The key results of the full-scale studies of sludge digestion technology with biomass recycle

Summary

For a number of years the specialists of R&D Centre of «Mosvodokanal» JSC have been developing and testing in a lab environment the technologies that can enhance the process of wastewater sludge digestion within the existing capacity of the treatment facilities. As a result a method was chosen which provided for thickening a part of sludge with subsequent thickened sludge returning back into the digester. The important advantage of this method is the possibility of increasing sludge retention time as dry matter without increasing the hydraulic retention time with simultaneous biomass retaining. Therefore, the required decomposition rate is provided in smaller size reactors. In the course of studying the process solutions on wastewater sludge digestion optimization the method of biomass recycle showed itself as the most economically viable. During the full-scale studies of the recycle option the decomposition of the ash-free basis increased in average to 56.6% (42.2% reference value) which was confirmed by the significant improvement of sludge dewatering properties. The average biogas yield increased by 3%. In the course of the experimental studies no adverse effects of the sludge recycling technology on the digester performance were observed. The results obtained during the full-scale studies evidence the long-term benefits of introducing the technology of wastewater sludge digestion with biomass recycle at the Moscow wastewater treatment facilities.

Key words

anaerobic fermentation , methane tank , decomposition of organic matter , biomass , sludge thickening , recycle

Key findings of full-scale tests of a sludge digestion technology
with biomass recycling

Summary

The results of laboratory studies and full-scale tests of the technology of wastewater sludge digestion with biomass recycling are presented. While conducting industrial tests of the technology with biomass recycling an increase in the disintegration of ash-free matter on average up to 56.6% (the value in the control option is 42.2%) was achieved. The disintegration of ash-free matter significantly improved the dewaterability of sludge. The average increase in biogas yield was 3%. During the experiments no negative impact of the sludge recycling technology on the operation of the digester was recorded. The obtained research results allow concluding that the introduction of sludge digestion technology with biomass recycling at the Moscow Wastewater Treatment Facilities is highly promising. Calculations showed that with the introduction of this technology a decrease in the dry matter amount at the outlet of the digesters compared with traditional technology by 9–10% can be expected. The demand for a flocculant for thickening the recycle is minimized by the improved dewaterability of sludge and, thus, the consumption of flocculant during dewatering is reduced.

Key words

anaerobic fermentation , wastewater sludges , sludge thickening , recycle , increase of ash-free matter disintegration

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