Preliminary Research On Phosphorus Removal Of Wastewater By Algae-daphnia System

Water pollution control is an urgent problem to all human beings. Physical, chemical remediation technologies and bioremediation have been explored to improve water quality, of which the last one is an environment-friendly, economical and less secondary pollution method, so it has become a hot topic in wastewater remediation. Disposing wastewater by algae is a better way of bioremediation, which is reported a lot by many researchers. Algae can absorb much nitrogen and phosphorus when it is nourished, but the key point of successful remediation is the removal of algae itself. In this research, Algae-Daphnia-Fish food chain was designed based on the ecology principles, so nitrogen and phosphorus can be transferred to the top of the food chain, and then phosphorus can be moved out from wastewater by fishing.In this research, phosphorus removal capacity of different incubated amount of Chlorella pyrenoidosa were tested in sterile environment, then phosphorus removal capacity of algae in open system was tested with nutrition added every day, thus, the best density of algae could be determined, at this density algae can remove phosphorus steadily. Then Algae system and Algae-Daphnia system were constructed at this algae density. Continuous cultivating mode was then developed to remove phosphorus after investigating the algae’s capacity. Ingestion capacity of Daphnia magna to Chlorella pyrenoid and Cryprinus carpiodto Daphnia magna were tested. Then a program was put forward that removing phosphorus from wastewater by the Algae-Daphnia-Fish food chain. The detailed results are as follows:(1)It was indicated from the test that Chlorella pyrenoidosa can absorb excessive phosphorus after being incubated in a new environment. Incubated in sterile wastewater for8hours, it achieved the max amount of phosphorus absorption, which was (3.12±0.39)×10-10mg/cell, and concentration of total phosphorus outside algae cells was not less than0.28mg/L at the same time.(2) When the phosphorus in the environment is sufficient, it can be absorbed at a normal situation, and saturated phosphorus content is (1.50±0.50)×10-10mg/cell. It well supported the theory that the algae have steady structure and it can be used to remove phosphorus from water by removing algae cells.(3) When inoculation quantity of algae was between1.0×105and3.7×106cells/mL, the more inoculation quantity the faster phosphorus removal rate was got. After being incubated in sterile wastewater for96hours, the steady phosphorus removal rate (75%) was got when inoculation quantity of algae was between1.0×105and3.7×106cells/mL, with the initial phosphorus concentration was0.31mg/L.(4) A20Liters-open system was constructed under the condition that adding nutrition to the system every day, when it worked well, after incubated for72hours,(6.36±0.17) liters algae cells can be taken out and(8.28±0.79) X109algae cells can be removed from the system per24hours. At the same time, total phosphorus concentration decreased (0.076±0.015) mg/L every day from72h to216h.(5) In the continuous20Liters-system, the density of Chlorellapyrenoidosacan keep at (2.28±0.08) millions cells/mL, and (4.87±0.09) liters wastewater was disposed per24hours. At the same time, phosphorus removal rate was (71.72±1.33)%of effluent wastewater (initial concentration of TP was (0.48±0.02) mg/L) when algae grew well.(6) Daphnia magna’s capacity on grazing Chlorella pyrenoidosa was tested, and an equation was got as follows:y=3×10-8x2-0.0879x+133956(R2=0.9996), in which y represented ingestion rate (cells/(Daphnia·h)) and x represented density of algae (cells/mL). And it was found that the removal rate of algae can reach91.54%after putting Daphnia magna in algae water under the condition that the amount ratio of Chlorellal Daphnia at1.57×106:1and ate for5days.(7) Algae-Daphnia system can work well by controlling the amount ratio of Chlorellal Daphnia at3.02×106:1when algae density was between0.928million and1.595million cells/mL.(8) Cryprinus carpiod’s capacity on grazing Daphnia magna was tested, and an equation was also got:y=4.947x-1.2794, R2=0.94, in which y represented ingestion rate (103Daphnia/(g·h)) and x represented the weight of Cryprinus carpiod (g). The experiment found that Cryprinus carpiod has a strong grazing capacity on Daphnia magna.This research showed that it is feasible to remove phosphorus by the complex system designed based on the Algae-Daphnia-Fish food chain. And the results offered a reference for the further investigation.