The Removal And Recycle Of Nitrogen And Phosphorus Nutrients And Wastewater Purification By Microalgae

The water resource per capita in China is already quite low. However, the water pollution caused by the emission of large volume of wastewater containing nitrogen, phosphorus and COD of high concentration further aggravates the shortage of water resources. Therefore, how to remove the pollutants such as nitrogen and phosphorus in wastewater needs to be solved. Although traditional treatments such as ammonia stripping and precipitation method can be used to remove nitrogen and phosphorus efficiently, addition of large amount of chemicals is required resulting in uneconomical consumption and secondary pollution. Biological method is beneficial, but the activated sludge produced in the procedure is difficult to be treated. In this paper, we explored a new way to treat the wastewater by using microalgae. It can not only remove a verity of pollutants but also achieve the recycling of resource in the form of algal protein.Although the volume of human urine is only 1% of the total municipal wastewater, its contribution to the nitrogen pollution is up to 80%-90% while phosphorus 37%-44%. What's more, the human urine containing abundant nitrogen, phosphorus and all kinds of trace element is the ideal culture medium for the algae. Therefore, the human urine was chosen as the culture medium for the algae in this research.The treatments of synthetic human urine (SHU) and real human urine (RHU) by microalgae-Spirulina Platensis and Chlorella were investigated, including removal efficiency of nitrogen, phosphorus and COD and the recycling of the algae resources. The results show that the microalgae can grow very well in the human urine. The microalgae can effectively utilize the NH4+-N in the urine. By adding organic carbon sources such as glucose and odium acetate, the inhibition of ammonia on the early growth stage of microalgae can be alleviated while the removal efficiency was improved and the microalgae biomass increased. With different initial ammonia concentration between 30-50mg/L, the dry cell weight obtained varied from 0.851-1.858g/L. When the initial ammonia concentration is 30mg/L, the removal efficiency is as high as 93.8% in the presence of 100mg/L sodium acetate while only 52.3% in absence of organic carbon. With the initial ammonia concentration of 50mg/L, over 90% removal efficiency can be achieved in the presence of organic carbon sources. The phosphorus can also be eliminated by microalgae and chemical precipitation.The COD value was minimal after about 7 days with a removal efficiency of 66% and then slightly rebound. This observation can be explained by the self-degradation and organic secretion of microalgae in its later growth stage. The results showed that the addition of glucose with an optimal concentration of 75mg/L can improve the removal efficiency of COD and increase the microalgae biomass by over 70%.In conclusion, the results demonstrate that using microalgae to treat wastewater is a promising method in wastewater purification for it can effectively remove nitrogen, phosphorus and COD in wastewater, and at the same time get microalgae biomass, achieving the recycling of resources.