Study On Structure And Combination Of Novel Basalt Fiber Carrier In Domestic Wastewater Treatment

In biological wastewater treatment,biological contact oxidation process is increasingly gaining attention.By introducing carrier media into activated sludge systems,this process not only significantly increases biomass and system stability,but also reduces the dependence on secondary clarification.Being one of the components of contact oxidation process,carrier media play a key role in wastewater treatment.Having high specific surface area and excellent hydraulic properties,fibrous carriers have been widely used in biological contact oxidation processes.Compared to conventional carrier,fibers introduced in contact oxidation tanks showed advantages in nitrogen removal,sludge detachment,energy consumption,bacterial adhesion and sludge reduction.According to previous findings in wastewater treatment,micron-sized basalt fiber(BF)introduced into activated sludge systems readily spread,tangle,forming biological aggregate with the size more than 10 cm,also called “bio-nest”.There is no specification for BF carrier application used in contact oxidation tanks currently,because they directly influence biomass amount,extracellular polymeric substances(EPS)and microbial community structures and compositions,and hence the process efficacy in wastewater treatment.For establishment of the specifications,synthetic domestic wastewater was treated with carriers of different sizes and vertical spacings to investigate EPS,microbial community and wastewater treatment efficacy of bio-nests and establish preliminary structure combination.The major research contents are listed as follows.(1)BF size influenced microbial community structure and composition and EPS contents,making the treatment efficacy different,based on which BF carrier size was determined.In this study synthetic domestic wastewater was treated with five sizes of BF carrier units(diameter of 5,10,15,20 and 25 cm)in contact oxidation tanks.The corresponding five bio-reactors labeled as D5,D10,D15,D20 and D25 running under same operating conditions were evaluated within 100 days.Subsequently,the samples collected from frozen bio-nests were separately analyzed in terms of EPS and microbial community.The finding showed that D15 achieved the highest COD,ammonia nitrogen,and total nitrogen removal efficiencies,which were 91.8%,98.4% and 84.1%,respectively.The ratio of protein(PN)to polysaccharide(PS)approached to 1.40-1.45,comparable to that of aerobic granular sludge.In addition,the proportion of genera Nitrosomonas and Nitrosospira were evidently higher than in other reactors.The microbial community contributed to enhanced nitrogen removal efficiency.Hence,BF carrier size was suggested to be 15 cm in use.(2)Based on the suggested size,vertical spacing between BF carriers were investigated in terms of EPS,microbial community and wastewater treatment efficiency for identification of the vertical spacing between carrier units.Synthetic domestic wastewater was treated in three reactors(S7,S10 and S14),run with different vertical spacings(7 cm,10 cm and 14 cm)under same operating conditions within 100 days.The treatment efficacies were analyzed,followed by EPS and microbial community in frozen bio-nests.The findings showed that S14 achieved the highest COD,ammonia nitrogen and total nitrogen removal efficiencies,which were 91.4%,98.1% and 83.5%,respectively.EPS analysis showed that the highest proportion of tightly-bound EPS and Nitrospirillum was obtained in S14.It resulted the improving nitrogen removal efficiency.Therefore,vertical spacing of BF carriers was suggested to be 14 cm in use.Based on the investigations,the primary combination could to be developed for biological contact oxidation processes with BF carriers.