WASTEWATER TREATMENT PLANTS

A Bayer and LANXESScompany

CURRENTA Environment’s wastewater treatment plants specialize in the treatment of wastewater with organic loads.

INTRoducTIoN

WASTEWATER TREATMENT PLANT – Introduction

Clean water is one of mankind’s most valuable resources. That’s why we treat it with a great deal of care and respect. We optimize processes to reduce the volume of water used, take all possible measures to prevent contamination and use highly effective methods – some of which we de-veloped ourselves – to treat contaminated water.

At CHEMPARK there is a long tradition of handling water re-sponsibly. As far back as 1901, a “Wastewater Commission” was in place to deal with this valuable raw material. Today, we implement the most effective wastewater treatment systems anywhere in the world, but that is still not en-ough for us – we continue to carry out further research to find the very best ways of handling this most precious of resources.

Water – a crucial role in chemistry

Water is absolutely crucial to chemistry – it is a key compo-nent in products, a solvent, a cleaning and cooling agent, a source of energy in the form of steam and, of course, plays an essential role in the everyday lives of the people who work with us.

CHEMPARK Leverkusen consumes approximately 240 million cubic meters of water each year. Around 95 percent of this is sourced either directly or indirectly from the River Rhine. Over the last 10 years, water consumption has been reduced significantly while production levels have re-mained more or less the same.

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State-of-the-art wastewater treatment at CURRENTA Environment

Three-quarters of this water is used for cooling purposes in the production facilities. During this process, the cooling water does not come into contact with products. After we have carried out suitable independent checks, we can there-fore feed this cooling water directly back into the Rhine via a separate system. Wastewater containing inorganic loads and few or no organic contaminants that does not require treatment can also be fed straight back into the Rhine, as can uncontaminated rainwater.

Only around ten percent of the water used actually comes into contact with products and subsequently requires treatment. This includes acidic, alkaline and organically loaded wastewater from the production facilities, laborato-ries and Technical Service Centers as well as sanitary and kitchen wastewater.

This water is thoroughly treated in our own biological waste-water treatment plant at Leverkusen-Bürrig. Physical/chemi-cal pre-treatment measures are carried out upstream – where the water is contaminated. Substances that could impede biological treatment or that cannot be eliminated using biological methods are removed in the production plants themselves. The treated wastewater then flows into the Rhine.

The wastewater treatment process

Contaminated municipal and industrial wastewater can be treated together extremely efficiently. Today’s state-of-the-art wastewater treatment is carried out in a number of stages depending on the specific substances contained in the water:• Mechanical removal of coarse matter and sand (screen, grit chamber)

• Neutralization (acidic and alkaline wastewater is neutral-ized to avoid any impact on the subsequent biological treatment process)

• Pre-clarification to simultaneously separate out undis-solved substances and substances precipitated during neutralization

• Equalization of the wastewater quality• Biological treatment – biodegradable substances are “consumed” by bacteria. New bacteria are created.

• Secondary clarification to separate the biological sludge from the treated water. A proportion of this biological sludge is fed back into the biological stage in order to maintain a constant sludge concentration. The rest of the sludge is transported to the sludge treatment section.

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The history of wastewater treatment

The first mechanical and biological processes for plants designed to treat municipal wastewater emerged as early as the end of the 19th century. Mechanical, biological and chemical treat-ment of industrial wastewater was introduced from around the mid-1950s. Prior to this, it had been assumed that chemical wastewater could not be treated biologically.

1901

1909

1928

1954

1958

1966

1971

1975

1978

1980

2002

2007

Bayer establishes a “Wastewater Commission” at its production site in Leverkusen.

The wastewater loading of the plant is recorded on a monthly basis.

Wastewater is subject to regular analysis for specific parameters (29 components).

A laboratory for the examination of wastewater and waste air is established (AWALU laboratory).

Bayer AG’s first wastewater treatment plant at the Dormagen site is constructed in cooperation with EC (Erdölchemie GmbH).

A mechanical/biological wastewater treatment plant in the Flittard section of the Leverkusen site follows the earlier 1958 project. The experience gained in this plant is then fed into the construction of the joint wastewater treatment plant in Leverkusen. This joint project treats the wastewater of the CHEMPARK and of the lower Wup-per catchment area (Wupper water authority).

The first expansion stage (now the second treatment stage) goes into operation.

The biological wastewater treatment plant at CHEMPARK Uerdingen is put into service.

The second mechanical/biological wastewater treatment plant is established at CHEMPARK Dormagen.

The second expansion stage of the Leverkusen plant is extended with the addition of Bayer Tower Biology.

The existing cooperation agreement on joint wastewa-ter treatment between Bayer Industry Services (now CURRENTA Environment) and the Wupper water authority is extended till 2011.

The first construction phase of the new Tower Biology unit is completed successfully. The “cascade biology” project is due to be completed by 2010 and aims to re- duce the nitrogenous wastewater load by over 40 percent.

