High Efficiency Treatment Of Ammonium-Rich Wastewater Based On Cultivation Of Chlorella Pyrenoidosa With Biomass Co-Production

The unicellular green algae-Chlorella contain a variety of protein,pigments and have various nutrition patterns.The growth rate of chlorella under optimal conditions was fast,and it had a wide range of applications in different types of wastewater.There are many kinds of wastewater,of which agricultural and industrial wastewater are the major pollution sources.Recently,huge quantity of agricultural and industrial wastewater with high nitrogen content discharged every year in China,which was great harmful to the ecological environment.However,traditional treatment technology has some shortcomings in cost and effect.Chlorella was considered as a good raw material of feed,which had strong environmental adaptability and high protein content.These features made it suitable for wastewater treatment,which can not only purified wastewater but also harvest high quality microalgae biomass at the same time.This paper optimized the conditions of mixotrophic growth for Chlorella pyrenoidosa and created high-cell-density biomass harvested method for large-scale cultivation.After that,the treatment efficiency and biomass yield of Chlorella pyrenoidosa in piggery sewage under outdoor conditions were investigated.Based on the characteristics of catalyst plants wastewater,the tolerance of Chlorella pyrenoidosa to high salt and high ammonia nitrogen wastewater was systematically evaluated.Finally,ammonia nitrogen uptake rate and the growth of Chlorella pyrenoidosa were further optimized under fermenter conditions.The main experimental results were as follows:1.In the process of nutritional growth characteristic of Chlorella pyrenoidosa,it was found that Chlorella pyrenoidosa can grow in a wide temperature range and the highest concentration of Chlorella pyrenoidosa（27.2 g/L）was obtained in 30℃,10 g/L glucose and 3.75 g/L sodium nitrate concentration.In the process of investigating Chlorella pyrenoidosa tolerance to glucose concentration（10-60 g/L）,it was found that high concentrations of glucose（>50 g/L）would inhibit cell growth of Chlorella pyrenoidosa significantly（p<0.05）.The pigment content in the cell was 3.6%and significantly higher than that of control group when Chlorella pyrenoidosa was cultivated in the medium with 5.0 g/L sodium nitrate.2.The effects of different pH values and initial inoculation concentration on the growth of Chlorella pyrenoidosa and purification of piggery sewage were systematically studied in shaking flask.The results showed that the best purification effect was obtained when the initial pH was 7 and the inoculation density was 5×10⁶ events/mL.Chlorella pyrenoidosa performed the best purification of the tertiary filtration pretreated wastewater,when the COD,NH₄⁺,PO₄^3-,TN and TP of raw swine wastewater were 710,491,54,590 and 108 mg/L,respectively,and the removal rates of colority and NH₄⁺more than 83%.When Chlorella pyrenoidosa were cultured in a vertical photobioreactor with the diameter of 10、5 cm,the yield（dry weight）were0.82 and 0.93 g/L,the highest protein content was 58.9%through recycling collection.The contents of mercury,arsenic,cadmium and lead in algal biomass were lower than 0.1,1.0,0.5and 4.0 mg/kg,respectively,which was in accordance with the standard Chlorella Powder for Feed（DB32/T 564-2010）.The removal rates of NH₄⁺,PO₄^3-,and colority in effluent after harvesting Chlorella were all over 90%,which basically met the national emission standards.It was proved that Chlorella pyrenoidosa could adapt to this circadian rhythm by intermittent pumping experiment in the day and night.3.In the process of effects of culture conditions（dilution ratio of wastewater,initial glucose concentration,inoculation density,light intensity and volume of liquid）on Chlorella pyrenoidosa growth and ammonia nitrogen uptake rate of wastewater were investigated by single factor experiments,the optimum culture conditions were determined:optimization dilution multiple of catalyst plant wastewater was 2;initial glucose concentration was 10 g/L,cell number inoculated shall not be less than 1×10⁸ events/mL.the maximum ammonia-nitrogen uptake efficiency and dry weight of Chlorella pyrenoidosa were 222 mg/L/d and 25.1 g/L respectively.The effects of sampling time,culture method,proportion of reused water,state of seed liquid on the growth of Chlorella pyrenoidosa and ammonia nitrogen uptake rate were systematically studied.The results showed that 12 h sampling and mixing culture,2:1 ratio of reused water to wastewater,logarithmic period or domestication condition of wastewater were more conducive to the growth of Chlorella pyrenoidosa and the purification of wastewater（p<0.05）.4.The results achieved in shake flask culture conditions were checked under photofermentation tank conditions with pH controlled.The results showed that the maximum tolerance of Chlorella pyrenoidosa to ammonia nitrogen wastewater concentration was 4800mg/L.In the two-stage culture process,NH₄⁺in wastewater decreased from 962,1061 mg/L to50 and 0 mg/L respectively,at 36 and 84 hours,with 40%,44%protein content was obtained in algae,at the same time.The maximum consumption rate of NH₄⁺,PO₄^3-and growth rate were960 mg/L/d,758 mg/L/d and 1.18 d^-1,respectively.In the three-stage photo-fermentation culture,the constant pH value was controlled at 6.5,the rotation speed,light intensity,and aeration were adjusted gradiently.After the update,the supplement amount of the medium was increased,and the NH₄⁺absorption rate in the first and third stages were better than the two-stage,9.6%and 13%higher,respectively,and the highest was 689 mg/L/d.In the four-stage culture,the NH₄⁺consumption rate of Chlorella pyrenoidosa reached 1426 mg/L/d at 48 h,and the highest average consumption rate was 1021 mg/L/d at the fourth stage.