Population And Phosphate Metabolism Of Yeasts In Anaerobic/Oxic Biofilm System

Exceeding of phosphorus content in natural water body has caused eutrophication and a series of accompanying environmental problems,while phosphorus is essential to plants as a nutrient element whose shortage might induce underproduction as well as another consequent trouble.Urban sewage has gained more and more attention in recent years,owing to its massive water volume and phosphorus containing ability.Biological treatment is the most potential method among numerous ways dealing with the removal and recovery of phosphorus from wastewater,though the existing methods have challenges of either low recovery efficiency from phosphorus-rich sludge or separating sludge from wastewater completely,an efficient new way is just around the corner.Yeast,as one of the monocelled microorganism,is very likely to be crystal nucleus during a crystallization process,due to its body size is just on the right range.Considering that yeast has good performance for adsorbing metal ions as well as remarkable capacity in removing phosphorous,it may be possible to consume organic pollutant in organic phosphorus containing wastewater and retrieve the precious deposits by means of crystallization at the same time,with the help of yeast species.The suggested method can accelerate the geochemical circulation of phosphorus to a certain degree,and then relieve the worldwide phosphorus shortage crisis and also promote the wastewater treatment to a recycling and energy saving direction.Typical biological aerated filter?BAF?was adopted in this research to provide biofilm for yeast extraction all the time,4 BAFs were altered to 3 different operating mode after the BAF had been established,namely anaerobic/oxic?A/O?alternant condition,anaerobic condition,oxic condition,respectively.It came out that the A/O alternant biofilm system reached stable state at 20 days after switching mode,and the removal rate of phosphorus?P?,ammonia nitrogen?NH₃-N?and COD_cr were 71%,97%and 95%,respectively.It was not until 60 days after the establishment of BAF that anaerobic biofilm system was steady,with removal ratios at 38%,-30%and 57%for P,NH₃-N and COD_cr,which indicated the system was still capable of eliminating organic pollutants.And the biofilm system under oxic condition could only remove 50%P,while 95%of NH₃-N and 96%COD_cr were wiped out,which met the first grade A standard of Urban Sewage Disposal Plant Contamination Integrated Discharge Standard?GB18918-2002?.Yeasts isolated from various biofilm systems at different periods were purified and then classified preliminarily,23 strains with diverse features were obtained.The distribution characteristics of yeast population varied with the change of operating condition and period.Desperate there existed differences of yeast species and strain from 4 BAFs,the total number of yeast colony was almost the same right after the establishment.Owing to that dissolved oxygen content rose along with inflow in BAF during initiating stage,total yeast colony decreased while yeast species went up,dominant species were BG?MG?BL1?HGFG?HG?HZ?ML2 and BRY,respectively.At stabilization stage,total yeast colony and strain number varied with different operating conditions,of all the 3 operating conditions the A/O alternant environment had the best population diversity and uniformity,and the relationship of total yeast colony under different conditions was as follows:A/O:O:A?4:2:1.Yeast strains that could live at all the operating conditions were BG?BL1?BL1-2?BL3 and MG.Under low temperature?15??,species abundance and evenness of yeasts from A/O alternant condition were reduced,even though total yeast colony and strain number increased.Traditional physiological and biochemical characteristics method was used to preliminary identificate the species or genus of 12 strains from A/O alternant biofilm system,it turned out there were 7 strains belong to Trichosporon sp.,1 of Issatchenkia sp.,2 of Candida sp.,and 2 of Pichia sp.,and more precisely,strain BL3 was identified as Candida rugosa,while strain BZ2 was Pichia occidentalis.After analyzing distribution characteristics and species of yeast population under various operating conditions,strains with good growth and better performance for removing phosphorus were screened by culturing them with high phosphorus containing wastewater.Tests results demonstrated that phosphorus content of dry heavy of the screened strains were all relatively high,while polyphosphate particles dyeing were all negative,indicating that phosphorus in the wastewater was either stored in yeast cells as another forms or fixed on the surface of yeast cytoderm.As for 4 selected strains,their phosphorus metabolism characteristics under different influence factors?pH,temperature and rotate speed of shaker?were all unlike,it came out that the influence of pH was not serious for phosphorus removal,and the speed of shaker had nothing to do with yeasts'final phosphorus removing quantity,while temperature could effectively affect phosphorus removal ratio,with the best effect acquired at 28?for all the4 strains.Exploration results of phosphorus crystallization induced by yeasts demonstrated strain HG was the only one of 12 screened yeasts that could assist the generation of crystalloid,analysis of this crystalloid indicated it might be a kind of mixed crystal of organic matters,compound of magnesium and phosphorus,oxycarbide or hydroxide of magnesium,as well as calcified living organisms.The role of yeasts in the crystallization might act as a crystal nucleus,and some extracellular proteins could also be secreted to assist the generation of crystalloid.The study of yeasts population's distribution characteristics in wastewater treatment system and the metabolism features of phosphorus under various culturing condition,in some degree replenished the blank area of research on yeasts in biofilm system,demonstrated the variation character of yeast strains under diverse operating conditions,and acted as a foundation of bio-crystallization synergistic process that producing crystal or crystalloid induced by yeast.