Facts and figures

STarT-up

FuncTion

Main aSSeMblieS

capaciTy

WaSTeWaTer voluMeS

DegraDaTion perForMance

niTrogen reMoval

phoSphaTe DegraDaTion

reSiDence TiMeS

1971: Basin biology

1980: Tower Biology

2005 - 2010: New construction of basin biology

Treatment of wastewater containing

organic loads

Neutralization, pre-clarification,

biological treatment, secondary clarification

Population equivalent of 1.7 million, of which

CHEMPARK: 1.4 million p.e.

Wupper water authority: 0.3 million p.e.

CHEMPARK: 40,000 m³/d

Wupper water authority: 60,000 m³/d

Up to 195,000 m³/d in wet weather

Bürrig: (sanitary, sludge pressing, rinse water from incineration plant, leachate): approx. 10,000 m³/d

95 % (the remaining 5 % is achieved through

the self-cleaning capacity of the Rhine)

Since 1995, an additional 800 metric tons of nitrogen has been eliminated annually from the wastewater through denitrification and nitrifi-cation. Further reduction in organic nitrogen compounds of > 40 % (cf. new construction of basin biology)

Simultaneous precipitation ensures discharge concentration < 0.6 mg/l

“Gisela” tunnel inflow: approx. 1.5 h

Neutralization: approx. 0.5 h

Pre-clarification: approx. 3 – 5 h

Intermediate storage: approx. 15 – 20 h

Tower Biology: approx. 18 – 22 h

Basin biology I & II: approx. 5 – 8 h

Secondary clarifier: approx. 6 – 8 h

Dortmund tank: approx. 8 – 10 h

Total residence time of the wastewater in the treatment plant: approx. 2 – 3 days

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WASTEWATER TREATMENT PLANT – The Leverkusen-Bürrig wastewater treatment plant

coarse mechanical cleaning

Biodegradable wastewater from the CHEMPARK in Lever-kusen flows to the treatment plant at Bürrig through a two kilometer long tunnel 12 meters underground. It takes two hours for the wastewater to complete this journey. In the treatment plant, a coarse screen is used to remove larger materials from the wastewater.

neutralization

Due to the nature of production, the wastewater is usually strongly acidic (pH value approx. 1.5). To protect the bacte-ria in the treatment plant, lime milk is added to the waste-water according to the pH level. This precipitates inorganic substances (including calcium, aluminum and iron com-pounds) and a part of the organic materials as well.

pre-clarification

In the next stage, pre-clarification, the precipitation prod-ucts of the neutralization process and other solids sink to

the bottom and are removed mechanically. The resulting sludge is collected along with sludge from the other treat-ment stages (see below) and transferred to the sewage sludge treatment system.

intermediate storage

The mechanically pre-treated and neutralized wastewater is stored in buffer tanks, where the concentration and vol-ume of the wastewater stream are equalized. This improves the degradation performance in the subsequent biological treatment.

Treatment in Tower biology

The concept – The processes involved in the biological treatment of wastewater are comparable to the natural self-cleaning capacity of rivers and lakes. Bacteria feed on the substances contained in the wastewater and use the oxygen dissolved in the water to transform these into carbon dioxide, water and biomass.In biological treatment plants, this process is carried out

Step by step: An overview of plant com-ponents and processes in the wastewater cycle.

THE LEVERKuSEN-BÜRRIGWASTEWATER TREATMENT PLANT

in a confined area and on a much shorter timescale than it would occur in nature.

The performance of the bacteria depends on their spe-cialization – this develops after a period of time and is determined by the substances contained in the water. The bacteria must also be well supplied with oxygen and the Tower Biology system achieves this extremely effec-tively. The process engineers at CURRENTA Environment have succeeded in finding a particularly energy-efficient method of introducing the atmospheric oxygen needed for biological degradation into the mixture of wastewater and bacterial sludge. Using “injectors” that operate on a principle similar to a water jet pump, compressed air is blown into the towers.

These injectors are a key component of Tower Biology. The conventional large, open clarifiers which have depths of three to seven meters and different aeration systems are replaced by covered towers 30 meters high.

The high liquid column means that the oxygen is used far more efficiently in the towers, thus generating less waste air. The waste air, which also contains expelled organic substances, is collected and incinerated in a thermal

waste gas treatment plant. This prevents any odors being released into the ambient air.

Intermediate clarification – The wastewater treated in the Tower Biology flows over cyclones that degasify the waste-water/sludge mixture and enters the suspended, elevated intermediate clarifier in which activated sludge and water are separated. The majority of the activated sludge is fed back into the towers using centrifugal pumps. A smal-ler amount is removed as unwanted surplus sludge and passed to the sewage sludge treatment system.

Nitrification, denitrification – In order to degrade nitroge-nous molecules such as ammonium compounds, further strains of bacteria are required in addition to those already used to break down carbon compounds. In an initial stage, nitrifying bacteria use oxygen to convert the ammonium compounds into nitrate at temperatures over ten degrees Celsius. In an upstream process, this nitrate is transformed into molecular nitrogen and passes into the ambient air.

