Anaerobic digestion – the key technology of municipal wastewater sludge treatment (part 2)

Summary

The technologic options of municipal wastewater sludge treatment are reviewed with different approaches to stabilization of organic matter. The technologic and environmental consequences of raw wastewater sludge landfilling are described. Aerobic sludge stabilization processes are considered. It is concluded that their use is restricted to the options when land utilization of the entire sludge volume is possible. It is shown that traditional aerobic stabilization that was widely used last century does not meet the present day requirements both to power consumption and organics decomposition depth. The aspects of the domestic approach to digestion that consist in using thermophilic mode with extremely low retention time of sludge in a digester are considered. The ways of solving these problems at the Kouryanovo and Lyubertsy wastewater treatment facilities in Moscow are described. It is concluded that in the XXI century anaerobic digestion of wastewater sludge in digesters does not have any other comparable alternative for large and mid-sized wastewater treatment facilities. The main trends in using digestion process, digester design, methods of enhancing the process are considered. The information on biogas properties is consolidated and various options of its utilization are reviewed. Process flow schemes with the use of digesting and combining with other sludge treatment processes (drying, incineration), methods of digested sludge utilization are considered. The information on environmental aspects of digestion – reducing greenhouse gas emissions and carbon footprint – is given. The technologies of purification of return flows of digested sludge dewatering are described. The advanced sludge treatment flow scheme based on digestion and recommended for large-scale facilities is given.

Key words

anaerobic fermentation , sludge , nitrogen , phosphorous , return flows , methane tank , stabilization , biogas utilization , energy budget

Process solutions to increase the efficiency of wastewater treatment with a low concentration of organic matter

Summary

Through the example of the Moscow wastewater treatment facilities, the ways of improving the efficiency of treatment of low-concentrated wastewater in terms of organic matter are considered: the acidification of raw sludge, addition of an external organic substrate, use of technologies independent of the concentration of organic substances. In the presence of refluxes containing nitrogen and phosphorus, the use of organic matter-independent technologies is promising to reduce the nitrogen and phosphorus load on the main biological treatment line. Process solutions that improve the efficiency of nitrogen and phosphorus removal from low-concentrated wastewater in terms of organic matter at the Liuberetsky and Kurianovsky treatment facilities are as follows: acidification of raw sludge to increase the concentration of readily available organic matter; local treatment of refluxes from the sludge treatment facilities to reduce the nitrogen and phosphorus load on the biological treatment using the Anammox process and obtaining a mineral fertilizer – struvite (magnesium ammonium phosphate). At the small-scale wastewater treatment facilities of New Moscow, the addition of yeast condensate as an additional organic matter provides for increasing the BOD₅/N_total ratio from 3.2 to 4.3, which under these conditions is sufficient for the successful denitrification and biological dephosphorization processes. This made it possible to ensure the standard level of removing nitrogen of nitrates and phosphorus of phosphates and, as a result, reduce the consumption of the chemical (ferric chloride).

Key words

wastewater treatment , removal of nitrogen and phosphorus , best available techniques , return flows , nutrients removal , struvite , Anammox technology , low concentration of organics in wastewater

Nitrogen Removal from Return Flows of Sludge Treatment Facilities by Means of Nitri-Denitrification Without an Additional Source of Carbon

Summary

Results of the study of the process of simultaneous nitri-denitrification using the nitrite for removal of ammonium from the filtrate of belt thickeners of digested sludge at the Kuryanovo treatment facilities are presented. Introduction of the developed technology of biological treatment of wastewater containing ammonium nitrogen of high concentration and stripped with organic compounds readily oxidized without an additional source of organic carbon makes it possible to obtain the high efficiency of removal of nitrogen, suspended substances, COD, BOD₅. Microorganisms capable to make denitrification using the organic substances not easily available that determines properties of activated sludge have been separated from activated sludge of a laboratory reactor.

Key words

filtrate , nitrogen removal , return flows , simultaneous nitri-denitrification , belt thickener , digested sludge of wastewater