganese content in the effluent continues to exceed the standard.
II. Increase in turbidity and suspended matter
Filter clogging
Symptoms : Effluent turbidity >5 NTU (normal <1 NTU), accompanied by increased suspended solids.
Cause : Insufficient backwashing intensity (<10L/(m²・s)) or insufficient aeration assistance leads to the accumulation of iron and manganese oxides in the filter media layer, forming a dense "mud cake layer".
Impact : Turbid water may clog downstream water appliances (such as water heaters and washing machines).
Symptoms : Effluent turbidity >5 NTU (normal <1 NTU), accompanied by increased suspended solids.
Cause : Insufficient backwashing intensity (<10L/(m²・s)) or insufficient aeration assistance leads to the accumulation of iron and manganese oxides in the filter media layer, forming a dense "mud cake layer".
Impact : Turbid water may clog downstream water appliances (such as water heaters and washing machines).
Water flow short circuit
Manifestation : After the filter media clumps together, the water flow bypasses the effective filtration area, carrying away the unretained iron and manganese oxides directly.
Causes : Incomplete backwashing or improper filter media gradation (too high proportion of fine materials).
Impact : The turbidity of the effluent fluctuates in a "wave-like" manner, making it difficult to consistently meet the standards.
Manifestation : After the filter media clumps together, the water flow bypasses the effective filtration area, carrying away the unretained iron and manganese oxides directly.
Causes : Incomplete backwashing or improper filter media gradation (too high proportion of fine materials).
Impact : The turbidity of the effluent fluctuates in a "wave-like" manner, making it difficult to consistently meet the standards.
III. Increased risk of microbial contamination
Bacteria thrive in oxygen-deficient environments
Symptoms : The effluent has a putrid odor and the total bacterial count exceeds the standard (e.g., total coliforms > 100 CFU/mL).
Cause : Insufficient aeration leads to dissolved oxygen in the filter media layer being <2mg/L, creating an anaerobic environment that breeds iron bacteria, sulfate-reducing bacteria, etc.
Impact : Additional disinfectant needs to be added, increasing operating costs.
Symptoms : The effluent has a putrid odor and the total bacterial count exceeds the standard (e.g., total coliforms > 100 CFU/mL).
Cause : Insufficient aeration leads to dissolved oxygen in the filter media layer being <2mg/L, creating an anaerobic environment that breeds iron bacteria, sulfate-reducing bacteria, etc.
Impact : Additional disinfectant needs to be added, increasing operating costs.
Biofilm blockage
Characteristics : The backwash drainage is black, and the filter media layer is sticky.
Cause : High-temperature water (40-60℃) accelerates biofilm growth, clogging aeration heads and filter media pores.
Impact : Reduces aeration efficiency, further deteriorating water quality.
Characteristics : The backwash drainage is black, and the filter media layer is sticky.
Cause : High-temperature water (40-60℃) accelerates biofilm growth, clogging aeration heads and filter media pores.
Impact : Reduces aeration efficiency, further deteriorating water quality.
IV. Chemical Imbalance and Secondary Pollution
pH value decrease
Results : When the influent pH is < 6.5, the iron and manganese oxidation efficiency decreases by more than 30%.
Cause : Insufficient aeration leads to the accumulation of carbon dioxide in the water.
Impact : Acidic water corrodes pipes, releases rust, pollutes the water, and creates a vicious cycle.
Results : When the influent pH is < 6.5, the iron and manganese oxidation efficiency decreases by more than 30%.
Cause : Insufficient aeration leads to the accumulation of carbon dioxide in the water.
Impact : Acidic water corrodes pipes, releases rust, pollutes the water, and creates a vicious cycle.
Scale and corrosion
Manifestations : Scaling on the inner wall of the pipe and rust contamination of the filter media after equipment corrosion.
Cause : In high-hardness water, aeration failure leads to calcium and magnesium deposition clogging the aeration heads, and corrosion of the carbon steel tank.
Manifestations : Scaling on the inner wall of the pipe and rust contamination of the filter media after equipment corrosion.
Cause : In high-hardness water, aeration failure leads to calcium and magnesium deposition clogging the aeration heads, and corrosion of the carbon steel tank.