As this process can only be carried out in the absence of oxygen (anoxia) and in the presence of carbon compounds, 80 percent of the wastewater flowing out of the towers is pumped into a separate tank. This tank contains very little

The wastewater cycle in the Leverkusen-Bürrig treatment plant

preliminary clarifier

lime silo

Storage tankWastewater from site neutralization

Denitrification

Tower biologySecondaryclarifier

air

open basin biology

Municipal wastewater

Sewage sludge treatment

Waste air incineration

Discharge

Flotation

Dortmund tank

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coarse screen

atmospheric oxygen and ample carbon compounds sourced from the untreated site wastewater that flows through the tank before being fed into the towers. This process is known as upstream denitrification.

Each year, this method is used to eliminate over 800 metric tons of nitrogen load from the wastewater. A significant proportion of the nitrogen load is also disposed of with the surplus sludge.

Phosphate elimination – During the neutralization process with lime milk, a large proportion of the phosphate is preci-pitated and separated along with the sludge produced at the pre-clarification stage. Phosphates are also precipita-ted through the addition of aluminum and iron salts at the biological treatment stage.

The advantages of Tower Biology – Compared to open, shallow basin biology, Tower Biology offers a range of advantages:• The injector ensures that the atmospheric oxygen intro-duced is used to full effect.

• The reduction in the volume of waste air cuts costs for waste air incineration.

• The enclosed design and waste air treatment prevent odors being released into the surrounding area.

• The injector system results in energy savings of up to 70 percent.

• The wastewater and activated sludge can be thoroughly mixed without the need for additional mechanical mixing equipment.

• Tower Biology contains no moving parts – as a result, the plant is extremely low maintenance and reliable.

• The tower design ensures safe, easy monitoring of any leakage. It is impossible for any wastewater to seep into the subsoil unnoticed.

• Tower Biology requires around 50 to 70 percent less space than conventional biological wastewater treatment plants.

Flotation

Flotation is a further stage in the treatment of the waste-water. In this process, gas bubbles attach to the flakes of sludge in the wastewater. As they are less dense than the substance around them, they then rise to the surface of the liquid and form a foam layer, or flotate, which is then removed.

Treatment in basin biology

The water produced from intermediate clarification in the Tower Biology tanks is then treated further along with the municipal wastewater from Leverkusen and the surround-

ing communities. This is carried out in open activated sludge tanks as a second biological process stage. Surface aerators are responsible for adding the oxygen and the mixing. Before being added to the tanks, the municipal wastewater is mechanically treated in a separate pre-treat-ment plant operated by the Wupper water authority using screens, grit chamber and settling tank.

Secondary clarification

Finally, the activated sludge is separated in three second-ary clarifiers and ten Dortmund tanks and the treated wastewater is fed into the Rhine under online supervision. The surplus sludge from the secondary clarification is fed into the sewage sludge treatment system.

Sewage sludge treatment

The sewage sludge generated in the Bürrig plant (indus-trial and municipal pre-clarification sludge and surplus sludge) is concentrated, equalized and de-watered using membrane filter presses. The filter cake is then disposed of in the sewage sludge incineration plant. The ash that is left after incineration is deposited at the landfill site.

The “Gisela” tunnel that carries the wastewater from CHEMPARK to Leverkusen-Bürrig can be entered by personnel.

Using a comprehensive range of tests, CURRENTA Environment ensures compliance with the complex requirements pertaining to sustainable waste disposal.

coNTRoL ANd MoNIToRING

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WASTEWATER TREATMENT PLANT – Control and monitoring

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The raw wastewater, the wastewater from the individual treatment stages and the water from the last treatment stage are subjected to regular biological and chemical analysis to ensure the treatment plant is operating reliably. The treated wastewater is checked constantly to ensure that the values adhere to those in the discharge permit. In addition to this, further parameters are used for ongoing checks of the efficiency of the treatment.

The analytical data of the inflow and outflow and the waste-water volume provide information about the load and com-position of the substances in the wastewater and about the efficiency of the treatment plant. The measurements taken include settleable substances, sum parameters such as the chemical and biochemical oxygen demand, key individual inorganic and organic substances and the salt content. There are also constant checks to establish whether sub-stances are present in the wastewater that could impact on the degradation performance of the bacterial sludge.

A permanently accessible control point for the biologically treated wastewater from the plant has been set up for the monitoring authorities. The authorities’ responsibilities in-clude taking samples from the outlet of the treatment plant and checking them to ensure compliance with the discharge permit. These samples can be taken by representatives of the authorities at any time, including weekends and during the night, without prior notification.

The quality of the treated wastewater is monitored constantly.

Published by

Currenta GmbH & Co. OHG

51368 Leverkusen

Germany

www.currenta.com

As at: March 2010