Common faults in the aeration system of a manganese sand filter can be categorized as follows, along with their specific manifestations, causes, and handling methods:
I. Substandard Aeration Efficiency (Core Fault)
Manifestation: Excessive iron and manganese content in the effluent (Fe > 0.3 mg/L, Mn > 0.1 mg/L).
Causes:
•Clogged aeration device or insufficient air volume: Aeration diffusers, injectors, or pipes are clogged with iron sludge or suspended solids, or the fan belt is aged, or the air intake filter is dirty, resulting in dissolved oxygen < 5 mg/L.
•Abnormal water quality conditions: Inlet water pH < 6.5 (inhibiting iron oxidation) or < 7.5 (difficult manganese oxidation), or water temperature < 10°C leading to slow oxidation reactions.
•Filter media failure: Manganese sand used for more than 3–5 years, with surface active components (MnO₂) worn or covered by oil or algae, reducing catalytic capacity.
Handling Methods:
•Clean or replace the aeration device (e.g., soak the aeration head in 5% dilute hydrochloric acid), and check the fan belt and filter.
•Adjust the inlet water pH to 7.5–8.5, and increase aeration time or add an oxidation tower if necessary.
•Replace the filter media (retain 10%–20% of the old media to accelerate biofilm formation).
II. Abnormal Operating Parameters (Decline in System Stability)
Manifestation: Inlet–outlet pressure difference > 0.15 MPa, flow fluctuations, or poor backwash effectiveness.
Causes:
•Filter layer clogging or hardening: Inlet water turbidity > 10 NTU, accumulation of suspended solids or iron–manganese oxides causing clogging of filter media gaps; insufficient backwash intensity (< 15 L/(m²·s)) or too short backwash time.
•Uneven water or air distribution: Damaged water distributor screens, clogged filter nozzles, or air leakage in aeration pipes, leading to uneven water or air flow.
•Equipment component failure: Wear of the backwash pump impeller, aging valve seals (leakage > 10% of rated value), or flow meter jamming.
Handling Methods:
•Shorten the backwash cycle (1–2 times daily), and use combined air–water backwash (air wash for 3–5 minutes + water wash for 10–15 minutes).
•Check the water distributor, valves, and flow meters, and replace damaged components.
•If the raw water turbidity is high, add pretreatment (e.g., quartz sand filtration).
III. Equipment Component Damage (Hardware Failure)
Manifestation: Valve jamming or water leakage, filter media loss, or aeration device damage.
Causes:
•Valve failure: Valve core stuck by iron sludge, aging seals, or gear wear in electric valve actuators.
•Filter media loss: Excessive backwash intensity (> 25 L/(m²·s)), or gaps in the filter nozzle > 0.3 mm, causing filter media to wash away with drainage.
•Aeration device failure: Aging or cracked aeration membranes, clogged aeration pipes, or worn fan bearings.
Handling Methods:
•Replace valve seals, filter nozzles, and damaged aeration membranes.
•Adjust the backwash intensity to 14–16 L/(m²·s), and check the support layer grading.
•Regularly lubricate valve stems, and keep critical spare parts (e.g., pumps, fans) on hand.
IV. Seasonal Faults (Environmental Influences)
Manifestation: Pipe freezing and cracking in winter, algae clogging in summer.
Causes:
•Residual water not drained from pipes in winter, causing water to freeze and expand at temperatures < 0°C.
•Algae proliferation in raw water during summer (chlorophyll a > 10 μg/L), adhering to aeration devices and filter media.
Handling Methods:
•Drain pipes completely after winter shutdown, and wrap them with insulation materials.
•Increase pre-oxidation in summer (e.g., adding sodium hypochlorite) or regularly clean aeration heads.
Special Note for the Dazu District, Chongqing
If the local groundwater has high iron and manganese content (e.g., > 5 mg/L), it is recommended to:
•Prioritize the use of an air compressor for aeration (ensuring stable air supply) to avoid injector failure due to insufficient inlet water pressure.
•Shorten the backwash cycle to once every 5–7 days to prevent filter media hardening.
•Regularly test the raw water pH (if < 7.5, adjust with lime milk).
Implementing the above measures can effectively reduce the failure rate of the aeration system and ensure the stable operation of the manganese sand filter.
