Design Of Continuous Treatment System For Pig Urine Based On Cultivation Of Chlorella Sp.

China is the world’s largest producer and consumer of pork.However,the environmental problems caused by large-scale pig production are becoming worse.The eutrophic water has been a serious issue due to large amount of pig wastewater discharged into the rivers and lakes.As one of the main parts of pig wastewater,pig urine is rich in nutrients such as nitrogen,phosphorus and potassium,which are the essential elements for plant growth.Pig urine is relatively pure and low turbidity.It can be used as growth medium of Chlorella sp.After simple pretreatment.The basic physical and chemical properties of pig urine were analyzed in this study.The cultures of Chlorella sp.in pig urine under different conditions were investigated.A treatment system for pig urine based on cultivation of Chlorella sp.was established.The system design,operation effect of the process,growth performance of Chlorella sp.and removal efficiencies of wastewater were discussed.The main results were as follows:(1)Through the analysis of the physical and chemical properties of the pig urine,the results showed that the ammonia nitrogen content of the original pig urine reached 1155.54 mg/L.There was a strong ammonia odor,the results indicated that pig urine ammonia nitrogen was volatile.p H was higher than 9.0.And it was a strong alkaline solution,the concentrations of total carbon and total nitrogen were more than 3000 mg/L,respectively,the results showed that lots of carbohydrate and protein in the pig urine were not decomposed.When it was used as a medium,the concentration of free ammonia should be decreased by p H regulation and dilution.The concentrations of Cd,Cu and Zn were extremely low in the pig urine,indicating that it is safe to use the harvest microalgal biomass from pig urine as animal feed.The concentrations of P,K and Mg,which were the essential elements for microalgal growth,were significantly different.The concentration of K was up to 1150.90 mg/L,which is far more than the necessary amount for plant growth.Mg was only 0.62 mg/L.(2)Single factor experiment was carried out to investigate the effect of dilution times of the pig urine,initial p H values,and light intensity,cultivation modes on the growth of Chlorella sp.and nutrients removal of the pig urine.The biomass concentration of Chlorella sp.was increased by adjusting the Mg concentration in the pig urine.The results showed that the dilution times of the pig urine had a significant effect on the growth of Chlorella sp.The Chlorella sp.was not able to grow in the pig urine diluted at low ratio.The optimal dilution ratio was 8 times with the maximum biomass(OD680)of 0.75.For p H adjustment strategy,the results showed that a relatively low p H value in a certain range of the pig urine can promote the growth of Chlorella sp.The Chlorella sp.could grow rapidly in the p H range of 5.0 to 7.0.Among them,the treatment of p H 6.0 was the best with the highest biomass(OD680)of 1.4.In the cultivation mode experiments,the culture aerated with air was better than the static culture.Aeration can shorten the adaptation period of Chlorella sp.and improve the biomass concentration significantly,probably due to the removal of the free ammonia through aeration.The light intensity was also an important factor affected the growth of Chlorella sp.The optimal light intensity was 2500 LX.Regulated Mg2+ to a proper concentration could efficiently improve the growth of Chlorella sp.(3)The treatment system for pig urine based on cultivation of Chlorella sp.was designed and established its process parameters such as water inlet flow rate,aeration rate and stirring rate could be controlled.For future large-scale production,the outdoor cultivation in running way pond using the sunshine as the sole light source for photosynthesis was tested.The growth curve of microalga in the reactor was recorded.It was found that the two factors,light intensity and water temperature,were closely related to the variation of the parameters of chlorophyll fluorescence dynamics.Through batch experiments,it was found that the growth of Chlorella sp.in the pig urine after the pretreatment was better than that of BG11 medium.The removal rates of ammonia nitrogen and total phosphorus were 84.95% and 92.89%,respectively.The nitrogen and phosphorus in the pig urine were removed during the photosynthesis process of the Chlorella sp.Through continuous input of the wastewater,the Chlorella sp.in the reactor were able to maintain high activity with a stable treatment performance at day 7.