In-situ sludge reduction based on Mn^(2+)-catalytic ozonation conditioning:Feasibility study and microbial mechanisms

To improve the sludge conditioning efficiency without increasing the ozone dose,an in-situ sludge reduction process based on Mn^(2+)-catalytic ozonation conditioning was proposed.Using ozone conditioning alone as a control,a lab-scale sequencing batch reactor coupled with ozonated sludge recycle was evaluated for its operating performance at an ozone dose of 75 mg O_(3)/g VSS and 1.5 mmol/L Mn^(2+)addition.The results showed a 39.4%reduction in MLSS and an observed sludge yield of 0.236 kg MLSS/kg COD for the O_(3)+Mn^(2+)group compared to the O_(3)group (15.3%and 0.292 kg MLSS/kg COD),accompanied by better COD,NH_(4)^(+)-N,TN and TP removal,improved effluent SS and limited impact on excess sludge properties.Subsequently,activity tests,BIOLOG ECO microplates and 16S rRNA sequencing were applied to elucidate the changing mechanisms of Mn^(2+)-catalytic ozonation related to microbial action:(1) Dehydrogenase activity reached a higher peak.(2) Microbial utilization of total carbon sources had an elevated effect,up to approximately 18%,and metabolic levels of six carbon sources were also increased,especially for sugars and amino acids most pronounced.(3) The abundance of Defluviicoccus under the phylum Proteobacteria was enhanced to 12.0%and dominated in the sludge,they had strong hydrolytic activity and metabolic capacity.Denitrifying bacteria of the genus Ferruginibacter also showed an abundance of 7.6%,they contributed to the solubilization and reduction of sludge biomass.These results could guide researchers to further reduce ozonation conditioning costs,improve sludge management and provide theoretical support.

Life-cycle assessment of two sewage sludge-to-energy systems based on different sewage sludge characteristics:Energy balance and greenhouse gas-emission footprint analysis

Anaerobic digestion and incineration are widely used sewage sludge(SS)treatment and disposal approaches to recovering energy from SS,but it is difficult to select a suitable technical process from the various technologies.In this study,life-cycle assessments were adopted to compare the energy-and greenhouse gas-(GHG)emission footprints of two sludge-to-energy systems.One system uses a combination of AD with incineration(the AI system),whereas the other was simplified by direct incineration(the DI system).Comparison between three SS feedstocks(VS/TS:57.61-73.1 ds.%)revealed that the AI system consistently outperformed the DI system.The results of sensitivity analyses showed that the energy and GHG emission performances were mainly affected by VS content of the SS,AD conversion efficiency,and the energy consumption of sludge drying.Furthermore,the energy and GHG emission credit of the two systems increased remarkably with the increase in the VS content of the SS.For the high-organic-content sludge(VS/TS:55%–80%),the energy and GHG emission credit of the AI system increase with the increase of AD conversion efficiency.However,for the low organic content sludge(VS/TS:30%–55%),it has the opposite effect.In terms of energy efficiency and GHG performance,the AI system is a good choice for the treatment of high-organic-content sludge(VS/TS>55%),but DI shows superiority over AI when dealing with low organic content sludge(VS/TS<55%).