Photosynthetic Bacteria Immobilization And Its Influence On Nitrogen And Phosphorus Removal From Wastewater

Photo synthetic bacteria are widely used in wastewater treatment process,which has the advantages of diverse metabolism and high tolerance to organic.While during wastewater treatment process,the photosynthetic bacterial cells are easily washed away.This will result in low effect and high cost in wastewater treatment process.In this study,the removal efficiencies of nitrogen,phosphorus and COD in sewage were investigated by fixed photosynthetic bacteria,including adsorption fixation and flocculation.Firstly,the growth conditions,including inoculum volume and initial pH for photosynthetic bacteria were optimized.The growth of photosynthetic bacteria was investigated under 10%,20%,and 30%inoculation(v/v).20%is the optimal inoculum for photosynthetic bacteria growth(OD660nm=1.74±0.06).Initial pH(5.0,6.0,7.0,8.0,9.0,10.0)had significant effects on the growth of photosynthetic bacteria.Under initial pH=8.0,the final biomass were the most,and the OD660nm was stable at 1.70,bacteria grown had the highest cell growth.Glass fiber,chopped activated carbon fiber,and felt activated carbon fiber were used for adhesive immobilization the photosynthetic bacteria.The determination of OD660nm in suspension liquid and observation by scanning electron microscopy showed that glass fiber is more suitable for photosynthetic bacteria adhesion than activated carbon fiber.The suspension cultured bacteria was used as the control,compared with the bacteria fixed by glass fiber(dry heat,damp heat pretreatment),the removal of nitrogen,phosphorus and COD in the sewage by immobilized photosynthetic bacteria was investigated.The process of the whole experiment is divided into three stages.The first stage(0-8 day)is to add different pretreated glass fibers and bacteria to the simulated sewage for cultivation.The second stage(8-14 days)is to replace the simulated sewage after the first stage is completed.The third stage(14-22 days)is to replace the simulated sewage after the completion of the second stage.The experimental results show that the dry heat treated glass fiber has the best result,and the ammonia nitrogen and phosphate removal rate is the best in the first stage and second stage.After the second stage,the ammonia nitrogen concentration in the sewage is 48.86±2.07 mg/L,and the removal rate is reached 75.00%,the concentration of phosphate was 51.70±0.56 mg/L,and the removal rate reached 64.90%.Compared with the first two stages,the third stage showed the phenomenon of bacteria loss,which resulted in a reduction in the removal rate of ammonia nitrogen and phosphate.After the third stage,the COD removal of the dry heat treatment group reached 1079.56 mg/L.In summary,the effect of glass fiber after dry heat pretreatment is the best.In the experiment of flocculation fixation,four flocculants(ferric sulfate,aluminum chloride hexahydrate,polyaluminum sulfate and chitosan)were selected to investigate the flocculation efficiency of photosynthetic bacteria.The flocculation efficiency of ferric sulfate,aluminum chloride hexahydrate,and polyaluminum sulfate to photosynthetic bacteria reached over 99%;chitosan reached 89%.However,considering the effects of iron salts and aluminum salts on biological activity,the amount of flocculant and cost,chitosan is more suitable for flocculation of photosynthetic bacteria,and the suitable concentration is 0.012 g/L.Subsequently,the effects of photosynthetic bacteria on the removal of ammonia nitrogen,phosphate and COD in simulated sewage were investigated after flocculation of chitosan.The results showed that the bacteria after flocculation fixation had the best treatment effect when the inoculation amount was 10%.The ammonia nitrogen concentration decreased to 39.64±8.47 mg/L,the phosphate decreased to 60.26±4.83 mg/L,and the COD removal amount was 1163.72 mg/L.