Anaerobic digestion – the key technology of municipal wastewater sludge treatment (part 1)

Summary

The technologic options of municipal wastewater sludge treatment are considered with different approach to stabilization of organic matter. The technologic and environmental consequences of raw wastewater sludge landfilling are considered: emission of malodors, dewatered sludge re-thinning that entails re-dewatering are described. 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 decomposition depth. The processes of autothermal thermophilic aerobic digestion and composting that provide for the production of safe and high-quality fertilizer from sludge are considered. It is concluded that the use of these processes is economically limited to the option of land utilization of the entire sludge volume. The issues of domestic approach to digestion that consist in using thermophilic mode with extremely low retention time of sludge in a digester are considered. The largest share of small particles in sludge digested by such technology caused numerous problems with dewatering in 1960–80-ies. The ways of solving these problems at the Kur’ianovo and Liubertsy wastewater treatment facilities in Moscow including the use of advanced dewatering equipment 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, the methods of enhancing the process (thermal hydrolysis, disintegration, ultrasonic, phasing, recycling of digested sludge) are considered. The information on biogas properties is consolidated. (To be continued).

Key words

composting , anaerobic fermentation , sludge , stabilization , thermophilic digestion

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