EU-LIFE-Project Sludge Redox Biogas from Sludge

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1 Disposal, RECYCLING, Engineering Waste Incineration Wastewater Treatment EU-LIFE-Project Sludge Redox Biogas from Sludge Layman s Report A company of Bayer and LANXESS

2 Final report on a demonstration project - with financial support from the EU LIFE program This report presents the results of a CURRENTA project to investigate a combination process to reduce the volume of sewage sludge from industrial sources on a pilot scale. A total of 20,000 metric tons per annum of dewatered surplus activated sludge are available for the generation of biogas at the CHEMPARK Leverkusen This is the outcome of a two-year demonstration project that received financial support from the European Union within the framework of the LIFE program. Sewage sludge is an ongoing subject Germany produces approximately 2 million metric tons (solids) of sewage sludge per annum. Around one third of this is currently used to fertilize areas in agricultural Wastewater treatment plant in the Leverkusen Waste Management Center The project Sludge Redox presented here is the last link to date in a long chain of research projects that have been carried out by Bayer AG, Bayer Industry Services and CURRENTA for over 20 years. The Porteous process a thermal process for treating sewage sludge with a high organic content was applied at the Leverkusen site in the 1980s to improve the dewatering of the sludge. The sludge was heated to 170 C in that process. In the 1990s a process was developed for the alkaline hydrolysis of sewage sludge. Sludge digestion, a common process in municipal wastewater treatment plants, was also tested. Unfortunately, it was not possible to convert industrial sewage sludge efficiently into biogas with this method. use. Sewage sludge from industrial sources which often contains residues e. g. heavy metals is incinerated. This process is expensive. The search for new sewage sludge disposal processes that are less expensive and have a lower environmental impact is important because of the large quantities of industrial sewage sludge generated. The EU therefore supports research activities that are aimed at developing new processes to reduce the quantity of sewage sludge and save energy. Membrane filter press for dewatering sludge at the wastewater treatment plant Leverkusen 2 Layman s Report

3 Industrial sewage sludge is a very special substance The challenges facing scientists in wastewater treatment plants of the chemical industry were fundamentally different to those in the communal sector. Wastewater from a Chemical Park has high concentrations of many different chemicals. Frequently it is necessary to pretreat plant effluents to make it biodegradable. Numerous chemicals are harmful to anaerobic bacteria that generate biogas from organic substances in the absence of air. For decades it proved impossible to generate biogas from chemical wastewater. But the wastewater loads have changed considerably in many Chemical Parks since the end of the 1990s as a result of new, more efficient manufacturing processes. Bacteria that could not withstand the wastewater conditions a few years ago can survive in wastewater today. Günter Müller shows the participants of the LIFE symposium lab-scale plant for sludge reduction Combined treatment process for industrial sewage sludge However, despite all of the process improvements the industrial sewage sludge generated today can still not be digested that readily. Chemists, biologists, engineers and technologists of CURRENTA have now shown how this is possible: The key to the process is the judicious combination of treatment steps that are already known. In the first step all water-soluble substances are removed using large volumes of water. Sulfate is also removed in this step as this would otherwise be converted by bacteria to foul-smelling hydrogen sulfide which is toxic to bacteria. The washing step is necessary to avoid subsequent adverse effects on digestion. The sludge floccules (which form surplus activated sludge) are then destroyed with sodium hydroxide at temperatures above 90 C. Organic components, especially proteins, lipids and carbohydrates are very largely converted into watersoluble substances. By this step the solid concentration can be reduced significantly. Before anaerobic treatment neutralization of the hydrolysate is necessary. The neutralized hydrolysate is treated in an anaerobic bioreactor at 35 C. In anaerobic treatment first longchain carboxylic acids are formed; these are further converted to short-chain carboxylic acids. In the final step anaerobic bacteria use this compounds to generate biogas (approx. 60 % methane and 40 % carbon dioxide). Biogas can be used for heating, electricity generation or after purification in compressed natural gas vehicles. Layman s Report 3

