For decades, urban drainage was guided by a simple philosophy: get the water off the streets and into the nearest river as fast as possible. However, as impervious surfaces expanded and extreme weather events became more frequent, this approach led to overwhelmed systems, urban flooding, and severe ecological damage to receiving waters.

The ATV-DVWK-A 131E (published by the German Association for Water, Wastewater and Waste, now DWA) represents a paradigm shift. It is the definitive guideline for the dimensioning and design of stormwater sewer systems. Unlike older empirical rules of thumb, A 131E relies on rigorous hydrological modeling and statistical rainfall analysis to design systems that handle flow rates effectively while minimizing environmental impact.

[ V_AS = \fracBOD_load \cdot \thetaX_MLSS ]

Where:

The standard includes:

If you cannot obtain the official PDF, consider these “top” alternatives:

| Resource | Type | Quality | |----------|------|---------| | DWA-A 131 (2016 German) | Official, more recent | Very high (but German only) | | EN 12255-8 (EU standard) | Parallel standard | High (broader scope) | | WEF MOP 8 (USA) | Design manual | Good (different approach) | | ATV-DVWK-A 131E summary notes (university lecture slides) | Educational | Medium (not full standard) |

For most professionals, waiting for the official PDF is worth it.

Sludge age (θ) is the design master variable. For nitrifying plants:

| Temperature (°C) | Minimum sludge age (days) | |----------------|---------------------------| | 10 | 10 | | 12 | 8 | | 15 | 6 | | 18 | 5 | | 20 | 4 |

For simultaneous denitrification, sludge age increases by ~1–2 days.

The standard provides a step-by-step approach:

The top PDF will have these formulas in clear mathematical notation (not scanned handwriting).

The German standard ATV-DVWK-A 131 (now superseded by DWA-A 131) provides design rules for single-stage activated sludge systems with secondary clarification, nitrification, and denitrification. It applies to municipal wastewater treatment plants serving >1,000 population equivalents (PE). The standard emphasizes:

The technical solidity of ATV-DVWK-A 131E lies in its comprehensive approach to the rainfall-runoff process. The standard breaks down the design process into three critical pillars:

1. Statistical Rainfall Analysis The standard utilizes the "Kostra" (Coordination of Heavy Rainfall) datasets. Instead of designing for a generic "worst-case scenario," A 131E allows engineers to design for specific statistical probabilities (e.g., a 1-year storm event vs. a 100-year event). This ensures that systems are neither over-engineered (wasting money) nor under-engineered (risking failure).

2. Surface Runoff Modeling A 131E introduces sophisticated parameters for calculating how much rain actually reaches the sewer. It accounts for:

By factoring in land use (roofs vs. asphalt vs. gardens), the standard allows for precise calibration of the runoff coefficient, moving away from generic "C-values" to dynamic, situation-specific modeling.

3. Hydraulic Routing (The Muskingum-Cunge Method) Perhaps the most technical feature of the standard is the adoption of the Muskingum-Cunge method for flow routing. This mathematical model calculates how a flood wave changes shape as it moves through a pipe network. This is crucial for preventing "water hammer" effects and ensuring that peak flows from different sub-catchments do not synchronize at a junction point, which is a common cause of urban flash flooding.