To address the availability of carbon sources for denitrification,the accelerated hydrolysis of the most abundant but low-availability fraction of particulate organic matter (POM) was investigated.Mesh sieves with different pore sizes were used as primary pretreatment at the start-up-stage of the biological process to separate some POM from the liquid system.The changes in soluble carbohydrates and proteins were monitored to investigate the hydrolysis performance of the sieved POM,with waste activated sludge (WAS) as the control test.The results showed that an average of 35％ POM could be entrapped before filtrate mat development.In addition,benefiting from the high polysaccharides concentration,as well as the high availability due to the relatively loose physical structure,a 23％ hydrolysis efficiency1of POM was obtained,in contrast to that of WAS (3.4％),with a hydrolysis constant of 0.39 h-.The prominent performance was also attributed to the unique microbial communities having been domesticated at a lower temperature,especially the cellulose-degrading bacteria Paraclostridium and psychrophile Psychrobacter,making up 6.94％ and 2.56％,respectively.Furthermore,the potential benefits and application of improved POM hydrolysis by start-up stage recovery via mesh sieves combined with anaerobic fermentation were evaluated,including selective POM entrapment,alleviation of blockage and wear,and a reduction in aeration energy.By the proposed strategy,carbon availability for biological nutrient removal (BNR) processes is anticipated to be improved more economically than that can be achieved by primary clarifier elimination.