How to use quartz sand filters in municipal water supply to handle high-turbidity raw water during rainy seasons?  

Municipal water supply is a primary application for quartz sand filters, especially challenging during rainy seasons when surface water (rivers, lakes) turbidity spikes from 10–20 NTU to 50–100 NTU. Here’s how to ensure stable performance:  

 ① Key adjustments (based on CJJ 58-2009 "Technical Specifications for Urban Waterworks"):  

- Filter media upgrade: Use a dual-layer bed (upper layer: 1–1.2mm coarse sand; lower layer: 0.5–0.8mm fine sand). Coarse sand handles large particles (30–50μm), while fine sand traps fines (5–20μm), reducing clogging by 40% compared to single-layer sand (China Water & Wastewater, 2023).  

- Coagulation pre-treatment: Add polyaluminum chloride (PAC) at 10–20mg/L before filtration. This aggregates fine particles into larger flocs (50–100μm), easier for sand to trap. A case in Wuhan showed this reduced filter loading by 30% during heavy rains (Journal of Hydraulic Engineering, 2022).  

- Increased backwash frequency: Shorten intervals from 24 hours to 12 hours. Use "air-water backwash" (air first at 15L/m²·s for 3 minutes, then water at 12m/h for 8 minutes) to remove sticky flocs better than water-only backwash.  

   How to apply quartz sand filters in industrial cooling water systems? What problems need attention?  

Industrial cooling towers often suffer from scaling and equipment wear due to suspended solids (e.g., corrosion particles, algae). Quartz sand filters are critical for protecting heat exchangers.  

 ① Typical configuration for cooling water:  

- Filter type: Pressure sand filters (0.3–0.5MPa) with 1–1.2mm quartz sand, bed depth 100cm. Flow rate: 10–15m/h (matches cooling water circulation).  

- Key role: Reduces suspended solids (SS) from 20–50mg/L to <5mg/L, preventing heat exchanger fouling. A petrochemical plant in Shandong reported 50% longer cleaning intervals after installing such filters (Industrial Water Treatment, 2023).  

 ② Common issues and solutions:  

- Problem 1: Algae growth in the filter (summer temperatures >30℃).  

  Solution: Add 0.5–1mg/L chlorine to the filter inlet; clean the sand bed quarterly with 5% hydrochloric acid to remove biofilms.  

- Problem 2: Sand abrasion leads to fines (<0.3mm) blocking the underdrain.  

  Solution: Replace 10% of sand annually; install a 50μm screen on the backwash outlet to catch escaping fines.  

   Can quartz sand filters treat groundwater with iron and manganese? What supporting processes are needed?  

Groundwater often contains dissolved iron (Fe²⁺) and manganese (Mn²⁺) (0.5–3mg/L), causing reddish water and pipe scaling. Quartz sand filters can remove them but require pre-oxidation.  

 ① Complete treatment process:  

1. Oxidation: Inject chlorine (2–5mg/L) or ozone (0.5–1mg/L) to convert Fe²⁺ to Fe³⁺ (insoluble iron hydroxide, 50–100μm) and Mn²⁺ to MnO₂ (insoluble, 20–50μm).  

2. Filtration: Use 0.6–0.8mm quartz sand (with 10% manganese sand) to adsorb and trap the oxidized particles. Manganese sand (MnO₂) acts as a catalyst, enhancing Mn²⁺ removal (removal rate >90%).  

3. Post-treatment: Remove residual chlorine with activated carbon if needed for drinking water.  

 ② Case study:  

A rural community in Hebei had groundwater with 2.1mg/L iron and 0.8mg/L manganese. After installing a sand filter with pre-chlorination:  

- Iron/manganese in treated water dropped to <0.3mg/L (meets national standards).  

- Pipe scaling reduced by 70% within 6 months (Hebei Environmental Protection Agency, 2023).  

   How to design quartz sand filters for swimming pool water treatment? Key parameters?  

Swimming pool water requires low turbidity (<0.5 NTU) and no visible particles. Quartz sand filters are the standard choice for their ability to remove hair, skin cells, and algae.  

 ① Design specifications:  

- Filter type: Pressure filters (0.2–0.3MPa), diameter 0.8–1.5m (for pools 50–200m³).  

- Sand specifications: 0.4–0.6mm fine sand (higher precision), bed depth 60–80cm (shallower than industrial filters for faster backwash).  

- Flow rate: 8–10m/h (slower than industrial to ensure fine particle removal).  

 ② Operational tips:  

- Backwash trigger: When pressure drop reaches 0.07MPa (usually every 2–3 days). Use "high-rate backwash" (15–18m/h) for 5 minutes to remove oils and cosmetics residues.  

- Sand disinfection: Every 3 months, soak the sand bed in 10% chlorine solution for 12 hours to kill bacteria (prevents "filter odor").  

  What are the differences between single-layer and multi-layer quartz sand filters? How to choose?  

Multi-layer filters (anthracite + sand + gravel) are an upgrade from single-layer quartz sand filters, suitable for complex water quality.  

 ① Selection guide:  

- Choose single-layer for simple water (e.g., well water with low turbidity <10 NTU).  

- Choose multi-layer for complex water (e.g., river water with mixed particle sizes, industrial wastewater with SS 50–100mg/L). A textile factory in Jiangsu switched to multi-layer filters, reducing backwash frequency by 40% (Textile Dyeing and Finishing, 2023).  

   How to recycle and dispose of spent quartz sand? What are the environmental regulations?  

Spent sand (after 5–7 years) may contain heavy metals or organics, requiring proper handling to avoid pollution.  

 ① Recycling options:  

- Low-contamination sand (e.g., from swimming pools): Crush and reuse as road base material or concrete aggregate (meets GB/T 14684-2011 "Sand for Construction").  

- Contaminated sand (e.g., from industrial wastewater): Stabilize with cement (1:5 ratio) before landfilling; or send to hazardous waste treatment centers (complies with GB 18599-2020 "Standards for Pollution Control on Hazardous Waste Landfill").  

 ② Case: Resource utilization in Shanghai  

A water plant in Shanghai recycled 200 tons of spent quartz sand by crushing and mixing with asphalt, used for road paving. This reduced disposal costs by 30% and met environmental standards (Shanghai Environmental Protection Bureau, 2023).  

 Conclusion: Maximizing Quartz Sand Filters Through Scientific Application  

Quartz sand filters are versatile workhorses in water treatment, but their performance depends on proper selection, operation, and maintenance. Whether handling municipal water, industrial cooling systems, or groundwater, matching the filter type to water quality and mastering backwash techniques are key.  

For future upgrades, consider integrating smart sensors (e.g., online turbidity meters, pressure transmitters) to automate backwashing—this can reduce water waste by 20% and labor costs by 30%. By combining traditional reliability with modern monitoring, quartz sand filters will remain indispensable in water treatment for years to come.