4 SLUDGE REDOX Method Water Alkaline solution Biogas Surplus activated sludge Washing step Alkaline hydrolysis Anaerobic treatment Residual sludge Watersoluble components Alkaline hydrolysis system Anaerobic treatment system 4 Layman s Report

5 Activated sludge, untreated Activated sludge after alkaline hydrolysis Sludge after anaerobic treatment The photomicrographs of sewage sludge bacteria below show that the sludge floccules are very largely dissolved after hydrolysis with sodium hydroxide. The subsequent anaerobic treatment converts the remaining floccules partially into biogas. All that remains are fragments of the previously numerous sludge floccules. The remaining sludge will be dewatered and incinerated. The sulphate containing washing water and the effluent of the anaerobic bioreactor are treated in the wastewater treatment plant. Surplus activated sludge Washed surplus activated sludge Balance of the solids after hydrolysis and anaerobic treatment Biogas 13 % 100 % 98 % 30 % Solids in residual sludge 2 % 55 % Solubilised solids to wastewater treatment plant Solubilised solids to wastewater treatment plant Layman s Report 5

6 Use of sewage sludge for energy production At the industrial wastewater treatment plant (wwtp) in Leverkusen sewage sludge is first thickened before adding lime and iron salts for conditioning. Afterwards the sludge is dewatered in a membrane filter press. the calorific value is low (3,000 to 4,000 kj/kg). Therefore it is necessary to add substances with high calorific value for sludge combustion. The Sludge Redox process generates biogas with a calorific value of 22,000 kj/nm 3 from. Each day 2,000 to 3,000 Nm 3 biogas can be generated at the wwtp Leverkusen. More than 50 % of the energy in the surplus activated sludge can be recovered in the biogas. In the same way the amount of waste from surplus activated sludge is reduced by 70 %. The remaining sludge is reduced in organic substances and therefore the calorific value is also reduced. Karl-Heinz Stürznickel shows a component of the pilot plant for sludge reduction. After this treatment the filter cake still has a water content of about 60 %. Because of the water content and high content of inorganic substances in the sludge LIFE symposion The results of the LIFE Project SLUDGE REDOX were presented at 17 th September 2007 in the Leverkusen Waste Management Center. Operators of industrial and municipal wastewater treatment plants and scientists from universities and research institutes participated the symposion. Presentation of Hartmut Mayer (Emschergenossenschaft, Essen) at the LIFE symposium. 6 Layman s Report

7 Cost-effectiveness of the combination process Although pilot-scale studies were successful, further studies will be necessary to make the new process economically viable. The large amount of sodium hydroxide solution needed to dissolve the sludge floccules means that the entire process costs per metric ton of sewage sludge and is therefore markedly more expensive than conventional sewage sludge incineration which costs per metric ton of sludge. Even if the savings made through the use of biogas for electricity generation are included in the calculation, the process still does not reach the point of being viable economically. Further work should focus on improving the economic viability of the process in a larger pilot plant. The process can be further improved by: - application of low-cost alkaline waste - reduction of the energy consumption in the process - increase of the biogas output Sludge digestion in the future Future work will focus on the utilization of the energy present in the sewage sludge. The use of sewage sludges to yield renewable energy is an important step to improve the energy efficiency of wastewater treatment plants and to reduce carbon dioxide emissions. Dr. Fritz Bremer explained the participants of the symposion the control room of the wastewater treatment plant and the process engineering unit at the Waste Management Center. For further information on the project please contact: Dr. Guenter Mueller, Currenta, Geb. 4242, Leverkusen, phone , guenter.mueller@currenta.de Layman s Report 7

INCINERATION PLANTS. Hazardous waste incineration Wastewater incineration Sewage sludge incineration. A Bayer and LANXESS company

INCINERATION PLANTS. Hazardous waste incineration Wastewater incineration Sewage sludge incineration. A Bayer and LANXESS company INCINERATION PLANTS Hazardous waste incineration Wastewater incineration Sewage sludge incineration A Bayer and LANXESS company HAZARDOUS WASTE INCINERATION Introduction INTRODUCTION The thermal treatment