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WASTEWATER TREATMENT PLANTS A Bayer and LANXESS company WASTEWATER TREATMENT PLANT – Introduction INTRODUCTION CURRENTA Environment’s wastewater treatment plants specialize in the treatment of wastewater with organic loads. 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 developed ourselves – to treat contaminated water. At CHEMPARK there is a long tradition of handling water responsibly. 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 enough for us – we continue to carry out further research to ﬁnd the very best ways of handling this most precious of resources. 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 remained more or less the same. Water – a crucial role in chemistry Water is absolutely crucial to chemistry – it is a key component 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. 02 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 therefore 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, laboratories and Technical Service Centers as well as sanitary and kitchen wastewater. This water is thoroughly treated in our own biological wastewater treatment plant at Leverkusen-Bürrig. Physical/chemical 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-ofthe-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 neutralized to avoid any impact on the subsequent biological treatment process) • Pre-clariﬁcation to simultaneously separate out undissolved 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. 03 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 treatment 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. Facts and ﬁgures 1901 1909 1928 1954 1958 Bayer establishes a “Wastewater Commission” at its production site in Leverkusen. START-UP 1971: Basin biology 1980: Tower Biology The wastewater loading of the plant is recorded on a monthly basis. 2005 - 2010: New construction of basin biology FUNCTION Wastewater is subject to regular analysis for speciﬁc parameters (29 components). Treatment of wastewater containing organic loads MAIN ASSEMBLIES A laboratory for the examination of wastewater and waste air is established (AWALU laboratory). Neutralization, pre-clariﬁcation, biological treatment, secondary clariﬁcation CAPACITY Bayer AG’s ﬁrst wastewater treatment plant at the Dormagen site is constructed in cooperation with EC (Erdölchemie GmbH). Population equivalent of 1.7 million, of which CHEMPARK: 1.4 million p.e. Wupper water authority: 0.3 million p.e. 1966 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 Wupper catchment area (Wupper water authority). WASTEWATER VOLUMES 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 1971 1975 1978 1980 2002 The ﬁrst expansion stage (now the second treatment stage) goes into operation. DEGRADATION PERFORMANCE NITROGEN REMOVAL 95 % (the remaining 5 % is achieved through the self-cleaning capacity of the Rhine) The biological wastewater treatment plant at CHEMPARK Uerdingen is put into service. Since 1995, an additional 800 metric tons of nitrogen has been eliminated annually from the wastewater through denitriﬁcation and nitriﬁcation. Further reduction in organic nitrogen compounds of > 40 % (cf. new construction of basin biology) 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. PHOSPHATE DEGRADATION RESIDENCE TIMES 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 The existing cooperation agreement on joint wastewater treatment between Bayer Industry Services (now CURRENTA Environment) and the Wupper water authority is extended till 2011. 2007 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 reduce the nitrogenous wastewater load by over 40 percent. 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 WASTEWATER TREATMENT PLANT – The Leverkusen-Bürrig wastewater treatment plant THE LEVERKUSEN-BÜRRIG WASTEWATER TREATMENT PLANT Step by step: An overview of plant components and processes in the wastewater cycle. Coarse mechanical cleaning Biodegradable wastewater from the CHEMPARK in Leverkusen 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. the bottom and are removed mechanically. The resulting sludge is collected along with sludge from the other treatment 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- Neutralization Due to the nature of production, the wastewater is usually strongly acidic (pH value approx. 1.5). To protect the bacteria in the treatment plant, lime milk is added to the wastewater according to the pH level. This precipitates inorganic substances (including calcium, aluminum and iron compounds) and a part of the organic materials as well. 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 Pre-clariﬁcation In the next stage, pre-clariﬁcation, the precipitation products of the neutralization process and other solids sink to 04 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 Lime silo Preliminary clariﬁer Storage tank Wastewater from site Coarse screen Neutralization Sewage sludge treatment Flotation Waste air incineration Denitriﬁcation Dortmund tank Discharge Open basin biology Secondary clariﬁer Municipal wastewater The wastewater cycle in the Leverkusen-Bürrig treatment plant Tower Biology Air in a conﬁned area and on a much shorter timescale than it would occur in nature. The performance of the bacteria depends on their specialization – 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 eﬀectively. 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 wastewater/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 smaller amount is removed as unwanted surplus sludge and passed to the sewage sludge treatment system. Nitriﬁcation, denitriﬁcation – In order to degrade nitrogenous 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 05 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. 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-treatment plant operated by the Wupper water authority using screens, grit chamber and settling tank. Secondary clariﬁcation Phosphate elimination – During the neutralization process with lime milk, a large proportion of the phosphate is precipitated and separated along with the sludge produced at the pre-clariﬁcation stage. Phosphates are also precipitated 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 introduced 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. The sewage sludge generated in the Bürrig plant (industrial 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. Finally, the activated sludge is separated in three secondary 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 Flotation Flotation is a further stage in the treatment of the wastewater. 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. The “Gisela” tunnel that carries the wastewater from CHEMPARK to Leverkusen-Bürrig can be entered by personnel. 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- WASTEWATER TREATMENT PLANT – Control and monitoring CONTROL AND MONITORING Using a comprehensive range of tests, CURRENTA Environment ensures compliance with the complex requirements pertaining to sustainable waste disposal. 06 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 wastewater volume provide information about the load and composition 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 substances 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 include 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. 07 Published by Currenta GmbH & Co. OHG 51368 Leverkusen Germany www.currenta.com As at: April 2008
"WASTEWATER TREATMENT PLANTS"