Wastewater Treatment System for 2000-head Pig Farm
25 Mar 2025
Wastewater Treatment System for 2000-head Pig Farm
Based on the actual scale of a 2000-head pig farm (producing about 20 tons of sewage daily), design a wastewater treatment system and cost details to meet the requirements of the "Emission Standards of Pollutants for Livestock and Poultry Breeding Industry" (GB18596-2001).
1. Water Quantity and Quality Parameters
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Sewage Volume: 20 tons/day (calculated at 10kg per head per day for 2000 pigs)
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Influent Water Quality (based on historical data from similar pig farming wastewater cases):
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COD: 8000-12,000mg/L
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NH₃N: 800-1200mg/L
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TP: 200-300mg/L
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SS: 2000-4000mg/L
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Effluent Target:
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Preliminary Plan: Meet GB18596-2001 standard (COD≤400mg/L, NH₃N≤80mg/L, TP≤8mg/L)
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2. Process Flow Optimization (20 tons/day scale)
"Solid-Liquid Separation + High-Efficiency Anaerobic + Integrated A/O MBR + Constructed Wetland"
A[Raw Water]>B(Solid-Liquid Separator) B>C(Regulation Tank) C>D(EGSB Anaerobic Reactor) D>E(Integrated MBR Equipment) E>F(Constructed Wetland) F>G[Effluent Meeting Standards]
Key Process Description
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Solid-Liquid Separator: Sieve mesh aperture 0.5mm, removes fibrous suspended solids (reducing subsequent membrane fouling risk)
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EGSB Anaerobic Reactor: Volumetric load 6-8kg COD/(m³·d), retention time 3-5 days, COD removal rate≥85%
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Integrated MBR Equipment: Integrated anoxic + aerobic + membrane pool, membrane flux 15L/(m²·h), membrane area≥30m²
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Constructed Wetland: Area 50m², planted with reeds, further nitrogen and phosphorus removal
3. Itemized Cost Details (unit: ten thousand yuan)
| Category | Sub-Item Name | Specifications/Parameters | Quantity | Unit Price/(ten thousand yuan) | Subtotal/(ten thousand yuan) |
|---|---|---|---|---|---|
| Pretreatment | Solid-liquid separator | Treatment capacity 2m³/h, stainless steel | 1 unit | 3.5 | 3.5 |
| Anaerobic Unit | EGSB reactor | Φ2.5m×6m, PE material | 1 set | 12 | 12 |
| MBR System | Integrated equipment (with membrane components) | Treatment capacity 1m³/h, PLC control | 1 set | 28 | 28 |
| Ecological Treatment | Constructed wetland | 50m², with fillers + plants | 1 item | 2.5 | 2.5 |
| Other Costs | Installation and commissioning fee | - | - | - | 5 |
| Total | - | - | - | - | 51 ten thousand yuan |
4. Operation Cost Analysis (calculated at 20 tons/day)
| Item | Unit Price | Daily Consumption | Daily Cost/(yuan) | Annual Cost/(ten thousand yuan) |
|---|---|---|---|---|
| Electricity Cost | 0.65 yuan/kWh | 60kWh | 39 | 1.42 |
| Chemical Cost | PAC: 2000 yuan/ton | 5kg | 10 | 0.36 |
| Membrane Replacement | 300 yuan/m² (5-year lifespan) | Annual replacement 6m² | - | 0.18 |
| Labor Cost | 5000 yuan/person·month | - | 83 | 3 |
| Total | - | - | 132 yuan/day | 4.96 ten thousand yuan/year |
5. Key Design Parameter Verification
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EGSB Anaerobic Reactor:
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Effective Volume: 25m³ (20 tons/day × 1.25-day retention time)
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Biogas Production: 20 tons/day × COD removal 8000mg/L × 0.35m³/kg = 56m³/day
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Usage: Can be used as fuel for farm kitchen (equivalent to saving 15kg liquefied gas daily)
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MBR System:
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Membrane Area Requirement: 20 tons/day ÷ 24h ÷ 15L/(m²·h) = 56m² (actual selection 30m², meeting demand by extending operation time)
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Sludge Concentration (MLSS): 8000-12,000mg/L
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6. Investment Return and Resource Utilization
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Direct Benefits:
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Biogas Utilization: 56m³/day × 0.5 yuan/m³ = 28 yuan/day → Annual revenue 1.02 ten thousand yuan
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Organic Fertilizer Production: Annual production of 10 tons of dewatered sludge, sold at 800 yuan/ton → Annual revenue 0.8 ten thousand yuan
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Indirect Benefits:
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Exemption from Discharge Fees (about 0.8 yuan/ton according to local standards) → Annual saving 0.58 ten thousand yuan
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Reclaimed Water Replacing Groundwater (20 tons/day × 0.5 yuan/ton) → Annual saving 0.36 ten thousand yuan
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Comprehensive Payback Period: Total revenue: 1.02 + 0.8 + 0.58 + 0.36 = 2.76 ten thousand yuan/year; Net operating cost: 4.96 - 2.76 = 2.2 ten thousand yuan/year
7. Implementation Suggestions
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Equipment Selection: Prioritize integrated MBR equipment (such as "Membrane Bioreactor for Rural Livestock Wastewater") to reduce civil engineering work.
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Operation and Maintenance Management:
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Daily check the screen clogging of the solid-liquid separator
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Monthly monitor the membrane flux of MBR, and perform chemical cleaning (sodium hypochlorite + citric acid) in time
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Expandable Design: Reserve 20% land for future expansion to 50 tons/day.
This is an initial plan. The scheme uses "compact anaerobic + integrated MBR" to achieve low investment (500,000 yuan level) and low operation & maintenance (within 50,000 yuan/year), suitable for farms with around 2000 pigs. Actual construction should be preceded by water quality testing and process combination adjustment according to site conditions.