| Food processing,leather,textile,pharmaceutical,petrochemical and other industries will produce a large amount of salty wastewater.The high-salt environment will inhibit the normal growth of microorganisms,resulting in the disadvantages of poor stability,low efficiency and high cost of traditional biological treatment technology.The Fuling District of Chongqing is currently the region with the highest output of mustard tuber in China.The annual discharge of salty wastewater such as mustard tuber wastewater is increasing rapidly.It is particularly important to develop high-efficiency,low-consumption,and resource-recyclable biological treatment methods for salty wastewater.Dunaliella salina has certain salinity tolerance and has recycling value.It is of positive significance to explore the use of Dunaliella salina to treat salty mustard wastewater.The thesis carried out a single factor influence experiment on the growth of Dunaliella salina,and investigated the effects of salinity,concentration of nitrogen and phosphorus,concentration of carbon source,and light intensity on the growth of Dunaliella salina,and screened the parameters that are conducive to the operation of the Dunaliella salina reactor.The Moving Bed Biofilm Reactor(MBBR)was started to pretreat the simulated mustard wastewater.The removal performance of MBBR on organic matter,nitrogen and phosphorus was investigated,and the effluent quality was controlled to facilitate the operation of the Dunaliella salina reactor.The Microalgae Biofilm Photobioreactor(MBPBR)was started.The removal performance of nitrogen and phosphorus,the biomass change in the reactor,and the physical and chemical properties of the Dunaliella biofilm were investigated.The microbial diversity was analyzed,and the balance of nitrogen and phosphorus was calculated.The MBBR-MBPBR series process had potential application value in the treatment of mustard wastewater.The research results of this thesis can provide theoretical basis and technical support for the application of Dunaliella salina to treat mustard wastewater.The main conclusions of this article are as follows:①The suitable salinity for the growth of Dunaliella salina was 1～3%.Increasing the salinity to 5%inhibited the growth of Dunaliella salina.Ammonia nitrogen inhibited the growth of Dunaliella salina,but it did not inhibit the growth of Dunaliella salina at a concentration of less than 1 mg/L.The results showed that the growth rate of Dunaliella salina was similar when concentration of NO3--N、PO43--P less than 200 mg/L and 100 mg/L,respectively.Dunaliella salina had a wide range of suitable nitrogen and phosphorus concentrations,and high concentrations of nitrogen and phosphorus did not inhibit the growth of Dunaliella salina.The most suitable concentration of HCO3-for the growth of Dunaliella salina was 1200 mg/L(calculated as carbon).Further increasing concentration of HCO3-significantly inhibited the growth of Dunaliella salina.In the range of less than 200 mg/L,increasing the concentration of glucose promoted the growth of Dunaliella salina.When the light intensity is lower than 300 μmol/(m2·s),increasing the light intensity promoted the growth of Dunaliella salina.The mass ratio of nitrogen in the dry weight of Dunaliella salina was 11.59%,the mass ratio of phosphorus was 3.82%,and the mass ratio of nitrogen to phosphorus was 3.03.② When the salinity was 1.6%,HRT(Hydraulic Rention Time)was 12 h and concentration of DO(Dissolved Oxygen)was 2.04-2.32 mg/L,MBBR achieved stable and good operating performance.The COD removal efficiency exceeded 80%,and the effluent concentration was 77.64±5.98 mg/L.The ammonia nitrogen was almost completely removed,and the concentration of ammonia nitrogen in effluent was less than 1 mg/L.Through simultaneous nitrification and denitrification,the TN removal efficiency of the reactor was close to 60%,the effluent was mainly NO3--N and the NO3--N concentration was 88.79±3.76 mg/L.The removal efficiency of PO43--P was 46.1±3.8%,the effluent concentration was 19.23±1.21 mg/L.The nitrogen-phosphorus ratio decreased from 5.96 in the influent to 4.62 in the effluent,which improved the adaptability of the Dunaliella salina reactor.By adding fillers and adding membrane modules,a higher sludge biomass was achieved in MBBR.The biomass of suspended sludge at 200 days was 10370 mg/L,and the biomass of attached sludge was 5142 mg/L.During the operation of MBBR,the microbial community richness of suspended sludge decreased,and the microbial community richness and microbial diversity of biofilms were higher than those of suspended sludge,and there were obvious differences between the community structure of biofilms and suspended sludge.The main AOB and NOB in the reactor were Nitrosomonas and Nitrospira,respectively.The main denitrifying bacteria were Phaeodactylibacter,Denitromonas,Nitratireductor,Candidatus_Competibacter,and the bacteria that can perform heterotrophic nitrification-aerobic denitrification metabolism included Photobacterium,Vibrio,and Paracoccus.It was speculated that the possible nitrogen conversion pathways of MBBR include autotrophic nitrification,anoxic denitrification and heterotrophic nitrification-aerobic denitrification.Paracoccus also had the function of denitrifying phosphorus,which was related to the biological phosphorus removal of MBBR.③After MBPBR ran stably,when the salinity was 1.6%,HRT was 3 d,and light intensity was 300 μmol/(m2·s),the removal efficiency of TN and TP by MBPBR were 63.5±2.2%、76.9±2.4%,respectively.After the MBBR-MBPBR series process ran stably,the removal efficiency of COD,ammonia nitrogen,TN,and TP were 84.2%,99.8%,83.2%,and 92.6%,respectively,and the effluent concentration were 69.52±4.69,0.33±0.21,36.96±3.03,3.12±0.98 mg/L,respectively,MBPBR unit’s contribution to the removal of TN and TP were 24.6%and 46.6%,respectively.The series process had good treatment performance for simulated mustard wastewater.The biomass of MBPBR was dominated by biofilm,which was 209.39±17.54 g/m2,of which microalgae and bacteria were 193.06±15.38 g/m2 and 16.33±4.23 g/m2,respectively.The thickness of the biofilm was 402.28±37.72μm,the density was 1.81±0.05 g/cm3,and the porosity was 67.7±2.3%.Adding a small amount of glucose in the MBPBR for a short period of time greatly increased the biomass and the thickness of the biofilm.Five species of microalgae were detected in MBPBR.The relative abundance of Dunaliella salina was about 90%,occupying an absolute advantage.The three microalgae Nodosilinea,Raphidiopsis curvata,Amphora ovalis had certain salinity tolerance.The growth of filamentous cyanobacteria named Nodosilinea made the surface of the Dunaliella salina biofilm appear filamentous.MBPBR mainly removed nitrogen and phosphorus through biofilms.The assimilation of microalgae was the main way for MBPBR to remove nitrogen and phosphorus.Autotrophic microorganisms such as Nodosilinea,and heterotrophic bacteria such as Hyphomonas,SM1A02,and Rhodobaclum enhanced the removal performance of nitrogen and phosphorus.The use of MBBR-MBPBR series process to treat mustard wastewater had high technical and economic feasibility and potential application value. |
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