Fast Start-up Of Anammox Reactor And Influence Of Organic Arsenic Compounds On Struvite Precipitation

In recent years,large amount of ammonium and phosphorus are discharged into aquatic environment,leading to eutrophication and algal blooms.Anaerobic ammonium oxidation(Anammox)process has many advantages such as high nitrogen removal efficiency,energy saving,no need of external organic carbon and low sludge production rate etc.Anammox process is suitable for the wastewater treatment with high concentration of ammonia and low ratio of C/N.However,the start-up time of anammox reactors is very long due to the low specific growth rate of anaerobic ammonium bacteria,which severely limits the practical application of anammox process.Struvite crystallization is a promising process due to the simultaneous recovery of phosphorus and ammonium.Furthermore,the struvite is a valuable nitrogen and phosphate fertilizer.The struvite fertilizer might be contaminated by toxic substances during precipitation,which would cause secondary pollution in soils.In this paper,the fast start-up of anammox reactor and the influence of organic arsenic compounds on struvite formation were investigated.The following results were obtained.(1)The fast start-up of two anammox reactors was investigated.Two anammox ASBR were successfully started-up from dewatered surplus activated sludge and mixed sludge.The maximum nitrogen loading rates of two anammox reactors were 224 g-N/m~3/d and 570 g-N/m~3/d,respectively.The anammox granular sludge appeared in the reactor R2 within 45 day,while there was no anammox granular sludge formed in the reactor R1.The dominant genus of anammox bacteria was Candidatus_Kuenenia in both reactors.These results imply that seeding with mixed sludge could significantly facilitate the start-up of anammox reactor and the formation of anammox granule.(2)The performance of anammox reactors seeded with anaerobic granular sludge and activated sludge was investigated.The start-up time of the reactor seeded with activated sludge was shorter than that of the reactors inoculated with anaerobic granular sludge.After 55 days operation with nitrogen loading rate(NLR)of 35 g-N/m~3/d,the removal efficiencies of total nitrogen(TN)of reactor 1-1,1-2,1-3,1-4 and 1-5 seeded with anaerobic granular sludge were 4.5%,10.0%,17.8%,21.5% and 29.8%,respectively.The start-up time of the reactor 2-1,2-2,2-3,2-4 and 2-5 seeded with activated sludge were 30 d,17 d,11 d,9 d and 6 d,respectively.The NLR of reactor 2-1 was 35 g-N/m~3/d,while the NLR of reactor 2-2,2-3,2-4 and 2-5 were 170 g-N/m~3/d.The removal efficiencies of TN were 44.9%,79.3%,82.2%,74.5% and 79.7%,respectively.Adding anammox sludge could obviously promote the start-up of Anammox reactors seeded with activated sludge.However,there was no distinct promotion for anaerobic granular sludge.These results might be due to the difference of microbial community structure in the sludge.(3)The influence of organic arsenic compounds on struvite was investigated.The results showed that the presence of ASA,ROX,As(III)and As(V)did not apparently affect the recovery efficiency of phosphorus in struvite precipitation,but their presence affected the particle diameter and surface shape of the precipitated struvite.The greatest mean arsenic contents of ASA,ROX,As(III)and As(V)in the struvite were 15.6,35.5,25.2 and 2325.0 mg/kg,respectively.With the increasing pH,the content of ASA and ROX in the precipitates decreased,while the content of As(III)and As(V)in the struvite increased.The As(V)was co-precipitated in struvite with the formation of MgNH4AsO4·6H2O,and the other arsenic species were adsorbed onto the struvite due to surface interactions.