Die Wiener Kläranlage: Sauberes Abwasser - sauberer Strom

Wastewater Treatment Process in Vienna

Overview of Vienna's Water Supply

• Vienna is renowned for its high quality of life, supported by fresh mountain spring water available to all residents.

• Each person in Vienna consumes approximately 130 liters of drinking water daily, with only 3 liters used for cooking and drinking; the majority is utilized for personal hygiene and toilet flushing.

Wastewater Management System

• The city has a complex wastewater system comprising 2,500 kilometers of pipes that transport sewage to treatment facilities located in Simmering.

• Approximately 6,000 liters of wastewater enter the treatment plant every second, operating continuously throughout the year.

Mechanical Treatment Stages

• The first stage involves removing large solids using a gravel trap where about 1.5 tons of material are extracted daily to prevent damage to subsequent equipment.

• A unique lift system elevates wastewater five meters using powerful screw pumps capable of handling up to 18,000 liters per second.

• The mechanical cleaning process includes four stages: screening (removal of food waste and other debris), sand settling (where sand particles settle out), and pre-treatment (sludge removal).

Biological Treatment Process

• After mechanical treatment, biological processes target organic pollutants like carbon compounds, nitrogen, and phosphorus to maintain water quality in the Danube River.

• Microorganisms play a crucial role in breaking down contaminants; they require oxygen supplied through air pumped into the treatment tanks via aeration systems.

Detailed Biological Cleaning Steps

• In aeration tanks, microorganisms consume dirt particles; trillions inhabit these tanks and help convert harmful substances into harmless gases.

• The process alternates between oxygen-rich and low-oxygen zones to optimize conditions for different types of microorganisms involved in nutrient breakdown.

• Excess sludge produced during this process is removed daily for energy recovery while cleaned water moves on for further processing.

Final Stages of Treatment

• The final biological stage focuses on nitrogen removal from urine components like urea and ammonium through multiple steps converting them into harmless nitrogen gas before entering clarification tanks.

Wastewater Treatment Process Overview

Quality of Treated Water

• The nachklärbecken (after-treatment basin) can hold 13 million liters of treated wastewater, which appears almost black due to an optical phenomenon. This indicates the absence of suspended particles, showcasing the high quality of the treatment process.

Final Steps Before Discharge

• After approximately 20 hours in the treatment plant, cleaned wastewater flows through submerged pipes towards the Danube Canal. Before being released into nature, it undergoes final analyses as part of continuous quality control conducted by EBS Wien staff.

Advanced Monitoring Technology

• The facility employs state-of-the-art control technology with thousands of sensors and pumps that send constant updates about their status—around 20,000 signals per hour are processed in the control room, which acts as the brain of the Vienna wastewater treatment plant.

Environmental Impact and Energy Consumption

• EBS Wien's operations prevent around 125 tons of pollutants from entering the Danube daily; carbon compounds are removed from Vienna's wastewater by up to 99%. However, this high-level treatment requires significant energy—over 60 gigawatt-hours annually, equivalent to what 25,000 households consume.

Renewable Energy Utilization

• As an environmentally conscious company, EBS Wien focuses on generating electricity and heat from renewable sources. A key area is utilizing waste products from wastewater treatment (the sludge), which contains substantial renewable energy potential that is maximized in their eco-power plant.

Sludge Processing Techniques

Initial Sludge Characteristics

• Initially very liquid with less than 1% dry matter content, sludge must be thickened through a two-step process: first using gravity to allow solids to settle and reduce volume by three-quarters while increasing dry matter content to about 4%.

Centrifugation for Further Thickening

• Powerful centrifuges further increase dry matter content to around 8%, ensuring that sludge remains transportable without becoming too thick for processing. This step is crucial for efficient handling and subsequent energy recovery processes.

Anaerobic Digestion Process

Faulbehälter (Digestion Tanks)

• The thickened sludge enters large anaerobic digestion tanks where it remains under airtight conditions for about 25 days. During this time, microorganisms break down organic materials in the sludge while producing biogas composed mainly of methane (about 60%).

Biogas Management

• The produced biogas rises within the tank and is directed into gas storage containers that maintain pressure stability through external blowers ensuring consistent operational efficiency during gas extraction processes.

Energy Generation from Biogas

Conversion into Electricity

• The purified biogas undergoes cleaning via activated carbon filters before being utilized in combined heat and power plants (BHKW). These massive engines convert gas into mechanical energy that generates electricity; excess heat is repurposed for heating operational buildings and warming sludge effectively.

Surplus Energy Contribution

• The Vienna wastewater treatment plant produces more clean energy than it consumes for its operations; surplus eco-energy is fed back into Vienna’s power grid contributing positively to local sustainability efforts.