Zero waste processing of wastewater sludge – production of biocoke

Summary

Municipal wastewater sludge has been dominant anthropogenic waste. The problem of its utilization is typical for any city operating a modern system of wastewater treatment. The tasks of optimal sludge utilization have not been solved on the global scale so far. In European practice different, often non-optimal technical solutions depending on the severity of the national environmental standards are applied. In a number of European countries expensive sludge incinerators have been built that provide for thermal utilization of the bulk sludge volume. The generated energy is used in the central heating systems. This technology is considered the most advanced though up to now it has not been supplemented with a cost-efficient and environmentally substantiated technology of processing generated ash. In Russia the bulk of sludge is landfilled; however, the need of developing efficient and environmentally acceptable technology of sludge utilization has become imminent. Pyrolysis is a possible solution of low waste sludge processing with conversion into a useful product – biocoke. The technologies of pyrolysis organic waste processing have a number of advantages over incineration.

Key words

wastewater , sludge , waste utilization , sludge incinerator , pyrolysis , biocoke

Zero waste processing of wastewater sludge – production of biocoke

Summary

An optimal method of wastewater sludge utilization has not been found so far. An advantageous method of wastewater sludge utilization (both economically and ecologically) can be production of biocoke – material that meets the following criteria: high concentration of pure carbon (more than 15–30%); low hydrogen concentration (H/C less than 0.2); the lack of organic toxicants; high porosity (about 40%); mechanical stability; good sorption properties. Method of production – pyrolysis at 400–900 °С temperature; raw material – organic wastes of different origin (wastewater sludge, agricultural wastes, milling wastes, poultry farm wastes). Biocoke can be used for soil conditioning, reclamation of solid waste landfills, reclamation of technogenic and abandoned territories for planting, mitigation of land erosion and desertization. Compared to other soil media biocoke has an advantage in the possibility of selecting material properties depending on the specific application. AktivIl Company has designed and commissioned a medium-scale multiple-hearth
pyrolysis reactor with a capacity of approximately 300 tons of biocoke annually; sludge from a wastewater treatment plant in one of the Moscow Area cities has been used as a raw material. Biocoke samples produced at different operating modes were analyzed and tested. The first results of the studies showed the possibility of reaching the required parameters of the product. The studies are going on within the frames of some national and international projects.

Key words

wastewater , sludge , waste utilization , pyrolysis , biocoke

The technology of wastewater sludge vitrification in comparison with other processing methodsThe technology of wastewater sludge vitrification in comparison with other processing methods

Summary

The experts of Ekopromtekh R & D Centre, LLC have developed an innovative technology for vitrification of wastewater sludge that provides for reducing significantly the volume of wastes and obtaining a safe vitrified material to be used in construction. A comparison of the vitrification technology with other methods of sludge processing is given: depositing, sludge digestion in digesters, drying, pyrolysis, catalytic and classical incineration. In Russia, more than 90% of the generated sludge is landfilled. If this trend persists, an increase in the sludge hauling distance is inevitable. Using unprocessed sludge as fertilizer increases the risk of soil contamination. Financial models of projects that envisage using digesters and selling biogas or electricity do not pay off. In case of using the drying method to obtain fuel from sludge, almost the same amount of thermal energy is consumed as the final product contains. Therefore, the cost of dried sludge as a fuel will not be less than the cost of natural gas, and taking into account other operating costs, including delivery to the consumer, will exceed the cost of gas by 2–3 times. Pyrolysis to obtain marketable products is under development and involves a lot of research. The technology of catalytic incineration of sludge without preliminary drying does not solve the main problems of any incineration process and causes certain difficulties: the risk of emission of superecotoxicants remains; the ash must be disposed of, the autothermal regime is difficult to maintain, the catalyst wears out and requires replacement. The vitrification technology has a number of advantages, it is ready for scaling and industrial implementation.

Key words

wastewater , methane tanks , incineration , sludge , pyrolysis , sludge drying , sludge cake , vitrification , thermal methods , vitrified material , zero landfilling