Vertical Subsurface Micro-Ecological Filter Bed | Sponge City Rainwater & Rural Wastewater Purification System
Application Scenarios: Sponge City rainwater purification, rural domestic sewage treatment (widely used vertical subsurface flow ecological filtration system)
Working Principle
Wastewater and rainwater infiltrate vertically from top to bottom. The system achieves water purification through three core mechanisms: filter media biofilm attachment, microbial degradation, and plant root absorption. Layered anaerobic, anoxic, and aerobic zones are formed inside the filter bed to effectively degrade COD, ammonia nitrogen, and total phosphorus. The treated clean water can be recycled for landscape and greening irrigation.
Raw Material List (Layered Layout from Bottom to Top)
1. Bottom Water Collection Layer (20~30cm)
Filled with large gravel/crushed stone (30–50mm). Perforated PVC water collection pipes are installed inside to collect filtered clean water. All pipes are wrapped with geotextile to prevent blockage.
2. Transition Layer (15cm)
Filled with small crushed stone/glass lightweight stone (20–30mm). It supports the upper filter media and protects the bottom water collection pipeline system.
3. Core Filter Media Layer (40~60cm, Core Functional Layer)
Common filter materials: Zeolite, volcanic rock, glass lightweight stone, biochar. Glass lightweight stone is preferred for its large pore structure and excellent biofilm adhesion performance. Zeolite features high ammonia nitrogen removal capacity, while biochar excels at organic matter adsorption.
Recommended mixing ratio: Zeolite : Volcanic Rock : Biochar = 5:3:2
4. Surface Filtration Layer (10~15cm)
Filled with fine quartz sand (3–8mm). It intercepts suspended solids in water and prevents the loss of fine filter particles.
5. Planting Layer (10cm)
Lightweight nutrient soil with low clay content to avoid soil compaction and ensure smooth water infiltration.
6. Anti-Seepage Materials
HDPE anti-seepage membrane + geotextile. Laid on the base and side walls of the filter bed tank to prevent sewage leakage and underground soil & groundwater pollution.
7. Wetland Plants
Yellow flag iris, iris, canna, umbrella grass. These pollution-resistant emergent plants transport oxygen to the filter bed substrate through root systems to optimize microbial living environment.
8. Supporting Facilities
Perforated PVC water distribution pipes, compound microbial agents (specialized nitrogen and phosphorus removal strains to accelerate biofilm formation). Bottom micro-aeration devices are optional for sewage treatment projects to enhance purification efficiency.
Step-by-Step Construction Process
1. Foundation Pit Excavation
Excavate the pit according to the designed length and width with a total depth of 1.1~1.4m. Compact and level the base with a 0.5% drainage slope to facilitate smooth water collection.
2. Anti-Seepage Layer Construction
Lay geotextile on the pit base, weld and install HDPE anti-seepage membrane with upward turnover on side walls, then cover another layer of geotextile to protect the membrane from puncture by sharp stones.
4. Layered Filter Media Backfilling
Backfill materials sequentially from bottom to top: coarse crushed stone → mixed functional filter media (zeolite/glass lightweight stone/biochar) → fine quartz sand. Isolate each layer with geotextile to avoid particle mixing and layer disorder.
5. Water Distribution System Installation
Cover surface nutrient soil and plant emergent wetland plants. Moisten the filter media with water, then add compound microbial agents for biofilm domestication. The microbial flora matures within 20~60 days.
Key Operation & Construction Notes
- Pre-treatment is critical. Sediments, floating debris and large particles must be intercepted and settled in advance to ensure long-term stable operation of the filter bed.